Effects of CO2 concentration during growth on subsequent photosynthetic CO2 fixation in Chlorella1

Abstract

The maximum rate of photosynthetic ¹⁴CO₂ fixation (V_max) as well as the concentration of CO₂ at which the rate of photosynthetic ¹⁴CO₂ fixation attains one-half its maximum velocity (K_m) in Chlorella vulgaris 11h cells was strongly dependent on the concentration of CO₂ continuously provided during the algal growth. The V_max (μmoles ¹⁴CO₂ fixed/ml pcv·min) and K_m (% CO₂) of the algal cells which had been grown in air containing 4% CO₂ (by volume) were ca. 10 and 0.15–0.17, while those in the cells which had been grown in ordinary air (containing 0.04% CO₂) were 7 and 0.05–0.06, respectively. When the concentration of CO₂ in the bubbling gas was lowered from 4 to 0.04% during the algal growth, their photosynthetic kinetics attained the respective lower steady levels after 5–10 hr. On the other hand, when the photosynthetic kinetics were determined 24 hr after raising the concentration of CO₂ from 0.04 to 4%, the V_max and K_m-values were found to have already attained the respective higher levels.