Physiological Responses Of Rice Seedlings To Water And/Or High Temperature Stresses

Water and high temperature stresses have become the main severe climate factors of rice production in China. Compared with high temperature stress or water stress, water and high temperature composite stress causes more damages on rice growth, even some irreversible damages. So the study of rice seedlings physiological responses to water stress and/or high temperature stresses will be significant. The growth, photosynthesis, membrane permeability and membrane lipid peroxidation, osmotic regulation substances of rice seedlings(Liao Xing No.1) were studied under water stress(PEG6000 concentration of 0%, 10%, 15%, 20%) and/or high temperature stress(28℃、35℃ and 40℃). The results of the study are as follows:(1) Compared with the control, rice seedlings height, root length and above-ground fresh weight did not change significantly under light water stress(PEG6000 concentration of 10%) and 35 ℃ treatment, moderate water stress(PEG6000 concentration of 15%) only reduced the above-ground fresh weight significantly, The height, root length and above-ground fresh weight were significantly reduced under severe water stress(PEG6000 concentration of 20%) and 40 ℃treatment. 35℃ composited with moderate and severe water stresses and 40℃ composited with water stresses at different concentrations significantly reduced the rice seedlings height, root length and above-ground fresh weight. Shows that the rice seedlings growth had certain adaptability under light water stress and 35℃, along with the deepening of water and high temperature stresses, the adaptability disappeared, the growth was severely inhibited.(2) Compared with the control, rice seedlings net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs) and intercellular CO2 concentration(Ci) were significantly reduced under severe water stress, 40℃, 35℃ composited with moderate and severe water stresses and 40℃ composited with water stresses at different concentrations. There were no significant changes under other stresses. Gs and Ci reduced at the same time, which means that the decrease of Pn under water and high temperature stresses was induced by stomatal limitation; Under severe water stress and 40℃, rice seedlings maximum fluorescence yield(Fm) was reduced significantly, the initial fluorescence yield(Fo) and photosystem II(PSII) maximum photochemical quantum yield(Fv/Fm) had no significant changes. 40℃ composited with water stress increased Fo significantly and decreased Fm and Fv/Fm significantly, which shows that photoinhibition occurred with the deepening of stress.;There were no significant changes of rice seedlings total chlorophyll(Chla+b) content and chlorophyll a/chlorophyll b(Chla/b) under light and moderate water stresses and 35℃, but significant decrease was detected under severe water stress and 40℃. 35℃ composited with moderate and severe water stresses and 40℃ composited with water stresses at different concentrations significantly reduced the Chla+b contents and Chla/b, which shows that Chla was more sensitive to water and high temperature stresses than Chlb.(3) Compared with the control, relative conductivity and malondialdehyde(MDA) content increased significantly under severe water stress and 40℃, 35℃ composited with moderate and severe water stresses and 40℃ composited with water stresses at different concentrations significantly increased relative conductivity and MDA content. Shows that water stress and temperature stress strengthened membrane peroxidation at a certain extent, and membrane permeability increased.(4) Compared with the control, the soluble sugar, soluble protein and free proline(Pro) content increased under water and high temperature stresses. According to the relative increasing amplitude under water and high temperature composited stresses, their relative contributions of withstanding adversity damage were Pro>soluble sugar>soluble protein.