A Mathematical Model for Fungal Development in Heterogeneous Environments
印度碗状红菇——一个中国新纪录种（英文）
热带作物学报2021, 42(9): 2542 2548 Chinese Journal of Tropical Crops收稿日期 2021-02-23；修回日期 2021-03-20基金项目 国家自然科学基金项目（No. 31770657，No. 31570544，No. 31900016）。
作者简介 陈 彬（1990—），男，博士研究生，研究方向：森林微生物资源遗传多样性。
*通信作者（Corresponding author ）：梁俊峰（Liang Junfeng ），E-mail ：*******************。
Russula indocatillus , a New Record Species in ChinaCHEN Bin 1, 2, SONG Jie 1, WANG Qian 1, LIANG Junfeng 1*1. Research Institute of Tropical Forestry, Chinese Academy of Forestry, Guangzhou, Guangdong 510520, China;2. Nanjing For-estry University, Nanjing, Jiangsu 210037, ChinaAbstract: Russula indocatillus was reported as new species to China. A detailed morphological description, illustrations and phylogeny are provided, and comparisons with related species are made. It is morphologically characterized by a brownish orange to yellow ochre pileus center with butter yellow to pale yellow margin, white to cream spore print, subglobose to broadly ellipsoid to ellipsoid basidiospores with bluntly conical to subcylindrical isolated warts, always one-celled pileocystidia, and short, slender, furcated and septated terminal elements of pileipellis. The combination of detailed morphological features and phylogenetic analysis based on ITS-nrLSU-RPB2 sequences dataset indicated that the species belonged to Russula subg. Heterphyllidia sect. Ingratae . Keywords: Russulaceae; new record species; phylogeny; taxonomy DOI 10.3969/j.issn.1000-2561.2021.09.014印度碗状红菇——一个中国新纪录种陈 彬1,2，宋 杰1，王 倩1，梁俊峰1*1. 中国林业科学研究院热带林业研究所，广东广州 510520；2. 南京林业大学，江苏南京 210037摘 要：本研究报道一个中国红菇属新记录种——印度碗状红菇（Russula indocatillus ）。
食品专业英语课件
Part 2 食品科技英语的阅读
Lesson 1 WHO Strategy on Food Safety
Summary WHO has been actively participating in the
development of principles and recommendations for the safety assessment of GM foods derived from genetically modified organisms(GMO). The results developed in the course of various expert consultations from the basis for guidelines on national levels and are presently being incorporated into internationally recognized standards. 对于由转基因生物生产的食品转基因食品，WHO一直以来积 极致力于制订其安全评价的原则和建议。不同专家基于本 译文 国的技术水平而商讨的结果是各国制定标准的指导性依据， 而且这些结论正逐渐成为公认的权威标准。
3. What can you learn from Paragraph 3 ?
A. Most developing countries are not willing to be responsible for the consequence of using the new technology. B. Most developing countries are willing to be responsible for the consequence of using the new technology. C. Most developed countries are not willing to be responsible for the consequence of using the new technology. D. Most developed countries are willing to be responsible for the consequence of using the new technology.
数字农业英语作文
数字农业英语作文Title: The Transformation of Digital AgricultureWith the advancement of technology, the agriculture industry has undergone a significant transformation in recent years. Digital agriculture, also known as precision agriculture, has emerged as a revolutionary approach to farming that leverages modern technologies to optimize production efficiency, reduce environmental impact, and ensure food security. This essay explores the key aspects and benefits of digital agriculture.One of the main components of digital agriculture is the use of precision farming techniques. This includes the adoption of drones, satellite imagery, and GPS technology to monitor and manage crop growth. With these tools, farmers can precisely analyze soil conditions, crop health, andirrigation needs, allowing for targeted interventions and optimized resource utilization.Moreover, data analytics plays a crucial role in digital agriculture. By collecting and analyzing vast amounts of data on weather patterns, soil quality, and crop performance, farmers can make informed decisions to improve productivity and profitability. Machine learning algorithms enable predictive modeling, helping farmers anticipate challenges and optimize farming practices.Another key aspect of digital agriculture is the development of smart farming equipment. From automated tractors to robotic harvesters, these technologies streamline farm operations and reduce manual labor. By integrating IoT sensors and cloud computing, farmers can remotely monitor and control equipment, leading to increased efficiency and reduced costs.Furthermore, digital agriculture promotes sustainable farming practices. By adopting precision irrigation systems and variable rate fertilization, farmers can minimize water usage and chemical inputs, reducing environmental impact and promoting biodiversity. This not only benefits the ecosystem but also enhances the long-term viability of farming operations.In addition to improving farm productivity, digital agriculture also plays a vital role in ensuring food security. By facilitating real-time monitoring of crop health and yield predictions, farmers can better plan and manage their harvests, reducing food waste and improving food distribution systems. This is particularly crucial in addressing globalfood challenges and ensuring access to nutritious food forall.Overall, digital agriculture represents a paradigm shiftin the way we approach farming. By harnessing the power oftechnology and data-driven insights, farmers can enhance sustainability, productivity, and resilience in the face of changing climates and market dynamics. As we continue to innovate and adopt new technologies, digital agriculture will play an increasingly vital role in shaping the future of food production.。
基于模糊数学法的辣木籽杂粮面包配方优化及其品质分析
吕俊丽，任志龙，云月英，等. 基于模糊数学法的辣木籽杂粮面包配方优化及其品质分析[J]. 食品工业科技，2023，44（23）：167−174. doi: 10.13386/j.issn1002-0306.2023010105LÜ Junli, REN Zhilong, YUN Yueying, et al. Formulation Optimization and Quality Analysis of Moringa Seed Multigrain Bread Based on Fuzzy Mathematics[J]. Science and Technology of Food Industry, 2023, 44(23): 167−174. (in Chinese with English abstract). doi:10.13386/j.issn1002-0306.2023010105· 工艺技术 ·基于模糊数学法的辣木籽杂粮面包配方优化及其品质分析吕俊丽1, *，任志龙2，云月英1，郭 慧1（1.内蒙古科技大学生命科学与技术学院，内蒙古包头 014010；2.包头轻工职业技术学院食品生物与检测系，内蒙古包头 014035）摘 要：为了满足人们对营养食品的需求，本研究以面包为载体，运用模糊数学感官评价法，以感官评分为依据，通过单因素和正交试验对辣木籽杂粮面包配方进行优化，在此基础上，分析了辣木籽杂粮面包的理化特性和抑菌特性。
结果显示：辣木籽杂粮面包的因素影响顺序为：辣木籽添加量>薏米添加量>红豆添加量>红薯泥的添加量，辣木籽杂粮面包最佳配方为：牛奶34%，黄油7.5%，全蛋液40%，酵母添加量为0.8%，白糖添加量5.1%，辣木籽的添加量为2.6%，红薯泥的添加量为2.1%，红豆的添加量为1.6%，薏米的添加量为2.1%。
此配方下面包的模糊数学感官评分最高（86.35分），此时面包味道浓郁，松软适口，过氧化值、酸价、菌落总数均符合国家标准，蛋白质含量比普通面包高5.6 g/100 g 。
2023-2024学年上海市静安区高三上学期期末教学质量调研考试英语试题
2023-2024学年上海市静安区高三上学期期末教学质量调研考试英语试题Directions: After reading the passage below, fill in the blanks to make the passages coherent and grammatically correct. For the blanks with a given word, fill in each blank with the proper form of the given word; for the other blanks, use one word that best fits each blank.Japan’s robot revolution in senior careJapan’s artificial intelligence expertise is transforming the elder care industry, with 1 (specialize) robotic care accomplishing more than just taking pressure off the critical shortage of caregivers. Senior care facilities across Japan are testing out such new robots 2 deliver a collection of social and physical health care and the government-backed initiative has been met with positive reviews by elderly residents.The rapidly graying population 3 (eye) by the government as a potential market for medical technology now. Disappointing government predictions show that by 2025, Japan's first baby boomers will have turned 75 and about 7 million people are likely to suffer from some form of dementia (痴呆). The nation won't be able to avoid a dementia crisis 4 an additional 380,000 senior care workers.The long-standing shortage of professional care workers has encouraged the Japanese government 5 (simplify) procedures for foreign caregivers to be trained and certified. The current Technical Intern Training Program between Vietnam, the Philippines, and Indonesia, under 6 Economic Partnership Agreement, was extended to include nursing care as well as agriculture, fishery, and construction sectors.7 the government made efforts to increase the numbers of senior care workers, the target number of foreign graduates has still fallen flat, with the national caregiver examination proving a major obstacle to pass. The success rate for foreign students was a merely 106 students last year, 8 has slightly improved to 216 students this year. Another depressing reality is that 19 to 38 percent of foreign nurses who pass the exam opt to leave the industry and return home, 9 (cite) tough work conditions and long hours. Given the challenges, this is 10 the government believes care robots will be able to step in.Directions: Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need.A. smoothingB. remainC. switchedD. likelihoodE. impactF. tipG. broadly H. headed I. booming J. positioning K. reliablySea-level rise predictionsA team of University of Idaho scientists is studying a fast-moving glacier in Alaska in hopes of developing better predictions on how quickly global sea levels will rise.Tim Bartholomaus, a professor in the Department of Geography and Geological Sciences, spent several weeks on Turner Glacier in Alaska’s southeastern 11 near Disenchantment Bay. The glacier is unique because, unlike other glaciers, it rises greatly every five to eight years.A surging glacier is defined, 12 , as one that starts flowing at least 10 times faster than normal. But the how and why of that glacial movement is poorly understood, although recent research suggests that global climate change increases the 13 of glacial surging.During Turner’s surges, the mass of ice and rock will increase its speed from roughly 3 feet a day to 65 feet per day.All of that is important because glaciers falling into the ocean are a major contributor to sea level rise, and current clima te change models don’t 14 account for these movements. For example, Greenland’s glaciers are one of the leading contributors to global sea-level rise. Since the early 2000s, Greenland 15 from not having any effect on world sea levels, to increasing sea level by about 1 millimeter per year. Half of that yearly increase is due to warmer average temperatures, which leads to more ice melting. The other half, however, is because glaciers in Greenland are, as a whole, moving faster and running into the ocean more frequently.Glacial movement has something to do with water running underneath the glacier. Glaciers are full of holes, and water runs through those holes. When the water pressure is high underneath a glacier, it starts to move, partly because it’s li fting the mass of ice and rock off the ground and partly because it’s 16 the underside of the glacier.But how exactly does that water move through the glacier, and how does the movement 17 the glacier’s speed? Those are the questions the scientists ho pe to answer.Bartholomaus, some graduate students and researchers from Boise State University, 18 onto the ice in August. They set up a base camp at the toe of the glacier and spent their days flying in on helicopters. They placed roughly 30 instruments, burying them deeply into the glacier and 19 them on rock outcroppings (露岩) alongside the glacier. This summer the team will return to get the instruments and replace batteries. Those instruments will 20 on and around the glacier until the glacier surge stops, providing researchers with before and after data.Investors probably expect that following the suggestions of stock analysts would make them better off than doing the exact opposite. _________, recent research by Nicola Gennaioli and his colleagues shows that the best way to gain excess return s would be to invest in the shares least favored by analysts. They compute that, during the last 35 years, investing in the 10 percent of U. S. stocks analysts were most _________ about would have yielded on average 3 percent a year._________, investing in the 10 percent of stocks analysts were most pessimistic about would have yielded a surprising 15 percent a year.Gennaioli and colleagues shed light on this _________ with the help of cognitive sciences and, in particular, using Kahneman and Tversky's concept of representativeness. Decision makers, according to this view, _________ the representative features of a group or a phenomenon. These are defined as the features that occur more frequently in that group than in a baseline reference group.After observing strong earnings growth—the explanation goes—analysts think that the firm may be the next Google. “Googles” are in fact more frequent among firms experiencing strong growth, which makes them _________. The problem is that “Googles” are very _________ in absolute terms. As a result, expectations become too optimistic, and future performance_________. A model of stock prices in which investor beliefs follow this logic can account both qualitatively and quantitatively for the beliefs of analysts and the dynamics (动态变化) of stock returns.In related work, the authors also show that the same model can _________ booms and busts in the volume of credit and interest rate spreads.These works are part of a research project aimed at taking insights from cognitive sciences and at__________them into economic models. Kahneman and Tversky's concept of “representativeness” lies at the heart of this effort. “In a classical example, we __________ to think of Irishmen as redheads because red hair is much more frequent among Irishmen than among the rest of the world,” Prof. Gennaioli says. “However, only 10 percent of Irishmen are redheads. In our work, we develop models of belief formation that show this logic and study the __________ of this important psychological force in different fields.”Representativeness helps describe __________ and behavior in different fields, not only in financial markets. One such field is the formation of stereotypes about social groups. In a recent experimental paper, Gennaioli and colleagues show that representativeness can explain self-confidence, and in particular the __________ of women to compete in traditionally male subjects, such as mathematics.A slight prevalence of __________ male math ability in the data is enough to make math ability un-representative for women, driving their under confidence in this particular subject.21.A．Consequently B．Furthermore C．Nevertheless D．Meanwhile22.A．curious B．controversial C．concerned D．optimistic23.A．In brief B．By contrast C．In addition D．Without doubt 24.A．engagement B．concentration C．puzzle D．definition25.A．memorize B．prioritize C．modernize D．fertilize26.A．representative B．argumentative C．executive D．sensitive27.A．harsh B．adaptable C．crucial D．rare28.A．cheers B．disappoints C．stabilizes D．improves29.A．account for B．count on C．suffer from D．hold up30.A．pouring B．admitting C．integrating D．tempting31.A．pretend B．afford C．offer D．tend32.A．effects B．delights C．intervals D．codes33.A．companions B．scales C．expectations D．findings34.A．necessity B．involvement C．perseverance D．reluctance35.A．equivalent B．exceptional C．mysterious D．distressing Montessori was born in Italy in 1870 with progressive parents, who frequently communicated with the country’s leading thinkers and scholars. This enlightened family environment provided Montessori with many advantages over other young girls of the time.Her mother’s support was vital for some impo rtant decisions, such as her enrolment in a technical school after her elementary education. Her parents’ support also proved to be essential for her decision to study medicine, a field that was dominated by men.Soon after graduating, in 1896, Montessori began work as a voluntary assistant in a clinic at the University of Rome, where she cared for children with learning difficulties. The rooms were bare, with just a few pieces of furniture. One day, she found that the children were enthusiastically playing with breadcrumbs (面包屑) that had dropped on the floor. It then occurred to her that the origin of some intellectual disabilities could be related with poverty. With the right learning materials, these and other young minds could be nurtured, Montessori concluded.The observation would lead Montessori to develop a new method of education that focused on providing optimal stimulation during the sensitive periods of childhood.At its centre was the principle that all the learning materials should be child-sized and designed to appeal to all the senses. In addition, each child should also be allowed to move and act freely, and use their creativity and problem-solving skills. Teachers took the role of guides, supporting the children without press or control.Mont essori opened her first Children’s House in 1907. When the Fascists (法西斯主义者) first came into power in Italy in 1922, they initially embraced her movement. But they soon came to oppose the emphasis on the children’s freedom of expression. Montessori’s value s had always been about human respect, and the rights of children and women, but the Fascists wanted to use her work and her fame.Things reached a breaking point when the Fascist tried to influence the schools’ educational content, and in 1934 Montessori and her son decided to leave Italy. She didn’t return to her homeland until 1947, and she continued to write about and develop her method until her death in 1952, at the age of 81.36. The primary reason for Montessori to develop a new educational method was ______.A．her family’s supportive influence on her educationB．her experience as a voluntary assistant in a clinicC．her observation of children playing with breadcrumbs happilyD．her decision to study medicine, a field dominated by men37. What was a central principle of Montessori’s educational method as described in the passage?A．Providing standardized, one-size-fits-all learning materials.B．Encouraging strict discipline and control over children’s actions.C．Focusing on rote memorization and competition.D．Creating a free and children-centered learning environment.38. Montessori decided to leave Italy in 1934 because .A．she wanted to explore other countries and culturesB．she wanted to avoid the Fascist’s influence on her workC．she was offered a better job in a different countryD．