The Arabidopsis thaliana HAK5 K+ Transporter Is Required for Plant Growth and K+ Acquisition from Low K+ Solutions under Saline Conditions

K+ uptake in the high-affinity range of concentrations and its components have been widely studied. In Arabidposis thaliana, the AtHAK5 transporter and the AtAKT1 channel have been shown to be the main transport proteins involved in this process. Here, we study the role of these two systems under two important stress conditions: low K+ supply or the presence of salinity. T-DNA insertion lines disrupting AtHAK5 and AtAKT1 are employed for long-term experiments that allow physiological characterization of the mutant lines. We found that AtHAK5 is required for K+ absorption necessary to sustain plant growth at low K+ in the absence as well as in the presence of salinity. Salinity greatly reduced AtHAK5 transcript levels and promoted AtAKT1-mediated K+ efflux, resulting in an important impairment of K+ nutrition. Although having a limited capacity, AtHAK5 plays a major role for K+ acquisition from low K+ concentrations in the presence of salinity.