Effects Of Endophytic Fungus On Roots Physiology And Molecular Mechanism Of Citric Acid Metabolism In Rice Seedling Exposed To Aluminum Stress

In recent years,the content of Al³⁺in the soil has seriously exceeded the standard with the continuous increase of acidic soils.A large amount of Al³⁺inhibits the growth of crop roots,which in turn leads to reduced crop yield and quality.In the present study,rice seedlings were infected with endophytic fungus High Y1-1.Different concentrations of AlCl₃（0,40μM,80μM,120μM）solutions were added to the rice seedlings inoculated with 5%fermentation broth（E+,endophyte-infected seedlings）or not（E-,endophyte-non-infected seedlings）respectively.The growth index,physiological index,citrate synthase gene,multi-drug toxic compound exhaustion family transporter（MATE）gene and plasma membrane H⁺-ATPase gene expression of rice seedlings were measured.The purpose of this study was to investigate the effects of endophytic on ameliorating the negative effects of Al³⁺stress on the growth of rice seedlings.The main results are as follows:1.Aluminum stress inhibited the growth and development of rice seedlings.Plant height,root length,dry matter mass and total root length were reduced.Root surface area and diameter were increased.Root tips were short and thick.The number of root tips was reduced.Compared with E-group,the plant height,root length and dry matter accumulation were increased with endophytic infection.Except for the average diameter of the root system,root morphological parameters were increased.Both the above-ground and underground parts were ameliorated.2.Under Al³⁺stress,the aluminum content in leaves and roots of rice seedlings increased with the increase of aluminum concentration.Endophytic infection significantly recduced the aluminum content in leaves and roots exposed to 120μM AlCl₃.3.Under low concentration aluminum stress,SOD and POD activities were increased compared to the control,but not under high concentration aluminum stress;the activity of CAT continued to decrease.The content of MDA continued to increase.MDA content was reduced and the activities of SOD,POD and CAT of roots were increased with inoculation endophytic fungus.4.In the E-group,the content of eight organic acids and the total organic acid content were increased compared with the control at the beginning exposed to Al³⁺stress.But the organic acid content showed inconsistent trends in the middle and late periods;In the E+group,the citric acid content and the total organic acid content（except the 120μM AlCl₃ treatment on the 6th day）were significantly increased compared to the E-.5.Plasma membrane H⁺-ATPase activity of rice roots was increased at low concentrations of aluminum stress,but not in high concentrations of AlCl₃.Plasma membrane H⁺-ATPase activity was increased with endophytic infection under low concentration stress.6.OsCS3,OsCS4,OsFRDL4,OSA1,OSA2,OSA4,OSA6,OSA7,OSA8,and OSA9 gene expressions were up-regulated under low concentration aluminum stress,but not under high concentration aluminum stress.Citrate synthase genes OsCS3 and OsCS4 were up-regulated with endophytic infection.The expression of MATE gene OsFRDL4 was up-regulated under high concentration aluminum stress.The plasma membrane H⁺-ATPase gene OSA2 was up-regulated under Al³⁺stress.The expressions of OSA7,OSA3,OSA5,OSA8 and OSA9 were up-regulated.