CHANGES IN PHOTOSYNTHETIC CHARACTERISTICS INDUCED BY TRANSFERRING AIR-GROWN CELLS OF CHLOROCOCCUM-LITTORALE TO HIGH-CO2 CONDITIONS

When air-grown cells of Chlorococcum littorale was enriched with CO2, growth was enhanced after a lag period of one to two days at 20% CO2, and 3 to 6 days at 40% CO2. Changes in the rate of photosynthesis meas ured as oxygen evolution and CO2 fixation, were similar to those obser ved for growth. During the initial inhibition of photosynthesis in 40% CO2, the activity of PSII was suppressed. In contrast, PSI activity w as greatly enhanced. Air-grown cells of C. littorale possessed compara tively high carbonic anhydrase (CA) activity which was localized insid e the cells and on the cell surface. Under high CO2 concentrations ext racellular CA activity was greatly suppressed and intracellular activi ty almost completely abolished. Phosphoenol pyruvate carboxylase activ ity was also suppressed in high CO2-grown cells. Ribulose-1,5-bisphosp hate carboxylase activity was higher in high-CO2 grown cells than in a ir-grown cells. The above results indicated that the lag phase induced by 40% CO2 was due to suppression of PSII activity.