, Volume 187, Issue 1, pp 152–156

Inorganic-carbon assimilation in the green seaweed Ulva rigida C.Ag. (Chlorophyta)

  • Mats Björk
  • Kurt Haglund
  • Ziyadin Ramazanov
  • Guillermo Garcia-Reina
  • Marianne Pedersén


Mechanisms of carbon assimilation were investigated in thalli and protoplasts of Ulva rigida by measuring HCO3-dependent O2 evolution at pH 6.5 and 8.6. In thalli, dextran-bound azetazolamide (DBAZ), a specific inhibitor of extracellular carbonic anhydrase (CA), inhibited the rate of O2 evolution at pH 8.6 when HCO3was the only available form of inorganic carbon (Ci) in the medium. At pH 6.5 when CO2 is accessible, DBAZ did not affect photosynthetic O2 evolution. Inhibition of total CA activity (extracellular and intracellular) by ethoxyzolamide (EZ) inhibited photosynthesis at pH 6.5 and 8.6. During illumination of thalli the medium was alkalized at a rate which increased with increasing light. This alkalization decreased during inhibition of extracellular CA by DBAZ. Protoplasts at pH 6.5 exhibited a higher rate of O2 evolution than in pH 8.6. Addition of CA to protoplasts at pH 8.6 increased the rate of O2 evolution, whereas EZ was inhibitory at both pH 6.5 and 8.6, and DBAZ did not affect photosynthesis at either pH. We suggest that both extracellular and intracellular CA are present and that Ulva rigida assimilates HCO3by an indirect mechanism. A theoretical scheme for carbon utilization is suggested.

Key words

Carbon-assimilation Carbonic anhydrase Photosynthesis (UlvaProtoplast (photosynthesis) Ulva 



carbonic anhydrase


inorganic carbon


dissolved inorganic carbon


dextran-bound acetazolamide




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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • Mats Björk
    • 1
  • Kurt Haglund
    • 1
  • Ziyadin Ramazanov
    • 2
  • Guillermo Garcia-Reina
    • 3
  • Marianne Pedersén
    • 1
  1. 1.Department of Physiological BotanyUppsala UniversityUppsalaSweden
  2. 2.Russian Academy of SciencesInstitute of Plant PhysiologyMoscowRussian Federation
  3. 3.Marine Plant Biotechnology LaboratoryUniversity of Las PalmasLas PalmasSpain
  4. 4.Departamento de Bioquimica, Facultad de CienciasUniversidad de CordobaSpain

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