Operation of the reductive pentose phosphate cycle daring the induction period of photosynthesis in Chlorella1

Abstract

When Chlorella oulgaris ll h cells grown in air containing 4% CO2 (high-CO2 cells) were given low concentrations of14CO2 (<150 ppm), the initial rate of photosynthetic 14CO2 fixation was very low and linear 14CO2 fixation was observed after an induction period which lasted for ca. 45 min. No such induction period was observed when high-CO2 cells were given high concentrations of 14CO2 (10,000 ppm) or when IOW-CO2 cells were given either low or high concentrations of 14CO2, supporting the observations by Briggs and Whittingham (l). However, irrespective of CO2 concentrations during growth and of 14CO2 concentrations during the experiments, most of the 14C was incorporated into phosphate esters during the initial periods of photosynthetic 14CO2 fixation. These results are in sharp contrast to the report by Graham and Whittingham (4).