The relationships of potato (Solanum tuberosum L.) tuber membrane permeability and membrane lipid composition to sugar accumulation were examined. Tubers from four potato cultivars were stored for 40 weeks at 30C and 90C. Rates of tuber membrane electrolyte leakage, total fatty acid composition, free fatty acid composition, and sugar content were measured throughout the storage period. Storage of tubers at 30C caused dramatic increases in total fatty acid unsaturation, membrane permeability, and sugar content compared to tubers stored at 90C. Cultivars with higher levels of fatty acid unsaturation had lower rates of membrane electrolyte leakage and lower sugar contents. We propose that high initial levels or high induced levels of membrane lipid unsaturation mitigate increases in tuber membrane permeability during storage, thus positively influencing the processing quality of stored potato tubers.Sucrose, glucose, and fructose are the major sugars which accumulate in potato (Solanum tuberosum L.) tubers. High levels of reducing sugars (glucose and fructose) lower the suitability of tubers for processing. Reducing sugars react with free amino groups during frying leading to the formation of a brown pigment, which can make chips and french fries (crisps and chips in the United Kingdom) unacceptable for consumers. Excess sugars in stored tubers commonly arise from two situations. Storage of tubers longer than 7 months can lead to 'senescent sweetening,' and storage below approximately 7°C can lead to 'cold-induced sweetening' (1). However, low temperature storage of potato tubers can also have the beneficial results of lowered respiration rates, slowed physiological aging, inhibition of sprouting, reduced evaporative water loss, and minimized microbial pathogenesis (1).Sugars accumulate in tubers when there is an imbalance between starch degradation, starch synthesis, and respiration of carbohydrate. One potential source of metabolic imbalance ' From a disseration submitted to the graduate school of the