BIOCHEMICAL ADAPTATIONS OF NEREIS-DIVERSICOLOR (POLYCHAETA) TO TEMPORARILY INCREASED HYDROGEN-PEROXIDE LEVELS IN INTERTIDAL SANDFLATS

Toxic hydrogen peroxide (H2O2) is photochemically generated in hyperoxic and normoxic intertidal pools. Surprisingly high amounts of H2O2 penetrate the redoxcline, and are measurable in pore water in spite of the anoxic conditions prevailing there. Bioturbate macrofauna inhabiting these sediments encounters oxic conditions with peroxide in surface pools and anoxic conditions with peroxide in the sediment. We studied antioxidative properties in the polychaete Nereis diversicolor. Antioxidant enzyme activities of catalase and superoxide dismutase (SOD) showed annual variations correlated to the environmental peroxide concentrations. Epitokous specimens from April exhibited very high enzyme activities. Catalase was predominantly localised in the mitochondria and is inducible by peroxide incubation under experimental conditions. SOD activities were not inducible during oxic peroxide incubation. In contrast, SOD had higher activities when the worms were kept anoxically in the presence of hydrogen sulfide (100 muM) or hydrogen peroxide (5 muM). The radical stress the worms encountered during anoxic peroxide incubation was reflected by a highly increased lactate formation. Under oxic conditions 500 nM H2O2 decreased oxygen uptake of N. diversicolor by 38 %. In epitokous N. diversicolor, this was accompanied by a conversion of heme to the green pigment biliverdin, a potent antioxidant. Biliverdin Wds accumulated by the worms during oogenesis under natural conditions. Therefore its formation during spawning seems to be a response to increasing hydrogen peroxide concentrations in sediment pore water during spring. Biliverdin was not formed under anoxic conditions, because the conversion requires oxygen. Atokous worms lacked the ability to form biliverdin when exposed to peroxide.