Spatial Variation of the Electrical Properties of Chara australis. II. Membrane Capacitance and Conductance as a Function of Frequency

Abstract

The water-film technique has been used to measure the frequency dependence of the membrane capacitance and conductance as a function of position along illuminated cells of C. australis. At low frequencies (< 1 Hz) the behaviour of the membrane capacitance was found to be strongly dependent upon both frequency and position. A complicated oscillatory pattern was observed which is possibly linked to interference effects between the impressed alternating current and the current normally circulating between alternate acid and alkaline zones. The area-specific membrane conductance was always higher in the alkaline zones than in the acid zones and at low frequencies was 0.45 - 1.3 S m-2 and 2.9 - 3.6 S m-2 respectively. The temperature dependence of the variation of the capacitance and conductance with frequency was also different in the acid and alkaline zones. The observed spatial and frequency dependence of the membrane electrical parameters is clearly associated with the dynamic homeostatis of the cell, and has consequences for the construction of realistic electrical models for the membrane of C. australis.