CO2 ACCUMULATION BY CHLORELLA SACCHAROPHILA (CHLOROPHYCEAE) AT LOW EXTERNAL pH: EVIDENCE FOR ACTIVE TRANSPORT OF INORGANIC CARBON AT THE CHLOROPLAST ENVELOPE1

The CO₂ uptake characteristics of the acid-tolerant alga Chlorella saccharophila (Krüger) Nadson have been examined. These, together with direct estimations of internal inorganic C concentrations, indicate that air-adapted cells of this alga possess a CO₂ accumulation mechanism similar to that reported in other members of the Chlorophyceae and in Cyanophyceae. This accumulation mechanism operates at external pH values of 4 and less. Under these conditions CO₂ must be the carbon species crossing the plasmlemma, and since preliminary evidence suggests that the transport mechanism is active primary uniport of HCO₃^–, it is proposed that the site of the CO₂ accumulation mechanism is the chloroplast envelope.