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  • Articles  (46)
  • Photosystem II  (46)
  • Springer  (46)
  • American Geophysical Union
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  • Articles  (46)
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  • Springer  (46)
  • American Geophysical Union
  • Annual Reviews
  • Blackwell Publishing Ltd
  • Wiley-Blackwell  (1)
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  • 2020-2024
  • 2005-2009
  • 1990-1994  (46)
  • 1980-1984
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  • 1
    Electronic Resource
    Electronic Resource
    Photoinhibition of photosystem II in vivo is preceded by down-regulation through light-induced acidification of the lumen: Consequences for the mechanism of photoinhibition in vivo (1993)
    Springer
    Planta 189 (1993), S. 359-368 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Down-regulation ; Energy-dependent quenching ; Photoinhibition ; Photosystem II ; Spinacia ; Vigna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanism of photoinhibition of photosystem II (PSII) was studied in intact leaf discs of Spinacia oleracea L. and detached leaves of Vigna unguiculata L. The leaf material was exposed to different photon flux densities (PFDs) for 100 min, while non-photochemical (qN) and photochemical quenching (qp) of chlorophyll fluorescence were monitored. The ‘energy’ and redox state of PSII were manipulated quite independently of the PFD by application of different temperatures (5–20° C), [CO2] and [O2] at different PFDs. A linear or curvilinear relationship between qp and photoinhibition of PSII was observed. When [CO2] and [O2] were both low (30 μl · l−1 and 2%, respectively), PSII was less susceptible at a given qp than at ambient or higher [CO2] and photoinhibition became only substantial when qp decreased below 0.3. When high levels of energy-dependent quenching (qE) (between 0.6 and 0.8) were reached, a further increase of the PFD or a further decrease of the metabolic demand for ATP and NADPH led to a shift from qE to photoinhibitory quenching (qI). This shift indicated that photoinhibition was preceded by down-regulation through light-induced acidification of the lumen. We propose that photoinhibition took place in the centers down-regulated by qE. The shift from qE to qI occurred concomitant with qP decreasing to zero. The results clearly show that photoinhibition does not primarily depend on the photon density in the antenna, but that photoinhibition depends on the energy state of the membrane in combination with the redox balance of PSII. The results are discussed with regard to the mechanism of photoinhibition of PSII, considering, in particular, effects of light-induced acidification on the donor side of PSII. Interestingly, cold-acclimation of spinach leaves did not significantly affect the relationship between qP, qE and photoinhibition of PSII at low temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194432
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  • 2
    Electronic Resource
    Electronic Resource
    Cold-hardening-induced resistance to photoinhibition of photosynthesis in winter rye is dependent upon an increased capacity for photosynthesis (1993)
    Springer
    Planta 189 (1993), S. 150-156 
    Details
    ISSN: 1432-2048
    Keywords: Chlorotophyll fluorescence ; Cold-hardening ; Quantum yield ; Photoinhibition (resistance) ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Analyses of chlorophyll fluorescence and photosynthetic oxygen evolution were conducted to understand why cold-hardened winter rye (Secale cereale L.) is more resistant to photoinhibition of photosynthesis than is non-hardened winter rye. Under similar light and temperature conditions, leaves of cold-hardened rye were able to keep a larger fraction of the PS II reaction centres in an open configuration, i.e. a higher ratio of oxidized to reduced QA (the primary, stable quinone acceptor of PSII), than leaves of non-hardened rye. Three fold-higher photon fluence rates were required for cold-hardened leaves than for non-hardened leaves in order to establish the same proportion of oxidized to reduced QA. This ability of cold-hardened rye fully accounted for its higher resistance to photoinhibition; under similar redox states of qa cold-hardened and non-hardened leaves of winter rye exhibited similar sensitivities to photoinhibition. Under given light and temperature conditions, it was the higher capacity for light-saturated photosynthesis in cold-hardened than in non-hardened leaves, which was responsible for maintaining a higher proportion of oxidized to reduced QA. This higher capacity for photosynthesis of cold-hardened leaves also explained the increased resistance of photosynthesis to photoinhibition upon cold-hardening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201355
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  • 3
    Electronic Resource
    Electronic Resource
    Deletion mutations in a long hydrophilic loop in the photosystem II chlorophyll-binding protein CP43 in the cyanobacterium Synechocystis sp. PCC 6803 (1993)
    Springer
    Plant molecular biology 23 (1993), S. 123-133 
    Details
    ISSN: 1573-5028
    Keywords: Photosystem II ; cyanobacteria ; directed mutagenesis ; psbC gene product
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to investigate the role and function of the hydrophilic region between transmembrane regions V and CI in the photosystem II core antenna protein CP43, we introduced eight different deletions in psbC of Synechocystis sp; PCC 6803 resulting in a loss of 7–11 codons in evolutionary conserved domains in this region. All deletions resulted in an obligate photoheterotrophic phenotype (requirement of glucose for cell growth) and the absence of any detectable oxygen evolution activity. The various deletion mutations showed a different impact on the amount of CP43 in the thylakoid, ranging from wild-type levels of (a now slightly smaller) CP43 to no detectable CP43 at all. All deletions led to a decrease in the amount of the D1 and D2 proteins in the thylakoids with a larger effect on D2 than on D1. CP47, the other major chlorophyll-binding protein, was present in reduced but significant amounts in the thylakoid. Herbicide binding (diuron) was lost in all but one mutant indicating the PSII components are not assembled into functionally intact complexes. Fluorescence-emission spectra confirmed this notion. This indicates that the large hydrophilic loop of CP43 plays an important role in photosystem II, and even though a shortened CP43 is present in thylakoids of most mutants, functional characteristics resemble that of a mutant with interrupted psbC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021425
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  • 4
    Electronic Resource
    Electronic Resource
    The psbB gene cluster of the Chlamydomonas reinhardtii chloroplast: sequence and transcriptional analyses of psbN and psbH (1993)
    Springer
    Plant molecular biology 22 (1993), S. 645-658 
    Details
    ISSN: 1573-5028
    Keywords: Chlamydomonas reinhardtii ; chloroplast DNA ; transcript maturation ; 10 kDa phosphoprotein ; psbH ; psbN ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have sequenced and characterized the complete psbB gene cluster of Chlamydomonas reinhardtii chloroplast DNA. Although the petB and petD genes are located elsewhere, the sequential order of psbB, ORF31, psbN and psbH is identical to that of the psbB operon in higher plants. Also, intergenic non-coding regions are much larger in the Chlamydomonas gene cluster. Northern blot analyses indicate the formation of dicistronic transcripts of psbB and ORF31 and monocistronic transcripts of psbN and psbH. It is unclear whether a psbB operon is transcribed to yield a large polycistronic precursor but northern blot analysis with total RNA from cells grown at 15°C does not detect an increased complexity of the transcripts, as has been found in studies of the psbB operon of higher plants. From primer extension and nuclease protection assays, it is apparent that 5′ and 3′ processing of the primary psbH transcript results in the accumulation of a heterogenous population of mRNAs. Northern blot analyses reveal transcription of Chlamydomonas psbN and show that its mRNA is much larger than that identified in liverwort and pea. The sequence identities of the PSII-H and PSII-N polypeptides as compared to their vascular plant counterparts is 50 to 62%. While the amino acid sequences of PSII-H and PSII-N proteins are significantly conserved, the mass of PSII-H from Chlamydomonas is significantly larger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00047405
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  • 5
    Electronic Resource
    Electronic Resource
    Chlorophyll-proteins from maize seedlings grown under intermittent light conditions (1993)
    Springer
    Planta 191 (1993), S. 265-273 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll-protein complex (stoichiometry) ; Chloroplast development ; Intermittent light ; Photosynthetic pigment ; Photosystem II ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the organization of the antenna system of maize (Zea mays L.) seedlings grown under intermittent light conditions for 11 d. These plants had a higher chlorophyll-a/b ratio, a higher ratio of carotenoids to chlorophyll and a lower ratio of chlorophyll to protein than plants grown in continuous light. We found all chlorophyll-protein complexes of maize to be present. However, the minor chlorophyll a/b-proteins CP29 and CP26, and to a greater extent CP24 and the major light-harvesting complex II were reduced relative to the photosystem (PS) II core-complex. Also the chlorophyll a/b-antennae of PSI were reduced relative to the reaction-centre polypeptides. When isolated by flatbed isoelectrofocussing, the chlorophyll-a/b complexes of PSII showed a higher chlorophyll-a/b ratio and a lower ratio of chlorophyll to protein than the same complexes from continuous light; additionally, they bound more carotenoids per protein than the latter. Thus the altered organization of the photosynthetic apparatus of plants from intermittent light is caused by two different factors: (i) the altered stoichiometry of chlorophyll-binding proteins and (ii) a different ratio of pigment to protein within individual chlorophyll-proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00199759
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  • 6
