EFFECTS OF HEAT-TREATMENT ON PLASMA-MEMBRANE OF APPLE FRUIT

Apple fruits (Golden Delicious) were held at 20 or 38 degrees C for four days prior to storage at 0 degrees C for five months. Plasma membrane composition and function were examined before and after storage. While fruits were held at 38 degrees C, membrane microviscosity and sterol content increased, phospholipid fatty acids became more saturated and there was increased electrolyte leakage from apple fruit discs. ATPase activity increased during the first day of heating and decreased thereafter. After five months of storage at 0 degrees C, microviscosity and leakage were lower in heated fruit, and increased more slowly during ripening at 20 degrees C than in control apples. ATPase activity was similar in both treatments. Phospholipid content was higher in membranes from heated apples than in those from control fruit. Although fatty acid content in apples from both treatments was similar after storage, the loss of unsaturated fatty acids during ripening occurred more rapidly in control apples. Heated apples recovered rapidly from stress and acclimated more successfully to 0 degrees C than did control apples.