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Cytokinin

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Cytokinins Cell division Delay leaf senescence Promote nutrient mobilization Modify apical dominance The formation and activity of shoot apical meristem Floral development

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Break bud dormancy Stimulate seed gemination Cytokinin mediate light-regulate development Chloroplast differentiation Development of autotrophic metabolism Leaf and cotyledon expansion

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and primary and secondary meristem( ) enlargement and differentiation cell division ( )

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( nucleus) wound healing( ) leaf abscission( ) http://botit.botany.wisc.edu/

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differentiated plant cell can resume division 1. Cortex( ) Phloem( ) secondary meristems vascular cambium( ) cork cambium( )

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2. leaf petiole ( ) abscission zone ( ) parenchyma cells( ) abscission

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3. Wound( ) wound-induce mitotic phloem fibers( ) guard cells( ) Wound-induce mitotic activity self-limiting

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Wound crown gall

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Philip White 1930 tomaoto roots medium Medium vitamines hormones stem tissue medium Auxin auxin-induced enlargement

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shoot tissues medium root shoot shoot root

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crown gall 42 crown gall tissue (bacteria-free) tumor tumor medium Callus tissue Callus tissue shoot Callus tissue

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Cytokinin Caplin and Steward 1948 Philip White medium auxin 10-20% callus tissue cytokinin zeatin

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Kinetin Folke Skoog 1940-1950 tobacco pith tissue adenine autoclave( ) Millery 1955 DNA Kinetin

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Kinetin Kinetin adenine 6-furfurylaminopurine

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Zeatin 1963 Letham kinetin trans-6-(4-hydroxy-3-methylbut-2- enylamino)purine zeatin Zeatin kinetin adenine

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Zeatin

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Zeatin trans cis zeatin isomerase trans is more active cis cytokinin receptor cis

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Other aminopurine and bound forms

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cytokinin auxin callus tissue callus

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cytokinin

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Cytokinins Cytokinins zeatin dihydrozeatin(DZ) isopentenyl adenine(iP) Cytokinins

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tRNA cis- zeatin

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Active Cytokinin Cytokinin receptor CRE1 free form trans-zeatin riboside ribotide DZ iP

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cytokinin cytokinin trans- zeatin iP cis-zeatin ribosides crown gall (A.tumefaciens) witchesbroom (Corynebacterium fascian)

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Cytokinins Zeatin iP isoprene isoprene Dimethylallyl Diphosphate (DMAPP) isoprene unit 1-hydroxy-2-methyl-2-(E)-butenyl 4- diphosphate (HMBDP)

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Crown gall cells cytokinin crown gall agrobacterium tumefaciens Ti- plasmid Ti- plasmid DNA Ti-plasmid T-DNA trans-zeatin Auxin

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T-DNA crown gall cell Opine Ipt gene isopentenyl transferase(IPT) Ipt gene Auxin gene phyto-oncogene ( ) T-DNA promoters eukaryotic

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opines

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Cytochrome P450 monooxygenase iPMP/iPDP/iPTP ZMP/ZDP/ZTP

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Cytokinin cytokinin cytolinin cytolinin zeatin riboside glucoside zeatin riboside

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Beveridge 1997 wild type pea mutant rms4 rms4 zeatin riboside 1/40 rms4 shoot + wild type root low [cytokinin] level wild type shoot + rms4 root high [cytokinin] level cytokinin

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cytokinin 7 IPT genes Phloem leaf axil ovules immature seeds columella root cap young fruit abscission zone IPT genes cytokinin down-regulate IPT genes Auxin up-regulate

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Cytokinin Cytokinin cytokinin oxydase adenine( O-glucoside DZ ) cytokinin Cytokinin 3,7,9 glucose O-glucoside Cytokinin glucosidase

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Cytokinins : LINCOLN TAIZ EDUARDO ZEIGER

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The Biological Roles of Cytokinins

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Cytokinins regulate cell division in shoots and roots Several evidence Shoot apical meristem (Werner et al. 2001) - This finding strongly supports the notion that endogenous cytokinins regulate cell division

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Overexpressing the gene for cytokinin oxidase

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Cytokinin oxidase enhancement of root growth (Werner et al. 2001) Root apical meristem (Werner et al. 2001) Cytokinins regulate cell division in shoots and roots

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A small reduction in cytokinin levels would increase root growth (data courtesy of F. J. Ferreira and J. J. Kieber.) Cytokinins regulate cell division in shoots and roots

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Triple-receptor mutants (ahk2/ahk3/cre1) (Nishimura et al. 2004.) Mutation in maize alters leaf phyllotaxy and the size lf the shoot apical meristem (abphyl1) (Giulini et al. 2004.) Cytokinins regulate cell division in shoots and roots

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Cytokinins regulate specific components of the cell cycle Cyclin-dependent protein kinases (CDKs) Cytokinin and auxin : regulating the passage from G 2 to M phase (Zhang et al. 1996) Overexpression of CYCD3 (Riou-Khamlichi et al. 1999)

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The auxin:cytokinin ratio regulates morphogenesis in cultured tissues Kinetin High auxin:cytokinin ratios roots Low auxin:cytokinin ratios shoots (Skoog and Miller 1965)

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T-DNA tms/tmr/tml v.s. tumors (Morris 1986) The auxin:cytokinin ratio regulates morphogenesis in cultured tissues

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Cytokinins modify apical dominance and promote lateral bud growth MAX4 and RMS1

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Cytokinins induce bud formation in a moss Funaria hygrometrica Protonema (plural protonemata) (Courtesy of K. S. Schumaker)

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Cytokinin overproduction has been implicated in genetic tumors Nicotiana Genetic tumors

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Cytokinins delay leaf senescence Delay senescence Limited expression of the ipt gene

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Cytokinins promote movement of nutrients Cytokinin-treated cotyledon has become a nutrient sink

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Cytokinins promote chloroplast development Dark-grown and light-grown (Chory et al. 1994)

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Cytokinins promote cell expansion in leaves and cotyledons The effect of CK on the expansion of radish cotyledons

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Cytokinin in plant physiology and development Shoot apical meristems v.s. leaves Leaves have higher chlorophyll levels Adventitious shoots may form from unwounded leaf veins and petioles

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Cytokinin in plant physiology and development Leaf senescence is retarded Apical dominance is greatly reduced More extreme CK- overproducing plants Root

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Cellular and Molecular Modes of Cytokinin Action

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A cytokinin receptor related to bacterial two-component receptors has been identified Simple tow-component systems Phosphorelay-type two- component signaling system

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Cytokinins increase expression of the type-A response regulator genes via activation of the type-B ARR genes ARR (Arabidopsis response regulator) Type A ARR and type B ARR

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Histidine phosphotransferases are also involved in cytokinin signaling Histidine phosphotransfer protein (Hpt)

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Thank you !!