Response Mechanism Of Alfalfa-arbuscular Mycorrhizal Association To Atrazine Stress

Arbuscular mycorrhiza(AM)fungi can promote the nutrients absorption,the levels of phosphorus,nitrogen and mineral nutrients of host plant,and also effectively enhance the tolerance of plant to abiotic stress factors.Meanwhile,researchers have gradually paid attention to the ability of AM fungi to efficient bioremediation in organic contaminated soil.However,the bioremediation mechanism of herbicide atrazine was not very clear because of complexity in AM fungi and host plant association.In this study,Funneliformis mosseae,including the spores,mycelia and mycorrhizal fragments were used as AM fungi inoculum.Medicago sativa was used as host plant.In pot experiment,the symbiotic system of F.mosseae associated with M.sativa was established and then atrazine was applied.The aim of this study was to reveal the responses mechanism of AM fungi associated with alfalfa to atrazine stress.The main results were as follows:1.F.mosseae alleviated the toxicity of atrazine to chloroplast function and structure.Inoculation of F.mosseae decreased the inhibition of atrazine on net photosynthesis and stomatal conductance Fv/Fm and PSII performance of M.sativa under atrazine stress.Inoculation of F.mosseae increased the level of Chl a,Chl b and carotenoid.In addition,inoculation of F.mosseae increased the number of plastoglobules and better grana stacking in chloroplasts.It was suggested that.mosseae prevents injury to the photosystem reaction centers of host plant M sativa.In addition,the profile of photosynthesis-related proteins in leaves of M sativa were constructed,which is beneficial to further reveal the mechanism of mitigating phototoxicity of atrazine on M sativa by.mosseae at protein level.2.F.mosseae significantly changed the composition and level of root metabolites under atrazine stress.F.mosseae significantly decreased the level of indole and its derivatives(p<0.05);although F.mosseae significantly decreased the level of jasmonic acid(p<0.05),jasmonic acid derivatives(methyl 7-epi-12-hydroxyjasmonate glucoside)significantly increased(p<0.05);D-proline and the majority of dipeptides significantly increased by F.mosseae(p<0.05);inoculation of F.mosseae significantly increased the non-enzymatic antioxidants tocotrienol,(iso)flavonoids and their derivatives in M.sativa roots(p<0.05),which increased in the form of methylation and glycosylation.It was suggested that F.mosseae promotes the level of some metabolites and antioxidant capacity in host plant M.sativa root.3.F.mosseae changed the species of host plant root exudates.In this study,the components of root exudates were identified in hydroponic conditions combined with resin adsorption,desorption and concentration.Octanoic acid was found to be a specific exudate produced by M.sativa roots inoculated with.mosseae,which may be the result of AM fungi exudation.It was suggested that F.mosseae changed the species of root exudates,which may have effect on rhizosphere bacterial community.4.F.mosseae changed the rhizosphere bacterial community during atrazine dissipation.Detection of atrazine metabolites by bacteria in rhizosphere soil showed that bacteria played an important role in atrazine dissipation by AM.At the level of family and genera of bacteria,F.mosseae significantly reduced Shannon’s index,and further significantly decreased the process of atrazine dissipation(p<0.05).However,atrazine significantly inhibited the evenness of bacterial community(p<0.01).During atrazine dissipation,inoculation of F.mosseae increased the relative abundance of atrazine-degrading bacteria Arthrobacter,Burkholderia,Mycobacterium and Streptomyces,but also decreased the relative abundance of Nocardioides,Pseudomonas,Bradyrhizobium and Rhizobium and so on.In addition,inoculation of F.mosseae enhanced the activities of soil dehydrogenase(DHA),urease(URE),acid phosphatase(ACP)and alkaline phosphatase(ALP).It was suggested that F.mosseae changes the rhizosphere bacterial community and enhances soil enzyme activities.5.F.mosseae hypha changed the abundance of atrazine-degrading genes in the rhizosphere.In this study,atrazine triazine degrading genes combination is atzBCDEF,E6.3.4.6 and ureA/ureB/ureAB/ureC.F.mosseae hypha increased the abundance of atzF and E6.3.4.6.Atrazine side-chain degrading genes combination is eutA/eutB/eutC.F.mosseae hypha increased the abundance of eutB,It was suggested that F.mosseae hypha increase the abundance of genes coded key enzymes in atrazine degradation pathway of bacteria.It was further confirmed that atrazine-degrading bacteria participated in atrazine dissipation by AM.In general,above results of this study further improved the theoretical basis of AM fungi for atrazine-contaminated soil remediation,and provided scientific evidence for AM fungi to remediate other type contaminated soil.