Effect of Oxygen on Photosynthetic14CO2Fixation inChroomonassp. (Cryptophyta) I. Some Characteristics of the Oxygen Effect

摘要

The effect of oxygen on photosynthetic14CO2fixation in the air-grown freshwater flagellateChroomonassp. (Cryptophyta) was studied. Considerable inhibition by anaerobiosis was observed only under light-saturated conditions with no effect from the CO2concentration. This inhibition was reversed by 2O2. With, more than 2O2, the rate of14CO2fixation was inhibited; 100O2caused about 20inhibition which could be reversed by 2O2. The degree of inhibition was only slightly higher at low concentrations (less than 0.43 mM NaHCO3) than at high CO2concentrations, indicating that photorespiration is not a main cause of this inhibition. Possible causes of the inhibitions by anaerobiosis and by oxygen are discussed.