Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/23/1996
Publication Date: N/A
Citation: Interpretive Summary: Protein is one of the most valuable components of soybean seed. Unfortunately, one of the major classes of seed protein is very deficient in sulfur-containing amino acids, which limits its nutritional value. It would be of great benefit to be able to manipulate the relative abundance of various classes of storage protein, thereby increasing the content of sulfur-containing amino acids. These researchers have measured the effect of different types of nitrogen on the amount of storage protein produced by the soybean seed. They determined that some forms of nitrogen help the plant produce more protein than other forms. They also determined that more of the protein that is nutritionally poor is produced than the good protein. This suggested to them that the relative abundance of sulfur available to the developing seed may affect the quality of the protein produced. This can have significant implications for fertilization and cultural strategies and may guide breeders in producing new high quality soybeans.
Technical Abstract: Effects of N nutrition of the synthesis of storage protein in soybean seed (Glycine max [L.] Merr. cv. Harper) were examined using a hydroponic system. Under N deficiency the concentration of each storage protein subunit, as well as of total protein, was decreased. However, the concentration of beta-conglycinin (7S), especially the beta-subunit, was decreased more than glycinin (11S). As well, different nutritional forms of N (nitrate, ammonia, and urea) during pod filling altered seed storage protein concentration and subunit composition. Under constant N supply, seed storage protein concentration was increased progressively by substituting urea for nitrate. Increased protein concentration resulted from a disproportionate increase of the beta-subunit of beta-conglycinin, which caused a decrease in the 11S/7S ratio. The relative abundance of alpha and alpha'-subunits was not changed by N nutritional conditions. Thus, N nutrition (quantity and form) seeds to control, at least in part, the proportion of the beta-subunit in beta-conglycinin, and consequently affects the 11S/7S ratio in seed storage protein. It is noteworthy that the concentration of glycinin remained constant while the total seed protein concentration increased. We speculate that these observed variations in seed storage protein composition result from the relative abundances of sulfur- and N-metabolites available to developing soybean seed.