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The Arabidopsis Na+/H+Exchanger AtNHX1 Catalyzes Low Affinity Na+ and K+ Transport in Reconstituted Liposomes

In saline environments, plants accumulate Na+ in vacuoles through the activity of tonoplast Na+/H+ antiporters. The first gene for a putative plant vacuolar Na+/H+ antiporter,AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl. However, AtNHX1mRNA was up-regulated by...

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Bibliographic Details
Published in:The Journal of biological chemistry 2002-01, Vol.277 (4), p.2413-2418
Main Authors: Venema, Kees, Quintero, Francisco J., Pardo, José M., Donaire, Juan Pedro
Format: Article
Language:English
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Summary:In saline environments, plants accumulate Na+ in vacuoles through the activity of tonoplast Na+/H+ antiporters. The first gene for a putative plant vacuolar Na+/H+ antiporter,AtNHX1, was isolated from Arabidopsis and shown to increase plant tolerance to NaCl. However, AtNHX1mRNA was up-regulated by Na+ or K+ salts in plants and substituted for the homologous protein of yeast to restore tolerance to several toxic cations. To study the ion selectivity of the AtNHX1 protein, we have purified a histidine-tagged version of the protein from yeast microsomes by Ni2+ affinity chromatography, reconstituted the protein into lipid vesicles, and measured cation-dependent H+ exchange with the fluorescent pH indicator pyranine. The protein catalyzed Na+ and K+ transport with similar affinity in the presence of a pH gradient. Li+ and Cs+ ions were also transported with lower affinity. Ion exchange by AtNHX1 was inhibited 70% by the amiloride analog ethylisopropyl-amiloride. Our data indicate a role for intracellular antiporters in organelle pH control and osmoregulation.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M105043200