Potassium and Phosphate Uptake in Corn Roots: Further Evidence for an Electrogenic H/K Exchanger and an OH/Pi Antiporter

Abstract

Evidence is presented that K(+) uptake in corn root segments is coupled to an electrogenic H(+)/K(+) -exchanging plasmalemma ATPase while phosphate uptake is coupled to an OH(-)/Pi antiporter. The plasmalemma ATPase inhibitor, diethylstilbestrol, or the stimulator, fusicoccin, altered K(+) uptake directly and phosphate uptake indirectly. On the other hand, mersalyl, an OH(-)/Pi antiporter inhibitor, inhibited phosphate uptake instantly but only slightly affected K(+) uptake. Collapse of the proton gradient across the membrane by (p-trifluoromethoxy) carbonyl cyanide phenylhydrazone resulted in immediate inhibition of K(+) uptake but only later inhibited phosphate uptake. Changing the pH of the absorption solution had opposite effects on K(+) and phosphate uptake. In addition, a 4-hour washing of corn root tissue induced a 5-fold increase in the rate of K(+) uptake with little or no lag, but only a 2- to 3-fold increase in phosphate uptake with a 30- to 45-minute lag. Collectively these differences strongly support the coupling of an electrogenic H(+)/K(+) -exchanging ATPase to an OH(-)/Pi antiporter in corn root tissue.