Screening And Identification Of Thermo-tolerant Rice Genotypes And Its Physiological Characterization

Rice (Oryza sativa L.) is one of the most important food crops in the world. Nearly half of population in the world is dependent on rice for food, especially in Asia, Africa and Latin America. In China, more than 60% of population is dependent on rice for food. Therefore, it is important to sustainably promote rice production in order to ensure food security and economic development. However, high temperature has become a major disastrous factor affecting rice productivity, and the temperature stress become more severe probably due to the global warming. Thus, it is imperative to investigate heat tolerance of rice and develop the rice cultivars with high tolerance to heat stress. Proteomics analyses of illustrating the regulation of gene expression in rice under high temperature may identify the gene groups associated'with heat stresses and reveal the impact of high temperature on rice metabolisms. The present study was carried out to determine the impact of high temperature on floret fertility and seedling growth, and compare the difference among rice genotypes in heat tolerance, so as to identify the genotypes with high tolerance and understand the mechanisms of heat tolerance at both physiology and proteomics levels. The main results are as follows:1. Seventy-two rice genotypes were treated with high temperature (40℃/35℃,14h/10h) for 12 d at heading stage, and floret fertility was examined. The results of two years' experiments showed the similar results that there was a distinctly genotypic difference in floret fertility as affected by heat stress. Consequently the thermo-tolerant genotypes were identified. When rice seedlings were subjected to heat stress, SPAD value, plant height, root length, shoot and root biomass were dramatically reduced, with tolerant genotypes being relatively less affected than sensitive ones. Meanwhile high temperature enhanced membrane lipid peroxidation, as expressed by increased malondialdehyde content and stimulated superoxide dismutase (SOD) activity. Tolerant genotypes had less and more increase of MDA content and SOD activity than sensitive ones under heat stress relative to the control. The genotypes CJ6, MY46 and JX17 are highly thermo-tolerant, while MH63, Kasalath and IRAT4217 are very sensitive. 2. Physiology and proteomics studies were carried out using MY46 (a heat-tolerant genotype) and MH63 (a heat-sensitive genotype). Under high temperature, floret fertility, SPAD value, plant height, root length and biomass were dramatically reduced, while contents of malondialdehyde, hydrogen peroxide, superoxide anions, and activity of superoxide dismutase were greatly increased, irrespectively of Seedling or heading stage. Moreover, MH63 was much more affected than MY46. Proteomic analysis showed that high temperature resulted in down-regulation of photosynthesis, energy and metabolism related proteins, while resistance-related proteins were up-regulated by high temperature. The results also showed that the heat tolerance of MY46 was much stronger than MH63. The up-regulation of anti-stress protein 2-cys peroxiredoxin BASl under heat stress.was first found in this study.