Relationship between Some Physiological and Biochemical Characteristics and Heat Tolerance at Flowering Stage in Rice

Rice may suffer serious heat stress during its growth period,which will affect the process of physiological metabolic activities of the plants.Using five hybrids as experimental materials,the changes in photosynthetic rate,chlorophyll content,soluble sugar content,free proline content,malondialdehyde(MDA) content and antioxidative enzyme activities were studied under high temperature conditions at flowering stage.The results indicated that high temperature stress decreased the photosynthetic rate and chlorophyll contents of flag leaves,increased contents of soluble sugar,free proline and malondialdehyde(MDA) as well as the activities of superoxide dismutase(SOD),catalase(CAT) and peroxidase(POD) in flag leaves at flowering stage.Correlation analysis showed that heat susceptibility index(HSI) was significantly or very significantly related to the relative changed percentage of the contents of chlorophyll,free proline and MDA and SOD activity under high temperature stress conditions.Therefore,these indexes could be selected as physiological identification for heat tolerance at flowering stage in rice.Under high temperature stress at flowering stage,those cultivars with strong heat tolerance would show a smaller decrease of chlorophyll content,a smaller increase of MDA and a bigger increase of proline content and SOD activity in flag leaves.The stepwise regression equation of HSI to relative changed percentage of the contents of MDA,free proline content and SOD activity was established,which could be used to evaluate the heat tolerance of rice cultivars.