Selection of Soybean Mutants with Increased Concentrations of Seed Methionine and Cysteine

Soybean [Glycine max (L.) Merr.] protein, which is deficient in the sulfur amino acids, especially methionine, is consumed world‐wide by both humans and other animals. Methionine deficiency is caused by an abundance of the β‐chain of β‐conglycinin, a seed storage protein that lacks methionine. De novo synthesis of the β‐chain is inhibited by an elevated concentration of methionine. The objectives of our investigations were to mutagenize soybean seeds, characterize a methionine over‐producing phenotype, and select several methionine over‐producing genetic lines. Mutant lines with a methionine over‐producing phenotype were isolated and crossed. Seeds from a cross, designated H82 × 20a2, contained a normal seed nitrogen concentration and an 18% increase in seed sulfur concentration. The S/N atomic ratio of line H82 × 20a2 was 16.2% greater than that of the parental line. Amino acid analyses of seeds from the derived and parental lines revealed mole percentages of 1.84 and 1.51, respectively, for methionine and 1.685 and 1.32, respectively, for cysteine. Thus, seed methionine and cysteine concentrations of H82 × 20a2 were each approximately 20% greater than those of the parental line. Protein produced by the derived line may fulfill nutritional requirements for methionine and cysteine.