The invention provides preselected DNA sequences and methods of using them to alter the nutritional content of plant seed. Methods of the invention are directed to increasing the weight percent of an amino acid essential to the diet of animals, or increasing the starch content, of a plant. One method involves stably transforming a cell of a plant with a preselected DNA sequence encoding an RNA molecule substantially identical or complementary to a messenger RNA encoding a plant seed storage protein. An alternative method employs stably transforming cells with at least two preselected DNA sequences, one of which encodes an RNA molecule substantially identical or complementary to a messenger RNA (mRNA) encoding a plant seed storage protein, and the other preselected DNA molecule which encodes a preselected polypeptide. The transformed cells are used to generate fertile transgenic plants and seeds, which are characterized by expression of the preselected DNA sequence.