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'Carotenoids' in keywords Facet   section ZfN Section C:Volume 054  [X]
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1999 (1)
1Author    NavassardV. Karapetyanab, Ute Windhövel3 ', AlfredR. Holzwarthc, Peter BögeraRequires cookie*
 Title    Physiological Significance of Overproduced Carotenoids in Transformants of the Cyanobacterium Synechococcus PCC7942  
 Abstract    The functional location of carotenoids in the photosynthetic apparatus of -crtB and -pys transformants of the cyanobacterium Synechococcus PCC7942 was studied and compared with a control strain -pF P l-3. These transformants overproduce carotenoids due to the insertion of an additional foreign phytoene synthase gene. A higher carotenoid content was found for -crtB and -pys transformants both in whole cells and isolated membranes; the -crtB transformant was also enriched with chlorophyll. 77-K fluorescence emission and excita­ tion spectra of the phycobilin-free membranes were examined for a possible location of overproduced carotenoids in pigment-protein complexes in situ. A similar ratio of the ampli­ tudes of fluorescence bands at 716 and 695 nm emitted by photosystems I and II, found for the three strains, indicates that the stoichiometry between photosystems of the transformants was not changed. Overproduced carotenoids are not located in the core antenna of photosys­ tem I, since 77-K fluorescence excitation spectra for photosystem I of isolated membranes from the studied strains do not differ in the region of carotenoid absorption. When illumi­ nated with light of the same intensity but different quality, absorbed preferentially by either carotenoids, chlorophylls or phycobilins, respectively, oxygen evolution was found always higher in the transformants -crtB and -pys than in -p F P l-3 control cells. Identical kinetics of fluorescence induction of all strains under carotenoid excitation did not reveal a higher activity of photosystem II in cells enriched with carotenoids. It is suggested that overpro­ duced carotenoids of the transformants are not involved in photosynthetic light-harvesting; rather they may serve to protect the cells and its membranes against photodestruction. 
  Reference    Z. Naturforsch. 54c, 191—198 (1999); received December 18 1998 
  Published    1999 
  Keywords    Carotenoid, Chlorophyll, Cyanobacterium, Fluorescence, Oxygen Evolution 
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 TEI-XML for    default:Reihe_C/54/ZNC-1999-54c-0191.pdf 
 Identifier    ZNC-1999-54c-0191 
 Volume    54