| Hydrogen is the simplest and abundant element in the universe.It has been identified as an important bio-regulator in plants.Further results revealed that H2 could act as an important gaseous molecule with multiple biological functions in plant responses against salinity-induced and paraquat-induced oxidative stress in Arabidopsis and alfalfa seedlings(Jin et al.2012;Xie et al.2012).It is well-known that the growth and development of plant is strongly influenced by the quality and amount of absorbed light.But when the amount of absorbed light exceeds the amount required for photosynthesis,the excess light can be harmful because it causes the production of reactive oxygen species(ROS).The accumulation of ROS leads to lipid peroxidation,the cell membrane damages,and consequently inhibits the photosynthesis,respiration and plant growth.Currently studies about HRW mainly focused on the root or the seed germination to explore the mitigation effects of HRW on abiotic stress in Arabidopsis,rice seeds,alfalfa,etc.However,whether H2 has a special effect on the growth and photosynthetic characteristics of maize seedlings and on the high light-induced oxidative damage is unclear.Therefore,we measuredg the generation and clean-up of ROS,the content of chlorophyll and analyzed the effects of HRW on the development of maize seedlings and the stability of photosynthetic apparatus under high irradiance stress.In our study,we used maize seedlings cultured with normal Hoagland's solution as control,and explored the effects of different concentrations of HRW(25%?50%?75%?100%)on the growth and photosynthesis of maize seedlings.The results showed that HRW had a significant concentration-dependent effect on plant height,chlorophyll content(SPAD),and fresh weight.Meanwhile the response of 50%concentration of HRW was the most obvious.The determination of stomatal density and opening degrees reflected that a certain concentration HRW could promote the development of stomata,such as increasing the stomatal density and promoting the stomatal opening.We assumed that this might be one of the important factors for HRW to promote photosynthetic rate in maize seedlings.To investigate the mechanism of HRW-mediated increased tolerance to high light stress in maize(Zea mays L.)seedlings,Plants were supplied with different concentrations of HRW and the chlorophyll fluorescence parameters(Fv/Fm?PIABS?RC/CS?Vk?1-Vj?DI/RC),the levels of superoxide radical(O2·-),hydrogen peroxide(H2O2)and the degrees of the oxidative damage to the membrane lipids,the activities of several antioxidative enzymes such as superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidase(APX)and glutathione reductase(GR)under high light stress were examined.With respect to samples treated with high light stress alone,exogenous H2 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 H2 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 O2·-and H2O2 as well as the content of thiobarbituric acid reactive substances.Taken together,our results suggested that exogenous H2 treatment could protect the photosynthetic apparatus from photo-damage through mitigating photo-oxidation enabled by a high level of antioxidative enzyme activities. |
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