The effect of desiccation on the activities of antioxidant enzymes in lichens from habitats of contrasting water status

Changes in the activities of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase were measured during wetting and drying c ycles in the lichens Peltigera polydactyla, Ramalina celastri and Teloschis tes capensis. These species normally grow in moist, xeric, and extremely xe ric microhabitats respectively. Enzyme activity was measured shortly after collection, after rehydration for 48 h, after desiccation for 14 d and 28 d , and during the first 30 min of subsequent rehydration with liquid water. In all species, enzyme activities tended to rise or stay the same following rehydration. After desiccation for 14 d, enzyme activities decreased, then decreased further to very low values after desiccation for 28 d. In all sp ecies, including the T. capensis from an extremely xeric habitat, the activ ities of all enzymes remained at very low values during the 30 min followin g rehydration, and were therefore unavailable to remove any reactive oxygen species accumulating in lichen tissues as a result of desiccation stress. We suggest that the enzymatic antioxidants are more likely to be involved i n removing reactive oxygen species produced during moderate stress or the n ormal metabolic processes of lichens.