XVI International Botanical Congess

The Arabidopsis root displays a simple and regular organisation of tissues, its ontogeny during and after embryogenesis is described at the cellular level, and despite rigid lineage relationships it exhibits astonishing developmental flexibility. We have investigated the role of the phytohormone auxin in flexible cell fate specification. Auxins, with indole-3-acetic acid as the major active form, have diverse roles in growth and development that have hitherto been difficult to disentangle. We have utilised an auxin-response promoter element to visualise auxin distribution in vivo. We show that auxin is asymmetrically distributed in the root with a peak concentration in columella initial cells. Mutants in auxin transport and response suggest that this distribution is required for patterning. Re-distribution of the auxin concentration peak by laser ablation and by polar auxin transport inhibitors correlates with changes in multiple cell fates and cell- and organ polarity. Thus, auxin and its transport machinery play major roles in organising pattern and polarity.