Biophysical Journal 63: 1493-1499 (1992)
© 1992 the Biophysical Society

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Dielectric spectroscopy of plant protoplasts

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611, Japan

ABSTRACT

The relative permittivity and conductivity of the mesophyll protoplasts isolated from Brassica campestris leaves and Tulipa gesneriana petals were measured over a frequency range from 1kHz to 500 MHz.These protoplasts showed a broad dielectric dispersion, which was composed of three subdispersions, termed ß₁-, ß₂-, and ß₃-dispersion in increasing order of frequency.The three subdispersions were assigned to the Maxwell-Wagner dispersion caused by charging processes at the interfaces of the surface and internal membranes; the plasma membrane, the tonoplast, and the membranes of cytoplasmic organelles (e.g., chloroplasts, granules, etc) primarily contribute to the ß₁-, ß₂-, and ß₃-dispersion, respectively. The whole dielectric dispersion curve was satisfactorily interpreted in terms of a spherical cell model taking a large vacuole and cytoplasmic organelles into account. Using this model the capacitances of the plasma membranes and the tonoplasts were estimated to be 0.6-0.7 µF/cm² and 0.9-1.0 µF/cm², respectively.