Identification of high levels of phytochelatins, glutathione and cadmium in the phloem sap of Brassica napus.: A role for thiol-peptides in the long-distance transport of cadmium and the effect of cadmium on iron translocation
Identification of high levels of phytochelatins, glutathione and cadmium in the phloem sap of Brassica napus.: A role for thiol-peptides in the long-distance transport of cadmium and the effect of cadmium on iron translocation
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DOI：
10.1111/j.1365-313x.2008.03410.x
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发表时间：
2008-04-01
期刊：
影响因子：
7.2
通讯作者：
Schroeder, Julian I.
中科院分区：
文献类型：
--
作者：
Mendoza-Cozatl, David G.;Butko, Emerald;Schroeder, Julian I.
植物螯合素(PC)是谷胱甘肽衍生的多肽，在植物和某些真菌中起着重金属解毒的作用。最近对拟南芥的研究表明，PC在根和茎之间进行长距离运输。然而，目前尚不清楚哪些组织或维管系统、木质部或韧皮部参与了PC的运输，以及PC运输是否有助于镉(Cd)在地上部和根之间的生理上的长距离运输。为了解决这些问题，从甘蓝型油菜中提取了木质部和韧皮部汁液，以定量分析哪些硫醇物种存在对Cd暴露的响应。结合质谱学和荧光高效液相色谱分析，在镉暴露的24小时内，韧皮部汁液中检测到高水平的PC。出乎意料的是，韧皮部汁液中的镉浓度是木质部汁液的四倍多。镉暴露显着降低了木质部和韧皮部汁液中的铁含量，而锌和锰等其他必需重金属的含量保持不变。数据表明，镉能抑制血管中铁的负荷，但不能抑制烟碱。韧皮部汁液中[PC]/[Cd]和[Glutathione]/[Cd]的高比值表明，PCs和谷胱甘肽(GSH)可以作为Cd的远程载体。相反，在木质部汁液中只检测到微量的PC。我们的结果表明，除了木质部Cd的定向运输外，韧皮部是Cd以PC-Cd和谷胱甘肽-Cd复合体的形式长距离源库运输的主要维管系统。
Phytochelatins (PCs) are glutathione-derived peptides that function in heavy metal detoxification in plants and certain fungi. Recent research in Arabidopsis has shown that PCs undergo long-distance transport between roots and shoots. However, it remains unknown which tissues or vascular systems, xylem or phloem, mediate PC translocation and whether PC transport contributes to physiologically relevant long-distance transport of cadmium (Cd) between shoots and roots. To address these questions, xylem and phloem sap were obtained from Brassica napus to quantitatively analyze which thiol species are present in response to Cd exposure. High levels of PCs were identified in the phloem sap within 24 h of Cd exposure using combined mass spectrometry and fluorescence HPLC analyses. Unexpectedly, the concentration of Cd was more than four-fold higher in phloem sap compared to xylem sap. Cadmium exposure dramatically decreased iron levels in xylem and phloem sap whereas other essential heavy metals such as zinc and manganese remained unchanged. Data suggest that Cd inhibits vascular loading of iron but not nicotianamine. The high ratios [PCs]/[Cd] and [glutathione]/[Cd] in the phloem sap suggest that PCs and glutathione (GSH) can function as long-distance carriers of Cd. In contrast, only traces of PCs were detected in xylem sap. Our results suggest that, in addition to directional xylem Cd transport, the phloem is a major vascular system for long-distance source to sink transport of Cd as PC-Cd and glutathione-Cd complexes.