    Electronic Resource
    Electronic Resource
    Analysing the responses of photosynthetic CO2 assimilation to long-term elevation of atmospheric CO2 concentration (1993)
    Springer
    Plant ecology 104-105 (1993), S. 33-45 
    Details
    ISSN: 1573-5052
    Keywords: Greenhouse effect ; Chlorophyll fluorescence ; RubisCQ ; Photosystem II ; Stomata ; Quantum efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Understanding how photosynthetic capacity acclimatises when plants are grown in an atmosphere of rising CO2 concentrations will be vital to the development of mechanistic models of the response of plant productivity to global environmental change. A limitation to the study of acclimatisation is the small amount of material that may be destructively harvested from long-term studies of the effects of elevation of CO2 concentration. Technological developments in the measurement of gas exchange, fluorescence and absorption spectroscopy, coupled with theoretical developments in the interpretation of measured values now allow detailed analyses of limitations to photosynthesisin vivo. The use of leaf chambers with Ulbricht integrating spheres allows separation of change in the maximum efficiency of energy transduction in the assimilation of CO2 from changes in tissue absorptance. Analysis of the response of CO2 assimilation to intercellular CO2 concentration allows quantitative determination of the limitation imposed by stomata, carboxylation efficiency, and the rate of regeneration of ribulose 1:5 bisphosphate. Chlorophyll fluorescence provides a rapid method for detecting photoinhibition in heterogeneously illuminated leaves within canopies in the field. Modulated fluorescence and absorption spectroscopy allow parallel measurements of the efficiency of light utilisation in electron transport through photosystems I and IIin situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00048143
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical assessment of alternative mechanisms for non-photochemical quenching of PS II fluorescence in barley leaves (1993)
    Springer
    Photosynthesis research 36 (1993), S. 119-139 
    Details
    ISSN: 1573-5079
    Keywords: energy dissipation ; photoinhibition ; photosynthesis ; Photosystem II ; quantum yield ; state transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The components of non-photochemical chlorophyll fluorescence quenching (qN) in barley leaves have been quantified by a combination of relaxation kinetics analysis and 77 K fluorescence measurements (Walters RG and Horton P 1991). Analysis of the behaviour of chlorophyll fluorescence parameters and oxygen evolution at low light (when only state transitions — measured as qNt — are present) and at high light (when only photoinhibition — measured as qNi — is increasing) showed that the parameter qNt represents quenching processes located in the antenna and that qNi measures quenching processes located in the reaction centre but which operate significantly only when those centres are closed. The theoretical predictions of a variety of models describing possible mechanisms for high-energy-state quenching, measured as the residual quenching, qNe, were then tested against the experimental data for both fluorescence quenching and quantum yield of oxygen evolution. Only one model was found to agree with these data, one in which antennae exist in two states, efficient in either energy transfer or energy dissipation, and in which those photosynthetic units in a dissipative state are unable to exchange energy with non-dissipative units.
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    URL: http://dx.doi.org/10.1007/BF00016277
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  • 8
    Electronic Resource
    Electronic Resource
    Oxygen evolution by Photosystem II: The contribution of backward transitions to the anomalous behaviour of double-hits revealed by a new analysis method (1993)
    Springer
    Photosynthesis research 36 (1993), S. 111-118 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; S-states ; oxygen evolution ; probabilities ; flashing light
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Backward transitions in the analysis of oxygen production under flashing light were introduced by Packham et al., 1988, Photosynth. Res. 15: 221–232. In order to take backward transitions into account, a new method of analysis is presented: the ‘eigenvalue method’. This method is based on the recurrence relation of oxygen production with four coefficients (also known as the four ‘sigma’ coefficients). It shows less susceptibility to round-off errors than other methods and permits the computation of double-hits directly from the coefficients, which was not possible before. With it we discovered that the inconsistent behaviour of double-hits observed previously under low flash intensities or low flash frequencies was mainly due to the inclusion of the backward transitions into the double-hit probability. In these conditions backward transitions seemed to be due either to the combination of an S-state deactivation and a miss, or to two S-state deactivations and a single-hit. In the presence of 3-(3, 4-Dichlorophenyl)-1, 1-dimethylurea (DCMU), the previous methods of ‘sigma’ analysis failed. In contrast, the new method resolved all four S-state probabilities; thus it has the further advantage of being more ‘robust’ (robustness being defined as the ability to yield a meaningful answer under difficult conditions).
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    URL: http://dx.doi.org/10.1007/BF00016276
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  • 9
    Electronic Resource
    Electronic Resource
    The degree of functional separation between the two photosystems in isolated thylakoid membranes deduced from inhibition studies of the imbalance in photoactivities (1993)
    Springer
    Photosynthesis research 36 (1993), S. 89-94 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; Emerson enhancement ; Photosystem I ; Photosystem II ; lateral heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to examine whether the two photosystems, PS I and PS II, are organized in specific electron transporting pairs, or randomly transport electrons from PS II to PS I, the photosystems imbalance of photoactivities (Emerson enhancement) was measured by modulated fluorimetry under different degrees of PS II inhibition in broken chloroplasts, where the granal structures were preserved by the presence of 5 mM MgCl. The results indicate a lack of any measurable specific functional pairing between individual PS I and PS II, in contrast to a previous research work in leaves (Malkin et al. 1986, Photosynth. Res. 10: 291–296). These results and this discrepancy are further discussed.
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    URL: http://dx.doi.org/10.1007/BF00016273
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  • 10
    Electronic Resource
    Electronic Resource
    Kok's oxygen clock: What makes it tick? The structure of P680 and consequences of its oxidizing power (1993)
    Springer
    Photosynthesis research 38 (1993), S. 297-301 
    Details
    ISSN: 1573-5079
    Keywords: P680 ; Photosystem II ; reaction center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract New insights in the structure of P680, the primary electron donor in Photosystem II, are summarized and the implications of its oxidizing power for energy transfer and singlet oxygen production are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046753
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  • 11
    Electronic Resource
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    NMR paramagnetic relaxation enhancements due to manganese in the S0 and S2 states of Photosystem II-enriched membrane fragments and in the detergent-solubilized Photosystem II complex (1993)
    Springer
    Photosynthesis research 38 (1993), S. 347-354 
    Details
    ISSN: 1573-5079
    Keywords: NMR ; nuclear spin relaxation ; water oxidation ; oxygen evolution ; Photosystem II ; manganese oxidation state ; S-state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The NMR paramagnetic relaxation enhancement (NMR-PRE) produced in the solvent proton resonance by manganese in the S0 and S2 states of the oxygen evolving center (OEC) has been recorded for three Photosystem II (PS II)-enriched preparations: (1) PS II-enriched thylakoid membrane fragments (TMF-2 particles); (2) salt-washed (2M NaCl) TMF-2 particles; and (3) the octylglucopyranoside (OGP)-solubilized PS II complex. The second and third preparations, but not the first, are depleted of the peripheral 17 and 23 kD polypeptides associated with the OEC. It has been proposed that depletion of these polypeptides increases the exposure of OEC manganese to the aqueous phase. The NMR-PRE response measures the quantity (T1m+τm)-1, where T1m is the spin relaxation time and τm is the mean residence time with respect to chemical exchange reactions of solvent protons in the manganese coordination sphere, and, thus, the NMR-PRE provides a direct measure of the solvent proton chemical exchange rate constant τm -1. This study tested whether the 17 and 23 kD polypeptides shield the OEC from the solvent phase and whether their depletion enhances the S2 and S0 NMR-PRE signals by removing a kinetic barrier to the solvent proton chemical exchange reaction. The amplitude of the S2 NMR-PRE signal, measured in its chemical exchange-limited regime (τm〉T1m), is slightly decreased, rather than increased, in preparations (2) and (3) relative to (1), indicating that removal of the 17 and 23 kD polypeptides slightly slows, rather than accelerates, the rate-limiting steps of the solvent proton chemical exchange reactions. In addition, the lifetime of the S2 state was shortened several-fold in the solubilized PS II complex and in salt-washed TMF-2 membranes relative to untreated TMF-2 control samples. The S0 NMR-PRE signal, which is present in TMF-2 suspensions, was not detected in suspensions of the solubilized PS II complex, even though these samples contained high concentrations of active manganese centers (approximately double those of the TMF-2 control) and exhibited an S2 NMR-PRE signal of comparable amplitude to that of the TMF-2 preparation. These results suggest that the 17 and 23 kD extrinsic polypeptides do not shield the NMR-visible water binding site in the OEC from the aqueous phase, although their removal substantially alters the proton relaxation efficiency by shortening T1m.
