so ma clonal
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Genetic variations in plants thatGenetic variations in plants thathave been produced by plant tissuehave been produced by plant tissueculture and can be detected asculture and can be detected as
genetic or phenotypic traits.genetic or phenotypic traits.
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Basic Features ofBasic Features of SomaclonalSomaclonal
VariationsVariations
VariationsVariations forfor KaryotypeKaryotype,, isozymeisozyme characteristicscharacteristics andandmorphologymorphology inin somaclonessomaclones maymay alsoalso bebe observedobserved..
CallicloneCalliclone (clones(clones ofof callus),callus), mericlonemericlone (clones(clones ofofmeristemmeristem)) andand protocloneprotoclone (clones(clones ofof Protoplast)Protoplast) ..
GenerallyGenerally heritableheritable mutationmutation persistpersist inin plantplant
populationpopulation eveneven afterafter plantationplantation intointo thethe fieldfield
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Mechanism of SomaclonalMechanism of Somaclonal
VariationsVariations1. Genetic (Heritable Variations)
Pre-existing variations in the somatic cells of
explant
Caused by mutations and other DNA changes
Occur at high frequency
2. Epigenetic (Non-heritable Variations)
Variations generated during tissue culture
Caused by temporary phenotypic changes
Occur at low frequency
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Callus Tissue
Organogenesis
Regenerated plants Hardening and Selfing
Somaclonal Variants
Steps involved in induction and selection ofSomaclonal Variations
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Causes of Somaclonal
Variations
Physiological
Cause
Genetic Cause
Biochemical
Cause
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Physiological CausePhysiological Cause
Exposure of culture to plant growthExposure of culture to plant growth
regulators.regulators.
Culture conditionsCulture conditions--genotype andgenotype andexplant,durationexplant,duration of cell culture.of cell culture.
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Physiological CausePhysiological Cause
Variation in chromosomeVariation in chromosome--preexistingpreexisting
chromosome variationchromosome variation
Nuclear fragmentationNuclear fragmentation
AbnormalitiesAbnormalities occuringoccuring in mitotic processin mitotic process
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Genetic CauseGenetic Cause
1.1. Change in chromosome numberChange in chromosome number Euploidy: Changes chromosome SetsEuploidy: Changes chromosome Sets
Aneuploidy: Changes in parts of chromosome SetsAneuploidy: Changes in parts of chromosome Sets
Polyploidy: Organisms with more than two chromosomePolyploidy: Organisms with more than two chromosomesetssets
Monoploidy: Organism with one chromasomes setMonoploidy: Organism with one chromasomes set
2.2. Change in chromosome structureChange in chromosome structure DeletionDeletion
InversionInversion
DuplicationDuplication
TranslocationTranslocation
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3.3. Gene MutationGene Mutation TansitionTansition
TransversionTransversion
InsertionInsertion
DeletionDeletion
4.4. Plasmagene MutationPlasmagene Mutation
5.5. Transposable element activationTransposable element activation
Genetic CauseGenetic Cause
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6.6. DNA sequenceDNA sequence
Change in DNAChange in DNA Detection of altered fragment size by using Restriction enzymeDetection of altered fragment size by using Restriction enzyme
Change in ProteinChange in Protein Loss or gain in protein bandLoss or gain in protein band
Alteration in level of specific proteinAlteration in level of specific protein
Methylation ofDNAMethylation ofDNA Methylation inactivates transcription process.Methylation inactivates transcription process.
Genetic CauseGenetic Cause
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Biochemical CauseBiochemical Cause
Lack of photosynthetic ability due to alterationLack of photosynthetic ability due to alterationin carbon metabolismin carbon metabolism
Biosynthesis of starch via carotenoid pathwayBiosynthesis of starch via carotenoid pathway
Nitrogen metabolismNitrogen metabolism
Antibiotic resistance.Antibiotic resistance.
