| Abstract: | Electrical impedance spectra (100 Hz–800 kHz) were measuredin leaves of Peperomia obtusifolia L. (a succulent) and Brassicaoleracea L. (cabbage). By measuring impedances at three or moreinter-electrode distances in a single leaf, electrode impedanceand specific tissue impedance were separated. Analysis of impedance data from B. oleracea leaves in relationto an equivalent circuit model showed that leaf developmentwas accompanied by increases in extracellular resistance, cytoplasmicresistance and vacuole interior resistance, together with decreasesin plasma membrane capacitance and tonoplast capacitance. AfterB. oleracea leaves were subjected to a –6 °C freeze-thawstress, extracellular resistance, cytoplasmic resistance andvacuole interior resistance decreased, but plasma membrane capacitanceand tonoplast capacitance did not change. These results indicatethat useful measurements of leaf parameters can be obtainedby this technique. Examination of the electrode impedance spectrum showed thatelectrode insertion produced a damaged collar, 0·4–0·5mm wide, around the electrode. This was confirmed by visualobservation of the damage in P. obtusifolia leaf. Key words: Peperomia obtusifolia L., Brassica oleracea L. (cabbage), electrical impedance, equivalent circuit, electrode polarization |
