The Alleviating Effect Of Exogenous Arachidonic Acid On Cadmium Toxicity In Brassica Juncea

Cadmium(Cd)pollution in soil is a widely concerned environmental issue.Cd in soil not only affects the growth and development of plants,but also threatens human health via the food chain.Brassica juncea has the characteristics of enriching Cd and has potential application in phytoremediation of Cd-contaminated soil.Therefore,some measures that alleviate the toxic effect of Cd on B.juncea has important application value.Arachidonic acid(ARA)is an unsaturated fatty acid and plays an essential role in the signaling network of stress and defense in plants.However,the effect of ARA on Cd stress tolerance in B.juncea is currently unclear.In this paper,we studied the alleviative effect of Cd toxicity in B.juncea by exogenous ARA,and its physiological and molecular mechanisms.The experimental results were as follows:1.The alleviating effect of exogenous ARA treatment on Cd toxicity in B.juncea.(1)Effects of different concentrations of Cd(0,25,50,100,200,and 400 mg/Kg)on the growth of B.juncea.The results showed that low concentration of Cd had no significant effect on the growth of B.juncea.When the concentration of Cd reached 200 mg/Kg,the growth of B.juncea was significantly inhibited.Compared with the control group,the biomass(shoot dry weight,root dry weight,and plant height),photosynthetic pigment contents(chlorophyll a,chlorophyll b,carotenoids,and total chlorophyll),and relative activity and relative conductivity of leaves cells of B.juncea showed significantly different.(2)The effects of different concentrations of ARA(0,0.1,1,10,and 100μM)on the biomass,photosynthetic pigment contents,relative activity of leaves cells,and relative conductivity of B.juncea under Cd(200 mg/Kg)stress were analyzed.The results showed that when the concentration of ARA was 10μM,the alleviating effect on Cd toxicity of B.juncea was the best.2.Effects of exogenous ARA on growth and antioxidantsystem of B.juncea under Cd stress.This experiment consists of four treatments,namely CT group(control group),Cd group(200 mg/Kg Cd treatment),and ARA group(10%μM ARA treatment),and Cd+ARA group(treated with 200 mg/Kg Cd and 10 μM ARA).The results showed that the growth of B.juncea was inhibited under Cd stress,while it was relieved following exogenous ARA application.Exogenous ARA increased of biomass,leaves cells relative activity,and photosynthetic pigment contents,decreased ROS(H2O2,O2-,and MDA),relative conductivity,and Cd accumulation contents,enhanced antioxidant enzymes activities:Superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbic acid peroxidase(APX),and glutathione reductase(GR),as well as increased non-enzymatic antioxidants contents:Reduced ascorbic acid(ASA),oxidative ascorbic acid(DHA),and reduced glutathione(GSH).3.Effect of exogenous ARA on gene expression profile in B.juncea leaves under Cd stress.Transcriptome sequencing and analysis of differentially expressed genes(DEGs)were performed in the four treatment groups(CT,ARA,Cd,and Cd+ARA).A total of 419 DEGs were identified in the Cd-vs-Cd+ARA group,of which 308 DEGs were up-regulated and 111 DEGs were down-regulated.The results of GO enrichment analysis indicated that the DEGs were enriched in the regulation of anthocyanin biosynthesis,cell wall,pectate lyase activity,and flavonol biosynthesis.The KEGG enrichment analysis results showed that the DEGs were enriched in photosynthesisantennal protein,photosynthesis,flavonoid biosynthesis,porphyrin and chlorophyll metabolism,flavonoid and flavonol biosynthesis,and glutathione metabolism.Eight DEGs were randomly selected to verify the transcriptome data by qRT-PCR,and the experimental results were basically consistent with the transcriptome data.