Efficiency of antioxidant response in Spartina densiflora: An adaptative success in a polluted environment

The effects of different culture conditions, unpolluted and polluted substrates, on an antioxidative system – antioxidant enzymes, such as catalase, ascorbate peroxidase and guaiacol peroxidase, and ascorbic acid – were investigated to establish its relationship with the acclimatization success of Spartina densiflora. Plants of this species growing in the polluted Odiel marshes (Huelva, Spain) showed high levels of catalase, ascorbate and guaiacol peroxidase activities and ascorbate concentration (reduced and oxidized ascorbate). In addition, we found significant oxidation of the ascorbate pool, since only 40% of ascorbate was reduced, and low levels of photosynthetic pigments, suggesting that an oxidative stress was impairing S. densiflora. Transplantation to an unpolluted substrate in the laboratory led to a gradual change in all tested parameters: antioxidative activities and total ascorbate concentration decreased while the percentage of reduced ascorbate and pigment concentrations increased; these data agreed with the hypothesis that oxidative stress conditions in S. densiflora habitat were due to a polluted substrate. After 28 days, the plants were transplanted for a second time to polluted conditions, equivalent to those in their habitats, and a rapid alteration of the antioxidative system was observed. In the first 24 h, catalase and guaiacol peroxidase activities and ascorbate concentration increased greatly and the percentage of reduced ascorbate fell drastically. Regardless of this fact, ascorbate peroxidase activity did not change until the end of the first week, while photosynthetic pigments declined at a constant rate during the whole culture period. Subsequently, we found that the antioxidative system improved its reductive capacity gradually and slowly – over weeks – but this reductive power was rapidly lost within days or even hours. It may be concluded that S. densiflora undergoes oxidative stress in its natural environment and is able to modulate its antioxidative system, based on the degree of pollution, in order to acclimatize successfully to its fluctuating environment.