Interactions of glycolate-, HCO 3 (-) -, Cl (-)-, and H (+)-balance of Scenedesmus obliquus.

Excretion and absorption of glycolate by young cells of Scenedesmus obliquus (Turp.) Krüger strain D3 grown synchronously with 2% CO2 was compared after no pretreatment with air (CO2-adapted) or after a 2 h adaptation to normal air (0.03% CO2) (air-adapted). At 21% O2, excretion occurred only from CO2-adapted cells at high pH (pH 8.0). Under conditions where no excretion occurred, external glycolate (0.2 mM) was taken up by both air-and CO2-adapted cells at a much faster rate at pH 5 than at pH 8. The uptake was accompanied by an apparent stoichiometric uptake of H(+). CO2-adapted algae exhibited high uptake rates that were even higher in the dark than in the light. Air-adapted algae showed high uptake rates in the light but only minimal uptake in the dark. The uptake rate was decreased to about 1/3 with 5% CO2, except with CO2-adapted cells in the light, in which a slight stimulation occurred. Cl(-) ions inhibited glycolate uptake by air-adapted cells in the light; conversely, light-stimulated Cl(-) uptake of these cells was inhibited by glycolate. A hypothesis is discussed according to which the internal pH regulates the uptake and release of Cl(-), HCO 3 (-) , and glycolate.