In vivo plant impedance measurements and characterization of membrane electrical properties: The influence of cold acclimation

Abstract

A procedure to measure both the real (resistance) and complex (reactance) part of plant tissue impedance is described. Bare metal electrodes were used and the impedance of electrodes was determined by obtaining measurements at four interelectrode distances. The frequency ( f) dependence of the impedance of birdsfoot trefoil ( Lotus corniculatus L.) stems could be modeled, approximately, by a resistor representing an extracellular resistance, a resistor representing an intracellular resistance, and a resistor and capacitor representing cell membranes. However, the membrane parameters appeared to be frequency dependent. Therefore, they were characterized by calculating a time constant at each frequency. For example, for one plant stem the time constant (τ) decreased from 1.19 × 10 −3 sec at 101 hz to 1.36 × 10 −6 sec at 100 KHz. This decrease with frequency could be described by an equation of the form: ln(τ) = a + bln(f) + c(ln[ f]) 2. Cold acclimation increased ( P ⩽ 0.05) the intracellular resistance. But cold acclimation did not have a significant effect on estimates of the extracellular resistance, the membrane resistance, or the membrane time constant. Depending on the cultivar, cold acclimation either decreased or increased the estimate of membrane capacitance.