Ripening Characteristics and Antioxidant Enzyme Activity of Ilmi under Heat Stress Condition

Heat stress during the ripening stage reduces the yield and quality of rice. Considering the adverse effects of global warming, it is necessary to breed heat stress tolerant rice cultivars and analyze their stress tolerance characteristics. We investigated the ripening characteristics and antioxidant enzyme activity of Ilmi under heat stress condition during the ripening stage. Ripening rate, 1000 brown grain weight, and rice quality of Ilmi were not significantly changed by heat stress during the ripening stage. Leaf chlorophyll, chlorophyll a/b ratio, and malondialdehyde (MDA) contents of Ilmi leaves were also less changed than those of Ilpum. These results strongly suggested that Ilmi has heat tolerance characteristics during the ripening stage. Analysis of antioxidant enzyme activity of Ilmi revealed that peroxidase (POX) activity was significantly higher than that of Ilpum, and showed a significant correlation with the change in chlorophyll a/b ratio and hydrogen peroxide content of flag leaves of Ilmi. These data suggest that the high POX enzyme activity of Ilmi could be considered one of its major heat tolerance characteristics.