Hydrogen-rich Water Alleviates Excess Boron-induced The Inhibition Of Rice Seed Germination

Boron is an essential micronutrient for plants,which is involved in plant growth,protein synthesis and material transport.However,boron becomes toxic to plants when occurs in excess in the soil or being used in a wrong way due to its narrow scope.Therefore,it is an urgent problem to improve rice resistance and obtain an integrative understanding of the molecular mechanism to boron toxicity.In recent years,hydrogen gas(H2),has been considered to be a new gaseous signaling molecule which plays an important role in antioxidation in plants.We therefore speculated that H2 has a positive effects in alleviating the boron toxicity.In our experiments,we used the hydrogen-rich water(HRW)instead of the hydrogen gas and studied the alleviating mechanism of boron toxicity.The results are as follows:1.HRW promoted the germination and growth in rice,and enhanced the resistance to boron toxicity.Compared with the control group(treated with deionized water),the boron content in rice roots was obviously increased under high concentration of boron acid solution(10 mM H3BO3),and the similar tendencies occurred in the germination rate,shoot length,root length and the sugar content.In contrast,when pretreated with 50%HRW for 24 h,the expression of transport protein BOR1 in rice roots was inhibited,and the accumulation of boron element was slowed down.Also,the amylase activity and the sugar content in rice seeds were increased,so does the germination and growth.2.HRW alleviated boron toxicity during rice root growth by regulating the water condition,the methyl pectin enzyme(PME)activity and the expansion protein(EXP)expression.The expression of NIP2;1 and the total water content in rice were decreased under boron toxicity,while HRW alleviated the decrease of expression of NIP2;1,enhanced the water uptake capacity(WUC)in rice and increased the water condition.Meanwhile,excess boron stimulated the expression of PME genes(PME 11,PME 14 and PME 27)and enhanced the PME activity,besides increased the expression of EXP genes(EXPA1 and EXPB5),thus inhibiting the growth of rice roots.In contrast,HRW inhibited the corresponding gene expression and depressed the activity of PME,therefore alleviating boron toxicity during rice roots growth.3.HRW alleviated oxidative damage caused by boron toxicity in rice.The TBARS content was increased rapidly under excess boron,while HRW inhibited the expression of lipoxygenase gene(LOX)and LOX activity,thus depressing the TBARS content and alleviating the lipid peroxidation damage.Meanwhile,HRW increased the gene expression of antioxidant enzymes(superoxide dismutase,SOD;ascorbic acid peroxidase,APX;catalase,CAT;and peroxidase,POD),enhanced the activity of antioxidant enzymes,and therefore alleviating the oxidative damage caused by boron toxicity.