To investigate the effects of light on the accumulation of assimilate
in rice seeds, ears were allowed to grow in darkness 10 d after their
formation. The lipid content of rice bran on the 40th day increased by
cultivation of ears in darkness whereas the dry weight and starch and
sucrose contents of the rice seeds decreased. In the light, the triac
ylglyceride (TG) content of rice seeds was lowest on the 20th day but
then increased continuously for the next 20 d, while the diacylglyceri
de (DG) content reached a maximum value on the 20th day. In darkness,
in contrast, rice seeds showed a higher TG content, with a lower DG co
ntent and lower levels of other lipids on the 20th day compared with s
eeds exposed to light. These results suggest that the biosynthesis of
starch and lipids in rice seeds is regulated by light.