MEASUREMENT OF HEAT INJURY IN PLANT-TISSUE BY USING ELECTRICAL-IMPEDANCE ANALYSIS

Electrical impedance spectra (100 Hz to 800 kHz) were measured in piec es of potato (Solanum tuberosum L.) tuber tissue that had been heat st ressed. Analysis of the impedance data based on equivalent circuits sh owed that tissue injury was revealed as decreases in membrane capacita nce and extracellular resistance. By using a single piece of tissue, m embrane thermostability (in relation to heat stress temperature or tim e of heat stress) was measured. Nonstressful temperature changes produ ced changes in tissue parameters that were fully reversible when the d irection of temperature change was reversed. Stressful temperature cha nges produced irreversible changes in parameters. During heat injury, decrease in extracellular resistance always preceded a decrease in ton oplast capacitance. It is suggested that two stages may be involved in heat injury to membranes: functional injury leading to electrolyte le akage to extracellular space, and structural damage leading to membran e disintegration. It is concluded that electrical impedance analysis i s useful in plant heat stress physiology.