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Flavin-containing polyamine oxidase is a hydrogen peroxide source in the oxidative response to the protein phosphatase inhibitor cantharidin in Zea mays L

Cona, Alessandra, Rea, Giuseppina, Botta, Maurizio, Corelli, Federico, Federico, Rodolfo, Angelini, Riccardo
Journal of experimental botany 2006 v.57 no.10 pp. 2277-2289
Zea mays, corn, oxidoreductases, hydrogen peroxide, cantharidin, oxidative stress, oxidation, phosphoprotein phosphatase, enzyme inhibitors, mesocotyls, spermidine, superoxide anion, histochemistry, epidermis (plant), in vitro studies, intercellular spaces
In this study, the specific contribution of polyamine oxidase (PAO), a hydrogen peroxide (H₂O₂)-producing enzyme, to the oxidative burst induced in maize mesocotyl by the phosphatase inhibitor cantharidin was examined. For this purpose, a pharmacological approach was applied using, either in vitro or in vivo, two strong inhibitors of maize PAO (MPAO), N-prenylagmatine (G3) and its structural analogue Ro5, as well as diphenyleneiodonium (DPI), an inhibitor of the phagocyte NAD(P)H oxidase. DPI was shown to be a good MPAO inhibitor in vitro. G3, Ro5, and DPI were very effective in inhibiting in vivo the extracellular accumulation of H₂O₂ that is released by mesocotyl segments upon spermidine supply. G3 and Ro5 did not show any inhibition in vitro of either horseradish peroxidase or barley oxalate oxidase. Moreover, G3 and Ro5 did not inhibit the extracellular accumulation of superoxide radical that is released in vivo upon NADH supply. G3, Ro5, and DPI strongly affected H₂O₂ production induced in maize mesocotyl by cantharidin. Histochemical localization of H₂O₂ in cantharidin-treated mesocotyl cross-sections revealed an increase of H₂O₂-specific staining in the epidermal and subepidermal tissues. The effect was also inhibited by G3 and DPI. Moreover, an increase in MPAO activity was observed in the same tissues upon cantharidin treatment. All these data suggest that G3 and Ro5 behave as powerful and selective inhibitors of MPAO activity either in vitro or in vivo and that MPAO activity contributes to a major part of the cantharidin-induced H₂O₂ synthesis in the apoplastic milieu of maize mesocotyl.