Physiological And Molecular Mechanism Of Soil Polybrominated Diphenyl Ether Pollution On Tobacco Toxicity

In order to reveal the response and adaptation mechanism of plants to organic pollutants polybrominated diphenyl ethers(PBDEs),physiological and transcriptomic techniques were used to study the effects of 2,2’,4,4’-tetra-bromodiphenyl ether(BDE47)and 2,2’,3,3’,4,4’,5,5’,6,6’-decabromodiphenyl ether(BDE209)exposure on tobacco plant growth,effects of chlorophyll synthesis and photosynthetic function.Also intensive research the response mechanisms of oxygen species(ROS)metabolism,proline metabolism,synthesis of some hormones abscisic acid(ABA)and jasmonic acid(JA)signal transduction.The results show that:(1)Both BDE47 and BDE209 exposure inhibited the growth of tobacco plants.In the transcriptome data,6866 and 5951 differentially expressed genes(DEGs)were identified under BDE47 and BDE209 exposure,respectively.The number of down-regulated DEGs under BDE47 exposure was significantly higher than that under BDE209 exposure,the effect of BDE47 on tobacco gene expression was greater than that of BDE209.(2)KEGG enrichment analysis showed that BDE47 and BDE209 mainly affected tobacco leaf photosynthesis-antenna proteins(map 00196),plant hormone signal transduction(map 04075),photosynthesis(map 00195),α-linolenic acid metabolism(map 00500)and other processes.Although both BDE47 and BDE209 lead to the decrease of chlorophyll(Chl)content,BDE47 mainly inhibits the synthesis of Chl a,and BDE209 exposure has a greater impact on Chl b.Most photosynthesis related DEGs were concentrated in PSⅡ and PSⅠ,the number of down-regulated DEGs in PSⅠ was significantly higher than PSⅡ,and the reduction range of PSⅠ activity was also higher than PSⅡ,that is,PSⅡ and PSⅠ(especially PSⅠ)were sensitive to BDE47 and BDE209 exposure in photosynthetic.The increase of the ratio of regulatory energy dissipation played an important protective role in alleviating PSⅡ photoinhibition.(3)BDE47 and BDE209 stress can lead to the accumulation of reactive ROS in tobacco leaves,but correspondingly,the activities of glutathione peroxidase(GPX),peroxidase(POD),catalase(CAT),superoxide dismutase(SOD),ascorbic acid peroxidase(APX),and the up-regulated expression of their coding genes play an important role in preventing excessive oxidative damage in tobacco leaves.(4)BDE47 and BDE209 stress also promoted the up regulation of the expression of genes related to the synthesis of proline(Pro)in tobacco leaves,especially the pro synthesis process of ORN pathway was promoted,while the Prodegradation related proline dehydrogenase gene(ProDH)was inhibited,that is,the accumulation of Proplayed an important role in the adaptation of tobacco leaves to PBDEs.(5)BDE47 and BDE209 exposure induced up-regulated expression of genes promoted the synthesis of ABA and JA,activated ABA and JA signal transduction pathways.In conclusion,both BDE47 and BDE209 inhibit the synthesis of chlorophyll and hinder the process of light energy capture and electron transfer in tobacco leaves,and the toxic effect of BDE47 is greater than that of BDE209.However,tobacco leaves can also adapt to BDE47 and BDE209 by regulating antioxidant system,accumulating Proand initiating hormone signal transduction process.The results of this study provide a theoretical basis for the phytotoxicity mechanism of PBDEs and potential phytoremediation.