Meeting Abstract

P2.176  Monday, Jan. 5  Patterns of Antioxidant Defenses Vary Among Zooxanthellate Symbioses TAPLEY, D.W.; Salem State College, MA dtapley@salemstate.edu

Cnidarian hosts experience hyperoxia as a result of photosynthesis by their endosymbiotic zooxanthellae. As a result, these hosts experience elevated exposure to reactive oxygen species (ROS), including superoxide, hydrogen peroxide, and the hydroxyl radical. The primary defenses against ROS in most metazoans include the enzymes superoxide dismutase (SOD) and catalase (CAT) as well as several low-molecular-weight organic molecules such as ascorbate, glutathione, and urate. Some cnidarian hosts, such as sea anemones in the genus Aiptasia, do not regulate activities of SOD and CAT in response to artificially elevated oxygen tensions or acclimation to increased light intensities. In fact, SOD activity is remarkably low in this genus. Other cnidarians, however, such as the temperate sea anemone Anthopleura elegantissima, do regulate some of these enzymes. The primary defenses against ROS in Aiptasia spp. appear to be saturating concentrations of uric acid, a potent scavenger of hydroxyl radicals, and constitutively elevated activities of CAT. Furthermore, CAT activity is inversely correlated with acclimation irradiance, indicating that direct photoinactivation of catalase in this symbiosis occurs. Given that defenses against ROS in other cnidarian zooxanthellate symbioses follow different patterns, including more robust enzymatic defenses, studies of such defenses among symbiotic cnidarians need to consider the exact pattern of defenses for the species under consideration.