| Hydrogen is the simplest and abundant element in the universe.Hydrogen gas was considered have no biological activity in vivo.But t has been identified recently 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 or cadmium stress in Arabidopsis and alfalfa seedlings(Jin et al.2012;Xie et al.2012).Root growth inhibition is the most rapid effects of Al on plant function.Because Al is so reactive,there are many potential sites for injury,including:(A)the cell wall,(B)the plasma membrane,(C)signal-transduction pathways,(D)the generation of ROS,and(E)DNA/nuclei.Damage of these potential sites may cause various inhibitions on plant growth.Currently studies about HRW mainly focused on the root 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,photosynthetic characteristics and Al-induced oxidative damage is unclear.Therefore,we measured the generation and clean-up of ROS,the content of chlorophyll and analyzed the nutrient content of maize seedlings and the stability of photosynthetic apparatus under Al 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 Al-stressed maize seedlings.The results showed that HRW had a significant concentration-dependent effect on plant height,chlorophyll content(SPAD),and root elongation.Meanwhile the response of 75%concentration of HRW was the most obvious.The determination of gas exchange parameter,chlorophyll a fluorescence parameter and activities of Rubisco&PEPC reflected that a certain concentration HRW could promote photosynthetic rate and activities of Rubisco&PEPC.With respect to samples treated with Al stress alone,exogenous H2 cotreatments differentially attenuated the damage of photosynthetic apparatus by Al stress.We assumed that this might be one of the important factors for HRW to protect photosynthetic apparatus and thus promote photosynthetic rate in maize seedlings.To investigate the mechanism of HRW-mediated increased tolerance to Al stress in maize(Zea mays L.)seedlings,plants under A1 stress were cotreated with different concentrations of HRW and 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 peroxidase(POD)were examined.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 POD.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 and proteins such as various enzymes from A1 stress through mitigating oxidation enabled by a high level of antioxidative enzyme activities.Further more,we investigated the effects of HRW on nutrient elements and Al content in Al stressed maize seedlings.Plants were cotreated with Al and different concentrations of HRW and the content of Ca,P,K,Mg,Fe,Mn and Al of these samples were measured.A general promotion of nutrient uptake as well as A1 content was discovered,indicating that exogenous H2 significantly alleviated the inhibition of Al-induced nutrient uptake.Meanwhile,compare with that in A1 stressed seedlings alone,the increase of A1 and nutrient content in Al and HRW cotreated seedlings indicating that H2 may improve the cation uptake ability of maize roots. |
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