Figure 5.
Predicted versus observed uptake of Cd, Zn, and Ni by spinach (right sections, the line is the 1:1 line), using a model that combines the diffusion equation with a competitive Michaelis-Menten equation (Fig. 1). The model was fitted on a dataset that covered a range of pH (5–7), free ion concentration, degree of buffering, and Ca and Mg concentration (full details in Supplemental Table S1). The left sections show all experimental uptake fluxes as function of the free ion concentration. For comparison, the left figures also show the diffusion flux in an unstirred, unbuffered solution (assuming an effective diffusive layer thickness δ of 0.8 mm) or, for Cd and Zn, in the most strongly buffered medium (reaction layer thickness μ of 1 μm) and the modeled internalization fluxes (solid lines) at low or high concentration of competitive ions (H+ for Cd and Zn uptake, Mg2+ for Ni uptake).