she wanted to retire and enjoy a peaceful life in another country39. Which of the following words can best describe Montessori in this passage?A．Observant and innovative. B．Traditional and emotional.C．Progressive and dependent. D．Open-minded and indifferent. Reducing the workweek to four days could have a climate benefit. In addition to improving the well-being of workers, cutting working hours may reduce carbon emissions. But those benefits would depend on a number of factors, experts emphasize, including how people choose to spend nonworking time.Commuting and travelTransportation is the biggest contributor to greenhouse emissions. A November 2021 survey of2,000 employees and 500 business leaders in the United Kingdom found that if all organizations introduced a four-day week, the reduced trips to work would decrease travel overall by more than 691 million miles a week.But the climate benefits of less commuting could be eliminated, experts said, if people choose to spend their extra time off traveling, particularly if they do so by car or plane.Energy usageShorter working hours could lead to reductions in energy usage, experts said. According to a 2006 paper, if the United States adopted European work standards, the country would consume about 20 percent less energy.Energy could also be conserved if fewer resources are needed to heat and cool large office buildings, reducing demands on electricity. For example, if an entire workplace shuts down on the fifth day, that would help lower consumption — less so if the office stays open to accommodate employees taking different days off.Lifestyle changesIt’s possible that fewer working hours may lead some people to have a larger carbon footprint, bu t experts say research suggests that most people are likely to shift toward more sustainable lifestyles.One theory is that people who work more and have less free time tend to do things in more carbon-intensive ways, such as choosing faster modes of transportation or buying prepared foods. Convenience is often carbon-intensive and people tend to choose convenience when they're time-stressed. Meanwhile, some research suggests that those who work less are more likely to engage in traditionally low-carbon activities, such as spending time with family or sleeping.“When we talk about the four-day workweek and the environment, we focus on the tangible, but actually, in a way, the biggest potential benefit here is in the intangible,” experts said.40. What is identified as the leading cause of greenhouse emissions according to the passage?A．The well-being of employees.B．The conservation of energy.C．Commuting and travel.D．The European work standard.41. What can be inferred from the underlined sentence “the biggest potential benefit here is in the intangible” in the last paragraph?A．People will have big potential in achieving intangible benefits while working.B．People are more likely to engage in carbon-intensive activities due to time constraints.C．People may shift toward more sustainable lifestyles and lower carbon footprints.D．People may travel more frequently by car or plane during their extra time off.42. The passage is mainly written to .A．highlight the importance of shortening working time in the context of well-beingB．provide an overview of transportation emissions worldwideC．analyze the impact of reduced working hours on mode of businessD．illustrate factors affecting the climate benefits of a shorter workweekThe cultivation of plants by ants is more widespread than previously realized, and has evolved on at least 15 separate occasions.There are more than 200 species of ant in the Americas that farm fungi (真菌) for food, but this trait evolved just once sometime between 45 million and 65 million years ago. Biologists regard the cultivation of fungi by ants as true agriculture appearing earlier than human agriculture because it meets four criteria: the ants plant the fungus, care for it, harvest it and depend on it for food.By contrast, while thousands of ant species are known to have a wide variety of interdependent relationships with plants, none were regarded as true agriculture. But in 2016, Guillaume Chomicki and Susanne Renner at the University of Munich, Germany, discovered that an ant in Fungi cultivates several plants in a way that meets the four criteria for true agriculture.The ants collect the seeds of the plants and place them in cracks in the bark of trees. As the plants grow, they form hollow structures called domain that the ants nest in. The ants defecate (排便) at designated absorptive places in these domain, providing nutrients for the plant. In return, as well as shelter, the plant provides food in the form of fruit juice.This discovery prompted Chomicki and others to review the literature on ant-plant relationships to see if there are other examples of plant cultivation that have been overlooked. “They have never really been looked at in the framework of agriculture,” says Chomicki, who is now at the University of Sheffield in the UK. “It’s definitely widespread.”The team identified 37 examples of tree-living ants that cultivate plants that grow on trees, known as epiphytes (附生植物). By looking at the family trees of the ant species, the team was able to determine on how many occasions plant cultivation evolved and roughly when. Fifteen is a conservative estimate, says Campbell. All the systems evolved relatively recently, around 1million to 3 million years ago, she says.Whether the 37 examples of plant cultivation identified by the team count as true agriculture depends on the definitions used. Not all of the species get food from the plants, but they do rely on them for shelter, which is crucial for ants living in trees, says Campbell. So the team thinks the definition of true agriculture should include shelter as well as food.43. According to biologists, why is ant-fungus cultivation considered as a form of true agriculture?A．Because it occurred earlier than human agriculture.B．Because it fulfills the standards typical of agricultural practices.C．Because it redefines the four criteria for true human agriculture.D．Because it is less common than previously thought.44. What motivated Chomicki and others to review the literature on ant-plant relationships?A．They determined on new family trees of the ant species.B．They overlooked some tree-living ants that provided nutrients for the plants.C．They never studied the ant-plant relationships within the context of agriculture.D．They never identified any an t species that engaged in cultivation of fungi.45. Which of the following statements is supported by the team's findings according to the passage?A．Ants’ cultivation of plants is limited to a few specific species.B．The cultivation of fungi by ants is considered the earliest form of agriculture.C．True agriculture in ants involves only food-related interactions with plants.D．Ants have independently cultivated plants on at least 15 distinct occasions.46. What is the passage mainly about?A．The evolution of ants in the plant kingdom.B．The widespread occurrence of ant-plant cultivation.C．The discovery of a new ant species engaging in agriculture.D．The contrast between ant agriculture and human agriculture.What is the likelihood of you having someone who looks just like you? Would it be a good thing? And if you did have one, would you want to meet them?Consider how often your facial features are used to identify you. Your passport, ID card and driving license all feature your face. 47 You may need your face to unlock your smartphone and possibly even need it to exclude you from being present at a crime scene.The word “doppelgänger” refers to a person who looks the same as you, essentially sharing your features; those that you thought were unique to you and your identity. Not identical twins, as a doppelgänger has no relation to you. The idea originated in German folklore. 48So, let's get real. What are the chances of you having one in the first place? There's said to be a one in 135 chance of an exact match for you existing anywhere in the world, so the chances are pretty low, despite folk wisdom promising you otherwise. And the chances of meeting? The mathematical certainty of finding this particular person is supposedly less than one in a trillion.That said, these statistics may be a good thing. Historically, having a double wasn't always a positive. Back in 1999, an innocent American man, indistinguishable from the real criminal, was sent to prison for robbery, where he stayed for 19 years. 49 . In a different case, a woman in New York was accused of trying to poison her doppelgänger with deadly cheesecake so that she could steal her identity!50 The fascination with doppelgängers may be rooted in historical beliefs that facial resemblance meant they were from the same family or had a common ancestor. It leads to the hope that one day you will meet your lookalike, creating the thrill of a potentially strange meeting. However, as these encounters can be both interesting and disturbing, we understand that after such an experience, you might not want to meet your doppelgänger again.passage in no more than 60 words. Use your own words as far as possible.Competitive CheerleadingOver the years, cheerleading has taken two primary forms: game-time cheerleading and competitive cheerleading. Game-time cheerleaders’ main goal is to entertain the crowd and lead them with team cheers, which should not be considered a sport. However, competitive cheerleading is more than a form of entertainment. It is really a competitive sport.Competitive cheerleading includes lots of physical activity. The majority of the teams require a certain level of tumbling (翻腾运动) ability. It’s a very common thing for gymnasts, so it’s easy for them to go into competitive cheerleading. Usually these cheerleaders integrate lots of their gymnastics experience including their jumps, tumbling, and overall energy. They also perform lifts and throws.Competitive cheerleading is also an activity that is governed by rules under which a winner can be declared. It is awarded points for technique, creativity and sharpness. Usually the more difficult the action is, the better the score is. That’s why cheerleaders are trying to experience great difficulty in their performance. Besides, there is also a strict rule of time. The whole performance has to be completed in less than three minutes and fifteen seconds, during which the cheerleaders are required to stay within a certain area. Any performance beyond the limit of time is invalid.Another reason for the fact that competitive cheerleading is one of the hardest sports is that it has more reported injuries. According to some research, competitive cheerleading is the number one cause of serious sports injuries to women. Generally, these injuries affect all areas of the body, including wrists, shoulders, ankles, head, and neck.There can be no doubt that competitive cheerleading is a sport with professional skills. It should be noted that it is a team sport and even the smallest mistake made by one teammate can bring the score of the entire team down. So without working together to achieve the goal, first place is out of reach. ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ___________________________________________________________________________52. 如果不好好准备，周五的演讲可能会变得一塌糊涂。
豆腐_豆浆_中屎肠球菌生长的温度预测模型
豆腐(豆浆)中屎肠球菌生长的温度预测模型李 博1 李里特1 辰巳英三2 李再贵1(11中国农业大学食品科学与营养工程学院,北京100083;21日本国农林水产省国际农林水产业研究中心)收稿日期:2002206207基金项目:中日国际合作项目作者简介:李 博,博士,副教授,主要从事食品安全和食品中微生物的研究。
摘 要 采用预测食品微生物学的方法研究了豆腐(豆浆)中主要腐败微生物屎肠球菌的生长规律,建立了屎肠球菌在豆浆培养基中的初级和二级预测模型,研究了0～55℃屎肠球菌的生长曲线。
结果表明,在适温阶段屎肠球菌的生长曲线呈典型的S 形,适合用G ompertz 模型拟合;当温度接近最低生长温度和最高生长温度时,适合用线性回归方程拟合。
屎肠球菌在豆浆中生长的温度模型符合Ratkowsky3式。
根据预测模型,屎肠球菌的最低生长温度为418℃,最高生长温度为5416℃,最适生长温度为41℃。
对模型进行了验证。
关键词 预测模型;屎肠球菌;豆腐;生长模型中图分类号 TS 20113;TS 21412 文章编号 100724333(2003)022******* 文献标识码 APredictive model for effect of temperature on the growth ofE.faecium in tofu (soymilk )Li Bo 1, Li Lite 1, Tatsumi Eizo 2, Li Zaigui 1(11College of Food Science &Nutritional Engineering ,China Agricultural University ,Beijing 100083,China ;21J apan International Research Center for Agricultural Sciences ,Ministry of Agriculutre ,Forestry and isheries )Abstract The growth characteristics of the major spoila ge bacteria in tofu - E.faecium was studie d by using themethod of pre dictive microbiology.And pre dictive models for the growth curves and the effects of temp erature on growth of microorganism were esta blishe d.Growth curves were fitte d by using the model of Logistic ,Gomp ertz and Monod functions ,and sp ecific growth rates derive d from the curve fitting were modele d.The exp eriment res ults were as follows :A study to build mathematical models that pre dict the growth of E.faecium in s oymilk (tofu )was carrie d out.Growth curves were obtaine d at 0-55℃.The Gomp ertz model were found to fit with repres entation of exp eri 2mental curves which are typical sigmoidal at 10-50℃.The Monod function were found to fit with the exp erimental curve at below 10℃or a bove 50℃.The variations of growth rate with temp erature were modele d.Data processing of the model has shown that the minimum growth temp erature for E.faecium is 418℃,the maximum growth temp erature is 5416℃and the optimal growth temp erature is 41℃.The validity of the pre dictive model was evaluate d under con 2trolle d la boratory conditions using s oymilk.K ey words pre dictive modeling ;Enterococcus faecium ;tofu ;growth model 豆腐是我国的传统食品。
Mathematical modeling of drying of pretreated
Mathematical modeling of drying of pretreated and untreated pumpkinT.Y.Tunde-Akintunde &G.O.OgunlakinRevised:13February 2011/Accepted:26April 2011#Association of Food Scientists &Technologists (India)2011Abstract In this study,drying characteristics of pretreated and untreated pumpkin were examined in a hot-air dryer at air temperatures within a range of 40–80°C and a constant air velocity of 1.5m/s.The drying was observed to be in the falling-rate drying period and thus liquid diffusion is the main mechanism of moisture movement from the internal regions to the product surface.The experimental drying data for the pumpkin fruits were used to fit Exponential,General exponential,Logarithmic,Page,Midilli-Kucuk and Parabolic model and the statistical validity of models tested were determined by non-linear regression analysis.The Parabolic model had the highest R 2and lowest χ2and RMSE values.This indicates that the Parabolic model is appropriate to describe the dehydration behavior for the pumpkin.Keywords Pumpkin fruits .Hot air drying .Effective diffusivity .Mathematical modellingNomenclature a Drying constant b Drying constant c Drying constant DR Drying rate (g water/g dry matter*h)k Drying constant,1/min M e Equilibrium moisture content(kg water/kg dry matter)M i Initial moisture content (kg water/kg dry matter)M R Dimensionless moisture ratioMR exp,i Experimental dimensionless moisture ratio MR pre,i Predicted dimensionless moisture ratio M t Moisture content at any time of drying (kg water/kg dry matter)M t +dtMoisture content at t +dt (kg water/kg dry matter)N Number of observationsn Drying constant,positive integer R 2Coefficient of determination t Time (min)W Amount of evaporated water (g)W 0Initial weight of sample (g)W 1Sample dry matter mass (g)z Number of constants χ2Reduced chi-squareIntroductionPumpkin (cucurbita mixta )is a fruit rich in Vitamin A,potassium,fiber and carbohydrates.It is a versatile fruit that can be used for either animal feed or for human consumption as a snack,or made into soups,pies and bread.The high moisture content of the fruit makes it susceptible to deterioration after harvest.The most common form of preservation being done locally is drying.It is a means of improving storability by increasing shelf-life of the food product.Dried products can be stored for months or even years without appreciable loss of nutrients.Drying also assist in reducing post harvest losses of fruits and vegetables especially which can be as high as 70%(Tunde-Akintunde and Akintunde 1996).Sun drying is the common method of drying in the tropical region.However the process is weather depen-T.Y .Tunde-Akintunde (*):G.O.Ogunlakin Department of Food Science and Engineering,Ladoke Akintola University of Technology,PMB 4000,Ogbomoso,Oyo State,Nigeria e-mail:toyositunde@J Food Sci TechnolDOI 10.1007/s13197-011-0392-2dent Also,the drying of food products with the use of sun-drying usually takes a long time thus resulting in products of low quality.There is a need for suitable alternatives in order to improve product quality.Hot air dryers give far more hygienic products and provide uniform and rapid drying which is more suitable for the food drying processes(Kingsly et al.2007a;Doymaz 2004a).Many types of hot-air dryers are being used for drying agricultural products.However the design of such driers for high-moisture foods constitutes a very complex problem owing to the characteristics of vegetable tissues.One of the most important factor that needs to be considered in the design of driers is the proper prediction of drying rate for shrinking particles and hence the appropriate drying time in the dryer needs to be investigated.This can be achieved by determination of the drying characteristics of the food material.Therefore the thin layer drying studies which normally form the basis of understanding the drying characteristics of food materials has to be carried out for each food material.Studies have been carried out on thin layer drying of some food materials(Gaston et al.2004), fruits(Doymaz2004a,c;Simal et al.2005),leaves and grasses(Demir et al.2004).Though there has been some literature on drying of pumpkin(Alibas2007;Doymaz2007b;Sacilik2007),the selection of appropriate model to describe the drying process for the variety common in the country and within the experimental conditions considered in this study is yet to be done.Thin layer drying models used in the analysis of drying characteristics are usually theoretical,semi-theoretical or purely empirical.A number of semi-theoretical drying models have been widely used by various researchers(Sharma and Prasad2004;Simal et al.2005;Sogi et al.2003;Togrul and Pehlivan2004).A number of pre-treatments can be applied depending on the food to be dried,its end use,and availability(Doymaz 2010).Pretreatment of food materials which includes; blanching,osmotic dehydration,soaking in ascorbic acid before or on drying have been investigated to prevent the loss of colour by inactivating enzymes and relaxing tissue structure.This improves the effect of drying by reducing the drying time and gives the eventual dried products of good nutritional quality(Kingsly et al.2007b;Doymaz 2010).Various commercially used pretreatments include potassium and sodium hydroxide,potassium meta bisul-phate,potassium carbonate,methyl and ethyl ester emul-sions,ascorbic and citric acids,(Kingsly et al.2007a,b; Doymaz2004a,b;El-Beltagy et al.2007).However non-chemical forms of pretreatment are generally preferred especially among small-scale processors in the tropics. Blanching as a pre-treatment is used to arrest some physiological processes before drying vegetables and fruits.It is a heat pre-treatment that inactivates the enzymes responsible for commercially unacceptable darkening and off-flavours.Blanching of fruits and vegetables is generally carried out by heating them with steam or hot water(Tembo et al.2008).However other forms of blanching i.e.oil-water blanching have been used by Akanbi et al.