Fluxes of H+ and K+ in Corn Roots
- 1 August 1987
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 84 (4), 1177-1184
- https://doi.org/10.1104/pp.84.4.1177
Abstract
We report here on an experimental system that utilizes ion-selective microelectrodes to measure the electrochemical potential gradients for H(+) and K(+) ions within the unstirred layer near the root surface of both intact 4-day-old corn seedlings and corn root segments. Analysis of the steady state H(+) and K(+) electrochemical potential gradients provided a simultaneous measure of the fluxes crossing a localized region of the root surface. Net K(+) influx values obtained by this method were compared with unidirectional K(+) ((86)Rb(+)) influx kinetic data; at any particular K(+) concentration, similar values were obtained by either technique. The ionspecific microelectrode system was then used to investigate the association between net H(+) efflux and net K(+) influx. Although the computed H(+):K(+) stoichiometry is dependent upon the choice of diffusion coefficients, the values obtained were extremely variable, and net K(+) influx rarely appeared to be charge-balanced by H(+) efflux. In contrast to earlier studies, we found the cortical membrane potential to be highly K(+) sensitive within the micromolar K(+) concentration range. Simultaneous measurements of membrane potential and K(+) influx, as a function of K(+) concentration, revealed similar K(m) values for the depolarization of the potential (K(m) 6-9 micromolar K(+)) and net K(+) influx (K(m) 4-7 micromolar K(+)). These data suggest that K(+) may enter corn roots via a K(+)-H(+) cotransport system rather than a K(+)/H(+) antiporter.Keywords
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