A study of dielectric membrane breakdown in theFucus egg

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Abstract
Summary 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 (τ p ) and 50 to 400 V field strength (U p cm−1). During exposure, the difference in electric potential across the plasmalemma (V m ) 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 uponU p and τ p is fully consistent with the assumption that the membrane undergoes a localized reversible dielectric breakdown and reseals within J. Membrane Biol. 22:73) and verify this model on a nonvacuolated plant cell. A thresholdV m for membrane breakdown (V c ) 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 forV c , and a reasonable value of the membrane's elastic modulus (i.e.,Y m ≈106 Nm−2), possible sites of membrane breakdown are dicussed in terms of membrane thickness and relative permittivity.