Role of cytokinin in plant tissue culture

Introduction
History
Definition
Structure of Cytokinin
Mode of Action
Roll of Cytokinins in Plant tissue culture
Functions of Cytokinin
Conclusions
References

1. Plant Tissue Culture
Roll of Cytokinin
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. Contents
Introduction
History
Definition
Structure of Cytokinin
Mode of Action
Roll of Cytokinins in Plant tissue culture
Functions of Cytokinin
Conclusions
References

3. Introduction
Cytokininsareessentialhormonesforplantgrowthand
development.
Theyarealsoofvitalimportanceforinvitromanipulationsof
plantcellsandtissues.
Cytokininshavebeenfoundinalmostallhigherplantsaswellas
mosses,fungi,bacteria,andalsointRNAofmanyprokaryotes
andeukaryotes.
Zeatin,foundinthemaizeplant,Zeatin,isthemostcommon
naturallyoccurringcytokinin.
Theyareabundantintheroottip,theshootapexandimmature
seeds.

4. History
1941:JohannesvanOverbeekdiscoveredthatthemilky
endospermfromcoconutalsohadthisability.
1955:CarlosMiller,agraduatestudentinFolkeSkoog's
laboratoryattheUniversityofWisconsin,identifieskinetin
fromherringsperm.
1956:MillerandSkoogdemonstratethattherationof
auxin:cytokininaltersorganogenesisinvitro.
1961-1963:MillerandLethamindependentlyisolatezeatin,a
naturallyoccurringcytokinin,frommaize.

5. Definition
‘Anyofaclassofplanthormonesthatpromotecelldivision
andgrowthanddelaythesenescenceofleaves.’
‘Planthormones thatthe separationof
daughtercellsaftermitoticdivisionofaparentcell.
Frequentlytheyarepurinederivatives.’
Examples:kinetin,zeatin,benzyladenine.

6. Distribution
Cytokininshavebeendetectedinawidevarietyofplants;from
unicellularyeasts,algaetomulticellularhigherplants.
Particularlyinhigherplants,cytokininsarefoundinroottips,
xylem,youngleaves;endospermsofdevelopingfruits,
germinatingseedsandtumourtissues.

7. structure of Cytokinin
Naturallyoccuringcytokininsareadeninederivativeswitha
sidechainattheN6-position.
ThestructureandconformationoftheN6-attachedsidechain
canmarkedlyinfluencethebiologicalactivityofthecytokinin.
DependingonthestructureoftheN6-substituent,cytokinins
areclassifiedasisoprenoidoraromaticcytokinins.

8. Isoprenoid cytokinins
Isoprenoidcytokininsarethemostabundantclass.
Theyareeitherisopentenyltypecytokinins,havingan
isopentenylN6-sidechain,orzeatin-typecytokinins,havinga
hydroxylatedisopentenylN6-sidechain.
Thesidechainofazeatin-typecytokininoccursineithercisor
transconfiguration,dependingonwhichofthetwomethyl
groupsishydroxylated.

11. Aromatic cytokinin
AromaticcytokininshaveanaromaticbenzylgroupatN6.
Theyoccurmorerarelyandmuchlessisknownaboutthem.
Becauseoftheirgreaterstabilityaromaticcytokininsareoften
usedintissueculture,anexampleisbenzyladenine.
Inaddition,syntheticcytokinins.Thesecytokininsarehighly
activebutdonotoccurnaturally.

14. Mode of action
Theratioofauxintocytokininplaysanimportantroleinthe
effectofcytokininonplantgrowth.
Whenculturedwithauxinbutnocytokinin,theygrowlarge
butdonotdivide.Whencytokininisadded,thecellsexpand
anddifferentiate.
Morecytokinininducesgrowthofshootbuds,whilemore
auxininducesrootformation.
Cytokininsareinvolvedinmanyplantprocesses,including
celldivisionandshootandrootmorphogenesis.
Cytokininshavebeenshowntoslowagingofplantorgansby
preventingproteinbreakdown,activatingproteinsynthesis,and
assemblingnutrientsfromnearbytissues.

15. RollofcytokininsinPlanttissueculture
Promotion OF Cell Division
Intissueculturescytokininsappeartobenecessaryfor
plantcelldivision.
Incultureswherecytokininislimiting,divisionofcell
nucleibecomesarrestedatonestageofthecellcycle.
Subcultureofthetissueontoamediumcontaininga
cytokinincanthencausethecellstodividesynchronously
afteralagperiod.
Morecytokinininducesgrowthofshootbuds,whilemore
auxininducesrootformation.

