Trehalose Protects PSⅡ Of Wheat By Stimulating Cyclic Electron Flow Under Heat And Drought Stresses

Wheat is an important grain crop,which is widely grown around the world.However,heat and drought have become the important factors which affect the production of wheat.And in natural production,heat and drought stresses often occur simultaneously.Environmental stresses destroy the photosynthetic structure and limit the growth and development of the wheat,leading to the reduction of its grain yield.A large number of reports show that the non-reducing disaccharide trehalose can improve the activity of photosystem Ⅱ,and protect or stabilize the reaction centers.However,the underlying mechanism is still unknown.Cyclic electron flow is an important protection mechanism under stresses,which can protect photosystem Ⅱ.This paper focused on the effects of exogenous trehalose on the activity of photosystem Ⅱ,the content of D1 protein,PQ pools and the activity of ATP synthase of wheat seedlings under heat and drought stresses.Meanwhile,it explored the relationship between trehalose and cyclic electron flow,and the mechanism about how to protect photosystem Ⅱ so that it can provide a theoretical basis for the protection of photosystem Ⅱ.The main results of this paper are as follows:1.Exogenous trehalose stimulates the cyclic electron flow in wheat seedlings under heat and drought stressesDuring heat stress,drought stress and their combination,the initial reduction rate of P700 of wheat seedlings is increased.Exogenous trehalose pretreatment significantly increases the initial reduction rate of P700+,so cyclic electron flow rate is stimulated,which can protect photosynthetic apparatus.When antimycin A is used to inhibit PGR5-dependent cyclic electron flow pathway,our results show that the initial reduction rate of P700+in wheat seedlings treated with exogenous trehalose decreased by more than 50%,indicating that exogenous trehalose pretreatment affects cyclic electron flow mainly by stimulating PGRS-dependent cyclic electron flow pathway.2.Exogenous trehalose alleviates the descent of photosystem Ⅱ activity in wheat seedlings under heat and drought stressesHeat stress,drought stress and their combination cause the photoinhibition in wheat seedlings,and the descent of PQ pools leads to blockage of the photosynthetic electron transport,resulting in the reduction of photochemical efficiency of photosystem Ⅱ and the inactivation of reaction centers.Furthermore,oxygen evolution rate is decreased.However,exogenous trehalose alleviates the destruction of D1 protein and enhances the oxygen evolution rate.Furthermore,the repairment of PSII is accelerated,whieh alleviates photosystem Ⅱ photoinhibition caused by drought and heat stresses.3.Exogenous trehalose accelerates the repairment of photosystem Ⅱ in wheat seedlings by stimulating cyclic electron flow under drought and heat stressesDuring heat stress,drought stress and their combination,exogenous trehalose can accelerate the acidification of the thylakoid lumen in wheat seedlings.At the same time,the activity of ATP synthase is increased,which promotes the mechanism of thermal dissipation,and accelerates the repairment of photosystem Ⅱ.When methyl viologen is used to inhibit cyclic electron flow.Results show that trans-membrane proton gradient(△pH)and the activity of ATP synthase is significantly decreased,which indicates that exogenous trehalose increases △pH across the thylakoid membrane and the activity of ATP synthase by facilitating cyclic electron flow.In summary,this paper reveals the protection mechanism of exogenous trehalose on the photosystem Ⅱ in wheat seedlings under drought and heat stresses.Exogenous trehalose can increase the acidification of the thylakoid lumen and the activity of ATP synthase by stimulating cyclic electron flow,which alleviates the destruction of D1 protein and protects oxygen evolving complex.Finally,it shows that exogenous trehalose can protect the photosystem Ⅱ.