Effects of nitrogen source and timing of sulfur deficiency on seed yield and expression of 11S and 7S seed storage proteins of soybean

• Published in: Field crops research 1998-10, Vol.59 (1), p.1-8
• Main Authors: Sexton, Peter J, Paek, Nam C, Shibles, Richard M
• Format: Article
• Language: English
• Subjects: AZOTE; AZUFRE; CALIDAD PROTEICA; CARENCE MINERALE; CISTEINA; CYSTEINE; DEFICIENCIA DE MINERALES; GLYCINE MAX; GRAINE; METHIONINE; METIONINA; MINERAL DEFICIENCIES; NITROGEN; NITROGENO; NUTRITIVE VALUE; PROTEIN QUALITY; PROTEINAS DE RESERVA; PROTEINE DE RESERVE; QUALITE PROTEIQUE; Seed yield; SEEDS; SEMILLA; SOUFRE; Soybean; STORAGE PROTEINS; Sulfur; SULPHUR; VALEUR NUTRITIVE; VALOR NUTRITIVO
• ISSN: 0378-4290; 1872-6852
• DOI: 10.1016/S0378-4290(98)00101-4

The nutritional value of soybean ( Glycine max [L.] Merr.) seed as a protein source for nonruminants is limited by the amount of the S-containing amino acids, methionine and cysteine, they contain. The nutritional quality of S soybean is known to be influenced by both S and N nutrition. The capacity of the plant for S assimilation during late seed filling is an additional factor that might limit protein quality even when S availability is more than adequate. This paper describes experiments conducted to examine the effects of S and reduced N availability on protein quality, and the capacity of the plant for assimilation of sulfate-S during seed filling. Availability of sulfate-S was varied in the hydroponic culture during various vegetative and reproductive stages and N was supplied as either urea (reduced form) or as nitrate (oxidized form). The ratio of 11S/7S seed storage proteins was used as an indicator of protein quality. The 11S protein is of greater nutritional value than is the 7S protein; therefore, the greater the 11S/7S ratio the better the nutritional quality of the seed protein. Provision of reduced N caused seed yield to increase across S treatments and the 11S/7S ratio to decline among plants that were S-sufficient but not among those that were S-deficient. Seed yield was very sensitive to S-deficiency occurring during vegetative growth, but not to S-deficiency occurring during reproductive growth. The 11S/7S ratio was strongly influenced by S-deficiency occurring during reproductive growth, but was relatively insensitive to S availability during vegetative growth. Provision of S near the middle of the seed filling period to previously S-deficient plants caused 11S/7S ratio to increase threefold over plants that were maintained S-deficient throughout seed filling. We conclude that the plant maintains a substantial capacity for S assimilation late into seed filling, and that mobilization of vegetative S is not a large source of S for developing seeds.