The Zn Accumulation Characteristic Of Dark Septate Endophyte (DSE,Exophiala Pisciphila) In Vivo And In Vitro And The Mechanism Of DSE Enhanced Maize Seedling Tolerance To Zn Stress

Dark septate endophytes(DSEs)are a group of endophytic fungi that can be cultivated and frequently colonize the roots of plants.It is found that DSE inoculation could obviously enhance host plant tolerance under HM stress,such as improved biomass and decreased HM's concentrations in the maize(Zea mays)shoot.However,the character of DSE's Zn accumulation in vivo and in vitro as well as the functional role of DSEs in their host plant growing in metal stressed environments is still to be elucidated.In this study,a DSE strain(Exophiala pisciphila,H93)isolated from a mine,which has a strong tolerance to heavy metals,was cultured under Zn stress to investigate its character of Zn accumulation,the distribution of Zn in the subcellular structure,and Zn concentrations of different chemical forms.The inoculation effect of H93 on the biomass of maize seedlings was evaluated under Zn stress.The accumulation of Zn in the shoots and roots of maize seedlings,the distribution of Zn in the subcellular structure,and Zn concentrations of different chemical forms were analyzed to insight into the mechanism of the enhanced HM(Zn)tolerance of maize by H93 inoculation.The main results are as follows:1.DSE(H93)could successfully colonize the maize roots and develop the typical DSE structures.The colonization intensities increased with the elevated Zn concentration in the culture solution.Inoculation of H93 in the roots of maize increased maize tolerance to Zn.2.Maize seedlings certainly absorbed and accumulated Zn.Moreover,with the increase of Zn concentration in the culture solution,the Zn accumulation in maize seedlings(shoot and root)increased.Inoculation with DSE couldn't alter this trend,but significantly reduce Zn uptake by maize seedlings under Zn stress.3.Comparing with the Zn accumulation characteristics in H93 mycelia in vitro,under Zn stress,the Zn accumulation in H93 mycelia decreased,and the proportion of low poisonous Zn and Zn in cell wall increased when H93 was cultured in vivo.4.The concentration of Zn in maize subcellular distributions all significantly increased with elevated Zn whether H93 was inoculated or not.Also,H93 inoculation significantly increased the proportion of Zn in the cell wall of maize seedling shoots and roots under Zn stress.Besides,the proportion of Zn in high poisonous forms in maize seedling shoots and roots decreased with H93 inoculation under Zn stress.Results of the research showed that,DSE culturted in vivo had a more accumulation of Zn.DSE in vivo accumulated more Zn in cell wall,while the poisonous Zn concentration and proportion in DSE decreased.H93 inoculation improved maize seedling tolerance to Zn.The biomass of maize seedlings was significantly increased by H93 inoculation.The involved mechanisms for these results may be that the extraradical mycelia of H93 reduce the absorption of Zn by maize,thus limited the accumulation of Zn in maize,H93 changed the subcellular distribution patterns and chemical forms of Zn in maize seedlings,and more Zn was accumulated in the cell wall of maize thus further released the excessive Zn stress to maize,and all of these together enhanced the tolerance of maize to Zn stress.