| Cadmium,as a heavy metal,has seriously polluted soil and water,and has posed a serious threat on the ecological environment and human health.Thus,the mechanisms of cadmium toxicity to plants and phytoremediation soil polluted by heavy metal have been drawn on a worldwide attention from human society.However,the precise mechanisms of how can extra-nitrogen alleviate the toxic symptom of plant caused by Cd are still unknown.The early study showed that adding appropriate nitrogen in nutrient solution can obviously enhance the development of pant and reverse the toxic effect of heavy metal on poplar plants.In order to probe into the mechanism of nitrogen on plant under Cd stress,the materials selected the "Populus.erlang shanensiscl.CN0728" poplar plants treated with cadmium,cadmium plus extra-nitrogen,respectively to analyze the relationship between nitrogen and poplar to cadmium accumulation.At the same time,to isolate the genes related to cadmium tolerance,the transcriptome sequence(RNA-Seq)will be utilized to detect the different expressional genes,which will lay a basis for understanding the detoxification mechanism of nitrogen to heavy metal stress in plant and further transferring genes.Result in the study is not only expected to enrich the theory of heavy metal biology,but provide a new idea and methodology to enhance the phytoremediation technology for heavy metal pollution.So it has an important scientific significance and practical value.The main findings are as follows:(1)Compared with CK,the growth of poplar was significantly inhibited under Cd treatment,the plant height and dry weight were decreased by 12.5%and 20.5%.After added nitrogen,plant height and dry weight were increased by 17.3%and 21.5%,which showed that extra-nitrogen could alleviate the toxic effects of poplar under cadmium stress.(2)After added nitrogen,cadmium content in soil was less than it under cadmium stress,the cadmium content decreased by 5.9 percent,while cadmium content of leaf and root was greater than it under cadmium stress significantly,the cadmium content increased by 62.6 percent and 98.4 percent,which showed that after adding nitrogen,poplar strengthened the enrichment of cadmium.(3)Cadmium inhibited poplar chlorophyll a,chlorophyll b,carotenoid,chlorophyll synthesis and photosynthetic pigments contents.While after added nitrogen,chlorophyll a,chlorophyll b,carotenoid and chlorophyll content were increased,photosynthetic pigments metabolism to speed up,and leaf color returned to normal.(4)Using illumine paired-end sequencing,approximately 48045828、46712688、46681202 and 48076990 clean reads were obtained in the treatment of CK、Cd、N+Cd and N.With the software SOAPaligner/SOAP2,we compared these clean reads with sequences of P.trichocarpa and analysed the different expression genes’ expression level between different-treatment samples.The results showed that 1355 genes were up-regulated,1945 genes were down-regulate between CK and Cd;581 genes were up-regulated,2638 genes were down-regulate between CK and N;1458 genes were up-regulated,1907 genes were down-regulate between CK and N+Cd;1498 genes were up-regulated,1240 genes were down-regulate between Cd and N+Cd.These different expression genes were mainly classified into 144 KEGG Pathway,and have 19 pathways related to heavy metals transport and cell detoxification,for example,plant hormone signal transduction、glutathione metabolism、ascorbate and aldarate metabolism、citrate cycle(TCA cycle)、cysteine and methionine metabolism、peroxisome、ABC transporters.After analysed different expression genes between Cd and N+Cd,we found that,After added nitrogen,the genes related to SOD、CAT、GPX、APX、GR、GPX were significantly up-regulated and some plant hormone(eg.tryptophan、zeatin、brassinosteroid)which can enhance the stress tolerance also significantly up-regulated.These results showed that extra-nitrogen can enhance the genes expression which related to cadmium tolerance and also lay a basis for further transferring genes. |
PDF Full Text Request