The extrinsic system is triggered by the release of tissue thromboplastin, a protein–phospholipid mixture that activates factor VII.

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#Unit 6. System Physiology – Plant

KNOX gene expression increases cytokinin levels in the shoot apical meristem by upregulating the cytokinin biosynthetic gene ISOPENTENYL TRANSFERASE7 (IPT7)

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#Unit 6. System Physiology – Plant

Cytokinin Primary site of synthesis -- root tips.

High concentrations -- immature seeds and developing fruits

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#Unit 6. System Physiology – Plant

Many plant tissues contain the enzyme cytokinin oxidase, which cleaves the side chain from zeatin (both cis and trans), zeatin riboside, iP, and their N-glucosides, but not their O-glucoside derivatives

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#Unit 6. System Physiology – Plant

Biological effects of cytokinins

Removes inhibitory phosphate

Promotes accumulation of G1 cyclins (CycD)

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#Unit 6. System Physiology – Plant

Cytokinin has been linked to the activation of a Cdc25- like phosphatase, whose role is to remove an inhibitory phosphate group from the Cdc2 kinase. 

Cytokinins elevate the expression of the CYCD3 gene, which encodes a D-type cyclin'

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#Id: 10205

#Unit 6. System Physiology – Plant

Cytokinin binds to the CRE1 receptors to initiate a response that culminates in the elevation of transcription of the type- BARRs/ type- A ARRs.