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Hydrodictyon africanum can photosynthesize at high pH under conditions in which HCO3− rather than CO2 is the carbon species entering the cell. A passive entry of HCO3− seems unlikely; a metabolic HCO3− pump is proposed. It is possible that such a pump is related to a light-dependent reaction specific to the use of HCO3−. This reaction is dependent on photosystem 2, but appears to be independent of ATP. These characteristics are similar to those of active lightdependent Cl influx in H. africanum, and suggest a similar energy source for the two pumps. The HCO3− pump may be electrogenic.
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John A. Raven (1968) studied this question.
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