Dielectric spectroscopy of plant protoplasts

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 β1-, β2-, and β3-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 β1-, β2-, and β3-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 0.6–0.7μF/cm2 and 0.9–1.0μF/cm2, respectively