Potassium transport into plant vacuoles energized directly by a proton-pumping inorganic pyrophosphatase.
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.
Davies
J M
JM
Biology Department, University of York, United Kingdom.
Poole
R J
RJ
Rea
P A
PA
Sanders
D
D
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*
D011755:Pyrophosphatases; D011188:Potassium