Development of vacuoles and vacuolar H+-ATPase activity under extremely high CO2 conditions in Chlorococcum littorale cells

The number and cross-sectional area of vacuoles in Chlorococcum littorale cells visualized with a differential interference fluorescence microscope increased after their transfer from air to 40% CO2. An immunological observation indicated that the level of subunit B of vacuolar H+-ATPase also increased under 40 % CO2 conditions. The activity of nitrate-sensitive ATPase associated with the vacuolar membrane was 2-fold higher in 40 % CO2-grown cells than in air-grown cells. The effects of inhibitors on the ATPase activity confirmed that these activities were derived from vacuolar-type H+-ATPase. These results suggest that vacuole development associated with that of vacuolar H+-ATPase occurred during the acclimatization of C. littorale cells to extremely high CO2 conditions.