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  • 1. Aksmann, Anna
    et al.
    Shutova, Tatiana
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Tukaj, Zbigniew
    The mechanism of anthracene interaction with photosynthetic apparatus: A study using intact cells, thylakoid membranes and PS II complexes isolated from Chlamydomonas reinhardtii2011In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 104, no 3-4, p. 205-210Article in journal (Refereed)
    Abstract [en]

    Intact cells of Chlamydomonas reinhardtii as well as isolated thylakoid membranes and photosystem II complexes were used to examine a possible mechanism of anthracene (ANT) interaction with the photosynthetic apparatus. Since ANT concentrations above 1 mM were required to significantly inhibit the rate of oxygen evolution in PS II membrane fragments it may indicate that the toxicant did not directly interact with this photosystem. On the other hand, stimulation of oxygen uptake by ANT-treated thylakoids suggested that ANT could either act as an artificial electron acceptor in the photosynthetic electron transport chain or function as an uncoupler. Electron transfer from excited chlorophyll to ANT is impossible due to the very low reduction potential of ANT and therefore we propose that toxic concentrations of ANT increase the thylakoid membrane permeability and thereby function as an uncoupler, enhancing electron transport in vitro. Hence, its unspecific interference with photosynthetic membranes in vitro suggests that the inhibitory effect observed on intact cell photosynthesis is caused by uncoupling of phosphorylation. 

  • 2. Allakhverdiev, Suleyman I.
    et al.
    Zharmukhamedov, Sergey K.
    Rodionova, Margarita V.
    Shuvalov, Vladimir A.
    Dismukes, Charles
    Shen, Jian-Ren
    Barber, James
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Govindjee,
    Vyacheslav (Slava) Klimov (1945-2017): A scientist par excellence, a great human being, a friend, and a Renaissance man2018In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 136, no 1, p. 1-16Article in journal (Other academic)
    Abstract [en]

    Vyacheslav Vasilevich (V.V.) Klimov (or Slava, as most of us called him) was born on January 12, 1945 and passed away on May 9, 2017. He began his scientific career at the Bach Institute of Biochemistry of the USSR Academy of Sciences (Akademy Nauk (AN) SSSR), Moscow, Russia, and then, he was associated with the Institute of Photosynthesis, Pushchino, Moscow Region, for about 50 years. He worked in the field of biochemistry and biophysics of photosynthesis. He is known for his studies on the molecular organization of photosystem II (PSII). He was an eminent scientist in the field of photobiology, a well-respected professor, and, above all, an outstanding researcher. Further, he was one of the founding members of the Institute of Photosynthesis in Pushchino, Russia. To most, Slava Klimov was a great human being. He was one of the pioneers of research on the understanding of the mechanism of light energy conversion and of water oxidation in photosynthesis. Slava had many collaborations all over the world, and he is (and will be) very much missed by the scientific community and friends in Russia as well as around the World. We present here a brief biography and some comments on his research in photosynthesis. We remember him as a friendly and enthusiastic person who had an unflagging curiosity and energy to conduct outstanding research in many aspects of photosynthesis, especially that related to PSII.

  • 3. ANDERSSON, A
    et al.
    FALK, S
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    HAGSTROM, A
    NUTRITIONAL CHARACTERISTICS OF A MIXOTROPHIC NANOFLAGELLATE, OCHROMONAS SP1989In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 17, no 3, p. 251-262Article in journal (Refereed)
  • 4.
    Benlloch, Reyes
    et al.
    Department of Forest Genetics and Plant Physiology, SLU.
    Shevela, Dmitriy
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hainzl, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grundström, Christin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shutova, Tatyana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sauer-Eriksson, Elisabeth
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Crystal structure and functional characterization of Photosystem II-associated carbonic anhydrase CAH3 in Chlamydomonas reinhardtii2015In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 167, no 3, p. 950-962Article in journal (Refereed)
    Abstract [en]

    In oxygenic photosynthesis, light energy is stored in the form of chemical energy by converting CO2 and water into carbohydrates.The light-driven oxidation of water that provides the electrons and protons for the subsequent CO2 fixation takes place inphotosystem II (PSII). Recent studies show that in higher plants, HCO3– increases PSII activity by acting as a mobile acceptor ofthe protons produced by PSII. In the green alga Chlamydomonas reinhardtii, a luminal carbonic anhydrase, CrCAH3, was suggested toimprove proton removal from PSII, possibly by rapid reformation of HCO3– from CO2. In this study, we investigated the interplaybetween PSII and CrCAH3 by membrane inlet mass spectrometry and x-ray crystallography. Membrane inlet mass spectrometrymeasurements showed that CrCAH3 was most active at the slightly acidic pH values prevalent in the thylakoid lumen underillumination. Two crystal structures of CrCAH3 in complex with either acetazolamide or phosphate ions were determined at 2.6- and2.7-Å resolution, respectively. CrCAH3 is a dimer at pH 4.1 that is stabilized by swapping of the N-terminal arms, a feature notpreviously observed in a-type carbonic anhydrases. The structure contains a disulfide bond, and redox titration of CrCAH3 functionwith dithiothreitol suggested a possible redox regulation of the enzyme. The stimulating effect of CrCAH3 and CO2/HCO3– on PSIIactivity was demonstrated by comparing the flash-induced oxygen evolution pattern of wild-type and CrCAH3-less PSIIpreparations. We showed that CrCAH3 has unique structural features that allow this enzyme to maximize PSII activity at lowpH and CO2 concentration.

  • 5. BORODIN, V
    et al.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    THE EFFECT OF LIGHT QUALITY ON THE INDUCTION OF EFFICIENT PHOTOSYNTHESIS UNDER LOW CO2 CONDITIONS IN CHLAMYDOMONAS-REINHARDTII AND CHLORELLA-PYRENOIDOSA1994In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 92, no 2, p. 254-260Article in journal (Refereed)
    Abstract [en]

    The effect of blue and red light on the adaptation to low CO2 conditions was studied in high-CO2 grown cultures of Chlorella pyrenoidosa (82T) and Chlamydomonas reinhardtii (137(+)) by measuring O-2 exchange under various inorganic carbon (C-i) concentrations. At equal photosynthetic photon flux density (PPFD), blue light was more favourable for adaptation in both species, compared to red light. The difference in photosynthetic oxygen evolution between cells adapted to low C-i under blue and red light was more pronounced when oxygen evolution was measured under low C-i compared to high C-i conditions. The effect of light quality on adaptation remained for several hours. The different effects caused by blue and red light was observed in C. pyrenoidosa over a wide range of PPFD with increasing differences at increasing PPFD. The maximal difference was obtained at a PPFD above 1 500 mu mol m(-2) s(-1). We found no difference in the extracellular carbonic anhydrase activity between blue- and red light adapted cells. The light quality effect recorded under C-i-limiting conditions in C. reinhardtii cells adapted to air, was only 37% less when instead of pure blue light red light containing 12.5% of blue light (similar PPFD as blue light) was used during adaptation to low carbon. This indicates that in addition to affecting photosynthesis, blue light affected a sensory system involved in algal adaptation to low C-i conditions. Since the affinity for C-i of C. pyrenoidosa and C. reinhardtii cells adapted to air under blue light was higher than that of cells adapted under red light, we suggest that induction of some component(s) of the C-i accumulating mechanism is regulated by the light quality.

  • 6.
    Buren, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ortega-Villasante, Cristina
    Ötvös, Krisztina
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Villarejo, Arsenio
    Use of the foot-and-mouth disease virus 2A peptide co-expression system to study intracellular protein trafficking in arabidopsis2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 12, p. e51973-Article in journal (Refereed)
    Abstract [en]

    Background: A tool for stoichiometric co-expression of effector and target proteins to study intracellular protein trafficking processes has been provided by the so called 2A peptide technology. In this system, the 16-20 amino acid 2A peptide from RNA viruses allows synthesis of multiple gene products from single transcripts. However, so far the use of the 2A technology in plant systems has been limited.

