Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2003
Publication Date: 10/1/2003
Citation: BENNETT, J.O., KRISHNAN, A.H., WIEBOLD, W.J., KRISHNAN, H.B. POSITIONAL AFFECT ON PROTEIN AND OIL CONTENT AND COMPOSITION OF SOYBEANS. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2003. V. 51(23). P. 6882-6886. Interpretive Summary: Soybean is a rich source of protein and oil. It has been noted that seeds from the upper portion of the plant have a higher content of protein and lower concentration of oil than seeds from the lower portion of the plant. The biochemistry underlying this variation in seed protein and oil content among the nodes was investigated in this study. A positional effect on protein and oil content and composition of soybeans was observed. Seeds from the top portion of the plant contained a higher percentage of the beta subunit of betaconglycinin, a protein deficient in sulfur-containing amino acids, which are essential in monogastric diets. Application of nitrogen fertilizer at different growth stages of the plant neither altered the abundance nor the distribution of fatty acids. The information obtained from this basic study indicates that nitrogen fertilization does not provide any significant improvement of soybean protein or oil content and quality. Biological nitrogen fixation presumably provides enough reduced nitrogen for the synthesis of soybean storage proteins. Thus, farmers can minimize their cost of soybean production by eliminating the use of nitrogen fertilizers.
Technical Abstract: Soybean (Glycine max [L.] Merr.) protein and oil qualities, with respect to monogastric nutrition, have been linked to the relative abundance of specific protein subunits and fatty acids, respectively. An analysis of field-grown soybean seeds by near-infrared spectroscopy revealed significant differences of their protein and oil contents as a function of nodal position. Seed proteins from the plant apex were high in protein and low in oil content, while those from the basal region exhibited an opposite pattern of accumulation. Sodium-dodecyl-sulfate-polyacrylamide-gel electrophoresis of total seed proteins revealed that the beta-subunit of beta-conglycinin content was four-fold higher in seeds from the apical nodes than in seeds from basal nodes. The glycinin A3 polypeptide content gradually increased in successively lower nodes from the top of the plant. Its accumulation was drastically reduced when nitrogen was applied at specific growth stages. Exogenous nitrogen did not alter the pattern of beta-subunit accumulation, but accrual of the acidic and basic polypeptides of glycinin was diminished. The remaining seed storage protein components were not influenced by nodal position or nitrogen application. Gas chromatographic analysis of fatty acids indicated that only the oleic (18:0) and linoleic (18:2) acids showed variability in accumulation at different nodes. Neither the abundance nor distribution of the fatty acids was altered by nitrogen application.