Cytokinin

• Cytokinins (CK) are a class of plant growth substances (phytohormones) that promote cell division, or cytokinesis, in plant roots and shoots
• They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence

• There are two types of cytokinins: adenine- typecytokinins represented by kinetin, zeatin, and 6-benzylaminopurine, and phenylurea- typecytokinins like diphenylurea and thidiazuron (TDZ).
• Most adenine-type cytokinins are synthesized in roots Cambium and other actively dividing tissues also synthesize cytokinins
• No phenylureacytokinins have been found in plants
• Cytokinins participate in local and long-distance signalling, with the same transport mechanism as purines and nucleosides
• Typically, cytokinins are transported in the xylem
• Cytokinins act in concert with auxin, another plant growth hormone

Physiological role

• Initiation of cell division
• Delay of senescence
• Use in tissue culture
• Counteract apical dominance

Action and application:

• Cell division
• Cell enlargement
• Morphogenesis
• Dormancy
• Apical dominance
• Mobility: Immobile obstructs moment of amino acid, phosphate and various other substances

• Nucleic acid metabolism: Quick increase in the amount of RNA and decreases DNA
• Protein synthesis: Increases DNA
• Protein synthesis: Increased rate