Measurement of heat injury in plant tissue by using electrical impedance analysis

Electrical impedance spectra (100 Hz to 800 kHz) were measured in pieces of potato (Solanum tuberosum L.) tuber tissue that had been heat stressed. Analysis of the impedance data based on equivalent circuits showed that tissue injury was revealed as decreases in membrane capacitance and extracellular resistance. By using a single piece of tissue, membrane thermostability (in relation to heat stress temperature or time of heat stress) was measured. Nonstressful temperature changes produced changes in tissue parameters that were fully reversible when the direction of temperature change was reversed. Stressful temperature changes produced irreversible changes in parameters. During heat injury, decrease in extracellular resistance always preceded a decrease in tonoplast capacitance. It is suggested that two stages may be involved in heat injury to membranes: functional injury leading to electrolyte leakage to extracellular space, and structural damage leading to membrane disintegration. It is concluded that e...