title: Potassium transport into plant vacuoles energized directly by a proton-pumping inorganic pyrophosphatase.
abstract: Potassium is accumulated in plant vacuoles against an inside-positive membrane potential. The mechanism facilitating energized K+ transport has remained obscure. However, electrogenic activity of the inorganic pyrophosphatase (H(+)-PPase) at the vacuolar membrane is dependent on cytoplasmic K+, raising the possibility that the enzyme translocates K+ into the vacuole. Membrane currents generated by the H(+)-PPase were measured (using a patch clamp technique) in intact vacuoles isolated from Beta vulgaris storage tissue. A significant orthophosphate-dependent outward current mediated by the enzyme in reverse mode is evoked only when potassium is present at the vacuolar face of the tonoplast, suggesting that potassium is a translocated ion. Furthermore, current-voltage analysis of the effects of extravacuolar potassium and pH on the reversal potential of the H(+)-PPase-generated current points to direct translocation of K+ and H+ by the enzyme. Thus the H(+)-PPase represents a distinct class of eukaryote translocase and could facilitate vacuolar K+ accumulation in vivo.
authors.affiliation: Biology Department, University of York, United Kingdom.
authors.forename: J M
authors.initials: JM
authors.lastname: Davies
authors.forename: R J
authors.initials: RJ
authors.lastname: Poole
authors.forename: P A
authors.initials: PA
authors.lastname: Rea
authors.forename: D
authors.initials: D
authors.lastname: Sanders
mesh_terms: D001693:Biological Transport, Active; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008564:Membrane Potentials; D009994:Osmolar Concentration; D010944:Plants / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011755:Pyrophosphatases / Q000378:metabolism*; D013816:Thermodynamics; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D011755:Pyrophosphatases; D011188:Potassium