title: Thermally-induced delayed fluorescence of photosystem I and II chlorophyll in thermophilic cyanobacterium Synechococcus elongatus.
abstract: Stationary delayed fluorescence (DF) of chlorophyll in isolated membrane preparations from thermophilic cyanobacterium Synechococcus elongatus was investigated as a function of temperature. Two peaks at different temperatures were observed. The low-temperature peak (54-60 degrees C) coincided with the main maximum of the thermally-induced delayed fluorescence of chlorophyll in intact cells and PSII-particles with active oxygen-evolving system. The high-temperature peak (78 degrees C) coincided with the minor band of delayed light emitted by intact cells. It was also observed in the delayed fluorescence emission from a PSI-enriched fraction preparation. The intensities of the DF peaks were dependent on the presence of inhibitors, donors and acceptors that cause specific effects on electron transport of the two photosystems. The low-temperature and high-temperature peaks were related to PSII and PSI, respectively. The manifestation of delayed fluorescence from PSI and PSII at different temperatures seems to be a specific property of thermophilic cyanobacteria. The reason for this may be a high thermal stability of the photosystems and the lack of the PSII antenna complex in isolated membranes. Consequently, the relative yield of delayed fluorescence from PSI markedly increases. Thermally-induced fluorescence seen in membranes of cyanobacteria showed a high sensitivity to structural and functional membrane alterations induced by pH changes, different electron transport stabilizing agents or different concentrations of MgCl2.
authors.affiliation: Department of Biophysics, Faculty of Biology, Moscow State University, Russia.
authors.lastname: Kaurov YuN
authors.forename: G E
authors.initials: GE
authors.lastname: Aksyonova
authors.forename: E R
authors.initials: ER
authors.lastname: Lovyagina
authors.forename: I I
authors.initials: II
authors.lastname: Ivanov
authors.forename: A B
authors.initials: AB
authors.lastname: Rubin
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D000458:Cyanobacteria / Q000378:metabolism*; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D015636:Magnesium Chloride / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D013816:Thermodynamics
chemical_list: D002951:Citrates; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D015636:Magnesium Chloride; D002734:Chlorophyll; D019343:Citric Acid