Occurrence of a Temperature-induced Phase Transition in Mitochondria Isolated from Apple Fruit

Mitochondria were isolated from fruit of six cultivars of apples differing in susceptibility to the physiological disorder, low temperature breakdown. The state 3 rate of succinate-dependent oxygen uptake and the motion of a spin label were measured at from 0 to 25 C. Arrhenius plots of the data showed that the apparent energy of activation of both respiration and motion of the spin label increased abruptly at low temperatures indicative of a temperature-induced phase change in the membrane lipids. The changes were detected with mitochondria from all of the cultivars, but the temperature at which the changes occurred did not correlate with the susceptibility of the cultivars to low temperature breakdown.