Transmembrane electrical potentials in growing maize roots : Anti-auxin effects.

The anti-auxin 4-chlorophenoxyisobutyric acid (PCIB) applied at a concentration of 10(-2) mol m(-3) to maize root segments was found to induce a transmembrane electrical potential of up to-130 mV (Δpd of 30 mV). The kinetics of this response were comparable to the time scale for PCIB-stimulated H(+)-extrusion. Both effects are eliminated by the addition of p-fluoromethoxycarbonyl cyanide phenylhydrazone (FCCP). Treatment with fusicoccin (FC) and PCIB together does not result in a hyperpolarization greater than with FC alone. Benzoic acid (10(-2) mol m(-3)) had no effect on the transmembrane electrical potentials. These results are discussed in relation to a possible electrogenic proton pump which may be regulated by perturbations in the cellular auxin content or activity.