Indoleacetic acid (IAA) is a molecule that is synthesized by plants and a few microbes (3, 4). In plants, IAA plays a key role in both root and shoot development. The hormone moves from one part of the plant to another by a designated importer (AUX1) and efflux pumps.
IAA stimulates overproduction of root hairs and lateral roots in plants and release of saccharides from plant cell walls during the elongation.
Different concentrations of IAA appear to have differing effects on root growth. These effects may vary from one species to another but generally at low concentrations IAA stimulates root growth while at higher concentrations it inhibits root growth.