Figure 3.

Rates of HCO₃⁻ (A) and CO₂ transport (B) during steady-state photosynthesis in Synechococcus sp. strain PCC7002. ○, Cells grown continuously on 20 μL of CO₂ L⁻¹ (low-Ci cells); □, cells grown continuously on 2% CO₂ (high-Ci cells); •, high-Ci cells subjected to the fast-induction protocol for 4 min in the presence of CA (100 units mL⁻¹); ▪, high-Ci cells subjected to the fast-induction protocol for 4 min in the absence of CA. Fast-induced cells were obtained after depletion of Ci in experiments similar to those shown in Figure 1. After Ci was depleted, an aliquot of cells containing 10 μg of Chl was centrifuged and resuspended in 4 mL of fresh CO₂-free assay buffer to a final [Chl] of 2.5 μg mL⁻¹. To fully inhibit CA activity, 50 μm AZA was added and HCO₃⁻ and CO₂ uptake were measured mass spectrometrically in relation to their respective substrates (see Methods).