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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Phytochelatin Synthesis Is Essential for the Detoxification of Excess Zinc and Contributes Significantly to the Accumulation of Zinc^1,[W],[OA]

Leibniz Institute of Plant Biochemistry, Department of Stress and Developmental Biology, 06120 Halle/Saale, Germany (P.T., D.P., C.B., S.C.); and University of Bayreuth, Department of Plant Physiology, 95440 Bayreuth, Germany (D.P., A.T., S.C.)

The synthesis of phytochelatins (PCs) is essential for the detoxification of nonessential metals and metalloids such as cadmium and arsenic in plants and a variety of other organisms. To our knowledge, no direct evidence for a role of PCs in essential metal homeostasis has been reported to date. Prompted by observations in Schizosaccharomyces pombe and Saccharomyces cerevisiae indicating a contribution of PC synthase expression to Zn²⁺ sequestration, we investigated a known PC-deficient Arabidopsis (Arabidopsis thaliana) mutant, cad1-3, and a newly isolated second strong allele, cad1-6, with respect to zinc (Zn) homeostasis. We found that in a medium with low cation content PC-deficient mutants show pronounced Zn²⁺ hypersensitivity. This phenotype is of comparable strength to the well-documented Cd²⁺ hypersensitivity of cad1 mutants. PC deficiency also results in significant reduction in root Zn accumulation. To be able to sensitively measure PC accumulation, we established an assay using capillary liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry of derivatized extracts. Plants grown under control conditions consistently showed PC2 accumulation. Analysis of plants treated with same-effect concentrations revealed that Zn²⁺-elicited PC2 accumulation in roots reached about 30% of the level of Cd²⁺-elicited PC2 accumulation. We conclude from these data that PC formation is essential for Zn²⁺ tolerance and provides driving force for the accumulation of Zn. This function might also help explain the mysterious occurrence of PC synthase genes throughout the plant kingdom and in a wide range of other organisms.

² Present address: University of Dresden, 01307 Dresden, Germany.

The author responsible for the distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Stephan Clemens (stephan.clemens{at}uni-bayreuth.de).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.127472

^* Corresponding author; e-mail stephan.clemens{at}uni-bayreuth.de.

Received August 1, 2008; accepted December 9, 2008; published December 12, 2008.