Development of endosperm and synthesis of starch in rice grain. II. Synthesis of starch.

Abstract

The brown rice grains (Japonica c.v. Koshihikari) fed with 14CO2 in different ripening stages were separated into the outer layer and inner portion by the wet-milling method, and starch granules were prepared. The specific radioactivity was higher in the inner portion starch when 14CO2 was fed in the early ripening stage, but in the outer layer starch in the late ripening stage. Specific radioactivity of amylose and amylopectin was similar in the inner portion starch when 14CO2 was fed in the early ripening stage. As grains ripened, however, the specific radioactivity of amylose became higher than that of amylopectin. No difference was found in the specific radioactivity between the inner chains and exterior chains of starch molecules. Most of the 14C fed in the early ripening stage existed in the portion resistant to glucoamylase and hydrochloric acid, and that in the late ripening stage was found in the digested fraction.