Enzymes of the pentose phosphate pathway in callus-forming potato tuber discs grown at various temperatures

Abstract

In callus-forming potato tuber discs growing at a low culture temperature (8°C) the activities of glucose-6-phosphate dehydrogenase, EC 1.1.1.49 (G6PDH) and 6-phosphogluconate dehydrogenase, EC 1.1.1.44 (6PGDH) were twice as high as during growth at a high culture temperature (28°C). After a transfer from 8°C to 28°C and vice versa an adaptation of 6PGDH activity to the new culture temperature took place. Phosphofructokinase, EC 2.7.1.11 (PFK) and alcohol dehydrogenase, EC 1.1.1.1 (ADH) activities tended to be lower during growth at a low culture temperature (ratio 6PGDH/PFK 3:1 in 8°C callus and 1:1 in 28°C callus).C1C6 ratios were independent of culture temperature, suggesting that although the in vitro capacity of the pentose phosphate pathway (PPP) is higher at low culture temperatures, the relative in vivo PPP activity is not influenced by the culture temperature. However, products of the PPP probably will re-enter glycolysis, thereby also releasing C6. It is speculated that at a low culture temperature this bypass of part of glycolysis has a special function to avoid the cold-sensitive PFK.