AC-IMPEDANCE MEASUREMENTS ON CHARA-CORALLINA .3. CHARACTERIZATION OF THE PLASMA-MEMBRANE COAT USING A NEW PRESENTATION OF IMPEDANCE SPECTRA

It has been shown that the measurement of electrical impedence can pro vide a non-invasive approach to detect the presence of the plasma memb rane coat (PMC). Further, the measurements provide an estimate of the geometrical properties of plasmalemmasomes (charasomes) which are simi lar to estimates determined from electron micrographs. Impedance measu rements were made in the range of 1-10(4) Hz. A transfer (network) fun ction with either four or five time constants was fitted to the spectr a. We present transfer functions as spectra in which peaks are observe d at the reciprocal of these time constants. We call the reciprocal ti me constants frequency constants. Our analysis suggests that two peaks in the frequency range of 1-10(2) Hz arise from the series combinatio n of the plasmalemma and tonoplast and a peak at very high frequencies (much greater than 10(4) Hz) arises from the static cytoplasm. The re maining two peaks in the frequency range of 10(2)-10(3) Hz we attribut e to the presence of the PMC. The peak at the higher frequency we ascr ibe to the PMC along smooth sections of plasmalemma and that at the lo wer frequency we ascribe to the PMC in plasmalemmasomes (charasomes). We found that this peak was not present in spectra obtained from cells without plasmalemmasomes. Our model for the ultrastructure of the PMC and plasmalemmasomes is in good agreement with electron micrographs o f these regions. Additionally, our measurements give a physiological r ange for the electrical properties of the PMC. Conductance and capacit ance ranges are 13.6-52 S m-2 and 6.7-17 mF m-2 respectively.