Intervarietal differences in some metabolic functions associated with protein accumulation in rice grains

Total nitrogen, amino nitrogen, glutamic acid dehydrogenase (GDH) activity and incorporation of (3)H-uridine and (14)C-amino acids into RNA and proteins, respectively, were compared in the developing grains of three high-protein stocks (IR-480-5-9, GMPR-51 and Erythroceros) and a high-yielding, medium-protein cultivar IR-8. The above parameters were also independently studied in the developing grains of IR-8 grown at 0, 60 and 120 kgN/ha. In addition, mobilization of nitrogen from flag leaf during kernel development was compared in a separate experiment. Higher protein concentration, both in high-protein stocks and in IR-8 grown at 120 kgN/ha, was associated with increased levels of: soluble amino nitrogen, GDH activity, (3)H-uridine and (14)C-amino acid incorporation. Significant variation was found among the high protein stocks in mobilization of nitrogen from flag leaf.