Abstract: The synthesis of assimilate such as starch, protein and lipid depends on the photosynthesis. Under stresses, the pigments, primary reaction and electronic transport chain which have relations with photosynthesis are hurt or inhibited. The effect of high temperature caused by “Greenhouse Effects” becomes more and more frequent. To elucidate the injury mechanism under high temperature in rice plants, the dynamic changes of chlorophyll content, chlorophyll fluorescence parameters and active oxygen resistance activity were measured and the grain quality indices including starch, protein, and chalkiness were also analyzed in rice plants of cultivars Xinongyou 30 and Fuyou 1 during grain-filling period under high temperature treatment in climatic cabinets. The results showed that under high temperature (33℃), chlorophyll content of leaves decreased, initial fluorescence (F_o) increased obviously, maximal photochemical efficiency of PS II (F_v/F_m) and the potential photochemical efficiency of PS II (F_v/F_o) decreased, F_v/F_o and F_v/F_m declined faster during the whole grain-filling period, especially in late period. Meanwhile, active oxygen resistance activity (AORA) lowered by 45.16 and 35.99% as compared with the control in the late grain-filling period; under high temperature condition, the total starch and amylose contents of grains were lower than those of control, the protein contents increased to a different degree, and chalkiness and 1000-grain weight changed significantly in two cultivars. The main reason of degeneration of grain quality under high temperature stress is related to the inhibition of primary reaction of photosynthesis, drop of active oxygen resistance activity and contraction of functional period in leaves of rice plants.

Key words: Rice (Oryza sativa L.), High temperature stress, Chlorophyll fluorescence, Active oxygen resistance activity, Grain quality