    Methodology/Principal Findings: The aim of this work was to assess the suitability of the 2A peptide technology to study the effects exerted by dominant mutant forms of three small GTPase proteins, RABD2a, SAR1, and ARF1 on intracellular protein trafficking in plant cells. Special emphasis was given to CAH1 protein from Arabidopsis, which is trafficking to the chloroplast via a poorly characterized endoplasmic reticulum-to-Golgi pathway. Dominant negative mutants for these GTPases were co-expressed with fluorescent marker proteins as polyproteins separated by a 20 residue self-cleaving 2A peptide. Cleavage efficiency analysis of the generated polyproteins showed that functionality of the 2A peptide was influenced by several factors. This enabled us to design constructs with greatly increased cleavage efficiency compared to previous studies. The dominant negative GTPase variants resulting from cleavage of these 2A peptide constructs were found to be stable and active, and were successfully used to study the inhibitory effect on trafficking of the N-glycosylated CAH1 protein through the endomembrane system.

    Conclusions/Significance: We demonstrate that the 2A peptide is a suitable tool when studying plant intracellular protein trafficking and that transient protoplast and in planta expression of mutant forms of SAR1 and RABD2a disrupts CAH1 trafficking. Similarly, expression of dominant ARF1 mutants also caused inhibition of CAH1 trafficking to a different extent. These results indicate that early trafficking of the plastid glycoprotein CAH1 depends on canonical vesicular transport mechanisms operating between the endoplasmic reticulum and Golgi apparatus.

  • 7.
    Burén, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Blanco-Rivero, Amaya
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Ortega-Villasante, Cristina
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Samuelsson, Göran
    Villarejo, Arsenio
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Specific suppression of the chloroplast N-glycosylated carbonic anhydrase (CAH1) has major impact on the photosynthetic performance of Arabidopsis thalianaManuscript (preprint) (Other academic)
  • 8.
    Burén, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ortega-Villasante, Cristina
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Blanco-Rivero, Amaya
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Martínez-Bernardini, Andrea
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Shutova, Tatiana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Villarejo, Arsenio
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    N-glycosylation is required for trafficking and activity of a chloroplast-localized carbonic anhydrase (CAH1) in Arabidopsis thalianaManuscript (preprint) (Other academic)
  • 9.
    Burén, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ortega-Villasante, Cristina
    Blanco-Rivero, Amaya
    Martínez-Bernardini, Andrea
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Shutova, Tatiana
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Shevela, Dmitriy
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Villarejo, Arsenio
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Importance of post-translational modifications for functionality of a chloroplast-localized carbonic anhydrase (CAH1) in Arabidopsis thaliana2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 6, p. e21021-Article in journal (Refereed)
    Abstract [en]

    Background

    The Arabidopsis CAH1 alpha-type carbonic anhydrase is one of the few plant proteins known to be targeted to the chloroplast through the secretory pathway. CAH1 is post-translationally modified at several residues by the attachment of N-glycans, resulting in a mature protein harbouring complex-type glycans. The reason of why trafficking through this non-canonical pathway is beneficial for certain chloroplast resident proteins is not yet known. Therefore, to elucidate the significance of glycosylation in trafficking and the effect of glycosylation on the stability and function of the protein, epitope-labelled wild type and mutated versions of CAH1 were expressed in plant cells.

    Methodology/Principal Findings

    Transient expression of mutant CAH1 with disrupted glycosylation sites showed that the protein harbours four, or in certain cases five, N-glycans. While the wild type protein trafficked through the secretory pathway to the chloroplast, the non-glycosylated protein formed aggregates and associated with the ER chaperone BiP, indicating that glycosylation of CAH1 facilitates folding and ER-export. Using cysteine mutants we also assessed the role of disulphide bridge formation in the folding and stability of CAH1. We found that a disulphide bridge between cysteines at positions 27 and 191 in the mature protein was required for correct folding of the protein. Using a mass spectrometric approach we were able to measure the enzymatic activity of CAH1 protein. Under circumstances where protein N-glycosylation is blocked in vivo, the activity of CAH1 is completely inhibited.

    Conclusions/Significance

    We show for the first time the importance of post-translational modifications such as N-glycosylation and intramolecular disulphide bridge formation in folding and trafficking of a protein from the secretory pathway to the chloroplast in higher plants. Requirements for these post-translational modifications for a fully functional native protein explain the need for an alternative route to the chloroplast.

  • 10.
    Burén, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ortega-Villasante, Cristina
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bako, Laszlo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Villarejo, Arsenio
    Department of Biology, Universidad Autónoma de Madrid, Spain.
    Optimization of the 2A peptide coexpression system to study trafficking of the plastid N-glycoprotein CAH1 in Arabidopsis thalianaManuscript (preprint) (Other academic)
  • 11. Eriksson, M
    et al.
    Villand, P
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Induction and regulation of expression of a low-CO2-induced mitochondrial carbonic anhydrase in Chlamydomonas reinhardtii1998In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 116, no 2, p. 637-641Article in journal (Refereed)
    Abstract [en]

    The time course of and the influence of light intensity and light quality on the induction of a mitochondrial carbonic anhydrase (CA) in the unicellular green alga Chlamydomonas reinhardtii was characterized using western and northern blots. This CA was expressed only under low-CO2 conditions (ambient air). In asynchronously grown cells, the mRNA was detected 15 min after transfer from air containing 5% CO2 to ambient air, and the 21-kD polypeptide was detected on western blots after 1 h. When transferred back to air containing 5% CO2, the mRNA disappeared within 1 h and the polypeptide was degraded within 3 d. Photosynthesis was required for the induction in asynchronous cultures. The induction increased with light up to 500 mu mol m(-2) s(-1), where saturation occurred. In cells grown synchronously, however, expression of the mitochondrial CA was also detected in darkness. Under such conditions the expression followed a circadian rhythm, with mRNA appearing in the dark 30 min before the light was turned on. Algae left in darkness continued this rhythm for several days.

  • 12. Eriksson, Mats
    et al.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    ISOLATION, PURIFICATION, AND CHARACTERIZATION OF MITOCHONDRIA FROM CHLAMYDOMONAS-REINHARDTII1995In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 107, no 2, p. 479-483Article in journal (Refereed)
    Abstract [en]

    Mitochondria were isolated from autotrophically grown Chlamydomonas reinhardtii cell-wall-less mutant CW 92. The cells were broken by vortexing with glass beads, and the mitochondria were collected by differential centrifugation and purified on a Percoll gradient. The isolated mitochondria oxidized malate, pyruvate, succinate, NADH, and a-ketoglutarate. Respiratory control was obtained with malate (2.0) and pyruvate (2.2) but not with the other substrates. From experiments with KCN and salicylhydroxamic acid, it was estimated that the capacity of the cytochrome pathway was at least 100 nmol O-2 mg(-1) protein min(-1) and the capacity of the alternative oxidase was at least 50 nmol O-2 mg(-1) protein min(-1). A low sensitivity to oligomycin indicates some difference in the properties of the mitochondrial ATPase from Chlamydomonas as compared to higher plants.

