Plant hormones (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis,[1] the regulation of organ size, pathogen defense,[2][3]stress tolerance[4][5] and through to reproductive development.[6] Unlike in animals (in which hormone production is restricted to specialised glands) each plant cell is capable of producing hormones.[7][8] Went and Thimanncoined the term “phytohormone” and used it in the title of their 1937 book.[9]
Phytohormones occur across the plant kingdom, and even in algae, where they have similar functions to those seen in higher plants.[10] Some phytohormones also occur in microorganisms, such as unicellular fungi and bacteria, however in these cases they do not play a hormonal role and can better be regarded as secondary metabolites.[11].
(Wikipedia accessed May 2022)
