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  • 1
    Electronic Resource
    Electronic Resource
    Inactivation of the photosynthetic carbon reduction cycle in isolated mesophyll protoplasts subjected to freezing stress (1987)
    Springer
    Photosynthesis research 14 (1987), S. 137-145 
    Details
    ISSN: 1573-5079
    Keywords: freezing damage ; high performance liquid chromatography ; light-activation of enzymes ; photosynthetic carbon reduction cycle (pool sizes) ; protoplasts (isolated) ; Valerianella locusta L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Isolated mesophyll protoplasts from Valerianella locusta L. were subjected to freeze-thaw cycles. Subsequently, steady-state pool sizes of 14C-labeled intermediates of the photosynthetic carbon reduction cycle were determined by high performance liquid chromatography. Protoplasts in which CO2 fixation was inhibited by preceding freezing stress, showed a strong increase in the proportion of fructose-1,6-bisphosphate, sedoheptulose-1,7-bisphosphate and triose phosphates. These results indicate an inhibition of the activities of stromal fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase. Furthermore, freezing stress caused a slight increase in the proportion of labeled ribulose-1,5-bisphosphate, which may be based on an inhibition or ribulose bisphosphate carboxylase activity. It was shown earlier (Rumich-Bayer and Krause 1986) that freezing-thawing readily affects photosynthetic CO2 assimilation independently of thylakoid inactivation. The present results are interpreted in terms of an inhibition of the light-activation system of the photosynthetic carbon reduction cycle, caused by freezing stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032318
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation of photosynthetic carbon metabolism during phosphate limitation of photosynthesis in isolated spinach chloroplasts (1987)
    Springer
    Photosynthesis research 14 (1987), S. 211-227 
    Details
    ISSN: 1573-5079
    Keywords: carbon metabolism ; chloroplasts ; phosphate ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Intact chloroplasts isolated from spinach were illuminated in the absence of inorganic phosphate (Pi) or with optimum concentrations of Pi added to the reaction medium. In the absence of Pi photosynthesis declined after the first 1–2 min and was less than 10% of the maximum rate after 5 min. Export from the chloroplast was inhibited, with up to 60% of the 14C fixed being retained in the chloroplast, compared to less than 20% in the presence of Pi. Despite the decreased export, chloroplasts depleted of Pi had lower levels of triose phosphate while the percentage of total phosphate in 3-phosphoglycerate was increased. Chloroplast ATP declined during Pi depletion and reached dark levels after 3–4 min in the light without added Pi. At this point, stromal Pi concentration was 0.2 mM, which would be limiting to ATP synthesis. Addition of Pi resulted in a rapid burst of oxygen evolution which was not initially accompanied by net CO2 fixation. There was a large decrease in 3-phosphoglycerate and hexose plus pentose monophosphates in the chloroplast stroma and a lesser decrease in fructose-1,6-bisphosphate. Stromal levels of triose phosphate, ribulose-1,5-bisphosphate and ATP increased after resupply of Pi. There was an increased export of 14-labelled compounds into the medium, mostly as triose phosphate. Light activation of both fructose-1,6-bisphosphatase and ribulose-1,5-bisphosphate carboxylase was decreased in the absence of Pi but increased following Pi addition. It is concluded that limitation of Pi supply to isolated chloroplasts reduced stromal Pi to the point where it limits ATP synthesis. The resulting decrease in ATP inhibits reduction of 3-phosphoglycerate to triose phosphate via mass action effects on 3-phosphoglycerate kinase. The lack of Pi in the medium also inhibits export of triose phosphate from the chloroplast via the phosphate transporter. Other sites of inhibition of photosynthesis during Pi limitation may be located in the regeneratige phase of the reductive pentose phosphate pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032706
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  • 3
    Electronic Resource
    Electronic Resource
    Control analysis of photosynthetic CO2 fixation (1990)
    Springer
    Photosynthesis research 24 (1990), S. 151-165 
    Details
    ISSN: 1573-5079
    Keywords: Calvin-Benson cycle ; mathematical model ; regulation of photosynthesis ; sensitivity analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The potential of control analysis to aid our understanding of regulation and control of photosynthetic carbon metabolism is investigated. Methods of metabolic control analysis are used to determine flux control coefficients of photosynthetic reactions from enzyme elasticities. Equations expressing control coefficients symbolically by enzyme elasticities are derived, and general properties of these expressions are analysed. Suggestions for experimental determination of flux control coefficients from enzyme elasticities are given. A simplified model of the Calvin-Benson cycle is used to illustrate interrelations between patterns of photosynthetic metabolites and that of control coefficients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00032595
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A simple model relating photoinhibitory fluorescence quenching in chloroplasts to a population of altered Photosystem II reaction centers (1991)
    Springer
    Photosynthesis research 30 (1991), S. 115-121 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; electron transport ; photochemical reaction (in Photosystem II) ; photoinhibition of photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS IIα and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, FVFM, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and FVFM ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00042009
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    Paper (German National Licenses)
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