| Phytoremediation is defined as the use of plants to decontaminate and/or remove pollutants from the environment. It has emerged as an alternative technique for removing toxic metals from soil and offers the benefits of being in situ, cost-effective and environmentally sustainable Plants with high metal uptake and accumulation capacity have been termed as hyperaccumulator species. At present, more than 450 species of hyperaccumulators belonging to 45 families have been identified. Unfortunately, most of them are low biomass and slow growing, severely limiting their potential for large-scale decontamination of polluted soils. Transferring the genes conferring the hyperaccumulating phenotype to plants that produce more shoot biomass and metal accumulation capacity has been suggested as a potential approach for making phytoremediation a viable commercial technology. However, progress towards this goal has been hindered by a lack of understanding of the basic biochemical, physiological, and molecular mechanisms involved in heavy metal hyperaccumulationSedum aljredii Hance has been identified as a new Zn-hyperaccumulating plant species native to China. We have found two contrasting ecotypes of Sedum aljredii Hance. One is a Zn/Cd hyperaccumulator designatured as the hyperaccumulating ecotype (HE) from the old mined area, while another is a non-hyperaccumulator designatured as non-hyperaccumulating ecotype (NHE) from the agricultural area of Hangzhou surburb, Zhejiang Province of China. In this study, solution culture experiment, soil culture experiment and simulation experiment were carried out to characterize Zn activation, uptake and transport in Sedum aljredii Hance by means of a series of chemical, biochemical methods, such as radiotracer techniques, AAS for elements determination, organic acid quantitation determined with HPLC, and so on. The major results were summarized as follows:1. Heavy metal uptake was enhanced in hyperaccumulator ecotype of Sedum aljredii Hance by increasing the contact area between soot and soil. Root length, root surface-area and root volume increased obviously due to 1000 umol L-1 Zn and/or 200/500 umol L-1 Pb/Zn combined treatments for the HE, whereas significantly decreased due to 200 μmol L-1Pb, 1000 μmol L-1Zn or Pb/Zn combined treatment for the NHE. Zinc and Pb concentrations in both ecotypes of Sedum aljredii Hance were positively correlated with root length, root surface area and root volume 1000 μmol L-1Zn and/or 200/1000 umol L-1 Pb/Zn combined treatments had little impact on root activity of the HE. Root activity of HE decreased by 200 umol L-1 Pb treatment in the first 2 days, but recovered afterwardsand close to the control at day 10 of the treatment. However, root activity of the NHE decreased by each metal treatment, and was not recovered with the advance of treatment time. Zn concentrations in the leaves and stems of the HE were 41 and 34 times higher, whereas lead concentrations were 1.9 and 2.4 times greater respectively, than those of the NHE when grown at 1000 μmol L-1 Zn and/or 100 μmol L-1 Pb. At combined supply of 500/100 μmol L-1 Zn/Pb, however, zinc concentrations in the stems and leaves of the HE decreased, while lead concentrations in the stems increased significantly, as compared with those of single metal treatment. Lead uptake of the HE was enhanced by Zn addition.2. Zn treatments had little impact on root activity of the HE, however, root activity of NHE decreased significantly when Zn concentration > 10 μmol L-1. Relatively conductance ratio of cell membrane and MDA concentration in NHE increased with increasing of Zn level in the solution. SOD activity of NHE was decreased significantly when Zn concentration > 50 μmol L-1. Cell membrane, MDA concentration, SOD activity, and proline concentration in root of HE were not correlated with Zn concentration in shoot and root of HE. Minimal linear relationships between root activity, SOD activity and Zn concentration in shoot and root of NHE were observed, however, MDA and pro...
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