| The symbiotic phenomenon of arbuscular mycorrhizae(AM)is ubiquitous in terrestrial ecosystems.This mutual benefit symbiotic relationship can increase host plant tolerance to many stress conditions(nutrients,drought,heavy metals,and pH,etc.),to improve the growth status of the host plant.In this study,the arbuscular mycorrhizal fungi(AMF)were inoculated with tomato(Solanum lycopersicum)under soil conditions of pH 4.5 and pH 6.5,and exogenous application of phytohormone abscisic acid(ABA)and auxin(IAA)to investigate the regulation of AM symbiosis by two hormones and their effects on the development and function of arbuscules.The main results are as follows:1.The low pH significantly reduced the fresh weight of the shoot and the root of tomato,and the root-shoot ratio increased significantly.Compared with the non-inoculated AMF treatment,the biomass of tomato plants treated with AMF increased at both pH conditions.2.Exogenous application of ABA and sodium tungstate treatment(ABA biosynthesis inhibitor)reduced the tomato plant biomass compared to the clear water control,and the extent of the biomass reduction of the tomato plants treated with exogenous ABA was reduced Larger,but compared with exogenous application of ABA and no treatment with AMF,exogenous application of ABA and inoculation with AMF increased the biomass of tomato plants,which was more pronounced at pH 6.5,reaching a significant level.The pH,AMF and exogenous ABA had significant effects on the biomass of tomato plants(p<0.05).3.Under both pH conditions,exogenous application of IAA increased the biomass of tomato plants compared to the control of clear water,and application of TIBA(IAA polar transport inhibitor)reduced tomato plant biomass.pH,AMF and exogenous IAA had significant effects on tomato plant biomass(p<0.05).4.The low pH significantly inhibited the formation of arbuscules.Exogenous application of ABA increased the infection rate(F%)and the colonization intensity(M%)of AMF to tomato host compared to the clear water control.The application of sodium tungstate inhibited infection rate(F%),colonization intensity(M%)and arbuscule abundance(A%)of AMF to the tomato host.Exogenous application of IAA increased the infection rate(F%),colonization intensity(M%),and arbuscule abundance(A%)of AMF to tomato host.Addition of TIBA also promoted the infection of AMF to tomato host,but The abundance of arbuscules significantly decreased.5.Under both pH conditions,exogenous application of ABA increased the content of ABA in tomato roots compared with that of clear water control,and application of sodium tungstate reduced the content of ABA in tomato roots.At the same pH,the content of ABA in tomato roots inoculated with AMF was lower than that in the corresponding non-inoculation treatment,but it did not reach a significant level.The content of IAA in tomato roots inoculated with AMF was higher than the corresponding non-inoculation treatment.Exogenous application of IAA did not significantly affect the content of IAA in tomato roots.The application of TIBA increased the content of IAA in tomato roots.6.Under both pH conditions,the ABA synthesis genes(LeNCED1 and LeNCED2)and ABA receptor genes(SlPYL1,SlPP2C7,and SlSnRK2.5)were up-regulated in the roots of AMF-inoculated tomato plants treated with exogenously applied ABA compared to the clear water controls.The expression of LeNCED1,SlPYL1,SlPP2C7,and SlSnRK2.5 was down-regulated during the application of sodium tungstate treatment;Under both pH conditions,the expression of LePT4 was reduced in exogenous ABA and sodium tungstate treatment compared to the clear water control,but the application of sodium tungstate treatment was reduced more.7.Under two pH conditions,exogenous application of IAA to the auxin receptor gene Sl-TIR1 was down-regulated in the inoculated AMF tomato roots compared to the corresponding water controls,and the treatment with TIBA applied increased the expression of Sl-TIR1;At pH 4.5,the strigolactone biosynthetic genes(Sl-MAX1,Sl-D27,and Sl-CCD8)in the tomato root were consistent with the Sl-IAA27 expression pattern,but at a pH of 6.5 The pattern of expression of the three synthetic genes is opposite to Sl-IAA27.Under both pH conditions,Sl-miR393,which has a negative regulatory effect on mycorrhiza,was down-regulated in exogenously applied IAA treatment compared to the corresponding water control,and upregulated in TIBA treatment;Compared with pH 6.5,the relative expression level of Sl-HA8,a gene related to arbuscule formation,was lower at pH 4.5. |
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