几种禾谷类作物介绍
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Cereal Grains
Outline
• Grasses as plants • Wheat
– domestication – farming basics – bread making
• corn
– domestication – hybrid corn – ethanol production
– wheat, corn, rice are the main grains, but also oats, barley, sorghum, millet, and rye – corn = maize
• Grasses make up 25% of all vegetation on Earth • Grasses are monocots • Tropical grasses (like corn but not wheat or rice) have C4 photosynthesis
– C4 means they can open their stomata at night, store carbon dioxide, and then close the stomata during the day and fix the CO2 into sugar while the Sun shines.
– Non-shattering = the grains don't fall off the stalk spontaneously. Makes it easier for humans to collect it, but harder for wild plants to disperse their seed.
Grain Processing
• • • Most grains are low in some essential amino acids. To get a complete protein, it is necessary to also eat something else, such as a legume. White flour, corn starch, white rice: just the endosperm, with the bran and germ removed. Brown rice, whole wheat flower, popcorn = the whole grain including bran and germ. – It contains much more protein and other nutrients than the endosperm alone. – But, it spoils faster due to fats in the germ, and bread made with whole flower doesn’t rise as well.
• Modern bread wheat is a hexaploid: three different diploid grasses hybridized to form it. These crosses occurred naturally, but were noticed and propagated by people. The starting point: einkorn wheat, which is a diploid wild grass. This means it was 2 sets of chromosomes (one set = 7 different chromosomes), or 14 chromosomes total.
– Branches (tillers) also start below ground.
Grass Flowers
• • • • • Grass flowers are small and inconspicuous: they are wind-pollinated so there is no need to attract pollinators. Many flowers grouped together (an inflorescence). Each one is called a floret. All angiosperm flowers have the same basic structure: from outside to inside there are four whorls, sepals, petals, stamens (male parts), carpels (female parts) In grasses, the sepals and petals are fused into a small structure (the lodicule) that swells up to open the flower. In place of sepals and petals are two bracts (leaves), the palea and the lemma.
Grass Family Characteristics
• Parallel leaf veins (like all monocots) • fibrous roots • either annual or perennial
– but crop species are all annuals
• Growing point is below ground until flowering. For most grasses, the flowers are at the tip of each branch.
Next Steps
• About 8000 years ago (very roughly), someone noticed a spontaneous hybrid between einkorn wheat and a closely related plant called goat grass.
– In the book of Genesis, at the beginning of the Bible, Adam and Eve are kicked out of the Garden of Eden and forced to grow wheat.
Domestication of Wheat
Wheat
Wheat
• Wheat (Triticum) is the source of most bread, noodles, beer. • The foundation of Western civilization: Middle East, Egypt, Mediterranean, Europe. • Wheat was domesticated at about the same time and place as barley and rye: the uplands of Turkey, Iran, and Iraq, roughly 10,000 years ago.
– At first, gains from wild einkorn wheat were harvested, and probably planted deliberately.
•
•
Archeological evidence shows that about 10,000 years ago, einkorn wheat with nonshattering heads was grown. This is the first step in domestication.
– Durum wheat is the source of pasta flour. It makes up 10% of today's wheat production in the US.
Fiwenku.baidu.comal Steps
• Tetraploid emmer wheat x another diploid goat grass = hexaploid bread wheat (Triticum aestivum). – Also a spontaneous event noticed and cultivated by humans, about 7000 years ago. – Six sets of chromosomes, 2 sets from each of the 3 parents = 42 total – Bread wheat is about 90% of today's wheat production. Wheat cultivation led to permanent settlements, plus a food surplus that led to having some people doing things other than gathering food i.e. the start of civilization Wheat cultivation spread out from this center over the next few thousand years.
Grass Fruits
• Each grain is a fruit: the ovary wall surrounding a single seed. Grain fruits are dry, not fleshy, and they are indehiscent: the seed does not fall out of them. • The embryo (which grows into the new plant) is called the germ. It is protein-rich. • The endosperm is mostly starch, with a little protein. It provides nutrients for the germinating seedling before photosynthesis starts. • The bran is the outer coat: it consists of the ovary wall fused to the seed coat. • In wild grasses (and some domesticated ones), the grain is surrounded by protective leaves, the chaff. Chaff has no nutrient value and must be removed.
– Much bigger grains – This is emmer wheat, a tetraploid (4 sets of chromosomes, 2 from each of the parents = 28 total chromosomes)
• further breeding of emmer wheat led to durum wheat, which is also tetraploid but has "naked grains": the chaff is much smaller and doesn't surround the grains.
