Protective effects of hydrogen-rich water on the photosynthetic apparatus of maize seedlings (Zea mays L.) as a result of an increase in antioxidant enzyme activities under high light stress

Hydrogen gas (H-2) is an endogenous gaseous molecule in plants. Although it is recently described as an important bio-regulator in plants, the role of H-2 in high light stress amelioration is largely unknown. This study investigated the mechanism of hydrogen-rich water (HRW)-mediated enhancement of tolerance against high light stress of maize (Zea mays L.) seedlings. Maize seedlings were supplied with different concentrations of HRW and its effects on the plant growth, the chlorophyll fluorescence parameters, the activities of several antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), the levels of superoxide radical (O-2 (-)), hydrogen peroxide (H2O2) and the degrees of the oxidative damage to the membrane lipids under high light stress were examined. With respect to samples treated with high light stress alone, exogenous H-2 pretreatments differentially attenuated the damage of photosynthetic apparatus by high irradiance. Further results showed that concentration-dependent effects of HRW were shown in stressed maize seedlings. Exogenous H-2 supplement could elevate the activities of antioxidative enzymes, including SOD, CAT, APX, and GR. These results were confirmed by the alleviation of oxidative damage, as indicated by a decrease of the level of O-2 (-) and H2O2 as well as the content of thiobarbituric acid reactive substances. Taken together, our results suggested that exogenous H-2 treatment could protect the photosynthetic apparatus from photo-damage through mitigating photo-oxidation enabled by a high level of antioxidative enzyme activities.