Somaclonal Variation.....................pptx

Somaclonal Variation.....................pptx

1. Somaclonal Variation

2. SOMACLONAL VARIATION

3. INTRODUCTION “ Somaclonal variation” term was coined by Larkin and Scowcroft (1981) According to Larkin and Scowcroft (1981), “Somaclonal variation is the genetic variability which is regenerated during tissue culture” or plant variants derived from any form of cell or tissue cultures . Genetic variations in plants that have been produced by plant tissue culture and can be detected as phenotypic traits.

4. The phenomenon of high variability in individuals from plant cell cultures or adventitious shoots is called Somaclonal variation. Somaclonal variation is the variation seen in plants that have been produced by plant tissue culture. This may lead to desirable characteristics like increased pest resistance etc. This work performed to achieve some of beneficial properties of plants like disease resistance, fruit quality, stress resistance, nutritional quality, yield improvement etc.

5. Somaclonal variation – Occur as a result of genetic heterogeneity in plant tissue culture (inside the plant or explant) that changes can passes from one to another generations. This may be due to: Expression of chromosomal mosaicism or genetic disorders Spontaneous mutations due to culture conditions or Physiological causes. Variation in karyotype, isozyme characteristics and morphology (number and structure of chromosome) in somaclones may be observed. Regenerated plant with altered chromosomal changes often show changes in leaf shapes, color, growth rate and habit.

6. MECHANISMS OF SOMACLONAL VARIATION KARYOTYPIC CHANGE Several plants alter their chromosome number in culture. Gross karyotypic alterations have been observed in tissue cultured plant cells. Certain karyotypic changes such as aneuploidy or polyploidy is responsible for the generations of clones. CHROMOSOMAL REARRANGEMENT: It has been elusive that several cryptic chromosomal rearrangements in tissue culture conditions are responsible for somaclonal variation. Tissue culture derived from Barley plants show breakage, reunion and translocations in their chromosomes.

7. The same kind of irregularities such as breaks, acentric and centric fragments, ring chromosomes and micronuclei was noticed in the mixoploidy garlic plants. This cryptic changes associated with chromosomal rearrangements not only result in the loss of genes and their function but also the expression of genes.

8. NUCLEOTIDE POOL IMBALANCE Imbalance is the nucleotide reserve may have serious implications on nuclear DNA as well as organellar DNA mutation. In addition, wide array of anomalies like chromosomal aberrations, aneuploidy and sister chromatid exchange result high degree of genetic variations. Plant tissue and cell culture provides ideal conditions for the induction of imbalance nucleotide reserve pool during serially transfer from depleted to fresh medium. This means that media components gets completely depleted towards the end of subculture. As a consequence, metabolic process fluctuates and may be responsible for somaclonal variation.

9. SOMATIC GENE REARRANGEMENT Somatic gene arrangements have been recorded in animal system, in which mouse embryonic cells to plasma cells involves chromosomal gene arrangements. It would also be possible that somatic gene arrangements will also occur in higher plants. If so then the regenerated plants form somatic cells by culture encourages somatic gene rearrangements seen in the new germline.

10. TYPES OF SOMACLONAL VARIATION

11. CAUSES OF SOMACLONAL VARIATION PHYSIOLOGICAL CAUSE

12. GENETIC CAUSE

13. BIOCHEMICAL CAUSE

14. Isolation of Somaclonal Variation 1) Generation of Somaclonal variation without in-vitro Selection .

15. WITHOUT IN-VITRO TECHNIQUE Unorganized callus and cells, grown in cultures for various periods on a medium that contain no selective agents, are induced to differentiate whole plants. An explant is cultivated on a suitable medium, supplemented with growth regulators. The unorganized callus and cells do not contain any selective agent. 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 varieties. LIMITATIONS Time consuming procedure Require screening in many plants. Appearance of desired traits are purely by chance.

16. 2) Generation of Somaclonal Variation with in-vitro selection.

