The Study On The Effects Of Al Toxicity In Two Salicylic Acid Arabidopsis Thaliana Mutants NahG And Npr1-1 Cultivars

Aluminum in acidic soil has an important impact on the development of plant root.Al toxicity was the major hazard to the suppression of the root apex growth.A1 toxicity is alleviated by organic acid efflux in plant root.The membrane lipid perdoxidation can be induced by reactive oxygen species(ROS)in Al stress.Al-induced ROS is cleaned by antioxidant systems enzymes and nonenzymatic groups in plant.Recently,the study of exogenous SA alleviating aluminum stress were increasing..However,there is no report of effect of SA on Arabidopsis under Al stress.In the study,two salicylic acid(SA)mutant of Arabidopsis nahG(SA lower than wild type)and nprl-1(SA higher than wild type)were used as the plant materials.We have investigated and discussed the effect of Al stress on the physiological biochemistry and genes express of the two mutants.The aim of the thesis is to reveal the potential molecular mechanism which SA alleviated Al toxicity in Arabidopsis plant.The main results are as follows:1.The results showed that the roots elongation of wild type(col),nahG,and nprl-1 were all remarkably suppressed by 300 ?mol/L Al treatment.the order of inhibition rate of roots elongation were nahG>col>nprl-1.The inhibition on root elongation of nahG under 300?mol/L Al stress was alleviated by low level SA(20,50,80,and 100?mol/L),which was most pronounced by 100?mol/L SA Afte npr1-1 was exposed to various concentrations of PAC(paclobutrazol,the inhibtor of SA synthesis),the inhibition of roots elongation were increased with the increase of PAC concentrations,which was most noticeable by 50?mol/L PAC treatment.Al tolerance of Arabidopsis was related to endogenous SA;and the root elongation inhibition induced by Al was alleviared by SA.2.With the treatment of 300?mol/L Al,the exudation of organic acid of both wild type and mutants,as well as the activities of SOD,POD and CAT were increased significantly.Exogenous 100?mol/L SA significantly increased the exudation of organic acid and the activities of SOD and POD in nahG under Al stress.It was observed that the exudation of organic acid and the activities of SOD and POD of npr1-1 under Al stress were reduced by 50?mol/L PAC Those results suggested that SA alleviated Al toxicity by increasing the exudation of organic acid and the activities of antioxidant enzymes(SOD and POD).3.The expression of ALMT1(Aluminum-activated Malate Transporter 1)and MATE(Aluminum-activated Citrate Transporter)in two mutants was increased in 300?mol/L Al stress,And the expression of ALMT1 and MATE of nahG were further increased under Al stress after 100?mol/L SA treatment.However,the expression of ALMT1 and MATE of npr1-1was suppressed by PAC under Al stress.It was suggested that Al-induced the exudation of organic acid may be relate to increased expression of ALMT1 and MATE.There was no changes of the expression of 14-3-3 and HA5 coding H+-ATPase in nahG regardless of SA treamtment.The expression of GF14mu,GF14phi chain,GF14chi and HA5 of npr1-1 in SA plus Al treatment were markedly increased,which would be suppressed by PAC.Results of Co-immunoprecipitation showed that the interaction of 14-3-3 protein with H+-ATPase,the activities of H+-ATPase and H+ pump were obviously increased by exogenous SA.And Al stress induced interaction of 14-3-3 protein and H+-ATPase,the activities of H+-ATPase and H+ pump in npr1-1,which can be suppressed by PAC.Thus,we infer that SA maybe increased the exudation of organic acid through improving interaction of 14-3-3 protein with H+-ATPase as well as the activity of H+ pump.4.The results of comparative analysis of RNA-seq showed that there were 357 up-regulated genes and 118 down-regulated genes in nahG under Al stress;and there were 911 up-regulated genes and 4320 down-regulated genes in npr1-1.In addition,it was observed that the expression of genes coding 6-phosphogluconate dehydrogenase and glucose-6-phosphate 1-dehydrogenase were decreased by Al3+.The expression of reactive oxygen scavenging system(GSSG/GSH)was also depressed,resulting in increased oxidative stress in nahG.The genes coding glutathione peroxidase(GPX),glutathione S-transferase(GST)and gamma-glutamyl transpeptidase/glutathione hydrolase(GGT)were up-regulated leading to reactive oxygen scavenging of GSH increased.There was nonenzyme group besides antioxidant enzyme system which alleviated Al toxicity.