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Published on March 21, 2008; 10.1104/pp.107.114546

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Received December 5, 2007
Accepted March 17, 2008

The Ionic Environment Controls the Contribution of the Barley HvHAK1 Transporter to Potassium Acquisition

Fabiana R. Fulgenzi , Maria Luisa Peralta , Silvina Mangano , Cristian H. Danna , Augusto J. Vallejo , Pere Puigdomenech , and Guillermo E. Santa-Maria *

Instituto de Investigaciones Biotecnologicas, Universidad Nacional de San Martin-CONICET, INTI, Edificio 24, Avda. General Paz 5445, San Martin, 1650, Provincia de Buenos Aires, Argentina; Departament de Genetica Molecular, CID-CSIC, Jordi Girona 18, 08034, Barcelona, Espana

* Corresponding author; email: gsantama{at}iib.unsam.edu.ar.

The control of potassium (K+) acquisition is a critical requirement for plant growth. Although HAK1 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 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 homologue HvHAK1b revealed the presence of two K+ responsive pathways, one repressed and the other insensitive to ammonium. Experiments with 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 unveils an increase of K+ uptake after K+ starvation. This increase does not occur in cells grown at high Na+ concentrations, but takes 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 only explained by changes in the membrane potential. It is shown that the yeast PPZ1 phosphatase as well as the HAL4/HAL5 kinases negatively regulate the HvHAK1-mediated K+ transport.






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