Study On Heat Tolerance Mechanism And Screening Physiological Identification Indexes Of Heat Tolerance At Late Growth Stage In Rice

The experiment was carried out in growth chamber under both normal and high temperature to investigate the effects of heat stress on morphological, growth and development indexes and physiological and biochemical characteristics during flowering, grain filling stage and the whole growth stage. Identification index of heat resistance during flowering and grain filling stage had been established preliminary. The effects of heat stress on morphological, physiological, biochemical and grain yield had been carried out deep research. This paper adequately expounded and proved the relationship between physiological and biochemical characteristics and heat resistance in rice and discussed the key physiological and biochemical mechanism of heat resistance during grain flowering stage. The results followed:1. High temperature stress on flowering stage decreased leaves' photosynthesis rate, contents of chlorophyll, increased contents of soluble sugar content, free proline content, malondialdehyde (MDA) content, as well as the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in leaves at flowering stage. Correlation analysis showed that heat susceptibility index significantly or very significantly correlated with relative changed percentage of contents of chlorophyll, free proline, MDA and SOD activity under both high temperature and normal conditions. Therefore, they could be selected as physiological identification indexes for heat tolerance at flowering stage in rice. Using stepwise regression equation to evaluate the heat tolerance of rice cultivars was considered scientifically and reliably.2. The ability of photosynthesis, osmotic adjustment and antioxidative enzyme activities were effected significantly in the high temperature condition at grain filling stage. The content of chlorophyll, soluble sugar, protein ,MDA, photosynthesis rate and the activity of SOD were correlated with heat resistance on grain filling stage. And heat tolerance on grain filling stage were different because of different cultivars.3. The content of chlorophyll, soluble sugar, protein, MDA, photosynthesis rate and the activity of SOD are correlative with heat tolerance at grain filling stage, which were synthesized to two new independent comprehensive indices by principal component analysis, Then the comprehensive evaluation of every rice varieties' heat tolerance was obtained by subordinate function value method (SFVM), Consequently, each cultivar' heat tolerance could be evaluated completely and correctly.4. The high temperature stress in the whole growth stage accelerated rice caducity and loss of protected functions, also lost the activities of antioxidative enzymes in leaves, decreased the osmotic adjustment of leaves, reduced the dry matters production, blocked the translocation and transformation of dry matters in stems and sheaths, decreased yields significantly. In the condition of higher environmental temperature, it should be important to strengthen the farming management in the late growth stage.