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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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  • 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
    Photosynthetic apparatus organization and function in the wild type and a chlorophyll b-less mutant of Chlamydomonas reinhardtii. Dependence on carbon source (2000)
    Springer
    Planta 211 (2000), S. 335-344 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Chlamydomonas (mutant) ; Chlorophyll b-less mutant ; Light-harvesting complex ; Photosynthesis ; Productivity (photosynthetic)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  The assembly, organization and function of the photosynthetic apparatus was investigated in the wild type and a chlorophyll (Chl) b-less mutant of the unicellular green alga Chlamydomonas reinhardtii, generated via DNA insertional mutagenesis. Comparative analyses were undertaken with cells grown photoheterotrophically (acetate), photomixotrophically (acetate and HCO− 3) or photoautotrophically (HCO− 3). It is shown that lack of Chl b diminished the photosystem-II (PSII) functional Chl antenna size from 320 Chl (a and b) to about 95 Chl a molecules. However, the functional Chl antenna size of PSI remained fairly constant at about 290 Chl molecules, independent of the presence of Chl b. Western blot and kinetic analyses suggested the presence of inner subunits of the Chl a-b light-harvesting complex of PSII (LHCII) and the entire complement of the Chl a-b light-harvesting complex of PSI (LHCI) in the mutant. It is concluded that Chl a can replace Chl b in the inner subunits of the LHCII and in the entire complement of the LHCI. Growth of cells on acetate as the sole carbon source imposes limitations in the photon-use efficiency and capacity of photosynthesis. These are manifested as a lower quantum yield and lower light-saturated rate of photosynthesis, and as lower variable to maximal (Fv/Fmax) chlorophyll fluorescence yield ratios. This adverse effect probably originates because acetate shifts the oxidation-reduction state of the plastoquinone pool, and also because it causes a decrease in the amount and/or activity of Rubisco in the chloroplast. Such limitations are fully alleviated upon inclusion of an inorganic carbon source (e.g. bicarbonate) in the cell growth medium. Further, the work provides evidence to show that transformation of green algae can be used as a tool by which to generate mutants exhibiting a permanently truncated Chl antenna size and a higher (per Chl) photosynthetic productivity of the cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250000279
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    State transitions, photosystem stoichiometry adjustment and non-photochemical quenching in cyanobacterial cells acclimated to light absorbed by photosystem I or photosystem II (1989)
    Springer
    Photosynthesis research 22 (1989), S. 157-166 
    Details
    ISSN: 1573-5079
    Keywords: State transitions ; excitation energy transfer ; photosystem stoichiometry ; chromatic acclimation ; non-photochemical quenching ; cyanobacteria ; Synechococcus 6301
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cells of the cyanobacterium Synechococcus 6301 were grown in yellow light absorbed primarily by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II), and in red light absorbed primarily by chlorophyll and, therefore, by photosystem I (PS I). Chromatic acclimation of the cells produced a higher phycocyanin/chlorophyll ratio and higher PBS-PS II/PS I ratio in cells grown under PS I-light. State 1-state 2 transitions were demonstrated as changes in the yield of chlorophyll fluorescence in both cell types. The amplitude of state transitions was substantially lower in the PS II-light grown cells, suggesting a specific attenuation of fluorescence yield by a superimposed non-photochemical quenching of excitation. 77 K fluorescence emission spectra of each cell type in state 1 and in state 2 suggested that state transitions regulate excitation energy transfer from the phycobilisome antenna to the reaction centre of PS II and are distinct from photosystem stoichiometry adjustments. The kinetics of photosystem stoichiometry adjustment and the kinetics of the appearance of the non-photochemical quenching process were measured upon switching PS I-light grown cells to PS II-light, and vice versa. Photosystem stoichiometry adjustment was complete within about 48 h, while the non-photochemical quenching occurred within about 25 h. It is proposed that there are at least three distinct phenomena exerting specific effects on the rate of light absorption and light utilization by the two photoreactions: state transitions; photosystem stoichiometry adjustment; and non-photochemical excitation quenching. The relationship between these three distinct processes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00035446
