Abstract
Two cultivars of rice (Oryza sativa L.) with different grain size were investigated to measure the free ABA contents during grain development. In both cultivars, the content and concentration of endogenous ABA in developing grain increased after heading, and attained a maximum value at about the middle of the linearly increasing period of grain dry weight. The ABA content and concentration subsequently decreased and maintained a low level after the termination of increase in grain dry weight. Higher ABA content was found in cultivar BG 1, which showed a larger grain size and a higher rate of grain filling, than in the other cultivar, Koshihikari, throughout all stages except at heading. The ABA concentration in both cultivars, on the other hand, showed similar values. These results suggest that ABA seems to play some role in assimilate accumulation into rice grain and to cause genetic difference in this process.
