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J Biol Chem. 2002 Jan 25;277(4):2413-8. Epub 2001 Nov 13.

The arabidopsis Na+/H+ exchanger AtNHX1 catalyzes low affinity Na+ and K+ transport in reconstituted liposomes.

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  • 1Departamento de Bioquimica, Biologia Celular y Molecular de Plantas, EstaciĆ³n Experimental del Zaidin, CSIC, Apartado 419, 18080 Granada, Spain.

Abstract

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, AtNHX1 mRNA 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 Ni(2+) 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.

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