Effect of metallic pollutants in marine algae pigments contents and evaluation of carotenes structural features in mimetic membranes / Efeito de poluentes metálicos nos níveis de pigmentos fotossintéticos presentes em algas marinhas e avaliação do papel estrutural de carotenos em membranas miméticas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

This work involves the study of the levels of photosynthetic pigments, carotenoids and chlorophylls, contained in the marine algae Tetraselmis gracilis and Gracilaria tenuistipitata, under conditions of cellular senescence and anthropogenic stress (metallic pollution). Due to the fundamental organizational role of carotenoids in thylakoid membranes, its structural features in lipid bilayers were evaluated. Also in this last mentioned study, it was employed the methanolic extract of T. gracilis. In order to perform these studies, the algae were cultivated and the growth curves determined. Also, the typical chromatograms were obtained, and some photosynthetic pigments were identified trough commercial standards, which were then analyzed and quantified in crude extracts of different growth phases. The toxicity of the metals Cd, Cu, Hg and Pb were determined trough bioassays, which led to the toxicological parameters EC15 and EC50 estimation (the effective concentration that causes 15 and 50% of reduction of the algal growth, respectively). For each metal, the acute and chronic stress models were built, and the photosynthetic pigments contentsquantified. Liposomes were constructed with the incorporation of carotenes and of the T. gracilismethanolic extract in the bilayer, which were then submitted to light scattering, calorimetric, hydrodynamic radius and phospholipid assays. Fluorescence and chemiluminescence measurements were used to study the NO kinetics of liberation and permeation. Also, it was accomplished the extraction and pre-isolation of carotenes contained in T. gracilis. For each type of metal and stress occasioned, different levels of pigments were observed, a consequence of the different mechanisms employed against reactive oxygen species. At higher exposure periods, higher pigmentscontents were quantified, which probably corresponds to an algae acclimatative strategy. The EC50 value found for Cu is higher than the standard one previously stated in the CONAMAs nº 357 resolution. This means that effluents containing Cu, in levels allowed by the law, may cause damage to the marine biota. Moreover, its suggested a reevaluation of the standard limiting value for this metal, in order to preserve aquatic ecosystems. A higher fluidity of the lipid bilayer, occasioned by a large perturbation of the membranes structure, was accomplished by incorporating the extract of T. gracilis. This was observed independently of the cellsgrowth phase. &$946;-carotene and licopene interfere in the lipid bilayer structure, lowering the hydrodynamic diameter of large unilamellar vesicles, an effect not previously reported in literature. This reduces the temperature were the phase transition initiates, broadens the transition gap, lowers the calorific capacity and enthalpy values, consequently, modifying the transition cooperation. Only β-carotene induces a higher fluidity of the lipid system and a faster NO permeation trough the membrane, which suggests that it may modify physical properties of the membrane.

ASSUNTO(S)

no permeation photosynthetic pigments algas marinhas pigmentos fotossintéticos liposomes lipossomos poluição metálica marine algae parâmetros ecotoxicológicos metallic pollution permeabilidade de no ecotoxicologycal parameters

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