(2006)in a previous study for pretreating chilli.These forms of blanching were observed to have an effect on the drying rate and quality of the dried chili. However oil-water blanching pretreatments have not been studied for pumpkin.The aim of this study was:(a)to study the effect of the different blanching pre-treatments on the drying times and rate,and(b)to fit the experimental data to seven mathematical models available in the literature.Materials and methodsExperimental procedureFresh pumpkin fruit were purchased from Arada,a local market in Ogbomoso,Nigeria.The initial average moisture content of fresh pumpkin samples was deter-mined by oven drying method(AOAC1990),and it was found to be91.7%(wet basis)or10.90(g water/g dry matter).The samples were washed and peeled after which the seeds were removed.The pumpkin was then sliced into pieces of5mm×5mm dimensions.The blanching pre-treatments for inactivation of enzymes are as indicated below while untreated samples(UT)were used as the control.i)Samples submerged in boiling water for3minutes andcooling immediately in tap water-(WB)ii)Samples steamed over boiling water in a water bath (WBH14/F2,England)for3minutes and cooled immediately in tap water-(SB)iii)Samples dipped for3minutes in a homogenized mixture of oil and water of ratio1:20(v/v)with0.1g of butylated hydroxyl anisole(BHA)heated to95°C-(O/W B)In all the pretreatments the excess water was removed by blotting the pretreated pumpkin samples with tissue paper.The moisture contents after pretreatment were12.69(g water/g dry matter)for water and oil-water blanching and11.5(g water/g dry matter)for steam blanching.Drying procedureThe drying experiments of pumpkin samples were carried out in a hot-air dryer(Gallenkamp,UK)having three tiers of trays. Perforated trays having an area of approximately0.2m2wereJ Food Sci Technolplaced on each tier and the trays were filled with a single layer of the pumpkin samples.The air passes from the heating unit and is heated to the desired temperature and channeled to the drying chamber.The hot air passes from across the surface and perforated bottom of the drying material and the direction of air flow was parallel to the samples.The samples utilised for each experimental condition weighed 200±2g.Drying of the pumpkin was carried out at drying temperatures of 40to 800C with 20°C increment,and a constant air velocity of 1.5m/s for all circumstances.The dryer was adjusted to be selected temperature for about half an hour before the start of experiment to achieve the steady state conditions.Weight loss of samples was measured at various time intervals,ranging from 30min at the beginning of the drying to 120min during the last stages of the drying process by means of a digital balance (PH Mettler)with an accuracy of ±0.01g.The samples were taken out of the dryer and weighed during each of the time intervals.Drying was stopped when constant weight was reached with three consecutive readings.The experiments were repeated twice and the average of the moisture ratio at each value was used for drawing the drying curves.Model nameModelReferencesExponential modelMR ¼exp Àkt ðÞEl-Beltagy et al.(2007)Generalized exponential model MR ¼Aexp Àkt ðÞShittu and Raji (2008)Logarithmic model MR ¼aexp ðÀkt Þþc Akpinar and Bicer (2008)(Page ’s model)MR ¼exp Àkt n ðÞSingh et al.(2008)Midilli –Kucuk model MR ¼aexp Àkt n ðÞþbt Midilli and Kucuk (2003)Parabolic modelMR ¼a þbt þct 2Sharma and Prasad (2004),Doymaz (2010)Table 1Mathematical models fitted to pretreated pumpkin drying curves100200300400Drying Time (min)WB SBO/W B UT0.10.20.30.40.50.60.70.80.910100200300Drying Time (min)M o i s t u r e R a t i o00.10.20.30.40.50.60.70.80.91M o i s t u r e R a t i oWB SB O/W B UT00.10.20.30.40.50.60.70.80.91M o i s t u r e R a t i o100200300Drying Time (min)WB SB O/W B UTbacFig.1Drying curve of pump-kin slices dried at (a )40,(b )60and (c )80°C (WB-water blanched,SB-steam blanched,O/W B-oil water blanched,UT-untreated).Each observation is a mean of two replicate experiments (n =2)J Food Sci TechnolMathematical modelingThe moisture content at any time of drying (kg water/kg dry matter),M t was calculated as follows:M t ¼W o ÀW ðÞÀW 1W 1ð1ÞWhere W 0is the initial weight of sample,W is the amount of evaporated water and W 1is the sample dry matter mass.The reduction of moisture ratio with drying time was used to analyse the experimental drying data.The moisture ratio,M R,was calculated as follows:M R ¼M t ÀM eM i ÀM e¼exp ÀKt ðÞð2ÞWhere M t ,M i and M e are moisture content at any time of drying (kg water/kg dry matter),initial moisture content (kg water/kg dry matter)and equilibrium moisture content (kg water/kg dry matter),respectively.The equilibrium moisture contents (EMCs)were deter-mined by drying until no further change in weight wasobserved for the pumpkin samples in each treatment and drying condition (Hii et al.2009)The drying constant,K ,is determined by plotting experimental drying data for each pretreatment and drying temperature in terms of Ln M R against time (t)where M R is moisture ratio.The slope,k,is obtained from the straight line graphs above.The drying rate for the pumpkin slices was calculated as follows:DR ¼M t þdt ÀM tdtð3ÞWhere DR is drying rate,M t +dt is moisture content at t +dt (kg water/kg dry matter),t is time (min).The moisture ratio curves obtained were fitted with six semi-theoretical thin layer-drying models,Exponential,Generalized exponential,Page,Logarithmic,Midilli -Kucuk and Parabolic models (Table 1)in order to describe the drying characteristics of pretreated pumpkin.These linear forms of these models were fitted in the experimental data using regression technique.To evaluate the models,a nonlinear regression procedure was per-formed for six models using SPSS (Statistical Package for00.020.040.060.080.10.12Drying Time (h)D r y i n g r a t e (g w a t e r /g D M .h )WB SB O/W B UT00.020.040.060.080.10.120.140.160.180246Drying time (h)D r y i n g r a t e (g w a t e r /g D M .h )WB SB O/W B UT00.010.020.030.040.050.060246Drying Time (h)D r y i n g R a t e (g w a t e r /g D M .h )WB SB O/W B UTbacFig.2Drying rate curve of pretreated pumpkin dried at (a )40,(b )60and (c )80°C (WB-water blanched,SB-steam blanched,O/W B-oil water blanched,UT-untreated).Each observation is a mean of two replicate experiments (n =2)J Food Sci Technolsocial scientists)11.5.1software package.The correlation coefficient (R 2)was one of the primary criteria to select the best equation to account for variation in the drying curves of dried samples.In addition to R 2,other statistical parameters such as reduced mean square of the deviation (χ2)and root mean square error (RMSE)were used to determine the quality of the fit.The higher the value of R 2and the lower the values of χ2and RMSE were chosen as the criteria for goodness of fit.(Togrul and Pehlivan 2002;Demir et al.2004;Doymaz 2004b ;Goyal et al.2006).The above parameters can be calculated as follows:#2¼PN i ¼1MR ðexp ;i ÞÀMR ðpred ;i ÞÀÁN Àz2ð4ÞRMSE ¼1N XN i ¼1MR pred ;i ÀMR exp ;i ÀÁ2"#12ð5ÞWhere MR exp,i and MR pre,i are experimental and pre-dicted dimensionless moisture ratios,respectively;N is number of observations;z is number of constantsResults and discussion Drying characteristicsThe characteristics drying curves showing the changes in moisture ratio of pretreated pumpkin with time at drying temperatures of 40,60and 80°C are given in Fig.1.Figure 2show the changes in drying rate as a function of drying time at the same temperatures.It is apparent that moisture ratio decreases continuously with drying time.According to the results in Fig.1,the drying air temperature and pre-treatments had a significant effect on the moisture ratio of the pumpkin samples as expected.This is in agreement with the observations of Doymaz (2010)for apple slices.The figures show that the drying time decreased with increase in drying air temperature.Similar results were also reported for food products by earlierTable 2Drying constant (K)values for pretreatment methods and drying temperaturesDrying Temperature (°C)Pretreatment method Steam Blanching Water Blanching Oil-Water Blanching Untreated 400.45290.44580.42260.4029600.62230.61630.60150.5637800.78840.78710.78370.7803Model nameCoefficient of determination (R 2)Reducedchi-square (χ)Root mean square error (RMSE)40°CGeneralized Exponential Model 0.95180.0058240.071384Exponential Model 0.96550.0051960.062424Logarithmic Model 0.96840.0056210.059272Page Model0.973750.0032790.048397Midilli –Kucuk model 0.863980.0277520.109059Parabolic model 0.99630.0004730.0164460°CGeneralized Exponential Model 0.98740.0013820.035049Exponential Model 0.98820.0013460.032351Logarithmic Model 0.99420.0007850.022878Page Model0.980390.001110.028847Midilli –Kucuk model 0.818570.0145140.085189Parabolic model 0.99410.0004480.01672680°CGeneralized Exponential Model 0.95640.0038620.058588Exponential Model 0.96220.0038610.054796Logarithmic Model 0.97250.0107950.082138Page Model0.95950.0086160.080386Midilli –Kucuk model 0.937020.022370.105759Parabolic model0.98650.0032920.04685Table 3Curve fitting criteria forthe various mathematical models and parameters for pumpkin pre-treated with water blanching and dried at temperatures of 40,60and 80°CJ Food Sci TechnolModel nameCoefficient of determination (R 2)Reducedchi-square (χ)Root mean square error (RMSE)40°CGeneralized Exponential Model 0.95930.0048430.065095Exponential Model 0.96890.0042740.056615Logarithmic Model 0.968960.0050650.056262Page Model0.95990.0045870.057237Midilli –Kucuk model 0.818470.0342380.121134Parabolic model 0.99490.0006490.01925260°CGeneralized Exponential Model 0.987370.0013540.034688Exponential Model 0.98760.0014480.033563Logarithmic Model 0.990810.0008640.023994Page Model0.97490.0012870.031073Midilli –Kucuk model 0.982270.0169220.091982Parabolic model 0.99410.0005980.01933680°CGeneralized Exponential Model 0.94360.0054840.069818Exponential Model 0.951870.0108440.060609Logarithmic Model 0.958190.0052010.082325Page Model0.922370.0065670.070179Midilli –Kucuk model 0.955020.0210930.102696Parabolic model0.979590.0047230.058882Table 4Curve fitting criteria for the various mathematical models and parameters for pumpkin pre-treated with steam blanching and dried at temperatures of 40,60and 80°CModel nameCoefficient of determination (R 2)Reducedchi-square (χ)Root mean square error (RMSE)40°CGeneralized Exponential Model 0.94540.0067290.076734Exponential Model 0.96030.0059530.066819Logarithmic Model 0.961750.0069530.065922Page Model0.96450.0045960.057295Midilli –Kucuk model 0.838010.0328130.118587Parabolic model 0.99560.0008220.02167260°CGeneralized Exponential Model 0.976650.0017910.039903Exponential Model 0.982710.002020.039642Logarithmic Model 0.986950.0016620.033287Page Model0.974690.0012580.03072Midilli –Kucuk model 0.88840.0083740.064708Parabolic model 0.99280.0004530.01682280°CGeneralized Exponential Model 0.947850.0047940.065279Exponential Model 0.95540.00480.061101Logarithmic Model 0.96250.0120260.086696Page Model0.932230.0106440.089346Midilli –Kucuk model 0.94940.0200940.100234Parabolic model0.983570.0043540.053874Table 5Curve fitting criteria for the various mathematical models and parameters for pumpkin pre-treated with oil-water blanching and dried at temperatures of 40,60and 80°CJ Food Sci TechnolModel nameCoefficient of determination (R 2)Reducedchi-square (χ)Root mean square error (RMSE)40°CGeneralized Exponential Model 0.948760.0058960.071829Exponential Model 0.95850.0056790.065264Logarithmic Model 0.959110.0067350.06488Page Model0.94120.0064750.068007Midilli –Kucuk model 0.78980.0399250.130808Parabolic model 0.985950.0018690.03267860°CGeneralized Exponential Model 0.97350.0024360.046534Exponential Model 0.97490.0028840.047363Logarithmic Model 0.981070.0011850.028035Page Model0.95840.0021470.040127Midilli –Kucuk model 0.76690.0163070.090296Parabolic model 0.990390.0011790.0272280°CGeneralized Exponential Model 0.949980.0045840.063836Exponential Model 0.95720.0047680.060896Logarithmic Model 0.959850.0050460.057999Page Model0.920160.0077380.069542Midilli –Kucuk model 0.95070.0179590.09476Parabolic model0.97750.0042850.056692Table 6Curve fitting criteria for the various mathematical models and parameters for untreated pumpkin and dried at temper-atures of 40,60and 80°CDrying Time (h)M o i s t u r e R a t i oDrying Time (h)M o i s t u r e R a t i oDrying Time (h)M o i s t u r e R a t i obacFig.3Comparison of experi-mental and predicted moisture ratio values using Parabolic model for pretreated pumpkin dried at (a )40,(b )60and (c )80°C (WBE-water blanched experimental,SBE-steam blanched experimental,O/W BE-oil water blanchedexperimental,UTE-untreated experimental,WBP-waterblanched predicted,SBP-steam blanched predicted,O/W BP-oil water blanched predicted,UTP-untreated predicted).Each observation is a mean of two replicate experiments (n =2)J Food Sci Technolresearchers(Sacilik and Elicin2006;Lee and Kim2009; Kumar et al.2010).The drying time required to lower the moisture ratio of water blanched samples to0.034when using an air temperature of40°C(5h)was approximately twice that required at a drying air temperature of80°C (2.5h).This same trend occurred for both untreated and other pretreatment methods.The drying time required to reach moisture ratio of0.018for drying temperature of60°C for samples pretreated with steam blanching was3h while the corresponding values for water blanched,oil-water blanched and control samples were3.5,3.9and4h respectively.The difference in drying times of pre-treated samples with steam blanching was16.7%,30%and33.3%shorter than water blanched,oil-water blanched and control samples,re-spectively.Similar trends were observed at drying temper-atures of40and80°C.All the pretreated samples had higher drying curves than the untreated samples generally(Fig.1).This is an indication of the fact that various forms of blanching pretreatments increase the drying rate for pumpkin samples. This is similar to the observations of Goyal et al.(2008), Doymaz(2007a),Kingsly et al.