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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The Ionic Environment Controls the Contribution of the Barley HvHAK1 Transporter to Potassium Acquisition^1,[W],[OA]

Instituto de Investigaciones Biotecnológicas, Universidad Nacional de San Martín-Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Tecnología Industrial, San Martín 1650, Provincia de Buenos Aires, Argentina (F.R.F., M.L.P., S.M., C.H.D., A.J.V., G.E.S.-M.); and Departament de Genètica Molecular, Centro de Investigaciones y Desarrollo-Consejo Superior de Investigaciones Científicas, 08034 Barcelona, Spain (P.G.)

The control of potassium (K⁺) acquisition is a critical requirement for plant growth. Although HAK1 (high affinity K⁺ 1) transporters provide a pathway for K⁺ acquisition, the effect exerted by the ionic environment on their contribution to K⁺ capture remains essentially unknown. Here, the influence of the ionic environment on the accumulation of transcripts coding for the barley (Hordeum vulgare) HvHAK1 transporter as well as on HvHAK1-mediated K⁺ capture has been examined. In situ mRNA hybridization studies show that HvHAK1 expression occurs in most root cells, being augmented at the outermost cell layers. Accumulation of HvHAK1 transcripts is enhanced by K⁺ deprivation and transiently by exposure to high salt concentrations. In addition, studies on the accumulation of transcripts coding for HvHAK1 and its close homolog HvHAK1b revealed the presence of two K⁺-responsive pathways, one repressed and the other insensitive to ammonium. Experiments with Arabidopsis (Arabidopsis thaliana) HvHAK1-expressing transgenic plants showed that K⁺ deprivation enhances the capture of K⁺ mediated by HvHAK1. A detailed study with HvHAK1-expressing Saccharomyces cerevisiae cells also revealed an increase of K⁺ uptake after K⁺ starvation. This increase did not occur in cells grown at high Na⁺ concentrations but took place for cells grown in the presence of NH₄⁺. 3,3'-Dihexyloxacarbocyanine iodide accumulation measurements indicate that the increased capture of K⁺ in HvHAK1-expressing yeast cells cannot be explained only by changes in the membrane potential. It is shown that the yeast protein phosphatase PPZ1 as well as the halotolerance HAL4/HAL5 kinases negatively regulate the HvHAK1-mediated K⁺ transport.

² These authors contributed equally to the article.

³ Present address: Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02114.

⁴ Present address: IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417 Buenos Aires, Argentina.

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: Guillermo E. Santa-María (gsantama{at}iib.unsam.edu.ar).

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

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.114546

^* Corresponding author; e-mail gsantama{at}iib.unsam.edu.ar.

Received December 5, 2007; accepted March 17, 2008; published March 21, 2008.