Potassium Transport to Shoot Organs by SHY3/AtKUP2

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To grow, plant cells take up water so that the resulting internalturgor pressure can push against the cell wall, causing it to stretch.Water uptake depends on osmotic potential provided principally byintracellular potassium (K+) ions, and potassium transport is therefore keyto plant cell growth. A mutation in the gene encoding the AtKUP2 potassiumtransporter of the model plant Arabidopsis thaliana causes the plants tohave small cells in the stem and leaves, probably because of a decrease inpotassium delivery to the shoot. This grant takes three approaches tounderstand the precise role of AtKUP2 in potassium movements within theplant. First, study of which cells turn on the gene encoding AtKUP2 willreveal in which tissues AtKUP2 may mediate K+ uptake. Second, examinationof the subcellular localization of AtKUP2 protein in these cells willreveal whether the transporter is in the plasma membrane or in a membraneof an internal storage vacuole, and whether the protein is asymmetricallylocalized. Third, studies of the kinetics of movements of rubidium ions(Rb+, a convenient substitute for K+) in normal and mutant plants willaddress where the putative block in potassium movement may be. Theseexperiments will reveal whether the AtKUP2 transporter acts to take uppotassium in root or in shoot cells, and will lead to further studies of K+nutrition and growth control.