Somaclonal variation

Somaclonal variation

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  Genetic variations inplants that have been produced by plant tissue culture and can be detected as genetic or phenotypic traits.
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  Variations in numberand structure of chromosomes are commonly observed. Regenerated plants with altered chromosomal changes often show changes in leaf shape and colour, growth rate and habit, and sexual fertility. It is generally heritable mutations and persist in plant population even after plantation into the field. Basic Features of Somaclonal Variations
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  Mechanism of SomaclonalVariations 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
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  Callus Tissue Organogenesis Regenerated plantsHardening and Selfing Somaclonal Variants Steps involved in induction and selection of Somaclonal Variations
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  Causes of Somaclonal Variations Physiological Cause GeneticCause Biochemical Cause
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  Exposure of cultureto plant growth regulators. Culture conditions Physiological Cause
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  1. Change inchromosome number aneuploidy – gain or loss of 1 or more chromosomes polyploidy – gain or loss of an entire genome translocation – arms of chromosomes switched inversion – piece of chromosome inverted 2. Change in chromosome structure Deletion Inversion Duplication Translocation Genetic Cause
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  3. Gene Mutation Transition Transversion Insertion Deletion 4.Plasmagene Mutation 5. Transposable element activation Genetic Cause
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  6. DNA sequence Change in DNA  Detection of altered fragment size by using Restriction enzyme  Change in Protein  Loss or gain in protein band  Alteration in level of specific protein  Methylation of DNA  Methylation inactivates transcription process. Genetic Cause
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  Lack of photosyntheticability due to alteration in carbon metabolism Biosynthesis of starch via carotenoid pathway Nitrogen metabolism Antibiotic resistance. Biochemical Cause
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  1. Analysis ofmorphological 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
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  4. Variant detectionby 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
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  7. Detection ofenvironmental 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) Detection and Isolation of Somaclonal Variants
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  Help in cropimprovement 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 Advantages of Somaclonal Variations
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  Improvement of existingclonal cultures sugarcane – selections for higher yield & disease resistance potatoes – yield & disease resistance improved geraniums (esp. scented varieties) woody ornamentals (e.g., Paulownia – selection for leaf variegation Applications to crop improvement
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  A serious disadvantageoccurs in operations which require clonal uniformity, as in the horticulture and forestry industries where tissue culture is employed for rapid propagation of elite genotypes Sometime leads to undesirable results Selected variants are random and genetically unstable Require extensive and extended field trials Not suitable for complex agronomic traits like yield, quality etc. May develop variants with pleiotropic effects which are not true. Disadvantages of Somaclonal Variations