Flux-Based Transport Enhancement as a Plausible Unifying Mechanism for Auxin Transport in Meristem Development
Figure 1
Comparison of two PIN orientation hypotheses.
The concentration of auxin in the cells is marked with green (the brighter green, the higher the concentration), the fluxes are depicted with yellow arrows, and PIN concentration at the membranes are indicated by red lines with variable thickness (the thicker the line the higher the concentration). Note that the fluxes might be independent from the concentrations. (E–H) show the principle of the concentration-based hypothesis and (A–D) show the principle of flux-based polarization hypothesis. In both cases the key question is how the cell marked with “?” should allocate the PINs to its membranes (A,E). In the case of the concentration-based hypothesis this cell makes the decision based on the concentrations in the neighbouring cells. The higher its neighbours auxin concentration, the more PIN will be inserted in the membrane (F). Flux-based polarization depends on the net flux between neighbouring cells. The higher the net flux to its neighbour the more PIN will be inserted in the membrane (B). In both cases the newly allocated PINs change the concentrations and fluxes (C,G), leading to the next iteration of the scenario (D,H).