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The high‐affinity K⁺ transporter HAK5 is a key system for root K⁺ uptake and, under very low external K⁺, the only one capable of supplying K⁺ to the plant. Functional HAK5‐mediated K⁺ uptake should be tightly regulated for plant adaptation to different environmental conditions. Thus, it has been described that the gene encoding the transporter is transcriptionally regulated, being highly induced under K⁺ limitation. Here we show that environmental conditions, such as the lack of K⁺, NO₃⁻ or P, that induced a hyperpolarization of the plasma membrane of root cells, induce HAK5 transcription. However, only the deprivation of K⁺ produces functional HAK5‐mediated K⁺ uptake in the root. These results suggest on the one hand the existence of a posttranscriptional regulation of HAK5 elicited by the low K⁺ signal and on the other that HAK5 may be involved in yet‐unknown functions related to NO₃⁻ and P deficiencies …