Development of endosperm and synthesis of starch in rice grain. I. Development of endosperm and distribution of 14C-labeled assimilates.

Abstract

Rice plant (Japonica c.v. Koshihikari) was exposed to 14CO2 during the ripening period. The autoradiography of brown rice grains showed that the 14C-labeled assimilates distributed throughout the whole grains fed till the 5th day after heading, then the reserve material accumulated first in the inner portion and late in turn to the outer layer. Total radioactivity rose from the 5th day before heading till the 18th day after heading, then dropped as the grains ripened. Most of the radioactivity was incorporated into starch with the maximum on the 18th day after heading. The incorporation of 14C into proteins, lipids and cell walls was more active in the early ripening stage for building the skeleton of endosperm cells and for preparation of starch synthesis. Radioactivity in the low molecular materials increased with ripening, because synthesis of the assimilates into starch slowed down.