Effect of Heat-Stress during Meiosis on Grain Yield of Rice Cultivars Differing in Heat-Tolerance and Its Physiological Mechanism

Abstract

Meiosis is the most stress-sensitive period in reproduction of rice plants. However, little is known how heat-stress dur-ing meiosis affects grain yield of rice. This study investigated the development of anthers and pollens, yield components, and some physiological parameters under the heat-stress during meiosis. Two indica rice cultivars with different heat-tolerance, Shuanggui 1 (heat-sensitive) and Huanghuazhan (heat-tolerant), were pot-grown and subjected to treatments of heat-stress (the mean temperature during the day 35℃) and natural temperature (the mean temperature during the day 33℃, CK). The results showed that the heat-stress significantly reduced anther dehiscence and pollen fertility rate of Shuanggui 1, while it much less affected those of Huanghuazhan. The number of spikelets per panicle, seed-setting rate, and 1000-grain weight were significantly decreased under the heat-stress for both cultivars, leading to a significant reduction in grain yield, with a more reduction in Shuanggui 1 than in Huanghuazhan. The heat-stress treatment significantly decreased grain width of Shuanggui 1 and obviously increased ratio of length to width of grain, whereas it less affected those of Huanghuazhan. The heat-stress significantly reduced root oxidation activity and ribonucleic acid (RNA) content of young panicles, and significantly increased malondialdehyde (MDA) content of leaves and ethylene evolution rate of young panicles, and the extent of the decrease or increase was more in Shuanggui 1 than in Huanghuazhan. The heat-stress treatment significantly increased activities of peroxidase, superoxide dismutase and catalase of leaves in Huanghuazhan, while it much less affected those in Shuanggui 1. The results indicate that stronger root acti-vity and antioxidative defense system, greater RNA content, and less ethylene synthesis and lower MDA content in rice plants during meiosis would be physiological mechanisms in maintaining a higher grain yield for a heat-tolerant cultivar under high- temperature stress.