H2O2 Metabolism During Senescence of Two Submerged Angiosperms Hydrilla and Ottelia: Changes in Enzyme Activities in Light and Darkness

Study of the role of H₂O₂ on senescence and photobleaching of chlorophyll revealed that pretreatment with H₂O₂ enhanced the loss of chlorophyll and protein in Hydrilla verticillata (L.f.) Royle and Ottelia alismoides (L.) Pers. leaves, more markedly so in the light than in the dark. Endogenous H₂O₂ and free phenol contents significantly increased during senescence, the effect being larger in light than in darkness. DCP (2,4-dichlorophenol, a monophenol) greatly accelerated the loss of chlorophyll and protein in the light while catechol (a diphenol) significantly retarded them. However, both these phenols retarded the loss of these components in the dark. Both peroxidase and chlorophyll oxidase activity greatly increased in light over dark treatment. The activity of superoxide dismutase and catalase declined more markedly in light than in darkness in either species. The possible involvement of oxygen free radicals and light-induced phenol peroxidase - H₂O₂ system in the photobleaching of chlorophyll and senescence development in the two submerged angiosperms has been suggested.