Somatic Somatic

EmbryogenEmbryogen

esisesisDr. Amit Kumar Dutta,

Ph.D

Somatic

Embryogenesis

Introduction

Formation of embryo is known as “Embryogenesis”

Two Type of Embryogenesis occurs in Plants

Zygotic Embryogenesis

Somatic Embryogenesis

Zygotic Embryogenesis

It is the process in which female gamete fuses with male gamete and form an unicellular zygote, which gives rise to a multicellular embryo.

In Plants another type of embryogenesis is also present in which embryo is formed

from somatic cells.

Somatic Embryogenesis mostly occurs indirectly via an intervening callus phase or directly from initial explant.

Invitro Somatic Embryogenesis is an important prerequisite for the use of biotechnological tools for genetic improvement, as well as for mass propagation.

Somatic Embryogenesis

The developmental pathway of numerous well-

organized, embryoids resembling to zygotic embryo

from the embryogenic potential somatic plant cells of

the callus tissue or cell suspension culture is known

as somatic embryogenesis.

 

Embryogenic Potential

The capacity of somatic plant cells to produce embryoids is known as embryogenic potential.

Embryoid

Embryoid is a small, well organized structure comparable to the sexual embryo, which is produced in tissue culture of dividing embryogenic potential somatic cells.

HISTORY

J. Reinert (1958 -59) - Reported his first observation of in vitro somatic embryogenesis in Daucus carota (carrot).

N. S. Rangaswami (1961) – Studied in detail the somatic embryogenesis in Citrus sp.

PRINCIPLE

Somatic Embryogenesis

Direct embryogenesis Indirect embryogenesis Cells of explant undergo direct embryogenesis from proembryogenic determine cells in absence of callus proliferation.

Cells of explant first undergo callus

proliferation and embryoids

develops within the callus tissue

from induced embryogenic cells.

Indirect somatic embryogenesis under in vitro condition two types of media required-a) Initiation media containing auxin b) Second media in which auxin is totally absence or

present in very concentration, for development of embryoid.

The embryogenic cells are characterized by dense cytoplasmic contents, large starch grains, and a relatively large nucleus with a darkly stained nucleolus.

In the development of embryoid, each developing embryoid passes through three sequential stages— Globular stage Heart shape stage

Torpedo stage

Fig: The morphological stages of somatic embryo development

PROTOCOL Explants placed on a solid MS media. 0.1mg/L 2,4-D After 4 weeks of callus growth, cell suspension

culture is to be initiated by transferring 0.2mg of callus into 250ml liquid media.

Placed on shaker with 125-160 rpm at 25 °C

Cells are transferred to 2,4-D free MS media

0.1-1µM ABA

After 3-4 weeks, the culture would contain numerous

embryoids in different stages of development.

Embryoids are placed on solid MS medium (2,4-D

free) for plantlet development.

Plantlet are transferred to Jiffy pot for subsequent

development

Fig: Diagramatic representation of somatic embryogenesis of carrot

FACTORS AFFECTING

(B) Reduced nitrogen In carrot culture ,the addition of reduced

nitrogen (ammonium chloride) produced more numbers of embryoids.

Glutamic acid , glutamin, urea and alanine are found to partially replace ammonium chloride .

(C) oxygen concentration Amount of dissolved oxygen in the medium

should be below the critical level of 1.5mg/lit to allow embryo development.

(D)Charcoal

It facilitated embryogenesis in several culture.

absorb a wide variety of inhibiory substance as well as hormones.

SIGNIFICANCE1) Production of artificial seed

FIG: ARTIFICIAL SEED

Artificial seeds are the living seed like structure which are made experimentally by a technique where somatic

embryoids derived from plant tissue culture are encapsulate by a hydrogel and such encapsulated embryoids behave

like true seeds if grown in soil and can be used as substitute of natural seeds.

The embryos,coated with sodium alginate solution,are dipped in calcium chloride solution to produce small gel

beads,each containing an encapsulated embryo.

This artificial seeds can be maintained in a viable state in liquide nitrogen till they are planted.

Fig: Diagram showing the production of Artificial seeds

2) Somatic embryogenesis leads to production of adventitious embryo which develops directly into complete plantlet.

3) Somatic embryo arise from single cell so it is special significance in mutagenic studies.

4)Plant derived from this techniques may be free of viral and other pathogenic infection.

DISADVANTAGES High probability of mutation arising.

This method is usually rather difficult.

Induction of embryogenesis is often very difficult or impossible with many plant sps.

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