Effects Of Phytohormones Assisted With EDDS On Cd And Pb Accumulation And Tolerance Mechanisms In Ramie

Cadmium(Cd) and lead(Pb) are highly toxic heavy metals, which can be taken up by plants, and further enter into the food chain. Compared to the traditional physical and chemical methods, phytoextraction is proposed as an environmentally friendly in situ remediation technique to maintain soil fertility and structure. However, the efficiency of phytoremediation is low due to limited metal immobilization in soil. Chelate-enhanced phytoremediation has been proposed by using chelant to improve the efficiency of phytoextration.Mature ramie has the high potential for the remediation of metal-contaminated soil, due to their large biomass and root system. In our country, ramie was harvested each year 2-3 season, and it is a kind of non-food crops, can cut off with the channels of the food chain enter human body, to eliminate the harm to human body. In this study, we selected ramie as goal plant, Cd and Pb as goal contaminant, biodegradable EDDS as soil additives and phytohormones as exogenous substances, aiming to investigate the effects of indole-3-acetic(IAA), kinetin(KN), and spermidine(Spd)assisted with EDDS on metal accumulation and tolerance mechanisms in ramie.In the first stage, the optimum concentrations of IAA, KN, and Spd were determined by analyzing the change of ramie physiological indexes(including the root length and shoot height?root activity?chlorophyll content?SOD activity and POD activity) under Cd and Pb compound stres s. The main results and discussions are as follows:Compared to the control, the root length and shoot height of the Cd/Pb treatment decreased to 54.1% and 42.4%, respectively, the root activity of ramie decreased by approximately 50%, and the SOD activity of ramie leaves decreased by 25.9%. However, the ramie grows well when spray 10?M IAA, 100 ?M KN or 100 ?M Spd on the leaves of ramie. The root length and shoot height ?root activity?chlorophyll content?SOD activity and POD activity reached the peak of IA A, KN and Spd each treatment, respectively. The results demonstrated that the optimum concentrations of IAA, KN, and Spd were 10 ?M, 100 ?M, and 100 ?M, respectively.In the secondary stage, the optimum concentrations of EDDS were determined by analyzing the change of ramie physiological indexes(including the ramie dry weight ?chlorophyll content and proline content) ?the uptake and distribution of heavy metals in ramie and the soil enzyme activity(including urease and catalase) under Cd and Pb compound stress. The main results and discussions are as follows:Compared to the control, the dry weight of shoots of the Cd/Pb treatment decreased from 3.62 g/pot to1.47 g/pot, the dry weight of roots of ramie decreased from1.86 g/pot to1.02 g/pot. The proline content of ramie leaves increased significantly, approximately 2.3 times than the control. When treated with 5 mmol/kg EDDS, the translocation factor(TF) of ramie for Cd and Pb was highest( 0.294 for Cd and 0.263 for Pb). The metal contents in roots, stems and leaves were 675.50, 324.50 and 72.88 mg/ kg DW for Cd, 992.50, 465.00 and 57.00 mg/ kg DW for Pb, respectively. The ramie dry weight ?chlorophyll content?proline content and the soil enzyme activity were approximately equal to the Cd/Pb treatment. On the whole, 5 mmol/kg EDDS increased the TF and phytoremediation efficiency of ramie, and had little influence for the physiological indexes and soil enzyme activity. The results demonstrated that the optimum concentrati on of EDDS was 5 mmol/kg.In the last stage, the effects of optimum exogenous substances assisted with EDDS on metal accumulation and tolerance mechanisms in ramie were determined by analyzing the uptake and distribution of heavy metals in ramie ?the change of MDA content?the activity of antioxidant enzyme(SOD ?POD and APX) and non-enzymatic antioxidant(GSH) under Cd and Pb compound stress. Determine the best combination of phytoremediation at the same time, in order to achieve the practical application of phytoremediation technology and efficient remediation of large area of soil heavy metal pollution in our country to provide theoretical reference and data support.The main results and discussions are as follows:The T7 treatment had the highest Cd and Pb contents in stems of ramie(434.75 mg kg-1dw for Cd and 639.25 mg kg-1dw for Pb). Both Cd and Pb in the roots of ramie were largely distributed in the apoplast, indicating that the nonselective apoplastic uptake dominated the translocation of Cd and Pb. EDDS dramatically increased the contents of Cd and Pb in the symplast. IAA, KN and Spd combined with EDDS slightly increased MDA content with respect to the Cd/Pb treatment. IAA, KN, and Spd assisted with EDDS could enhance the contents of antioxidant enzyme s and non-enzymatic antioxidant. Compared to T2 treatment, IAA, KN and Spd combined with EDDS decreased MDA content, and increased the SOD activity and GSH content. The results demonstrated that IAA, KN, and Spd assisted with EDDS could be applied to improve the bioremediation efficiency of Cd and Pb contaminated soils, and KN assisted with EDDS had the best effect of phytoremediation.