Low-frequency Impedance of Chara coralinna: Simultaneous Measurements of the Separate Plasmalemma and Tonoplast Capacitance and Conductance

Abstract

Simultaneous measurements of the separate plasmalemma and tonoplast capacitance and conductance (as a function of frequency) are described. For frequencies > 1 Hz, the capacitance of both membranes increased with decreasing frequency. Below 1 Hz, two distinctly different types of behaviour were observed: either the membrane capacitances continued to increase, reaching values of 0.5 F/m² (50 µF/cm²) at 0.07 Hz, or the membranes became inductive at very low frequencies. At frequencies > 10 Hz, the tonoplast capacitance was 1.5-3 times higher than that of the plasmalemma and increased more rapidly with decreasing frequency. Notwithstanding this, in each case the frequency dependence of the capacitance determined from vacuolar measurements (i.e. tonoplast, cytoplasm and plasmalemma in series) was nearly the same as that of the plasmalemma alone. The conductance of the tonoplast at all frequencies was 4-10 times higher than that of the plasmalemma.