Glycolate Oxidase Is Involved In The Formation Of Iron Plaque On Rice Roots Under Alternative Wetting And Drying Condition

The rhizosphere oxidants and root oxidation ability were reported to influencetheironplaque?IP?formation.The formation of IP on the root surface is a biologically mediated process.As an effective water-saving irrigation technology,alternative wetting and drying?AWD?can improve rhizosphere oxidationenvironment and induce IP formation.However,the effect of AWD on IP formation and its possible mechanism were not clear.In this study,we studied theeffectof AWD on IP formation of rice and explored the relationshipbetweent glycolate oxidase?GLO?,hydrogen peroxide?H₂O₂?and IP formation in this process.The results were as follows.1.Cmpared with continuous flooding?CF?,AWD one time significantly increased the DCB-Fe content of Zhonghua11 rice root by 25.4%.Furthermore,the reddish brown iron plaque?RIP?was increase by 63.0%while there was no difference between non-reddish brown iron plaque?NRIP?.Energy spectrum analysis showed that the content of iron and oxygen on the root surface was increased after AWD treatment.2.AWD one time increased the root GLO activity by 84.1%,and its shoot catalase?CAT?activity was 39.6%of CF.Further analysis of GLO expression revealed that AWD enhanced the expression of OsGLO3and OsGLO4in base root,OsGLO1?OsGLO3and OsGLO5in root apex.3.Treatment with?-hydroxy-2-pyridinemethanesulfonic acid?HPMS?treatment inhibited GLO activity and reduced RIP content by 50.2%,while glycolic acid?GLC?raised GLO activity by 88.9%and IP content by 33.3%;4.Exogenous addition of 600?mol/LH₂O₂ rasied the IP content by 51.4%.Inhibition of CAT activity increased root H₂O₂ and IP content by 33.1%and 30.6%respectively,while a H₂O₂ scavenger dimethylthiourea?DMTU?reduced it.5.With overexpression of OsGLO4,its GLO and CAT activity was 270.3%and 59.2%of those of WT under CF conditon.However,there was no difference between WT and OX under AWD condition.6.The H₂O₂ content in base rootand root apex of OX was 150.0%and 132.6%of WT.Interestingly,the distribution of H₂O₂ in the epidermal cells was consistent with the spatial distribution of IP on root surface.AWD increased root H₂O₂ content of WT,and had no significant effect on OX.But the H₂O₂content of OX was always higher than WT.7.After re-wetting for 48 h,the rhizosphere Eh of WT and OX under AWD conditon was 40.9%and 46.3%higher than that of CF,and the rhizosphere Eh of OX was 13.1%higher than WT.The dissolved oxygen content of AWD treatment was significantly higher than that of CF,and WT and OX were increased by 1.06 mg/L and 0.68 mg/L,respectively.8.The IP content on rice root surface of OX was significantly higher than that of WT,no matter it was CF or AWD treatment.Compared with CF,the RIP content of WT and OX under AWD condition were increased by 57.5%and 36.1%,respectively.Results with X-ray diffraction analysis indicated that OX had a higher proportion of Fe^III compoundin IP in comparison to WT.Meanwhile,AWD also could increase the proportion of Fe^III in IP.Taken together,our findings suggested that AWD could regulate the expression of glycolate oxidase gene,increase GLO activity,promote the root H₂O₂ accumulation,improve the content of rhizosphere oxidants,and then induce more Fe²⁺oxidation on the root surface to increase IP content.