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  • FALK, S, et al. (författare)
  • CHANGES IN PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII EXPOSED TO INCREASING LEVELS OF IRRADIANCE IN RELATIONSHIP TO THE PHOTOSYNTHETIC RESPONSE TO LIGHT
  • 1992
  • Ingår i: Photosynthesis Research. - 0166-8595. ; 31:1, s. 31-40
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200-mu-mol m-2 s-1 on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780-mu-mol m-2 s-1 where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600-mu-mol m-2 s-1 where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of Q(B)-reducing centers and 3) a second photoinhibitory range above 1600-mu-mol m-2 s-1 where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS II(alpha) centers and a large increase in spill-over in energy to PS I.
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  • Park, Y I, et al. (författare)
  • Role of a novel photosystem II-associated carbonic anhydrase in photosynthetic carbon assimilation in Chlamydomonas reinhardtii
  • 1999
  • Ingår i: FEBS Letters. - 0014-5793. ; 444:1, s. 102-105
  • Tidskriftsartikel (refereegranskat)abstract
    • Intracellular carbonic anhydrases (CA) in aquatic photosynthetic organisms are involved in the CO2-concentrating mechanism (CCM), which helps to overcome CO2 limitation in the environment. In the green alga Chlamydomonas reinhardtii, this CCM is initiated and maintained by the pH gradient created across the chloroplast thylakoid membranes by photosystem (PS) II-mediated electron transport. We show here that photosynthesis is stimulated by a novel, intracellular alpha-CA bound to the chloroplast thylakoids. It is associated with PSII on the lumenal side of the thylakoid membranes. We demonstrate that PSII in association with this lumenal CA operates to provide an ample flux of CO2 for carboxylation. (C) 1999 Federation of European Biochemical Societies.
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  • Rojdestvenski, I, et al. (författare)
  • A carbonic anhydrase catalyzed CO2 pump in Chlamydomonas reinhardtii : In vivo experiments, computer modelling, and theory
  • 2000
  • Ingår i: Russian journal of plant physiology. - 1021-4437. ; 47:5, s. 613-621
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the bicarbonate depletion effects on photosynthesis in high-CO2 grown-cell wall-less mutants of Chlamydomonas reinhardtii with (cw92) and without (cia3/cw15) active carbonic anhydrase (CA) associated with photosystem II (PSII). The mutants were grown in a high-CO2 medium and then washed with a CO2-free buffer. We discuss the shutdown of oxygen evolution in cw92 as a consequence of CO2 depletion of the Calvin cycle. It is suggested that CA acts as part of a PSII-driven pump delivering CO2 from the lumen into the stroma, where it becomes available to the Calvin cycle. Our model is supported by computer simulation data and accommodates the results of in vivo experiments as well as the differences between cw92 and cia3 mutants. We also present a simple theory of the phenomena discussed, based on a time-scale hierarchy approach, which describes the CO2 depletion in cw92 using only two rate constants-V-max and K-m of the Calvin cycle.
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  • Siedlecka, A, et al. (författare)
  • Primary carbon metabolism in Phaseolus vulgaris plants under Cd/Fe interaction
  • 1997
  • Ingår i: Plant physiology and biochemistry (Paris). - 0981-9428. ; 35:12, s. 951-957
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of the Cd/Fe interaction on primary carbon metabolism in Phaseolus vulgaris L. cv. Slowianka plants was investigated. It was documented earlier that Cd induced a decrease in the leaf Fe content, and increased levels of Fe may reduce Cd toxicity. The aim of the present study was to check whether Cd is toxic to Calvin cycle enzymes and especially if different Fe levels can modify the Cd effect. Bush-bean seedlings were cultivated in the presence of different Cd concentrations (0, 10, 20, 50 mu M) and at different Fe doses (deficient: 0 mmol, normal: 0.25 mmol, excessive: 0.5 mmol). Leaf content of ATP, ADP, Calvin cycle metabolites, activity of RUBISCO and carbonic anhydrase were measured. The influence of Cd/Fe interaction on the content of Calvin cycle metabolites seemed to be of both direct and indirect nature. The Cd-induced increase in ATP content, and in the ATP/ADP ratio, resulted from a decreased ATP consumption. At a higher Fe dose, the Cd/Fe interaction resulted in a revitalisation of the adenylate pool and Calvin cycle metabolites. The inhibition of RUBISCO carboxylase activity may be considered as the primary plant response to Cd-stress. The mechanisms of RUBISCO activation operate to overcome this limitation, although their efficiency was decreased by high Cd concentrations, resulting in decreased RUBISCO activity. At a low Cd concentration, the increase in RUBISCO activity was correlated with increased carbonic anhydrase activity.
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