The Electrical Properties of Plant Cell Membranes: Cable Properties involving the Plasmalemma, Tonoplast and Cytoplasm in Chara

Abstract

The electrical 'cable' properties associated with the two membranes (plasmalemma and tonoplast) and the conductive cytoplasm present in plant cells are analysed for a cylindrical radially symmetric geometry. Calculations indicate that the interpretation of measurements made via vacuolar electrodes on the charophytes Chara and Nitella will not usually be significantly in error if the presence of a longitudinally conductive cytoplasm is neglected. However because of their different conductances, the individual cable properties of the plasmalemma and tonoplast will normally differ. Thus if current is injected into the vacuole at only a single point, the ratio of the consequent potential differences developed across the plasmalemma and tonoplast will vary with longitudinal position on the cell surface, and consequently caution should be exercised in calculating the resistances of the plasmalemma and tonoplast in long cylindrical cells which are not space-clamped. It is also shown that the presence of a longitudinally conductive cytoplasm will ensure that any current leakage around a cytoplasmic electrode will not significantly alter the interpretation of measurements.