Future Perspectives in Plant Biology The Power of Auxin in Plants

The existence of auxin as a mobile growth regulator was famously inferred by Charles and Frances Darwin, as described in their 1880 book, The Power of Movement in Plants (Darwin and Darwin, 1880). However, auxin was not isolated until much later by Went (1926). Its first ever mention in Plant Physiologywas in Went’s obituary, written by George Peirce, which credits Went with having “introduced into plant physiology the general conception of regulators or coordinators” (Peirce, 1936, p. 222), exemplified by the enduring value of the Cholodny-Went hypothesis, which posits that dynamic redistribution of auxin directs tropic growth (Whippo and Hangarter, 2006). Peirce continues, “ The conception of hormones is now common, and some day it may become clear!” (p. 222). Three-quarters of a century later, the picture is still rather hazy, an enticing destination shimmering indistinctly on the horizon, but it is at least in view. Perhaps it is the vanity of every generation to imagine enlightenment is just around the corner. But I think there is no better time to be an auxin biologist. The past few decades of auxin biology have been primarily occupied with nuts and bolts and other component parts. A formidable cast of players has been assembled: receptors, transporters, synthesizers, inactivators (for recent reviews, see Chapman and Estelle, 2009; Lokerse and Weijers, 2009; Petrasek and Friml, 2009; Zhao, 2010). There are surely still some important components missing, but nonetheless, a noticeable shift in the main focus has now begun, toward understanding how the parts act and interact to “regulate and co-ordinate,” as envisaged by Went (Peirce, 1936, p. 222). How do whole plant-level patterns and behaviors emerge from the actions and interactions of the molecular components of the auxin machinery? Striking and pervasive features of the answer to this question are the extraordinary selforganizing and self-regulating properties of auxin biology, which characterize auxin action at every level (Benjamins and Scheres, 2008; Jaillais and Chory, 2010).