Ion Transport in Isolated Protoplasts from Tobacco Suspension Cells: III. Membrane Potential.

The membrane electrical potential difference was measured in cultured cells and isolated protoplasts of tobacco (Nicotiana glutinosa L.) by inserting a microelectrode into cells held fast by a suction micropipette. The potential difference (+/- standard deviation) for unplasmolyzed tobacco cells was -52 +/- 12 millivolts, for cells in 0.3 molar mannitol, -50 +/- 11 millivolts; and for cells plasmolyzed in 0.7 molar mannitol, -49 +/- 12 millivolts all inside negative. The potential difference for isolated protoplasts in 0.7 molar mannitol was -49 +/- 16 millivolts, inside negative. In both cultured cells and protoplasts, the addition of 0.1 millimolar KCN caused a depolarization of the membrane potential. It was concluded that plasmolysis and enzymic release of the protoplast had no significant effect on the membrane potential of cultured tobacco cells.