Figure 1.

Development of photosynthetic parameters in media containing high-[CO₂]-grown Synechocystis sp. PCC 6803 (A and B) and S. elongatus PCC 7942 (C and D). A and C, Time courses of medium oxygen concentration (red traces) and relative Chl fluorescence (black traces). Initially, media containing cyanobacteria (10 μg Chl mL⁻¹) were kept dark; illumination with measuring light (ML) and actinic light (AL; 200 μmol photons m⁻² s⁻¹) started as indicated. The downward shift in the Chl fluorescence signal (F_o) after the start of ML illumination is due to increasing the instrument amplification from 200 to 100 mV. Chl fluorescence parameters are as defined in the text. NaHCO₃ (final concentration, 10 mm) was added as indicated. α, β, and γ denote times at which oxygen evolution rates were determined in separate experiments. From about the time of maximum oxygen concentration to the addition of NaHCO₃, photosynthesis can be considered CO₂ limited. The experiments were performed four times, and representative data are shown. B and D, Time courses of Y(II), calculated for the corresponding measurements of F_m′ as (F_m′ − F_s)/F_m′. Values shown are means ± sd (n = 4).