Abstract: Super hybrid rice Tianyou 998 was investigated under different high temperature levels (daily highest temperature was 32,35,38,40 and 42℃,the daily range 6℃)in climate chambers during different growth stages(heading,milk,soft dough,and hard dough stage).The results showed that SOD(Superoxide Dismutase)and POD(Peroxidase)enzyme activities decreased gradually but the content of MDA(Malondialdehyde)increased.The flag leaf photosynthetic activity was affected adversely,especially in the soft dough stage and hard dough stage.Meanwhile,the seed setting rate decreased,and the content of soluble sugar and protein of spikelets increased.The development process of upper-middle-basal sink in heading stage was seriously disturbed,and so did middle-basal sink in milk stage.When the daily highest temperature was up to 38℃,both heading and milk stage’s flag leaf was damaged significantly,compared with grain in 35℃.The flag leaf photosynthetic activity of the soft and hard dough stage declined significantly when the daily highest temperature was above 35℃,while the influence on grain was not serious.It was suggested that when the daily highest temperature was above 38℃,the source and sink of the rice was affectedseriously in heading and milk stages,but mainly affected the photosynthetic activity in soft dough and hard dough stages.

Key words: Rice, High temperature, Characteristics of source-sink, Membrane protective enzyme, Photosynthesis, Seed setting rate, Soluble substance