Electrical conductance of red onion scale tissue during freeze-thaw injury

Abstract

SUMMARY Changes in the electrical conductance of red onion bulb scale tissue in relation to freeze–thaw treatments were measured by implanting wire electrodes in pieces of the tissue. Continuous measurements were made during the imposition of the stress. Tissue frost-hardiness was assayed by both vital staining and the retention of anthocyanin in vacuoles of outer epidermal cells. Results showed that the tissue had an LT50 of — 15°C. Treatments of — 3 and — 6°C caused only sublethal injury (no dead cells). Tissue conductance was stable during cooling cycles involving only supercooling, but all frozen–thawed samples displayed a rapid increase in conductance during thawing, followed by constant conductance within 30 min of the initiation of thawing. Estimation of the relative quantities of electrolytes released showed that apoplasmic electrolytes increased by 300–400% following sublethal injury and by 600–900% following lethal injury. Electrolyte leakage following sublethal injury was unaffected by time spent frozen, but freeze–thaw cycles produced cumulative leakage.