Skip to main content
. 2012 Mar 1;3:37. doi: 10.3389/fpls.2012.00037

Figure 1.

Figure 1

Oat (Avena sativa) coleoptile (A) and schematic rendering of polar auxin (IAA) transport according to the chemiosmotic model (B). Auxin influx can result from the passive diffusion of the protonated form of IAA (IAAH across the plasma membrane) or by active transport of the dissociated form (IAA−) by a 2H+–IAA− permease symporter (denoted as PH+ co). The passive diffusion of IAA is dependent on the pH of the cell wall. Plasma membrane H+-ATPases normally maintain the cell wall at approximately pH 5.0 via protonation. Polar transport is governed by the efflux of IAA at the base of cells via auxin anion efflux carriers (EC) that transport IAA− out of the cell (driven by a negative membrane potential). The PIN family of proteins have been identified as the EC. See Figure 5 for a logic circuit rendering of IAA polar transport. In addition, the mode of IAA action is illustrated.