Responses Of Photosynthetic Apparatus To High Light And High Temperature Co-stress In Wheat

In China,wheat is an important food crop.However,biotic stress and abiotic stresses usually cause great damage to wheat plants.The study on wheat resistance mechanism can significantly improves wheat yield.Environmental stresses have many effects on photosynthesis in wheat.Photosynthesis has been closely related with food crisis,energy shortage,lack of resources and environmental problems.Therefore,the investigation of photosynthesis is very important.The molecular mechanism about the conversion and utilization of light energy is the key problem of photosynthetic research.The study about photosynthetic apparatus response to environmental stresses can reveal the molecular mechanism of the light energy conversion and utilization and improve the crop yield.In the past few decades,extreme weather conditions with high temperature and long light exposure increased dramatically,which significantly affect the photosynthesis of plants.In this study,the effects of high light and high temperature co-stress on PS? and antioxidant defense systems were studied.Under the action of high temperature and high light,the chlorophyll content,relative water content and PS? photochemical activity of wheat decreased,the level of reactive oxygen species(ROS)and total protein content increased.At the same time,the activity of six antioxidant enzymes increased rapidly after 1h of high light and high temperature co-stress.Immunoblot analysis showed that thylakoid protein D1 decreased significantly after 3 h of high light and heat co-stress.However,Lhcb5(CP26)and Lhcb6(CP24)increased significantly after 1h of high light and heat co-stress.In addition,Lhcb4(CP29)and D2 protein were highly phosphorylated after 1 h of high light and high temperature co-stress,and PS?-LHC?supramolecular complex was dissociated.Based on the above,the wheat seedling was pretreated with salicylic acid(SA)under high light and high temperature co-stress.The results showed that chlorophyll content,chlorophyll a/b ratio,protein content and relative water content in SA pretreated wheat plants were significantly higher than these plants exposed to high light and high temperature co-stress.In addition,the content of H2O2,MDA and electrolyte leakage of SA treated plants were significantly lower than these plantsexposed to high light and heat co-stress.The activities of POD,CAT and GR significantly increased after spraying SA,and the activities of six enzymes were higher thanthe plants after 3 h of high light and high temperature co-stress.In addition,SA application could significantly inhibited the decrease in Fv/Fm,?DPS? and qP under high light and high temperature co-stress.In summary,our results suggested that PS? protein phosphorylation and PS?-LHC? supercomplex structures play an important role in preventing damage to PS? under environmental stresses.The photosynthetic parameters(?PS?,Fv/Fm and qP)of SA treated plants were higher indicating that the proper concentration of SA had a protective effect on PS? under high light and high temperature co-stress.In addition,our results indicated that SA application could increase the antioxidant capacity of wheat under high light and high temperature co-stress and decrease the damage of peroxidation.