Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom.
Plant Physiol. 2010 Apr;152(4):2211-21. doi: 10.1104/pp.109.150862. Epub 2010 Feb 3.
Complexation of arsenite [As(III)] with phytochelatins (PCs) is an important mechanism employed by plants to detoxify As; how this complexation affects As mobility was little known. We used high-resolution inductively coupled plasma-mass spectrometry and accurate mass electrospray ionization-mass spectrometry coupled to HPLC to identify and quantify As(III)-thiol complexes and free thiol compounds in Arabidopsis (Arabidopsis thaliana) exposed to arsenate [As(V)]. As(V) was efficiently reduced to As(III) in roots. In wild-type roots, 69% of As was complexed as As(III)-PC4, As(III)-PC3, and As(III)-(PC2)2. Both the glutathione (GSH)-deficient mutant cad2-1 and the PC-deficient mutant cad1-3 were approximately 20 times more sensitive to As(V) than the wild type. In cad1-3 roots, only 8% of As was complexed with GSH as As(III)-(GS)3 and no As(III)-PCs were detected, while in cad2-1 roots, As(III)-PCs accounted for only 25% of the total As. The two mutants had a greater As mobility, with a significantly higher accumulation of As(III) in shoots and 4.5 to 12 times higher shoot-to-root As concentration ratio than the wild type. Roots also effluxed a substantial proportion of the As(V) taken up as As(III) to the external medium, and this efflux was larger in the two mutants. Furthermore, when wild-type plants were exposed to l-buthionine sulfoximine or deprived of sulfur, both As(III) efflux and root-to-shoot translocation were enhanced. The results indicate that complexation of As(III) with PCs in Arabidopsis roots decreases its mobility for both efflux to the external medium and for root-to-shoot translocation. Enhancing PC synthesis in roots may be an effective strategy to reduce As translocation to the edible organs of food crops.
亚砷酸盐 [As(III)] 与植物螯合肽 (PCs) 的络合是植物解毒 As 的重要机制；这种络合如何影响 As 的迁移性知之甚少。我们使用高分辨率电感耦合等离子体质谱和精确质量电喷雾电离质谱与 HPLC 相结合，鉴定和定量了暴露于砷酸盐 [As(V)] 的拟南芥 (Arabidopsis thaliana) 中 As(III)-硫醇络合物和游离硫醇化合物。As(V) 在根中被有效还原为 As(III)。在野生型根中，69%的 As 与 As(III)-PC4、As(III)-PC3 和 As(III)-(PC2)2 络合。谷胱甘肽 (GSH) 缺陷突变体 cad2-1 和 PC 缺陷突变体 cad1-3 对 As(V)的敏感性比野生型高约 20 倍。在 cad1-3 根中，只有 8%的 As 与 GSH 络合形成 As(III)-(GS)3，未检测到 As(III)-PCs，而 cad2-1 根中，As(III)-PCs 仅占总 As 的 25%。这两个突变体具有更高的 As 迁移性，在 shoot 中积累了更多的 As(III)，且 shoot-to-root As 浓度比野生型高 4.5 至 12 倍。根还将吸收的相当一部分 As(V) 作为 As(III) 排出到外部介质中，并且在两个突变体中这种排出量更大。此外，当野生型植物暴露于 l-丁硫氨酸亚砜或缺乏硫时，As(III)的外排和根到茎的转运都增强。结果表明，拟南芥根中 As(III)与 PCs 的络合降低了其向外部介质外排和向根到茎转运的迁移性。增强根中 PC 的合成可能是减少 As 向食用作物可食器官转运的有效策略。
