Heat-shock Treatments Alter the Kinetics of Ion Leakage from Chilled Tomato Pericarp Tissue

Abstract

Heat-shock induced chilling tolerance in excised discs of tomato fruit pericarp tissue significantly alter the kinetics of chilling-induced ion leakage from the discs into an aqueous isotonic mannitol solution. Pericarp discs were excised from mature-green tomato fruit, trimmed of locular material to 5-mm thickness, held overnight (ca. 16 h) at 20 °C and then subjected to various heat-shock (45 °C) treatments before being chilled at 2.5 °C for up to 30 days. Two discs were immersed in 20 mL of 0.3 m mannitol in a 50-mL plastic centrifuge tube and the conductivity of the aqueous solution periodically measured. The tube was capped and frozen at -20 °C. Total conductivity was measured once the tube had warmed to 20 °C with shaking. The percent ion leakage was calculated as the percent of total, and subjected to an analysis to partition rates of leakage into symplastic and apoplastic components. The symplastic component was not affected by the heat-shock treatment, while the apoplastic component showed reductions consistent with reduced chilling-induced damage to the cellular membrane. The protective heat-shock treatments also significantly increased the tissues resistance to fungal infection.