The Responses Of Chloroplast Proteome And Respiratory Pathway To Exogenously-supplied Trehalose Under Heat Stress In Wheat Seedlings

As the wheat supplys 20%of the total dietary calories and proteins for the human being and feeds about 40%of the world's population,no matter it can be one of the most important food crops in the world.However,in recent years,the global warming and the high frequence of extreme climate has seriously affected the wheat photosynthesis,respiration and absorption of mineral elements and so on,and then limited the growth of wheat and thereby affected the yield and quality of the wheat.As a result,it is important to improve the heat tolerance of wheat in the future.Recently,many studies have shown that trehalose can enhance the stress tolerance of organisms.The present work aimed to explore the underlying mechanisms of trehalose to improve heat tolerance of wheat seedlings by studying the effects of exogenous trehalose on photosynthesis and chloroplast proteome in wheat and its effects on the respiration under heat stress,and thereby to provide the reference for the further research and utilization of trehalose.The main results were as follows:1.Heat stress reduced photosystem ?(PSII)photochemical efficiency,suppressed the electron transfer rate and lowered the energy for photochemical reaction,and thus resulted in the damage of PSII photochemical activity.However,compared with the control group,wheat seedlings pretreated with exogenously-supplied trehalose showed higher values in parameters such as Fv/Fm,Y(11),qP and ETR(?),suggesting that trehalose could relief the damage of high temperature to the photosynthetic activity,and thus diminish the adverse effects of heat stress on the photochemical efficiency.Besides,although the activity of photosystem ?(PSI)was generally stable,the photochemical efficiency of PSI was lowered and the non-photochemical quantum yield was increased in order to protect PSI;heat stress significantly increased the photoprotection index Y(ND),while the Y(ND)in the trehalose pretreatment group under heat stress was the highest,indicating that trehalose pretreatment improved the photoprotection proeedure of wheat seedlings.2.Under heat stress,the maintenance of light reaction in the trehalose-pretreated seedlings mainly depended on the up-regulation of its protein elements,including PsbP,Cytb6f,FNR,PsaD and ATPase.Meanwhile,the maintenance of fiunctional Calvin cycle relied on the up-regulation of Rubisco and FBPA.The up-regulation of Cytb6f can help enhance the CEF which is involved in the maintenance of ATP production.Meanwhile,the up-regulation of ATPase and FNR in the trehalose pretreatment group also helps to maintain the balance of reducing power while reduce the ROS generation under heat stress.Besides,the level of some other proteins also changed,and this might be due to the damage in the chloroplast membrane system induced by heat stress..3.During heat stress and the subsequent recovery period,no significant change in the total respiration rate of wheat seedling leaves was observed.However,the alternative pathway(AP)capacity continued to increase and the cytochrome pathway(CP)showed lower proportion.Meanwhile,heat stress treatment significantly increased the expression of AOXla gene.Trehalose pretreatment can effectively improve the alternative pathway capacity(VAox)by up-regulating the expression of AOXI genes under heat stress in wheat seedlings.Additionally,under heat stress,trehalose pretreatment can effectively protect the activities of Complex ? and ?,especially the coupling degree of oxidative phosphorylation with Complex ?,and thus mitigate the damage of heat stress to cytochrome pathway.4.AP plays an important role in the maintenance of photosynthetic activity under heat stress and during the subsequent recovery period.Under heat stress,when the AP was inhibited by SHAM in wheat seedlings,the Fv/Fm in control group and trehalose pretreatment group was significantly lower than that before high temperature treatment.Besides,in the trehalose pretreatment group,NAD-/NADP-MDH activities were higher than the control group under heat stress,and thus trehalose pretreatment could promote the dissipation of excessive reduction equivalents in chloroplasts and play a protective role in the balance of chioroplast redox homeostasis.In conclusion,this study suggested that:the photo synthetic performance of wheat seedlings was damaged under heat stress,but exogenously-supplied trehalose could alleviate the damage to some extent.The maintenance of light reaction in the trehalose pretreated seedlings mainly depended on the up-regulation of its protein elements,including Psbp,Cytbf6f,FNR,PsaD and ATPase,while the maintenance of functional Calvin cycle relied on the up-regulation of Rubisco and FBPA.These also alleviated the heat damage to the photosynthetic activity and protected the photochemical efficiency under heat stress to a certain degree.And consequently,it promoted the photoprotection process of wheat seedlings.At the same time,exogenously-supplied trehalose could effectively enhance the AP activity in wheat seedlings under heat stress and alleviate the damage of heat stress to CP.The AP can promote the dissipation of excess reduction equivalent in chloroplasts and thus play a protective role in the maintenance of cytosolic redox homeostasis.