Fig. 3: Purified PSII complexes show decreased activity at successive light exposures.

PSII complexes were isolated from C. reinhardtii wild-type strain CC124 cells, and their activity was tested by a Pyroscience FireSting O₂ probe, (a). The complexes were tested in the absence or presence of 10 mM (actual 7.5 mM) NaHCO₃ to mimic high carbon conditions, and examined under either aerobic or anoxic conditions. Complexes were exposed twice for 10 s of light, with a dark period of a minute in-between. Shown are the rates of the 1st (blue) and 2nd (white) exposures, for each set of conditions. Also stated are the residual activity rates between each aligned exposure (according to the averaged rate). Complexes in the presence of NaHCO₃ were also tested during increased periods of illuminations of 5, 10, 20, or 30 s (purple, blue, cyan, and green, respectively), under either aerobic (striped) or anoxic (solid) conditions in the presence of 10 mM (actual 7.5 mM) NaHCO₃ (b). Presented are the residual rate of O₂, which was accumulated in the second exposure, compared to the initial illumination. The table below presents the rates of the 1st and 2nd exposures for each treatment (µmol O₂ mg Chl⁻¹ h⁻¹) as well as the repetitions number for each result. In addition, the difference between the aerobic and anoxic treatments were analyzed using a student t-test. P-values are stated for each couple. Each experiment was repeated using at least three biological replicates. Data is presented in box plots.