Cytokinin

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Zeatin is named after the genera of corn, "Zea" as it was first discovered in corn.

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 are two kinds of cytokinins:

Adenin cytokinins

Examples: kinetin, zeatin, benzyl adenine ( same as 6-Benzylaminopurine). The DNA base adenine is a structural analogue of cytokinins and have low cytokinin bioactivity.

Phenylurea cytokinins

Example: N, N'-diphenylurea

Although their chemical compositions differ, there is a structural correlation between adenine cytokinins and urea cytokinin, and both show similar biological activities.

[edit] 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

[edit] Effects

Cytokinins generally promote shoot development and inhibit 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)