Abstract: Effects of exogenous oxalate on photosynthesis, chlorophyll fluorescence and xanthophyll cycle in cucumber leaves under high temperature stress at 40℃ were studied. The cucumber leaves were sprayed by 5 mmol·L-1 oxalate solution for 3 days before high temperature stress. The results showed that oxalate pretreatment alleviated the decreases of photosynthetic rate (Pn), transpiration rate (Tr), intrinsic photochemical efficiency (Fv/Fm), quantum yield of PSII (φPSⅡ), photochemical quenching (qP) and non-photochemical quenching (NPQ) by higher temperature, but has no effect on stomatal conductance (Gs) was observed. The xanthophyll cycle pool and (A+Z)/(V+A+Z) (the de-epoxidation extent of xanthophyll cycle) pretreated by oxalate was evidently higher than the control. The decrease of xanthophyll cycle pool, chlorophyll and carotenoid content, and the later period decrease of (A+Z)/(V+A+Z) during high temperature stress was inhibited by oxalate pretreatment. These results suggested that oxalate has a protective role against the damage of photosynthetic apparatus during high temperature stress.

Key words: Cucumber, Oxalate, High temperature stress, Photosynthesis, Chlorophyll fluorescence, Xanthophyll cycle