(2007a),Doymaz(2004b) for apples,tomato,peach slices and mulberry fruits.The difference in drying is more pronounced at the initial stages of drying when the major quantity of water is evaporated while at the latter stages of drying the difference in the amount of water evaporated is not as pronounced as the early drying stages.The difference in the drying of the different pretreatments experienced in the initial stages becomes less pronounced with increase in drying temper-ature.This may be because at higher temperatures the driving force due to diffusion from the internal regions to the surface is higher thus overcoming hindrances to drying more effectively resulting in more uniform drying.The K values for pretreated samples were higher than that of untreated samples for all the drying temperatures(Table2). This confirms the fact that the various forms of blanching pretreatments increased the rate at which drying took place.Analysis of the drying rate curves(Fig.2)showed no constant-rate period indicating that drying occurred during the falling-rate period.Therefore,it can be considered a diffusion-controlled process in which the rate of moisture removal is limited by diffusion of moisture from inside to surface of the product.This is similar to the results reported for various agricultural products such Amasya red apples (Doymaz2010),peach(Kingsly et al.2007a),yam(Sobukola et al.2008),and tumeric(Singh et al.2010).Fitting of drying curveSPSS statistical software package for non-linear regression analysis was used to fit moisture ratio against drying time to determine the constants of the four selected drying models.The R2,χ2and RMSE used to determine the goodness of fit of the models are shown in Tables3,4,5 and6.The Parabolic model gave the highest R2value which varied from0.9963to0.9775for experimental conditions considered in this study.The values ofχ2and RMSE for the Parabolic model which varied from0.000448 to0.004723and0.01644to0.058882respectively were the lowest for all the models considered.From the tables,it is obvious that the Parabolic model therefore represents the drying characteristics of pretreated pumpkin(for individual drying runs)better than the other models(Generalized exponential,Exponential,Logarithmic,Page or Midilli–Kucuk)considered in this study.The comparison between experimental moisture ratios and predicted moisture ratios obtained from the Parabolic model at drying air temperature of40°C,60°C and80°C for pumpkin samples are shown in Fig.3.The suitability of the Parabolic model for describing the pumpkin drying behaviour is further shown by a good conformity between experimental and predicted moisture ratios as seen in Fig.3.This is similar to the observations of Doymaz(2010)for drying of red apple slices at55,65and75°C.ConclusionThe effect of temperature and pre-treatments on thin layer drying of pumpkin in a hot-air dryer was investigated. Increase in drying temperature from40to80°C decreased the drying time from5hours to4hours for all the samples considered.The pretreated samples dried faster than the untreated samples.Samples pretreated with steam blanch-ing had shorter drying times(hence higher drying rates) compared to water blanched,oil-water blanched and control samples The entire drying process occurred in falling rate period and constant rate period was not observed.The suitability of four thin-layer equations to describe the drying behaviour of pumpkin was investigated.The model that had the best fit with highest values of R2and lowest values ofχ2,MBE and RMSE was the Parabolic model. Thus this model was selected as being suitable to describe the pumpkin drying process for the experimental conditions considered.ReferencesAkanbi CT,Adeyemi RS,Ojo A(2006)Drying characteristics and sorption isotherm of tomato slices.J Food Eng73:141–146 Akpinar AK,Bicer Y(2008)Mathematical modelling of thin layer drying process of long green pepper in solar dryer and under open sun.Energy Conver Manag49:1367–1375Aliba I(2007)Microwave,air and combined microwave–air-drying parameters of pumpkin slices.LWT40:1445–1451J Food Sci TechnolAOAC(1990)Official methods of analysis,15th edn.Association of Official Analytical Chemists,ArlingtonDemir V,Gunhan T,Yagcioglu AK,Degirmencioglu A(2004) Mathematical modeling and the determination of some quality parameters of air-dried bay leaves.Biosys Eng88(3):325–335 Doymaz I(2004a)Drying kinetics of white mulberry.J Food Eng61(3):341–346Doymaz I(2004b)Pretreatment effect on sun drying of mulberry fruit (Morus alba L.).J Food Eng65(2):205–209Doymaz I(2004c)Convective air drying characteristics of thin layer carrots.J Food Eng61(3):359–364Doymaz I(2007a)Air-drying characteristics of tomatoes.J Food Eng 78:1291–1297Doymaz I(2007b)The kinetics of forced convective air-drying of pumpkin slices.J Food Eng79:243–248Doymaz I(2010)Effect of citric acid and blanching pre-treatments on drying and rehydration of Amasya red apples.Food Bioprod Proc 88(2–3):124–132El-Beltagy A,Gamea GR,Amer Essa AH(2007)Solar drying characteristics of strawberry.J Food Eng78:456–464Gaston AL,Abalone RM,Giner SA,Bruce DM(2004)Effect of modelling assumptions on the effective water diffusivity in wheat.Biosys Eng88(2):175–185Goyal RK,Kingsly ARP,Manikantan MR,Ilyas SM(2006)Thin layer drying kinetics of raw mango slices.Biosys Eng95(1):43–49 Goyal RK,Mujjeb O,Bhargava VK(2008)Mathematical modeling of thin layer drying kinetics of apple in tunnel dryer.Int J Food Eng 4(8):Article8Hii CL,Law CL,Cloke M,Suzannah S(2009)Thin layer drying kinetics of cocoa and dried product quality.Biosys Eng102:153–161 Kingsly RP,Goyal RK,Manikantan MR,Ilyas SM(2007a)Effects of pretreatments and drying air temperature on drying behaviour of peach slice.Int J Food Sci Technol42:65–69Kingsly ARP,Singh R,Goyal RK,Singh DB(2007b)Thin-layer drying behaviour of organically produced tomato.Am J Food Technol 2:71–78Kumar R,Jain S,Garg MK(2010)Drying behaviour of rapeseed under thin layer conditions.J Food Sci Technol47(3):335–338 Lee JH,Kim HJ(2009)Vacuum drying kinetics of Asian white radish (Raphanus sativus L.)slices.LWT-Food Sci Technol42:180–186Midilli A,Kucuk H(2003)Mathematical modeling of thin layer drying of pistachio by using solar energy.Energy Conver Manag 44(7):1111–1122Sacilik K(2007)Effect of drying methods on thin-layer drying characteristics of hull-less seed pumpkin(Cucurbita pepo L.).J Food Eng79:23–30Sacilik K,Elicin AK(2006)The thin layer drying characteristics of organic apple slices.J Food Eng73:281–289Sharma GP,Prasad S(2004)Effective moisture diffusivity of garlic cloves undergoing microwave convective drying.J Food Eng65(4):609–617Shittu TA,Raji AO(2008)Thin layer drying of African Breadfruit (Treculia africana)seeds:modeling and rehydration capacity.Food Bioprocess Technol:1–8.doi:10.1007/s11947-008-0161-zSimal S,Femenia A,Garau MC,Rossello C(2005)Use of exponential,page and diffusion models to simulate the drying kinetics of kiwi fruit.J Food Eng66(3):323–328Singh S,Sharma R,Bawa AS,Saxena DC(2008)Drying and rehydration characteristics of water chestnut(Trapa natans)as a function of drying air temperature.J Food Eng87:213–221Singh G,Arora S,Kumar S(2010)Effect of mechanical drying air conditions on quality of turmeric powder.J Food Sci Technol47(3):347–350Sobukola OP,Dairo OU,Odunewu A V(2008)Convective hot air drying of blanched yam slices.Int J Food Sci Technol43:1233–1238 Sogi DS,Shivhare US,Garg SK,Bawa SA(2003)Water sorption isotherms and drying characteristics of tomato seeds.Biosys Eng 84(3):297–301Tembo L,Chiteka ZA,Kadzere I,Akinnifesi FK,Tagwira F(2008) Blanching and drying period affect moisture loss and vitamin C content in Ziziphus mauritiana(Lamk.).Afric J Biotech7:3100–3106Togrul IT,Pehlivan D(2002)Mathematical modeling of solar drying of apricots in thin layers.J Food Eng55:209–216Togrul IT,Pehlivan D(2004)Modeling of thin layer drying kinetics of some fruits under open air sun drying process.J Food Eng65(3):413–425Tunde-Akintunde TY,Akintunde BO(1996)Post-harvest losses of food crops:sources and solutions.Proceedings of the Annual Conference of the Nigerian Society of Agricultural Engineers, Ile-Ife,Nigeria from November19–22,1996.V ol18:258–261J Food Sci Technol。
北美数学建模PROBLEMA、B、C、D题翻译-6页
PROBLEM A:The Ultimate Brownie Pan终极布朗尼潘When baking in a rectangular pan heat is concentrated in the 4 corners and the product gets overcooked at the corners (and to a lesser extent at the edges). In a round pan the heat is distributed evenly over the entire outer edge and the product is not overcooked at the edges. However, since most ovens are rectangular in shape using round pans is not efficient with respect to using the space in an oven. 当在一个矩形的锅热烘烤时，热量被浓缩在4个角落中，并在拐角处（以及在较小程度上在边缘处）：产品会过头。
在一个圆形盘中，热量被均匀地分布在整个外缘，并且在边缘处的产品不过头。
然而，因为大多数烤炉使用圆形平底锅，而形状是矩形的，这样是效率不高的相对于使用在烘箱中的空间。
Develop a model to show the distribution of heat across the outer edge of a pan for pans of different shapes -rectangular to circular and other shapes in between. 开发一个模型来显示横跨平底锅平底锅不同形状-矩形之间的圆形和其他形状的外边缘的热量分布。
Assume1. A width to length ratio of W/L for the oven which is rectangular in shape.2. Each pan must have an area of A.3. Initially two racks in the oven, evenly spaced.1宽度与长度之比（W / L）的是矩形的烘箱。
数学产品英语作文
数学产品英语作文Mathematics is a fundamental subject that is essentialfor understanding the world around us. From basicarithmetic to advanced calculus, mathematics plays acrucial role in various fields such as science, engineering, finance, and even art. In this essay, I will discuss someof the key products and concepts in mathematics and their significance.One of the most important products in mathematics is the concept of numbers. Numbers are the building blocks of mathematics and are used to quantify and measure quantities. They can be classified into different types such as natural numbers, integers, rational numbers, irrational numbers,and real numbers. Each type of number has its own unique properties and applications in various mathematical concepts.Another significant product in mathematics is theconcept of functions. A function is a relation between aset of inputs and a set of possible outputs with the property that each input is related to exactly one output. Functions are used to model and analyze various real-worldphenomena and are fundamental in calculus, algebra, and other branches of mathematics. They are also used to describe the behavior of mathematical systems and are essential for understanding the concept of change and variation.Furthermore, the concept of geometry is a key product in mathematics. Geometry is the branch of mathematics that deals with the properties and relationships of points, lines, angles, surfaces, and solids. It is used to study shapes, sizes, and properties of space and is fundamental in fields such as architecture, engineering, and physics. Geometry has also played a crucial role in the development of modern mathematics and has led to the discovery of various mathematical concepts and theorems.In addition, the concept of algebra is another important product in mathematics. Algebra is the branch of mathematics that deals with symbols and the rules for manipulating those symbols. It is used to solve equations, analyze patterns, and study the properties of mathematical operations. Algebra is also essential for understanding the concept of variables, equations, and functions, and isfundamental in various fields such as computer science, physics, and economics.Furthermore, the concept of calculus is a significant product in mathematics. Calculus is the branch of mathematics that deals with the study of change and motion. It is used to analyze and model various real-world phenomena such as motion, growth, and decay, and is fundamental in fields such as physics, engineering, and economics. Calculus has also led to the development of various mathematical concepts such as limits, derivatives, and integrals, and has played a crucial role in the advancement of modern science and technology.In conclusion, mathematics is a fundamental subject that is essential for understanding the world around us. From the concept of numbers to the principles of calculus, mathematics plays a crucial role in various fields and has led to the development of various mathematical products and concepts. It is important to continue to study and explore the beauty and significance of mathematics in order to further our understanding of the world and its many complexities.数学是一门基础学科，对于理解我们周围的世界至关重要。
algebra thomas w.hungerford 简介 -回复
algebra thomas w.hungerford 简介-回复Thomas W. Hungerford is a highly renowned mathematician and author who has made significant contributions to the field of algebra. His works and publications have greatly influenced students and researchers around the world. In this essay, we will explore the life, achievements, and impact of Thomas W. Hungerford, focusing on his contributions to the field of algebra.Thomas W. Hungerford was born on October 15, 1936, in Chicago, Illinois, United States. He developed an early interest in mathematics and pursued it further during his academic career. Hungerford attended the University of Chicago, where he earned his undergraduate degree in 1958. He then went on to complete his Ph.D. in mathematics at Princeton University under the guidance of the eminent mathematician John Tukey in 1963.After completing his doctorate, Hungerford embarked on his career as a mathematician. His research primarily focused on algebra, with an emphasis on ring theory and homological algebra. Hungerford made significant contributions to these areas, particularly in commutative algebra and the theory of rings and modules.One of Hungerford's most notable achievements in algebra is the book "Abstract Algebra: An Introduction," which is widely recognized as one of the most comprehensive and influential textbooks in the field. First published in 1974, this book provides a rigorous introduction to the fundamental concepts of abstract algebra. It covers a wide range of topics, including group theory, ring theory, field theory, and Galois theory. The book has been widely used as a textbook in undergraduate and graduate courses in algebra, and it continues to be highly regarded for its clarity, rigor, and depth.In addition to "Abstract Algebra: An Introduction," Hungerford has authored several other books and research papers in algebra. Some of his other notable works include "Algebra," "Algebraic Geometry: A First Course," and "Introduction to Algebraic Structures." These works have further solidified Hungerford's reputation as an authority in the field and have continued to serve as valuable resources for students and researchers alike.Apart from his research and publications, Hungerford has also made significant contributions as an educator. He has taughtmathematics at various prestigious institutions, including the University of Rochester, Ohio State University, and Western Illinois University. Hungerford's teaching style is known for its clarity and precision, allowing students to grasp complex algebraic concepts with ease. Many of his former students have gone on to become successful mathematicians and researchers themselves, further highlighting the impact of his teaching and mentorship.Hungerford's contributions to the field of algebra extend beyond his own research and teaching. He has served as the editor or associate editor for several mathematical journals, including the "Journal of Algebra" and "Communications in Algebra." He has also been actively involved in various professional societies, such as the American Mathematical Society, serving on committees and contributing to the advancement of algebraic research.In recognition of his contributions to the field, Hungerford has received numerous awards and honors throughout his career. He was elected as a Fellow of the American Mathematical Society in 2012 for his contributions to teaching and research in algebra. His works continue to be referenced and studied by mathematicians worldwide, making him a highly respected figure in the field ofalgebra.In conclusion, Thomas W. Hungerford is an esteemed mathematician who has made significant contributions to the field of algebra. Through his research, publications, and teaching, he has greatly influenced the study and understanding of algebraic concepts. Hungerford's books, particularly "Abstract Algebra: An Introduction," continue to be widely used and revered in the mathematical community. His impact as an educator and mentor has also been significant, with many of his students going on to make their mark in the field. Overall, Thomas W. Hungerford's work and influence have solidified his place among the leading figures in the field of algebra.。
2023-2024学年江西省赣州市南康中学高考英语三模试卷含解析
2024年高考英语模拟试卷注意事项：1．答卷前，考生务必将自己的姓名、准考证号、考场号和座位号填写在试题卷和答题卡上。
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第一部分（共20小题，每小题1.5分，满分30分）1．—I will be a vice president in a year or two.—You can’t be serious!_______.A．I can’t make it B．I can’t help it C．I won’t tell a soul D．I wouldn’t bet on it2．Tom’s comments on this issue are confusing because they appear to ______the remarks on the same issue made earlier by him.A．violate B．induce C．clarify D．contradict3．一When he know the result of today’s job interview?一In a couple of days．A．should B．may C．shall D．must4．While working in Kunming, he checked the weather each morning for months ________he realized it would be the same every day.A．when B．afterC．before D．since5．_______, I have never seen anyone who's as capable as John.A．As long as I have traveled B．Much as I have traveledC．Now that I have traveled so much D．As I have traveled so much6．一Excuse me，sir．You can’t enter0ffice without permission．一But the manager is expecting me．A．the；a B．an；the C．the；不填D．不填；不填7．--- Mom, can you give me an extra 200 yuan a month?--- Son, we have just bought a house, and from now on we need to practise strict .A．economy B．medicine C．self-control D．patience8．My mom once worked in a very small village school, which is__________only on foot.A．acceptable B．adequate C．accessible D．appropriate9．I hope that we will be able to make it through the tough times and back to the business of working together ________ our common goals.A．on behalf of B．in honor of C．on top of D．in search of10．Class Two, our class became the Basketball Champion of our school.A．Beating B．to beat C．Beaten by D．Having beaten11．________ your blog, I would have written back two days ago.A．If I read B．Should I readC．Had I read D．If I could have read12．At school, it is essential that every child ______ equally regardless of family background.A．treating B．treated C．be treated D．is treated13．If we use the new recycling method, a large number of trees .A．are saved B．will save C．will be saved D．have saved14．As to the long-term effects of global warming some believe that the damage has been done,______________________.A．otherwise we take steps to make up nowB．now that we take steps to make upC．whether we take steps to make up now or notD．unless we take steps to make up now15．The old woman who ________ in the deserted house alone for ten years has been settled in a nursing home now. A．lived B．has livedC．had lived D．has been living16．Sometimes, the kind of food we serve a person suggests ________ we show our gratitude.A．when B．whatC．why D．how17．—I'm going to order chicken and salad．What about you?—.I'll have the same.A．I'm afraid not B．It's up to youC．That sounds good to me．D．That depends18．Peterson, a great archaeologist, said: “Archaeologists have been extremely patient because we were led to believe that the ministry was ________ this problem, but we feel that we can't wait any longer.”A．looking out B．bringing out C．carrying out D．sorting out19．I thought it hard to complete the project then, but I ________ my mind.A．will change B．would changedC．have changed D．had changed20．Was it at the beginning _____ you made the promise ____ you would do all to help make it?A．that; that B．when; thatC．that; when D．when; when第二部分阅读理解（满分40分）阅读下列短文，从每题所给的A、B、C、D四个选项中，选出最佳选项。
2021年美国大学生数学建模竞赛题目A--真菌范文六篇(含Matlab源代码)
do the different fungi interact and decompose ground litter in a fixed patch of land in different
?12122?1142?1???1???11112206?12?2242?2???1???2222110102025wheremoisturetoleranceiswelldeterminedby
2021年美国大学生数学建模竞赛题目A--真菌范文六
篇（含Matlab源代码）
问题A：真菌……………………………………………………………………2
Include predictions about the relative advantages and disadvantages for each species and
combinations of species likely to persist, and do so for different environments including arid,
(difference of each isolate’s competitive ranking and their
moisture niche width, both scaled to [0,1]) of various fungi
and the resulting wood decomposition rate (% mass loss
Your complete solution.
