The prospective lens cells secrete paracrine factors that instruct the optic vesicle to form the retina. 

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#Id: 7558

#Unit 6. System Physiology – Plant

Cytokinin biosynthesis, catalyzed by isopentenyl transferase (IPT), is the addition of the isopentenyl side chain from DMAPP (dimethylallyl diphosphate) to an adenosine moiety (ATP or ADP). iPRTP or iPRDP is converted to ZTP or ZDP respectively by cytochrome P450 monooxygenase (CYP735A) and eventually is converted to zeatin.

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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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#Id: 7560

#Unit 6. System Physiology – Plant

Cytokinin Primary site of synthesis -- root tips. High concentrations -- immature seeds and developing fruits

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#Id: 7561

#Unit 6. System Physiology – Plant

Biological effects of cytokinins

Removes       Promotes accumulation of G1 cyclins (CycD)

inhibitory

phosphate 

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#Id: 7562

#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: 7563

#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.