Respiration of Potato Mitochondria and Whole Tubers and Relation to Sugar Accumulation

SUMMARY: We have made a quantitative assessment of the changes in reducing and non‐reducing sugar contents and respiration in stored White Rose potato tubers as a function of temperature of storage. The increase in sugar content with decrease in storage temperature and the decrease in sugars with increase in temperature is accounted for in only a minor way by the corresponding decrease or increase in respiratory’activity of the tubers. The maximal possible contribution of respiratory activity to the changes in sugar content varied from less than 1% to 13% depending on the particular storage conditions. The temperature‐dependence of respiratory activity of potato mitochondria was compared to that of whole tubers, and a quantitative comparison was made of the potential respiratory activity of the mitochondria to respiration of the whole tubers. The potential mitochondrial activity is such that respiration of whole tubers would not be limited by this factor at any temperature studied although it is recognized that the effect of mitochondrial activity could be an indirect one. Unlike whole tubers, mitochondria displayed a temperature response typical of an enzymic reaction with an apparent energy of activation of 14,000 cal/mole with succinate as substrate. The temperature‐dependence of potato mitochondrial respiration is typical of that found for other plant mitochondrial systems but differs markedly from that of mitochondria of mammals and poikilotherms.