Seeds provide a mechanism by which many types of plants propagate, and they are an important food source for many animals, including humans. The seed contains a dormant embryo and a mixture of stored metabolites (protein, starch, and lipid) that support its germination and prephotosynthetic growth. The storage proteins are a source of nitrogen and sulfur for the synthesis of new enzymes in the germinating seedling, while the starch and lipid initially provide the energy and carbon skeletons for making a variety of organic molecules. In angiosperms, which include most seed crops of agricultural importance, these storage compounds are deposited in one or more specialized tissues in the seed: the endosperm (especially in the cereals), the cotyledons of the embryo (particularly in legumes), or more rarely, the maternal perisperm tissue, as in the case of beet (Bewley and Black, 1995).
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