The Uptake And Accumulation Characteristics Of Heavy Metals And Expression Of Cd Stress Response Genes In Ramie(Boehmeria Nivea(L.)Gaud.)

With the development of mining, industry and agriculture, heavy metals pollution becomes more and more serious, and has threatened soil ecosystem, agricultural production and human health seriously. Phytoremediation is attracting interest and attention from governments and enterprises technique as a potentially engineering-economical, cost-effective, and green to clean up heavy metal from polluted soil.Ramie (Boehmeria nivea(L.) Gaud.), also named "China grass", is an important source of cellulose-rich natural fibres(bast fibres) which has anti-stress ability, rapid growth and higher biomass. Ramie's primary purpose is making clothing, culturing ramie could minimizes the potential hazard of bringing toxic metals into food chains. It is significative to renovate heavy metals from contaminated soil with ramie due to its high accumulation and high economic value.In this study, heavy metal concentrations and bioaccumulation of ramie growing on 3 mining areas in Shimen, Lengshuijiang and Liuyang of Hunan Province were analyzed. Then, pot and field experiments were carried out to investigate the Cd tolerance of 9 ramie varieties, screen the tolereance index and analyse the capacity of ramie varieties to absorb Cd from contaminated soil. At the last, expression of Cd stress response genes were researched using solexa sequencing. The main results are as follows:1.Heavy metal concentrations and bioaccumulation of ramie growing on mining areasSoils from realgar mine area(Shimen) was heavily contaminated by As, while soils from antimony mine area(Lengshuijiang) was highly contaminated by Sb, and Qibao mountain area(Liuyang) was mainly contaminated by Cd. Ramie from these 3 sites grew well in different metal-contaminated habitats. In these 3 sites, Cd, As, Sb concentrations in ramie were 2-10,9.9-147.5,1.2-338 times higher than that in other plant species, respectively. And Sb, As concentration in ramie leaves were higher than that in roots and stems. Cd, As concentrations in ramie shoot were significantly correlated to Cd, As concentration in soil respectively. While Pb, Sb, Zn and Cu concentration in ramie shoot was not significantly correlated to Pb,Sb,Zn and Cu concentration in soil. Among these samples, the highest bioaccumulation factor(BF) and transfer factor(TF) of Cd were 2.07 and 3, those of As were 1.04 and 12.42, and those of Sb were 1.91 and 9.04,respectively. The total accumulations of Cd, Pb, As, Sb, Zn and Cu in these ramie samples were reached 0.11,1.17,0.72,7.97,6.71 and 1.69 kg/hm2 respectively. Ramie is a good candidate for phytoremediation of mining areas contaminated by multi-metals.2. Adaptability and tolerance evaluation of ramie varieties to CdHeight, diameter of stem, thickness of bark, biomass and chlorophyll of ramie were significantly reduced by Cd concentration in pot and field culture.Low Cd concentration enhanced the growth of some varieties of ramie, biomass of Shiqianzhugen,Yichun hongxin,and Chuanzhu No.1 which grown in Cd solution (46mg/L) were higher than that grown in control, biomass of Shiqianzhugen and Zhongzhu No.1 which grown on soil added with Cd(25mg/kg) were higher than that grown in control. The TI of Cd in ramie varies with varieties. The physiological and agronomic traits related to Cd tolerance of pot and field experiment were measured and analyzed, the results showed that screening ramie genotype by using height, biomass of shoot, biomass of root and chlorophyl of ramie grown in Cd solution as screening index would probably be an effective method to screen ramie genotype with high Cd tolerance. Nine ramie varieties were clusting 3 types by response to Cd, high-tolerance type, middle-tolerance and low-tolerance type.3. Uptake and accumulation of Cd in different ramie varietiesCd concentration in bark was significantly higher than that in other organs of ramie. When Cd concentrations were 23,46,91 and 182mg/L in solution respectively, Cd concentration in aboveground parts were 22.93,37.22,70.60 and 86.97mg/kg, which was significantly correlated to Cd concentration in solution. In field experiment, there were significant differences in Cd concentrations of aboveground part, under CK and Cd treatments(25,100mg/kg), Cd concentrations in shoot were 7.75,28.19 and 45.11mg/kg respectively. BF was decreased with the increase of Cd concentration. There were significance differences in Cd accumulation in shoot between Cd treatment and varieties. Two varieties were selected to renovate different pollution soil, Zhongzhu No.1 is fit for moderate contaminated soil by Cd(1-2mg/kg), Fushunqingma is fit for highly contaminated soil by Cd(25 and 100mg/kg). Nine varieties would class to four types by Cd concentration and tolerance:high-tolerance and low concentration, high-tolerance and high-concentration, low-tolerance and low-concentration, low-tolerance and high-concentration.4.Expression of Cd stress response genes in ramieTwo RNA libraries of Cd stress(100mg/kg) and control of ramie root were sequenced using solexa, and over 3.5 million short sequence reads were produced.3887 differently expressed genes of ramie root under Cd stress were selected referring to the significance of digital gene expression profiles. By blasting search to NCBI, we found most of differently expressed genes were unknown. The results of gene ontology functional enrichment analysis for differently expressed genes showed that main functions of these genes were binding and catalytic activity, and the main cell component which these genes enriched were plasma membrane and vacuole.The main pathways of these genes were glutathione metabolism and cysteine and methionine metabolism.