林木病理学_东北林业大学中国大学mooc课后章节答案期末考试题库2023年
林木病理学_东北林业大学中国大学mooc课后章节答案期末考试题库2023年1.According to plant pathology, which of the following is not caused by viraldiseases?答案:Bacterial gall on the stem2.Parasite is答案:an organism that grows part or all of the time on or within another organism of a different species(known as its host),and from which it derives all or part of its food.3. A pathogen is答案:an organism that causes disease.4.Biotic disease is答案:Disease caused by living organisms.5.Host is答案:An organism upon which an organism of a different species grows and from which all or most of its food is derived.6.which feature is not characteristic of mushroom structure?答案:leaf7.What is plant disease?答案:sustained physiological and structural damage to plant tissues caused by biological and non-biological agents ending sometimes in plant death.8.abiotic disease is答案:Disease resulting from nonliving agents.9.Saprophyte is答案:An organism that lives on dead organic matter.10.What is the definition of obligate parasite?答案:A parasite that is incapable of existing independently of living tissues.11.What is the definition of Facultative saprophytes?答案:are mostly parasitic, but have the faculty to live on dead organic matter, like Phytophthora spp.12.What is the definition of toxicity?答案:The inherent ability of a toxicant to damage plants and animals. 13.What is the possible diameter for mushroom spores?答案:10μm14.which of the following cells or structures are associated with sexualreproduction in fungi?答案:ascospores15.All fungi share which of the following characteristics?答案:heterotrophic16.chestnut blight is a kind of _____ disease.答案:Infectious17.Crown gall often grows on willow in Sun Island Park，Crown gall is a _____disease.答案:Bacterial18.对Forest decline正确的理解的是答案:森林衰退19.Diplodia Blight of Pines（松枯梢病）is casused by Sphaeropsis sapinea, syn.Diplodia pinea，which of the following is the correct description of thedisease.答案:A fungal infectious disease20.According to the knowledge of Plant Pathology, the correct description of thevirus is:答案:Viruses are too small to be seen even with the aid of a powerful lightmicroscope.Viruses are systemic pathogens.21.Viruses are characteristically composed of which one?答案:a protein coata nucleic acid core22.The correct description of fungi is答案:Fungi are heterotrophs that feed by absorptionFungi play key roles in nutrient cycling, ecological interactions, and human welfareFungi produce spores through sexual or asexual life cyclesFungi have radiated into a diverse set of lineages23.Which are biotic factors in the following items？答案:Bacteria Fungi。
Fungal phytotoxins as mediators of virulence
Available online at Fungal phytotoxins as mediators of virulenceNadine Mo¨bius1,2and Christian Hertweck1,2Many phytopathogenic fungi exert their destructive effects byproducing and secreting toxic low molecular weightcompounds.In the past years a large number of novel fungalvirulence factors and their modes of action have beenidentified.This review highlights effective phytotoxin-mediatedstrategies to distress,weaken or kill the plant host.Addresses1Leibniz Institute for Natural Product Research and Infection Biology,HKI,Beutenbergstr.11a,07745Jena,Germany2Friedrich Schiller University,Jena,GermanyCorresponding author:Hertweck,Christian(christian.hertweck@hki-jena.de)Current Opinion in Plant Biology2009,12:390–398This review comes from a themed issue onBiotic InteractionsEdited by Xinnian Dong and Regine KahmannAvailable online14th July20091369-5266/$–see front matter#2009Elsevier Ltd.All rights reserved.DOI10.1016/j.pbi.2009.06.004IntroductionAmong the causal agents of infectious diseases of cropplants phytopathogenic fungi play an important role.Notonly by causing devastating epidemics,but also throughthe less spectacular although persistent and significantannual crop yield losses fungal plant pathogens havea serious economic impact.Many protein factors areinvolved in the process of infection and the establishmentof a parasitic fungal–plant interaction,such as cell walldegrading enzymes(cutinases,hydrolytic enzymes,etc.)[1].Even so,low molecular weight phytotoxins often playa key role in infection and virulence.Typically,suchfungal secondary metabolites alone reproduce some oreven all of the symptoms of the disease caused by thefungal producer organisms[2].In the past years a largenumber of novel fungal virulence factors and their modesof action have been identified.Apart from improvedanalytical methods for the elucidation of metabolitestructures,research in thisfield has been propelled bythe availability of full genome sequences of fungal patho-gens[3,4 ]and the application of‘omics’tools andbioinformatics.‘Genome mining’approaches aid in pre-dicting biosynthetic pathways of yet unknown toxicmetabolites in silico[5 ].Molecular tools help to veryeffectively generate knock out of implicated genes andallow producing toxin deficient mutants for functionalanalyses.By studies at the biochemical level importantinsights into the destructive modes of action of thephytotoxins have been gained.The strategies for exertingvirulence can be manifold:In general,necrotrophicpathogens use toxins to elicit plant cell death and derivenutrition from the dead tissue,whereas biotrophic patho-gens rely on living plant tissue.Phytotoxins may interactwith a range of cellular targets,alter gene expression orundermine membrane integrity.A number of phytotoxinsinhibit the activity of plant enzymes,thereby disruptingthe biosynthesis of crucial metabolites.Other fungi inter-fere with the plants’physiology by producing plant hor-mones,such as gibberelin or gibberellic acid(GA,fromthe rice pathogen Gibberella fujikuroi)[6]or the auxinindole-3-acetic acid(IAA,e.g.from Ustilago maydis,Tri-choderma and Moniliophthora perniciosa)[7].Finally,plantcells may be damaged by the production of reactiveoxygen species(ROS)(Figure1).Some phytotoxins are host-specific on the genus or evenon the species level and determine the host range of thefungus by targeting specific enzymes or metabolic path-ways[8].Such host-specific toxins(HSTs)induce patho-genicity only in the host species,where a gene product isthe direct or indirect target of the toxin.Nearly all fungiproducing HST(i.e.fungi of the genera Alternaria,Cochliobolus,Leptosphaeria,Venturia,Ascochyta and Pyreno-phora)belong to the order Pleosporales and appear tohave a tendency to lateral gene transfer[1,2].Finally,it should be noted that already in the primaryinfection process secondary metabolites can play animportant role.Many fungal pathogens penetrate plantleaves from a specialized cell,the appressorium.Theappressorium of Magnaporthe oryzae,a rice blast pathogen,is melanized by oxidative polymerization of polyketideprecursors and forms an effective barrier to solute move-ment.Water is entering and an enormous turgor pressureof approximately80atmospheres is produced.The result-ing force is usually applied to gain entry into plant tissue[9].Shedding light on plant-damagingphotosensitizersVarious phytopathogenic fungi produce so-called photo-sensitizers to generate ROS and thus impair plant cells byinduction of apoptosis and damage to membrane lipids.This mechanism has been observed for metabolites shar-ing a3,10-dihydroxy-4,9-perylenequinone chromophore,such as cercosporin and elsinochrome(Figure2).Afterabsorption of light energy,perylenequinones adopt anactivated triplet state.The radical can then react withoxygen to form ROS (O 2À,H 2O 2)and singlet oxygen or induce oxidative lipid decomposition,thus causing major damages to the host cell membrane [10].Cercosporin is produced by Cercospora species that infect corn,soybean,coffee and other plants.The light-induced damage leads to leakage of nutrients in the intracellular space,thus making them available for fungal hyphae.The fungus protects itself probably via toxin export and quenchers [10].A polyketide synthase,CTB1,plays a key role in cercosporin biosynthesis in Cercospora nicto-nianae ,as CTB1mutants cause fewer necrotic lesions on tobacco leaves [11].Interestingly,expression of the CTB1gene is highly regulated by light.Disruption of ctb4,a gene coding for a putative membrane transporter,results in decreased cercosporin emission and reduced virulence against tobacco cells [11].The red-pigmented elsinochromes are produced by Elsi-noe fawcettii when exposed to light [12].Citrus cells,when in contact with the fungus,are rapidly killed whereasaddition of b -carotene or superoxide dismutase dampens plant cells damage.The polyketide synthase gene Efpks1essential for elsinochrome production has been identified by gene disruption,and the resulting elsinochrome-nega-tive mutant has a significantly reduced ability to form lesions in lemon leaves [12].Another light-dependent plant-damaging mechanism has been identified in the context of Ramularia collo-cygni leaf spot disease on barley.Rubellin D (Figure 2),an anthraquinone derivative,induces peroxidation of alpha-linoleic acid in a light dependent manner,predominantly caused by singlet oxygen formation [13].Furthermore,chlorophyll bleaching was observed in toxin-treated leaves.Interestingly,ferrous ions enhance the rubel-lin-induced reaction,but repress the action of cercos-porin [13].Protein targetingEpipolythiodioxopiperazines (ETPs)contain a character-istic internal di-sulphide or tri-sulphide bridge (Figure 2).Fungal phytotoxins as mediators of virulence Mo¨bius and Hertweck 391Figure1Overview on the cellular targets and the mode of action of several fungal phytotoxins,GDC,glycine decarboxylase;CerS,ceramide synthase,ER,enoyl reductase;HDAC,histone deacetylase complex;NO,nitric oxide;PCD,programmed cell death;PM,plasma membrane.Although the exact mode of action is not yet fully under-stood,an involvement of this structural feature in protein conjugation [14]or generation of ROS via redox cycling is plausible [14].Prominent examples of such toxins are sirodesmin PL produced by Leptosphaeria maculans and gliotoxin produced by Trichoderma spp.and Aspergillus fumigatus [15].A mutant with a disruption of the bimod-ular NRPS gene (sirP )of L.maculans stalls the production of sirodesmin PL,causes fewer lesions and is half as effective as the wild-type in colonizing stems of Brassica napus (Canola)[15].Phytotoxins affecting membrane integrityToxin-mediated inhibition of enzymes involved in lipid biosynthesis is a common strategy applied by phyto-pathogenic fungi.Important examples are the closely related toxins fumonisin (from Fusarium spp.)and AAL-toxin (from Alternaria alternata ),which act as sphingosine analogs and inhibit sphinganine –N -acetyltransferase and ceramide synthase (Figure 3)[16,17 ].In this way,lipid biosynthesis is hampered,resulting in a perturbed mem-brane ordering and increased membrane permeability.Itshould also be noted that toxin-induced changes in ceramide metabolism may have severe consequences for a variety of regulatory processes,as ceramides are involved in intracellular signaling pathways.Gibberella moniliformis ,the cause of maize seedling blight,produces fumonisin B1as one of its virulence factors.Although fumonisin-insensitive maize strains are not resistant to infection,systemic colonization of seedlings is reduced [18].Cyperin (Figure 3),a diphenyl ether phytotoxin produced by several fungal plant pathogens,interferes with lipid biosynthesis by inhibiting enoyl reductase (ER)[19].Cyperin is bound to the ER active site by p -p stacking of a phenyl ring and the nicotinamide ring of NAD +.At high concentrations cyperin also blocks protoporphyrino-gen oxidase,a key enzyme in porphyrin synthesis [19].A straightforward way of membrane damage is exerted by the fungus Cercospora beticola using so-called beticolins (Figure 3)or yellow toxins.The polyketides can self-assemble into multimeric structures and form ion392Biotic InteractionsFigure2Structures of apoptosis-inducing phytotoxins victorin and DON,the protein-attacking mycotoxins gliotoxin and sirodesmin (ETP),the actin skeleton targeting cytochalasin B and the photosensitizers cercosporin,elsinochrome A and rubbellin D.channels in the host membrane (Figure 1).Effects of the pore formation are dramatic loss of solutes,inhibition of ATP-dependent H +-transport and membrane depolariz-ation in various plant species [20].Taking what’s not given—siderophores in virulenceUpon infection –and in particular after penetration –a fungus becomes dependent on the availability ofnutrients inside of the host.Iron is an essential nutrient and the major redox mediator in cellular processes and thus essential for survival of the pathogen [21].Iron acquisition is carried out via the secretion and subsequent uptake of low-molecular-weight chelators,so called side-rophores,like ferricrocin (A.brassicicola )or triacetylfusar-inine C (TAFC,F.gramineum,Figure 4).Mechanisms for iron uptake can be regarded as virulence determinants that lead to iron depletion in the host.Deletion of genesFungal phytotoxins as mediators of virulence Mo¨bius and Hertweck 393Figure3Molecules targeting membrane integrity.Sphingosin and phytotoxic analogs AAL-toxin and fumonisin;structure of cyperin,an inhibitor of enoylreductase and of the pore-forming toxin beticolin 0.coding for non-ribosomal peptide synthetases involved in siderophore biosynthesis,for example nps6(C.heterostro-phus )and sid1(F.gramineum ),led to a reduction in virulence to the host plant and to a simultaneous increase in ROS sensitivity in C.heterostrophus .The defects could be compensated by exogenous application of iron [21].By contrast,the biotroph U.maydis relies on reductive iron uptake rather than on siderophores.Deletion of fer1and fer2(encoding a high-affinity iron permease and an iron multicopper oxidase)proved to be much less virulent [22].Energy breakdownThe blockage of ATP-hydrolysis leads to complete energy breakdown in the plant cell.Tentoxin (Figure 4),a host-selective toxin,produced by Alternaria species targets this energy transfer process in the chlor-oplast.The cyclic tetrapeptide blocks ATP hydrolysis by binding to the surface between the a and b subunits of chloroplast ATPase.The crystal structure of spinach chloroplast F1with bound tentoxin was solved,and it was shown that a single molecule of the toxin affects ADP release in a non-competitive mechanism [23].T-toxin,a polyketide synthesized by Cochliobolus heterostrophus ,is associated with high virulence on certain genotypes of maize.It selectively targets T cytoplasm mitochondria mediated by the T-urf13protein,which results in con-formational changes and pore formation followed by mitochondrial swelling.Changes in oxidative phosphoryl-ation and respiration as well as leakage of nutrients andcalcium has been observed [24].The toxin is assembled by action of two polyketide synthases (PKSs).One PKS provides the polyketide starter unit for the second PKS,which produces the mature T-toxin molecule.A third biosynthetic gene codes for a decarboxylase (DEC1)[25 ].These genes reside in AT-rich DNA that is unique to T-toxin-producing strains (race T).The biosynthetic genes have probably undergone lateral gene transfer,as race T harbors an additional 1.2Mb of DNA compared with the weakly pathogenic race 0lacking the Tox1locus [24].An energy breakdown may also be caused by phytotoxins that affect the integrity of plant plasma membranes (see above),which results in an increased membrane per-meability and nutrient leakage,or target H +-ATPase,thus disrupting the electrochemical gradient.It has been shown that fusicoccin,a glycosylated diterpene,aug-ments potassium uptake with concomitant proton extru-sion in rice plants,which leads to an increased extracellular acidification [26].Binding of fusicoccin to the plant plasma membrane H +-ATPase is mediated by a regulatory protein belonging to the 14-3-3family.A stable complex with the C-terminus of the H +-ATPase is formed,leading to its permanent activation and irreversible stomata opening.Its mode of action has been elucidated by X-ray crystallographic analysis of the ternary complex of fusicoccin,a plant 14-3-3protein,and a phosphopeptide derived from the394Biotic InteractionsFigure4Structures of molecules causing energy breakdown in plant cells,and the siderophore triacetylfusarinine C.C-terminus of H+-ATPase.Structural analysis and iso-thermal titration calorimetry indicated that peptide and toxin mutually increase each other’s binding affinity throughfilling a cavity in the interaction surface[27 ]. In Arabidopsis thaliana cells,fusicoccin induces an H+-ATPase state-independent increase in the extracellular H2O2level.Measurement on exogenous catalase activity indicated a reduced capability of the cells to degrade H2O2formed in cell-free media.Apparently an as yet unidentified factor accumulates in the incubation med-ium of cells treated with fusicoccin,which acts as a non-competitive catalase inhibitor and is able to reduce the cell’s capacity for H2O2scavenging[28].Apart from the mode of action,also the fusicoccin biosynthetic machin-ery is quite intriguing:PaFS,a