Polar auxin transport pathway of Arabidopsis. Even though we have shown a representative diagram of influx and efflux proteins on different but adjacent cells, the auxin influx and efflux transport proteins when present in the same cell, are often located in the plasma membrane of cell's opposite side or on the sides (left/right). All the different paralogs of influx and efflux proteins may not be present in the same cell. Often their expression and localization is tissue, cell, organ and development stage specific. This helps in directing the flow of auxin towards 'auxin maxima' sites in plant organs and cells as needed. In some cases auxin can permeate through the plasma membrane.
The Arabidopsis gene products PIN5, PIN6 and PIN8 were removed from the pathway since they are known to be involved in intracellular auxin transport rather than the intercellular auxin transport.