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    URL: http://dx.doi.org/10.1007/BF00046760
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  • 12
    Electronic Resource
    Electronic Resource
    Thermoluminescence properties of the S2-state in chloride-depleted water oxidizing complexes after reconstituting treatments with various monovalent anions (1993)
    Springer
    Photosynthesis research 38 (1993), S. 395-400 
    Details
    ISSN: 1573-5079
    Keywords: anionic cofactors ; chloride effect ; oxygen evolution ; Photosystem II ; Spinacea oleracea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Under conditions that assured rebinding of the extrinsic 17 and 23 kDa polypeptides, Cl--depleted Photosystem II membranes isolated from spinach chloroplasts were subjected to reconstituting treatments in media containing NaF, NaCl, NaBr, NaI or NaNO3, or they were kept in a medium without any added salt other than the buffer. After removing most of the unbound reconstituting anions by washing, the O2-evolution activities and thermoluminescence properties of the membranes were compared. While the temperature of maximal thermoluminescence emission was lowest for membranes treated with Cl-, no uniform correlation was evident between the temperature profile of the thermoluminescence emission and the apparent activating effectiveness of the anions in the membranes' water oxidizing machinery. However, the differences between the thermoluminescence features did conform to a trend according to which the emission temperatures were upshifted as the size of the activating anion increased, and its hydration energy decreased, i.e. Cl-〈Br-〈NO3 -〈I-. The inactive F- anions were not well retained by the membranes. To explain the experimental data it is suggested that the structural environment of the charge accumulating Mn-center is influenced by the ionic conditions encountered by the Photosystem II membranes after Cl- removal, further enforced by the binding of compatible anions, and then stabilized by the 17 and 23 kDa extrinsic polypeptides. If, as some concepts imply, the anion binding sites are located at or near the functional Mn, only very exceptional characteristics of the water-oxidizing mechanism may account for the observation that the potentially electron-donating I- anion can serve as activator and that it stabilizes rather than destabilizes the S2-state.
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    URL: http://dx.doi.org/10.1007/BF00046766
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  • 13
    Electronic Resource
    Electronic Resource
    Can CO2 assimilation in maize leaves be predicted accurately from chlorophyll fluorescence analysis? (1993)
    Springer
    Photosynthesis research 37 (1993), S. 89-102 
    Details
    ISSN: 1573-5079
    Keywords: C4 photosynthesis ; chlorophyll fluorescence ; CO2 assimilation ; maize ; Photosystem II ; quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Analysis is made of the energetics of CO2 fixation, the photochemical quantum requirement per CO2 fixed, and sinks for utilising reductive power in the C4 plant maize. CO2 assimilation is the primary sink for energy derived from photochemistry, whereas photorespiration and nitrogen assimilation are relatively small sinks, particularly in developed leaves. Measurement of O2 exchange by mass spectrometry and CO2 exchange by infrared gas analysis under varying levels of CO2 indicate that there is a very close relationship between the true rate of O2 evolution from PS II and the net rate of CO2 fixation. Consideration is given to measurements of the quantum yields of PS II (φ PS II) from fluorescence analysis and of CO2 assimilation ( $$\phi _{CO_2 } $$ ) in maize over a wide range of conditions. The $${{\phi _{PSII} } \mathord{\left/ {\vphantom {{\phi _{PSII} } {\phi _{CO_2 } }}} \right. \kern-\nulldelimiterspace} {\phi _{CO_2 } }}$$ ratio was found to remain reasonably constant (ca. 12) over a range of physiological conditions in developed leaves, with varying temperature, CO2 concentrations, light intensities (from 5% to 100% of full sunlight), and following photoinhibition under high light and low temperature. A simple model for predicting CO2 assimilation from fluorescence parameters is presented and evaluated. It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO2 assimilation rates in maize.
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    URL: http://dx.doi.org/10.1007/BF02187468
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  • 14
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    Electronic Resource
    The role of calcium in the pH-dependent control of Photosystem II (1993)
    Springer
    Photosynthesis research 37 (1993), S. 117-130 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; calcium ; oxygen evolution ; primary quinone acceptor ; redox potential ; fluorescence quenching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract pH-dependent inactivation of Photosystem (PS) II and related quenching of chlorophyll-a-fluorescence have been investigated in isolated thylakoids and PS II-particles and related to calcium release at the donor side of PS II. The capacity of oxygen evolution (measured under light saturation) decreases when the ΔpH is high and the pH in the thylakoid lumen decreases below 5.5. Oxygen evolution recovers upon uncoupling. The pH-response of inactivation can be described by a 1 H+-transition with an apparent pK-value of about 4.7. The yield of variable fluorescence decreases in parallel to the inactivation of oxygen evolution. pH-dependent quenching requires light and can be inhibited by DCMU. In PS II-particles, inactivation is accompanied by a reversible release of Ca2+-ions (one Ca2+ released per 200 Chl). In isolated thylakoids, where a ΔpH was created by ATP-hydrolysis, both inactivation of oxygen evolution (and related fluorescence quenching) by internal acidification and the recovery of that inactivation can be suppressed by calcium-channel blockers. In the presence of the Ca2+-ionophore A23187, recovery of Chl-fluorescence (after relaxation of the ΔpH) is stimulated by external Ca2+ and retarded by EGTA. As shown previously (Krieger and Weis 1993), inactivation of oxygen evolution at low pH is accompanied by an upward shift of the midpoint redox-potential, Em, of QA. Here, we show that in isolated PS II particles the pH-dependent redox-shift (about 160 mV, as measured from redox titration of Chl-fluorescence) is suppressed by Ca2+-channel blockers and DCMU. When a redox potential of −80 to −120mV was established in a suspension of isolated thylakoids, the primary quinone acceptor, QA, was largely reduced in presence of a ΔpH (created by ATP-hydrolysis) but oxidized in presence of an uncoupler. Ca2+-binding at the lumen side seems to control redox processes at the lumen- and stroma-side of PS II. We discuss Ca2+-release to be involved in the physiological process of ‘high energy quenching’.
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    URL: http://dx.doi.org/10.1007/BF02187470
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  • 15
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    Perspectives on the structure of the photosynthetic oxygen evolving manganese complex and its relation to the Kok cycle (1993)
    Springer
    Photosynthesis research 38 (1993), S. 265-277 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; oxygen evolution ; manganese
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This review describes the progress in our understanding of the structure of the Mn complex in Photosystem II over the last two decades. Emphasis is on the research from our laboratory, especially the results from X-ray absorption spectroscopy, low temperature electron paramagnetic resonance and electron spin echo envelope modulation studies. The importance of the interplay between electron paramagnetic resonance studies and X-ray absorption studies, which has led to a description of the oxidation states of manganese as the enzyme cycles through the Kok cycle, is described. Finally, the path, by which our group has utilized these two important methods to arrive at a working structural model for the manganese complex that catalyzes the oxidation of water to dioxygen in higher plants and cyanobacteria, is explained.
