MEMBRANE LIPID DYNAMICS AND LIPID-PEROXIDATION IN THE EARLY STAGES OFLOW-TEMPERATURE SWEETENING IN TUBERS OF SOLANUM-TUBEROSUM

Sugar accumulation and membrane lipid parameters associated with membr ane permeability in chilling injury and senescence were followed in th e early stages of low-temperature sweetening in Solanum tuberosum tube rs to monitor their dynamics. Norchip, a low-temperature sweetening-su sceptible potato cultivar, and North Dakota 860-2, a low-temperature s weetening-tolerant selection, were stored for 55 days at 4 and 12 degr ees C. Sugar accumulations were nor linear and were characterized by f luctuations or cycles over storage time. Sucrose cycling and accumulat ion were greatest for Norchip tubers stored at 4 degrees C as compared to the other treatments. increases in membrane permeability were not detected by increases in electrolyte leakage. No significant changes i n the phospholipid, galactolipid, free sterol levels or phospholipid t o Free sterol ratio were observed. The double bond index obtained from the fatty acid profiles of the total lipid fraction decreased signifi cantly (decreased unsaturation) for Norchip tubers at 4 degrees C over time. Free fairy acid and diene conjugation values fluctuated and inc reased over time for all treatments with greater amplitude of fluctuat ions observed for Norchip tubers stored at 4 degrees C. These latter e ffects may be due to the high levels of lipid acyl hydrolase and lipox ygenase found in potato tubers. When free fatty acid and diene conjuga tion values were plotted with glucose accumulation over time, a possib le relationship among the variables was revealed. The observed peroxid ation products could relate low-temperature stress and the resultant l ow-temperature sweetening to chilling injury and drought stress, The a nti-oxidative potential of potato tubers should be considered for futu re cultivar development as a mechanism to lessen the severity or rate of low-temperature sweetening development.