Song Won-Yong, Mendoza-Cózatl David G, Lee Youngsook, Schroeder Julian I, Ahn Sang-Nag, Lee Hyun-Sook, Wicker Thomas, Martinoia Enrico
POSTECH-UZH Cooperative Laboratory, Department of Integrative Bioscience and Biotechnology, Pohang University of Science and Technology, Pohang, 790-784, Korea.
Plant Cell Environ. 2014 May;37(5):1192-201. doi: 10.1111/pce.12227. Epub 2013 Dec 8.
Cadmium (Cd) and arsenic (As) are toxic to all living organisms, including plants and humans. In plants, Cd and As are detoxified by phytochelatins (PCs) and metal(loid)-chelating peptides and by sequestering PC-metal(loid) complexes in vacuoles. Consistent differences have been observed between As and Cd detoxification. Whereas chelation of Cd by PCs is largely sufficient to detoxify Cd, As-PC complexes must be sequestered into vacuoles to be fully detoxified. It is not clear whether this difference in detoxification pathways is ubiquitous among plants or varies across species. Here, we have conducted a PC transport study using vacuoles isolated from Arabidopsis and barley. Arabidopsis vacuoles accumulated low levels of PC2 -Cd, and vesicles from yeast cells expressing either AtABCC1 or AtABCC2 exhibited negligible PC2 -Cd transport activity compared with PC2 -As. In contrast, barley vacuoles readily accumulated comparable levels of PC2 -Cd and PC2 -As. PC transport in barley vacuoles was inhibited by vanadate, but not by ammonium, suggesting the involvement of ABC-type transporters. Interestingly, barley vacuoles exhibited enhanced PC2 transport activity when essential metal ions, such as Zn(II), Cu(II) and Mn(II), were added to the transport assay, suggesting that PCs might contribute to the homeostasis of essential metals and detoxification of non-essential toxic metal(loid)s.
镉（Cd）和砷（As）对包括植物和人类在内的所有生物都有毒性。在植物中，Cd和As通过植物螯合肽（PCs）和金属（类金属）螯合肽进行解毒，并通过将PC-金属（类金属）复合物隔离在液泡中来实现。在As和Cd解毒之间已观察到一致的差异。虽然PCs对Cd的螯合在很大程度上足以使Cd解毒，但As-PC复合物必须被隔离到液泡中才能完全解毒。目前尚不清楚这种解毒途径的差异在植物中是否普遍存在，还是因物种而异。在这里，我们使用从拟南芥和大麦中分离的液泡进行了PC转运研究。拟南芥液泡积累的PC2-Cd水平较低，与PC2-As相比，表达AtABCC1或AtABCC2的酵母细胞囊泡表现出可忽略不计的PC2-Cd转运活性。相比之下，大麦液泡很容易积累相当水平的PC2-Cd和PC2-As。钒酸盐可抑制大麦液泡中的PC转运，但铵盐则不能，这表明ABC型转运蛋白参与其中。有趣的是，当在转运试验中添加必需金属离子，如Zn（II）、Cu（II）和Mn（II）时，大麦液泡表现出增强的PC2转运活性，这表明PCs可能有助于必需金属的稳态和非必需有毒金属（类金属）的解毒。
