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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Iron Acquisition by Phytosiderophores Contributes to Cadmium Tolerance^1,[OA]

Molecular Plant Nutrition, Institute of Plant Nutrition, University of Hohenheim, 70593 Stuttgart, Germany (A.R.M., E.B.S., U.E.P., G.S., N.v.W.); Soil Science and Plant Nutrition, Faculty of Agriculture, Cukurova University, 01330 Adana, Turkey (B.E.); and Institute for Analytical Sciences, 44139 Dortmund, Germany (H.H., G.W.)

Based on the ability of phytosiderophores to chelate other heavy metals besides iron (Fe), phytosiderophores were suggested to prevent graminaceous plants from cadmium (Cd) toxicity. To assess interactions between Cd and phytosiderophore-mediated Fe acquisition, maize (Zea mays) plants were grown hydroponically under limiting Fe supply. Exposure to Cd decreased uptake rates of ⁵⁹Fe(III)-phytosiderophores and enhanced the expression of the Fe-phytosiderophore transporter gene ZmYS1 in roots as well as the release of the phytosiderophore 2'-deoxymugineic acid (DMA) from roots under Fe deficiency. However, DMA hardly mobilized Cd from soil or from a Cd-loaded resin in comparison to the synthetic chelators diaminetriaminepentaacetic acid and HEDTA. While nano-electrospray-high resolution mass spectrometry revealed the formation of an intact Cd(II)-DMA complex in aqueous solutions, competition studies with Fe(III) and zinc(II) showed that the formed Cd(II)-DMA complex was weak. Unlike HEDTA, DMA did not protect yeast (Saccharomyces cerevisiae) cells from Cd toxicity but improved yeast growth in the presence of Cd when yeast cells expressed ZmYS1. When supplied with Fe-DMA as a Fe source, transgenic Arabidopsis (Arabidopsis thaliana) plants expressing a cauliflower mosaic virus 35S-ZmYS1 gene construct showed less growth depression than wild-type plants in response to Cd. These results indicate that inhibition of ZmYS1-mediated Fe-DMA transport by Cd is not related to Cd-DMA complex formation and that Cd-induced phytosiderophore release cannot protect maize plants from Cd toxicity. Instead, phytosiderophore-mediated Fe acquisition can improve Fe uptake in the presence of Cd and thereby provides an advantage under Cd stress relative to Fe acquisition via ferrous Fe.

² These authors contributed equally to the paper.

The author responsible for 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: Nicolaus von Wirén (vonwiren{at}uni-hohenheim.de).

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.094474

^* Corresponding author; e-mail vonwiren{at}uni-hohenheim.de; fax 49–711–45923295.

Received December 8, 2006; accepted February 15, 2007; published March 2, 2007.

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