Studies on Arabidopsis athak5, atakt1 double mutants disclose the range of concentrations at which AtHAK5, AtAKT1 and unknown systems mediate K plus uptake

The high-affinity K+ transporter AtHAK5 and the inward-rectifier K+ channel AtAKT1 have been described to contribute to K+ uptake in Arabidopsis thaliana. Studies with T-DNA insertion lines showed that both systems participate in the high-affinity range of concentrations and only AtAKT1 in the low-affinity range. However the contribution of other systems could not be excluded with the information and plant material available. The results presented here with a double knock-out athak5, atakt1 mutant show that AtHAK5 is the only system mediating K+ uptake at concentrations below 0.01 mM. In the range between 0.01 and 0.05 mM K+ AtHAK5 and AtAKT1 are the only contributors to K+ acquisition. At higher K+ concentrations, unknown systems come into operation and participate together with AtAKT1 in low-affinity K+ uptake. These systems can supply sufficient K+ to promote plant growth even in the absence of AtAKT1 or in the presence of 10 mM K+ where AtAKT1 is not essential.