ENHANCED TRANSPORT OF INORGANIC CARBON INTO ALGAL CELLS AND ITS IMPLICATIONS FOR THE BIOLOGICAL FIXATION OF CARBON1,2

Kinetics of uptake of inorganic carbon by the freshwater green alga Chlamydomonas reinhardtii Dang. suggest that rates of fixation may be enhanced at low tensions of CO₂ by transport of bicarbonate from the cell surface to the chloroplast. Results are evaluated in the context of models that treat diffusion and reaction of dissolved inorganic carbon across a 3 dimensional finite boundary layer, and they are consistent with the claim that CO₂ alone is the substrate used during carbon fixation. An alternative hypothesis, which presumes that both CO₂ and bicarbonate are used as substrates, yields predictions which are inconsistent with the data. Instead, bicarbonate seems to act only as a vehicle for the transport of inorganic carbon into the cell, thereby adding its flux to that of CO₂, and enhancing rates of synthesis that would otherwise be restricted by uptake of CO₂ alone.