Somatic Embryogenesis

Embryos are of the following types:

• Zygotic embryos
• Non-zygotic embryos

Zygotic embryos are formed by the zygote or the fertilized egg. Non-zygotic embryos can further be segregated into:

• Somatic embryos: These are formed by the sporophytic cells in an in-vitro scenario. These somatic embryos directly emerging from the other organs or embryos are referred to as adventive embryos.
• Androgenetic embryos: Formed by the male gametophytes.
• Parthenocapic embryos: Formed by the unfertilized egg.

Somatic embryogenesis is a significant biotechnological tool illustrating vital merits in the streams of clonal propagation, genetic transformation etc., which when applied are most propitious of their applications.

It was in 1958 that Stewart first introduced embryos in carrots via the suspension culture.

Table of Contents

• What Is Somatic Embryogenesis? – Somatic Embryogenesis Definition
• Process Of Somatic Embryogenesis
• Types Of Somatic Embryogenesis
• Advantages Of Somatic Embryogenesis
• Factors Affecting Somatic Embryogenesis
• Somatic Embryogenesis Stages – Steps Of Somatic Embryogenesis
• Difference Between Organogenesis And Somatic Embryogenesis
• Difference Between Somatic Embryos And Zygotic Embryos

What is Somatic Embryogenesis? – Somatic Embryogenesis Definition

Somatic embryogenesis is the process wherein somatic cells differentiate into somatic embryos. It is not a naturally occurring process, an artificial one wherein an embryo or plant is obtained from one somatic cell. Somatic embryos take form from the cells of the plants, which usually do not take part in embryo development. Neither a seed coat nor endosperm is formed around the somatic embryo.

In the process, one cell or a cluster of cells initiates the developmental route, which results in reproducible regeneration of non-zygotic embryos, which can germinate for the formation of an entire plant.

The cells which are derived from potential source tissues are subject to a culture medium for the formation of an undifferentiated cluster of cells referred to as the callus. In the tissue culture medium, the plant growth regulators can be formed for the induction of the formation of calluses and hence modified to induce the embryos for the formation of calluses.

Process of Somatic Embryogenesis

The somatic embryogenesis procedure is a three-step procedure, which causes the induction of embryogenesis, development of the embryo and its maturation.

The principle of somatic embryogenesis finds its basis on the topic of totipotency of the plant cells; it illustrates two facets of plant embryogenesis:

• The process of fertilization can be replaced by an endogenous mechanism.
• The other types of cells of the plant, apart from the fertilized egg cells, can retrieve the capacity to form an embryo.

Since the process of somatic embryogenesis does not entail the procedure of fertilization, it promotes the large scale propagation of plants at a faster rate. In addition, it also assists in the genetic transformation of plants, serving as a promising resource for the cryo-storage of the embryo and germplasm.

Somatic embryogenesis – Induction

Cells are reactivated to differentiate and develop embryos, which occur through two processes: direct somatic embryogenesis and indirect somatic embryogenesis.

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Direct somatic embryogenesis

It involves the development of the embryos in a direct way from the cells of the explants, such as the cells of the immature embryos. Here, there is no intermediary stage (like the formation of the callus). The explants of the somatic embryogenesis are seen to entail PEDCs (pre-embryogenic determined cells).

Indirect somatic embryogenesis

It includes the formation of somatic embryos by reiterating numerous cycles of cell divisions. It includes intermediary steps of growth of the callus, and hence the process includes multiple steps.

The cells which do not carry the pre-embryogenic determined cells are caused to differentiate for the formation of the embryo by revealing different treatments. The cells modify into IEDs (induced embryogenic pre-determined cells).

Types of Somatic Embryogenesis

Somatic embryogenesis is of two types:

• Direct somatic embryogenesis

Here, the embryos start directly from the explants when callus formation does not take place. Embryos, in this case, are formed as a result of Pre-induced Embryogenic Determined Cells (PEDCs).

• Indirect somatic embryogenesis

The callus from the explants occurs from where the embryo develops. Here, the embryos are formed as a result of Induced Embryogenic Determined Cells (IEDCs).

