TISSUE-SPECIFIC EXPRESSION OF ARABIDOPSIS AKT1 GENE IS CONSISTENT WITH A ROLE IN K+ NUTRITION

AKT1, a putative inwardly directed K+ channel of Arabidopis, restores long-term potassium uptake in a yeast mutant defective in K+ absorptio n. In this paper, the expression pattern of the gene encoding AKT1 is described. Northern blots indicate that AKT1 transcripts are preferent ially accumulated in Arabidopsis roots. Owing to the difficulties in p roducing large quantities of Arabidopsis roots under hydroponic condit ions, experiments were undertaken with Brassica napus, a related speci es. Potassium starvation experiments on B. napus plants show that chan ges in the K+ status of the organs do not modify AKT1 mRNA accumulatio n. Western blot analysis of B, napus proteins confirms the presence of AKT1 at the root plasma membrane. Tissue-specific expression directed by the Arabidopsis AKT1 gene promoter was investigated by analysis of beta-glucuronidase (GUS) activity in transgenic Arabidopsis containin g an AKT1-GUS gene fusion. As determined by fluorimetric and histochem ical tests, the AKT1 promoter directs preferential expression in the p eripheral cell layers of root mature regions. The discrete activity fo und in leaves relates to leaf primordia and to small groups. of cells, hydathodes, found on toothed margins of the Arabidopsis leaf lamina. These data are discussed with regard to a possible role of AKT1 in Knutrition of plants.