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Plant and Cell Physiology, 1978, Vol. 19, No. 2 303-315
© 1978

Article

An electrophysiological study of the membrane in aplanospore-like cell of Boergesenia forbesii

Michikazu Samejima and Takao Sibaoka

Biological Institute, Faculty of Science, Tohoku University Sendai 980, Japan

Membrane potential and resistance, each of which was the sum of those of the plasmalemma and tonoplast, measured in the coenocytic thallus of Boergesenia forbesii were 6.7 mv inside positive and 2.8 k{Omega}.cm2, respectively.

Protoplasm squeezed from the thallus into artificial sea water (ASW) formed numerous spherical bodies, which are termed aplanospore-like cells (simply "spores"). The following electrical properties of the "spores" 20–40 hr after squeezing were obtained: potential difference (p.d.) across plasmalemma (Eco) was –66 mv (– means inside negative), plasmalemma resistance 665 {Omega}cm2, p.d. across the tonoplast (Evc) +73 mv, and tonoplast resistance 2.6 k{Omega}.cm2. Tenfold increase in external [K+] caused +45 mv change in Eco and +17 mv in Evc. The plasmalemma was entirely depolarized in Ca++-free ASW or ASW containing Triton X-100.

When the "spore" was immersed in potassium-rich (277 mil) ASW, Eco was almost zero and the tonoplast showed two states (I and II, Eve about +70 mv and +20 mv, respectively). Evc went back and forth between the two states spontaneously or when a small current was applied. In most cases oscillatory changes in Evc occurred after the lapse of a long time in the K+-rich sea water. Membrane resistances in states I and II were 5 and 9 k{Omega}.cm2, respectively.

(Received July 11, 1977; )
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