Figure 1.

A minimal transporter network for nutrient exchange in arbuscular mycorrhizal symbiosis. (A) The exchange zone was modeled as a three-compartment system with the 100 nm thick interfacial apoplast between plant and fungus and 50-fold larger cytoplasmic volumes. Note that different cytoplasms/apoplasm values do not qualitatively change the obtained results. The pH values were kept constant to pHcyt = 7.0 and pHapo = 6.0 to reflect the proton-buffer capacities (see also Discussion for the flexibility of these values). Transport of sugar or phosphate was mediated by H⁺/sugar (H/C) and H⁺/phosphate (H/P) cotransporters. The background conductance gathers the H⁺-ATPase and other potential ionic conductances. In order to include the exchange of nitrogen sources, the network could be enlarged by ${\text{NH}}_4^{+}$-channels and electrogenic H⁺/${\text{NO}}_3^{-}$, H⁺/amino acid or H⁺/peptide co-transporters (Smith and Smith, 2011; Casieri et al., 2013). The qualitative conclusions would be identical to the considered P/C-exchange system. (B) Screenshot of the implementation of the three compartment model in VCell.