Exogenous putrescine alleviates photoinhibition caused by salt stress through cooperation with cyclic electron flow in cucumber
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When plants suffer from abiotic stresses, cyclic electron flow (CEF) is induced for photo-protection. Putrescine (Put), a primary polyamine in chloroplasts, plays a critical role in stress tolerance. However, the relationship between CEF and Put in chloroplasts for photo-protection is unknown. In this study, we investigated the role of Put-induced CEF for salt tolerance in cucumber plants (Cucumis sativus L). Treatment with 90 mM NaCl and/or Put did not influence the maximum photochemical efficiency of PSII (Fv/Fm), but the photoactivity of PSI was severely inhibited by NaCl. Salt stress induced a high level of CEF; moreover, plants treated with both NaCl and Put exhibited much higher CEF activity and ATP accumulation than those exhibited by single-salt-treated plants to provide an adequate ATP/NADPH ratio for plant growth. Furthermore, Put decreased the trans-membrane proton gradient (ΔpH), which was accompanied by reduced pH-dependent non-photochemical quenching (NPQ) and an increased the effective quantum yield of PSII (Y(II)). The ratio of NADP+/NADPH increased significantly with Put in salt-stressed leaves compared with the ratio in leaves treated with NaCl, indicating that Put relieved over-reduction pressure at the PSI acceptor side caused by salt stress. Collectively, our results suggest that exogenous Put creates an excellent condition for CEF promotion: a large amount of pmf is predominantly stored as Δψ, resulting in moderate lumen pH and low NPQ, while maintaining high rates of ATP synthesis (high pmf).
KeywordsCyclic electron flow Cucumber Photoprotection Putrescine Salt stress
Cyclic electron flow
Protein gradient regulation 5
Linear electron flow
Thanks to my supervisor, Guo Shirong, for his valuable support for my work. I am grateful to the numerous individuals who participated in this research. Mr. Sheng Shu and Mr. Yu Wang provided critical discussion and comments, I also thank Ruonan Yuan for help with the experiment technology.
This work was supported by the National Natural Science Foundation of China (Nos. 31672199 and 31471869) and was supported by China Agriculture Research System (CARS-23-B12).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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