Tissue‐specific expression of <i>Arabidopsis AKT1</i> gene is consistent with a role in K⁺ nutrition

<jats:p>AKT1, a putative inwardly directed K<jats:sup>+</jats:sup> channel of <jats:italic>Arabidopis</jats:italic>, restores long‐term potassium uptake in a yeast mutant defective in K<jats:sup>+</jats:sup> absorption. In this paper, the expression pattern of the gene encoding AKT1 is described. Northern blots indicate that <jats:italic>AKT1</jats:italic> transcripts are preferentially accumulated in <jats:italic>Arabidopsis</jats:italic> roots. Owing to the difficulties in producing large quantities of <jats:italic>Arabidopsis</jats:italic> roots under hydroponic conditions, experiments were undertaken with <jats:italic>Brassica napus</jats:italic>, a related species. Potassium starvation experiments on <jats:italic>B. napus</jats:italic> plants show that changes in the K<jats:sup>+</jats:sup> status of the organs do not modify <jats:italic>AKT1</jats:italic> mRNA accumulation. Western blot analysis of <jats:italic>B. napus</jats:italic> proteins confirms the presence of AKT1 at the root plasma membrane. Tissue‐specific expression directed by the <jats:italic>Arabidopsis AKT1</jats:italic> gene promoter was investigated by analysis of β‐glucuronidase (GUS) activity in transgenic <jats:italic>Arabidopsis</jats:italic> containing an <jats:italic>AKT1‐GUS</jats:italic> gene fusion. As determined by fluorimetric and histochemical tests, the <jats:italic>AKT1</jats:italic> promoter directs preferential expression in the peripheral cell layers of root mature regions. The discrete activity found in leaves relates to leaf primordia and to small groups of cells, hydathodes, found on toothed margins of the <jats:italic>Arabidopsis</jats:italic> leaf lamina. These data are discussed with regard to a possible role of AKT1 in K<jats:sup>+</jats:sup> nutrition of plants.</jats:p>