Effect of methionine on growth and protein composition of cultured soybean cotyledons

lmmature soybean cotyledons were cultured in vitro on a ‘complete’ medium with and without supplementation with methionine. The supplement increased dry wt by 23 %. The growth increase indicated that under these conditions the cotyledons could not synthesize methionine rapidly enough to supply the methionine required for maximum protein synthesis. This indication was supported by finding that aminoacylation of methionyl-transfer RNA was increased 18 % by methionine supplementation. Supplemental methionine also increased the methionine content of the protein fraction by more than 20 %, decreased the arginine content by 11 % and significantly affected several other amino acids. These latter results indicate that the amino acid composition of seed protein can be influenced by the supply of amino acids.