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 a scientist at the University of Wisconsin-Madison named Folke Skoog.
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. Cambium and possibly other actively dividing tissues are also sites of cytokinin biosynthesis. There is no evidence that the phenylurea cytokinins occur naturally in plant tissues. 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.
Cytokinins are involved in many plant processes, including cell division, shoot and root morphogenesis, chloroplast maturation, cell enlargement, auxiliary bud release and senescence. The ratio of auxin to cytokinin is crucial during cell division and the differentiation of plant tissues. Auxin is known to regulate the biosynthesis of cytokinin.
Adenosine phosphate-isopentenyltransferase (IPT) catalyses the first reaction in the biosynthesis of isoprene cytokinins. It may use ATP, ADP or AMP as substrates and may use dimethylallyl diphosphate (DMAPP) or hydroxymethylbutenyl diphosphate (HMBDP) as prenyl donors. This reaction is the rate limiting step in cytokinin biosynthesis. DMAPP and HMBDP used in cytokinin biosynthesis are produced by the methylerythritol phosphate pathway (MEP).
Cytokinins can also be produced by recycled tRNAs in plants and bacteria. tRNAs with anticodons that start with a uridine and carrying an already prenylated adenosine adjacent to the anticodon release on degradation the adenosine as a cytokinin. The prenylation of these adenines is carried out by tRNA-isopentenyltransferase.
Researchers Submit Patent Application, "Structure of Cytokinins and Cytokinin Receptors, and Modulation of Cytokinin Signaling", for Approval
Jan 22, 2013; By a News Reporter-Staff News Editor at Life Science Weekly -- From Washington, D.C., NewsRx journalists report that a patent...
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