Glucose catabolism in leaves of cold-treated winter rape plants

The ratio of glycolysis to the pentose phosphate pathway (PPP) estimated by yields of 14CO2 from 14C-1- or 14C-6-glucose and C6/C1 ratio as well as the activities of the key enzyme of PPP, glucose 6-phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) and glycolysis: PPi-dependent and ATP-dependent phosphofructokinases (PPi-PFK, E.C. 2.7.1.90 and ATP-PFK, E.C. 2.7.1.11) were determined in cold-acclimated winter rape plants (Brassica napus L. var. oleifera cv. Górczański). The results of measurements performed at 2 °C and 20 °C showed that the effect of temperature on 14CO2 output was more pronounced for 14C-6-glucose than for 14C-1-glucose. During the first 8 days of plant growth in the cold, the 14CO2 output from both forms of the labelled glucose, and the C6/C1 ratio decreased when measured at 2 °C or 20 °C. After two weeks of cold acclimation, glucose catabolism became less responsive to the temperature of measurement and the C6/C1 ratio remained stable. The results of enzymatic measurements showed a predominance of G6PDH activity in comparison to that of the glycolytic enzymes. These results indicate that under cold conditions, the contribution of PPP in glucose catabolism increases in relation to glycolysis; thereby, PPP affects the redox status of cell.