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  • 1
    Electronic Resource
    Electronic Resource
    Photoinhibition and repair in Dunaliella salina acclimated to different growth irradiances (1996)
    Springer
    Planta 198 (1996), S. 640-646 
    Details
    ISSN: 1432-2048
    Keywords: D1 protein ; Dunaliella ; Green algae ; Photodamage ; Photoinhibition ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The light-dependent rate of photosystem-II (PSII) damage and repair was measured in photoautotrophic cultures of Dunaliella salina Teod. grown at different irradiances in the range 50–3000 μmol photons · m−2· s−1. Rates of cell growth increased in the range of 50–800 μmol photons·m−2·s−1, remained constant at a maximum in the range of 800–1,500 μmol photons·m−2 ·s−1, and declined due to photoinhibition in the range of 1500–3000 μmol photons·m−2·s−1. Western blot analyses, upon addition of lincomycin to the cultures, revealed first-order kinetics for the loss of the PSII reaction-center protein (D1) from the 32-kDa position, occurring as a result of photodamage. The rate constant of this 32-kDa protein loss was a linear function of cell growth irradiance. In the presence of lincomycin, loss of the other PSII reaction-center protein (D2) from the 34-kDa position was also observed, occurring with kinetics similar to those of the 32-kDa form of D1. Increasing rates of photodamage as a function of irradiance were accompanied by an increase in the steady-state level of a higher-molecular-weight protein complex (≈ 160-kDa) that cross-reacted with D1 antibodies. The steady-state level of the 160-kDa complex in thylakoids was also a linear function of cell growth irradiance. These observations suggest that photodamage to D1 converts stoichiometric amounts of D1 and D2 (i.e., the D1/D2 heterodimer) into a ≈160-kDa complex. This complex may help to stabilize the reaction-center proteins until degradation and replacement of D1 can occur. The results indicated an intrinsic half-time of about 60 min for the repair of individual PSII units, supporting the idea that degradation of D1 after photodamage is the rate-limiting step in the PSII repair process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262653
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Photoinhibitory damage is modulated by the rate of photosynthesis and by the photosystem II light-harvesting chlorophyll antenna size (1998)
    Springer
    Planta 205 (1998), S. 288-296 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Chlorophyll antenna size ; D1 protein ; Dunaliella (photoinhibition) ; Electron transport ; Photoinhibition ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. We investigated the effect of photosynthetic electron transport and of the photosystem II (PSII) chlorophyll (Chl) antenna size on the rate of PSII photoinhibitory damage. To modulate the rate of photosynthesis and the light-harvesting capacity in the unicellular chlorophyte Dunaliella salina Teod., we varied the amount of inorganic carbon in the culture medium. Cells were grown under high irradiance either with a limiting supply of inorganic carbon, provided by an initial concentration of 25 mM NaHCO3, or with supplemental CO2 bubbled in the form of 3% CO2 in air. The NaHCO3-grown cells displayed slow rates of photosynthesis and had a small PSII light-harvesting Chl antenna size (60 Chl molecules). The half-time of PSII photodamage was 40 min. When switched to supplemental CO2 conditions, the rate of photodamage was retarded to a t1/2 = 70 min. Conversely, CO2-supplemented cells displayed faster rates of photosynthesis and a larger PSII light-harvesting Chl antenna size (500 Chl molecules). They also showed a rate of photodamage with t1/2 = 40 min. When depleted of CO2, the rate of photodamage was accelerated (t1/2  = 20 min). These results indicate that the in-vivo susceptibility to photodamage is modulated by the rate of forward electron transport through PSII. Moreover, a large Chl antenna size enhances the rate of light absorption and photodamage and, therefore, counters the mitigating effect of forward electron transport. We propose that under steady-state photosynthesis, the rate of light absorption (determined by incident light intensity and PS Chl antenna size) and the rate of forward electron transport (determined by CO2 availability) modulate the oxidation/reduction state of the primary PSII acceptor QA, which in turn defines the low/high probability for photodamage in the PSII reaction center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050323
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  • 3
    Electronic Resource
    Electronic Resource
    Dna insertional mutagenesis for the elucidation of a Photosystem II repair process in the green alga Chlamydomonas reinhardtii (1997)
    Springer
    Photosynthesis research 53 (1997), S. 173-184 
    Details
    ISSN: 1573-5079
    Keywords: Chlamydomonas reinhardtii ; mutagenesis ; photoinhibition ; Photosystem II ; repair cycle ; transformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The work outlines the isolation of transformant Chlamydomonas reinhardtii cells that appear to be unable to repair Photosystem II from photoinhibitory damage. A physiological and biochemical characterization of three mutants is presented. The results show differential stability for the D1 reaction center protein in the three mutants compared to the wild type and suggest lesions that affect different aspects of the Photosystem II repair mechanism. In the ag16.2 mutant, significantly greater amounts of D1 accumulate in the thylakoid membrane than in the wild type under steady-state growth conditions, and D1 loss is significantly retarded in the presence of the protein biosynthesis inhibitor chloramphenicol. Moreover, aberrant electrophoretic mobility of D1 in the ag16.2 suggests that this protein is modified to an as yet unknown configuration. These results indicate that the biosynthesis and/or degradation of D1 is altered in this strain. A different type of mutation occurred in the kn66.7 and kn27.4 mutants of C. reinhardtii. The stability of D1 declined much faster as a function of light intensity in these mutants than in the wild type. Thereby, the threshold of photoinhibition in these mutants was significantly lower than that in the wild type. It appears that kn66.7 and kn27.4 are similar conditional mutants, with the only difference between them being the amplitude of the chloroplast response to the mutation and the differential sensitivity they display to the level of irradiance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005867709441
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    Paper (German National Licenses)
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