Exogenous trehalose protects photosystem II by promoting cyclic electron flow under heat and drought stresses in winter wheat.

Drought and the rising global temperature are important factors reducing wheat production. Trehalose protects the reaction center and improves photosystem II (PS II) activity under diverse stress conditions. However, the underlying mechanism remains unknown. Cyclic electron flow (CEF) plays an important role in protecting PS II under environmental stresses. Our study focused on the effects of exogenous trehalose on the activity of PS II, D1 protein content, plastoquinone (PQ) pool, and ATP synthase activity in wheat seedlings under heat and drought stresses to explore the relationship between trehalose and CEF. These results indicated that heat and drought stresses decreased the maximal photochemical efficiency of PS II (Fv/Fm) and the electron transport rate of PS II (EFR(II)), whereas the trehalose pretreatment improved photochemical efficiency and the electron transport rate of PS II. The trehalose pretreatment stimulated CEF under heat and drought stresses. Furthermore, the proton gradient (ΔpH) across the thylakoid membrane and ATPase activity increased. The higher ΔpH and ATPase activity played a key role in protecting PS II under stresses. Trehalose pretreatment could reduce the inhibition of heat and drought stresses on PQ pool. Thus, our results indicated that photoinhibition of heat and drought-stressed plants was alleviated by the trehalose pretreatment, which was mediated by CEF and PQ pool.