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    URL: http://dx.doi.org/10.1007/BF00046751
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  • 16
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    High misses after odd flashes in oxygen evolution in thoroughly dark-adapted thylakoids from pea and Chenopodium album (1993)
    Springer
    Photosynthesis research 38 (1993), S. 309-314 
    Details
    ISSN: 1573-5079
    Keywords: chloroplasts ; oxygen evolving complex ; Photosystem II ; quinone acceptors ; S-states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Photosystem II (PS II), water is oxidized to molecular oxygen and plastoquinone is reduced to plastoquinol. The oxidation of water requires the accumulation of four oxidizing equivalents, through the so-called S-states of the oxygen evolving complex; the production of plastoquinol requires the accumulation of two reducing equivalents on a bound plastoquinone, QB. It has been generally believed that during the flash-induced transition of each of the S-states (Sn → Sn+1, where n=0, 1, 2 and 3), a certain small but equal fraction of the PS II reaction centers are unable to function and, thus, ‘miss’ being turned over. We used thoroughly dark-adapted thylakoids from peas (Pisum sativum) and Chenopodium album (susceptible and resistant to atrazine) starting with 100% of the oxygen evolving complex in the S1 state. Thylakoids were illuminated with saturating flashes, providing a double hit parameter of about 0.07. Our experimental data on flashnumber dependent oscillations in the amount of oxygen per flash fit very well with a binary pattern of misses: 0, 0.2, 0, 0.4 during S0 → S1, S1 → S2, S2 → S3 and S3 → S0 transitions. Addition of 2 mM ferricyanide appears to shift this pattern by one flash. These results are consistent with the ‘bicycle’ model recently proposed by V. P. Shinkarev and C. A. Wraight (Oxygen evolution in photosynthesis: From unicycle to bicycle, 1993, Proc Natl Acad Sci USA 90: 1834–1838), where misses are due to the presence of P+ or QA - among the various equilibrium states of PS II centers.
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    URL: http://dx.doi.org/10.1007/BF00046755
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    Kinetic factors in the bicycle model of oxygen evolution by Photosystem II (1993)
    Springer
    Photosynthesis research 38 (1993), S. 315-321 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; oxygen evolution ; S-states ; quinones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced oxygen evolution and many related processes in thylakoids of oxygenic organisms are modulated with period four by the S-state transitions associated with the oxygen evolving system of Photosystem II (PS II). To analyze these phenomena, we have interpreted the S-state model on the basis of the charge accumulating activities on both sides of PS II-4 charges on the donor side and 2 charges on the acceptor side. This results in the recognition of two parallel reaction center cycles V and W of PS II function (V.P. Shinkarev and C.A. Wraight (1993) Proc Natl Acad Sci USA 90: 1834–1838). The description of damping of the period four oscillations is here extended to include kinetic sources of misses in both cycles. Such misses arise in reaction centers (RCs) in which back reaction between P+ and QA - occurs before the electron transfer equilibria on the donor and acceptor sides of the RC are reached. These are in addition to misses which are determined by reaction centers (RCs) that are inactive at the time of the flash due to the presence of either P+ or QA - according to the electron transfer equilibria on the donor and acceptor sides of the RC. Using known or estimated values of the equilibrium and rate constants for donor and acceptor side reactions of the RC, this provides a natural and quantitatively reasonable description of the flash number dependence of oxygen evolution and other period four modulated processes of PS II. The estimated miss factors are different for both cycles V and W and are dependent on flash number and pH. Estimates based on existing data show that miss factors of the first type (kinetic) are dominant at low pH, while those of the second type (equilibrium) are dominant at high pH.
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    Analytical procedures for the quantification of isotopic amino acid incorporation into photosynthetic proteins of Synechocystis PCC 6803 (1993)
    Springer
    Photosynthesis research 38 (1993), S. 379-386 
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    ISSN: 1573-5079
    Keywords: auxotroph ; mass spectrometry ; Photosystem II ; tyrosine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanism of oxygen evolution has been an enigma for nearly two centuries. Pioneering work by Bessel Kok, Pierre Joliot, and many others during the last quarter century has provided valuable insight into this most unique and important chemical reaction. The late 1970s and early 1980s saw the introduction of biochemical techniques for the purification of photosynthetic complexes that have, in turn, stimulated the biophysical chemists and spectroscopists to apply high resolution techniques in order to resolve the structure/function relationships in these protein complexes. Valuable information about events at the atomic level can be gained through isotopic substitution of particular amino acids thought to be important in the catalytic process. The ability to generate functional auxotrophs in the photosynthetic cyanobacterium Synechocystis 6803 has been used successfully to identify the redox active components Z and D as tyrosine residues in the reaction center of Photosystem II. In this report, we present results of the application of specific isotopic labeling for high resolution spectroscopy of purified PS II particles. We have developed analytical procedures for monitoring the incorporation of both 2H and 17O labeled amino acids by gas chromatography-mass spectroscopic analysis. We also show that the growth curve of cells subjected to obligate auxotrophy displays two distinct stationary phases; one that corresponds to depletion of exogenous amino acids, and a second that corresponds to the normal cell density at stationary phase. Cells harvested at the second stationary phase show little or no retention of the labeled amino acid.
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    Increases in peroxide formation by the Photosystem II oxygen evolving reactions upon removal of the extrinsic 16, 22 and 33 kDa proteins are reversed by CaCl2 addition (1993)
    Springer
    Photosynthesis research 38 (1993), S. 417-423 
    Details
    ISSN: 1573-5079
    Keywords: calcium effects ; extrinsic proteins ; O2 evolution ; peroxide formation ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This communication introduces a new spectrophotometric assay for the detection of peroxide generated by Photosystem II (PS II) under steady state illumination in the presence of an electron acceptor. The assay is based on the formation of an indamine dye in a horseradish peroxidase coupled reaction between 3-(dimethylamino)benzoic acid and 3-methyl-2-benzothiazolinone hydrazone. Using this assay, we found that as the O2 evolution activity of PS II-enriched membrane fragments is decreased by treatments which cause the dissociation of the 33 and/or 23 and 16 kDa extrinsic proteins (i.e., CaCl2-washing, NaCl-washing, lauroylcholine-treatment and ethylene glycol-treatment), light-induced peroxide formation increases. Both the losses of O2 evolution and increases in peroxide formation seen under these conditions are reversed by CaCl2 addition, indicating that the two activities originate from the water-splitting site. However, the increased rates of peroxide formation do not quantitatively match the losses in O2 evolution activity. We suggest that a rapid consumption of the peroxide takes place via a catalase/peroxidase activity at the water-splitting site which competes with both the O2 evolution and peroxide formation reactions. The observed peroxide formation is interpreted as arising from enhanced water accessibility to the catalytic site upon perturbation of the extrinsic proteins which then leads to alternate water oxidation side reactions.
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    URL: http://dx.doi.org/10.1007/BF00046769
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    Events near the reaction center in O2 evolving PS II enriched thylakoid membranes: The presence of an electric field during the S2 state in a population of centers (1993)
    Springer
    Photosynthesis research 37 (1993), S. 205-215 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; electrochromic changes ; heterogeneity ; oxygen-evolving complex ; Photosystem II ; S states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced absorption changes at 515 nm observed as a function of flash number are examined in relation to the flash-induced fluorescence yields in inside-out thylakoids. After partial dissipation of the delocalized transmembrane electric field by adding gramicidin, the analysis of period 4 oscillations and of the kinetics in the 10 ms–1 s range suggest that the variation of the absorption changes at 515 nm as a function of flash number is the result of at least two processes:1) an electric field increase related to the S2 state and 2) the fact that the field generated by the water protons inside the membrane decreases when these protons are released outside the membrane. The former field correlates with the flash-induced fluorescence yield increase induced by the donor side of Photosystem II. Both measurements show similar oscillations as a function of flash number, with maxima on the 1st, 5th and 9th flash. These oscillations, after a shift of two flashes, appear to be different from those of the O2 yield observed under similar conditions. It is proposed that, in a population of centers the electric field during the S2 state reflects the presence of a stabilized positive equivalent in the protein close to the Mn complex.
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    URL: http://dx.doi.org/10.1007/BF00032824
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    Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves (1993)
    Springer
    Photosynthesis research 38 (1993), S. 15-26 
    Details
    ISSN: 1573-5079
    Keywords: CO2 assimilation ; light harvesting chlorophyll a/b protein complex ; Photosystem I ; Photosystem II ; protein phosphorylation ; quantum yield ; State transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO2 assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO2 assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO2 assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C3 leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO2 assimilation.
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    Polyamines in the photosynthetic apparatus (1993)
    Springer
    Photosynthesis research 38 (1993), S. 83-88 
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    ISSN: 1573-5079
    Keywords: polyamines ; thylakoids ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The three main polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) were characterized by HPLC in intact spinach leaf cells, intact chloroplasts, thylakoid membranes, Photosystem II membranes, the light-harvesting complex and the PS II complex. All contain the three polyamines in various ratios; the HPLC polyamine profiles of highly resolved PS II species (a Photosystem II core and the rection center) suggest an enrichment in the polyamine Spm.
