ELECTRICAL-IMPEDANCE ANALYSIS IN PLANT-TISSUES - IMPEDANCE MEASUREMENT IN LEAVES

Electrical impedance spectra (100 Hz-800 kHz) were measured in leaves of Peperomia obtusifolia L. (a succulent) and Brassica oleracea L. (ca bbage). By measuring impedances at three or more inter-electrode dista nces in a single leaf, electrode impedance and specific tissue impedan ce were separated. Analysis of impedance data from B. oleracea leaves in relation to an equivalent circuit model showed that leaf developmen t was accompanied by increases in extracellular resistance, cytoplasmi c resistance and vacuole interior resistance, together with decreases in plasma membrane capacitance and tonoplast capacitance. After B. ole racea leaves were subjected to a -6-degrees-C freeze-thaw stress, extr acellular resistance, cytoplasmic resistance and vacuole interior resi stance decreased, but plasma membrane capacitance and tonoplast capaci tance did not change. These results indicate that useful measurements of leaf parameters can be obtained by this technique. Examination of t he electrode impedance spectrum showed that electrode insertion produc ed a damaged collar, 0.4-0.5 mm wide, around the electrode. This was c onfirmed by visual observation of the damage in P. obtusifolia leaf.