17. WITH IN-VITRO TECHNIQUE Cell lines are analyzed from plant cultures for their capability to survive in the presence of a toxic substance in medium or under environmental stress conditions 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. The plants resistant to the toxin are selected and grown further by vegetative propagation . The subsequent generations are analyzed for disease resistant plants against the specific pathogenic organism. Advantages of With in-vitro Selection Specific approach for isolation of desired trait Less time consuming procedure as compared without in-vitro approach

18. Applications of Somaclonal 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 Examples: Sugarcane: Selections for higher yield and disease resistance. Potatoes: Yield and disease resistance Paulownia: selection for leaf variegation.

19. Production of agronomically useful plants (Novel Variants) As a result of somaclonal variations, several novel variants of existing crops have been developed e.g. An improved scented Geranium variety named ‘ Velvet Rose’, Pure thorn-less blackberries etc.

20. 2) Production of Abiotic stress resistance variety: Somaclonal variation has resulted in several interesting biochemical mutants, which are being successfully used in plant metabolic pathway studies, i.e. amino acid and secondary metabolic pathways. Investigations have shown that level of free amino acids, especially proline, increases during cold hardening. In vitro selection has also been used to obtain plants with increased acid soil, salt, aluminium and herbicide resistance.

21. COLD TOLERANCE Lazar et.al., 1988 developed somaclonal variants for freezing tolerance in Norstar winter wheat. A significant positive correlation between proline level and frost tolerance has been found in a broad spectrum of genotypes. In vitro selection and regeneration of hydroxyproline resistant lines of winter wheat with increased frost tolerance and increased proline content has been reported in 1997. The results showed strong correlation of increased frost tolerance with increased proline content

22. SALT TOLERANCE Plant tissue culture techniques have been successfully used to obtain salt tolerant cell lines or variants in several plant species, tobacco, rice, maize, Brassica, Solanum nigrum, Sorghum etc. Mandal et.al., 1999 developed a salt tolerant somaclone BTS24 from indigenous rice cultivar pokkali.

23. ALUMINIUM TOLERANCE In recent years, considerable research has been focused on the understanding of physiological, genetic and molecular processes that lead to aluminium tolerance. Aluminium toxicity during in-vitro selection in rice by making several modifications in the media.( Low pH, low phosphate and calcium concentrations.) DROUGHT TOLERANCE Wang et al., 1993 used in vitro selection technique for generation of somaclonal variants for Russian wheat aphid ( Diuraphis noxia) in wheat. Variant of Bermuda grass ( Cynodon dactylon) called Brazos R-3 with increased resistance to fail armyworm.

24. 3) Disease Resistance Development of disease resistance in many crops: Rice, Wheat, Maize, Sugarcane, Tobacco, Apple, Tomato etc.. Selected crops somaclonal variants, with increasing disease resistance developed, without in-vitro selection are respectively. Resistance first reported in Sugarcane for Eye spot disease ( Helminthosporium sacchari), Downy mildew ( Sclerospora sacchari) and Fiji virus disease by regenerating plants from the callus of susceptible clones and screening the somaclones.

25. 4) HERBICIDE RESISTANCE Through in-vitro selection several cell lines resistant to herbicides have been isolated and few have been regenerated into complete plants. Tobacco resistant to Glyphosate, Sulfonylurea and Picloram Carrot resistant to Glyphosate Lotus resistant to 2,4 dichlorophenoxyacetic acid(2,4D)

26. 5) Improved Seed Quality Recently, a variety Bio L 212 of Lathyrus sativa has been identified for cultivation in central India. This has been developed through somaclonal variation and has low ODAP (𝛃-N-oxalyl-2-𝛂, 𝜷 diamino propionic acid), a neurotoxin, indication the potential of somaclonal variation for the development of varieties with improved seed quality

27. Advantages and Disadvantages of Somaclonal variation

28. Reference:- Evans D.A., Sharp W.R., Medina H. “Somaclonal and Gametoclonal Variation” Am J Botany (1984) 759-774 Satyanarayana U. “Somaclonal Variation, Biotechnology, 9th Ed,(2015) 855: 546-549 Larkin P.J., Margaret N. “Sources and Frequency of Somaclonal variation” HortiSci 29.11 ( 1994) 1232-1237