Hydrogen-rich water pretreatment alters photosynthetic gas exchange, chlorophyll fluorescence, and antioxidant activities in heat-stressed cucumber leaves

Hydrogen gas (H-2) has recently been recognized as an important plant bio-regulator, inducing tolerance to several abiotic stresses. However, any role for H-2 in amelioration of high-temperature-induced stress remains largely unknown. We investigated the mechanism of hydrogen-rich water (HRW)-mediated enhancement of heat-tolerance in cucumber seedlings exposed to high-temperature stress. The 3 weeks seedlings were pretreated with 50 or 100% HRW for 7 days, the effects on photosynthesis, chlorophyll content, chlorophyll fluorescence parameters, electrolyte leakage, lipid peroxidation, and antioxidant activity were examined when cucumber seedlings subjected for 3 days to heat stress treatment. With respect to samples treat with high temperature stress alone, HRW pretreatment remarkably alleviated stress-induced effects on the above parameters. Furthermore, after 3 days of treatment, HRW pretreatment also significantly increased the activities of antioxidative enzymes, promoted high-level accumulation of osmoprotectants, and upregulated HSP70 expression in cucumber leaves. All of these data suggest that pretreatment with exogenous HRW partially alleviated the detrimental effects of high-temperature stress on the growth of cucumber seedlings by improving the photosynthetic capacity, increasing the antioxidant response, and promoting the accumulation of HSP70 and osmolytes. Therefore, HRW pretreatment may improve cucumber seedlings heat-tolerance.