Evidence for the Contribution of Surface Potential to the Transtonoplast Potential Difference Measured on Isolated Vacuoles with Microelectrodes

In order to elucidate the origin of the transtonoplast potential difference (PD) measured on isolated vacuoles, the possible contribution of the surface potential to the transmembrane PD was studied. The PD and the electrophoretic mobility were measured on vacuolar preparations, isolated from Beta vulgaris roots and Acer pseudoplatanus cells. Zeta potential was calculated from the electrophoretic mobility. The changes in zeta potential, in response to pH or to a cationic surfactant, were shown to induce parallel variations in the PD. These results suggest that the surface potential could contribute to the transmembrane PD of isolated vacuoles. Various hypotheses on the origin of this transtonoplast PD are discussed.