Presented by :Anuj Kumar Sharma
M.Sc. Biotechnology 2nd sem.
Contents:1.
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introduction to Somaclonal Variation
Schemes for obtaining somaclonal variation
Detection and Isolation of Somaclonal Variants
Factor affecting somaclonal variation
Mechanism of Somaclonal Variations
Advantages of Somaclonal Variations
Disadvantages:
Application of somaclonal variation in crop improvement
Control of Somaclonal Variation
To Increase Somaclonal Variation
Targets for Somaclonal Variation
References
It is the term used to describe the
variation seen in plants that have been
produced by plant tissue culture.
Chromosomal rearrangements are an
important source of this variation
Kohleria „Orange Glow“, eine durch
mutagene
Behandlung von Gewebekulturen
erhaltene Mutante
(Oben) im Vergleich zur
Ausgangsform (links).
Schemes for obtaining
somaclonal variation
Two schemes
1.Without in vitro selection
2.With in vitro selection
1.Without in vitro selection
A flow diagram for generation of somaclonal variation
without in vitro selection
2. With in vitro selection :-
Continue………….
Continue……….
Detection and Isolation of
Somaclonal Variants
1. Analysis of morphological characters
Qualitative characters: Plant height, maturity date,
flowering date and leaf size
Quantitative characters: yield of flower, seeds and wax
contents in different plant parts
2. Variant detection by cytological Studies
Staining of meristematic tissues like root tip, leaf tip
with feulgen and acetocarmine provide the number and
morphology of chromosomes.
3. Variant detection by DNA contents
Cytophotometer detection of feulgen stained nuclei can
be used to measure the DNA contents
Detection and Isolation of
Somaclonal Variants
4. Variant detection by gel electrophoresis
Change in concentration of enzymes, proteins and hemical
products like pigments, alkaloids and amino acids can be
detected by their electrophoretic pattern
5. Detection of disease resistance variant
Pathogen or toxin responsible for disease resistance can
be used as selection agent during culture.
6. Detection of herbicide resistance variant
Plantlets generated by the addition of herbicide to the cell
culture system can be used as herbicide resistance plant.
Detection and Isolation of
Somaclonal Variants
7. Detection of environmental stress tolerant
variant
Selection of high salt tolerant cell lines in tobacco
Selection of water-logging and drought resistance cell
lines in tomato
Selection of temperature stress tolerant in cell lines in
pear.
Selection of mineral toxicities tolerant in sorghum plant
(mainly for aluminium toxicity)
Factor affecting somaclonal
variation
1.Genotype
2.Explant source
3.Duration of cell culture
4.Culture condition
Mechanism of Somaclonal
Variations
1. 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
A] Genetic variations are:
1.changes in chromosome
2.chromosome structure
3.DNA sequence
1.changes in chromosome numbers;
Euploidy- changes in whole chromosome sets
Aneuploidy- changes in parts of chromosome sets
Ploidy: number of basic chromosome sets (a diploid has
2 sets; a hexaploid has 6 sets)
Euploid: organism containing multiples of the basic
chromosome set
Monoploid: organisms with one chromosome set (in
essentially diploid taxa)
Polyploid: organism containing more than two
chromosome sets
2.Structural Changes in
Chromosomes
Deletion
Inversion
Duplication
Translocation
3.DNA sequence (base mutations).
Change at DNA level
 Detected using restriction enzyme
analysis (altered fragment size)
Changes at protein levels
 Loss or gain of protein band
 Altered levels of specific proteins
DNA methylation
 Methylation of a gene inactivates its
transcription
B] Epigenetic change
Due to gene expression not gene
alteration
Often temporary
Some examples
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Morphological change - leaf shape
Earlier flowering
Improved adventitious rooting
Increased vigor
Plageotropic growth
Advantages of Somaclonal
Variations
Benefit of somaclonal variation is in plant improvement
Creation of additional genetic varitions
Increased and improved production of secondary
metabolites
Selection of plants resistant to various toxins, herbicides,
high salt concentration and mineral toxicity
Suitable for breeding of tree species
Characteristics for which somaclonal mutants can be
enriched during in vitro culture include resistance to
disease pathotoxins, herbicides and tolerance to
environmental or chemical stress.
Disadvantages:
No control - may change in undesirable direction
Variations are random in nature
May not be genetically stable
Require extensive field testing
May not occur for complex agronomic traits
Application of somaclonal variation in
crop improvement :Improve by
1.selecting novel varients
2.Disease resistant
3.Abiotic stress resistance
4.Salt tolerance
5.Aluminium tolerance
6.Herbicide resistance
7.Insect resistance
8.Seed quality
Disease Resistant Success using Somaclonal Variation
Crop
Pathogen
Toxin
Alfalfa
Colletotrichum sp.
Culture filtrate
Banana
Fusarium sp.
Fusaric acid
Coffee
Colletotrichum sp
Partially purified culture
filtrate
Maize
Helminthosporium
maydis
T-toxin
Oat*
Helminthosporium
victoriae
Victorin
Sugarcane**
Helminthosporium sp.
Culture filtrate
Potato**
Phytophthora infestans
Culture filtrate
Rice
Xanthomonas oryzae
Culture filtrate
Tobacco*
Alternaria alternata
Partially purified toxin
*Shown to be heritable through sexual propagation
**Shown to be stable through vegetative propagation
Somaclonal variation in trees:
Somatic variation may be a better mans for tree
improvement
Direct gene insertion or agrobacteruim –
mediated transformation have many technical
difficulties that must be overcome with this
methods.
It have the potential to significantly change tree
breeding programs by reducing the time
required for selecting and improving desired
traits .
Applying soma clonal technology to forest
trees offers an even greater advantage
because of the long generation times of
trees and the opportunity to introduce
desired traits not possible through
traditional breeding.
Somaclonal technology is simpler to
exploit than other types of genetic
engineering.
Control of Somaclonal Variation:
Regular reinitiation of clones from new
explants might reduce variability over time.
Avoid 2,4-D in the culture medium, as this
hormone is known to introduce variation.
The duration of the culture cycle may
influence the variability.
To Increase Somaclonal Variation:
Callus and suspension cultures for several
cycles
Regeneration of large number of plants
from long-term cultures
Testing of selected somaclones for genetic
stability
Multiplication of genetically stable
somaclones for developing new cultivars
Targets for Somaclonal Variation
• Specific amino acid accumulators
– Screen for specific amino acid production
– e.g. Lysine in cereals
• Abiotic stress tolerance
– Add or subject cultures to selection agent
– e.g.: salt tolerance, temperature stresses, etc…
• Disease resistance
– Add toxin or culture filtrate to growth media
– Examples shown on next slide →
References:
Chawla.H.S.(2008),introduction to plant biotechnology ,
somaclonal variation , Oxford & IBH publishing co.(110123)
Rajdan.M.K.(2007),plant tissue culture , somaclonal
variation .(125-135)
Collen.H.A. and Edwards.S(2009),plant cell culture
,selection of somaclonal variants,bioes scientific publisher
(91-101)
www.amazon.co.uk/Somaclonal-Variation-CropImprovement-Biotechnology
http://www.studentsguide.in/plant-biotechnologygenomics/tissue-culture-micropropagation-somaclonalvariation