Effects Of Epichlo(?) Bromicola Endophyte Infection On Cadmium Tolerance In Hordeum Brevisubulatum

In this study,wild barley（Hordeum brevisubulatum）infected（E+）and uninfected（E-）by Epichlo（?） bromicola were used for hydroponic experiments during the seedling stage.The effects of endophytic fungi on the growth and development of wild barley,the absorption of cadmium（Cd）and essential mineral elements（Ca,Mg,Fe,Mn,Cu,Zn）,subcellular distribution,and chemical forms were investigated under CdCl₂ stress.The study was aimed to provide a reference basis for the improvement of heavy metal polluted soil in northern mining areas by using H.brevisubulatum-E.bromicola symbionts as an ecological grass.The main research findings are:（1）Epichlo（?） endophyte infection showed varying degrees of impact on photosynthetic indicators such as transpiration rate,stomatal conductance,net photosynthetic rate,water use efficiency,and chlorophyll content of plants under Cd stress.Under 50μM Cd stress,the net photosynthetic rate and water use efficiency of E+plants were significantly higher than those of E-（P<0.05）,increasing by 72.01%and 42.80%,respectively.Similarly,under 100μM Cd stress,the transpiration rate and chlorophyll content of E+plants significantly increased by 97.20%and 12.82%（P<0.05）.Finally,under 50μM and 100μM Cd stress,the stomatal conductance of E+plants increased by 44.71%and 71.24%compared to E-plants（P<0.05）.（2）It was found that Epichlo（?） endophyte infection had different effects on the distribution of Cd,subcellular cells of plants,and the content and distribution proportion of Cd in six chemical forms in different parts.The distribution of Cd in wild barley was root>stem>leaf.Under 50μM and 100μM Cd stress,the Cd content in the stems of E+plants was significantly higher than that of E-（P<0.05）,which was 33.52%and 17.45%higher,respectively.The Epichlo（?） endophyte infection had the most significant effect on the distribution of Cd in subcellular components in roots.The concentration sites of Cd were soluble components（40.47%～70.33%）>cell walls（19.24%～30.45%）>organelles（10.43%～29.08%）in order of proportion.The proportion of Cd in organelle components of root showed that E+was significantly higher than E-（P<0.05）,while the content and proportion of soluble component Cd increased with the increase of stress concentration,showing that E+was significantly lower than E-（P<0.05）.Chemical forms analysis results showed that the inorganic state(F_Ethanol)was combined and water-soluble state（FH₂O）dominated in plant leaf and root,while stems in various form was relatively uniformly distributed.Under 50μM and 100μM Cd stress,the Cd contents of pectin acid or protein chelate(F_NaCl)in stems and FH₂O in roots of E+plants were significantly lower than of E-（P<0.05）,and the Cd content of F_NaCl in roots was significantly lower than that of E-（P<0.05）under 100μM Cd stress The content of F_Ethanol+FH₂O+F_NaCl in the roots of E+plants was significantly lower than that of E-（P<0.05）,with a decrease of25.04%and 24.60%.（3）Epichlo（?） endophyte infection had different effects on essential mineral elements,including content in plant,subcellular distribution and chemical morphology.Also,it showed significant effects on Ca,Fe and Mn in various parts of plant.For instant,under 100μM Cd stress,Ca content and its proportion in roots of E+plants were significantly lower than of E-（P<0.05）,decreased by 34.08%and25.92%.While,the content of Fe and Mn was in contrast,with E+plants having a19.25%and 45.72%higher body content than E-plants,and roots having a 55.38%and 121.35%increment than E-plants（P<0.05）.The Epichlo（?） endophyte infection significantly reduced the positive correlation between Ca-Fe and Ca-Mn in roots（P<0.01）.In subcellular distribution,Epichlo（?） endophyte infection had significant effects on soluble components in stems and roots;Under 100μM Cd stress,the contents of Fe,Mn and Cu in the soluble components in the stems of E+plants were significantly higher than those of E-plants（P<0.05）,with an increase of 555.82%,626.67%and 106.71%respectively.Meanwhile,the contents of Ca,Mg,Mn,Cu and Zn in the roots of E+plants were significantly higher than those of E-plants（P<0.05）,with an increase of 341.17%,246.39%,111.62%,91.48%and 68.18%respectively.Epichlo（?） endophyte infection significantly decreased the negative correlation of soluble components Cd-Cu,Cd-Ca and Cd-Mg in root（P<0.01）.In chemical morphology analysis,the Epichlo（?） endophyte effectively increased the Ca,Mg,Fe,Mn,Cu contents of F_NaCl in stems（P<0.05）,with an increase of 58.06%,83.72%,193.80%,417.81%,328.19%under 100μM Cd stress,respectively.The endophyte infection reduced the correlation between Cd and mineral elements in F_NaCl of stems.The above research results indicated that endophytic fungi can regulate the content,distribution and existing forms of Cd and essential mineral elements,so that wild barley can keep healthy growth while accumulating more Cd²⁺,showing strong cadmium tolerance.