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Journal of Experimental Biology 168,219-241 (1992)
Published by Company of Biologists 1992

Oxygen Radical Production in the Sea Anemone Anthopleura Elegantissima and its Endosymbiotic Algae

JAMES A. DYKENS ¹, J. MALCOLM SHICK ², CRAIG BENOIT ³, GARRY R. BUETTNER ⁴, and GARY W. WINSTON ³

¹ Department of Biology, Grinnell College, Grinnell, IA 50112, USA; Present address: Immunopathology, Parke-Davis Pharmaceutical Research, 2800 Plymouth Road, Ann Arbor, MI 48106, USA
² Department of Zoology, University of Maine, Orono, ME 04469, USA
³ Department of Biochemistry, Louisiana State University, Baton Rouge, LA 70803, USA
⁴ ESR Center, College of Medicine, University of Iowa, Iowa City, IA 52242, USA

Host animals in algal-invertebrate endosymbiotic associations are exposed to photosynthetically generated hyperoxia while in sunlight, conditions conducive to photodynamic excitations and production of cytotoxic oxygen-derived radicals such as the superoxide anion (O₂^-) and the hydroxyl radical (OH). All previous vidence of oxyradical production in symbiotic associations has been circumstantial. We here present direct evidence, from electron paramagnetic resonance studies on tissue homogenates of the photosymbiont-containing sea anemone Anthopleura elegantissima (Brandt), of substantial light-dependent OH and O₂ production that is abolished by dichlorophenyldimethylurea (DCMU), an inhibitor of photosynthesis. Shade-adapted A. elegantissima lacking endosymbiotic algae likewise show OH production upon illumination. The latter flux is not dependent on photosynthesis, and DCMU has no effect. Rather, OH production in apozooxanthellate anemones is via direct photoexcitations. The selective reaction of dimethyl sulfoxide (DMSO) with OH to form methane sulfinic acid allows quantification of OH produced in vivo. Such in vivo measurements confirm the production of OH in both host and algae in illuminated zooxanthellate anemones, where the amount of OH in the zooxanthellae is disproportionately large relative to their fractional contribution to the biomass of the symbiosis. In vivo studies using DMSO also suggest a photochemical production of OH in apozooxanthellate anemones exposed to simulated sunlight enriched in ultraviolet (UV) wavelengths, and the enhancement by UV light of OH production in zooxanthellate individuals. Such chronic radical exposure necessitates defenses

Key words: superoxide radical (O₂^-), hydroxyl radical (OH), symbiosis, electron paramagnetic resonance, photo-oxidative stress, zooxanthellae, dimethyl sulfoxide, spin trap, Anthopleura elegantissima

Accepted on March 31, 1992