STUDY OF DIELECTRIC MEMBRANE BREAKDOWN IN THE FUCUS EGG

Unfertilized eggs and zygotes of the marine brown alga, Fucus serratus, have been subjected to single external electric field pulses of 1 to 1760 μsec duration (τp) and 50 to 400 V field strength (Upcm-1). During exposure, the difference in electric potential across the plasmalemma (Vm) was recorded intracellularly from single eggs, and the efflux of86Rb+(K+) from the cytoplasm was measured on egg populations. A given single pulse instantaneously depolarizes the plasmalemma by a few (i.e., 6) millivolts and releases a certain fraction (i.e., 5%) of the cytoplasmic86Rb+(K+). The dependence of these responses upon Up and τp is fully consistent with the assumption that the membrane undergoes a localized reversible dielectric breakdown and reseals within <3 sec. The data are treated in terms of the electro-mechanical model for a compressible membrane by H.G.L. Coster and U. Zimmermann (1975, J. Membrane Biol.22:73) and verify this model on a nonvacuolated plant cell. A threshold Vm for membrane breakdown (Vc) of 0.58 and 0.51 V is estimated for the turgorless undertilized eggs and the turgescent (4.8 bar) zygotes, respectively. Using these values for Vc, and a reasonable value of the membrane's elastic modulus (i.e., Ym≈106 Nm-2), possible sites of membrane breakdown are dicussed in terms of membrane thickness and relative permittivity. © 1979 Springer-Verlag New York Inc.