Effect of photosynthetic characteristic and dry matter accumulation of rice under high temperature at heading stage

The dry matter of rice grain mainly originates from photosynthetic outcome. The relationships between photosynthetic characteristic and dry matter accumulation were measured based on room experiments with two rice varieties (Yangdao6 and Nanjing43) under different high temperature stress of heading stage in 2007 and 2008. The results showed that grain yield, chlorophyll content, net photosynthetic rate (NPn), superoxide dismutase activity (SOD) and leaf area index (LAI) suffered a sharply decline. On the other hand, relative conductivity and malondialdehyde content (MDA) increased gradually with the elevation of stress temperature and extension of stress time. The increasing rate (reducing rate) of some physiological and biochemical indexes in Yangdao6 were lower than that in Nanjing43 compared with the CK under the same temperature stress. It was shown that response of Nanjing43 to high temperature was bigger than that of Yangdao6. According to the correlation analysis, grain yield showed a positive correlation with NPn and LAI at 0.01 level, the correlation coefficients of them were 0.94 and 0.88 respectively. The correlation between grain yield and DW after initial at mature stage, the export percentage of the matter in stem-sheath (EPMSS) and the transformation percentage of the matter in stem-sheath (TPMSS) were not significant. It was showed that grain yield under high temperature stress originated mostly from the photosynthesis and LAI of leaves after heading stage.