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Embryogenesis
- As we know that Genesis Mean Formation and plant embryo are the area of seed where root stem and leaves start their earliest transformation. So Definition of embryogenesis:
- Embryogenesis is the formation or production of the embryo.
Somatic Embryogenesis
- Somatic cells (cells from any part of the plant except the reproductive cells.)
- The bipolar embryo which is produced from somatic tissues without involving a sexual process is known as a Somatic embryo.
Somatic embryogenesis is the formation of embryos from somatic cells under in vitro conditions.
or
Somatic embryogenesis is a process in plant tissue culture where somatic cells are induced to undergo embryogenesis, leading to the development of somatic embryos.
Unlike zygotic embryogenesis, which occurs through the fusion of male and female gametes during sexual reproduction, somatic embryogenesis bypasses the need for seeds or fertilization.
Types of Somatic Embryogenesis
- Types and routes of somatic embryogenesis are the same.
- Sharp et al. (1980) give two routes by which somatic embryogenesis can be carried out.
1. Direct embryogenesis :
When the embryo directly obtain from the explant and the callus formation is absent, is called Direct embryo genesis
2. Indirect embryogenesis / Via callus formation :
Indirect embryogenesis involves an intermediary stage(callus formation) from which embryos are developed.
Process of somatic embryogenesis
1. Initiation:
Somatic cells are isolated from a plant and cultured in a suitable nutrient medium, often supplemented with plant growth regulators like auxins and cytokinin.
*stage 2, 2. a occur in only indirect embryogenesis.
2. Dedifferentiation:
Under the influence of specific growth regulators, the somatic cells lose their specialized characteristics and revert to a less-differentiated state known as a callus.
2. a Shape change:
Before becoming a somatic embryo the callus needs to adopt the globular stage and then convert into a heart shape which is ultimately converted into a torpedo shape.
3. Embryogenic callus formation:
Within the callus mass, certain cells become reprogrammed and acquire embryogenic potential, initiating the formation of somatic embryos.
4. Maturation:
The somatic embryos undergo further development and maturation, resembling zygotic embryos with distinct shoot and root meristems.
5. Germination:
Finally, somatic embryos are transferred to a suitable medium where they can develop into complete plantlets with roots and shoots.
Application/ Importance
1. Clonal propagation:
It allows the rapid multiplication of elite plant varieties with desirable traits, bypassing the need for seeds.
2. Genetic transformation:
Somatic embryos can be used for introducing foreign genes into plants, creating genetically modified organisms (GMOs) with improved characteristics like pest resistance or increased yield.
3. Germplasm conservation:
It provides a means to preserve endangered or rare plant species by storing somatic embryos in vitro.
4. Disease elimination:
By subjecting plant tissues to somatic embryogenesis, it is possible to eliminate certain diseases that affect conventional propagation methods.
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Advantages
1. Enhanced Genetic Stability:
Somatic embryogenesis often results in higher genetic stability compared to other tissue culture techniques, leading to a reduced likelihood of genetic variations and somaclonal variations in regenerated plants.
2. Direct Embryo Formation:
Somatic embryogenesis involves the direct formation of embryos from somatic cells, bypassing the formation of callus or other intermediate stages, which can be advantageous in terms of efficiency and time-saving.
3. Controlled Embryo Development:
Somatic embryos can be synchronized and developed in a controlled environment, allowing better manipulation of the developmental stages and producing uniform plantlets with desirable traits.
4. Tolerance to Stressors:
Somatic embryos are sometimes better equipped to tolerate abiotic stressors (such as drought, salinity, or temperature extremes) due to their developmental characteristics, making them useful for producing stress-resistant plants.
5. Preserved Epigenetic Memory:
Somatic embryogenesis has the potential to maintain the epigenetic memory of the parent plant, enabling the transmission of specific traits and adaptations to the regenerated offspring.
6. Genetic Transformation Efficiency:
When it comes to genetic modification, somatic embryogenesis has been shown to have higher transformation efficiency compared to other tissue culture methods, allowing for more successful gene transfer and expression.
7. Higher Regeneration Frequency:
Some plant species or varieties that do not respond well to conventional tissue culture methods may exhibit a higher regeneration frequency through somatic embryogenesis, offering an alternative route for propagation.
8. Improved Plantlet Survival:
Somatic embryos are often more robust than other types of tissue culture-derived plantlets, leading to higher survival rates during acclimatization and subsequent transplantation.
9. Fewer Contamination Risks:
The direct initiation of embryos in somatic embryogenesis minimizes the risk of contamination from microorganisms or other undesirable agents that can affect tissue culture processes.
10. Eco-friendly Propagation:
Somatic embryogenesis reduces the reliance on conventional propagation methods, such as seed germination, which can have positive environmental implications by conserving resources and reducing the need for large-scale seed production.
Disadvantage
These disadvantages highlight some of the challenges and limitations associated with somatic embryogenesis.
1. Limited Applicability:
Somatic embryogenesis might not be successful or applicable to all plant species or varieties.
2. Complexity of Induction:
The induction of somatic embryogenesis can be a complex and genotype-dependent process, requiring specific growth regulators, culture conditions, and precise timing, which may increase the difficulty and variability of the technique. Hence direct embryogenesis is not common.
3. Epigenetic Variations:
While somatic embryogenesis can preserve epigenetic memory in some cases (as mentioned in the advantages), it can also lead to epigenetic variations.
4. Higher Synchronization Requirements:
Achieving synchronous development of somatic embryos can be more challenging compared to other tissue culture methods.
5. Risk of Somaclonal Variation:
Although somatic embryogenesis can offer genetic stability (as mentioned in the advantages), it is not completely immune to somaclonal variation.
6. Cost and Infrastructure:
Establishing and maintaining facilities for somatic embryogenesis can be costly for small-scale production.
7. Reduced Genetic Diversity:
Somatic embryogenesis primarily produces genetically identical plants, leading to reduced genetic diversity.
Factor affecting
1. Explant:
Meanly somatic cells are only selected for somatic embryogenesis. Younger explants are more often selected than older explants due to high yield
2. Plant Growth Regulators:
The selection of growth regulators depends on the type of embryogenesis. Because auxin promotes call formation and cytokinin stimulates direct embryo development.
3. Stress Conditions:
Certain stress conditions, such as osmotic stress, temperature variations, or exposure to specific chemicals, can promote or inhibit somatic embryogenesis in certain plant species. However, the effects of stress on embryogenic induction are highly dependent on the plant's physiological and genetic characteristics.
4. Synchronization:
Achieving synchronization of somatic embryo development is critical for obtaining uniform plantlets. Factors influencing the synchronization of somatic embryogenesis, such as the timing of growth regulator application or the stage of embryo maturation, can significantly affect the regeneration process.
5. Physical Factors:
Physical factors like light intensity, photoperiod, and culture vessel type can also affect somatic embryogenesis. Some plant species may require specific light conditions for efficient embryogenic development.
6. Endogenous Factors:
The intrinsic factors within the plant cells, such as the expression of specific genes, epigenetic regulation, or hormonal balance, can influence the competence of somatic cells to undergo embryogenic development.
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Pundhan Singh. 2016. Objectives Plant biotechnology. Kalyani publishes, New Delhi.