The Regulation Of Jasmonic Acid In Response To Nitrogen In Rice Seedlings Roots

Rice is a kind of important food crops,in recent years,the improvement of rice yield largely relied on the application of nitrogen fertilizer.In China,the application of fertilizer is much higher than the world average,but the Ministry of Agriculture made up a program in 2015,to achieve the goal of zero growth in fertilizer in 2020.Therefore,it's necessary to investigate the effect of nitrogen on the establishment of root morphology and the influence of root morphology change on nitrogen uptake.Previous studies have shown that both nitrogen and Jasmonic acid can inhibit root elongation and promote root hair formation and elongation.But,the regulation mechanism of Jasmonic acid on rice seedlings root system response to nitrogen is not clear.With Wild type?WT,Oryza sativa.japonica?rice and its transgenic line COI1-RNAi?COI1 is Jasmonic acid receptor?as experiment material,we investigated the effects of ammonium and nitrate on the rice seedling root growth and the regulation of Jasmonic acid on rice seedling root growth response to nitrogen.The main results are as follows:1.Ammonium inhibits seminal roots elongation growth and promotes root hair growth in rice seedlings;nitrate had little effect on the elongation growth of seminal roots,but also promoted root hair formation and elongation in rice seedlings.In the experiment,rice seedlings were treated with different level of NH₄⁺ and NO₃^-,with the results as follows: low level?0.25 mM?of NH₄⁺ and NO₃^-both inhibit the elongation growth of seminal roots in rice seedlings at significant level?P<0.05?,and the inhibition rate of NH₄⁺ on root elongation growth?23.2%?was greater than that of NO₃^-?6.4%?;with the increase in nitrogen treatment concentration,the inhibitory effect of NH₄⁺ on the elongation growth of seminar roots is more and more obvious,while the inhibitory effect is no longer increase of NO₃^-on the elongation growth of seminar roots,the inhibitory rates of 4 mM NH₄⁺ and 4 m M NO₃^-on root elongation were 61.1% and 6.4% respectively.Both NH₄⁺ and NO₃^-promoted root hair formation and elongation.In certain concentrations?0-4 m M?,with the increase in nitrogen,the promotion effect on the growth of root hair is more and more obvious.2.The increase of Jasmonic acid content induced by NH₄⁺ enhances the absorption? transport and assimilation of ammonium;the increase of Jasmonic acid content induced by NO₃^-enhances the absorption ? transport and assimilation of nitrate.The rice seedlings were treated with 4 m M NH₄⁺ and 4 m M NO₃^-respectively,with the results as follows: Both NH₄⁺ and NO₃^-induced the expression of Jasmonic acid biosynthesis related genes,therefore promoting the biosynthesis of Jasmonic acid and increased Jasmonic acid content in the rice seedlings roots;NH₄⁺ enhanced the expression of ammonium uptake?transport and assimilation related genes,thereby promoting transport and assimilation of ammonium in the roots;NO₃^-enhanced the expression of nitrate uptake ? transport and assimilation related genes,thereby promoting transport and assimilation of nitrate in the roots.Treating the rice seedlings with 3 ?M IBU and NH₄⁺ simultaneously,the increase of Jasmonic acid content induced by NH₄⁺ was alleviated,the up-regulated expression of ammonium uptake?transport and assimilation genes was alleviated.Treating the rice seedlings with 3 ?M IBU and NO₃^-simultaneously,the increase of Jasmonic acid content induced by NO₃^-was alleviated,the up-regulated expression of nitrate uptake ? transport and assimilation genes was alleviated.3.The increase of Jasmonic acid content induced by NH₄⁺ enhances transition zone?one layer of cells which between the meristem zone and elongation zone?cell differentiation,then inhibits the meristem zone size,and leads a shorter root.The rice seedlings were treated with 4 mM NH₄⁺,with the results as follows: NH₄⁺ induced the increase of Jasmonic acid content in rice seedling roots;NH₄⁺ enhanced the expression of OsIAA3?The gene promotes transition zone cell differentiate into elongated cell?,then promoting transition zone cell differentiation;NH₄⁺ decreased the meristem size in root tip,only 48.5% of the control,thus resulting a short root.Treating the rice seedlings with 3 ?M IBU and NH₄⁺ simultaneously,the decrease of meristem size induced by NH₄⁺ was eliminated;the inhibition of root elongation growth induced by NH₄⁺ was eliminated.In addition,NH₄⁺ had little inhibitory effect on root elongation growth in COI1-RNAi rice seedlings compared with WT.The WT and COI1-RNAi rice seedlings were treated with 4 mM NH₄⁺ respectively,with the results shown as follows: The inhibition ratio of roots elongation growth by NH₄⁺ was 61.05% in WT,and 32.45% in COI1-RNAi;the expression of OsIAA3 was not enhanced by NH₄⁺,the size of the meristem was alleviated in COI1-RNAi.It's shown from the results that,NH₄⁺ induced the increase of Jasmonic acid level by enhance the Jasmonic acid biosynthesis in rice seedling roots,thereby promoting transition zone cell differentiation,reducing meristem size,and inhibiting root elongation growth.4.The increase of Jasmonic acid content induced by NH₄⁺ and NO₃^-enhances the expression of root hair formation and elongation related genes,thereby promoting root hair formation and elongation in rice seedling.The rice seedlings were treated with 4 m M NH₄⁺ and 4 mM NO₃^-respectively,the results show that: the Jasmonic acid content was increased in the roots;root hair formation and elongation related genes were up-regulated;root hair formation and elongation was promoted.Treated the rice seedlings with NH₄⁺ and NO₃^-respectively,adding 3 ?M IBU simultaneously,root hair formation and elongation induced by NH₄⁺ and NO₃^-was inhibited.In addition,compared with WT,the promotion of root growth induced by NH₄⁺ and NO₃^-were alleviated,and the expression of root hair formation and elongation related genes were not enhanced by NH₄⁺ and NO₃^-in COI1-RNAi rice seedlings.The results further confirmed that the growth of root hair is associated with Jasmonic acid.It's shown from the results that,NH₄⁺ and NO₃^-the increase of Jasmonic acid level by enhancing the Jasmonic acid biosynthesis in rice seedling roots,thereby enhancing the expression of root hair formation and elongation related genes,and promoting root hair formation and elongation.In this study,With Oryza sativa japonica and it's COI1-RNAi rice as experiment material,we found Jasmonic acid involved in the regulation of NH₄⁺ inhibiting the elongation growth of roots in rice seedling,and Jasmonic acid involved in the regulation of NH₄⁺ and NO₃^-inhibiting the formation and elongation growth of root hair in rice seedling.In-depth study found that NH₄⁺ promoted the expression of OsIAA3 by increasing the Jasmonic acid content in rice seedling roots,and enhanced transition zone cell differentiation,inhibited the meristem zone size,and inhibited root elongation growth in rice seedlings.NH₄⁺ and NO₃^-promoted the expression of root hair formation and elongation related genes by increasing the Jasmonic acid content in rice seedling roots,and promoted the formation and elongation of root hair.