Photoprotection Of Cyclic Electron Transport In Response To Low Night Temperature Stress In Tomato

Photosynthesis was the determinant of crop yield.In the cultivation and production of winter and spring facility vegetables in Northern China,low night temperature often causes plant photoinhibition or photosynthetic structure to be destroyed,which causes photosynthesis to decline and affects crop yield and quality.CEF is an important photoprotective mechanism in plants,mainly mediated by PGR5/PGRL1 proteins and chloroplast NADH dehydrogenase–like?NDH?complex.In this study,photosynthesis,cyclic electron transport rate,photochemical activity of PSI and PSII were measured by means of exogenous spraying inhibitor under LNT,the transmembrane proton potential and its components,reactive oxygen species were analyzed.The anti-oxidase activity and related gene expression were analyzed to reveal the photoprotective of different pathways of CEF under LNT.The main results are as follows:1.Protection of photosynthesis of CEF under LNT.The results showed that the net photosynthetic rate decreased significantly when the CEF was inhibited,?especially the PGR5 pathway?.Compared with the control,the exogenous application of rotenone and antimycin A solution further aggravated the Pn,Gs,Ci and Tr of tomato under LNT.2.Photoprotection of photosystem ??PSII?by CEF under LNT.This study found that the inhibition of CEF exacerbated the decrease of Fv/Fm,Y?II?,ETR?II?,NPQ,qP caused by LNT,while 1-q P showed the opposite trend.At the same time,the relative variable fluorescence of the K point?V_k?and the J point?V_J?was increased,further deepening the photoinhibition of PSII.It was indicated that NDH and PGR5/PGRL1 may play a regulatory role in reducing the inhibition of photosynthetic electron transport and promoting energy dissipation,PGR5/PGRL1 plays a major role.Gene expression analysis of the major proteins in the PSII complex revealed that LNT significantly promoted the expression of Psb B,Psb C and Psb D,while CEF was inhibited and down-regulated the expression of the above genes,indicating rotenone and antimycin A treatment can affect the expression of PSII complex protein in transcription level under LNT.3.Photoprotection of photosystem ??PSI?by CEF under LNT.The treatment of rotenone and antimycin A exacerbated the decrease in the photochemical efficiency Y?I?,ETR?I?and Y?NA?of PSI under LNT,Y?ND?was significantly higher than the control,Y?NA?was significantly lower than the control,resulting in increased side restriction of PSI and decreased donor side restriction,indicating that cyclic electron transport has an important protective effect on the PSI reaction center of tomato leaves under LNT.LNT significantly promoted the expression of the major constituent proteins Psa A,Psa C and Psa D in the PSI complex.The expression of Psa A,Psa C and Psa D was decreased when the CEF was inhibited,the antimycin A treatment was significantly decreased.4.CEF increased the trans-thylakoid membrane proton motive force?pmf?under LNT.In study,exogenous sprayed rotenone and antimycin A treatment significantly reduced the pmf and its component transmembrane proton gradient??p H?,transmembrane potential????in tomato leaves compared to LNT.It was indicated that these two pathways can jointly adjust the ?p H and the ?p H provided by the two pathways is beneficial to maintain the CO₂ assimilation.5.CEF played a photoprotective role by scavenging ROS under LNT.DAB and NBT were used to stain H₂O₂ and O₂^·- in tomato leaves respectively.It was found that LNT caused a large accumulation of ROS in tomato leaves,rotenone and antimycin A treatment greatly deepened the staining depth of leaves.Enzyme activities such as CAT,APX,POD and SOD were also strongly inhibited,while the relative expression levels of CAT,APX and Cu/Zn SOD were significantly down-regulated,indicating that CEF can increase antioxidant enzyme activity under LNT.The level of transcription responds to the production of ROS to protect plants from oxidative stress,thereby resisting stress and maintaining normal plant growth.