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Identifier uch.biology.msc//2002sfichi
Title Η συνεισφορά της φωτοσυνθετικά ενεργής ακτινοβολίας στη ρύθμιση των επαγόμενων από την UV-B ακτινοβολία αλλαγών στη δομή και λειτουργία του φωτοσυνθετικού μηχανισμού
Alternative Title The contribution of photosynthetically active radiation intensity to the modulation of UV-B induced changes on the structure and function of photosynthetic apparatus
Author Sfichi, Liliana
Thesis advisor Κοτζαμπάσης, Κυριάκος
Abstract The contribution of photosynthetically active radiation (PAR; 400-700 nm) intensity to the modulation of UV-B effects on the structure and functioning of the photosynthetic apparatus has been studied in the unicellular green alga Scenedesmus obliquus. Cultures of Scenedesmus obliquus incubated in different illumination conditions, namely darkness, low light (87 μmol m-2 s-1) and high light (700 μmol m-2 s-1), were irradiated for 3 h with a dose of 0,420 mW cm-2 UV-B radiation. The changes induced by UV-B radiation on the algal photosynthetic apparatus, were similar to those observed during photoadaptation to low light intensity, e.g. increase of antenna size, decrease of Chl a/b and Put/Spm ratios and decrease of active reaction center density. PAR intensity influenced the magnitude of these responses, which were strongly expressed in cultures incubated in light conditions, versus the dark-incubated cultures. This result is consistent with the possibility that the degree of photoadaptation that cultures adopt in different illumination conditions influences their sensitivity to UV-B radiation, by means that low PAR and UV-B act synergistically producing a more intense response, whereas high PAR and UV-B act antagonistically and the effects induced by UV-B radiation are dimished. During UV-B irradiation, Put/Spm ratio decreased, but it later recovered, suggesting that this ratio constitutes an important adaptive mechanism to UV-B radiation. The ability of cultures to recover from UV-B effects were investigated after the removal of UV-B source in cultures incubated in similar conditions as those used during UV-B irradiation, or after transfer to different conditions, such as darkness for cultures incubated in low light conditions during UV-B irradiation. Recovery was partially accomplished in cultures maintained in continuous light conditions, while in other illumination conditions, the changes caused by UV-B radiation were intensified and recovery did not occur. These results are consistent to the hypothesis that mechanisms assuring the recovering ability of UV-B irradiated cultures are light-regulated and function in both UV-B irradiation and recovery periods.
Language English
Issue date 2002-03-27
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
Permanent Link https://elocus.lib.uoc.gr//dlib/d/d/a/metadata-dlib-2002sfichi.tkl Bookmark and Share
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