ABSTRACT
The phytohormone auxin plays a major role in plant growth, development and responses to various external and internal signals. Indole-3-acetic acid (IAA), the most common natural auxin, has been linked to plant characteristics such as apical dominance; tropic responses; lateral and adventitious root growth; tissue and organ patterning; vascular, fl ower and fruit development; and abscission. At the cellular level, auxin functions as a key signal for division, expansion and differentiation across the entire life cycle of a plant (Guilfoyle et al. 1998; Fig. 9-1) Auxin levels and gradients are important in establishing and achieving several above-and belowground plant growth features, leading to its label as a “morphogen” (Bhalerao and Bennett 2003). IAA activity as well as the plant’s response to IAA may be subject to control at various checkpoints including biosynthesis, conjugation, long-distance transport, cellular and subcellular transport, perception and signal transduction. These checkpoints are coordinated
Figure 9-1 Cartoon of a Populus plant depicting roles of auxin in various plant developmental and physiological stages. Note the fl oral organs depicted in the cartoon do not typically develop in Populus until a tree reaches reproductive maturity [5-15 years of vegetative growth].
