Figure 1

Peach sugar metabolism [ [3], [12], [30]]. Proposed sugar metabolism pathway in peach fruit as built from partial literature data. The metabolites and enzymatic capacities that were assayed in the present study are framed and highlighted. In peach, carbon enters the fruit in the form of sucrose and sorbitol, the two main end products of photosynthesis in source organs [12]. Sucrose, which is the major sugar in peach fruit, is hydrolysed into fructose and UDP-glucose by sucrose synthase (SuSy, EC 2.4.1.13) in the cytosol and into fructose and glucose by invertases, in the cell wall, the cytosol (NI, neutral invertase EC 3.2.1.26) or the vacuole (AI, acid invertase EC 3.2.1.26). Cytosolic sorbitol is converted to fructose via sorbitol dehydrogenase (SDH, EC 1.1.1.14) and to glucose via sorbitol oxidase (SO) [12]. Fructose and glucose can be stored in the vacuole or phosphorylated in the cytosol via reactions catalyzed by fructokinase (FK, EC 2.7.1.4) and hexokinase (HK, EC 2.7.1.1), respectively, to form fructose-6-phosphate (F6P) and glucose-6-phosphate (G6P) [3]. F6P is then converted into fructose 1,6-bisphosphate (F16BP) by PPi-phosphofructokinase (PFP, EC 2.7.1.90), ATP-phosphofructokinase (PFK, EC 2.7.1.11) and the inverse reaction is catalyze by fructose-1,6-bisphosphatase (F16BPase, EC 3.1.3.11) [30]. Phosphoglucose isomerase (PGI, EC 5.3.1.9), phosphoglucomutase (PGM, EC 5.4.2.2) and UDP-glucose pyrophosphorylase (UGPase, EC 2.7.7.9) catalyze the inter-conversion between the hexose phosphates. Sucrose phosphate synthase (SPS, EC 2.4.1.14) and sucrose-phosphate phosphatase (SPP EC 3.1.3.24), involve in the sucrose re synthesis via a futile cycle.