Regulation of Hexose-Phosphate Cycle Determines Glucose and Fructose Accumulation in Cherimoya (Annona cherimola Mill.) during Ripening

Summary Cherimoya ( Annona cherimola Mill. cv. Fino de Jete ) is a climacteric fruit. Starch stores are converted mainly to glucose and fructose in equimolar concentrations during ripening. There is little accumulation of sucrose, which is consistent with the induction of invertase 2 days after harvesting. Activities of enzymes involved in the hexose-phosphate cycle have been determined during ripening. ATP-dependent phosphofructokinase shows a slight increase in maximum velocity independent of the presence of fructose 2,6-bisphosphate. Pyrophosphate-dependent phosphofructokinase and fructose 1,6-bisphosphatase, on the other hand, are activated and inhibited by fructose 2,6-bisphosphate, respectively, at the onset of ripening. Activities of these enzymes, as well as concentrations of fructose 2,6-bisphosphate, fructose 1,6bisphosphate and fructose 6-phosphate, suggest that glycolysis and gluconeogenesis are differentially activated and hexose-phosphate cycling is important in the regulation of carbon flux from starch during ripening.