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    Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 169-176 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen-evolving complex ; UV asorbance changes ; EPR signal II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron acceptors, electron transport was limited to a single turnover. Addition of the electron acceptors DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the QB-site. In contrast to PS II membranes, all active centers were in state S1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z+S1→ZS2 and Z+S2→ZS3 transitions, respectively, had half-times of 95 and 380 μs, similar to those reported for PS II membrane fragments. The decrease due to the Z+S3→ZS0 transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 μs was observed, which might be due to the Z+S0→ZS1 transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S0 to S1 in the dark, which had a half-time of 2–3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z+S3.
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    Proton release during the redox cycle of the water oxidase (1993)
    Springer
    Photosynthesis research 38 (1993), S. 279-296 
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    ISSN: 1573-5079
    Keywords: electrochromic changes ; oxygen-evolving complex ; Photosystem II ; proton release ; protolytic reactions ; Tyrosine Z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Old and very recent experiments on the extent and the rate of proton release during the four reaction steps of photosynthetic water oxidation are reviewed. Proton release is discussed in terms of three main sources, namely the chemical production upon electron abstraction from water, protolytic reactions of Mn-ligands (e.g. oxo-bridges), and electrostatic response of neighboring amino acids. The extent of proton release differs between the four oxidation steps and greatly varies as a function of pH both, but differently, in thylakoids and PS II-membranes. Contrastingly, it is about constant in PS II-core particles. In any preparation, and on most if not all reaction steps, a large portion of proton transfer can occur very rapidly (〈20 μs) and before the oxidation of the Mn-cluster by Yz + is completed. By these electrostatically driven reactions the catalytic center accumulates bases. An additional slow phase is observed during the oxygen evolving step, S3⇒S4→S0. Depending on pH, this phase consists of a release or an uptake of protons which accounts for the balance between the number of preformed bases and the four chemically produced protons. These data are compatible with the hypothesis of concerted electron/proton-transfer to overcome the kinetic and energetic constraints of water oxidation.
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    A recollection of the development of the Kok-Joliot model for photosynthetic oxygen evolution (1993)
    Springer
    Photosynthesis research 38 (1993), S. 225-227 
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    ISSN: 1573-5079
    Keywords: Bessel Kok ; Kok-Joliot model ; oxygen evolution ; Photosystem II ; Pierre Joliot
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Twenty-five years of period-four O2-flash yield oscillation are celebrated with a personal recollection of the development of the Kok-Joliot model for photosynthetic oxygen evolution.
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    Water cleavage by solar radiation—an inspiring challenge of photosynthesis research (1993)
    Springer
    Photosynthesis research 38 (1993), S. 229-247 
    Details
    ISSN: 1573-5079
    Keywords: absorption spectroscopy ; ENDOR ; EPR ; EXAFS ; manganese ; P680 ; Photosystem II ; S-states ; water oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Solar energy exploitation by photosynthetic water cleavage is of central relevance for the development and sustenance of all higher forms of living matter in the biosphere. The key steps of this process take place within an integral protein complex referred to as Photosystem II (PS II) which is anisotropically incorporated into the thylakoid membrane. This minireview concentrates on mechanistic questions related to i) the generation of strongly oxidizing equivalents (holes) at a special chlorophyll a complex (designated as P680) and ii) the cooperative reaction of four holes with two water molecules at a manganese containing unit WOC (water oxidizing complex) resulting in the release of molecular oxygen and four protons. The classical work of Pierre Joliot and Bessel Kok and their coworkers revealed that water oxidation occurs via a sequence of univalent oxidation steps including intermediary redox states Si (i = number of accumulated holes within the WOC). Based on our current stage of knowledge, an attempt is made a) to identify the nature of the redox states Si, b) to describe the structural arrangement of the (four) manganese centers and their presumed coordination and ligation within the protein matrix, and c) to propose a mechanism of photosynthetic water oxidation with special emphasis on the key step, i.e. oxygen-oxygen bond formation. It is assumed that there exists a dynamic equilibrium in S3 with one state attaining the nuclear geometry and electronic configuration of a complexed peroxide. This state is postulated to undergo direct oxidation to complexed dioxygen by univalent electron abstraction with YZ ox and simultaneous internal ligand to metal charge transfer. Key questions on the mechanism will be raised. The still fragmentary answers to these questions not only reflect our limited knowledge but also illustrate the challenges for future research.
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    Characterization of the psbK locus of Synechocystis sp. PCC 6803 in terms of Photosystem II function (1993)
    Springer
    Photosynthesis research 38 (1993), S. 369-377 
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    ISSN: 1573-5079
    Keywords: molecular biology ; Photosystem II ; psbK gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The psbK gene encodes a small protein of Photosystem II. The gene has previously been cloned and sequenced in Synechocystis sp. PCC 6803. Our new results, presented here, confirm the conclusions of Ikeuchi et al. Based on Northern hybridization and primer extension analyses, we show that psbK is transcribed as a monocistronic message in this cyanobacterium. Analysis of DNA sequence immediately upstream of the transcription start site revealed an E. coli-like-10 consensus sequence. A deletion mutant was constructed where the psbK gene was replaced by a kanamycin resistant cartridge. In situ complementation experiments, as well as Southern and Northern hybridization analyses, confirmed that the mutant strain contains a lesion in psbK. The psbK-less mutant could grow photoautotrophically as well as photoheterotrophically both in liquid culture and on agar plates. The rate of growth was slightly less compared with the wild-type as clearly observed by in situ complementation experiments. Although the mutant showed correspondingly lower rates of electron transport, thermoluminescence, oxygen flash yield and chlorophyll a fluorescence measurements did not detect any significant modification of the reactions of PS II. Moreover, the mutant was no more susceptible to excess light than the wild-type. It is, therefore, concluded that the product of the psbK gene is not crucial for PS II activity and possibly plays some other role in the metabolism of Synechocystis.
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    Functional characterisation of a purified homogeneous Photosystem II core complex with high oxygen evolution capacity from spinach (1993)
    Springer
    Photosynthesis research 35 (1993), S. 41-53 
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    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core complexes ; thermoluminescence ; oxygen yield ; fluorescence quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The functional properties of a purified homogeneous spinach PS II-core complex with high oxygen evolution capacity (Haag et al. 1990a) were investigated in detail by measuring thermoluminescence and oscillation patterns of flash induced oxygen evolution and fluorescence quantum yield changes. The following results were obtained: a) Depending on the illumination conditions the PS II-core complexes exhibit several thermoluminescence bands corresponding to the A band, Q band and Zv band in PS II membrane fragments. The lifetime of the Q band (Tmax=10°C) was determined to be 8s at T=10°C. No B band corresponding to S2QB − or S3QB − recombination could be detected. b) The flash induced transient fluorescence quantum yield changes exhibit a multiphasi relaxation kinetics shich reflect the reoxidation of Q A − . In control samples without exogenous acceptors this process is markedly slower than in PS II membrane fragments. The reaction becomes significantly retarded by addition of 10 μM DCMU. After dark incubation in the presence of K3[Fe(CN)6 c) Excitation of dark-adapted samples with a train of short saturating flashes gives rise to a typical pattern dominated by a high O2 yield due to the third flash and a highly damped period four oscillation. The decay of redox states S2 and S3 are dominated by short life times of 4.3 s and 1.5 s, respectively, at 20°C. The results of the present study reveal that in purified homogeneous PS II-core complexes with high oxygen evolution isolated from higher plants by β-dodecylmaltoside solubilization the thermodynamic properties and the kinetic parameters of the redox groups leading to electron transfer from water to QA are well preserved. The most obvious phenomenon is a severe modification of the QB binding site. The implications of this finding are discussed.
