Cytokinin
Encyclopedia : C : CY : CYT : Cytokinin
Cytokinins are a class of plant growth substances (plant hormones) active in promoting cell division, and are also involved in cell growth, differentiation, and other physiological processes. Their effects were first discovered through the use of coconut milk in the 1940s.
There two kind of cytokinins:
- Adenin cytokinins
- Phenylurea cytokinins
Although their chemical compositions differ, there is a structural correlation between adenine cytokinins and urea cytokinin, and both show similar biological activities.
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
- Rapidly transported in xylem stream at the plant level
- At the cell level, transported by purine transporters
- Reduced in plants suffering from 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 that would normally cause a shoot meristematic cell to produce CK
- Directly or indirectly induced by high levels of GA/BA
Effects
Cytokinins are generally promoting shoot development and inhibiting root development, although they are necessary for cell division in both shoot and root apical meristems.
- Promotes Chlorophyll production and leaf unrolling
- Promotes photosynthesis
- Stimulates cell broadening
- Promotes shoot formation
- 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
- Participates in morphogenesis
- Promotes stomatal opening (theoretical)
- Induces xylem and phloem
- Directly induces GA/BA at high levels (theoretical)
- Inhibits C4 Photosynthesis
- Stimulates the rate of metabolism of cells in the shoot (that are not at their peak metabolism rates) in response to an increase in the levels minerals and water (theoretical)
- Inhibits root growth (theoretical)
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