Localisation of antioxidant enzymes in the cnidarians Anemonia viridis and Goniopora stokesi

Antioxidant enzymes scavenge to protect cells against destructive oxyradicals. In excess, reactive radicals can have wide-reaching consequences, including lipid peroxidation, protein degradation and DNA damage, resulting in tissue damage and cell death. Recently, oxyradicals have been implicated in coral-bleaching, but only the activities of antioxidant enzymes in the host and endosymbiotic algae have been reported. To locate the potential cellular targets of excess oxyradicals in cnidarians, it is important to establish in which cell areas these enzymes are active. Using immunocytochemical techniques, the antioxidant enzymes superoxide dismutase [SOD], catalase [CAT] and glutathione peroxidase [GPX] were localised in the sea anemone Anemonia viridis (Forskal) and the coral Goniopora stokesi (Edwards & Haime). Using affinity-purified primary antibodies and transmission electron microscopy, antioxidant enzymes were found predominantly associated with granulated vesicles, accumulation bodies of endosymbiotic algae and cnida. SOD and CAT gold-labelling was localised in all forms of cnida, with SOD being particularly pronounced on the ruptured threads and shafts of b-mastigophores in A. viridis, possibly suggesting that the b-mastigophores had undergone autolysis and required SOD to prevent damage to host cells. The presence of both SOD and CAT in the accumulation body of endosymbiotic algae is consistent with the hypothesised role of these bodies in digestion and cell-ageing. CAT was also found in isolated electron-dense bodies, often near microvillous borders in G. stokesi. Similar bodies were recorded in A. viridis, but contained GPX rather than CAT. GPX was also present in symbiotic algae, where it was associated with electron-dense bodies.