16. Control of Aging Patterns
Cytokininshavealsobeenshowntoslowagingofplantorgans
bypreventingproteinbreakdown,activatingproteinsynthesis,
andassemblingnutrientsfromnearbytissues.
Itwashypothesizedthatcytokininmayaffectenzymesthat
regulateproteinsynthesisanddegradation.
Theyhavebeenshowntoinduceresistanceagainst
PseudomonassyringaeinArabidopsisthalianaandNicotiana
tabacum.

17. Adventitious Shoot Formation
Cytokininsareveryeffectiveinpromotingdirectorindirect
shootinitiation.
Abalancebetweenauxinandcytokininnormallygivesthe
mosteffectiveorganogenesis.
LeafsegmentsofCrassulaargenteaformcallusinresponseto
wounding,whichthengivesrisetorootsandlater,shoots.

18. Embryogenesis
Alowconcentrationofcytokinin(typically0.5-2.5μM)is
oftenaddedtomediafortheinductionofembryogeniccallus,
especiallyinbroad-leafedplants.
Thepresenceofcytokininmayalsoberesponsibleforthe
inabilitytoobtainembryogenesisinsomegenotypes.
Leafsectionsofgrasscontainedlessnaturalcytokininthan
thosewhichwerecapableofproducingembryogeniccallus.

19. Use In Shoot Cultures
Axillary shoot proliferation
Toencouragethegrowthofaxillarybuds,andreduceapical
dominanceinshootculturesofbroadleafedplants,oneormore
cytokininsareusuallyincorporatedintothemediumatStageII.
Asuccessfultreatmentinducesthegrowthofseveralsmall
shootsfromeachexplantovera4-6weekperiod.
Levelsofcytokinin,whicharetoohigh,causemanysmall
shootstobeproduced,whichtypicallyfailtoelongate.

20. Adventitiousshootbudformation
Theformationofadventitiousshoots,whetherdirectlyfrom
explantedtissues,orindirectlyfromcallus,isregulatedbyan
interactionbetweenauxinsandcytokinins.
Inhibitionofrootformation
Highconcentrationsofcytokinin(0.5-10mg/l)generallyinhibit
ordelayrootformationandalsopreventrootgrowthandthe
promotiveeffectsofauxinsonrootinitiation.
Sometimesmorethanonesubculturetoacytokinin-free
mediummayberequireduntilthelevelofcytokininwithinthe
tissueshasbeensufficientlyreduced.

21. Functions of cytokinin
Cell cycle
Cytokininsarerequiredforcelldivisionduring
embryogenesis,intheshootapicalmeristem,youngleaves,the
cambiumandculturedplantcells.
Incontrast,theyhaveanegativeregulatoryroleintheroot
meristem.
Cytokininrestrictsrootgrowthasitcontrolstheexitof
dividingcellsfromthemeristem.

22. PlantDevelopmentandGrowth
Cytokininparticipatesinregulatingnumerousaspectsofplant
developmentthroughoutthelifecycle.
Theseincludeseedgermination,chloroplastdifferentiation,
differentiationofvasculartissue,apicaldominance(shoot
branching),rootelongationandbranching,flowerandfruit
development,andplant-pathogeninteractions.
Duringembryonicdevelopmentcytokininsarerequiredto
maintainmeristemactivityandleafdevelopmentintheplant
shoot.

23. Pathogenicity
Cytokininsareproducedbyseveralplantpathogenicbacteria
andplayaroleinpathogenicity.
OnesuchpathogenisAgrobacteriumtumefaciens,thecausative
agentofthecrowngalldisease.
Othercytokinin-synthesizingpathogensarePseudomonas
syringae,whichinducesgallformationandRhodococcus
fascians,whichcausesfasciationandagrowthabnormalitycalled
witches´broomdisease.
Theroot-noduleformingandnitrogen-fixingplantsymbiont
Rhizobiumspec.isalsoknowntoproducecytokinin.

24. Biotechnology
Practicaluseofcytokinininagriculturaliscurrentlylimited.
Modulationofthecytokinincontentofplantsorinterfering
withcytokininsignallinghasahighpotentialfor
biotechnologicalapplicationsinagriculture.
Animprovedrootsystemmeansimprovedacquisitionof
mineralsandwater,factorswhichareoftenlimitingforplant
growth.

25. References
MK Razdan-Introdutionto Plant Tissue Culture 2
nd
Edition
SS Bhojwani& MK Razdan-Plant Tissue Culture
H.S.Chawla-Introdutionto Plant Biotechnology
Internet
www.plant-hormones.info
www.boundless.com/cytokinins