  • 13.
    Eriksson, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Ramazanov, Zakir
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Discovery of an algal mitochondrial carbonic anhydrase: molecular cloning and characterization of a low-CO2-induced polypeptide in Chlamydomonas reinhardtii1996In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 93, no 21, p. 12031-12034Article in journal (Refereed)
    Abstract [en]

    In green unicellular algae, several polypeptides are induced upon exposure to limiting CO2. We report here on the localization and characterization of one of these, a 22-kDa polypeptide in Chlamydomonas reinhardtii. This nuclear-encoded polypeptide is induced in the mitochondria by a lowering of the partial pressure of CO2 in the growth medium from 5% to air CO2 levels. Sequencing of two different cDNA clones coding for the polypeptide identified it as a 20.7-kDa beta-type carbonic anhydrase (CA; carbonate dehydratase, carbonate hydro-lyase, EC 4.2.1.1). The two clones differ in their nucleotide sequences but code for identical proteins, showing that this CA is encoded by at least two genes. Northern blot hybridization reveals that mRNA transcripts are only present in cells transferred to air CO2 levels. A comparison of the deduced amino acid sequence with those of other beta-CAs shows the largest degree of similarity with CA from the cyanobacterium Synechocystis (50% identity and 66% similarity). To our knowledge, this is the first identification and characterization of a mitochondrial CA from a photosynthetic organism.

  • 14. FALK, S
    et al.
    LEVERENZ, JW
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Oquist, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    CHANGES IN PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII EXPOSED TO INCREASING LEVELS OF IRRADIANCE IN RELATIONSHIP TO THE PHOTOSYNTHETIC RESPONSE TO LIGHT1992In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 31, no 1, p. 31-40Article in journal (Refereed)
    Abstract [en]

    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.

  • 15. FALK, S
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    RECOVERY OF PHOTOSYNTHESIS AND PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII AFTER EXPOSURE TO 3 LEVELS OF HIGH LIGHT1992In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 85, no 1, p. 61-68Article in journal (Refereed)
    Abstract [en]

    Recovery from 60 min of photoinhibitory treatment at photosynthetic photon flux densities of 500, 1400 and 2200-mu-mol m-2 s-1 was followed in cells of the green alga Chlamydomonas reinhardtii grown at 125-mu-mol m-2 s-1. These light treatments re resent photoregulation, moderate photoinhibition and strong photoinhibition, respectively. Treatment in photoregulatory light resulted in an increased maximal rate of oxygen evolution (P(max)) and an increased quantum yield (PHI), but a 15% decrease in F(V)/F(M). Treatment at moderately photoinhibitory light resulted in a 30% decrease in F(V)/F(M) and an approximately equal decrease in PHI. Recovery in dim light restored F(V)/F(M) within 15 and 45 min after high light treatment at 500 and 1 400-mu-mol m-2 s-1 respectively. Convexity (THETA), a measure of the extent of co-limitation between PS II turnover and whole-chain electron transport, and PHI approached, but did not reach the control level during recovery after exposure to 1 400-mu-mol m 2 s-1, whereas P(max) increased above the control. Treatment at 2200-mu-mol m-2 s-1 resulted in a strong reduction of the modeled parameters PHI, THETA and P(max). Subsequent recovery was initially rapid but the rate decreased, and a complete recovery was not reached within 120 min. Based on the results, it is hypothesized that exposure to high light results in two phenomena. The first, expressed at all three light intensities, involves redistribution within the different aspects of PS II heterogeneity rather than a photoinhibitory destruction of PS II reaction centers. The second, most strongly expressed at 2200-mu-mol m-2 s-1, is a physical damage to PS II shown as an almost total loss of PS II(alpha) and PS II Q(B)-reducing centers. Thus recovery displayed two phases, the first was rapid and the only visible phase in algae exposed to 500 and 1 400-mu-mol m-2 s-1. The second phase was slow and visible only in the later part of recovery in cells exposed to 2 200-mu-mol m-2 s-1.

  • 16. FALK, S
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Oquist, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    TEMPERATURE-DEPENDENT PHOTOINHIBITION AND RECOVERY OF PHOTOSYNTHESIS IN THE GREEN-ALGA CHLAMYDOMONAS-REINHARDTII ACCLIMATED TO 12 AND 27-DEGREES-C1990In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 78, no 2, p. 173-180Article in journal (Refereed)
  • 17. Hanson, D T
    et al.
    Franklin, L A
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Badger, M R
    The Chlamydomonas reinhardtii cia3 mutant lacking a thylakoid lumen-localized carbonic anhydrase is limited by CO2 supply to rubisco and not photosystem II function in vivo2003In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 132, no 4, p. 2267-2275Article in journal (Refereed)
    Abstract [en]

    The Chlamydomonas reinhardtii cia3 mutant has a phenotype indicating that it requires high-CO2 levels for effective photosynthesis and growth. It was initially proposed that this mutant was defective in a carbonic anhydrase (CA) that was a key component of the photosynthetic CO2-concentrating mechanism (CCM). However, more recent identification of the genetic lesion as a defect in a lumenal CA associated with photosystem II (PSII) has raised questions about the role of this CA in either the CCM or PSII function. To resolve the role of this lumenal CA, we re-examined the physiology of the cia3 mutant. We confirmed and extended previous gas exchange analyses by using membrane-inlet mass spectrometry to monitor O-16(2), O-18(2), and CO2 fluxes in vivo. The results demonstrate that PSII electron transport is not limited in the cia3 mutant at low inorganic carbon (Ci). We also measured metabolite pools sizes and showed that the RuBP pool does not fall to abnormally low levels at low Ci as might be expected by a photosynthetic electron transport or ATP generation limitation. Overall, the results demonstrate that under low Ci conditions, the mutant lacks the ability to supply Rubisco with adequate CO2 for effective CO2 fixation and is not limited directly by any aspect of PSII function. We conclude that the thylakoid CA is primarily required for the proper functioning of the CCM at low Ci by providing an ample supply of CO2 for Rubisco.

  • 18.
    Hiltonen, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bjorkbacka, H
    Forsman, C
    Clarke, A K
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Intracellular beta-carbonic anhydrase of the unicellular green alga Coccomyxa1998In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 117, no 4, p. 1341-1349Article in journal (Refereed)
    Abstract [en]

    Carbonic anhydrase (CA) (EC 4.2.1.1) enzymes catalyze the reversible hydration of CO,, a reaction that is important in many physiological processes. We have cloned and sequenced a full length cDNA encoding an intracellular P-CA from the unicellular green alga Coccomyxa. Nucleotide sequence data show that the isolated cDNA contains an open reading frame encoding a polypeptide of 227 amino acids. The predicted polypeptide is similar to beta-type CAs from Escherichia coli and higher plants, with an identity of 26% to 30%. The Coccomyxa cDNA was overexpressed in E. coli, and the enzyme was purified and biochemically characterized. The mature protein is a homotetramer with an estimated molecular mass of 100 kD. The CO2-hydration activity of the Coccomyxa enzyme is comparable with that of the pea homolog. However, the activity of Coccomyxa CA is largely insensitive to oxidative conditions, in contrast to similar enzymes from most higher plants. Fractionation studies further showed that Coccomyxa CA is extrachloroplastic.

  • 19.
    Hiltonen, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Clarke, Adrian K
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    A cDNA coding for glutathione S-transferase from the unicellular green algae Coccomyxa sp1996In: Gene, ISSN 0378-1119, E-ISSN 1879-0038, Vol. 176, no 1-2, p. 263-264Article in journal (Refereed)
    Abstract [en]

    A cDNA coding for glutathione S-transferase (GST) was cloned and sequenced from the unicellular green algae Coccomyxa sp. The predicted 215 amino acid polypeptide (23.9 kDa, pI 5.3) is most similar to the theta-type GSTs found in a variety of different eukaryotic organisms. Within this sub-class, the Coccomyxa GST is 42% identical (63% similar) to the flatfish Pleuronectes platessa homologue, and 24 to 35% (49-57%) to other theta-type GST's.

