Electrical Impedance Analysis in Plant Tissues8

Abstract

Electrical impedance spectra (100 Hz–800 kHz) were measured in leaves of Peperomia obtusifolia L. (a succulent) and Brassica oleracea L. (cabbage). By measuring impedances at three or more inter-electrode distances in a single leaf, electrode impedance and specific tissue impedance were separated. Analysis of impedance data from B. oleracea leaves in relation to an equivalent circuit model showed that leaf development was accompanied by increases in extracellular resistance, cytoplasmic resistance and vacuole interior resistance, together with decreases in plasma membrane capacitance and tonoplast capacitance. After B. oleracea leaves were subjected to a −6 °C freeze-thaw stress, extracellular resistance, cytoplasmic resistance and vacuole interior resistance decreased, but plasma membrane capacitance and tonoplast capacitance did not change. These results indicate that useful measurements of leaf parameters can be obtained by this technique. Examination of the electrode impedance spectrum showed that electrode insertion produced a damaged collar, 0·4–0·5 mm wide, around the electrode. This was confirmed by visual observation of the damage in P. obtusifolia leaf.