Somatic Embryogenesis

Somatic Embryogenesis:

• Definition: The process of producing embryos from a single somatic (non-reproductive) cell, which eventually develops into a complete plant.

• Simplified Steps:
  A single cell → Callus → Embryo → Plant.

Technique

1. Plant Material Selection

• Choose a suitable explant (callus, root, leaf petiole, or any part of the plant).

• The technique was first demonstrated in Daucus carota (carrot).

2. Sterilization of Explant

• Sterilize the explant in:

• 70% alcohol, followed by

• 0.1% HgCl₂ (Mercuric chloride).

3. Initiation of Callus Formation

• Place the sterilized explant in a liquid medium containing:

• 2,4-D (2,4-Dichlorophenoxyacetic acid) (a synthetic auxin).

• 2% sucrose as an energy source.

• This medium promotes callus growth (mass of undifferentiated cells).

4. Induction of Somatic Embryogenesis

• Transfer the callus to a medium containing:

• Abscisic acid (ABA), which promotes embryogenesis.

• A reduced level of auxin, as high auxin concentrations inhibit embryo formation.

• In this medium, the callus differentiates into somatic embryos.

5. Development of Plantlets

• The embryos are transferred to a nutrient-rich medium such as MS medium (Murashige and Skoog medium).

• This medium supports the growth of embryos into plantlets.

Factors affecting somatic embryogenesis:

1. Auxin

• Role in Callus Formation:

• Auxins promote callus production during the initial stages of somatic embryogenesis.

• Inhibition of Embryo Formation:

• Auxin, when combined with cytokinin in later stages, may inhibit embryo formation.

• Alternative Auxins:

• NAA (Naphthaleneacetic acid) or IBA (Indole-3-butyric acid) can substitute other auxins.

• 2,4-D (2,4-Dichlorophenoxyacetic acid):

• A synthetic auxin effective in inducing callus formation.

2. Coconut Milk

• Contains natural plant growth regulators.

• Used to induce somatic embryogenesis effectively.

3. Nitrogen Sources (Ammonium Salts)

• Ammonium salts serve as nitrogen sources in the medium.

• Potassium nitrate (KNO₃) can also be used as an alternative nitrogen source.

4. Organic Acids

• Glutamic acid and aspartic acid can replace KNO₃ as nitrogen sources.

5. Activated Charcoal

• Added to the medium to absorb inhibitory components that may hinder the formation of embryoids.

• Helps create a more favourable environment for embryogenesis.

Applications of Somatic Embryogenesis

1. Plant Propagation

• Provides a reliable method for large-scale propagation of plants.

• Useful for producing uniform and disease-free plants.

2. Cloning of Zygotic Embryos

• Zygotic embryos, such as those from rice, can be cloned and propagated efficiently.

3. Production of Secondary Metabolites

• Enables the production of secondary metabolites (e.g., alkaloids, flavonoids) in higher amounts.

• These metabolites are important for pharmaceuticals, cosmetics, and agriculture.

4. Synthetic Seed Production

• Somatic embryos can be encapsulated in calcium alginate beads to produce synthetic seeds.

• These seeds can germinate into plantlets under favourable conditions.

5. Protein and Metabolite Extraction

• Plant tissue culture via somatic embryogenesis is used to obtain:

• Proteins with medicinal or industrial applications.

• Valuable secondary metabolites for research and commercial use.

Types

1. Somatic embryogenesis could be induced either directly from the explant tissue bypassing the callus formation stage or via the formation of callus from the explant. 

2. Direct somatic Embryogenesis
• It can be achieved directly from the explant through pre embryogenic determined cells. Such cells are found in the embryonic tissue of nucellus etc. 
3. Indirect somatic Embryogenesis
• It is achieved through the establishment of callus from which embryos are developed. Here the embryo developed from an induced embryogenic determined cell.