The ionic environment controls the barley high-affinity potassium transporter HvHAK1.

S. MANGANO, F. FULGENZI, M.L. PERALTA, G. E. SANTA-MARÍA

Valencia

Congreso; XIV Internacional Workshop Plant Membrana Biology; 2007

The ionic environment controls the barley high-affinity potassium transporter HvHAK1 Silvina Mangano, Fabiana Fulgenzi, María Luisa Peralta, and Guillermo E. Santa-María Instituto de Investigaciones Biotecnológicas, INTI, Edificio 24, San Martín, 1650, Provincia de Buenos Aires, Argentina. The control of potassium (K+) acquisition is a critical requirement for plant growth during acclimation to most environments. Members of subgroup I of HAK-KUP-KT transporters play a major role in inducible K+ uptake. We explored the way by which the ionic environment modulates the capacity of yeast cells expressing the barley K+ transporter, HvHAK1, during the response to K+-starvation. Studies with yeast cells expressing HvHAK1 unveil a reversible increase of K+-uptake (and Rb+) after K+ starvation. This increase does not involve a switch between different modes of action, being the result of a 3-4 fold increase in Vmax. Exposure to a high NaCl concentration –but not to NH4+- during the course of K+ starvation prevents the subsequent increase of Rb+ uptake mediated by HvHAK1. These effects should not be confounded with the direct inhibitory effects of Na+ and NH4+ on Rb+ uptake formerly reported. Flow cytometry analyses with DiOC6 indicate that the “long-term” effect of Na+ must not be attributed to membrane depolarization. It is shown that the yeast PPZ1 phosphatase acts as a negative regulator of K+ transport in HvHAK1 expressing yeast cells, being an equivalent role for the yeast HAL4/HAL5 kinases also proposed. In turn, Arabidopsis thaliana seedlings expressing HvHAK1 under the control of the 35S promoter showed an increase of Rb+ transport following K+ deprivation. That increase does not take place when a high Na+ (and to a lesser extent NH4+) concentration is supplied during the course of the K+-starvation process. Our results suggest a complex and tightly regulated control on the transport of K+ mediated by a HAK-KUP-KT transporter, which helps plants to ensure K+ capture under a wide range of ionic environments.