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  • 6
    Electronic Resource
    Electronic Resource
    The role of chloroplast-encoded protein biosynthesis on the rate of D1 protein degradation in Dunaliella salina (1995)
    Springer
    Photosynthesis research 45 (1995), S. 147-155 
    Details
    ISSN: 1573-5079
    Keywords: lincomycin ; photoinhibition ; Photosystem II ; pulse-chase labeling ; thylakoid membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mechanistic aspects of the Photosystem II (PS II) damage and repair cycle in Dunaliella salina were investigated. The work addressed the role of chloroplast-encoded protein biosynthesis on the rate of the D1 protein (chloroplast psbA gene product) degradation, following photoinhibition of PS II under in vivo conditions. Cells were grown under different light-intensities and the rate of D1 photodamage and degradation was measured via pulse-chase measurements with (35S)sulfate. It is shown that no detectable difference exists in the rate of D1 degradation in D. salina, measured in the presence or absence of lincomycin, a chloroplast protein biosynthesis inhibitor. The results suggest that de novo D1 biosynthesis does not play a role in the regulation of D1 degradation. In low-light (100 μmol photons m−2 s−1) grown cells, the rate of photodamage to D1 did not exceed the rate of its degradation and replacement. In high-light (2200 μmol photons m−1 s−1) grown cells, the rate of D1 photodamage was faster than the rate of its degradation, resulting in a significant accumulation of photoinactivated PS II centers in the chloroplast thylakoids (chronic photoinhibition). The latter was coincident with the appearance of a 160 kD complex that contained photodamaged D1. Electron micrographs of D. salina thylakoids revealed extensive grana stacks in the thylakoid membrane of low-light grown cells. Only rudimentary appressions consisting of simple membrane pairings were found in the high-light grown cells. The results are discussed in terms of the regulation of D1 degradation in chloroplasts under in vivo conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032586
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of a 160 kD Photosystem II reaction center complex isolated from photoinhibited Dunaliella salina thylakoids (1995)
    Springer
    Photosynthesis research 46 (1995), S. 207-211 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; photoinhibition ; Photosystem II ; reaction center ; damage and repair cycle ; Dunaliella salina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition in the green alga Dunaliella salina is accompanied by the formation of inactive Photosystem II reaction centers. In SDS-PAGE analysis, the latter appear as 160 kD complexes. These complexes are structurally stable, enough to withstand re-electrophoresis of excised gel slices from the 160 kD region. Western blot analyses with specific polyclonal antibodies raised against the D1 or D2 reaction center proteins provided evidence for the presence of both of these polypeptides in the re-electrophoresed 160 kD complex. Incubation of excised gel slices from the 160 kD region, under aerobic conditions at 4°C for a prolonged period of time, caused a break-up of the 160 kD complex into a ∽52 kD D1-containing and ∽80 and ∽26 kD D2-containing pieces. Western blot analysis with polyclonal antibodies raised against the apoproteins of CPI (reaction center proteins of PS I) did not show cross-reaction either with the 160 kD complex or with the ∽52, ∽80 and ∽26 kD pieces. The results show the presence of both D1 and D2 in the 160 kD complex and strengthen the notion of a higher molecular weight D1- and D2-containing complex that forms upon disassembly of photodamaged PS II units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020432
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  • 8
    Electronic Resource
    Electronic Resource
    Chromatic regulation inChlamydomonas reinhardtii alters photosystem stoichiometry and improves the quantum efficiency of photosynthesis (1996)
    Springer
    Photosynthesis research 47 (1996), S. 253-265 
    Details
    ISSN: 1573-5079
