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

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11.
  • PALMQVIST, K, et al. (författare)
  • PHOTOBIONT-RELATED DIFFERENCES IN CARBON ACQUISITION AMONG GREEN-ALGAL LICHENS
  • 1994
  • Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 195:1, s. 70-79
  • Tidskriftsartikel (refereegranskat)abstract
    • 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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12.
  • PALMQVIST, K, et al. (författare)
  • ROLE OF CARBONIC-ANHYDRASE IN ASSIMILATION OF INORGANIC CARBON IN DUNALIELLA-SALINA
  • 1991
  • Ingår i: SOVIET PLANT PHYSIOLOGY. - 0038-5719. ; 38:3, s. 339-345
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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Gardeström, Per, 195 ... (5)
Palmqvist, K (5)
Falk, S. (4)
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