Fig. 7

Proton balance in relation with sucrose translocation and growth conditions. The proton balance was predicted by FBA in all three compartments of the model: mesophyll, phloem and root. The presented ‘light’ conditions are: photorespiration/photosynthesis = 0.25 and FQR/FNR = 0.37. Under these constraints the ATP balance in plastid is predicted to be self-sufficient (Fig. 6), therefore there was no ATP and H⁺ exchange between plastid and cytosol. The contribution of major H⁺-producing/consuming processes into overall proton balance in each compartment was summarized and denoted as percentages of contribution. Different shapes and colours of the nodes represent the different pools of protons. The proton turnovers in each compartment were normalized per cytoplasm of root, since it was almost invariant under both light conditions. The ‘root’ compartment exchanged protons with the environment, which were acquired in symport with the nutrients and excreted via H⁺/ATPase. N – nutrients