Traits And Gene Expression In Vicia Faba L. Of Different Generations Under Continuous Lead Pollution

Lead is common and highly toxic heavy metal.The previous studies have investigated an acute influence of short-term Pb pollution,but the long-term continuous effects of plant traits among different generations under Pb stress change and related gene expression have not been systematically reported.We selected the fourth,eighth,tenth,thirteenth and fifteenth generation seeds of broadbean harvested from the continuous Pb stress in 250 mg·kg~-11 Pb polluted field as experimental material and compared them with unpolluted broadbean of same generation using potted method.From three aspects including morphological and quantitative traits,physiological and biochemical indexes and transcriptional level,the differences in the early development of broadbean seedlings were analyzed and compared.We explored the ecological differentiation of plants under the long-term sustainable lead stress,and analyzed the adaptation mechanism of plants to lead continuous pollution and the response mechanism of plants to long-term persistent pollution.The results are as follows:(1)Continuous long-term Pb stress significantly inhibits the growth and development of broadbean.With the increase of pollution generation,plant height and root length present the tendency to rise first and then decrease.And the result of each pollution generation was significantly lower than that of the same generation in control group.In the 13th generation,the height of the broadbean plant was reduced to a maximum,which decreased by 26.00%compared with the same generation in control group.In the fourth generation,the root length decreased to a maximum,which decreased by 10.54%compared with the same generation in control group.(2)The chlorophyll content associated with the photosynthetic capacity of broadbean was decreased with the increase of the stress time,but it was still lower than that of the control group under the long-term continuous Pb stress.The content of soluble sugar,protein,MDA,PRO and SOD,GR and MDH in antioxidant enzyme system were all higher than that in the control group,and showed a trend of decreasing and gradually stabilizing.(3)By sequencing the transcriptomes of different generations of broadbean under long-term continuous Pb stress,a large number of differentially expressed genes were obtained.And corresponding gene and metabolic pathways were obtained by performing GO and KEGG annotation on the differential gene sequences respectively.The items enriched in the notes are mainly stress response,redox process,sugar metabolism process,cell wall?membrane?oxidoreductase activity,metal ion binding,ATP binding,etc.;KEGG annotation enriched items are mostly secondary Synthesis of metabolites(such as phenylalanine metabolism,phenylpropanoid biosynthesis),metabolic pathways(such as starch and sucrose metabolism,carbon metabolism)and signal transduction pathways(such as ion binding,MAPK signal transduction pathways)and so on.(4)We selected 12 genes involved in the synthesis of secondary metabolites and related to signal transduction from the obtained differential genes and analyzed five generations of broadbeans under long-term continuous Pb stress using real-time fluorescence quantitative PCR analysis.The results showed that,the up or down regulation of 12 genes was consistent with the results of transcriptome sequencing.The expressions of differential genes in different generations during the early period of stress changed significantly.Some of them increased.Some decreased.And they produced some stress.With the extension of stress time,the expression level gradually changed to the opposite trend,and the expression level became stable after the 15th generation.(5)The changes in expression of differential genes under long-term continuous stress are the same as changes in growth and physiological indicators under long-term stress;there are several differentially expressed genes involved in metabolic pathways such as redox,glucose,and carbon metabolism at the transcriptome level.These differentially expressed genes were all related to tolerance to Pb long-term stress in broadbeans.It is believed that under long-term continuous Pb stress,the adaptability of the broadbean population to Pb stress is continuously enhanced,microevolution may happen.