The Water-Film Electrode: A New Device for Measuring the Characean Electro-Potential and -Conductance Distributions along the Length of the Internode

A "water-film electrode" has been developed to study time dependenciesof the distributions of electrical potential (Vm) and conductance(Gm) as a function of position along the length of a singleCharacean internode. The water-film is formed by dipping a ring-shapedAg/AgCl wire covered with an agar block into detergent-containingartificial pond water. The use of uncalcified internodes produced the following results:(1) Both Vm and Gm were relatively uniform along the internodein darkness. (2) Illumination induced hyperpolarization andincreased Gm along the entire length of the internode withinfew minutes. During this period, small electro-potential differentiationof as much as 20 mV was sometimes observed. Thereafter, severaldepolarized regions (D-regions) with highGm values appeared;as much as 100 mV of depolarization. (3) The positions of theD-regionsin light remained unchanged for several days even when the lightwas turned off for a period of more than 1 h. (4) When the internodewas partially exposed to light, the D-region appeared, or formed,only in the illuminated part. In calcified internodes electro-differentiation was inducedby illumination as it was in uncalcified ones. Slightly depolarizedregions, however, remained even in darkness. Unlike noncalcifiedinternodes, the conductance of the depolarized region was generallyless than that of the neighboring hyperpolarized regions (H-regions). (Received August 2, 1982; Accepted March 24, 1983)