  • 20.
    Hiltonen, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    PALMQVIST, K
    CLARKE, AK
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    PURIFICATION AND CHARACTERIZATION OF AN INTRACELLULAR CARBONIC-ANHYDRASE FROM THE UNICELLULAR GREEN-ALGA COCCOMYXA1995In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 195, no 3, p. 345-351Article in journal (Refereed)
    Abstract [en]

    An intracellular carbonic anhydrase (CA; EC 4.2.1.1) was purified and characterised from the unicellular green alga Coccomyxa sp. Initial studies showed that cultured Coccomyxa cells contain an intracellular CA activity around 100 times higher than that measured in high-CO2-grown cells of Chlamydomonas reinhardtii CW 92. Purification of a protein extract containing the CA activity was carried out using ammonium-sulphate precipitation followed by anion-exchange chromatography. Proteins were then separated by native (non-dissociating) polyacrylamide gel electrophoresis, with each individual protein band excised and assayed for CA activity. Measurements revealed CA activity associated with two discrete protein bands with similar molecular masses of 80 +/- 5 kDa. Dissociation by denaturing polyacrylamide gel electrophoresis showed that both proteins contained a single polypeptide of 26 kDa, suggesting that each 80-kDa native protein was a homogeneous trimer. Isoelectric focusing of the 80-kDa proteins also produced a single protein band at a pH of 6.5. Inhibition studies on the purified CA extract showed that 50% inhibition of CA activity was obtained using 1 mu M azetazolamide. Polyclonal antibodies against the 26-kDa CA were produced and shown to have a high specific binding to a single polypeptide in soluble protein extracts from Coccomyxa. cells. The same antiserum, however, failed to cross-react with soluble proteins isolated from two different species of green algae, Chlamydomonas reinhardtii and Chlorella vulgaris. Correspondingly, antisera directed against pea chloroplastic CA, extracellular CA from C. reinhardtii and human CAII, showed no cross-hybridisation to the 26-kDa polypeptide in Coccomyxa. The 26-kDa protein was confirmed as being a CA by N-terminal sequencing of two internal polypeptide fragments and alignment of these sequences with that of previously identified CA proteins from several different species.

  • 21. HOFSLAGARE, O
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    HALLGREN, JE
    PEJRYD, C
    SJOBERG, S
    A COMPARISON BETWEEN 3 METHODS OF MEASURING PHOTOSYNTHETIC UPTAKE OF INORGANIC CARBON IN ALGAE1985In: Photosynthetica (Praha), ISSN 0300-3604, E-ISSN 1573-9058, Vol. 19, no 4, p. 578-585Article in journal (Refereed)
  • 22. HOFSLAGARE, O
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    SJOBERG, S
    CADMIUM EFFECTS ON PHOTOSYNTHESIS AND NITRATE ASSIMILATION IN SCENEDESMUS-OBLIQUUS - A POTENTIOMETRIC STUDY IN AN OPEN CO2-SYSTEM1985In: Environmental and Experimental Botany, ISSN 0098-8472, E-ISSN 1873-7307, Vol. 25, no 1, p. 75-82Article in journal (Refereed)
  • 23. HOFSLAGARE, O
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    SJOBERG, S
    INGRI, N
    A PRECISE POTENTIOMETRIC METHOD FOR DETERMINATION OF ALGAL ACTIVITY IN AN OPEN CO2 SYSTEM1983In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 6, no 3, p. 195-201Article in journal (Refereed)
  • 24. HOFSLAGARE, O
    et al.
    SJOBERG, S
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    THE EFFECT OF ARSENATE AND ARSENITE ON PHOTOSYNTHESIS IN SCENEDESMUS-OBLIQUUS - A POTENTIOMETRIC STUDY IN A CLOSED CO2-SYSTEM1994In: Chemical speciation and bioavailability, ISSN 0954-2299, E-ISSN 2047-6523, Vol. 6, no 4, p. 95-102Article in journal (Refereed)
    Abstract [en]

    A potentiometric titration method was used to study the adverse effect of arsenate (As(V) and arsenite (As(III) on inorganic carbon uptake in suspensions of the green alga Scenedesmus obliquus. The measurements were performed in a closed CO2-system with diluted synthetic seawater (1 parts per thousand salinity) as ionic medium. Usually, the algal chlorophyll concentration was 0.4 mg dm-3, while the arsenate- and arsenite-concentrations were varied within the limits 0.1 to 200 mumol dm-3. In some experiments arsenate toxicity was studied in the presence of 1 to 100 mumol dm-3 of phosphate (P(V)). With concentrations of arsenate or arsenite less than 0.1 mumol dm-3 no toxic effects were observed. However, at As-concentrations of 200 mumol dm-3, the algal carbon uptake was reduced by 41% with arsenate and 29% with arsenite, i.e., arsenate is more toxic to Scenedesmus obliquus than arsenite. The toxicity of arsenate was negligible in the presence of a ten fold excess of phosphate. This is probably due to chemical similarities between arsenate and phosphate causing competition between the ions for the binding sites. The importance of taking the speciation as well as the buffer capacity of the algal system into account, when calculating the carbon uptake, is also discussed.

  • 25.
    Huang, Shenghua
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hainzl, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Grundström, Christin
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Forsman, Cecilia
    Orphan Biovitrum AB, Umeå, Sweden.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Sauer-Eriksson, A Elisabeth
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Structural studies of β-Carbonic Anhydrase from the Green Alga Coccomyxa: Inhibitor complexes with Anions and Acetazolamide2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 12, p. e28458-Article in journal (Refereed)
    Abstract [en]

    The β-class carbonic anhydrases (β-CAs) are widely distributed among lower eukaryotes, prokaryotes, archaea, and plants. Like all CAs, the β-enzymes catalyze an important physiological reaction, namely the interconversion between carbon dioxide and bicarbonate. In plants the enzyme plays an important role in carbon fixation and metabolism. To further explore the structure-function relationship of β-CA, we have determined the crystal structures of the photoautotroph unicellular green alga Coccomyxa β-CA in complex with five different inhibitors: acetazolamide, thiocyanate, azide, iodide, and phosphate ions. The tetrameric Coccomyxa β-CA structure is similar to other β-CAs but it has a 15 amino acid extension in the C-terminal end, which stabilizes the tetramer by strengthening the interface. Four of the five inhibitors bind in a manner similar to what is found in complexes with α-type CAs. Iodide ions, however, make contact to the zinc ion via a zinc-bound water molecule or hydroxide ion - a type of binding mode not previously observed in any CA. Binding of inhibitors to Coccomyxa β-CA is mediated by side-chain movements of the conserved residue Tyr-88, extending the width of the active site cavity with 1.5-1.8 Å. Structural analysis and comparisons with other α- and β-class members suggest a catalytic mechanism in which the movements of Tyr-88 are important for the CO(2)-HCO(3) (-) interconversion, whereas a structurally conserved water molecule that bridges residues Tyr-88 and Gln-38, seems important for proton transfer, linking water molecules from the zinc-bound water to His-92 and buffer molecules.

  • 26.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Clarke, Adrian K
    Chen, Zhi-Yuan
    Hugghins, Stephanie Y
    Park, Youn-II
    Husic, H David
    Moroney, James V
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    A novel α-type carbonic anhydrase associated with the thylakoid membrane in Chlamydomonas reinhardtii is required for growth at ambient CO21998In: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 17, no 5, p. 1208-1216Article in journal (Refereed)
    Abstract [en]

    A 29.5 kDa intracellular α-type carbonic anhydrase, designated Cah3, from the unicellular green alga Chlamydomonas reinhardtii is the first of this type discovered inside a photosynthetic eukaryote cell. We describe the cloning of a cDNA which encodes the protein. Immunoblot studies with specific antibodies raised against Cah3 demonstrate that the polypeptide is associated exclusively with the thylakoid membrane. The putative transit peptide suggests that Cah3 is directed to the thylakoid lumen, which is confirmed further by the presence of mature sized Cah3 after thermolysin treatment of intact thylakoids. Complementation of the high inorganic carbon concentration-requiring mutant, cia-3, with a subcloned cosmid containing the cah3 gene yielded transformants that grew on atmospheric levels of CO2 (0.035%) and contained an active 29.5 kDa alpha-type carbonic anhydrase. Although, cia-3 has reduced internal carbonic anhydrase activity, unexpectedly the level of Cah3 was similar to that of the wild-type, suggesting that the mutant accumulates an inactive Cah3 polypeptide. Genomic sequence analysis of the mutant revealed two amino acid changes in the transit peptide. Results from photosynthesis and chlorophyll a fluorescence parameter measurements show that the cia-3 mutant is photosynthetically impaired. Our results indicate that the carbonic anhydrase, extrinsically located within the chloroplast thylakoid lumen, is essential for growth of C.reinhardtii at ambient levels of CO2, and that at these CO2 concentrations the enzyme is required for optimal photosystem II photochemistry.

