Cytokinin

Cytokinins are a class of plant growth substances (plant hormones) active in promoting cell division. Also involved in cell growth and differentiation and in other physiological processes. Examples: kinetin , zeatin , benzyl adenine . Their effects were first discovered through the use of coconut milk in the 1940s.

Location, Characteristics and Occasions for Synthesis Induction

• Synthesized in root and shoot meristematic tissue
• Synthesized in meristematic regions of roots
• Synthesized in mature roots – small amount
• Rapid transport in xylem stream
• CK activity reduced in plants suffering drought
• Peaks during the day
• Synthesized in mature shoot cells
• Released by meristematic cells when they have enough minerals and water to support both themselves and any dependent cells
• Released by all cells when they are experiencing conditions which would normally cause a shoot meristematic cell to produce CK
• Directly or indirectly induced by high levels of GA/BA

Effects

• CK promotes Chlorophyll production and leaf unrolling
• CK promotes photosynthesis
• Stimulates cell broadening
• Also promotes shoot formation
• Also promotes the unloading of sugar from phloem
• Causes the outgrowth of secondary shoot buds – breaks shoot apical dominance/ lateral bud development
• Delays leaf senescence
• Stimulates cell division with Auxin
• Involved in morphogenesis
• Promotes stomatal opening
• Induces xylem and phloem
• Directly induces GA/BA at high levels
• Inhibits C4 Photosynthesis
• (From Theory II) Stimulates the rate of metabolism of cells in the shoot (who are not at their peak metabolism rates) in response to an increase in the levels minerals and water