Effect of cold acclimation on bulk tissue electrical impedance: I. Measurements with birdsfoot trefoil at subfreezing temperatures.

The resistive and reactive components of electrical impedance were measured for birdsfoot trefoil (Lotus corniculatus L.) stems at freezing temperatures to -8 degrees C. As temperature decreased the specific resistance at frequencies between 49 hertz and 1.11 megahertz of stems from cold acclimated plants increased more rapidly than from nonacclimated plants. This temperature dependence of specific resistance could be characterized by an Arrhenius activation energy; cold acclimated stems had a larger Arrhenius activation energy than nonacclimated stems. The low frequency resistance is believed to characterize the extracellular region of the stems and the high frequency resistance is believed to characterize the intracellular region of the stems. Cold acclimation increased the intracellular but not the extracellular resistance at nonfreezing temperatures. Cold acclimated stems were not injured by freezing to -8 degrees C and thawing, but nonacclimated stems were injured by freezing to temperatures between -2.2 and -5.6 degrees C and thawing. Injury to nonacclimated stems at freezing temperatures below -2.2 degrees C was indicated by a decrease in the ratio of resistance at 49 Hz to that at 1.11 megahertz.