  • 27.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hiltonen, Thomas
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Husic, H David
    Ramazanov, Zakir
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Intracellular carbonic anhydrase of Chlamydomonas reinhardtii1995In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 109, no 2, p. 533-539Article in journal (Refereed)
    Abstract [en]

    An intracellular carbonic anhydrase (CA; EC 4.2.1.1) was purified to homogeneity from a mutant strain of Chlamydomonas reinhardtii (CW 92) lacking a cell wall. Intact cells were washed to remove periplasmic CA and were lysed and fractionated into soluble and membrane fractions by sedimentation. All of the CA activity sedimented with the membrane fraction and was dissociated by treatment with a buffer containing 200 mM KCI. Solubilized proteins were fractionated by ammonium sulfate precipitation, anionic exchange chromatography, and hydrophobic interaction chromatography. The resulting fraction had a specific activity of 1260 Wilbur-Anderson units/mg protein and was inhibited by acetazolamide (50% inhibition concentration, 12 nM). Final purification was accomplished by the specific absorption of the enzyme to a Centricon-10 microconcentrator filter. A single, 29.5-kD polypeptide was eluted from the filter with sodium dodecyl sulfate-polyacrylamide gel electrophoresis sample buffer, and a 1.5 M ammonium sulfate eluate contained CA activity. In comparison with human CA isoenzyme II, the N-terminal and internal amino acid sequences from the 29.5-kD polypeptide were 40% identical with the N-terminal region and 67% identical with an internal conserved region. Based on this evidence, we postulate that the 29.5-kD polypeptide is an internal CA in C. reinhardtii and that the enzyme is closely related to the alpha-type CAs observed in animal species.

  • 28.
    Karlsson, Jan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    RAMAZANOV, Z
    Hiltonen, Thomas
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    EFFECT OF VANADATE ON PHOTOSYNTHESIS AND THE ATP ADP RATIO IN LOW-CO2-ADAPTED CHLAMYDOMONAS-REINHARDTII CELLS1994In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 192, no 1, p. 46-51Article in journal (Refereed)
    Abstract [en]

    We have assessed the effect of vanadate as an inhibitor of plasma-membrane ATPase on photosynthesis and the ATP/ADP ratio in Chlamydomonas reinhardtii CW-92 (a mutant strain lacking a cell wall). This effect was compared in low-CO2-adapted cells grown in media bubbled with air containing 400 or 70 muL . L-1 CO2. Evidence is presented indicating that cells grown at 70 muL . L-1 CO2 have a higher rate of photosynthetic O2 evolution than cells grown at 400 muL . L-1 CO2, at limiting carbon concentrations. Extracellular and intracellular carbonic-anhydrase activities were, however, similar in cells grown in both of the low-carbon conditions. Vanadate inhibited, to a different extent, the HCO3--dependent O2 evolution in cells grown at 400 and 70 muL . L-1 CO2. At 400 muM vanadate, inhibition reached 70-75 % in cells grown at 400 muL . L-1 but only 50 % in those grown at 70 muL . L-1 CO2. The ATP/ADP ratios determined with and without vanadate at limiting concentrations of dissolved inorganic carbon indicated that more ATP was hydrolysed in algae grown at 70 muL . L-1 than in those grown at 400 muL . L-1 CO2. We conclude that the maximal capacity to accumulate dissolved inorganic carbon is inversely related to the CO2 concentration in the medium. Activation and - or synthesis of vanadate-sensitive ATPase may be the major explanation for the higher capacity for HCO3--dependent O2 evolution in cells grown under limited CO2 concentrations.

  • 29.
    Koroidov, Sergey
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shevela, Dmitriy
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shutova, Tatyana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mobile hydrogen carbonate acts as proton acceptor in photosynthetic water oxidation2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 11, no 17, p. 6299-6304Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria, algae and plants oxidize water to the O2 we breathe, and consume CO2 during the synthesis of biomass. Although these vital processes are functionally and structurally well separated in photosynthetic organisms, there is a long-debated role for CO2/HCO3 in water oxidation. Using membrane-inlet mass spectrometry we demonstrate that HCO3 acts as a mobile proton acceptor that helps to transport the protons produced inside of photosystem II by water-oxidation out into the chloroplast's lumen, resulting in a light-driven production of O2 and CO2. Depletion of HCO3 from the media leads, in the absence of added buffers, to a reversible down-regulation of O2 production by about 20%. These findings add a previously unidentified component to the regulatory network of oxygenic photosynthesis, and conclude the more than 50-y-long quest for the function of CO2/ HCO3 in photosynthetic water oxidation.

  • 30. Kromer, S
    et al.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Regulation of the supply of cytosolic oxaloacetate for mitochondrial metabolism via phospho enolpyruvate carboxylase in barley leaf protoplasts .1. The effect of covalent modification on PEPC activity, pH response, and kinetic properties1996In: Biochimica et Biophysica Acta - General Subjects, ISSN 0304-4165, E-ISSN 1872-8006, Vol. 1289, no 3, p. 343-350Article in journal (Refereed)
    Abstract [en]

    The regulation of the supply of oxaloacetate (OAA) for mitochondrial metabolism via phosphoenolpyruvate carboxylase (PEPC) by covalent modification is studied in barley (Hordeum vulgare L.) leaf protoplasts in light or darkness as well as under photorespiratory or non-photorespiratory conditions. Extracts for studies on in vivo PEPC phosphorylation were prepared from barley leaf protoplasts by rapid filtration, fractionating the cell within less than 1 s. Measurements of in vitro PEPC activity were performed on samples quickly frozen in liquid nitrogen to break the cell and stop metabolism and thus preserve the in vivo activation state. The relative PEPC phosphorylation state increased upon illumination and decreased upon redarkening under photorespiratory and non-photorespiratory conditions. PEPC activity measured in the presence of malate (3 mM) under photorespiratory conditions showed the same response indicating that a light-induced increase in PEPC activity and decrease in malate sensitivity is caused by an increased phosphorylation level of the PEPC protein. PEPC activity was pH dependent. At the physiological cytosolic pH, activity was suboptimal, but most sensitive towards malate inhibition and glucose 6-phosphate stimulation. The presence of malate increased the sensitivity of PEPC activity towards pH changes. The response of PEPC activity to changing pH was not affected by changes in the activation state of the enzyme. The K-m (phosphoenolpyruvate, PEP) is about 1 mM. Upon illumination the K-m (PEP) decrease significantly. V-max was unaffected by the light treatment. The presence of physiological concentrations of glucose 6-phosphate decreased K-m (PEP) 5- to 10-fold and increased V-max by about 35%. The effect of glucose 6-phosphate was strongest (up to 7-fold) at subsaturating PEP concentrations stimulating PEPC activity to nearly maximal rates. The results show that an increase in PEPC phosphorylation state causes an increase in PEPC activity as well as in substrate affinity leading to an increased production of OAA in the light.

