Cytokinin
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ZeatinII.png
ZeatinII.png
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. 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
- 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
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Auxins - Cytokinins - Ethylene - Gibberellins - Abscisic acid - Brassinosteroids - Jasmonates - Salicylic acid |