multifunctional enzyme of Phomopsis amygdali,plays a key role with prenyltransfer-ase(responsible for condensation of isoprene units)and terpene cyclase(cyclization of C-20precursor)activity. Both enzymatic functions required for diterpene biosyn-thesis are normally carried out by two independent enzymes[29 ].Strategies to trigger apoptosisThe induction of apoptosis,or programmed cell death (PCD)in plants,is a major strategy of phytopathogenic fungi to acquire nutrients from plants.However,the underlying mechanisms can be manifold. Trichothecenes,such as deoxnivalenol(DON),are non-volatile sesquiterpenoids produced by Fusarium grami-nearum(Figure2).DON is a host-specific virulence factor that is frequently found in contaminated cereal crops[30]. In Arabidopsis DON inhibits translation without inducing a plant defense response[30].Thefirst gene of the trichodiene pathway catalyzes the cyclization of farnesyl pyrophosphate to trichodiene.Dis-ruption of this trichodiene synthase(a terpene cyclase-type enzyme)gene results in a DON-non-producing strain.Conidia of the mutant are still able to infect but disease symptoms are significantly reduced.Mutants deficient in crucial toxin biosynthetic genes exhibited reduced virulence on wheat seedlings but were unaf-fected with respect to causing disease on barley[31]. These results indicate that these fungal toxins confer host specificity to Fusarium pathogenicity.Notably,wheat infection by the mutants is associated with thickening of the cell wall in the rachis node,a plant induced defense [31].Self-resistance to DON is conferred by the enzyme trichothecene3-O-acetyltransferase(Tri101),which transforms DON into3-acetyldeoxynivalenol(3-ADON). Heterologous expression of Tri101in rice plants signifi-cantly reduced phytotoxic effects[32].Victorin(Figure2)is a cyclic pentapeptide produced by the fungus Cochliobolus victoriae that causes Victoria oat blight[33].The toxin enters mitochondria by a mito-chondrial permeability transition(MPT)and binds to P-protein of the mitochondrial matrix,a subunit of theglycine decarboxylase complex(GDC,part the photo-respiratory cycle).After incubation with victorin a rapidresponse is observed,in particular DNA laddering,lipidoxidation and cleavage of RUBISCO,followed by theinhibition of photorespiration[34].Recently,victorin-insensitive mutants were isolated,with resistance con-ferred to specifically by a mutation in liv1(locus ofinsensitivity to victorin1).The gene product is thioredoxinh5(ATTRX5),a member of a large family of disulphideoxidoreductases[34].Sensitivity to the toxin in Arabidop-sis thaliana relies on the gene lov1that codes for a coiled-coil–nucleotide binding site leucine-rich repeat protein.Ironically,lov1is a member of the NBS–LRR resistancegene family[35 ].Finally,PCD can also be induced by the above-men-tioned fusiccocin.An apoptotic-like form of PCD thatinvolves typical apoptotic characteristics like chromatincondensation,Cytochrome c release and DNA ladderingand is inhibited by cyclosporin A,an inhibitor of thepermeability transition pore of animal mitochondria[36]. Breaking the cell’s bones—destroying the actin skeletonDisaggregation of the cytoskeleton can ultimately alsolead to PCD and is another plant-damaging effect causedby fusiccocin(see above).Actin depolymerization seemsto be mediated by induction of NO production and can bedecreased by the addition of NO scavengers or actinstabilizing drugs[36].By contrast,toxins belonging to the family of cytochala-sans(gr.:kytos–cell,and chalasis–relaxation)specifi-cally bind to actinfilaments,thus blocking cytokinesis,while mitosis remains unaffected[37].This structurallydiverse group of polyketide–amino acid hybrids includes,among others,cytochalasin A,cytochalasin B(phomin),and chaetoglobosins,which are particularly active repre-sentatives(Figure2)[37].The molecular basis for chae-toglobosin A and C biosynthesis was elucidated inPenicillium expansum.A PKS–NRPS hybrid synthetase(CheA)assembles the linear polyketide–amino acid back-bone thatfinally undergoes a Diels–Alder reaction toyield the tricyclic framework[38].Interestingly,related genes coding for PKS-NRPShybrids are present in the genome[3]of Magnaportheoryzae.The M.oryzae ACE1avirulence gene encodes aputative hybrid polyketide synthase(PKS)-nonribosomalpeptide synthetase(NRPS),with the structure of thebiosynthetic product not yet elucidated.Thus,it is notclear whether the product of this gene will affect the actincytoskeleton.Expression of ACE1occurs early duringinfection and coincides with penetration of the cuticle[39].Fungal phytotoxins as mediators of virulence Mo¨bius and Hertweck395To sight the core-transcription factors,epigenetic modifiers and antimitotic agentsManipulation of the replication machinery and altering gene expression profiles are other important effects mediated by secreted fungal compounds.An important example is Ustilago maydis ,a ubiquitous biotrophic fungus and maize pathogen.While its complete genome sequence has revealed only few secondary biosynthetic genes [4 ],it was found that auxin (indole-3-acetic acid,IAA)is produced.Since the concentration of auxin in U.maydis induced tumors is significantly higher (up to 20-fold)in tumor tissue than in the surrounding plant tissues,fungal production of this plant growth hormone was implicated in tumor induction [40].According to the current model IAA is involved in targeted protein degra-dation of the Aux/IAA transcriptional repressors via the auxin receptor TIR1and thereby regulates transcription [41].However,a quadruple mutant that is unable to produce IAA in culture was unaffected in tumor induc-tion,suggesting the elevated IAA levels in tumor tissue are likely to result from fungus-induced changes in plant hormone levels [40].As the biotrophic lifestyle requires efficient protection against plant defense reactions.Notably,in the genome of U.maydis a gene coding for a Yap1-related protein has been identified that serves as the central regulator pro-viding S.cerevisiae .In U.maydis this transcription factor is involved in detoxification of plant produced ROS and fundamental for full virulence [42].Another growth-regulating phytohormone is the already mentioned gibberellin (GA)that belongs to a group of diterpenoid acids responsible for stem elongation and seed germination [43].It was first isolated from the pyhtopathogenic fungus Gibberella fujikuroi ,which causes the rice plant disease Bakanae whose most prominent characteristics are strongly elongated seedlings [6].The plant and fungal biosynthetic pathways differ only in thelast steps [6].Recently the GA receptor GID1has been identified in Arabidopsis.GID1is located in the nucleus and enables degradation of a repressor bound to GA-dependent transcription factors through ubiquitin ligation and leads to gene transcription [43].Another mechanism to alter gene expression involves epigenetic modification.This strategy is employed by Cochliobolus carbonum,a fungus that is highly virulent on certain maize genotypes.C.carbonum produces HC-toxin,a cyclic tetrapeptide containing D-amino acids (Figure 5),and is highly virulent on certain genotypes of maize.Production of the host-selective compound is under the control of a complex locus (tox2)coding for HTS1(HC-toxin synthetase),an NRPS [44].The putative HC-toxin efflux carrier encoded by tox A is probably involved in a self-protection mechanism.The toxin is an inhibitor of histone deacetylases (HDACs)leading to hyperacety-lation and thereby to changes in gene expression in the plant.In vitro kinetic studies revealed that the inhibition is uncompetitive and reversible [45].HC-toxin stimulates the uptake of organic and inorganic molecules such as nitrate into the maize roots.Resistant maize plants carry the Hm1resistance gene that encodes an HC-toxin reductase (HCTR)[45].Chromosomal segregation is of vital importance for cell division and growth,and its inhibition is an effective strategy of a pathogenic organism.The antimitotic agent rhizoxin (Figure 5),a macrocyclic polyketide,is known as the virulence factor of the rice seedling blight fungus Rhizopus microsporus .Rhizoxin binds to b -tubulin,thus preventing heterodimerization with a -tubulin and con-sequently the formation of microtubules [46 ].Only recently,it was found that the toxin is not produced by the fungus,but by bacterial endosymbionts that reside within the fungal cytosol [46 ].Isolation and cultivation of the symbionts clearly demonstrated that the toxin complex is produced by the endofungal bacterium396Biotic InteractionsFigure5Molecules targeting processes in the nucleus;phytotoxins acting as epigenetic modifier (HC-toxin)or blocking mitosis (rhizoxin).Burkholderia rhizoxinica[47].Furthermore,the molecular basis for rhizoxin production was elucidated by sequen-cing a gene cluster coding for a modular PKS–NRPS assembly line in the bacterial genome[48].A specific mutation of b-tubulin confers resistance to the fungal host and is probably a precondition for the establishment of the symbiosis[49].This is thefirst described case where a phytotoxin employed by a fungus is actually produced by endosymbionts.Here,the pathogenic relationship be-tween the plant and the infecting fungus is extended to a tripartite system including a symbiotic alliance of fungus and bacterium.The fungus benefits from plant nutrients but is itself dependent on bacteria for toxin production and even for reproduction as spore formation can only occur in the presence of the bacterial symbionts [50].ConclusionIn conclusion,phytopathogenic fungi employ an array of strategies to distress,weaken or kill the host plant in order to gain access to nutrients.The captivating structural and mechanistic diversity of the toxins teaches us a lesson on the complexity of pathogenic relationships—up to the point where a metabolically lean fungus hosts a bacterium for toxin production.Understanding toxin biosynthesis pathways and their regulation,the modes of action and how this relates to fungal virulence will not only help to gain new insights into cellular processes in general but is also a stepping stone to develop ways to protect plants from fungal infections.With the help of advanced genomics,proteo-mics and analytical skills we will soon understand more about phytotoxins as mediators of plant virulence. AcknowledgmentThe authors are grateful forfinancial support of original research in this area by the Jena School for Microbial Communication(JSMC). References and recommended readingPapers of particular interest,published within the annual period of review,have been highlighted as:of special interestof outstanding interest1.Friesen TL,Faris JD,Solomon PS,Oliver RP:Host-specifictoxins:effectors of necrotrophic pathogenicity.Cell Microbiol 2008,10:1421-1428.2.Oliver RP,Solomon PS:Recent fungal diseases of crop plants:is lateral gene transfer a common theme?Mol Plant MicrobeInteract2008,21:287-293.3.Dean RA,Talbot NJ,Ebbole DJ,Farman ML,Mitchell TK,Orbach MJ,Thon M,Kulkarni R,Xu JR,Pan HQ et al.:The genome sequence of the rice blast fungus Magnaporthe grisea.Nature 2005,434:980-986.4. Kamper J,Kahmann R,Boelker M,Ma LJ,Brefort T,Saville BJ, Banuett F,Kronstad JW,Gold SE,Muller O et al.:Insights from the genome of the biotrophic fungal plant pathogen Ustilagomaydis.Nature2006,444:97-101.This work provides the molecular ground to understanding the virulence of the important mayze pathogen.Deduction of the full inventory of enzymatic functions that are involved in the production of secondary metabolites will greatly profit from the genome sequence of U.maydis. Some of the predicted genes are suggested to be subject to high genetic and genomic variation.5.Bergmann S,Schuemann J,Scherlach K,Lange C,Brakhage AA, Hertweck C:Genomics-driven discovery of PKS–NRPS hybrid metabolites from Aspergillus nidulans.Nat Chem Biol2007,3:213-217.Thefirst report and proof of concept that silent biosynthetic gene clusters can be activated to yield metabolites(e.g.the cytotoxic aspyridones) usually not observed under laboratory conditions.6.Kawaide H:Biochemical and molecular analyses ofgiberellin biosynthesis in fungi.Biosci Biotechnol Biochem2006,70:583-590.7.Boelker M,Basse CW,Schirawski J:Ustilago maydis secondarymetabolism—from genomics to biochemistry.Fungal GenetBiol2008,45:S88-S93.wrence CB,Mitchell TK,Craven KD,Cho Y,Cramer RA,Kim KH:At death’s door:Alternaria pathogenicity mechanisms.PlantPathol J2008,24:101-111.9.Ebbole DJ:Magnaporthe as a model for understanding host–pathogen interactions.Ann Rev Phytopathol2007,45:437-456.10.Daub ME,Herrero S,Chung KR:Photoactivatedperylenequinone toxins in fungal pathogenesis of plants.Fems Microbiol Lett2005,252:197-206.11.Choquer M,Lee MH,Bau HJ,Chung KR:Deletion of a MFStransporter-like gene in Cercospora nicotianae reducescercosporin toxin accumulation and fungal virulence.FEBSLett2007,581:489-494.12.Liao HL,Chung KR:Genetic dissection defines the roles ofelsinochrome phytotoxin for fungal pathogenesis andconidiation of the citrus pathogen Elsinoe fawcettii.Mol Plant Microbe Interact2008,21:469-479.13.Heiser I,Hess M,Schmidtke KU,Vogler U,Miethbauer S,Liebermann B:Fatty acid peroxidation by rubellin B,C and D, phytotoxins produced by Ramularia collo-cygni(Sutton et Waller).Physiol Mol Plant Pathol2004,64:135-143.14.Chai CLL,Waring P:Redox sensitive epidithiodioxopiperazinesin biological mechanisms of toxicity.Red Rep2000,5:257-264.15.Fox EM,Gardiner DM,Keller NP,Howlett BJ:A Zn(II)(2)Cys(6)DNA binding protein regulates the sirodesmin PL biosynthetic gene cluster in Leptosphaeria maculans.Fungal Genet Biol2008,45:671-682.16.Williams LD,Glenn AE,Zimeri AM,Bacon CW,Smith MA,Riley RT:Fumonisin disruption of ceramide biosynthesis in maize roots and the effects on plant development and Fusariumverticillioides-induced seedling disease.J Agric Food Chem2007,55:2937-2946.17.Spassieva SD,Markham JE,Hille J:The plant disease resistance gene Asc-1prevents disruption of sphingolipid metabolismduring AAL-toxin-induced programmed cell death.Plant J2002,32:561-572.The product of the host gene of Asc-1is able to relieve an AAL-toxin-induced block on sphingolipid synthesis and thereby prevent pro-grammed cell death.18.Desjardins AE,Busman M,Muhitch M,Proctor RH:Complementary host–pathogen genetic analyses of the role of fumonisins in the Zea mays-Gibberella moniliformisinteraction.Physiol Mol Plant Pathol2007,70:149-160.19.Dayan FE,Ferreira D,Wang YH,Khan IA,McInroy JA,Pan ZQ:Apathogenic fungi diphenyl ether phytotoxin targets plantenoyl(acyl carrier protein)reductase.Plant Physiol2008,147:1062-1071.20.Goudet C,Milat ML,Sentenac H,Thibaud JB:Beticolins,nonpeptidic,polycyclic molecules produced by thephytopathogenic fungus Cercospora beticola,as a new family of ion channel-forming toxins.Mol Plant Microbe Interact2000, 13:203-209.Fungal phytotoxins as mediators of virulence Mo¨bius and Hertweck397。
Fungal Mycorrhizal Fungi Culture
Fungal Mycorrhizal Fungi Culture Mycorrhizal fungi are a crucial component of the soil ecosystem, forming symbiotic relationships with the roots of plants. These fungi play a vital role in enhancing plant growth, nutrient uptake, and overall soil health. As such, the culture of fungal mycorrhizal fungi has garnered significant attention in the agricultural and environmental sectors. However, the process of culturing these fungi presents several challenges and complexities that need to be addressed. One of the primary challenges in the culture of mycorrhizal fungi is the need for specialized techniques and equipment. Unlike traditional plant cultures, mycorrhizal fungi require specific environmental conditions and substrates to thrive. This necessitates the use of sterile laboratory settings, precise temperature and humidity controls, and specialized growth media. Additionally, the culturing process often involves intricate procedures such as spore isolation, hyphal culturing, and inoculum production, which demand a high level of expertise and technical skill. Furthermore, the diversity of mycorrhizal fungi poses a significant obstacle in their culture. There are various types of mycorrhizal fungi, including arbuscular mycorrhizae, ectomycorrhizae, and ericoid mycorrhizae, each with its unique requirements and characteristics. Culturing a diverse rangeof mycorrhizal fungi necessitates a comprehensive understanding of theirindividual needs and behaviors, making the process intricate and labor-intensive. Another critical aspect to consider is the commercial viability of mycorrhizalfungi culture. While there is a growing demand for mycorrhizal inoculants in agriculture and horticulture, the production and distribution of these products pose economic challenges. The cost of maintaining a sterile laboratory environment, procuring specialized equipment, and conducting research and development can be substantial. Additionally, the shelf life of mycorrhizal inoculants and the logistics of storage and transportation add further complexity to the commercialization of mycorrhizal fungi culture. In addition to the technical and economic challenges, ethical and environmental considerations also come into playin the culture of mycorrhizal fungi. As these fungi form symbiotic relationships with plants, the extraction and cultivation of mycorrhizal spores raise questions about their impact on natural ecosystems. There is a need for sustainable andethical practices in sourcing mycorrhizal fungi, as well as ensuring that their cultivation does not disrupt or deplete natural fungal populations in the soil. Despite these challenges, the culture of mycorrhizal fungi holds immense potential for revolutionizing sustainable agriculture and environmental restoration. By enhancing plant health and nutrient uptake, mycorrhizal fungi can contribute to reducing the reliance on chemical fertilizers and pesticides, thereby promoting eco-friendly farming practices. Moreover, the restoration of degraded soils through mycorrhizal inoculation can aid in combating desertification andmitigating the impacts of climate change. In conclusion, the culture of mycorrhizal fungi presents a myriad of challenges, ranging from technical and economic complexities to ethical and environmental considerations. However, the potential benefits of mycorrhizal fungi in agriculture and environmental restoration underscore the importance of addressing these challenges. By investing in research, innovation, and sustainable practices, we can unlock the full potential of mycorrhizal fungi culture and harness its power to create a more sustainable and resilient ecosystem.。