  • 31. Kromer, S
    et al.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Regulation of the supply of oxaloacetate for mitochondrial metabolism via phospho enolpyruvate carboxylase in barley leaf protoplasts .2. Effects of metabolites on PEPC activity at different activation states of the protein1996In: Biochimica et Biophysica Acta - General Subjects, ISSN 0304-4165, E-ISSN 1872-8006, Vol. 1289, no 3, p. 351-361Article in journal (Refereed)
    Abstract [en]

    The regulation of the supply of oxaloacetate (OAA) for mitochondrial metabolism via phosphoenolpyruvate carboxylase (PEPC) by metabolites is studied in barley (Hordeum vulgare L.) leaf protoplasts in light or darkness as well as under photorespiratory or non-photorespiratory conditions. Measurements on PEPC activity were performed on samples quickly frozen in liquid nitrogen to break the cell and stop metabolism and thus preserve the in vivo activation state. Glycine, serine, pyruvate, acetyl-CoA, glycolate, fructose 1,6-bisphosphate, fructose 2,6-bisphosphate and ADP had no significant effect on PEPC activity. Malate, aspartate and glutamate were strong inhibitors of PEPC activity decreasing the activity more in light versus darkness. However, at the physiological cytosolic concentration of these metabolites under the respective conditions, inhibition of PEPC activity was about the same with the exception of aspartate which inhibits more under non-photorespiratory than under photorespiratory conditions. 2-Oxoglutarate and glyoxylate decreased PEPC activity by 20 to 40% in the range of its physiological cytosolic concentration. Inhibition by physiological cytosolic concentrations of glutamine was limited. Glucose B-phosphate, fructose B-phosphate, 3-phosphoglycerate, dihydroxyacetonphosphate and P-i stimulated PEPC activity significantly in their physiological cytosolic concentration range. Physiological cytosolic concentrations of glucose 6-phosphate and fructose 6-phosphate activated PEPC activity to about the same extent under all conditions applied, while 3-phosphoglycerate and dihydroxyacetonphosphate stimulating Stronger under non-photorespiratory versus photorespiratory conditions. Moreover, dihydroxyacetonphosphate stimulated PEPC activity more in light versus darkness under non-photorespiratory conditions. P-i activation of PEPC activity decreases in light versus darkness under non-photorespiratory conditions. Stimulation of PEPC activity by citrate in its physiological concentration range is limited. Glucose 1-phosphate and AMP activated PEPC activity only at concentrations higher than their physiological levels in the cytosol. Determinations of PEPC activity in the presence of different malate/glucose 6-phosphate ratios revealed that glucose 6-phosphate totally relieved the inhibitory effect of malate. The regulatory properties of PEPC activity will be discussed in relation to its functions in C-3 plants.

  • 32. Kupriyanova, Elena
    et al.
    Villarejo, Arsenio
    Markelova, Alexandra
    Gerasimenko, Lyudmila
    Zavarzin, Georgy
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Los, Dmitry A
    Pronina, Natalia
    Extracellular carbonic anhydrases of the stromatolite-forming cyanobacterium Microcoleus chthonoplastes.2007In: Microbiology, ISSN 1350-0872, Vol. 153, no Pt 4, p. 1149-56Article in journal (Refereed)
    Abstract [en]

    Active extracellular carbonic anhydrases (CAs) were found in the alkaliphilic stromatolite-forming cyanobacterium Microcoleus chthonoplastes. Enzyme activity was detected in intact cells and in the cell envelope fraction. Western blot analysis of polypeptides from the cell envelope suggested the presence of at least two polypeptides cross-reacting with antibodies against both {alpha} and beta classes of CA. Immunocytochemical analysis revealed putative {alpha}-CA localized in the glycocalyx. This {alpha}-CA has a molecular mass of about 34 kDa and a pI of 3.5. External CAs showed two peaks of activity at around pH 10 and 7.5. The possible involvement of extracellular CAs of M. chthonoplastes in photosynthetic assimilation of inorganic carbon and its relationship to CaCO3 deposition during mineralization of cyanobacterial cells are discussed.

  • 33. Larsson, S
    et al.
    Bjorkbacka, H
    Forsman, C
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Olsson, O
    Molecular cloning and biochemical characterization of carbonic anhydrase from Populus tremula x tremuloides1997In: Plant Molecular Biology, ISSN 0167-4412, E-ISSN 1573-5028, Vol. 34, no 4, p. 583-592Article in journal (Refereed)
    Abstract [en]

    A leaf cDNA library from hybrid aspen, Populus tremula x tremuloides, was constructed. From this two different cDNA clones, denoted CAla and CAlb, encoding a chloroplastic carbonic anhydrase (CA) were isolated and DNA sequenced. Analysis of the deduced amino acid sequences showed that the isolated CAs belong to the beta-CA family, and have identities around 70% to other dicotyledonous plant CAs. The two hybrid aspen cDNA clones display a high nucleotide sequence identity, only 12 nucleotides differ. Since only one gene copy of this soluble chloroplastic CA is present in the nuclear genome, we postulate that the two isolated cDNA clones are alleles. Northern blot hybridization revealed a CA transcript of ca. 1300 bases, 140 bases shorter than in pea. Western and northern blot hybridizations on crude protein extracts and on total RNA, respectively, isolated from stem and leaves, showed that hybrid aspen CA is expressed specifically in the leaf under the growth conditions used. Based on the deduced amino acid sequence, the mature hybrid aspen CA enzyme subunit has a molecular mass of 24.8 kDa. The enzyme was over-expressed in Escherichia coli, and purified by affinity chromatography. Biochemical characterization showed that the protein structure and the CO2-hydration activity are similar to the pea enzyme. Molecular characterization of a CA from a perennial plant has not previously been performed, and it demonstrates that both the structure and activity of hybrid aspen CA resembles CAs from annual plants.

  • 34. LEVERENZ, JW
    et al.
    FALK, S
    PILSTROM, CM
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    THE EFFECTS OF PHOTOINHIBITION ON THE PHOTOSYNTHETIC LIGHT-RESPONSE CURVE OF GREEN PLANT-CELLS (CHLAMYDOMONAS-REINHARDTII)1990In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 182, no 2, p. 161-168Article in journal (Refereed)
  • 35. LONNEBORG, A
    et al.
    KALLA, SR
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Oquist, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    LIGHT-REGULATED EXPRESSION OF THE PSB A TRANSCRIPT IN THE CYANOBACTERIUM ANACYSTIS-NIDULANS1988In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 240, no 1-2, p. 110-114Article in journal (Refereed)
  • 36. LONNEBORG, A
    et al.
    KALLA, SR
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Oquist, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    LIGHT-REGULATED EXPRESSION OF THE PSB A TRANSCRIPT IN THE CYANOBACTERIUM ANACYSTIS-NIDULANS1988In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 240, no 1-2, p. 110-114Article in journal (Refereed)
  • 37. LONNEBORG, A
    et al.
    KALLA, SR
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Oquist, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    LIGHT-REGULATED EXPRESSION OF THE PSB A TRANSCRIPT IN THE CYANOBACTERIUM ANACYSTIS-NIDULANS1988In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 240, no 1-2, p. 110-114Article in journal (Refereed)
  • 38. Lundin, Björn
    et al.
    Thuswaldner, Sophie
    Shutova, Tatiana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Eshaghi, Said
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Barber, James
    Andersson, Bertil
    Spetea, Cornelia
    Subsequent events to GTP binding by the plant PsbO protein: Structural changes, GTP hydrolysis and dissociation from the photosystem II complex2007In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1767, no 6, p. 500-508Article in journal (Refereed)
    Abstract [en]

    Besides an essential role in optimizing water oxidation in photosystem II (PSII), it has been reported that the spinach PsbO protein binds GTP [C. Spetea, T. Hundal, B. Lundin, M. Heddad, I. Adamska, B. Andersson, Proc. Natl. Acad. Sci. U.S.A. 101 (2004) 1409–1414]. Here we predict four GTP-binding domains in the structure of spinach PsbO, all localized in the β-barrel domain of the protein, as judged from comparison with the 3D-structure of the cyanobacterial counterpart. These domains are not conserved in the sequences of the cyanobacterial or green algae PsbO proteins.MgGTP induces specific changes in the structure of the PsbO protein in solution, as detected by circular dichroism and intrinsic fluorescence spectroscopy. Spinach PsbO has a low intrinsic GTPase activity, which is enhanced fifteen-fold when the protein is associated with the PSII complex in its dimeric form. GTP stimulates the dissociation of PsbO from PSII under light conditions known to also release Mn2+ and Ca2+ ions from the oxygen-evolving complex and to induce degradation of the PSII reaction centre D1 protein. We propose the occurrence in higher plants of a PsbO-mediated GTPase activity associated with PSII, which has consequences for the function of the oxygen-evolving complex and D1 protein turnover.

