Cytokinins (CK) are a class of plant growth substances (plant hormones) that promote cell division. They are primarily involved in cell growth, differentiation, and other physiological processes. Their effects were first discovered through the use of coconut milk in the 1940s by Adicott at the University of Wisconsin-Madison named Folke Skoog. [1]

There are two types of cytokinins: adenine-type cytokinins represented by kinetin, zeatin and 6-benzylaminopurine, as well as phenylurea-type cytokinins like diphenylurea or thidiazuron (TDZ). The adenine-type cytokinins are synthesised in stems, leaves and roots, which is the major site.[citation needed] Cambium and possibly other actively dividing tissues are also sites of cytokinin biosynthesis.[2] There is no evidence that the phenylurea cytokinins occur naturally in plant tissues.[3] Cytokinins are involved in both local and long distance signalling, the latter of which involves the same in planta transport mechanism as used for transport of purines and nucleosides.[4]