Somatic embryogenesis, in plant tissue culture 2

Introduction
Types of somatic embryogenesis
Developmental stages
Factors affecting somatic embryogenesis
Importance
Conclusions
References
The process of regeneration of embryos from somatic cells, tissue or organs is regarded as somatic or asexual embryogenesis.
opposite of zygotic or sexual embryogenesis.
Embryo-like structures which can develop into whole plants in a way that is similar to zygotic embryos are formed from somatic cells.

1. Plant Tissue Culture “ Somatic Embryogenesis” By KAUSHAL KUMAR SAHU Assistant Professor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )

2. Contents Introduction Types of somatic embryogenesis Developmental stages Factors affecting somatic embryogenesis Importance Conclusions References

3. Introduction The process of regeneration of embryos from somatic cells, tissue or organs is regarded as somatic or asexual embryogenesis. opposite of zygotic or sexual embryogenesis. Embryo-like structures which can develop into whole plants in a way that is similar to zygotic embryos are formed from somatic cells.

4. History First recognized by Steward et al . (1958) and Reinert (1958, 1959) in culture of Daucus carota . In this four different stages are there:- Initiation stage Proliferation stage Maturation stage Germination

5. Various terms for non-zygotic embryos Adventious embryos – somatic embryos arising directly from other organs or embryos . Parthenogenetic embryos – formed by the unfertilized egg. Androgenetic embryos – formed by the male gametophyte.

6. Types Direct somatic embryogenesis Indirect somatic embryogenesis Direct embryogenesis Somatic embryos develop directly on excised plant without undergoing callus formation, it referred to as somatic embryogenesis. Direct somatic embryogenesis is generally rare. The characteristic features of direct embryogenesis is avoiding the possibility of introducing somaclonal variation in the propagated plants.

7. Indirect somatic embryogenesis In indirect embryogenesis, the cells from explant are made to proliferate and form callus, from which cell suspension cultures can be raised. Certain cells referred to as induced embryogenic determined cells from the cell suspension can form somatic embryos. Embryogenesis is made possible by the presence of growth regulators & under suitable environment condition. Explant → Callus Embryogenic → Maturation → Germination

8. Indirect somatic embryogenesis in carrot ( dauctus carota ) Indirect Somatic embryogenesis

9. Induction - Auxins required for induction. Pro embryogenic masses form. 2,4-D most used. Development Auxin must be removed for embryo development. Continued use of auxin inhibits embryogenesis. Maturation Require complete maturation with apical meristem , radicle , and cotyledons. Germination May only obtain 3-5% germination. Sucrose (10%), mannitol (4%) may be required.

10. Development patterns Torpedo embryo

11. Somatic embryogenesis is influenced by several factors Explant Genotype Growth regulators Nitrogen source

12. Explant Immature zygotic embryos best explant for recalcitrant species. Petiole section from youngest fully expanded leaves establishment of embryonic cultures of Alfalfa. Development of embryos from somatic cells (epidermis, parenchymatous cells of petioles, secondary root phloem).

13. Genotype Explant genotype has a marked influence on SE regeneration. Strong genotypic effects have been shown in many species. e.g. alfalfa, wheat, maize, rice etc. In case of wheat, chromosome 4B is important in regeneration.

14. Growth regulators Embryo initiation - auxin in the medium is generally essential. 2, 4-D 0.5 mg per l. - induces differentiation of localized groups of meristematic cells called embryogenic clumps. Embryo development - auxin free media. CYTOKININS Effective concentration range for kinetin is 0.5-5.0 micro M. Also important in somatic embryo maturation and cotyledon development. Required for growth of embryos to plantlets.

15. Nitrogen source The form of nitrogen has a marked effect on somatic embryogenesis. In carrot NH+ 4 has a promotive effect on SE regeneration. SE development medium containing NO- 3 as the sole nitrogen source. Addition of reduced nitrogen in the medium helps in both embryo initiation and maturation. Other suppliments L-glutamine plays an important role among all the amino acids. Another factor is the chelated form of iron in the media. In absence of Fe, embryo development fails to pass from the globular to the heart shaped stage.

16. Presence of auxin in the medium is generally essential for embryo initiation. Tissues maintained continuously in an auxin free medium do not form embyos . When transferred to low auxin medium embryogenic clumps develop in to mature embryos. Light generally promotes embryogenesis. High temp. usually favorable for somatic embryogenesis. 16

17. Importance of somatic embryogenesis Raising somaclonal variants Synthesis of artificial seeds Synthesis of metabolites Clonal propagation Genetic transformation Conservation of genetic resources

18. Disadvantage High probability of mutations. The method is usually rather difficult. Losing regenerative capacity become greater with repeated subculture. Induction of embryogenesis is very difficult with many plant species. A deep dormancy often occurs with somatic embryogenesis.

19. References Introduction to plant tissue culture By M. K. Razdan 1 st edition Plant biotechnology By H. S. Chawla internet www.plant-molecularbiotechnology.com www.wikipedia.com/somaticembryos.html