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Sökning: swepub > Umeå universitet > Tidskriftsartikel > (1990-1994) > Samuelsson Göran 1951

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1.
  • PAWLIK, B, et al. (författare)
  • pH-dependent cadmium transport inhibits photosynthesis in the cyanobacterium Synechocystis aquatilis
  • 1993
  • Ingår i: Environmental and Experimental Botany. - 0098-8472. ; 33:2, s. 331-337
  • Tidskriftsartikel (refereegranskat)abstract
    • Short-term (5-120 sec) transport of cadmium (Cd-109) into cells of the unicellular cyanobacterium Synechocystis aquatilis was studied using a rapid filtration technique. The transport was strongly pH-dependent, occurring at pH 7, but not at pH 5.5, and was also observed in long-term (40 min) experiments. For this process the optimum pH was approximately 7.5; uptake was considerably reduced at lower pHs. The entrance of cadmium disturbed photosynthetic activity and related processes. At pH 7, cadmium (8.9 muM) decreased CO2 fixation by about 55%, inhibited carbonic anhydrase activity (completely in intact cells, by 65%, in cell-free extracts) and photosynthetic O2-evolution by about 50%. At pH 5.5 no effects were observed.
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2.
  • BORODIN, V, et al. (författare)
  • THE EFFECT OF LIGHT QUALITY ON THE INDUCTION OF EFFICIENT PHOTOSYNTHESIS UNDER LOW CO2 CONDITIONS IN CHLAMYDOMONAS-REINHARDTII AND CHLORELLA-PYRENOIDOSA
  • 1994
  • Ingår i: Physiologia Plantarum : An International Journal for Plant Biology. - 0031-9317. ; 92:2, s. 254-260
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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3.
  • 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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4.
  • FALK, S, et al. (författare)
  • RECOVERY OF PHOTOSYNTHESIS AND PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII AFTER EXPOSURE TO 3 LEVELS OF HIGH LIGHT
  • 1992
  • Ingår i: Physiologia Plantarum : An International Journal for Plant Biology. - 0031-9317. ; 85:1, s. 61-68
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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6.
  • HOFSLAGARE, O, et al. (författare)
  • THE EFFECT OF ARSENATE AND ARSENITE ON PHOTOSYNTHESIS IN SCENEDESMUS-OBLIQUUS - A POTENTIOMETRIC STUDY IN A CLOSED CO2-SYSTEM
  • 1994
  • Ingår i: Chemical speciation and bioavailability. - 0954-2299. ; 6:4, s. 95-102
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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7.
  • Karlsson, Jan, 1966-, et al. (författare)
  • EFFECT OF VANADATE ON PHOTOSYNTHESIS AND THE ATP ADP RATIO IN LOW-CO2-ADAPTED CHLAMYDOMONAS-REINHARDTII CELLS
  • 1994
  • Ingår i: Planta. - 0032-0935. ; 192:1, s. 46-51
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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10.
  • PALMQVIST, K, et al. (författare)
  • MECHANISMS OF ADAPTATION OF MICROALGAE TO CONDITIONS OF CARBON-DIOXIDE LIMITATION OF PHOTOSYNTHESIS - POSSIBLE ROLE OF CARBONIC-ANHYDRASE
  • 1990
  • Ingår i: SOVIET PLANT PHYSIOLOGY. - 0038-5719. ; 37:5, s. 680-686
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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