PHOSPHOFRUCTOKINASE IN RELATION TO SUGAR ACCUMULATION IN COLD-STORED POTATO-TUBERS

The accumulation of sucrose and reducing sugars in potato tubers (Solanum tuberosum L. cv. Bintje and a breeding clone KW74-2618) during storage at 2-degrees-C occurs with a concomitant decrease in maximum activity of the assumed cytosolic phosphofructokinase (PFK). This decrease is most extensive in cv. Bintje. The change is reversed when the tubers are transferred to 13-degrees-C. The activity of plastidic PFK hardly changes during the same experiments. The Arrhenius plots of cytosolic and plastid PFK are biphasic, showing a discontinuity at about 12.5-degrees-C and 14.5-degrees-C, respectively, with an increased slope as temperature is reduced to 2-degrees-C, indicating cold sensitivity. However, no cold inactivation of the partially purified PFK enzymes has been observed during incubation at low temperature during 90 min. The results are discussed in relation to the view that during cold storage of potato tubers diminished PFK activity plays a role in the reduction of the rate of glycolysis, causing sugars to accumulate.