The ionic environment controls the contribution of the barley HvHAK1 transporter to potassium acquisition

FULGENZI FABIANA; PERALTA MARÍA LUISA; MANGANO SILVINA; DANNA CRISTIAN; VALLEJO AUGUSTO; PUIGDOMENCH PERE; SANTA MARIA G.E.

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 2008 vol. 147 p. 252 - 262

0032-0889

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 situmRNA 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 tookplace 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 regulatethe HvHAK1-mediated K1 transport.