Relation between permeability to potassium and sodium ions and fusicoccin-stimulated hydrogen-ion efflux in barley roots

Abstract

Measurements are described of fusicoccin (FC)-stimulated H(+) efflux in barley (Hordeum vulgare L.) roots when K(+) and Na(+) concentrations were varied. In low-salt roots H(+) efflux was stimulated in both 5 mM KCl and NaCl. In salt-saturated roots H(+) efflux was stimulated more effectively in KCl than in NaCl solution. The stimulation of H(+) efflux thus is parallel with the selectivity of these different root preparations for K(+) and Na(+) and with estimates of permeability ratios (P Na/P K) determined from electrical measurements. It is suggested that the results support electrogenic coupling between FC-stimulated H(+) efflux and cation uptake.

Fluxes of H+ and K+ in Corn Roots

“…Using this system, we have been able to simultaneously determine the 'instantaneous' net H+ and K+ fluxes associated with a localized region on the corn root. Whereas it has generally been accepted that K+ uptake in roots is coupled to the efflux of H+, either directly through the action of a H+/K+ ATPase (8, 18), or indirectly via electrical coupling to a H+ translocating ATPase (1,6,17), we obtained no experimental support for this putative coupling. Based on our instantaneous flux and electrophysiological data, we propose that K+ influx into corn roots occurs via a H+-K+ cotransport mechanism.…”

“…5). These results, which have been previously observed (9,17), could be due to either the response of the H+-ATPase to excess cation uptake (K2SO4 conditions), or to a diminution of the proton gradient, as protons are consumed via the H+/Cl-cotransport system that has been shown to operate in Chara corallina and is believed to function in higher plants (10,21,22).…”

Natural H+ Currents Traverse Growing Roots and Root Hairs of Barley (Hordeum vulgare L.)

“…The failure of the inward current density to respond to K' and Na+ deletion or to Ca2" deletion suggests that these three main (1,21,22). Individual internodal cells of Nitella seem to drive large H+ ion currents through themselves (29,31).…”

High Affinity K+ Uptake in Maize Roots

“…Although the mechanism(s) of K+ absorption into plant cells has not been elucidated, there is a persistent view in the literature that plasmalemma K+ influx is coupled to the active extrusion of protons (21,29 23,24,[26][27][28]. It should be noted here that interpretation of the literature in this area is complicated by the observation that different researchers have conducted their studies at different K+ concentrations, ranging from relatively low to quite high external concentrations (2 gM to 25 mM K+).…”

“…Based on the results presented here, we propose that high affinity active K+ absorption into maize root cells is not mediated by a K+/H+ exchange mechanism. Instead, it is either due to the operation of a K -H cotransport system, as has been hypothesized for Neurospora, or based on the striking lack of sensitivity to changes in extracellular pH, uptake could be mediated by a K+-ATPase as reported for Escherichia cofi and Saccharomyces.Although the mechanism(s) of K+ absorption into plant cells has not been elucidated, there is a persistent view in the literature that plasmalemma K+ influx is coupled to the active extrusion of protons (21,29 23,24,[26][27][28]. It should be noted here that interpretation of the literature in this area is complicated by the observation that different researchers have conducted their studies at different K+ concentrations, ranging from relatively low to quite high external concentrations (2 gM to 25 mM K+).…”