Ion channels in the vacuoles of the seagrass Posidonia oceanica

Voltage-dependent ionic channels were investigated by the patch-clamp technique in the vacuolar membrane from the leaves of the seagrass Posidonia oceanica. Vacuoles extruded from the meristematic white part of the leaves displayed rectifying slow currents which activated in several seconds at positive potentials and deactivated at negative voltages within a few hundreds of ms. Like the Slow Vacuolar (SV) channel already identified in the tonoplast of terrestrial plants, the SV voltage-dependent channel of Posidonia leaves was activated by micromolar concentrations of Ca2+ and was equally permeable to K+ and Na+. The single-channel conductance of the Posidonia SV-type channel was 106 +/- 12 pS (in symmetric 400 mM K+). In the same ionic solutions, another channel, occasionally observed in vacuoles from the green part of the leaves, displayed a single-channel conductance of 47 +/- 4 pS. To our knowledge, this is the first electrophysiological characterization of ion transport pathways in Posidonia, a marine plant of crucial importance for the ecology of the Mediterranean sea.