Fungal Mycoparasite Specimen
Fungal Mycoparasite Specimen Fungal mycoparasites are fascinating organisms that play a crucial role in the ecosystem by preying on other fungi. These mycoparasites, also known as fungal parasites, have evolved unique mechanisms to invade and consume their fungal hosts. One such mycoparasite specimen that has garnered attention in the scientific community is the Trichoderma species. Trichoderma is a genus of mycoparasiticfungi that are commonly found in soil and plant roots. These fungi are known for their ability to attack and destroy pathogenic fungi, making them valuable alliesin agriculture. The mycoparasitic activity of Trichoderma is due to its ability to produce enzymes and toxins that can break down the cell walls of other fungi, effectively killing them. One of the most intriguing aspects of Trichoderma mycoparasites is their complex interactions with their fungal hosts. These interactions can range from direct physical contact to the release of chemical signals that trigger defense responses in the host fungus. Through these interactions, Trichoderma is able to outcompete and eventually kill its fungal prey, thereby reducing the spread of plant diseases caused by pathogenic fungi.In addition to their role in biological control, Trichoderma mycoparasites also have potential applications in biotechnology and medicine. Researchers have been exploring the use of Trichoderma enzymes in various industrial processes, such as the production of biofuels and the degradation of environmental pollutants. Furthermore, some studies have shown that certain Trichoderma species have antimicrobial properties, making them promising candidates for the development of new antifungal drugs. Despite their beneficial qualities, Trichoderma mycoparasites can also pose challenges in certain contexts. For example, in agricultural settings, the indiscriminate use of Trichoderma-based biocontrol agents can lead to unintended consequences, such as the disruption of beneficial microbial communities in the soil. Additionally, some Trichoderma species have been reported to cause infections in humans with weakened immune systems, highlighting the need for careful monitoring and regulation of their use. Overall, the study of fungal mycoparasites, particularly the Trichoderma species, offers valuable insights into the complex interactions that occur in the microbial world. By understanding the mechanisms underlying mycoparasitism, researchers can developmore sustainable and effective strategies for controlling plant diseases and promoting environmental health. As we continue to unravel the mysteries of these fascinating organisms, it is clear that fungal mycoparasites have much to offer in terms of both scientific knowledge and practical applications.。
荧光假单胞菌(Pseudomonas fluorescens)MF11对根结线虫病的防效评价
江苏农业学报(Jiangsu J.qfAgr.Sci.),2021,37(2)：326-332http：// 326周冬梅，何亮亮,李伟山，等.荧光假单胞菌(Pseudomonas Jluqrescens)MFH对根结线虫病的防效评价[J].江苏农业学报,2021, 37(2)：326-332.(loi：10.3969/j.issn.l000-4440.2021.02.007荧光假单胞菌(Pseudomonas fluorescens)MF11对根结线虫病的防效评价周冬梅1,何亮亮,李伟山⑴，冯辉1,赵敏1,纠敏3,魏利辉(1.江苏省农业科学院植物保护研究所，江苏南京210014； 2.南京农业大学植物保护学院，江苏南京210095； 3.河南科技大学食品与生物工程学院，河南洛阳471023)摘要：在根结线虫危害严重的番茄田块采集健康植株的根际，从中分离并筛选对根结线虫病具有防治作用的生防菌株。
采用稀释分离法以及离体试验获得16株能显著杀灭南方根结线虫二龄线虫(J2)的菌株，其中菌株MF11对J2的致死率最高。
基于生理生化分析、gyrB和16S rRNA基因碱基序列比对，确定菌株MF11为荧光假单胞菌(Pseudomonas fluorescens)o菌株MF11发酵液浸泡番茄幼苗24h后,J2在番茄根尖的聚集数量显著减少，侵入番茄根尖的虫量下降80.65%,表明菌株MF11可降低J2对番茄的侵染力。
温室试验结果表明，菌株MF11发酵液处理可以显著降低番茄植株86.53%根结数，以及70.2%的卵块数。
田间试验结果表明,菌株MF11发酵液处理降低了根结线虫病的病情指数，其平均防效达66.71%,与10%噻唑膦颗粒剂处理防效相当。
综上所述，菌株MF11不仅对根结线虫具有毒杀作用，还能降低根结线虫的侵染、发育和繁殖能力，从而有效防治作物根结线虫病。
关键词：南方根结线虫；生防菌；荧光假单胞菌；防治效果中图分类号：S432.4+5文献标识码：A文章编号：1000-4440(2021)02-0326-07 Evaluation of the control effect of Pseudomonas fluorescens MF11on diseases caused by Meloidogyne incognita in tomatoZHOU Dong-mei1,HE Liang-liang1，2,U Wei-shan1，3,FENG Hui1,ZHAO Min1,JIU Min3,WEI Li-hui1，2 (1.Institute of Plant Protection,Jiangsu Academy of Agricultural Sciences,Nanjing210014,China； 2.College qf Plant Protection,Nanjing Agricultural University,Nanjing210095 ,China； 3.College of Food and Bioengineering,Henan University of Science and Technology,Luoyang471023,China) Abstract:Rhizosphere of healthy tomato plants in fields severely infected by root-knot nematode was collected to isolate and screen biocontrol strains with antagonistic effects on diseases caused by Meloidogyne incognita.16bacterial strains with significant nematocidal activity on the second-stage larvae(J2)of M.incognita were obtained by separation method of dilution and in vitro experiment.Among them,MF11strain showed the highest lethality rate to J2.The MF11strain was identified to be Pseudomonas fluorescens based on physiological,biochemical analysis and gene sequence alignment between gyrB and16S rRNA.The number of J2aggregated around the root tips of tomatoes decreased significantly24h after the tomatoseedlings immersed in the fermentation broth of MF11strain.收稿日期：2021-01-21基金项目：国家自然科学基金项目(31871943)；江苏省农业科技自主创新基金项目[CX(18)2005]作者简介:周冬梅(1985-)，女，江苏仪征人，博士，助理研究员，从事植物病原菌的致病机制和生防菌的作用机理研究。
Fungal Mycorrhizal Root Specimen
Fungal Mycorrhizal Root Specimen The fungal mycorrhizal root specimen is a fascinating and crucial component of the natural world. Mycorrhizal fungi form symbiotic relationships with the roots of plants, providing them with essential nutrients and aiding in their growth and development. This relationship is vital for the health and vitality of many plant species, making the fungal mycorrhizal root specimen an object of great interest and importance for scientists and environmentalists alike. From a scientific perspective, the study of fungal mycorrhizal root specimens provides valuable insights into the intricate and complex interactions that occur within ecosystems. By examining these specimens, researchers can gain a better understanding of the specific species of fungi involved, as well as the ways in which they interact with plant roots. This knowledge can then be used to inform conservation efforts, agricultural practices, and even the development of new technologies aimed at improving plant health and productivity. Furthermore, the study of fungal mycorrhizal root specimens can also shed light on the broader impacts of these symbiotic relationships on the environment. For example, mycorrhizal fungi play a crucial role in nutrient cycling and soil structure, which in turn can influence the overall health and resilience of ecosystems. By studying these specimens, scientists can gain a better understanding of how these processes work and how they may be impacted by factors such as climate change or human activity. On an emotional level, the fungal mycorrhizal root specimen can also evoke a sense of wonder and awe at the intricate and interconnected web of life that exists within the natural world. The idea that plants and fungi can form such intimate and mutually beneficial relationships is a powerful reminder of the beauty and complexity of the natural world. It can inspire a sense of reverence for the delicate balance of life on Earth and a desire to protect and preserve it for future generations. In addition to its scientific and emotional significance, the fungal mycorrhizal root specimen also has practical implications for various fields, including agriculture, forestry, and horticulture. Understanding the role of mycorrhizal fungi in plant health and productivity can help inform more sustainable and environmentally friendly practices in these industries. By harnessing the power of these symbiotic relationships, it may be possible toreduce the need for chemical fertilizers and pesticides, leading to healthier and more resilient ecosystems. In conclusion, the fungal mycorrhizal root specimen is a subject of great importance and interest from multiple perspectives. From a scientific standpoint, it offers valuable insights into the complex interactions that occur within ecosystems, while also providing practical implications for various industries. On an emotional level, it serves as a reminder of the beauty and interconnectedness of the natural world, inspiring a sense of wonder and reverence. Overall, the study of fungal mycorrhizal root specimens is essentialfor gaining a deeper understanding of the natural world and finding ways toprotect and preserve it for future generations.。
写一篇关于农作物的英语作文发挥想象力
写一篇关于农作物的英语作文发挥想象力全文共3篇示例，供读者参考篇1The Mysterious Crops From Planet XenonIt was just another typical day in Ms. Johnson's 5th grade class at Oakdale Elementary School. We had just finished our math quiz on long division when Ms. Johnson announced it was time for our weekly creative writing assignment."Alright class, listen up!" Ms. Johnson's voice rang out over the din of students packing up their pencils and calculators. "For this week's assignment, I want you to use your imagination and write a short story about...crops!"A collective groan went up from the class. Crops? How boring! What kind of exciting story could we possibly write about plants?"I know, I know," Ms. Johnson said with a sly grin. "Crops may not seem like the most thrilling subject at first. But that's why you'll need to make use of those incredible imaginations of yours! Your story can be set anywhere - the present day, the future, even another planet light years away. As long as cropsplay a central role, you can make it as creative andout-of-this-world as you'd like."Suddenly, crops didn't seem quite so dull anymore. My hand shot up. "Can we write about alien crops from another planet?""You certainly can!" Ms. Johnson replied with an approving nod. "I'm looking forward to reading all your imaginative tales. Don't forget, your stories are due next Monday. You're dismissed."The wheels in my brain immediately began turning as I gathered my books and headed for the door. Alien crops from another planet? This could actually be a really cool story idea!Over the next few days, I imagined all sorts of strange and bizarre crops that could grow on a distant planet unlike anything here on Earth...It was the year 3022 and the human scientists aboard the Xenon Observation Station were in an absolute frenzy of excitement. For decades, the strange agriculture practices of the alien Xenonites on the planet below had baffled our crew of researchers. We had observed the tall, slender extraterrestrials meticulously tending to their vibrant crops that seemed to shimmer and almost glow in the blazing twin suns of the Xenonsystem. But it wasn't until recently that we had finally cracked the code on these mysterious plants and uncovered their incredible, almost supernatural properties."නනනනනන, did you run the test again on the crop samples?" Dr. Rajesh asked his lab partner as he rushed into the observation room, his white lab coat billowing behind him."Affirmative," නනනනනන replied in her computerized voice. As an AI model encased in a sophisticated android body, she always spoke with cool precision. "The results are the same as before - these crops possess extraordinary abilities."She punched a command into the holographic control panel, and a large 3D image appeared, magnifying the molecular structure of the alien crop. It looked like one of the tiny seeds we had retrieved during a daring ground sample expedition. However, unlike any seeds found on Earth, this one seemed to be humming with energy, glowing faintly with intricate circuitry-like patterns threaded within."As you can see, this 'seed' is not like any we've encountered before," නනනනනන continued. "It's almost as if it's been digitized, encoded with computational data. That would explain the electromagnetic signatures and energy output we detected."I leaned in closer, my eyes wide with wonder and scientific curiosity. "So you're saying...this is some kind of digital crop? Like... binary botany?""Precisely," Dr. Rajesh said with a proud smile. "We're looking at the universe's first known example of crops being cultivated digitally rather than organically. These aren't just simple plants - they're technological marvels."නනනනනන nodded and changed the hologram to show the mapped process we had observed the Xenonites using to "grow" their crops. "From what we can tell based on their planting and harvesting procedures, the Xenonites start by essentially'printing' or rendering these digitized seeds using some kind of sophisticated molecular 3D printing technique."She highlighted part of the image, zooming in on the strange tool the aliens used to plant the crops which almost looked like a cross between a shovel and a computer stylus. "They use these plasma-based implement to literally 'draw' the crops into the ground, transcribing the digital seed's data into physical, molecular form. From there, the crops rapidly germinate and grow over the course of only a few days thanks to the concentrated photon energy from Xenon's twin stars.""This holographic sun simulation shows the amazing effects of the radiation bombardment," Dr. Rajesh chimed in, bringing up a new hologram that replicated the growing process in accelerated time lapse. What had once been a tiny proto-crop nub erupted into a towering, sparkling stalk covered in glistening orbs and fronds."The intense energies catalyze growth at an exponential rate, causing the digital seed data to rapidly compile into physical form much like an Earth 3D printer builds an object layer by layer. Only in this case, the layers are biodigital material compiling into a living, energy-based lifeform!"My head was spinning trying to take in all this incredible new information. Earth's crops suddenly seemed so simple and antiquated compared to this hyper-advanced "digital cultivation." I couldn't help but envision how such technology could transform our own agricultural industries."Have you figured out what those shimmering orbs are that the mature crops produce?" I asked. "They look like some kind of energy storage unit.""An astute observation," නනනනනන replied. "We believe those orbs are essentially energized 'storage drives' containing hyper-compressed data collected by the crop during itsaccelerated biodigital growth cycle. The Xenonites seem to be harvesting these for use as concentrated power and data sources."Dr. Rajesh's face beamed with excitement. "Which could revolutionize energy production and data storage as we know it! Can you imagine - digital crops that can produce powerful energy and data codes simply by growing under sunlight? With self-replicating crops like these, Xenon may have solved their world's energy crisis and effectively created unlimited storage and computing power!"He began pacing back and forth, his mind clearly racing with the scientific implications of what we had discovered."This could explain how the Xenonites have been able to develop such wildly advanced technology - their civilization has been able to piggyback off the crops' biodigital processes! Oh, the possibilities!"I felt like I could barely contain my amazement at these incredible digital crops. This was the type of mind-blowing scientific discovery I had dreamed about since I was a kid."Dr. Rajesh, do you think there's any possibility we could retrieve a viable seed and attempt to grow one of these cropsourselves?" I asked hopefully. "Can you imagine what we could learn from actually cultivating and studying one up close?"The esteemed xenobotanist opened his mouth to respond, but was interrupted by a sudden blaring alarm and red flashing lights."Warning!" නනනනනන's computerized voice announced with surprising urgency. "Xenon sun flare detected incoming trajectory is headed straight towards the observation station!"I watched in horror as the hologram displayed a massive wave of superheated plasma erupting from the twin suns, rapidly expanding outwards in a deadly shockwave. And we were directly in its path.To be continued...?