Auxin and tropisms

Abstract

From the very beginnings, attempts to identify mechanisms underlying polar auxin transport in higher plants have been intimately linked to studies on the regulation of plant tropisms. Already in the nineteenth century Charles Darwin came up with a concept, suggesting that a transmissible signal might be involved in controlling directional plant growth in response to an environmental stimulus. Much later, plant physiologists identified auxin as a candidate molecule that could mediate tropic growth responses. However, it was not until establishment of Arabidopsis genetics and novel molecular techniques at the end of the twentieth century that enabled the characterization of auxin-signaling pathways and resulted in mechanistic insights into control of polar auxin transport and its significance for plant tropisms. In this chapter, essential aspects of the current framework of molecular events are presented, highlighting the role of auxin in directional plant growth.