ELECTRICAL-IMPEDANCE ANALYSIS IN PLANT-TISSUES - ON THE BIOLOGICAL MEANING OF COLE-COLE-ALPHA IN SCOTS PINE NEEDLES

Electrical impedance spectra (80 Hz-1 MHz) in Scots pine needles were found to be characterized by spectrum skewness in the Cole-Cole plot. These spectra were subjected to analysis with two distributed models: (i) the Cole-Cole function and (ii) an equivalent circuit which takes account of the presence of air spaces within the needles (Model-A). In analysis with untreated needles (without artificial infiltration with water), Model-A fitted better than the Cole-Cole function to the expe rimental data. After infiltration of water into the needles, the exten t of spectrum skewness was substantially decreased compared with the p re-infiltration condition and the Cole-Cole function fitted better tha n Model-A to the measured impedance data. The Cole-Cole alpha decrease d from 0.47 in non-infiltrated needles to 0.42 in the infiltrated need les. The exceptionally large value of alpha in non-infiltrated needles can be explained by the presence of air spaces, which produce transmi ssion line properties in the mesophyll. In support of the validity of Model-A, this new model provided specific membrane resistances of 1190 +/-83 Omega cm(2) in cold hardened and non-hardened needles respective ly. These specific membrane resistance are comparable with previous re ports of membrane resistances in other biological systems. It is concl uded that in this exceptionally spongy tissue, Cole-Cole alpha is like ly to be due to the effects of the transmission line properties of cel ls which are surrounded by air spaces and only thin cell walls outside the insulating cell membranes.