SOMACLONAL VARIATION AND ITS SIGNIFICANCE.pptx

Somaclonal variations-introduction, history, source material for somaclonal variation, selection of somaclonal variation, kinds of variation, types of variation, causes of somaclonal variation, isolation of somaclonal variation, factors responsible for variation, application for somaclonal variation. Disadvantage.

1. SOMACLONAL VARIATION AND ITS SIGNIFICANCE

2. CONTENTS Introduction Brief History Source and selection of somaclonal variation Kinds and types of variation Causes Application Advantages and disadvantages Conclusion Reference

3. INTRODUCTION “Soma” mean Vegetative and “clones” means the Identical copy. Genetic variation in plants arising from undifferentiated cells during tissue culture is called somaclonal variation. The name somaclonal variation was coined by Larkin and Scowcroft in 1981. Tissue cultured plants which have genetic characters not seen in parent plants are known as somaclonal variants. Somaclonal variations is not restricted to, but is particularly common in, plants regenerated from callus. somaclonal variants raised from Calli are called Calli clones, those raised from cells are called cell clones and those raised from protoplast are called protoclones . If genetic variability is established in plants by culturing gametic cells, then it is said to be gametoclonal variation.

4. BRIEF HISTORY S.K. Pillai (1969) observed variability in plant populations raised from tissue culture of geranium. M. Krishnamurthi (1974) isolated disease resistant variants of sugarcane from tissue culture. J.F. Shepard, D. Bidney and E. Shahin (1980) isolated potato variant plant lines. D. A. Evans and W.R. Sharp (1983) analyzed somaclonal variations in a large number of plants regenerated from leaf explants of tomato.

5. SOURCE MATERIAL FOR SOMACLONAL VARIATION Somaclonal variation can be created both in monocots and dicots. The regeneration source can be callus, protoplasts, adventitious shoots, anthers,pollens or individual cells. It is known to occur both in asexually and sexually reproducing plants.

6. SELECTION OF SOMACLONAL VARIATIONS Without Selection Pressure In this method, no selection pressure is applied to the tissue culture. No toxin or inhibitory substance is added to the culture. The cells or tissues are cultured in vitro into calli and plantlets are regenerated from the calli . With Selection Pressure In this method, first a selection pressure is applied to cell or tissue culture and then variant cell lines are screened from the culture to regenerate plantlets from them .

7. KINDS OF VARIATIONS Cytogenetic Deletion which is found partial chromosomal loss after breakage. Inversion and interchange that show intrachromosomal breakage and reunion. Genetic The variations are associated with point mutation where base sequence alteration was found. Epigenetic The epigenetic variation is found in a process where alteration in DNA methylation takes place and this variation is due to cytokinin habituation

8. TYPES OF VARIATIONS Late replicating heterochromatin In replication process, heterochromatic regions of the chromosome replicate later than euchromatic segments. This character can be vulnerable to fluctuations in the mitotic cell cycle. In late replication of heterochromatin certain “shocks” to the genome caused the activation of transposable elements. This activation is the outcome of tissue culture.

9. Chromosomal aberration The changes in chromosome numbers in regenerated plants have been the major clue for complete understanding of somaclonal variation. Cytoplasmic gene changes In somaclonal variants the chloroplast or mitochondrial genes exist in high frequency.

10. CAUSES OF S.C VARIATIONS The causes may be Genetic Physiological Biochemical

11. GENETIC Pre-existing variations in the somatic cells of explant that are caused by mutations and other DNA changes. Typical genetic alterations are Changes in chromosome numbers (polyploidy and aneuploidy) Change in chromosome structure (translocations, deletions and duplications) DNA sequence (base mutations) Occur at high frequency

12. PHYSIOLOGICAL Exposure of culture to plant growth regulators Culture conditions BIOCHEMICAL Lack of photosynthetic ability due to alteration in carbon metabolism Antibiotic resistance

13. ISOLATION OF S.C VARIATION Phenotypic characters This is a long term technique for isolation of somaclonal variations. Cytological technique As the cells of the variants show increase in chromosome number and morphology, the traditional squash technique was employed.

14. Biochemical technique Assay of biochemical products of regenerated plant extracts plant parts have an important parameter for detection of the somoclonal variations . Stress tolerance The capacity of certain regenerated plants is to tolerate different environmental stresses like high temperature, mineral toxicity, salt, water logging Pathogenic technique The pathogen is selected for isolation of the somaclonal variations.

