Electrical Impedance Analysis in Plant Tissues3

Based on the electrical model for plant tissue proposed by Hayden, Moyse, Calder, Crawford, and Fensom (1969), a method is described for calculating symplasmic resistance and cell membrane capacitance from impedances measured over a range of alternating current (AC) frequencies. The method of calculation has been applied to ten different plant organs using frequencies from 20 Hz to 300 KHz. In contrast with previous assumptions, it was found that both the symplasmic resistance and the membrane capacitance were not constant but decreased with increasing frequency, given the constraints of the Hayden model. In cucumber fruit tissue, the symplasmic resistance was 20 000 ohms at 3 KHz but only 1200 ohms at 200 KHz; the capacitance was 2.4 nF at 3 KHz but only 0.8 nF at 200 KHz. The changes were similar in other materials, such as carrot root and cabbage leaf. It is concluded that the Hayden model does not represent plant tissues accurately. It is suggested that a better representation would be obtained by including a capacitor in the component of the circuit which represents the symplasm, in order to make allowance for membranes of organelles, particularly the vacuole.