Molecular Biology of Plant Pathways / Genetic Engineering of Seed Storage Proteins
The Nature of Seeds
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).