Stimulation of Potassium Uptake by Abscisic Acid in Potato Tuber Tissues. Relation with H+ and Ca2+ Fluxes

The potassium uptake by potato tuber discs tissues freshly cut and after 24 h of ageing in the presence or not of abscisic acid was investigated. Uptake kinetics revealed a biphasic dependence on external K+ concentrations. At concentration less than 10 mM, uptake was mediated by a saturable component and a linear component became apparent at higher concentrations. At low K+ concentrations (lmM), the capacity of K+ uptake diminished by 2 times after ageing. Treatment of tissues with ABA increased the rate of K+ uptake. In both fresh and aged tissues the uptake was strongly enhanced by fusicoccin and decreased by several metabolic inhibitors and ATPase inhibitors, underlying the active nature of uptake and suggesting the involvement of a plasmalemma H+-ATPase in K+ transport system.