Contrasting roles for pyrophosphate:fructose-6-phosphate phosphotransferase during aging of tissue slices from potato tubers and carrot storage tissues

Abstract

The role of pyrophosphate:fructose-6-phosphate phosphotransferase (PFP) during wounding-induced respiration in tissue slices from a starch-storing tissue (potato tubers) and a sucrose-storing tissue (carrot root) has been compared. (a) In both tissues, there was a rapid decrease of glycerate-3-phosphate, a gradual increase of triose-phosphate and fructose-1,6-bisphosphate, no change or an increase of hexose phosphates, and a rapid increase of fructose-2,6-bisphosphate. Inorganic pyrophosphate responded differently in the two tissues, decreasing in potato and increasing in carrot. (b) Comparison of key enzyme activities in extracts showed differences between the two tissues. Potato tubers contained high pyruvate kinase, relative to ATP-dependent phosphofructokinase, and also contained high PFP. Carrot roots contained comparable capacities of pyruvate kinase and ATP-dependent phosphofructokinase, and two-fold lower PFP. (c) It is argued that PFP probably has a glycolytic function in potato tubers, supplementing the rather low ATP-dependent phosphofructokinase activity. In carrot, ATP-dependent phosphofructokinase is relatively high, allowing PFP to operate in the reverse direction, and generate inorganic pyrophosphate which is needed for sucrose mobilisation.