Somatic embryogenesis is an artificial procedure in which a plant or embryo is generated from a single somatic cell. Somatic embryos are created from plant cells that are not ordinarily involved in the development of embryos, i.e., regular plant tissue. No endosperm or seed coat is developed around a somatic embryo.
Cells taken from competent source tissue are grown to generate an undifferentiated mass of cells called a callus. Plant growth regulators in the tissue culture medium can be altered to stimulate callus formation and afterwards changed to induce embryos to form the callus. The ratio of different plant growth regulators necessary to trigger callus or embryo production varies with the kind of plant. Somatic embryos are mainly created in vitro and for scientific purposes, utilising either solid or liquid nutritional solutions which contain plant growth regulators (PGR’s). The main PGRs employed are auxins but can contain cytokinin in a lower amount. Shoots and roots are monopolar but somatic embryos are bipolar, allowing them to produce a full plant without cultivating on several media types. Somatic embryogenesis has served as a model to understand the physiological and biochemical events that occur throughout plant developmental processes as well as a component to biotechnological innovation. The earliest documentation of somatic embryogenesis was by Steward et al. in 1958 and Reinert in 1959 with carrot cell suspension cultures.
Plant regeneration by somatic embryogenesis
Plant regeneration via somatic embryogenesis is a five-step process that includes the establishment of embryogenic cultures, their proliferation, the prematuration of somatic embryos, their maturation, and plant development on nonspecific media. The initiation and proliferation of meristematic cells take place in an auxin-rich media, which drives differentiation of the localised meristematic cells. Typically, 2,4-D is utilised as the auxin. These cells can then develop into mature embryos when transferred to a medium containing little or no auxin. The somatic embryo can germinate only when it has developed sufficiently to have functional root and shoot apices.
Application of somatic embryogenesis
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- The process of somatic embryogenesis has a variety of functions and applications, which are discussed in this section.
- It is the primary method of in vitro propagation for woody plants. It is crucial for clonal propagation, synthetic seed generation, germplasm conservation, and cryopreservation in this context.
- It is used to rapidly propagate plants on a huge scale in order to produce secondary chemicals and pharmaceuticals.
- It is a great system for studying plant cell biology and embryo development at a fundamental level.
- Additionally, it provides a more comprehensive framework for studying the differentiation and process of totipotency expression in plant cells.
Stages of somatic embryogenesis
The stages of somatic embryogenesis are as follows:
Induction – Auxins, specifically 2, 4-D, are often required for the induction process. Exogenous auxin is required to promote somatic embryogenesis due to the nature of the explants used in conjunction with a proportionate concentration of auxins.
Development – Once the process of cell division and proliferation are reactivated in the presence of auxins, embryogenic cells are freed in the auxin-free condition. These cells are classified as PEMs, which are clusters of cytoplasmic cells (Pro Embryonic Mass of Cells).
Maturation – The standard of somatic embryos is degraded in terms of conversion to plants and germinability as a result of often normal-appearing somatic embryos that are actually deficient in their development. In contrast to seed embryos, somatic embryos do not undergo the final stage of embryogenesis known as embryo maturation, which is characterised by the accumulation of embryo-specific reserve food components and proteins that confer desiccation tolerance on the embryos. At this stage, the embryos do not grow in size.
Examples of somatic embryogenesis
Carrot somatic embryogenesis was the subject of the first recorded study, published in 1958. (Daucus carota). It has since evolved into a model organism for scientific investigation. Somatic embryogenesis in diverse plants has been studied extensively, with more than 300 research presently available.
Listed below are some examples of other plants that have been investigated using this method:
Floral tissues are utilised in the embryogenesis of Ranunculus sceleratus. The medium utilised to stimulate the procedure is 10 percent coconut milk with or without IAA, and it takes three weeks for the embryo to develop completely.
The development of the embryo in the loblolly pine (Pinus taeda) is aided by the induction of cotyledonary tissue. In this scenario, the media contains 2.6 mg/L abscisic acid, and cold storage is used to promote competence and effectiveness.
For the purpose of inducing somatic embryogenesis in Japanese larch (Larix kaempferi), immature zygotic embryos are cultured and the callus is harvested in order to produce the somatic embryo. Culture of the calli for one month on half-strength Quoirin and Lepoivre media containing 90 mM sucrose and 7.6 mM ABA is carried out on the calli obtained in the field. To increase the yield, this is done.
Explanations of Eucalyptus globulus leaf and shoot apex were used to promote somatic embryogenesis in the presence of 40 M Picloram in the medium.
To encourage the production of the somatic embryo in the East Indian sandalwood tree (S. album L.), nodal explants are placed on culture media containing 2.5 mg/L 2,4-D and 3 mg/L kinetin, respectively.
Conclusion
Somatic embryogenesis is a biological process in which a somatic cell in a plant can dedifferentiate into a totipotent embryonic stem cell capable of forming an embryo given the right conditions. This newly formed embryo has the potential to evolve into a whole plant.