  • 39. Moroney, J V
    et al.
    Bartlett, S G
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Carbonic anhydrases in plants and algae2001In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 24, no 2, p. 141-153Article, review/survey (Refereed)
    Abstract [en]

    Carbonic anhydrases catalyse the reversible hydration of CO2, increasing the interconversion between CO2 and HCO3- + H+ in living organisms. The three evolutionarily unrelated families of carbonic anhydrases are designated alpha-, beta -and gamma -CA. Animals have only the alpha -carbonic anhydrase type of carbonic anhydrase, but they contain multiple isoforms of this carbonic anhydrase. In contrast, higher plants, algae and cyanobacteria may contain members of all three CA families. Analysis of the Arabidopsis database reveals at least 14 genes potentially encoding carbonic anhydrases. The database also contains expressed sequence tags (ESTs) with homology to most of these genes. Clearly the number of carbonic anhydrases in plants is much greater than previously thought. Chlamydomonas, a unicellular green alga, is not far behind with five carbonic anhydrases already identified and another in the EST database. In algae, carbonic anhydrases have been found in the mitochondria, the chloroplast thylakoid, the cytoplasm and the periplasmic space. In C-3 dicots, only two carbonic anhydrases have been localized, one to the chloroplast stroma and one to the cytoplasm. A challenge for plant scientists is to identify the number, location and physiological roles of the carbonic anhydrases.

  • 40. Moskvin, O V
    et al.
    Shutova, Tatyana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Khristin, M S
    Ignatova, L K
    Villarejo, Arsenio
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Klimov, V V
    Ivanov, B N
    Carbonic anhydrase activities in pea thylakoids.: A photosystem II core complex-associated carbonic anhydrase2004In: Photosynthesis Research, ISSN 0166-8595, Vol. 79, no 1, p. 93-100Article in journal (Refereed)
    Abstract [en]

    Pea thylakoids with high carbonic anhydrase (CA) activity (average rates of 5000 µmol H+ (mg Chl)–1 h–1 at pH 7.0) were prepared. Western blot analysis using antibodies raised against the soluble stromal beta-CA from spinach clearly showed that this activity is not a result of contamination of the thylakoids with the stromal CA but is derived from a thylakoid membrane-associated CA. Increase of the CA activity after partial membrane disintegration by detergent treatment, freezing or sonication implies the location of the CA in the thylakoid interior. Salt treatment of thylakoids demonstrated that while one part of the initial enzyme activity is easily soluble, the rest of it appears to be tightly associated with the membrane. CA activity being measured as HCO3 – dehydration (dehydrase activity) in Photosystem II particles (BBY) was variable and usually low. The highest and most reproducible activities (approximately 2000 µmol H+ (mg Chl)–1 h–1) were observed in the presence of detergents (Triton X-100 or n-octyl-beta-D-glucopyranoside) in low concentrations. The dehydrase CA activity of BBY particles was more sensitive to the lipophilic CA inhibitor, ethoxyzolamide, than to the hydrophilic CA inhibitor, acetazolamide. CA activity was detected in PS II core complexes with average rate of 13,000 µmol H+ (mg Chl)–1 h–1 which was comparable to CA activity in BBY particles normalized on a PS II reaction center basis.

  • 41. Nikitina, Julia
    et al.
    Shutova, Tatyana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Melnik, Bogdan
    Chernyshov, Sergey
    Marchenkov, Victor
    Semisotnov, Gennady
    Klimov, Vyacheslav
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Importance of a single disulfide bond for the PsbO protein of photosystem II: protein structure stability and soluble overexpression in Escherichia coli.2008In: Photosynthesis Research, ISSN 0166-8595, Vol. 98, p. 391-403Article in journal (Refereed)
    Abstract [en]

    PsbO protein is an important constituent of the water–oxidizing complex, located on the lumenal side of photosystem II. We report here the efficient expression of the spinach PsbO in E. coli where the solubility depends entirely on the formation of the disulfide bond. The PsbO protein purified from a pET32 system that includes thioredoxin fusion is properly folded and functionally active. Urea unfolding experiments imply that the reduction of the single disulfide bridge decreases stability of the protein. Analysis of inter-residue contact density through the PsbO molecule shows that Cys51 is located in a cluster with high contact density. Reduction of the Cys28–Cys51 bond is proposed to perturb the packing interactions in this cluster and destabilize the protein as a whole. Taken together, our results give evidence that PsbO exists in solution as a compact highly ordered structure, provided that the disulfide bridge is not reduced.

  • 42.
    OQUIST, G
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    HAGSTROM, A
    ALM, P
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    RICHARDSON, K
    CHLOROPHYLL-A FLUORESCENCE, AN ALTERNATIVE METHOD FOR ESTIMATING PRIMARY PRODUCTION1982In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 68, no 1, p. 71-75Article in journal (Refereed)
  • 43.
    OQUIST, G
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    SEQUENTIAL EXTRACTION OF CHLOROPHYLL FROM CHLOROPHYLL-PROTEIN COMPLEXES IN LYOPHILIZED PEA THYLAKOIDS WITH SOLVENTS OF DIFFERENT POLARITY1980In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 50, no 1, p. 57-62Article in journal (Refereed)
  • 44.
    OQUIST, G
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    BISHOP, NI
    ON THE ROLE OF BETA-CAROTENE IN THE REACTION CENTER CHLOROPHYLL A ANTENNAE OF PHOTOSYSTEM-I1980In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 50, no 1, p. 63-70Article in journal (Refereed)
  • 45.
    Oquist, Gunnar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    LONNEBORG, A
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    PHOTOINHIBITION AND RECOVERY OF PHOTOSYNTHESIS IN ANACYSTIS-NIDULANS1987In: ACTA CHEMICA SCANDINAVICA SERIES B-ORGANIC CHEMISTRY AND BIOCHEMISTRY, ISSN 0302-4369, Vol. 41, no 2, p. 108-111Article in journal (Refereed)
  • 46. Palmqvist, K
    et al.
    de los Rios, A
    Ascaso, C
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Photosynthetic carbon acquisition in the lichen photobionts Caccomyxa and Trebouxia (Chlorophyta)1997In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 101, no 1, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Processes involved in photosynthetic CO2 acquisition were characterised for the isolated lichen photobiont Trebouxia erici (Chlorophyta, Trebouxiophyceae) and compared with Coccomyxa (Chlorophyta), a lichen photobiont without a photosynthetic CO2-concentrating mechanism. Comparisons of ultrastructure and immune-gold labelling of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) showed that the chloroplast was larger in T. erici and that the majority of Rubisco was located in its centrally located pyrenoid. Coccomyxa had no pyrenoid and Rubisco was evenly distributed in its chloroplast. Both species preferred CO2 rather than HCO3- as an external substrate for photosynthesis, but T. erici was able to use CO2 concentrations below 10-12 mu M more efficiently than Coccomyxa. In T. erici, the lipid-insoluble carbonic anhydrase (CA; EC 4.2.1.1) inhibitor acetazolamide (AZA) inhibited photosynthesis at CO2 concentrations below 1 mu M, while the lipid-soluble CA inhibitor ethoxyzolamide (EZA) inhibited CO2-dependent O-2 evolution over the whole CO2 range. EZA inhibited photosynthesis also in Coccomyxa, but to a much lesser extent below 10-12 mu M CO2. The internal CA activity of Trebouxia, per unit chlorophyll (Chi), was ca 10% of that of Coccomyxa. Internal CA activity was also detected in homogenates from T. erici and two Trebouxia-lichens (Lasallia hispanica and Cladina rangiferina). In all three, the predominating CA had a-type characteristics and was significantly inhibited by low concentrations of AZA, having an I-50 below 10-20 ruM. In Coccomyxa a beta-type CA predominates, which is much less sensitive to AZA. Thus, the two photobionts differed in three major characteristics with respect to CO2 acquisition, the subcellular location of Rubisco, the relative requirement of CA and the biochemical characteristics of their predominating internal CA. These differences may be linked to the ability of Trebouxia to accumulate dissolved inorganic carbon internally, enhancing their CO2 use efficiency at and below air-equilibrium concentrations (10-12 mu M CO2) in comparison with Coccomyxa.

