Dielectric Spectroscopy of Chloroplasts Isolated from Higher Plants-Characterization of the Double-Membrane System

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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 intermembrane 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 visible 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 motion) lead to curves analogous to Cole-Cole curves, with semicircles in all quadrants of the coordinate system. Differences between these results and impedance data are discussed.
日本植物生理学会の論文