| Lead contamination has become a major environmental concern over the past several decades. Pot experiment and hydroponic culture were conducted to investigate the effect of EDTA on Pb uptake and accumulation of high biomass plants such as Maize and Mustard. In addition, the mechanism of this induction of chelate uptake and accumulation was pointed out preliminary in this study.Application of EDTA to the Pb-contaminated soils significantly increased the exchangeable Pb concentration of soils, affected the seedling growth, decreased the total transpiration of Maize. However, the contents of Pb in the shoots of Maize and Mustard were effectively improved. The highest shoot Pb content of Maize and Mustard was 3000 and 11900μg/gDW respectively. These contents were 35-fold and 336-fold higher than the controls (no EDTA application). Under all EDTA treatments, shoot Pb contents of Maize were higher than those of Mustard. Lengthing treatment could lead to increased shoot Pb cotents of the two plants. There was a close positive correlation between the contents of Pb and EDTA in the shoots of Maize and Mustard, showing that Pb was translocated in the plants as the Pb-EDTA complex.Hydroponic cultures showed that Pb and EDTA treatments could inhibitate the growth of Maize and Mustard. Root growth was more sensitive to Pb and shoot growth was more sensitive to EDTA when biomass was considerated. When Maize and Mustard were exposed Pb without EDTA, the two plants retained most Pb in their roots and only minimal were transported to the shoots. Compared with Mustard, when the concentration of Pb in the hydroponic system was identical, Pb contents in the shoots of Maize were heavilyhigher, But it was on the contrary as far as the roots were concerned. Pb contents in plantroots and shoots increased with increasing Pb concentration in solution and lengthening treatment time. When the two plants were treated with 500μM Pb and EDTA, the contents of Pb in the shoots were highly improved, the translocation of Pb from stems to leaves was increased too. Of the two plants, Mustard was more sensitive than Maize. A close positive correlation can be seen between the contents of Pb and root cells electrolytic leakage of Maize and Mustard when treated with Pb alone. Meanwhile, shoot Pb contents were positively correlated to shoot EDTA contents when the two plants were treated with Pb withthe addition of EDTA.Maize and Mustard were pretreated with MC solution, 0.1M HC1 or 60-70℃ water, which coule effectively benefit the Pb translocation to the shoots. When Mustard was treated with 500μM Pb+EDTA solution, Ca, Mg, Mn and Zn contents in the roots and shoots were reduced, shoot Fe contents were increased.The distribution of elements was analysed in Maize and Mustard using energy-dispersive X-ray microanalysis of frozen-dry tissuses. The distribution of Pb in Maize root showed phloem cell>xylem cell=cortical cell>epidermal cell when treated with 500μM Pb without EDTA. However, Pb was observed only in epidermal cell and cortical cell in Mustard root. Compared with the treatment of 500μM Pb without EDTA, the addition of 250μM EDTA could lead to an increase of Pb content in epidermal cell and cortical cell. The contents of Pb in phloem cell decreased and Pb was not found in xylem cell. On the other hand, Pb contents in epidermal cell and cortical cell increased. The distribution of Pb was observed in phloem cell and xylem cell . Pb contents were in the order of cortical cell>epidermal cell>phloem cell>xylem cell. Increasing the concentration of EDTA to 3000μM, the distribution of Pb was not found in all cells. The percentage of Ca, K and P in total inorganic ions could be changed when the plants were treated with Pb and EDTA.With transmission electron microscopy, ultrastructural observations were carried out on ultra-thin sections derived from Maize and Mustard. In root tissues, treated with 500μM Pb without EDTA, the structures of endodermis cell and stelar cell were affected slightly. The distribution of Pb could...
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