Regulation of carbonic-anhydrase activity,inorganic-carbon uptake and photosynthetic biomass yield inChlamydomonas reinhardtii |
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Authors: | B N Patel M J Merrett |
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Institution: | (1) Plant and Microbial Metabolism Research Group, School of Biological Sciences, University College of Swansea, Singleton Park, SA2 8PP Swansea, UK |
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Abstract: | The regulation of carbonic anhydrase by environmental conditions was determined forChlamydomonas reinhardtii. The depression of carbonic anhydrase in air-grown cells was pH-dependent. Growth of cells on air at acid pH, corresponding to 10 m CO2 in solution, resulted in complete repression of carbonic-anhydrase activity. At pH 6.9, increasing the CO2 concentration to 0.15% (v/v) in the gas phase, corresponding to 11 M in solution, was sufficient to completely repress carbonic-anhydrase activity. Photosynthesis and intracellular inorganic carbon were measured in air-grown and high-CO2-grown cells using a silicone-oil centrifugation technique. With carbonic anhydrase repressed cells limited inorganic-carbon accumulation resulted from non-specific binding of CO2. With air-grown cells, inorganic-carbon uptake at acid pH, i.e. 5.5, was linear up to 0.5 mM external inorganic-carbon concentration whereas at alkaline pH, i.e. 7.5, the accumulation ratio decreased with increase in external inorganic-carbon concentration. It is suggested that in air-grown cells at acid pH, CO2 is the inorganic carbon species that crosses the plasmalemma. The conversion of CO2 to HCO
3
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by carbonic anhydrase in the cytosol results in inorganic-carbon accumulation and maintains the diffusion gradient for carbon dioxide across the cell boundary. However, this mechanism will not account for energy-dependent accumulation of inorganic carbon when there is little difference in pH between the exterior and cytosol. |
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Keywords: | Carbon (inorganic) accumulation Carbonic anhydrase Chlamydomonas Photosynthesis and biomass yield |
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