The Effects Of Exogenous Hydrogen Sulfide On Rice Photosythesis And Its Protective Role Under High Light Stress

The study on the increase of crops yield has great significance in China. Photosynthesis is an important way of biomass accumulation in crops, thus promotion of photosynthesis or improvement of photosynthesis under stress has become one of the important way in super-yield crops breeding. There are many measures which could affect the photosynthesis, such as RuBPCase kinetics parameter screening, RuBPCase activase stability improvement under heat, as well as engineering C4 pathway into C3 rice. Hydrogen sulfide (H2S) is considered to be the third signal molecule besides the NO and CO, and was numerously studies in animals, while recent researches have indicated that H2S also plays an active role in regulating the physiological processes in plants, such as up-regulation photosynthesis of spinach leaves.In this work, the rice (Oryza saliva) cultivar ’Ilyou 084’ was used to explore the effect of low concentration NaHS (donor of H2S) on photosynthesis of rice seedlings. When the seedlings were grown to fourth leaf, they were divided into two groups. One group were treated by NaHS with different concentrations (0,0.01,0.1,0.5 and 1 mM) for ten days, then its effects on growth and photosynthetic physiology such as photosynthesis, photorespiration, chlorophyll fluorescence and stomata were investigated. Anther group were treated with strong light, meanwhile treated with 0.01 mM exogenous NaHS, then the photosynthesis, PSII photoinhibition, the accumulation of O2- and H2O2 in rice leaf were investigated. Results were as follows:1. Through treatments by different concentrations of exogenous H2S on rice in growth light, the data revealed that low concentrations of NaHS could improve rice biomass and chlorophyll content, while high concentrations had an adverse effect. Net photosynthetic rate, stomatal conductance and ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity were also increased under low concentrations of NaHS. Under SEM stomatal aperture and density were increased by low concentrations of H2S. However photosynthetic oxygen evolution rate, photosynthetic electron transfer as well as photochemical efficiency of PSII were not affected by H2S treatment. Moreover photosynthesis oxygen sensitivity, CO2 compensation point and glycolate oxidase (EC 1.1.3.1) activity were reduced by H2S treatment and thus photorespiration was down-regulated. According to above results it could be deduced that H2S in low concentrations improved rice photosynthesis by increasing its stomatal aperture and density, which may resulted from reduced photorespiration.2. Through treatment with 0.01 mM exogenous H2S on rice in strong light, the data revealed that low concentrations of NaHS could improve rice photosynthesis and stomatal conductance; reduce the proportion of the closed PSII reaction centers and the degree reduction of Qa; increase the quantum yield of electron transfer and the ratio of energy which transferred to the downstream; promote the transfer of PSII to PSI under photoinhibition; improve the capacity of the photosynthetic apparatus to scavenge ROS. Above results indicated that exogenous H2S could relieve the down-regulation of photosynthesis and ROS damage under photoinhibition.