The Significant Role Of Cyclic Electron Flow In Plants’ Adaptation To Environmental Stresses

Light is the driving force of photosynthesis. However, excess light energy could induce photoinhibition. Environmental stresses induce the decrease in photosynthetic rate so that leads to the increase in excess light energy and then cause photoinhibition. Plants develop several mechanisms to protect leaves against excess light energy, such as cyclic electron flow (CEF), which has been widely studied in recent years. In order to explore the significant role of CEF in acclimation of plants to environmental stresses, the present study focuses on the response of CEF to chilling temperature, drought stress and high light. The results indicat that:1) The extreme sensitivity of photosystem Ⅱ (PSⅡ) to chilling-and-light stress is an important mechanism for why tropical plants cannot survive the winter in subtropical areas;2) In contrast to the traditional understanding of photoinhition of PSⅡ, the present study gives support to the new two-step scheme responsible for the photoinhibition of PSⅡ in tropical trees illuminated at chilling temperature;3) The extent of stimulation of CEF at chilling temperature determines the extent of photoinhibition of photosystem Ⅰ (PSI) and PSⅡ in tropical trees when illuminated at chilling temperature;4) After chilling-and-light treatment, CEF is stimulated under low light to help the fast recovery of PSⅡ activity at room temperature;5) Cyclic electron flow plays an important role during the acclimation of tropical trees to winter in marginal tropical areas;6) Cyclic electron flow plays an important role in photoprotection for resurrection plant under drought stress;7) Resurrection plant has the ability to rapidly repair PSI reaction centers, which contrasts to the low rate of recovery of PSI activity in non-resurrection plants;8) One role of CEF in alleviating PSⅡ photodamage is to protect oxygen-evolving complex, and the photodamage to oxygen-evolving complex is a limiting step of PSⅡ photoinhibitiom;9) An important mechanism of leaf folding is to remedy the deficiency of CEF and non-photochemical quenching. The present study indicates that CEF plays an impotant role in tropical trees under environmental stresses, such as chilling temperature, drought and high light. Furthermore, we found that a role of CEF in photoprotection for PSⅡ is stabilizing oxygen-evolving complex, which extends our understanding in the role of CEF.