Figure 1. O₂ reduction rates and Flv3 and Flv4 protein accumulation in cells grown in low (LC) and high CO₂ (HC).

(A, B) O₂ reduction rate of WT, flv4-2/OE and (D) the M55 mutant (∆ndhB) was recorded in darkness (gray background) and under illumination (white background). The experiment was conducted in three independent biological replicates and a representative plot is shown. (Figure 1—source data 1). (C) Immunoblot detection of Flv3 and Flv4 in WT and flv4-2/OE. Pre-cultures were grown in BG-11, pH 8.2 under 3% CO₂ (HC) for 3 days, after that cells were harvested and resuspended in fresh BG-11, pH 8.2 at OD₇₅₀ = 0.2. The experimental cultures were grown under HC or under LC. For the MIMS experiments the cells were harvested and resuspended in fresh BG-11, pH 8.2 at 10 µg Chl a mL⁻¹. O₂ photoreduction was recorded during the transition from darkness to high-light intensity of 500 µmol photons m⁻²s⁻¹. In order to create comparable conditions for MIMS measurements, LC-grown cells were supplemented with 1.5 mM NaHCO₃ prior to the measurements. Independent experiments performed on WT cells grown in BG-11 lacking Na₂CO₃, but supplied with 1.5 mM NaHCO₃ prior to MIMS measurement showed no significant difference in O₂ photoreduction rates (Figure 1—figure supplement 2), thus allowing confident comparison of the MIMS results. Different phases of O₂ photoreduction kinetics are indicated as {I}, {II}, {III}. 50% WT, corresponds to 1:2 diluted WT total protein sample.

Figure 1—figure supplement 1. O₂ reduction rates under high CO₂.

Cells were grown under 3% CO₂ (BG-11, pH 8.2), harvested and resuspended in fresh BG-11 at 10 µg Chl a mL⁻¹ . O₂ uptake was recorded during the transition from dark to high-light (500 µmol photons m⁻² s⁻¹).

Figure 1—figure supplement 2. O₂ reduction rates during the dark-to-light transition of WT cells with and without addition of 1.5 mM NaHCO₃ prior MIMS measurements.

The cells were harvested and inoculated in the fresh BG-11 7.5 without Na₂CO₃. Prior to MIMS measurement, cells were supplemented with 1.5 mM NaHCO₃ (solid line), or measured in the absence of an additional carbon source.