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    Can charge recombination as caused by pH-dependent donor-side limitation in PS 2 account for high-energy-state quenching? (1993)
    Springer
    Photosynthesis research 35 (1993), S. 97-100 
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    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; excitons ; Photosystem II ; triplet states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Schreiber and Neubauer (Photosynthesis Research 25: 279–293, 1990) have proposed a model which explains energy quenching by enhanced triplet formation as caused by charge recombination due to pH-dependent donor-side limitation. Quenching under these conditions is assumed to result from two mechanisms. Firstly, there is the withdrawal of excited states by charge recombination and formation of triplet states. Secondly, these triplet states can result in carotenoid triplets in the antenna which are supposed to quench excitons. Here, it is shown that quenching caused by both mechanisms can account for only about 25% of the experimentally observed energy quenching even under extremely favorable conditions. More likely, this number is less than 15%, as the contribution of the second step in the proposed triplet cycle is expected to be low as the life times of the carotenoid triplets are not long enough to cause the assumed quenching of excitons in the antenna.
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    Cloning and sequencing of mutantpsbB genes of the cyanobacteriumSynechocystis PCC 6803 (1993)
    Springer
    Photosynthesis research 37 (1993), S. 139-146 
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    ISSN: 1573-5079
    Keywords: chlorophyll-binding protein CP47 ; DNA sequence ; gene analysis ; mutagenesis ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ten strains from a collection of mutants ofSynechocystis 6803 defective in Photosystem II (PS II) function were transformed with chromosomal DNA of wild-type and mutant cells. Cross hybridization data allowed to identify four groups of PS II-mutants. Highly efficient transformation was observed between different mutant groups, but not within the groups. Restoration of photosynthetic activity of the mutant cells was also achieved by transformation with different parts of a 5.6 kbBam HI fragment of wild typeSynechocystis DNA containing thepsbB gene. Each group of mutants was transformed to photoautotrophic growth by specific subfragments of thepsbB gene. DNA fragments of four selected mutant strains hybridizing with thepsbB gene were isolated and sequenced. The mutations were identified as a single nucleotide insertion or substitution leading to stop codon formation in two of the mutants, as a deletion of 12 nucleotides, or as a nucleotide substitution resulting in an amino acid substitution in the other two mutants. Deletion of 12 nucleotides in mutant strain PMB1 and stop codon formation in strain NF16 affect membrane-spanning regions of the gene product, the CP 47 protein.
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    Manganese K-edge X-ray absorption spectra of the cyclic S-states in the photosynthetic oxygen-evolving system (1993)
    Springer
    Photosynthesis research 38 (1993), S. 331-339 
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    ISSN: 1573-5079
    Keywords: manganese cluster ; oxygen evolution ; Photosystem II ; water oxidation ; XANES
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A set of Mn K-edge XANES spectra due to the redox states S0−S3 of the OEC were determined by constructing a highly-sensitive X-ray detection system for use with physiologically native PS II membranes capable of cycling under a series of saturating laser-flashes. The spectra showed almost parallel upshifts with relatively high K-edge half-height energies given by 6550.9±0.2 eV, 6551.7±0.2 eV, 6552.5±0.2 eV and 6553.6±0.2 eV for the S0, S1, S2 and S3 states, respectively. The successive difference spectra between S0 and S1, S1 and S2, and S2 and S3 states were found to exhibit a similar peak around 6552–6553 eV, indicating that one Mn(III) ion or its direct ligand is univalently oxidized upon each individual S-state transition from S0 to S3. The present data, together with other observations of EPR and pre-edge XANES spectroscopy, suggest that the oxidation state of the Mn cluster undergoes a periodic change; S0: Mn(III,III,III,IV) → S1: Mn(III,IV,III,IV) → S2: Mn(III,IV,IV,IV) → S3: Mn(IV,IV,IV,IV) or Mn(III,IV,IV,IV)·L+ with L being a direct ligand of a Mn(III) ion.
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    Evidence for the contribution of the S-state transitions of oxygen evolution to the initial phase of fluorescence induction (1993)
    Springer
    Photosynthesis research 36 (1993), S. 81-88 
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    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; fluorescence induction ; Photosystem II ; S-state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fluorescence induction of isolated spinach chloroplasts was measured by using weak continuous light. It is found that the kinetics of the initial phase of fluorescence induction as well as the initial fluorescence level Fj are influenced by the number of preilluminating flashes, and shows damped period 4 oscillation. Evidence is given to show that it is correlated with the S-state transitions of oxygen evolution. Based on the previous observations that the S states can modulate the fluorescence yield of Photosystem II, a simulating calculation suggests that, in addition to the Photosystem II centers inactive in the plastoquinone reduction, the S-state transitions can also make a contribution to the intial phase of fluorescence induction.
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    Selective extraction of 22 kDa and 10 kDa polypeptides from Photosystem II without removal of 23 kDa and 17 kDa extrinsic proteins (1993)
    Springer
    Photosynthesis research 36 (1993), S. 11-16 
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    ISSN: 1573-5079
    Keywords: Photosystem II ; oxygen evolution ; extrinsic proteins ; 22 kDa polypeptide ; 10 kDa polypeptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Selective solubilization of Photosystem II membranes with the non-ionic detergent octyl thioglucopyranoside has allowed the isolation of a PS II system which has been depleted of the 22 and 10 kDa polypeptides but retains all three extrinsic proteins (33, 23 and 17 kDa). The PS II membranes which have been depleted of the 22 and 10 kDa species show high rates of oxygen evolution activity, external calcium is not required for activity and the manganese complex is not destroyed by exogenous reductants. When we compared this system to control PS II membranes, we observed a minor modification of the reducing side, and a conversion of the high-potential to the low-potential form of cytochrome b 559.
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    The relationship between Photosystem II intrinsic quantum yield and millisecond luminescence in thylakoids (1993)
    Springer
    Photosynthesis research 37 (1993), S. 131-138 
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    ISSN: 1573-5079
    Keywords: luminescence ; Photosystem II ; quantum efficiency ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between charge recombination at Photosystem II (PS II), as indicated by millisecond luminescence, and PS II quantum yield was studied in spinach thylakoids during electron flow to methylviologen. Under the low magnesium conditions used, a decrease in quantum yield was observed in the absence of non-photochemical excitation quenching, and therefore cannot be due to a restriction in excitation delivery to the reaction centre. It was found that the decrease of the parameter Φp, which is a measure of the intrinsic quantum yield of ‘open’ PS II centers, correlates with an increase in luminescence per ‘open’ center. The relationship between these two parameters was the same whether Φp was manipulated by dissipation of the transthylakoid pH gradient or of the electrical potential. This indicates that the mechanism by which Φp decreases depends in the same way on the two components of the protonmotive force as does the charge recombination at PS II. Calculation of the yield of luminescence with respect to the back reaction will be necessary to determine whether the charge recombination occurs at a sufficiently high rate to be directly responsible for the Φp decrease.
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    On the rates of cyclic electron transport around Photosystem II in the presence of donor side limitation (1993)
    Springer
    Photosynthesis research 37 (1993), S. 147-158 
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    ISSN: 1573-5079
    Keywords: Photosystem II ; cyclic electron transport ; energetic quenching ; pH, chlorophyll fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosystem II cyclic electron transport was investigated at low pH in spinach thylakoids and PS II preparations from the cyanobacteriumPhormidium laminosum. Variable fluorescence (Fv) quenching at a very low light intensity was examined as an indicator of cyclic electron flow. A progressive quenching of Fv was observed as the pH was lowered; however, this was shown to be mainly due to an inhibition of oxygen evolution. Cyclic electron flow in the uninhibited centres was estimated to occur at a rate comparable to or smaller than 1 μ mole O2 mg Chl−1 h−1 in the pH range 5.0 to 7.8. The quantum yeeld of oxygen production is known to decrease at low pH and has been taken to indicate cyclic electron flow (Crofts and Horton (1991) Biochim Biophys Acta 1058: 187–193). However, a direct all-or-none inhibition of oxygen production at low pH has also been reported (Meyer et al. (1989) Biochim Biophys Acta 974: 36–43). We have analysed the effects of light intensity on the rates of oxygen evolution in order to calculate ΦU, the quantum yield of open and uninhibited centres. ΦU was found to be constant over a broad pH range, and by using ferricyanide and phenyl-p-benzoquinone as electron acceptors the maximum possible rate of cyclic electron transport was equivalent to no more than 1 μmole O2 mg Chl−1 h−1. The rate was no greater when the acceptor was adjusted to provide the most favourable conditions for cyclic flow.
