5 CONCLUSIONS
In conclusion, the damage to PS II observed after the heat and drought stress was attributed to blocked linear electron transport caused by a decrease in the PQ pool. CEF protects PS II from heat and drought-induced photo-inhibition. Exogenous trehalose alleviated the PS II photo-inhibition caused by heat and drought stress by promoting CEF. The water-water cycle as well as CEF may play a key role protecting PS II under heat and drought plus heat stress by increasing ΔpH and ATPase activity.