The Double-Water-Film Electrode: A Device for Measuring the Resistance and the Capacitance of the Internode/Node Interface of Chara as Functions of Time and Temperature.
A "double-water-film electrode technique" has been developed for the long-term characterization of the electrical properties across the interface between the nodal (N) and internodal (A or B) cells and the vacuole along the length of an internode of Chara as a function of time and temperature. The electrode unit consisted of a pair of the water-film electrodes described elsewhere (Chilcott 1988; Chilcott and others 1983; Coster and others 1984; Lucas 1985; and Ogata 1983). The distance between two water-film probes was fixed at 1.0 cm. By scanning the electrode unit, the spatial variations in electrical resistance and capacitance along the longitudinal axis of Chara were observed. Analysis was performed by applying an electrical equivalent circuit for the biomembrane (Philippson 1921). Across the internode (-A or -B)/central nodal cells interface, the specific parallel resistance (Rm) and the parallel capacitance (Cm) at 20 degrees C were 30 +/- 5 x 10(-3) Omegam(2) and 1.5 +/- 0.5 x 10(-1)Fm(-2) (at 30 Hz), respectively. And the series resistance, corresponding to the vacuole of the internode was 8 x 10(-3) Omegam(2). Study of temperature dependencies of Rm and Cm suggested that a dynamic homeostatic regulation was operating at the interface where numerous plasmodesmata were observed with an electron microscope (Pickett-Heaps 1967; Spanswick and Costerton 1967). Assuming that the individual cylinder of plasmodesma was filled only with cytoplasm, the number of plasmodesma per interface was estimated at 2.6 x 10(5).
Ogata
K
School of Health Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishiku, 807-8555 Fukuoka, Japan