CADIC   02618
CENTRO AUSTRAL DE INVESTIGACIONES CIENTIFICAS
Unidad Ejecutora - UE
capítulos de libros
Título:
Oxidative stress in Antarctic algae and molluscs
Autor/es:
MALANGA G; GÓNZALES P; ESTEVEZ M S; S. PUNTARULO
Libro:
Reports on Polar and Marine Research. The Antarctic ecosystem of Potter Cove King-George Island (Isla 25 de Mayo)
Referencias:
Año: 2008; p. 208 - 216
Resumen:
Since the discovery of the importance of radical reactions in normal biological processes, there has been an explosion of research into pro-oxidant and antioxidant processes, principally in mammalian. The normal fate of most of the molecular oxygen consumed by animals is tetravalent reduction to water coupled to the oxidation of food and the production of energy. Partial reduction results in the formation of reactive oxygen species, including superoxide anion radical (O2-), hydroxyl radical (·OH), peroxyl radical (ROO·), alkoxyl radical (RO·), hydrogen peroxide (H2O2), singlet oxygen (1O2) and peroxynitrite (ONOO-). It has been estimated that about 1–3% of O2 consumed in animal systems is converted to ROS. Moreover, Fe can catalyze the conversion of H2O2 into ·OH, via Fenton or Haber-Weiss reactions. Of more recent interest, has been reactive oxygen species production and resulting oxidative damage as a mechanism of toxicity in aquatic organisms. Recently, new information on the formation of reactive oxygen species by mitochondria in aquatic organisms was reported. Reactive species produced in biological systems are detoxified by antioxidant defenses, which are broadly investigated in aquatic organisms. The aim of this work was to characterize the oxidative status of both, algae and molluscs, isolated from the nearshore waters around the Antarctic Continent and islands (Potter Cove, King George Island, Antarctic Peninsula).   A number of biochemical alterations have been described following exposure of cells to partially reduced oxygen species generated under stressful environmental conditions. The significant increase in NO and related enzymatic activities at the triggering of log phase of growth was observed in the two tested species from Antarctic environments (Chlorella sp and Chlamydomona sp) but not in Chlorella cells from temperate climate. This fact suggested that NO could be part of the signalling network operative under specific growing conditions, such as low temperature stress, and could be an adaptive mechanism to allow cell survival. Since previous data indicated that nitrate uptake by Antarctic phytoplankton and ice algae is decreased by UV exposure, further studies into NO metabolism in Antarctic algae should be considered to explore the effect of the change of environmental conditions (UV, Fe, etc.) on cellular growth. Intertidal limpets, like N. concinna, undergo transient metabolic depression during low tides, a behaviour common to intertidal molluscs during air exposure. The shell closure strategy prevents desiccation and predation during low tides and triggers a hypoxic response in the enclosed animal, consisting in metabolic reduction and on switch to anaerobic metabolism. Thus, adaptation to high shore environments involves extended periods of metabolic reduction which may reduce the overall rate of metabolically produced oxygen radicals compared to subtidal limpet species. Morever, oxidative stress may be enhanced by a frequent shift between low oxygen and normoxic conditions, comparable to ischemia-reperfusion insult. In N. concinna specimens, we conjecture that Antarctic high shore conditions, involving regular exposure to air and presumably also thermal stress on sunny days during the Antarctic summer season, cause a necessity to ward off higher oxygen radical species production by increasing its antioxidant defence. Moreover, our data shows that the highly abundant polar bivalve L. elliptica obviously accumulates significant levels of Fe, thus it might also be prone to oxidative stress and presumably will constitute a sensitive monitoring organism for studies of contamination and human impact on Antarctic coastal waters. Taken as a whole, the data presented here on oxidative stress conditions in algae and molluscs from King George Island showed that a wide array of complex metabolic pathways could be involved to limit oxidative damage and allow survival of the species adapted to the extreme environmental conditions