Table I.

Effect of O2 and OAA on the transition state 2-to-state 1 in C. reinhardtii, wild type

Chlamydomonas cells containing 150 μg of chlorophyll mL−1 were incubated at 25°C in the oxygen electrode cell in the minimal medium (see “Materials and Methods”) supplemented with 5 mm NaHCO3 and catalase. The cells were allowed to consume O2 in the dark until anaerobiosis was reached (several minutes were required, during which F0 and Fm were monitored by the PAM fluorimeter). After 5 min in the dark anaerobic condition, state 2 was established, as indicated by the stable fluorescence parameters. The initial (state 1) Fv/Fm ratio was 0.72 ± 0.0 (30 measurements, with several cell cultures), and 0.41 in the dark anaerobic condition (state 2). No influence of OAA on these parameters was ever observed. Light was then turned on and O2 was simultaneously generated (by catalase) as required upon the injection of H2O2. Light was of an intensity producing 20% to 25% of the maximal photosynthetic rate measured under light saturation. The lag time (see Fig. 1) in the control (no additions) is dependent upon light intensity at any particular chlorophyll concentration. Under the conditions indicated here (light intensity was 58 μE m−2 s−1), it was of 489 ± 86 s, and in each experiment the values observed in the treated samples were normalized to their control. Photosynthetic O2 evolutions at steady state were, respectively, 35.1, 35.4, 35 μmol mg chlorophyll h−1 in the control, with O2, OAA, or O2 + OAA added. The light-saturated rate was 146. All figures are averages ± se. The figures in parentheses indicate the number of experiments.

NoneO2 30 μmOAA 2 mmOAA + O2
Lag (s)10064.9 ± 3.279 ± 9.861 ± 10