Effects Of Exogenous MeJA On Photosynthetic Carbon Metabolism And Physiological Characteristics Of Strawberry Seedlings Under High Temperature Stress

High temperature seriously affects the growth of strawberry seedlings.It is of great significance to find measures to alleviate the physiological and biochemical damage of strawberry seedlings caused by high temperature stress for the cultivation of strawberry seedlings.In this experiment,’Xuelixiang’strawberry was used as the experimental material to study the effects of high temperature stress on the physiological and biochemical characteristics of strawberry and the mitigation effect of Me JA on high temperature stress.The main results are as follows:1.Spraying different concentrations of Me JA under high temperature stress conditions can improve the photosynthesis of strawberry seedlings,maintain osmotic pressure balance,and inhibit the accumulation of reactive oxygen species,while spraying 200μmol·L^-1Me JA has the most significant effect.2.Under high temperature stress,the photosynthesis of strawberry seedlings was damaged,thus affecting carbon metabolism.Spraying appropriate concentration of Me JA could significantly improve the photosynthesis of strawberry seedlings.The chlorophyll content,Pn,Gs,Fv/FM,ФPSII and q P in seedling leaves increased by 7.26-28.14%,7.65-33.16%,33.12-138.1%,4.75-18.74%,1.5-26.43%and 10.18-128.57%,respectively,while Ci and NPQ decreased by 4.11-33.52%and 11.13-63.62%,respectively.It could significantly reduce the accumulation of carbohydrates such as soluble sugar,starch,sucrose and fructose in strawberry seedlings.The contents of starch,sucrose and fructose in the leaves of seedlings decreased by 6.76-17.82%,5.14-26.1%and 10.33-39.56%,respectively,under the stress of 0-8h,while the contents of soluble sugar,starch,sucrose and fructose in the new stems of seedlings decreased by 38.12-92.66%,5.11-41.49%,18.58-38.87%and14.2-51.83%,respectively.In addition,the activities of SS,SPS,AI and NI,the key enzymes of carbohydrate metabolism,were also enhanced.Under the stress of 0-8 h,the activities of SS and SPS in seedling leaves were relatively stable,and the activities of AI and NI increased by 9.52-41.52%and 2.14-7.84%,respectively.The activity of NI in the new stems of seedlings was relatively stable,and the activities of SS,SPS and AI increased by 4.9-27.44%,15.38-23.58%and 4.44-7.09%,respectively.3.Under short-term high temperature stress,the accumulation of ROS in strawberry seedlings increased the content of O₂^-and H₂O₂,and strawberry seedlings alleviated seedling damage by increasing the activity of antioxidant enzymes and antioxidants.Under long-term high temperature stress,the activities of antioxidant enzymes and antioxidants in strawberry seedlings decreased rapidly,resulting in seedling damage.After spraying appropriate concentration of Me JA,the content of O₂^-and H₂O₂in strawberry seedlings decreased significantly.Under the stress of 0-8 h,the content of O₂^-and H₂O₂in seedling leaves decreased by 11.2-35.06%and 9.98-21.52%,respectively,while in the new stems of seedlings decreased by 24.32-50.87%and 19.82-48.3%,respectively,and the activities of SOD,POD,CAT,As A and GSH increased.The activities of SOD,POD,CAT,As A and GSH in the leaves of seedlings increased by 18.87-36.88%,15.38-71.76%,17.86-41.59%,15.87-69.26%and 38.93-84.9%respectively under 0-8h stress,while in the new stems of seedlings increased by 8.12-25%,26.87-88.17%,7.48-32.42%,8.92-21.15%and11.41-45.58%respectively.4.Under high temperature stress,the degree of membrane lipid peroxidation in strawberry seedlings increased,resulting in the increase of REC,MDA and LOX.Spraying appropriate concentration of Me JA could effectively inhibit the increase of REC,MDA and LOX,and alleviate the peroxidation damage of seedlings.Under the condition of 0-8h stress,REC,MDA and LOX in seedling leaves decreased by 7.68-59.62%,2.86-26.19%and14.71-43.31%,respectively,while MDA and LOX in new stems of seedlings decreased by2.03-8.96%and 20.92-57.01%,respectively.5.Under high temperature stress,the osmotic pressure balance in strawberry seedlings was broken,resulting in the increase of Pro and SP content.Spraying appropriate concentration of Me JA significantly reduced the content of Pro and SP in seedlings and maintained the osmotic pressure balance.Under the stress of 0-8h,the content of Pro and SP in seedling leaves decreased by 3.25-11.02%and 7.33-15.4%,respectively,while in the new stems of seedlings decreased by 4.13-24.87%and 5.86-20.23%,respectively.6.Under the condition of high temperature stress,the leaves and new stems of strawberry seedlings were sampled and measured.It was found that the response of new stems to high temperature stress was more intense than that of leaves,indicating that new stems were more vulnerable to stress damage.After spraying Me JA,the mitigation effect of new stems was more significant than that of leaves.