Browsing by Author "Alarcon, Emilio"

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    Abundances and morphotypes of the coccolithophore Emiliania huxleyi in southern Patagonia compared to neighbouring oceans and Northern Hemisphere fjords
    (COPERNICUS GESELLSCHAFT MBH, 2021) Diaz Rosas, Francisco; Alves de Souza, Catharina; Alarcon, Emilio; Menschel, Eduardo; Gonzalez, Humberto E.; Torres, Rodrigo; von Dassow, Peter
    Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (omega(cal)). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late spring 2015 and early spring 2017. Surface omega(cal) exhibited large variations driven mostly by freshwater inputs. High-omega cal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. omega(cal) ranged from 2.0-2.6 in the western Strait of Magellan and 1.5-2.2 in the inner channel and was subsaturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolithophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderately calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low omega(cal) values in Chilean and Peruvian coastal upwellings, were a minor component associated with high omega(cal) levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH and omega(cal) conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderately calcified A morphotype exhibited the widest niche breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically related coccolithophore species. The occurrence of E. huxleyi in naturally low pH-omega(cal) environments indicates that its ecological response is plastic and capable of adaptation.
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    Chemiluminescence associated with singlet oxygen reactions with amino acids, peptides and proteins
    (WILEY, 2007) Alarcon, Emilio; Henriquez, Carola; Aspee, Alexis; Lissi, Eduardo A.
    Low level chemiluminescence (CL) is observed after protein oxidation mediated by singlet oxygen produced in Rose Bengal (RB) irradiation. This CL lasts for several minutes after the end of the photolysis. In this work, the mechanism of the process was assessed from the spectral characteristics of the CL and the effect of antioxidants (Trolox or ascorbate), Ebselen (a compound with peroxidase-like activity), azide (a singlet oxygen scavenger) and D2O, added prior to or after RB irradiation. It is concluded that most of the light emission is due to formation of excited states generated in the decomposition of peroxides and/or hydroperoxides accumulated during the photolysis. Experiments carried out in the presence of several amino acids (Cys, Met, His, Tyr and Trp) and di- and tripeptides suggest that peroxides (and/or hydroperoxides) of Trp residues are mainly responsible for the CL observed after singlet oxygen-mediated protein oxidation. The much weaker CL observed after the oxidation of proteins without Trp residues supports this conclusion. A comparison of the results obtained employing free Trp, Ala-Trp and Trp-Ala dipeptides, Ala-Trp-Ala tripeptide and Trp-containing proteins supports the conclusion that blocking the amino group of the Trp moiety strongly increases the efficiency of the chemilummescent process, producing approximate to 2.5x10(-8) photons per oxidized Trp group in Alla-Trp. A mechanism comprising two chemiluminescent oxidation pathways of Trp residues is proposed to explain the results.