Grain size, sucrose level and starch accumulation in developing rice grain

Abstract

Five rices ( Oryza sativa L.) differing in final grain size were studied at the midmilky stage to determine if any factor could be identified which might limit rate of starch accumulation. Only UDP glucose pyrophosphorylase activity increased with increasing grain size. Detached rice panicles incubated in liquid medium containing 1% sucrose and 0.1% glutamine, in addition to minerals and vitamins, produced grains similar to those on intact plants. Sucrose level (0–1.5%) in the medium determined the extent of dry matter and starch accumulation and influenced physiological development of the ripening grains. Chemical and enzymic composition of the grain were similar to previously reported levels in grains of intact panicles analysed at regular intervals after anthesis. Addition of 3-P glycerate or K + to the medium did not improve dry matter accumulation in the developing grain.