Relative contribution of AtHAK5 and AtAKT1 to K ⁺ uptake in the high‐affinity range of concentrations

The relative contribution of the high‐affinity K + transporter AtHAK5 and the inward rectifier K + channel AtAKT1 to K + uptake in the high‐affinity range of concentrations was studied in Arabidopsis thaliana ecotype Columbia (Col‐0). The results obtained with wild‐type lines, with T‐DNA insertion in both genes and specific uptake inhibitors, show that AtHAK5 and AtAKT1 mediate the ‐sensitive and the Ba 2+ ‐sensitive components of uptake, respectively, and that they are the two major contributors to uptake in the high‐affinity range of Rb + concentrations. Using Rb + as a K + analogue, it was shown that AtHAK5 mediates absorption at lower Rb + concentrations than AtAKT1 and depletes external Rb + to values around 1 μ M . Factors such as the presence of K + or during plant growth determine the relative contribution of each system. The presence of in the growth solution inhibits the induction of AtHAK5 by K + starvation. In K + ‐starved plants grown without , both systems are operative, but when is present in the growth solution, AtAKT1 is probably the only system mediating Rb + absorption, and the capacity of the roots to deplete Rb + is reduced.