Fig. 5. Localization of LCIB around the pyrenoid periphery reduces Ci leakage out of the chloroplast.

a, Schematics of varying activity and end radius of LCIB in a modelled chloroplast employing an impermeable starch sheath and active HCO₃⁻ pumping across the chloroplast envelope under very low CO₂. Colour code as in Fig. 4a. The LCIB domain starts at the pyrenoid radius (0.3 on the x axis in b and c). b,c, Normalized CO₂ fixation flux (b) and ATP spent per CO₂ fixed (c) when the designated characteristics of LCIB are varied. d, Schematics of inorganic carbon fluxes for the LCIB states (i–iii) indicated in b and c. Colour code as in Fig. 4f. Simulation parameters as in Fig. 4. Active LCIA^P-mediated HCO₃⁻ pumping is described by the rate ${\kappa }_{\mathrm{chlor}}^{H^{-}}$ = 10⁻⁴ m s⁻¹ and the reversibility γ = 10⁻⁴. To show a notable variation in normalized CO₂ fixation flux, a model with shortened thylakoid tubules is simulated (Methods). The qualitative results hold true independent of this specific choice.