Abstract
Various tissues of the marine bivalve__Mytilus galloprovincialis__were analysed histochemically for oxidases capable of generating reactive oxygen species (ROS) using the ceriumβDAB technique. Incubations were performed on unfixed cryostat sections using polyvinyl alcohol and semipermeable membranes. High xanthine oxidoreductase anddβamino acid oxidase (DAOX) activities were observed in kidney epithelial cells of mussels. DAOX also presented a strong activity in all the digestive epithelia. No xanthine oxidase activity was observed in any of the mussel tissues tested suggesting the presence of an enzyme only showing dehydrogenase activity. Mannitol oxidase, associated with special organelles called βmannosomesβ of terrestrial gastropods, presented a weak activity in the stomach epithelium and a strong specific activity in the haemocytes. Only DAOX presented a discrete granular distribution compatible with a peroxisomal compartmentalization. No urate oxidase activity could be demonstrated in tissues of mussels. These observations suggest a role for peroxisomes in ROS generation and determine the tissues capable of producing oxygen radicals in the digestive gland. This study raises the question of the behaviour of these enzymes in conditions in which ROSβgenerating organic xenobiotics are accumulated in the digestive gland of molluscs.