Redox control of oxidative stress responses in the C3-CAM intermediate plant Mesembryanthemum crystallinum

Crassulacean acid metabolism (CAM) is named after the Crassulaceae family of succulent plants, in which this type of metabolism was first discovered at the beginning of the 19th century. In recent years, Mesembryanthemum crystallinum, a facultative halophyte and C-3-CAM intermediate plant, has become a favoured plant for studying stress response mechanisms during C-3-CAM shifts. Recent studies in this and related areas can provide a new model of how such mechanisms could operate for acclimation to high salinity or excess excitation energy. These include roles for photosynthetic electron transport chain components and reactive oxygen species. The diumal rhythms of catalase, superoxide dismutase and some CAM-related enzyme activities are discussed in relation to the protective role of photorespiration during C-3-CAM transition. The role of excess excitation energy and redox events in the proximity of photosystem II (PSII) in regulation of ascorbate peroxidase (APX), superoxide dismutase (SOD): copper/zinc SOD (Cu/ZnSOD), iron SOD (FeSOD); and NAD(P)-malic enzyme gene expression are also discussed. We suggest a model in which the chloroplast plays a major role in regulation of acclimation to high salinity and/or excess exitation energy. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.