Expression and stress-dependent induction of potassium channel transcripts in the common ice plant.

We have characterized transcripts for three potassium channel homologs in the AKT/KAT subfamily (Shaker type) from the common ice plant (Mesembryanthemum crystallinum), with a focus on their expression during salt stress (up to 500 mM NaCl). Mkt1 and 2, Arabidopsis AKT homologs, and Kmt1, a KAT homolog, are members of small gene families with two to three isoforms each. Mkt1 is root specific; Mkt2 is found in leaves, flowers, and seed capsules; and Kmt1 is expressed in leaves and seed capsules. Mkt1 is present in all cells of the root, and in leaves a highly conserved isoform is detected present in all cells with highest abundance in the vasculature. MKT1 for which antibodies were made is localized to the plasma membrane. Following salt stress, MKT1 (transcripts and protein) is drastically down-regulated, Mkt2 transcripts do not change significantly, and Kmt1 is strongly and transiently (maximum at 6 h) up-regulated in leaves and stems. The detection and stress-dependent behavior of abundant transcripts representing subfamilies of potassium channels provides information about tissue specificity and the complex regulation of genes encoding potassium uptake systems in a halophytic plant.