CHANGES IN ENZYME-ACTIVITIES ASSOCIATED WITH CARBOHYDRATE-METABOLISM DURING THE DEVELOPMENT OF RICE ENDOSPERM

Changes in activities of 18 enzymes involved in carbohydrate metabolism from sucrose to starch were analyzed in relation to amounts of starch, soluble sugars, and soluble protein, as well as grain weight and water content during endosperm development of Japonica rice (Oryza sativa L., cv. Fujihikari). The developmental patterns of ADPglucose pyrophosphorylase and starch branching enzyme (Q-enzyme) differed from the other enzymes examined in that they exhibited the greatest enhancement during endosperm development. In addition, both ADPglucose pyrophosphorylase and Q-enzyme activities increased 7-8 days after anthesis, when activities of the other enzymes including soluble starch synthase had already reached their highest levels. The accumulation patterns for the former two enzymes correlated well with the curve for starch production. The increases in ADPglucose pyrophosphorylase, soluble starch synthase and Q-enzyme were distinct, suggesting that synthesis of these enzymes are independently modulated genetically. The results strongly suggest that both ADPglucose pyrophosphorylase and Q-enzyme play key roles in starch biosynthesis of rice endosperm.