Figure 3. Comparison of the CO₂ uptake and the proton gradient across thylakoid membranes between WT and ΔndhV strains.

(A,B) The rate of CO₂ uptake in WT, ΔndhV and M55 strains at 100 μmol photons m⁻²s⁻¹ (A) or at 300 μmol photons m⁻²s⁻¹ (B). The cells of WT and mutant strains were harvested at mid-logarithmic phase (OD₇₃₀ ≈ 0.5) and chlorophyll a concentration was adjusted to 400 μg ml⁻¹. 30 μl of the cell suspensions were placed on the BG-11 agar plate. The activity of CO₂ uptake was measured at 30 °C. The CO₂ concentration was controlled at 400 or 2000 μmol mol⁻¹. Values are means ± SE of three independent measurements. Asterisk indicates significant differences (t-test, *P < 0.05 and **P < 0.01). (C) Analysis of proton gradient across thylakoid membranes using QA (quinacrine) fluorescence quenching in WT, ΔndhV and M55 strains. Intact cells of WT and mutant strains were harvested at mid-logarithmic phase (OD₇₃₀≈0.5) and then suspended at a final chlorophyll a concentration of 150 μg ml⁻¹ in a reaction medium contained 5 mM Tris/MES (pH 8.0), 0.3 M mannitol, 2 mM DTT, 5 mM D-Glucose, 1.5 mM ATP, 5 μM quinacridine. The quenching of QA fluorescence was induced by adding the cells sample to 2 ml reaction mixture after the background fluorescence reached steady state about 2 min after started the measurement. The QA fluorescence quenching of WT is 5.02%. Values are means ± SE of three independent measurements. Asterisk indicates significant differences (t-test, *P < 0.05 and **P < 0.01).