Vassil AD, Kapulnik Y, Raskin I, Salt DE
Plant Physiol. 1998 Jun;117(2):447-53. doi: 10.1104/pp.117.2.447.
Indian mustard (Brassica juncea) plants exposed to Pb and EDTA in hydroponic solution were able to accumulate up to 55 mmol kg-1 Pb in dry shoot tissue (1.1% [w/w]). This represents a 75-fold concentration of Pb in shoot tissue over that in solution. A threshold concentration of EDTA (0.25 mm) was found to be required to stimulate this dramatic accumulation of both Pb and EDTA in shoots. Below this threshold concentration, EDTA also accumulated in shoots but at a reduced rate. Direct measurement of a complex of Pb and EDTA (Pb-EDTA) in xylem exudate of Indian mustard confirmed that the majority of Pb in these plants is transported in coordination with EDTA. The accumulation of EDTA in shoot tissue was also observed to be directly correlated with the accumulation of Pb. Exposure of Indian mustard to high concentrations of Pb and EDTA caused reductions in both the transpiration rate and the shoot water content. The onset of these symptoms was correlated with the presence of free protonated EDTA (H-EDTA) in the hydroponic solution, suggesting that free H-EDTA is more phytotoxic than Pb-EDTA. These studies clearly demonstrate that coordination of Pb transport by EDTA enhances the mobility within the plants of this otherwise insoluble metal ion, allowing plants to accumulate high concentrations of Pb in shoots. The finding that both H-EDTA and Pb-EDTA are mobile within plants also has important implications for the use of metal chelates in plant nutritional research.
在水培溶液中暴露于铅和乙二胺四乙酸（EDTA）的印度芥菜植株，其地上部干组织中能够积累高达55 mmol·kg⁻¹的铅（1.1%[w/w]）。这意味着地上部组织中铅的浓度是溶液中铅浓度的75倍。发现需要0.25 mmol的EDTA阈值浓度来刺激地上部中铅和EDTA的这种显著积累。低于该阈值浓度时，EDTA也会在地上部积累，但速率降低。对印度芥菜木质部渗出液中铅与EDTA的复合物（Pb - EDTA）进行直接测量证实，这些植物中的大部分铅是与EDTA配位运输的。还观察到地上部组织中EDTA的积累与铅的积累直接相关。将印度芥菜暴露于高浓度的铅和EDTA会导致蒸腾速率和地上部含水量降低。这些症状的出现与水培溶液中游离质子化EDTA（H - EDTA）的存在相关，这表明游离H - EDTA比Pb - EDTA的植物毒性更强。这些研究清楚地表明，EDTA对铅运输的配位作用增强了这种原本不溶性金属离子在植物体内的移动性，使植物能够在地上部积累高浓度的铅。H - EDTA和Pb - EDTA在植物体内都具有移动性这一发现，对于在植物营养研究中使用金属螯合物也具有重要意义。
