Abscisic acid, ethylene and antioxidative systems in rice grains in relation with grain filling subjected to postanthesis soil-drying

This study tested the hypothesis that abscisic acid (ABA) and ethylene may mediate the effect of post-anthesis soil drying on grain filling of rice (Oryza sativa L.) through regulating its anti-oxidative systems. Two rice cultivars were pot-grown and exposed, from 9 days post anthesis until maturity, to three soil drying treatments: well-watered (WW), moderate drying (MD), and severe drying (SD). The MD treatment, compared with the WW treatment, increased grain filling rate and the activities of CAT, POD, and SOD in superior and inferior spikelets, whereas the SD treatment decreased them. Both MD and SD treatments enhanced the grain contents of ABA, superoxide anion, and MDA, with a higher rise in the SD than in the MD. The MD treatment decreased ethylene evolution rate and 1-aminocycopropane-1-carboxylic acid (ACC) content, whereas the SD treatment increased them. The ratio of ABA-ACC (ABA/ACC) was the highest under the MD and the lowest under the SD treatment. There was a significant positive correlation between the ABA content, the activities of CAT, POD, SOD, and ABA/ACC with the grain filling rate, while the levels of ethylene and ACC and the contents of superoxide anion and MDA correlated negatively with the parameter. Exogenous chemical application verified the roles of ABA and ethylene in grain filling. The results suggest that an increase in ABA and decrease in ethylene in the grains under post-anthesis moderate soil drying could enhance the anti-oxidative enzyme activities, thus reducing free radicals in grains and accelerating grain filling rate of rice.