Pressure Effects on Membrane Potentials of Mesophyll Cell Protoplasts and Epidermal Cell Protoplasts ofCommelina communisL.

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Abstract
Pantoja, O. and Willmer, C. M. 1986. Pressure effects on membrane potentials of mesophyll cell protoplasts and epidermal cell protoplasts of Commelina communis L.—J. exp. Bot. 37: 315–320. Membrane potentials of epidermal cell protoplasts and mesophyll cell protopiasts of Comnelina communis were measured when the protoplasts were immobilized in a suction micropipette. When zero suction was employed, membrane potentials of both protoplast types were near to zero. As suction pressure was increased, membrane potentials became increasingly more negative with gradients of 14·3 mV/kPa and 10·5 mV/kPa for mesophyll cell protoplasts and epidermal cell protoplasts, respectively. The plasma membrane is stretched when suction pressure is applied to protoplasts and it is considered that this simulates cell turgor pressure which is associated with negative membrane potentials of intact cells. The results help to explain why some investigators obtain positive membrane potentials for protoplasts while others obtain negative values. The results also indicate that considerable caution is needed in the interpretation of ion flux data when protoplasts are used.