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Dehydroascorbate and traces of ascorbate were present apoplastically in living spruce (Picea abies) twigs. Since the proposed apoplastic ascorbate degradation pathway contains several steps that possibly generate H₂O₂, the effects of ascorbate and some of its degradation products were tested on apoplastic H₂O₂ concentrations in a cell culture of P. abies as a model and on non-enzymic H₂O₂ production in vitro. Ascorbate scavenged H₂O₂ in the culture medium of lignin-producing Picea cells and in spent and boiled spent medium; in the presence of Cu²⁺ or fresh medium, ascorbate led to the non-enzymic generation of H₂O₂. Preparations of dehydroascorbate (the initial oxidation-product of ascorbate), and diketogulonate (the hydrolysis-product of dehydroascorbate) induced H₂O₂ accumulation both non-enzymically and enzymically in Picea cell-suspensions. Paper electrophoresis showed that the …