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Detection and Isolation of SomaclonalDetection and Isolation of Somaclonal
VariantsVariants
1.1. Analysis of morphological charactersAnalysis of morphological characters Qualitative characters: Plant height, maturity date,Qualitative characters: Plant height, maturity date,
flowering date and leaf sizeflowering date and leaf size
Quantitative characters: yield of flower, seeds and waxQuantitative characters: yield of flower, seeds and wax
contents in different plant partscontents in different plant parts
2.2. Variant detection by cytological StudiesVariant detection by cytological Studies Staining of meristematic tissues like root tip, leaf tip withStaining of meristematic tissues like root tip, leaf tip with
feulgen and acetocarmine provide the number andfeulgen and acetocarmine provide the number andmorphology of chromosomes.morphology of chromosomes.
3.3. Variant detection by DNA contentsVariant detection by DNA contents Cytophotometer detection of feulgen stained nuclei canCytophotometer detection of feulgen stained nuclei can
be used to measure the DNA contentsbe used to measure the DNA contents
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4.4. Variant detection by gel electrophoresisVariant detection by gel electrophoresis Change in concentration of enzymes, proteins andChange in concentration of enzymes, proteins and
chemical products like pigments, alkaloids and aminochemical products like pigments, alkaloids and amino
acids can be detected by theiracids can be detected by their electrophoreticelectrophoretic patternpattern
5.5. Detection of disease resistance variantDetection of disease resistance variant Pathogen or toxin responsible for disease resistance canPathogen or toxin responsible for disease resistance can
be used as selection agent during culture.be used as selection agent during culture.
6.6. Detection of herbicide resistance variantDetection of herbicide resistance variant Plantlets generated by the addition of herbicide to the cellPlantlets generated by the addition of herbicide to the cell
culture system can be used as herbicide resistance plant.culture system can be used as herbicide resistance plant.
Detection and Isolation of SomaclonalDetection and Isolation of Somaclonal
VariantsVariants
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7.7. Detection of environmental stress tolerantDetection of environmental stress tolerant
variantvariant
Selection of high salt tolerant cell lines in tobaccoSelection of high salt tolerant cell lines in tobacco Selection of waterSelection of water--logging and drought resistance celllogging and drought resistance cell
lines in tomatolines in tomato
Selection of temperature stress tolerant in cell lines in pear.Selection of temperature stress tolerant in cell lines in pear.
Selection of mineral toxicities tolerant in sorghum plantSelection of mineral toxicities tolerant in sorghum plant
(mainly for aluminium toxicity)(mainly for aluminium toxicity)
Detection and Isolation of SomaclonalDetection and Isolation of Somaclonal
VariantsVariants
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Advantages of Somaclonal VariationsAdvantages of Somaclonal Variations
Help in crop improvementHelp in crop improvement
Creation of additional genetic variationsCreation of additional genetic variations
Increased and improved production ofIncreased and improved production ofsecondary metabolitessecondary metabolites
Selection of plants resistant to variousSelection of plants resistant to various
toxins, herbicides, high salt concentrationtoxins, herbicides, high salt concentrationand mineral toxicityand mineral toxicity
Suitable for breeding of tree speciesSuitable for breeding of tree species
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Disadvantages of SomaclonalDisadvantages of Somaclonal
VariationsVariations
AA seriousserious disadvantagedisadvantage occursoccurs inin operationsoperations whichwhich requirerequireclonalclonal uniformity,uniformity, asas inin thethe horticulturehorticulture andand forestryforestryindustriesindustries wherewhere tissuetissue cultureculture isis employedemployed forfor rapidrapid
propagationpropagation ofof eliteelite genotypesgenotypes SometimeSometime leadsleads toto undesirableundesirable resultsresults
SelectedSelected variantsvariants areare randomrandom andand geneticallygenetically unstableunstable
RequireRequire extensiveextensive andand extendedextended fieldfield trialstrials
NotNot suitablesuitable forfor complexcomplex agronomicagronomic traitstraits likelike yield,yield, qualityquality
etcetc.. MayMay developdevelop variantsvariants withwith pleiotropicpleiotropic effectseffects whichwhich areare notnot
truetrue..
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