Dielectric spectroscopy of chloroplasts isolated from higher plants-characterisation of the double membrane system. Plant Cell Physiology 31

The dielectric dispersion of individual chloroplasts has been measured between 1 kHz and 32 MHz. As measuring techniques, both electrorotation and dielectrophoresis were used. We analysed the dispersion data on the basis of a "three-shell model", in which three concentric shells are taken to represent the outer and inner envelope membranes of the plastid and the in-termembrane space. The measurements revealed that the outer and inner envelope membranes of the chloroplasts were different in terms of their electrical properties. Both membranes are visi-ble in the rotation spectra as different relaxation processes under particular conditions. Less in-formation can be obtained about the intermembrane space and the thylakoid systems. A set of parameters describing the electrical properties of plastids can be obtained, however, for each plastid compartment, with different degrees of accuracy. Dielectrophoretic motion of individual chloroplasts was measured between 4 kHz and 32 MHz and the results were in good agreement with a theoretical analysis. Plots of both types of spectrum (rotational and dielectrophoretic mo-tion) lead to curves analogous to Cole-Cole curves, with semicircles in all quadrants of the coor-dinate system. Differences between these results and impedance data are discussed. Key words: Cole-Cole plot — Dielectric dispersion — Dielectrophoresis — Electrorotation