The Physiological Mechanism Of Hydrogen Sulfide Regulating Shade Tolerance Of Festuca Arundinacea

Turf plays a positive role in beautifying and improving the living environment for our human beings.With the continuous development of the economy in China,the demand for turf is becoming stronger than before.At present,the development of turf in China is still facing many problems that need to be solved urgently.It has been reported that there are about50%of turf under shade environment in China.Shade stress will lead to the decline of turf quality and increase the cost of turf establishment and maintenance.Hydrogen sulfide（H₂S）is a significant gas signal molecule,which plays a significant role in regulating the growth and development of plants.In recent years,the research on the regulation of abiotic stress by H₂S has become one of the hotspots.However,the research on the regulation of shade resistance of tall fescue by H₂S has not been reported.Therefore,tall fescue,which is widely used all over the world,was used as the research material.We applied Na HS to increase the content of endogenous H₂S and reduced the content of endogenous H₂S by hypotaurine（HT）to study the effect of H₂S on shade tolerance of tall fescue and explore its preliminary physiological mechanism.The results are as follows:（1）The optimum Na HS concentration for regulating shade resistance of tall fescue was500μmol·L^-1.The 500μmol·L^-1Na HS significantly reduced the accumulation of malondialdehyde（MDA）and improved the activities of guaiacol peroxidase（POD）,superoxide dismutase（SOD）,and ascorbate peroxidase（APX）in tall fescue leaves.Shade increased the activity of L-cysteine desulfhydrase（LCD）and promoted the accumulation of H₂S content in tall fescue leaves.In turn,higher endogenous H₂S content further increased the activities of POD,SOD,and APX,and decreased the accumulation of MDA in tall fescue.（2）Shade stress significantly inhibited the accumulation of photosynthetic pigments such as chlorophyll and carotenoids in tall fescue.However,the contents of chlorophyll a,chlorophyll b,total chlorophyll and carotenoids in tall fescue leaves increased significantly after the application of H₂S.Besides,H₂S up-regulating the expression level of chlorophyll-synthesis-related genes and increased the contents of precursor substances of chlorophyll synthesis,such as 5-aminolevulinic acid,porphobilinogen,and protochlorophyllide.H₂S also down-regulating chlorophyll degradation-related genes.In addition,H₂S up-regulated the expression level of some carotenoid synthesis-related genes,further increasing the contents of many kinds of carotenoids such as lutein,violaxanthin,and neoxanthin.（3）The photosynthetic rate of tall fescue leaves decreased significantly under shade treatment.After the application of H₂S,maximal quantum yield of photosystem II photochemistry,effective quantum yield of photosystem II photochemistry,stomatal conductance,and the activity of ribulose-1,5-bisphosphate carboxylase of tall fescue were significantly increased at the same time.Furthermore,the photosynthetic rate of tall fescue leaves under shade stress was increased,and more soluble sugar and soluble protein were accumulated in tall fescue leaves.The increase of photosynthetic rate might be an important way for H₂S to enhance the shade tolerance of tall fescue.（4）H₂S also induced the synthesis of endogenous gibberellin（GA）.However,inhibition or application of GA had almost no effect on the content of endogenous H₂S.When paclobutrazol（PAG）was used to inhibit GA,the effect of H₂S on the increase of plant height of tall fescue was weakened.However,the total chlorophyll accumulation of tall fescue was significantly increased.These results might suggest that H₂S is also involved in the shade avoidance of tall fescue.To conclude,H₂S could enhance the shade tolerance of tall fescue by increasing the efficiency of photosynthesis of tall fescue.The high efficiency of photosynthesis could be attributed to high activities of antioxidant enzyme,high contents of photosynthetic pigments,and high activities of photosystem II.At the same time,H₂S could enhance the shade avoidance of tall fescue by promoting plant height.To some extent,the regulation of H₂S on shade avoidance of tall fescue might depend on the GA,because of inhibiting GA could enhance the regulation effect of H₂S on shade tolerance of tall fescue.