title: Phosphate uptake inLemna gibba G1: energetics and kinetics.
abstract: Phosphate uptake was studied by determining [(32)P]phosphate influx and by measurements of the electrical membrane potential in duckweed (Lemna gibba L.). Phosphate-induced membrane depolarization (ΔE m ) was controlled by the intracellular phosphate content, thus maximal ΔE m by 1 mM H2PO 4 (-) was up to 133 mV after 15d of phosphate starvation. The ΔE m was strongly dependent on the extracellular pH, with a sharp optimum at pH 5.7. It is suggested that phosphate uptake is energized by the electrochemical proton gradient, proceeding by a 2H(+)/H2PO 4 (-) contransport mechanism. This is supported also by the fusicoccin stimulation of phosphate influx. Kinetics of phosphate influx and of ΔE m , which represent mere plasmalemma transport, are best described by two Michaelis-Menten terms without any linear components.
authors.affiliation: Institut für Botanik der Technischen Hochschule, Schnittspahnstrasse 3, D-6100, Darmstadt, Germany.
authors.forename: C I
authors.initials: CI
authors.lastname: Ullrich-Eberius
authors.forename: A
authors.initials: A
authors.lastname: Novacky
authors.forename: A J
authors.initials: AJ
authors.lastname: van Bel