Indole-3-acetic acid

Indole-3-acetic acid, also known as IAA, is a member of the group of phytohormones called auxins. IAA is generally considered to be the most important native auxin.

Auxin
It is produced in cells in the apex (bud) and young leaves of a plant. Plant cells synthesize IAA from tryptophan. It has many different effects, as all auxins do, such as inducing cell elongation and cell division with all subsequent results for plant growth and development. There are less expensive and metabolically stable synthetic auxin analogs on the market for use in horticulture, such as indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA).

Studies of IAA in the 1940s led to the development of the phenoxy herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Like IBA and NAA, 2,4-D and 2,4,5-T are metabolically and environmentally more stable analogs of IAA. However, when sprayed on broad-leaf dicot plants, they induce rapid, uncontrolled growth, eventually killing them. First introduced in 1946, these herbicides were in widespread use in agriculture by the middle of the 1950s.

Chemical properties of IAA
IAA can be produced by the reaction of indole with potassium glycolate at 250 C, but this compound is chemically unstable in particular when exposed to light or changing temperature.