title: H extrusion and potassium uptake associated with potential hyperpolarization in maize and wheat root segments treated with permeant weak acids.
abstract: The rapid uptake of weak acids permeant in the uncharged form is accompanied in maize and wheat root segments by a hyperpolarization of the transmembrane electrical potential and an increase in K(+) uptake, suggesting a stimulation of the plasmalemma H(+) pump. The evaluation of weak acid-induced H(+) extrusion must take into account the alkalinization of the medium due to the rapid uptake of the uncharged form of the acid, partially masking the proton pump-mediated extrusion of H(+). The data corrected for this interference show that the lipophilic butyric acid and trimethyl acetic acid induce in maize and in wheat root segments a significant increase in ;real' H(+) extrusion, roughly matching the increase in net K(+) uptake. The presence of K(+) significantly increases the rate of uptake of the weak acid, possibly as a consequence of an alkalinization of the cytosol associated with K(+) absorption. In maize root segments, the effects of fusicoccin and those of butyric acid on both K(+) uptake and H(+) extrusion are clearly synergistic, thus suggesting distinct modes of action. These results support the view that the activity of the plasmalemma H(+) pump is regulated by the value of cytosolic pH.
authors: Dipartimento di Biologia, Università di Milano, 20133 Milano.
authors: G
authors: G
authors: Romani
authors: M T
authors: MT
authors: Marrè
authors: M
authors: M
authors: Bellando
authors: G
authors: G
authors: Alloatti
authors: E
authors: E
authors: Marrè