  • 47. PALMQVIST, K
    et al.
    RAMAZANOV, Z
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    THE ROLE OF EXTRACELLULAR CARBONIC-ANHYDRASE FOR ACCUMULATION OF INORGANIC CARBON IN THE GREEN-ALGA CHLAMYDOMONAS-REINHARDTII - A COMPARISON BETWEEN WILD-TYPE AND CELL-WALL-LESS MUTANT-CELLS1990In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 80, no 2, p. 267-276Article in journal (Refereed)
  • 48. PALMQVIST, K
    et al.
    RAMAZANOV, ZM
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    MECHANISMS OF ADAPTATION OF MICROALGAE TO CONDITIONS OF CARBON-DIOXIDE LIMITATION OF PHOTOSYNTHESIS - POSSIBLE ROLE OF CARBONIC-ANHYDRASE1990In: SOVIET PLANT PHYSIOLOGY, ISSN 0038-5719, Vol. 37, no 5, p. 680-686Article in journal (Refereed)
    Abstract [en]

    We studied the rate of assimilation of inorganic carbon (C(in)) in relation to CO2 concentration in Dunaliella salina. Chlorella vulgaris, Scenedesmus obliguus, and Chlamydomonas reinhardtii WT grown at 5 and 0.03% CO2. It is demonstrated that K(m) (CO2) of photosynthesis reached 50-60-mu-M in algae grown at 5% CO2, but 2-5-mu-M at 0.03% CO2. Carbonic anhydrase (CA) activity of intact cells and in the homogenate was significantly higher in algae grown at 0.03% CO2 than at 5% CO2. Several forms of CA are present, viz., soluble (sCA), membrane-bound CA of cytoplasmic (cCA) and thylakoid (tCA) membranes, and CA of intact cells (iCA). Acetoazolamide lowered the rate of C(in) assimilation in algae grown at 0.03% CO2, whereas ethoxyzolamide totally suppressed the ability of the algae to adapt to low CO2 concentrations. The inhibitor of plasmalemma ATPase vanadate likewise suppressed the rate of C(in) assimilation in the algae. It is concluded that enzymatic reactions catalyzed by CA and plasmalemma ATPase are involved in adaptation of algae to low CO2 concentrations and in mechanisms of C(in) concentration. Mechanisms governing adaptation of algae to conditions of carbon dioxide limitation of photosynthesis are discussed in the paper.

  • 49. PALMQVIST, K
    et al.
    RAMAZANOV, ZM
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    ROLE OF CARBONIC-ANHYDRASE IN ASSIMILATION OF INORGANIC CARBON IN DUNALIELLA-SALINA1991In: SOVIET PLANT PHYSIOLOGY, ISSN 0038-5719, Vol. 38, no 3, p. 339-345Article in journal (Refereed)
    Abstract [en]

    We studied changes in the rate of photosynthetic assimilation of inorganic carbon (C(i)) in relation to CO2 concentration by Dunaliella salina cells adapted to high (5%) and low (0.03%) concentrations of CO2. It is demonstrated that the rate of C(i) assimilation was higher in algae adapted to 0.03% CO2 than in culture adapted to 0.03% CO2. The period of adaptation of D. salina to low CO2 concentrations lasted 5-6 h, during which time activity of carbonic anhydrase (CA) increased on the cell surface and inside cells. Soluble CA (sCA) was detected in D. salina, together with membrane-bound CA of cytoplasmic (cCA) and thylakoid (tCA) membranes. The effect of CA inhibitors - acetazolamide (AZA) and ethoxyzolamide (EZA) - on photosynthesis of D. salina cells was studied in the work. It turned out that EZA lowered the rate of O2 evolution in algae adapted to 5% CO2 and totally suppressed this process in algae adapted to 0.03% CO2. Acetazolamide lowered the photosynthetic rate only in algae adapted to 0.03% CO2. It is concluded that intracellular forms of CA are needed for functioning of the C1-concentration mechanism in algae adapted to conditions of carbon dioxide limitation of photosynthesis. The authors discuss the mechanisms of adaptation of D. salina to low CO2 concentrations and the role played by CA in this process.

  • 50. PALMQVIST, K
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    BADGER, MR
    PHOTOBIONT-RELATED DIFFERENCES IN CARBON ACQUISITION AMONG GREEN-ALGAL LICHENS1994In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 195, no 1, p. 70-79Article in journal (Refereed)
    Abstract [en]

    The photosynthetic properties of a range of lichens (eight species) containing green algal primary photobionts of either the genus Coccomyxa, Dictyochloropsis or Trebouxia were examined with the aim of obtaining a better understanding for the different CO2 acquisition strategies of lichenized green algae. Fast transients of light/dark-dependent CO2 uptake and release were measured in order to screen for the presence or absence of a photosynthetic CO2-concentrating mechanism (CCM) within the photobiont. It was found that lichens with Trebouxia photobionts (four species) were able to accumulate a small pool of inorganic carbon (DIC; 70-140 nmol per mg chlorophyll (Chl)), in the light, which theoretically may result in, at least, a two- to threefold increase in the stromal CO2 concentration, as compared to that in equilibrium with ambient air. The other lichens (four species), which were tripartite associations between a fungus, a cyanobacterium (Nostoc) and a green alga (Coccomyxa or Dictyochloropsis) accumulated a much smaller pool of DIC (10-30 nmol.(mg Chl)(-1)). This pool is most probably associated with the previously documented CCM of Nostoc, inferred from the finding that free-living cells of Coccomyxa did not show any signs of DIC accumulation. In addition, the kinetics of fast CO2 exchange for free-living Nostoc were similar to those of intact tripartite lichens, especially in their responses to the CCM and the carbonic anhydrase (CA) inhibitor ethoxyzolamide. Trebouxia lichens had a higher photosynthetic capacity at low and limiting external CO2 concentrations, with an initial slope of the CO2-response curve of 2.6-3.9 mu mol.(mg Chl)-1.h(-1).Pa-1, compared to the tripartite lichens which had an initial slope of 0.5-1.1 mu mol.(mg Chl)(-1).h(-1).Pa-1, suggesting that the presence of a CCM in the photobiont affects the photosynthetic performance of the whole lichen. Regardless of these indications for the presence or absence of a CCM, ethoxyzolamide inhibited the steady-state rate of photosynthesis at low CO2 in all lichens, indicating a role of CA in the photosynthetic process within all of the photobionts. Measurements of CA activity in photobiont-enriched homogenates of the lichens showed that Coccomyxa had by far the highest activity, while the other photobionts displayed only traces or no activity at all. As the CCM is apparently absent in Coccomyxa, it is speculated that this alga compensates for this absence with high internal CA activity, which may function to reduce the CO2-diffusion resistance through the cell.

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