Somatic embryogenesis, in plant tissue culture

INTRODUCTION
HISTORY
SOMATIC EMBRYOGENESIS DEVELOPMENT
- INDUCTION
- DEVELOPMENT
- MATURATION
SYNTHETIC SEED
FACTORS AFFECTING SOMATIC EMBRYOGENESIS
APPLICATIONS
REFERENCE

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 HISTORY SOMATIC EMBRYOGENESIS DEVELOPMENT - INDUCTION - DEVELOPMENT - MATURATION SYNTHETIC SEED FACTORS AFFECTING SOMATIC EMBRYOGENESIS APPLICATIONS REFERENCE

3. introduction The act of fertilization trigger the egg cell (called zygote after fertilization) to divide and develop into an embryo. and the process of embryo development is known as embryogenesis.

4. SOMATIC EMBRYOGENESIS In plant tissue culture, the process of embryo initiation and development from vegetative cell or non - gametic cell is known as somatic embryogenesis. ZYGOTIC EMBRYOGENESIS It is the process in which female gamete fuse with the male gamete and form embryo is called zygotic embryogenesis .

5. HISTORY The first observation of somatic embryogenesis were made in Daucus Carota (carrot) by Steward et al. 1958. Ever since, this species have been widely used to investigate various aspects of in vitro somatic embryogenesis. Other plants in which this phenomenon has been studied in some detail are Citrus sp. by Rangaswamy, 1961 and in Coffea sp. Monaco et al. 1977.

6. Somatic embryogenesis development INDIRECTLY - Somatic embryogenesis mostly occurs indirectly through an intervening callus. DIRECTLY- In direct somatic embryogenesis the embryo directly form a cell or small group of cell without a production of an intervening callus. Direct somatic embryogenesis is generally rare compared with indirect somatic embryogenesis.

7. INDUCTION An auxin 2,4-D is generally necessary to induce embryogenesis in plant such as carrot. However the requirement of exogenous auxin for the induction of somatic embryogenesis depends on the nature of the explant used. Initially exposure of 2,4-D for 2-7 days is necessary to acquire competence to form embryo. An important phenomenon associated with the induction of somatic embryogenesis is change of cellular polarity.

8. PGR employed for the induction of embryogenesis by altering the cell polarity and promotion of asymmetric cell division. Due to asymmetric division only small daughter cell develop into embryo. Since the root pole of the somatic embryogenesis is always oriented toward the large cell.

9. DEVELOPMENT To start embryonic development, suspension culture is to expose, explants to a high conc. of 2,4-D. After initiation of cell division a period of cell proliferation and then embryonic cell transfer into auxin free medium. This cell are in the form of cluster of cytoplasmic cell. (Pre embryonic cell mass). SUSPENSION CULTURE CONTAIN SINGLE CELL OF TWO TYPE- Small and Cytoplasmic cell Large and vacculated cell

10. Small and cytoplasmic cell - small PEM cell (400-800) μ m3 . - connected with the plasmodesmata, many starch grains (5-25) per cell and small vacuoles. - high density of ribosome, many endoplasmic reticulum and high hydrogenase activity B. Large and vacculated cell - large size (1000-3000) μ m3. - few plasmodesmata, few starch (1-2)per cell. - bigger vaccule, less ribosome density, few endoplasmic reticulum and low hydrogenase activity.

11. Auxin cause cell elongation and then it is removed from the medium. Embryonic culture transfer to auxin free medium and disruption stop. And globules developed into globular embryo. Globular embryo then continues further development and form embryo. Because after embryogenic induction, embryo start synthesis their own auxin.

12. Maturation of somatic embryo The quality of somatic embryogenesis with regards to their conversion into plants, has been very poor 3-5%. This is because the apparently normal looking somatic embryo are actually incomplete in their development. Somatic embryo normally do not go through the final phase of embryogenesis called ‘embryo maturation’. Which is characterised by the accumulation of embryo specific reserve food material and protein which impart desiccation tolerance to the embryo size of the embryo do not increase during this phase.

13. ABA is known to trigger the expression of genes which normally express during the drying-down phase of seed . ABA promote maturation of somatic embryo is also known as stress hormone.

14. SYNTHETIC SEED Naked embryos are converted into synthetic seed by encapsulating in a protective covering. CURRENTLY TWO TYPE OF SYNTHETIC SEEDS ARE BEING DEVELOPED Desiccated synthetic seed- First synthetic seed produce by Kitto and Janick 1982 . Involve encapsulation of multiple somatic embryos. They have selected polyoxyethylene which is readily soluble in water and dries to form a thin film.

15. It does not support growth of microorganism and it is non toxic to the embryo. B . Hydrated synthetic seed In 1984 Redenbaugh et al. developed a technique for encapsulation of single hydrated somatic embryo of alfalfa. Ca-alginate encapsulation widely used for production hydrated synthetic seed. SE are mixed with 2% w/v solution of Na-alginate into a 100 mM solution of Ca(NO3)2. Ion exchange reaction occur and sodium ion replaced by calcium ion forming Ca-alginate. Gelling complete within 30 min.

16. FACTOR AFFECTING SOMATIC EMBRYOGENESIS EXPLANTS – Immature embryo have proved to be the best explant to raise embryonic culture. GENOTYPE – 500 varieties of rice can be studied by Kamiya et al. 1988, 19 showed 65-100% embryogenesis, 41 showed 35-64%embryogenesis and remaining 440 were less efficient. - Genotype variation are due to endogenous level of hormones.

17. GROWTH REGULATORS – (AUXIN) a synthetic auxin for induction of somatic embryogenesis. - 2,4-D most commonly used auxin. (CYTOKININ) - it inhibit the embryonic potential. NITROGEN SOURCE – addition of small amount of nitrogen in the form of NH4Cl in the presence of KNO3 allow embryo development. POLYAMINE – increase in the level of endogenous polyamine will induce the induction of somatic embryogenesis.

18. application Synthetic seed production. Genetic engineering. Quarantine and international exchange. Germplasm conservation.

19. REFERENCE PLANT TISSUE CULTURE theory and practice, a revised Edition by- S.S.Bhojwani M.K. Razdan