• rice • barley and beer making • sorghum
pages
• Chap. 12
The Grass Family
• More than 50% of the calories consumed by humans comes from members of the grass family (Poaceae):
Outline
• Grasses as plants • Wheat
– domestication – farming basics – bread making
• corn
– domestication – hybrid corn – ethanol production
– wheat, corn, rice are the main grains, but also oats, barley, sorghum, millet, and rye – corn = maize
• Grasses make up 25% of all vegetation on Earth • Grasses are monocots • Tropical grasses (like corn but not wheat or rice) have C4 photosynthesis
– C4 means they can open their stomata at night, store carbon dioxide, and then close the stomata during the day and fix the CO2 into sugar while the Sun shines.
– Non-shattering = the grains don't fall off the stalk spontaneously. Makes it easier for humans to collect it, but harder for wild plants to disperse their seed.
Grain Processing
• • • Most grains are low in some essential amino acids. To get a complete protein, it is necessary to also eat something else, such as a legume. White flour, corn starch, white rice: just the endosperm, with the bran and germ removed. Brown rice, whole wheat flower, popcorn = the whole grain including bran and germ. – It contains much more protein and other nutrients than the endosperm alone. – But, it spoils faster due to fats in the germ, and bread made with whole flower doesn’t rise as well.
• Modern bread wheat is a hexaploid: three different diploid grasses hybridized to form it. These crosses occurred naturally, but were noticed and propagated by people. The starting point: einkorn wheat, which is a diploid wild grass. This means it was 2 sets of chromosomes (one set = 7 different chromosomes), or 14 chromosomes total.
– Branches (tillers) also start below ground.
Grass Flowers
• • • • • Grass flowers are small and inconspicuous: they are wind-pollinated so there is no need to attract pollinators. Many flowers grouped together (an inflorescence). Each one is called a floret. All angiosperm flowers have the same basic structure: from outside to inside there are four whorls, sepals, petals, stamens (male parts), carpels (female parts) In grasses, the sepals and petals are fused into a small structure (the lodicule) that swells up to open the flower. In place of sepals and petals are two bracts (leaves), the palea and the lemma.
Grass Family Characteristics
• Parallel leaf veins (like all monocots) • fibrous roots • either annual or perennial
– but crop species are all annuals
• Growing point is below ground until flowering. For most grasses, the flowers are at the tip of each branch.
Next Steps
• About 8000 years ago (very roughly), someone noticed a spontaneous hybrid between einkorn wheat and a closely related plant called goat grass.
– In the book of Genesis, at the beginning of the Bible, Adam and Eve are kicked out of the Garden of Eden and forced to grow wheat.
Domestication of Wheat
Wheat
Wheat
• Wheat (Triticum) is the source of most bread, noodles, beer. • The foundation of Western civilization: Middle East, Egypt, Mediterranean, Europe. • Wheat was domesticated at about the same time and place as barley and rye: the uplands of Turkey, Iran, and Iraq, roughly 10,000 years ago.
– At first, gains from wild einkorn wheat were harvested, and probably planted deliberately.
•
•
Archeological evidence shows that about 10,000 years ago, einkorn wheat with nonshattering heads was grown. This is the first step in domestication.
– Durum wheat is the source of pasta flour. It makes up 10% of today's wheat production in the US.
Fiwenku.baidu.comal Steps
• Tetraploid emmer wheat x another diploid goat grass = hexaploid bread wheat (Triticum aestivum). – Also a spontaneous event noticed and cultivated by humans, about 7000 years ago. – Six sets of chromosomes, 2 sets from each of the 3 parents = 42 total – Bread wheat is about 90% of today's wheat production. Wheat cultivation led to permanent settlements, plus a food surplus that led to having some people doing things other than gathering food i.e. the start of civilization Wheat cultivation spread out from this center over the next few thousand years.
Grass Fruits
• Each grain is a fruit: the ovary wall surrounding a single seed. Grain fruits are dry, not fleshy, and they are indehiscent: the seed does not fall out of them. • The embryo (which grows into the new plant) is called the germ. It is protein-rich. • The endosperm is mostly starch, with a little protein. It provides nutrients for the germinating seedling before photosynthesis starts. • The bran is the outer coat: it consists of the ovary wall fused to the seed coat. • In wild grasses (and some domesticated ones), the grain is surrounded by protective leaves, the chaff. Chaff has no nutrient value and must be removed.
– Much bigger grains – This is emmer wheat, a tetraploid (4 sets of chromosomes, 2 from each of the parents = 28 total chromosomes)
• further breeding of emmer wheat led to durum wheat, which is also tetraploid but has "naked grains": the chaff is much smaller and doesn't surround the grains.
• rice • barley and beer making • sorghum
pages
• Chap. 12
The Grass Family
• More than 50% of the calories consumed by humans comes from members of the grass family (Poaceae):