Polar Auxin Transport

Isabelle Bohn Courseau, INRA, Versailles, France
Jan Traas, INRA/ENS‐Lyon, Lyon, France

Published online: July 2007

DOI: 10.1002/9780470015902.a0020116

Auxin is a plant hormone involved in a wide range of processes. It is transported from cell to cell by a process known as polar auxin transport (PAT), which plays a major role in plant development and physiology.

Keywords: auxin; hormone; polar transport; plant

Figure 1. The key components of the chemiosmotic theory of (PAT). (a) PAT at the cellular level. IAAH enters the cell by diffusion or via the influx carrier AUX1. In the cytoplasm, the pH is higher than the pKa of IAAH/IAA–, so IAAH tends to dissociate into IAA– and H+. IAA– can only exit the cell via the efflux carrier PIN, which has a polar localization; (b) AUX1 secondary structure and protein topology. (From Swarup et al., 2004. Copyright American Society of Plant Biologists, reprinted with permission); (c) PIN1 secondary structure and protein topology [(From Palme and Gälweiler, 1999).]
Figure 2. The role of PAT in embryo patterning. After the asymmetric division, PIN7 directs the auxin in the upper cells of the two-celled embryo (left). At the globular stage (right), PIN1 and PIN7 are oriented downwards, so auxin accumulates in the hypophysis and lower cell. PIN4 reinforces this auxin flux (From Tanaka et al., 2006. Reproduced with permission of Birkhauser Vurlag AG.)
Figure 3. The PAT in the plant: its role in the organogenesis in the shoot apical meristem. (a, b) Wild type and pin1 mutant of Arabidopsis. In the mutant PAT is disrupted and no flowers are initiated; (c) AUX1:AUX1–YFP in the shoot apical meristem of Arabidopsis thaliana. AUX1 does not seem to be polarized; (d) anti-PIN1 immunolabelling in the shoot apical meristem of Arabidopsis, showing complex PIN1 distribution. Locally, PIN1 is clearly polarized (From Barbier de Reuille et al., 2006. Copyright National Academy of Sciences of the United States of America); (e) detail of PIN1 immunolabellings showing PIN orientation towards the centre of a future primordium; (f) model for the contribution of PIN1 (red) and AUX1 (blue) to PAT at the meristem surface. In this model, AUX1 helps to concentrate auxin at the surface layer of the meristem (L1). This auxin is then redistributed at the meristem surface by PIN1. Bars, 50 m (c, d) – 10 m (e).
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Intracellular and Extracellular Signalling | Plant Development
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Article Title: Polar Auxin Transport
 
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Courseau, Isabelle Bohn, and Traas, Jan(Jul 2007) Polar Auxin Transport. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020116]