Plant hormones are a group of naturally occurring organic substances that, at low concentrations, influence physiological processes such as growth, differentiation, and development. Many plant hormones are transported from one place in the plant to another, thus coordinating growth throughout the plant, while others act in the tissues in which they are produced.

For a hormone to have an effect it must be synthesized, reach the site of action, be detected, and have that detection transferred into a final biochemical action. The steps following detection are called signal transduction, while the components of the signal transduction chain are referred to as second messengers. Because the concentration of hormone molecules affects the intensity of the response, the level of the hormone is also significant. The level is determined by the biosynthesis of the active hormone molecule and its removal by metabolism to inactive...