    Keywords: Chlamydomonas reinhardtii ; chromatic acclimation ; photosynthesis ; photosystem stoichiometry ; quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The work addressed the adjustment of the photosystem ratio in the green algaChlamydomonas reinhardtii. It is shown that green algae, much like cyanophytes and higher plants, adjust and optimize the ratio of the two photosystems in chloroplasts in response to the quality of irradiance during growth. Such adjustments are compensation reactions and helpC. reinhardtii to retain a quantum efficiency of oxygen evolution near the theoretical maximum. Results show variable amounts of PS I and a fairly constant amount of PS II in chloroplasts and suggest that photosystem stoichiometry adjustments, occurring in response to the quality of irradiance during plant growth, are mainly an adjustment in the concentration of PS I. The work delineates chromatic effects on chlorophyll accumulation in the chloroplast ofC. reinhardtii from those pertaining to the regulation of the PS I/PS II ratio. The detection of the operation of a molecular feedback mechanism for the PS I/PS II ratio adjustment in green algae strengthens the notion of the highly conserved nature of this mechanism among probably all oxygen evolving photosynthetic organisms. Findings in this work are expected to serve as the basis of future biochemical and mutagenesis experiments for the elucidation of the photosystem ratio adjustment in oxygenic photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184286
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  • 9
    Electronic Resource
    Electronic Resource
    Quantitation of plastoquinone photoreduction in spinach chloroplasts (1986)
    Springer
    Photosynthesis research 8 (1986), S. 3-16 
    Details
    ISSN: 1573-5079
    Keywords: Absorbance change ; fluorescence induction ; photosystem II ; plastoquinone ; spinach chloroplasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The question of plastoquinone (PQ) concentration and its stoichiometry to photosystem I (PSI) and PSII in spinach chloroplasts is addressed here. The results from three different experimental approaches were compared. (a) Quantitation from the light-induced absorbance change at 263 nm (ΔA263) yielded the following ratios (mol:mol); Chl:PQ=70:1, PQ:PSI=9:1 and PQ:PSIIα=7:1. The kinetics of PQ photoreduction were a monophasic but non-exponential function of time. The deviation of the semilogarithmic plots from linearity reflects the cooperativity of several electron transport chains at the PQ pool level. (b) Estimates from the area over the fluorescence induction curve (Afl) tend to exaggerate the PQ pool size because of electron transfer via PSI to molecular oxygen (Mehler reaction) resulting in the apparent increase of the pool of electron acceptors. The reliability of the Afl method is increased substantially upon plastocyanin inhibition by KCN. (c) Quantitation of the number of electrons removed from PQH2 by PSI, either under far-red excitation or after the addition of DCMU to preilluminated chloroplasts, is complicated due to the competitive loss of electrons from PQH2 to molecular oxygen. The latter is biphasic reaction occurring with half-times of about 2 s (30–40% of PQH2) and of about 60 s (60–70% of PQH2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028472
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanism of photoinhibition: photochemical reaction center inactivation in system II of chloroplasts (1986)
    Springer
    Photosynthesis research 9 (1986), S. 79-88 
    Details
    ISSN: 1573-5079
    Keywords: photosystem II ; charge separation ; fluorescence ; photoinhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition of photosynthesis is manifested at the level of the leaf as a loss of CO2 fixation and at the level of the chloroplast thylakoid membrane as a loss of photosystem II electron-transport capacity. At the photosystem II level, photoinhibition is manifested by a lowered chlorophyll a variable fluorescence yield, by a lowered amplitude of the light-induced absorbance change at 320 nm (ΔA320) and 540-minus-550 nm (ΔA540–550), attributed to inhibition of the photoreduction of the primary plastoquinone QA molecule. A correlation of the kinetics of variable fluorescence yield loss with the inhibition of QA photoreduction suggested that photoinhibited reaction centers are incapable of generating a stable charge separation but are highly efficient in the trapping and non-photochemical dissipation of absorbed light. The direct effect of photoinhibition on primary photochemical parameters of photosystem II suggested a permanent reaction center modification the nature of which remains to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029734
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