Advantages of Somatic Embryogenesis

In comparison with zygotic embryogenesis, somatic embryogenesis has these benefits:

• A huge number of embryos are obtained
• The development and environmental stage of somatic embryos can be regulated
• This process of embryogenesis can be monitored easily

The significance of somatic embryogenesis is as follows:

• Production of artificial seeds
• Higher rate of propagation
• Apt in suspension culture
• Labour savings

Factors Affecting Somatic Embryogenesis

The aspects which affect the process of somatic embryogenesis are as follows:

Traits of explant

Despite the fact that variations of explants can be used, the apt stage of development of explants is vital too to initiate the embryogenic callus; whereas juvenile explants tend to give rise to more somatic embryos compared to older explants. Also, different explant explants tissues from the same mother plant generated embryogenic callus at varying frequencies.

The desired species of plants to be induced for embryogenesis decides the choice of explants. For the majority of plant species, explants of immature zygotic embryos are apt for somatic embryogenesis.

Growth regulators

Cytokinins: These have been in use in the primary medium consistently at the time of embryogenesis of the crop plants. They are vital in speeding up the process of maturation of somatic embryos, the cotyledon development, precisely.

Auxins: These alone or in combination with cytokinin seemingly are vital for the start of growth and the induction of the embryogenesis of all the auxins. Auxins find immense importance in the first step of this process – the step of induction. High levels of auxins can lead to the inhibition of embryogenesis in the explants of the citrus plants.

Abscisic acid: These are supplied at the inhibitory levels. It facilitates the development and maturation of the somatic embryos, while also inhibiting the unusual proliferation and the initiation of the accessory embryos.

Genotype

The process of embryogenesis is also affected by the genotypic variation seen in different plants; as per research, it can also be as a result of the endogenous levels of the hormones.

Sources of nitrogen

Nitrogen forms that are utilised in the media have an influence on the process of embryogenesis in plants. Forms of nitrogen have a marked influence on somatic embryogenesis. Somatic embryo development takes place on a medium that contains NO^–₃ as the only source of nitrogen.

Polyamines

The concentration of polyamines in media or explants is said to have an effect on the process. Experts observe the concentration of polyamines to be seen in higher concentrations in the polyembryonates compared to monoembryonates.

Electrical stimulation

Electrical stimuli apparently facilitate the differentiation of the structured embryo by influencing the cell polarity via modifications in the structure of the microtubules and the induction of first asymmetric division.

Somatic Embryogenesis Stages – Steps of Somatic Embryogenesis

The process of somatic embryogenesis occurs in the following stages:

Induction

For the process of induction, auxins, specifically 2, 4-D are typically essential. The necessity of exogenous auxin to induce somatic embryogenesis is based on the nature of the explants, which are made use of with a proportional concentration of the auxins.

Development

Once reinitiation of the process of cell division and a stage of cell proliferation occurs in the presence of auxins, embryogenic cells are liberated in the auxin-free medium. Such cells are in groups of cytoplasmic cells referred to as the PEMs (Pro Embryonic Mass of Cells).

Maturation

The standard of the somatic embryos in aspects of their conversion into plants or germinability is degraded as a result of usually normal-seeming somatic embryos, which in actuality are incomplete in their development. The somatic embryos, as opposed to seed embryos, do not experience the last stage of embryogenesis referred to as embryo maturation that is distinguished by the collection of embryo-specific reserve food substances and proteins imparting desiccation tolerance to the embryos. The size of the embryos does not increase at this stage.

Difference between Organogenesis and Somatic embryogenesis

In the development of an entity, both organogenesis and embryogenesis are vital. While embryogenesis involves the formation of an embryo from the zygote as a result of syngamy, organogenesis, on the other hand, involves the development of organs and tissues of the entity from the three germ layers of the embryo. The main difference lies in the formation of organs and embryos.

The table below provides some key differences between Organogenesis and Somatic embryogenesis.

Difference between Somatic Embryos and Zygotic Embryos

Tabulated below are some important differences between somatic embryos and zygotic embryos. Read on to find out:

Fields of Application of Somatic Embryogenesis

Today, the process of somatic embryogenesis finds its application in different fields of science; some of them are:

• In vitro selection
• In vitro conservation
• Large scale propagation
• Genetic transformation

This was an overview of Somatic embryogenesis, its types, factors affecting it, different stages, advantages and some important comparisons. For related information, visit NEET BYJU’S.

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