Oxidation of dehydroascorbic acid and 2,3-diketogulonate under plant apoplastic conditions

► Catabolism of vitamin C non-enzymically under conditions mimicking the apoplast. ► Dehydroascorbic acid + H2O2 yield two interconvertible oxalyl-threonate (OxT) isomers. ► 3-OxT and 4-OxT differ in acidity and are separable by paper electrophoresis. ► Diketogulonate + H2O2 yield two partially characterised acidic products. ► Possible signalling or defence roles of these metabolites await exploration.