篇2Crops: The Beating Heart of Our WorldAs I gaze upon the vast expanse of fields stretching out before me, a tapestry of emerald greens and golden hues, I can't help but feel a profound sense of wonder. These crops, these humble plants that carpet the earth, are the lifeblood of ourexistence, sustaining billions and shaping the very course of human civilization.In my mind's eye, I envision a world without crops, a barren landscape devoid of the vibrant colors that now paint the horizon. It's a stark and unsettling sight, one that sends shivers down my spine. For without these resilient and bountiful crops, our species would be lost, adrift in a sea of scarcity and hunger.But let's not dwell on such bleak imaginings. Instead, let us celebrate the incredible diversity and importance of these botanical marvels that have nourished us for millennia.Consider the humble wheat plant, its slender stalks swaying gently in the breeze. This unassuming grass has been the backbone of human sustenance for thousands of years, its golden grains transformed into breads, pastas, and countless other culinary delights. The cultivation of wheat marked a pivotal moment in our evolution, allowing our ancestors to transition from nomadic hunter-gatherers to settled agrarian societies, laying the foundations for the civilizations we know today.Then there's the mighty corn, a crop so deeply woven into the fabric of human history that it has become a cultural icon in its own right. From the ancient Mesoamerican civilizations that revered it as a sacred gift from the gods, to the modern-dayfarmers who nurture its towering stalks, corn has been a constant companion on our journey through time. Its versatility knows no bounds, serving as a staple food, animal feed, and even a source of biofuel in our ever-evolving world.But crops are more than just sustenance; they are also a source of beauty and inspiration. Imagine the vibrant hues of a field of sunflowers, their brilliant yellow petals tracking the sun's journey across the sky. Or the delicate blossoms of a cotton plant, their soft white tufts waiting to be plucked and woven into garments that adorn us with their natural elegance.As a student of the natural world, I am in awe of the intricate processes that govern the growth and development of these remarkable plants. From the miraculous germination of a tiny seed, to the complex biochemical pathways that transform sunlight, water, and nutrients into the fruits and grains we consume, every aspect of a crop's life cycle is a testament to the wonders of nature.Yet, as I ponder the majesty of these crops, I cannot help but feel a sense of urgency. Our planet, our precious home, is facing unprecedented challenges – climate change, environmental degradation, and a rapidly growing population that demands ever-increasing quantities of food. It is a scenario that threatensthe very foundation upon which our existence rests: the ability to cultivate and sustain these vital crops.But fear not, for the human spirit is resilient, and our ingenuity knows no bounds. Even as we grapple with these formidable challenges, scientists and researchers around the globe are tirelessly working to develop new and innovative techniques to ensure the continued abundance and sustainability of our crops.I envision a future where genetically modified crops, engineered to thrive in harsh conditions and resist pests and diseases, become the norm, ensuring bountiful harvests even in the face of adversity. Where precision agriculture, powered by cutting-edge technologies like drones and satellite imaging, optimizes every aspect of crop management, maximizing yields while minimizing environmental impact.And beyond these technological marvels, I see a world where traditional knowledge and sustainable farming practices are embraced and celebrated, honoring the wisdom of our ancestors while adapting to the needs of the modern era.In this future, urban agriculture flourishes, with vertical farms and rooftop gardens transforming concrete jungles into verdant oases, bringing fresh, locally-grown produce to even the mostdensely populated cities. Aquaponics and hydroponics systems become commonplace, allowing us to grow crops inwater-scarce regions and even in the vast expanses of space, ensuring that future generations can continue to enjoy the bounty of the earth, no matter where their journey takes them.But perhaps most importantly, I see a world where we, as a species, recognize the intrinsic value of these crops that sustain us. A world where we treat them with reverence and respect, nurturing them with care and ensuring their continued prosperity for generations to come.For in the end, these crops are not just plants; they are the beating heart of our world, the foundation upon which our entire existence is built. Without them, we are but mere shadows, lost in a barren and inhospitable landscape.So let us embrace these botanical wonders, these humble yet mighty crops that have accompanied us on our journey through time. Let us celebrate their diversity, their resilience, and their enduring role in shaping the course of human civilization. And let us pledge to be faithful stewards of these precious gifts, ensuring that they continue to nourish and sustain us for eons to come.篇3An Imaginative Essay on CropsHave you ever really thought about the amazing crops growing all around us? From the golden wheat fields swaying in the breeze to the vibrant orange pumpkin patches dotting the rural landscapes, crops are so much more than just food sources. They are living, breathing organisms teeming with untold secrets and stories just waiting to be uncovered by an inquisitive mind. Let me take you on an imaginative journey into the world of crops.Imagine you could speak the language of corn. Those towering green stalks standing at attention in orderly rows would reveal the complex underground network of roots and nutrient sharing happening between them. They would explain how they communicate through chemical signals, warning each other of pest invasions or offering critical resources to sickly neighbors. You would learn about their unique partnership with bacteria to "fix" nitrogen from the air into soil nutrients. The cornstalks would divulge their fears of droughts, floods and poor soil quality that could decimate an entire crop. Yet they would also radiate a quiet strength and resilience that has allowed corn to flourish across the globe for thousands of years.If potatoes could talk, they would shake the dirt from their knobby skins and regale you with raucous laughter about the absurdity of the 17th century idea that they caused leprosy, syphilis, early death and an entire host of societal ills. These humble tubers would take pride in their role as a staple food source for billions and key part of many indigenous cuisines across the Americas. They would giddily describe the amazing journey explorers like Sir Walter Raleigh took to bring them to the old world after first discovering them in the New World. You would gain an appreciation for the incredible biodiversity that still exists among potatoes, from the thousands of wild varieties to the specially cultivated strains that thrive in unique environments like the Andes mountains. A conversation with potatoes would be both humorous and educational.The lush green leaves of soybean plants would tell stories far beyond the culinary realm. These versatile legumes would explain how they sustainably contribute plant-based protein to fed the growing global population. They would describe the innovative techniques being used to boost yields while being increasingly environmentally-friendly, like cover crops, no-till agriculture and precision fertilization. You would learn about the relatively recent domestication of soybeans in ancient China and how they spread throughout Asia before being introduced to theWest in the 18th century. Soybeans would open your eyes to their importance not just as food, but products ranging from biodiesel fuel to industrial lubricants and inks. These plants have transformed human societies in innumerable ways that often go unnoticed.Imagine you had the power to understand the alien-like communications of fungus among mushrooms, truffles and the myriad other crops of the mushroom kingdom. What wisdom would this ancient life form impart if we could hear their whispers through complex underground mycelium networks spanning miles? You might gain insight into their unique role decomposing organic matter to create the incredibly fertile soils that enabled human agriculture and civilization to flourish. They would divulge secrets on recycling scarce nutrients in forest ecosystems. Perhaps we would even unlock the tantalizing mysteries around the neurological effects of psilocybin mushrooms and potential medical applications still being explored. The mushroom realm speaks in a language we have yet to fully comprehend.Moving from the practical to the mystical, ponder what the bewitching poppy flowers might convey with their brilliant red petals and hypnotizing opium production. You could learn aboutthe dual nature of this distinctive crop that has brought both pain relief as an important medicine, and immense human suffering from the opiate addiction crisis. The poppies may shed light on their domestication over 5,000 years ago, lush cultivation during the Opium Wars, and eventually concerted global efforts toward regulation. These enigmatic flowers have shaped human history in profound ways while maintaining an almost mythical aura across diverse cultures spanning the ancient world to modern times.Perhaps my favorite conversation would come from fruit and nut trees like the humble almond or stately peach tree. These long-living perennial crops could share oral histories stretching back hundreds of years since their initial planting. The trees would describe追忆generations of human cultivators who lovingly tended the orchards as the years marched by. You could envision scenes of wealthy orchard owners from decades past instructing legions of farmhands during harvest, or close-knit families meticulously picking every last fruit in commemoration of time-honored traditions. The trees may narrate epic tales of devastating frosts, droughts or infestations that pruned the weaker branches but allowed the hardiest trees to persevere. They could unpack the fascinating intermingling of wild and domesticated strains that continually generated new cultivarsvalued for their flavor, color or growing characteristics. Just like people, each tree would have a unique story shaped by triumphs, tragedies and unwavering perseverance spanning lifetimes.I've merely scratched the surface of the captivating stories encapsulated within our crops both humble and grand. Every plant has an innate wisdom and rich history just waiting to be deciphered. My mind runs wild pondering the profound insights we could gain if we could communicate directly with our crops. Perhaps we would realize their essential role in sustaining human life on this planet. Or be awed by their unique evolutionary traits honed over thousands of years. We may even gain a deeper respect for the farmers who work tirelessly cultivating these crops to feed nations. One thing is certain - our crops have more to share than we ever imagined if we just take the time to listen. The potential revelations are as boundless as the fields of crops painting our landscapes. All we need is a little imagination to hear what they are trying to say.。
Fungi and biotechnology
➢ phosphate of phytate can be used by animals
phytate phosphate storage of plants
free phosphorus digestable by poultry and pigs
Fungi in biotechnology
What are fungi used for in biotechnology?
acidifies an originally sweet taste
Aspergillus niger (Glucose oxidase)
Gluconic acid
coagulates soy protein in the production of tofu
Fungi in biotechnology
The three categories of biotechnology green biotechnology (plant) white biotechnology (industrial) red biotechnology (pharmaceutical)
1. Fungi in biotechnology
Fungi in biotechnology – food and beverages
• Penicillium spp. – cheese production
Penicillium camemberti
Penicillium gorgonzola Penicillium roqueforti
- most likely discovered by accident
and biotransformations)
Rhizopus nigricans Rhizopus arrhizus
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The internal substrate is also considered to be motile and the motility ability of the fungus to translocate nutrients around the mycelial netverified by Olsson (see [9,10]), translocation can be reasonable modelled
(iii) an internal substrate concentration, these components *=D dt The spatial movement
asin
a =
Aa+a2s
in - w,
asex Dssxhx =
at
at
Dsl,ASin a2sin f(a, +
- f(a,
systems
systems). Therefore, they provide an experimentally and observationally accessible model system for investigating the dynamic origins of phenotype patterns in such systems. However, their utility in this role has been limited on two counts: first, by the tendency to treat them as purely additive assemblages of effectively discrete, individual lengths of hyphae (hyphal growth units) that duplicate at regular intervals. Second, all previous models have considered fungi grown in perfectly uniform conditions. This is certainly not the situation fungi encounter when growing in any natural environment, and a consideration of the effects of heterogeneity is essential for any true understanding of their form and function. That such environments by Ritz cause dramatic [I], Rayner changes to their growth characteristics has been shown experimentally the geometric setting discussed below, by Park [4]. [2,3], and in
We would like to thank A. D. M. Rayner for his significant supported by EPSRC Grants GR/J35511 and GR/K92641, interest.
contribution to this ongoing project. This work was
and analyzed a model for In a series of papers, Davidson et al. (see [5-B]) h ave formulated the macroscopic development of mycelia growing in homogeneous environmental conditions. The model considers the mycelium in its most abstracted form, as a continuous self-fueling system which uses energy gained from nutrients and water in the environment to produce biomass which in turn assimilates more energy. The model therefore, does not require the consideration of the
Appl. Math. L&t. Vol. 11, No. 6, pp. 51-56, 1998 @ 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0893-9659/98 $19.00 + 0.00
PII: SO893-9659(98)00102-S
active transport we now discuss. Essentially, nutrients can pass though the hyphal wall by three main mechanisms-passive diffusion, facilitated diffusion, and active transport. The last involves the action of membranebound enzymes that use energy derived from the hydrolysis of ATP to pump out protons, so generating a proton gradient across which nutrients can be transferred against a concentration gradient. It can reasonably be assumed that active transport of nutrients is the major mechanism by which fungi gains energy from their environment and the main loss of nutrients to the exterior occurs simply in response to a gradient in the concentration from inside to outside (see [2, pp. 42441). The other mechanisms stated above may play secondary roles in cross membrane transport, but in this model we shall assume their effects to be negligible. Unlike Edelstein and Segel [ll] who have also developed a model for fungal growth including internal/external nutrient concentrations (but consider growth in homogeneous environments), as suggested above, we include a mechanism by which internal nutrients are transported to the exterior. Hence, the transport function has two parts f = fin + f,,“t, where fin and f,,“t stand for the influx and leakage terms, respectively. As the activator is necessary for the absorption of nutrients, we assume that &(O, a, .) = 0. It is also assumed that the activator concentration is positively correlated to the rate of absorption, i.e., -1 2 0. As the influx of nutrients
and we also thank B. D. Sleeman for his continued
Typeset 51
by A&-w
52
F. A. DAVIDSON AND A. W. PARK
microscopic distribution of hyphal boundaries nor depend on knowledge of specific physiological or genetic mechanisms. In this paper, we present a new model formulated to investigate the response of fungal mycelia to a heterogeneous simulations external environment. Comparisons The model is introduced with experimental and one-dimensional are made. numerical are discussed. observations
Sin,
Sin,
s,,),
(1)
sex)%
is modelled here by the simple
of the activator
and external
substrate
mechanism of diffusion. rate is a measure of the work. As experimentally by diffusion. The ratio represent high efficiency.