Definition - What does Cytokinins mean?
Cytokinins are a type of plant hormone that primarily stimulates cell division and are a derivative of the purine adenine. They are produced by the roots and travel upward through the xylem. This promotes tissue growth and budding and, on application, retards plant senescence.
Since auxins, another type of plant hormone, travel down from the growing tip and act to suppress lateral growth, these two types of hormones (cytokinins and auxins) strike a balance. This relationship persists in tissue culture.
MaximumYield explains Cytokinins
Cytokinins comprise of a group of signaling molecules that help to regulate the growth and development of plants, acting both locally and at a distance. The first cytokinin was discovered from degraded autoclaved herring sperm DNA by Miller in 1955.
Most cytokinins are produced in the meristem of the roots. The meristem is the name for a region of tissue within the plant that actively promotes cell division. Thus, the meristem is any place that's still growing (like the tips of the roots or the tops of the stems).
Cytokinins have been found in all complex plants, as well as mosses, fungi, and bacteria. There are about 200 different natural and synthetic cytokinins known to botanists today. Cytokinin also can be found in coconut milk.
Up to now, 18 types of cytokinins have been discovered. Some of them are constituents of transfer RNAs. Roots seem to be the major source of cytokinin synthesis, and from roots the cytokinins pass upwardly through xylem.
Some cytokinin synthesis also takes place in other areas where cell divisions are occurring like endosperm region of seeds, growing embryos and developing seeds, young fruits, developing shoots buds, etc. Cytokinins are more abundant in developing tissues and organs, such as root tip, shoot apex, cambium, and immature organs. Initially it was thought that cytokinins are synthesized in these limited tissues and organs.