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    Inactivation of photosynthetic oxygen evolution by UV-B irradiation: A thermoluminescence study (1993)
    Springer
    Photosynthesis research 38 (1993), S. 455-462 
    Details
    ISSN: 1573-5079
    Keywords: oxygen evolution ; photodamage ; Photosystem II ; thermoluminescence ; UV-B radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S2QB - (B band) and S2QA − (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of QA - with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block QA to QB electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced QB. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the QB/DCMU binding site. The preferential loss of dark stable QB - may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.
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    Chemical oxidation and reduction of the O2-evolution center in Photosystem II (1993)
    Springer
    Photosynthesis research 38 (1993), S. 441-448 
    Details
    ISSN: 1573-5079
    Keywords: hydroxylamine ; hypochlorite ; manganese ; oxygen evolution ; Photosystem II ; S-states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Treatment of Photosystem II (PS II) with low concentrations of hydroxylamine is known to cause a two-flash delay in the O2-evolution pattern, and in the formation of the S2-state multiline EPR signal, due to the two-electron reduction of the S1-state by hydroxylamine to form the S-1-state. Past work has shown that these delays are not reversed by washing out the hydroxylamine nor by adding DCBQ or ferricyanide to oxidize the residual hydroxylamine, but are reversed by illumination with two saturating flashes followed by a 30-min dark incubation. We have examined the effects of treatments aimed at restoring the normal flash-induced O2-evolution pattern and S2-state multiline EPR signal after treatment of PS II with 40 μM hydroxylamine. In agreement with past work, we find that the two-flash delay in O2 evolution is not reversed when the hydroxylamine is removed by three cycles of centrifugation and resuspension in hydroxylamine-free buffer nor by adding ferricyanide or DCBQ to oxidize the unreacted hydroxylamine. However, the normal flash-induced O2-evolution pattern is restored by illumination with two saturating flashes followed by a 30-min dark incubation (after the sample was first treated with 40 μM hydroxylamine and the unreacted hydroxylamine was removed); illumination with one saturating flash followed by a 30-min dark incubation is only partially effective. These results show that ferricyanide and DCBQ are not effective at oxidizing the S-1-state to the S1-state. In contrast, adding hypochlorite (OCl-) after treatment with hydroxylamine restored the normal flash-induced O2-evolution pattern and also restored the formation of the S2-state multiline EPR signal by illumination at 200 K. We conclude that hypochlorite is capable of oxidizing the S-1-state to the S1-state. This is the first example of a chemical treatment that advances the delayed flash-induced O2 evolution pattern.
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    URL: http://dx.doi.org/10.1007/BF00046772
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    Characterization of inhibitory effects of NH2OH and its N-methyl derivatives on the O2-evolving complex of Photosystem II (1993)
    Springer
    Photosynthesis research 38 (1993), S. 449-453 
    Details
    ISSN: 1573-5079
    Keywords: anions ; Cl- ; hydroxylamines ; manganese ; O2 evolution ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inorganic cofactors (Mn, Ca2+ and Cl-) are essential for oxidation of H2O to O2 by Photosystem II. The Mn reductants NH2OH and its N-methyl derivatives have been employed as probes to further examine the interactions between these species and Mn at the active site of H2O oxidation. Results of these studies show that the size of a hydroxylamine derivative regulates its ability to inactivate O2 evolution activity, and that this size-dependent inhibition behavior arises from the protein structure of Photosystem II. A set of anions (Cl-, F- and SO4 2-) is able to slow NH2OH and CH3NHOH inactivation of intact Photosystem II membranes by exerting a stabilizing influence on the extrinsic 23 and 17 kDa polypeptides. In contrast to this non-specific anion effect, only Cl- is capable of attenuating CH3NHOH and (CH3)2NOH inhibition in salt-washed preparations lacking the 23 and 17 kDa polypeptides. However, Cl- fails to protect against NH2OH inhibition in salt-washed membranes. These results indicate that the attack by NH2OH and its N-methyl derivatives on Mn occurs at different sites in the O2-evolving complex. The small reductant NH2OH acts at a Cl--insensitive site whereas the inhibitions by CH3NHOH and (CH3)2NOH involve a site that is Cl- sensitive. These findings are consistent with earlier studies showing that the size of primary amines controls the Cl- sensitivity of their binding to Mn in the O2-evolving complex.
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    URL: http://dx.doi.org/10.1007/BF00046773
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    Modification of the thermoluminescence properties of Ca2+ depleted Photosystem II membranes by the 23 kDa extrinsic polypeptide and by oligocarboxylic acids (1993)
    Springer
    Photosynthesis research 35 (1993), S. 29-39 
    Details
    ISSN: 1573-5079
    Keywords: Ca2+-requirement ; extrinsic polypeptides ; Photosystem II ; water oxidizing complex ; thermoluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosystem II membranes were isolated from chloroplasts of pokeweed (Phytolacca americana) and rendered deficient in Ca2+, an inorganic cofactor of photosynthetic water oxidation. The thermoluminescence properties of such membranes were found to depend on the Ca2+-depleting method used. This feature was analyzed with respect to the thermoluminescence emission that accompanied the recombination reaction between the reduced acceptor QA − and the oxidant of the S2 state. It was determined that the differences observed among various preparations of Ca2+-depleted membranes were attributable to the presence or absence of the extrinsic 23 kDa polypeptide on the membranes. The binding of this polypeptide to Ca2+-depleted membranes devoid of the 17 and 23 kDa extrinsic polypeptides caused the thermoluminescence to be emitted at a higher temperature due to a further stabilization of an already abnormally stable S2 state. Addition of the chelators EDTA or EGTA and of citrate brought about a similar response. The conditions required for the upshift of the emission temperature of thermoluminescence strongly resembled those identified by Boussac et al. (FEBS Lett. 277 (1990) 69–74) as responsible for modifying the EPR multiline signal from the S2 state of Ca2+-depleted PS II membranes. Consistent with the authors' interpretation of the reason for this modification, we conclude that the elevated emission temperature of the thermoluminescence emission reflects an abnormal ligand environment of the Mn-center in PS II that may be created by a direct ligation of the added agents to Mn. Evidence is also presented that the return to a normal S2 after an addition of Ca2+ occurs via yet another condition of S2 which, in terms of its thermoluminescence properties, resembles that of Ca2+-depleted membranes before addition of modifying agents, but is not identical to it.
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    URL: http://dx.doi.org/10.1007/BF02185409
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    Photosystem II reaction centres stay intact during low temperature photoinhibition (1993)
    Springer
    Photosynthesis research 35 (1993), S. 191-200 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; D1-protein ; fluorescence quenching ; low temperature ; photoinhibition ; photosynthesis ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition of photosynthesis was studied in intact barley leaves at 5 and 20°C, to reveal if Photosystem II becomes predisposed to photoinhibition at low temperature by 1) creation of excessive excitation of Photosystem II or, 2) inhibition of the repair process of Photosystem II. The light and temperature dependence of the reduction state of QA was measured by modulated fluorescence. Photon flux densities giving 60% of QA in a reduced state at steady-state photosynthesis (300 μmol m−2s−1 at 5°C and 1200 μmol m−2s−1 at 20°C) resulted in a depression of the photochemical efficiency of Photosystem II (Fv/Fm) at both 5 and 20°C. Inhibition of Fv/Fm occurred with initially similar kinetics at the two temperatures. After 6h, Fv/Fm was inhibited by 30% and had reached steady-state at 20°C. However, at 5°C, Fv/Fm continued to decrease and after 10h, Fv/Fm was depressed to 55% of control. The light response of the reduction state of QA did not change during photoinhibition at 20°C, whereas after photoinhibition at 5°C, the proportion of closed reaction centres at a given photon flux density was 10–20% lower than before photoinhibition. Changes in the D1-content were measured by immunoblotting and by the atrazine binding capacity during photoinhibition at high and low temperatures, with and without the addition of chloramphenicol to block chloroplast encoded protein synthesis. At 20°C, there was a close correlation between the amount of D1-protein and the photochemical efficiency of photosystem II, both in the presence or in the absence of an active repair cycle. At 5°C, an accumulation of inactive reaction centres occurred, since the photochemical efficiency of Photosystem II was much more depressed than the loss of D1-protein. Furthermore, at 5°C the repair cycle was largely inhibited as concluded from the finding that blockage of chloroplast encoded protein synthesis did not enhance the susceptibility to photoinhibition at 5°C. It is concluded that, the kinetics of the initial decrease of Fv/Fm was determined by the reduction state of the primary electron acceptor QA, at both temperatures. However, the further suppression of Fv/Fm at 5°C after several hours of photoinhibition implies that the inhibited repair cycle started to have an effect in determining the photochemical efficiency of Photosystem II.
