This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (59) Citing Articles via Google Scholar Google Scholar Articles by Moroney, J. V. Articles by Tolbert, N. E. Search for Related Content PubMed PubMed Citation Articles by Moroney, J. V. Articles by Tolbert, N. E. Agricola Articles by Moroney, J. V. Articles by Tolbert, N. E.

Articles

Inorganic Carbon Uptake by Chlamydomonas reinhardtii¹

Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824

The rates of CO₂-dependent O₂ evolution by Chlamydomonas reinhardtii, grown with either air levels of CO₂ or air with 5% CO₂, were measured at varying external pH. Over a pH range of 4.5 to 8.5, the external concentration of CO₂ required for half-maximal rates of photosynthesis was constant, averaging 25 micromolar for cells grown with 5% CO₂. This is consistent with the hypothesis that these cells take up CO₂ but not HCO₃^– from the medium and that their CO₂ requirement for photosynthesis reflects the K_m(CO₂) of ribulose bisphosphate carboxylase. Over a pH range of 4.5 to 9.5, cells grown with air required an external CO₂ concentration of only 0.4 to 3 micromolar for half-maximal rates of photosynthesis, consistent with a mechanism to accumulate external inorganic carbon in these cells. Air-grown cells can utilize external inorganic carbon efficiently even at pH 4.5 where the HCO₃^– concentration is very low (40 nanomolar). However, at high external pH, where HCO₃^– predominates, these cells cannot accumulate inorganic carbon as efficiently and require higher concentrations of NaHCO₃ to maintain their photosynthetic activity. These results imply that, at the plasma membrane, CO₂ is the permeant inorganic carbon species in air-grown cells as well as in cells grown on 5% CO₂. If active HCO₃^– accumulation is a step in CO₂ concentration by air-grown Chlamydomonas, it probably takes place in internal compartments of the cell and not at the plasmalemma.

This article has been cited by other articles:

				J. V. Moroney and R. A. Ynalvez Proposed Carbon Dioxide Concentrating Mechanism in Chlamydomonas reinhardtii Eukaryot. Cell, August 1, 2007; 6(8): 1251 - 1259. [Full Text] [PDF]