15. ISOLATION OF S.C VARIANTS Without in vitro selection Within vitro selection

16. Without in Vitro Selection: An explant (leaf, stem, root etc.) is cultured on a suitable medium, supplemented with growth regulators. The unorganized callus and cells do not contain any selective agent (toxic or inhibitory substance). These cultures are normally sub-cultured, and transferred to shoot induction medium for regeneration of plants. The so produced plants are grown in pots, transferred to field, and analyzed for somaclonal variants Somaclonal variants of several crops have been successfully obtained by this approach e.g., sugarcane, potato, tomato, cereals etc.

17. Limitations of without in vitro selection approach There is no directed and specific approach for the isolation of somaclones without in vitro selection. Consequently, the appearance of a desired trait is purely by chance. Further, this procedure is time consuming and requires screening of many plants

18. With in Vitro Selection Isolation of somaclones with in vitro selection method basically involves handling of plant cells in cultures (protoplast, callus) like microorganisms and selection of biochemical mutants. The cell lines are screened from plant cultures for their ability to survive in the presence of a toxic/inhibitory substance in the medium or under conditions of environmental stress. The differentiated callus, obtained from an explant is exposed in the medium to inhibitors like toxins, antibiotics, amino acid analogs. Selection cycles are carried out to isolate the tolerant callus cultures and these calli are regenerated into plants. The plants so obtained are in vitro screened against the toxin (or pathogen or any other inhibitor).

19. The plants resistant to the toxin are selected and grown further by vegetative propagation or self-pollination. The subsequent generations are analyzed for disease resistant plants against the specific pathogenic organism. Besides the disease resistant plants, plants with herbicide resistance and antibiotic resistance have also been developed with in vitro selection approach.

20. Advantages of with in vitro selection approach: The major advantage of with in vitro selection method is the specific selection of the desired trait rather than a general variation found at the plant level. This procedure is less time consuming when compared to without in vitro selection approach.

21. FACTORS RESPONSIBLE FOR VARIATION Ploidy The chromosomal changes or the ploidy influences the frequency and nature of the variation. In general, polyploids exhibit greater somaclonal variation than diploids Procedure in tissue culture Protoplast regeneration is associated with more somaclonal variation than regeneration from cell explants. this clearly indicates the possibility of the role of tissue culture procedure in somaclonal variation

22. Media composition The variation in chromosome number can be influenced by the addition of different types of growth regulators in the medium. Hence, the media composition is one of the factor its controlling the somaclonal variation in tissue culture Genotype The variations observed in different plants are not of same frequency i.e. in begonia haemalis there is 43% of regenerates are variant in one variety while only 7% are variant in another variety. From the evidences it can be assumed that there is a genotypic component to instability in culture

23. Tissue source The different frequencies of somaclonal variations are found in different types of tissues. Thus the tissue source is the one of the factors in somaclonal variations. In chrysanthemum, difference in somaclonal variations were found between petal and pedicel derived plants. Differences in stability between different pea tissues have been reported as the stem callus being more stable than root callus .

24. APPLICATIONS OF S.C VARIATIONS Production of agronomically useful plants Resistance to disease Resistance to abiotic stresses Resistance to herbicides Improved seed quality and geraniums(esp. scented varieties) Woody ornamentals

25. ADVANTAGES OF S.C VARIATIONS Help in crop improvement Creation of additional genetic variations 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

26. DISADVANTAGES OF S.C VARIATIONS A serious disadvantage occurs 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 fields trials Not suitable for complex agronomic traits like yield, quality etc. May develop variants with pleiotropic effects which are not true.

27. CONCLUSION Somaclonal variation is a valuable tool in plant breeding, wherein variation in tissue culture regenerated plants from somatic cells can be used in the development of crops with novel traits.

28. REFERENCE Shekhawat.M.S .,(2010).Plant Cell and Tissue Culture. Saras publication,Kanyakumari , pp- 145-162 https://www.slideshare.net/SharmasClasses/somaclonal-variation-and-its-crop-improvement-248395910 https://www.slideshare.net/mobile/RIZWANABBAS3/plant-regeneration-and-somaclonal-variations https://www.slideshare.net/RakeshKumar440/somaclonal-variation-26537134

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