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    Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants (1993)
    Springer
    Photosynthesis research 35 (1993), S. 265-274 
    Details
    ISSN: 1573-5079
    Keywords: C3 plants ; C4 plants ; light ; Photosystem II ; quantum yield ; fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The light dependence of quantum yields of Photosystem II (ΦII) and of CO2 fixation were determined in C3 and C4 plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO2 fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=ΦCO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+Rl)/Ia=ΦCO2·], where RL is the rate of respiration in the light. The dependence of the ΦII/ΦCO2 and ΦII/ΦCO2 * ratios on light intensity was then evaluated. In both C3 and C4 plants there was little change in the ratio of ΦII/ΦCO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of ΦII/ΦCO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO2 fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO2 fixation under low light intensity may be due to respiratory loss of CO2. Using dark respiration as an estimate of RL, the calculated ΦII/ΦCO2 * ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO2 fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and ΦII were made by illuminating upper versus lower leaf surfaces of representative C3 and C4 monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of ΦII/ΦCO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower ΦII values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of ΦII/ΦCO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO2 fixation.
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    Characterization of a non-detergent PS II-cytochrome b/f preparation (BS) (1993)
    Springer
    Photosynthesis research 37 (1993), S. 227-236 
    Details
    ISSN: 1573-5079
    Keywords: absorption ; antenna size ; aqueous two-phase partitioning ; cytochrome b/f ; fluorescence ; Photosystem II ; plastoquinone pool ; sonication ; thylakoid membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A non-detergent photosystem II preparation, named BS, has been characterized by countercurrent distribution, light saturation curves, absorption spectra and fluorescence at room and at low temperature (−196°C). The BS fraction is prepared by a sonication-phase partitioning procedure (Svensson P and Albertsson P-Å, Photosynth Res 20: 249–259, 1989) which removes the stroma lamellae and the margins from the grana and leaves the appressed partition region intact in the form of vesicles. These are closed structures of inside-out conformation. They have a chlorophyll a/b ratio of 1.8–2.0, have a high oxygen evolving capacity (295 μmol O2 per mg chl h), are depleted in P700 and enriched in the cytochrome b/f complex. They have about 2 Photosystem II reaction centers per 1 cytochrome b/f complex. The plastoquinone pool available for PS II in the BS vesicles is 6–7 quinones per reaction center, about the same as for the whole thylakoid. It is concluded, therefore, that the plastoquinone of the stroma lamellae is not available to the PS II in the grana and that plastoquinone does not act as a long range electron transport shuttler between the grana and stroma lamellae. Compared with Photosystem II particles prepared by detergent (Triton X-100) treatment, the BS vesicles retain more cytochrome b/f complex and are more homogenous in their surface properties, as revealed by countercurrent distribution, and they have a more efficient energy transfer from the antenna pigments to the reaction center.
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    URL: http://dx.doi.org/10.1007/BF00032826
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    Photosynthetic water oxidation: The protein framework (1993)
    Springer
    Photosynthesis research 38 (1993), S. 249-263 
    Details
    ISSN: 1573-5079
    Keywords: oxygen evolution ; photosynthesis ; Photosystem II ; thylakoid membranes ; water oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Approximately 20 protein subunits are associated with the PS II complex, not counting subunits of peripheral light-harvesting antenna complexes. However, it is not yet established which proteins specifically are involved in the water-oxidation process. Much evidence supports the concept that the D1/D2 reaction center heterodimer not only plays a central role in the primary photochemistry of Photosystem II, but also is involved in electron donation to P680 and in ligation of the manganese cluster. This evidence includes (a) the primary donor to P680 has been shown to be a redox-active tyrosyl residue (Tyr161) in the D1 protein, and (b) site-directed mutagenesis and computer-assisted modeling of the reaction center heterodimer have suggested several sites with a possible function in manganese ligation. These include Asp170, Gln165 and Gln189 of the D1 protein and Glu69 of the D2 protein as well as the C-terminal portion of the mature D1 protein. Also, hydrophilic loops of the chlorophyll-binding protein CP43 that are exposed at the inner thylakoid surface could be essential for the water-splitting process. In photosynthetic eukaryotes, three lumenal extrinsic proteins, PS II-O (33 kDa), PS II-P (23 kDa) and PS II-Q (16 kDa), influence the properties of the manganese cluster without being involved in the actual catalysis of water oxidation. The extrinsic proteins together may have multiple binding sites to the integral portion of PS II, which could be provided by the D1/D2 heterodimer and CP47. A major role for the PS II-O protein is to stabilize the manganese cluster. Most experimental evidence favors a connection of the PS II-P protein with binding of the Cl- and Ca2+ ions required for the water oxidation, while the PS II-Q protein seems to be associated only with the Cl- requirement. The two latter proteins are not present in PS II of prokaryotic organisms, where their functions may be replaced by a 10–12 kDa subunit and a newly discovered low-potential cytochrome c-550.
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    Absorbance difference spectra of the S-state transitions in Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 323-330 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen evolving complex ; UV absorbance changes ; S-state spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S0 → S1 → S2 → S3 → S0, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S3 state with an inactive state, perhaps related to Ca2+-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S1 → S2 transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S2 → S3 transition was similar to that reported by Lavergne 1991 for PS II membranes. The S0 → S1 transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.
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    URL: http://dx.doi.org/10.1007/BF00046757
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    Functional size of Photosystem II determined by radiation inactivation (1993)
    Springer
    Photosynthesis research 38 (1993), S. 363-368 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; water oxidation ; radiation inactivation ; D1/D2/cytochrome b 559reaction center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The functional size of Photosystem II (PS II) was investigated by radiation inactivation. The technique provides an estimate of the functional mass required for a specific reaction and depends on irradiating samples with high energy γ-rays and assaying the remaining activity. The analysis is based on target theory that has been modified to take into account the temperature dependence of radiation inactivation of proteins. Using PS II enriched membranes isolated from spinach we determined the functional size of primary charge separation coupled to water oxidation and quinone reduction at the QB site: H2O → (Mn)4 → Yz → P680 → Pheophytin → Q → phenyl-p-benzoquinone. Radiation inactivation analysis indicates a functional mass of 88 ± 12 kDa for electron transfer from water to phenyl-p-benzoquinone. It is likely that the reaction center heterodimer polypeptides, D1 and D2, contribute approximately 70 kDa to the functional mass, in which case polypeptides adding up to approximately 20 kDa remain to be identified. Likely candidates are the α and β subunits of cytochrome b 559and the 4.5 kDa psbI gene product.
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    URL: http://dx.doi.org/10.1007/BF00046762
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    Slow oxygen release on the first two flashes in chemically stressed Photosystem II membrane fragments results from hydrogen peroxide oxidation (1993)
    Springer
    Photosynthesis research 38 (1993), S. 425-431 
    Details
    ISSN: 1573-5079
    Keywords: hydrogen peroxide ; hydroxylamine ; kinetics ; manganese ; oxygen release ; photosynthesis ; Photosystem II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced amperometric signals were measured with a Joliot-type O2 rate electrode in spinach Photosystem II (PS II) membrane fragments exposed to very low concentrations of added hydroxylamine or hydrogen peroxide. In both cases ‘anomalous O2 signals’ were observed on the first two flashes, and oscillating four-flash patterns were observed on subsequent flashes. The anomalous signals were eliminated in the presence of catalase but not EDTA. The rise times of the O2-release kinetics associated with the anomalous signals were slow (ca. 20 ms with NH2OH and ca. 120 ms with H2O2) compared to the kinetics of O2 release on subsequent flashes and in control membranes (3–6 ms). It is proposed that when the intact PS II O2-evolving complex is perturbed with small concentrations of added reductant, H2O2 can gain access and bind to the complex. Bound H2O2 can then reduce lower S states in some centers leading to anomalous O2 signals on the first two flashes. A model is presented to explain both types of anomalous O2 production. Oxygen observed on the third and subsequent flashes is due to the normal photosynthetic O2-evolution process arising from the S3-state. Anomalous O2 production could be a protective mechanism in PS II centers subjected to stress conditions.
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    URL: http://dx.doi.org/10.1007/BF00046770
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