Figure 1.
Auxin transport across the cell membrane. Both forms of auxin (IAAH/IAA−) exist in cytoplasm (left/blue) and cell wall (right/grey) in different fractions (fIAAH). Passive transport across the cell membrane is possible only for the electrically neutral form (IAAH). The auxin ion (IAA−) uses efflux (PIN1) and influx (AUX1) mediators to move between compartments. Active transport is especially important for efflux of auxin from the cell because of the strong dissociation of auxin in the cytosol. Synthesis, degradation (to and from ∅ in the figure), and reversible conjugation of auxin also regulate the amount of hormone available in the cell.