Photoprotection Of Cyclic Electron Flow In Response To High Temperature Stress In Tomato

Protected vegetable cultivation has become an important industry in China's agricultural system.Among them,tomato is an important vegetable crop that accounts for one-fifth of the vegetables in the protected vegetable.It is often subjected to high temperature(HT)stress in summer,which seriously reduces the yield and quality of toamtos.Photosynthesis is the most important physiological response to stress.HT causes the decrease of tomato photosynthetic rate,PSII and PSI photoinhibition and photodamage,and ROS accumulates,which leads to reduced of the ability of plants to absorb and utilize light energy and ability to fix carbon,this will affects the yield of plants.Cyclic electron flow(CEF)around PSI is an important way for plants to response stress and alleviate photoinhibition.However,the specific contribution of PGR5/PGRL1 and NDH-mediated CEF pathways in response to HT stress in tomato is unclear.This study evaluated the role of the PGR5/PGRL1 pathway and the NDH pathway in response to HT stress in tomato by using antimycin A(AA)(PGR5/PGRL1 pathway inhibitor)and rotenone(R)(NDH pathway inhibitor).The results are as follows:1.The photoprotective of CEF on tomato under high temperature stress was determined.HT stress promoted the increase of CEF rate in tomato leaves,while HT+AA and HT+R treatments inhibited the increase of CEF rate under HT stress,and the HT+AA inhibition effect was more significant.At the same time,HT+AA treatment further led to a decreased of photosynthetic rate in tomato leaves under HT stress.These results indicated that PGR5/PGRL1-mediated CEF played a more important role in tomato response to high temperature stress.2.The photoprotective of CEF on PSII in tomato leaves under high temperature stress was determined.HT treatment resulted in a decrease of Fv/Fm and Y(II)in tomato leaves,while significant increase in NPQ,1-q P,Y(NPQ)and Y(NO);HT+AA and HT+R treatments were further processed the decrease of Fv/Fm and Y(II)and increase of 1-q P,Y(NPQ)and Y(NO)in tomato leaves compared to HT treatment,but HT+AA treatment significantly inhibited the increase of NPQ.In addition,OJIP curve analysis showed that HT+AA treatment resulted in blocked electron transport of QA-QB,decreased in OEC activity and integrity of thylakoid membrane in tomato leaves.3.The photoprotective of CEF on PSI in tomato leaves under high temperature stress was determined.HT,HT+R and HT+AA treatments all caused a decrease in Pm and Y(I)and an increase in Y(NA)in tomato leaves;compared with HT treatment,HT+AA treatment resulted in significant decrease in Y(ND)and significantly increased of Y(NA),indicating that the decrease in PSI activity in tomato leaves was mainly caused by PSI receptor side restriction.Analysis of the redox kinetics curve of P700 found that HT+AA treatment destroyed the redox balance of the PSI reaction center in tomato leaves,which caused the more severe oxidative damage on PSI.Analysis of changes in the P515 signal also revealed that compared to other treatments,HT+AA treatment resulted in a significant decrease in ?p H on tomato leaves,as well as a decrease in thylakoid membrane integrity and ATPase activity.In addition,in each treatment,HT+AA treated tomato leaves DAB and NBT stained the deepest,H2O2 content and O2-production rate were also significantly higher than other treatments.At the same time,HT treatment resulted in a significant increase in CAT,POD,APX,MDHAR and DHAR activities;whereas HT+AA treatment resulted in a significant decrease in SOD,CAT and MDHAR enzyme activities under HT stress,and caused a slight decrease in other enzyme activities;HT+ R treatment only caused a significant decrease in APX,DHAR and GPX enzyme activities and the remaining enzyme activities were not significantly different from HT.4.The effects of CEF on the expression of photo-encoding protein and antioxidant enzyme-encoding genes in tomato leaves under high temperature stress were determined.HT,HT + AA and HT + R treatment not only caused serious damage to tomato leaf photosystem and antioxidant system,but also affects the expression of key protein-coding genes and antioxidant enzyme-encoding genes in the photosystem complex.Compared with HT treatment,HT + AA treatment significantly reduced the expression of PGR5/PGRL1 and NDH pathway genes,core protein encoding genes in PSII and PSI and the main antioxidant enzyme encoding genes in plants.Therefore,we speculate that CEF can adversely affect the expression of nuclear genes.