Role Of Root Apoplast Barrier On Adaptation To Drought Stress Of Elymus Sibiricus

As the most important abiotic stress for the growth and development of forage grass,one of the strategies that plants adapt to water deficit is modifying root growth and architecture.A specialized cell layer in roots called endodermis,which has cell walls reinforced with apoplastic barriers formed by Casparian strip(CS)and suberin lamellae(SL)deposits,regulates radial nutrient transport,and protects the vascular cylinder against abiotic threats.Elymus sibiricus is one of important economic species of Elymus.It’s a dominant grass species suitable for artificial grassland establishment and natural grassland,based on the characteristic of fast growth,developed root system and drought resistance etc.In this study we reported the novel physiological roles of endodermal barriers in regulation of growth and drought tolerance of a Gramineous meso-xerophytic forage grass E.sibiricus,two E.sibiricus genotypes,a drought tolerant(DT)and a drought sensitive(DS)were grown hydroponically.The plants were subjected to osmotic stress(20%PEG 6000,～-0.8MPa)at 21 days.Fluorescence staining and gas chromatography-mass spectrometry(GC-MS)were used to analyze the development of apoplast barriers,the composition and content of suberin,the effects of apoplast barriers on water and nutrients transport in roots under osmotic stress were analyzed by measuring root hydraulic conductivity(Lp_r),apoplastic fluorescence tracer and ionomics;transcriptome sequencing and q RT-PCR were used to analyze the expression of apoplastic barriers related genes.So as to reveal the role of apoplast barriers in the adaptation of E.sibiricus to drought stress.The main experimental results are as follows:1.The study on root morphology and architecture of drought tolerant(DT)and drought sensitive(DS)under osmotic stress showed that the number of total root length,surface area and forks of DT and DS decreased under osmotic stress,and the decrease of DT was significantly higher than that of DS,indicating that the root length was maintained lower under osmotic stress root morphological characteristics such as surface area and more lateral root numbers,so as to maintain the ability of normal growth from plants,may be one of the important strategies in response to drought stress.2.The structures of suberin lamellae and Casparian strip of two E.sibiricus Germplasms in the control group and the treatment group were observed by root cross-section fluorescence staining.It was found that the root system of E.sibiricus had no exodermis,and DT formed apopplastic barriers early in the control group.Osmotic stress induced the early formation of DS in the treatment group,which had no significant effect on DT.Therefore,osmotic stress could induce the formation of root apoplast barriers.3.Using GC-MS analysis,found E.sibiricus root suberin composed mainly of aromatic,unsubstituted fatty acid,ω-hydroxy acids and?α,ω-dicarboxylic acids;under osmotic stress,the contents of DT monomers were significantly higher than DS.Osmotic stress could induce the content of suberin monomers,and DT was still significantly higher than DS after induction.Therefore,osmotic stress could induce the thickening of root apoplast barriers,and root apoplast barriers responded to osmotic stress more timely than the cuticle above ground.4.Through the root hydraulic conductance,apoplastic fluorescence tracing of solutes and ions content analysis in leaves,found the stronger and earlier formation of endodermal barriers decreased apoplastic bypass flow,but under osmotic stress,the sealed endodermal apoplast markedly limited the uncontrolled backflow of water from the root to the medium.Furthermore,under osmotic stress,the decreases in the accumulation of Na and Zn and increases in the accumulation of B,Mg,Al,K,Ca,Mn,Fe,Ni and Cu in the shoot were associated with apoplastic barriers formation.5.Through GO enrichment analysis,root differential genes were mainly involved in metabolic process,catalytic metabolism and cellular processes.KEGG pathway enrichment analysis,enrichment of root differentially expressed genes in 19 pathways,mainly involved in the global and overview maps,carbohydrate metabolism and genetic information processing,etc.The results of q RT-PCR showed that the 8 DEGs related to apoplastic barriers of root under osmotic stress in the different periods of differentially expressed results,most DEGs expression quantity increase under 24 h osmotic stress,showed that regulated genes of apoplastic barriers can enhance the and suberin increased under osmotic stress,resulting in increased plant drought resistance,to reveal the root apoplastic barriers in the E.sibiricus molecular response to drought stress.The above conclusions revealed that apoplast barriers in E.sibiricus adapt to drought stress play an important role.