Organisms are made up of different types of cells. These cells are specialised in performing different functions of the body. Initially, when a single cell is formed, it is known as a zygote. The cells are then formed into various tissues and organs in the body.
Organogenesis and somatic embryogenesis are both associated with the development of an organ. Still, the difference is that organogenesis is related to the evolution of an organ but somatic embryogenesis is related to the growth of an embryo from a somatic cell.
In plants, organogenesis occurs continuously and only ends when the plant dies. In the shoot, the shoot apical meristems regularly generate new lateral organs and lateral branches.
Organogenesis is defined as a process in which the three germ tissue layers of the embryo, the ectoderm, endoderm, and mesoderm, develop into the internal organs of an organism.
Endoderm: It is the innermost layer of the three primary germ cells of an embryo which is present both in vertebrates and invertebrates. It is responsible for the formation of the gut and the associated organs.
Ectoderm: It is the outermost layer of the cell. It appears early in the development of an animal embryo. In vertebrates, ectoderm gives rise to hair, skin, nails, the epithelia of sense organs, the nasal cavity, the sinuses, the mouth, and the anal canal.
Mesoderm: It is the middle of the three germ layers or masses of cells that lies in between the ectoderm and endoderm. In vertebrates, it gives rise to muscle, connective tissue, cartilage, bone, notochord, blood, bone marrow, lymphoid tissue, and the epithelia of blood vessels, lymphatic vessels, and body cavities, kidneys, ureters, gonads, genital ducts, adrenal cortex.
The germ layers are formed during the process of gastrulation when the hollow ball of cells that constitutes the blastula begins to differentiate into more-specialised cells that become layered across the developing embryo.
Organogenesis in plant tissue culture consists of two different phases: dedifferentiation and redifferentiation. Dedifferentiation begins after the isolation of the explant tissues with an acceleration of cell division and a consequent formation of a mass of undifferentiated cells which are called callus.
Redifferentiation, also called budding in plant tissue culture, begins any time after the first callus cell forms. In this process, tissue called an organ, and primordia are differentiated from a single or a group of callus cells. Primordia is an organ that gives rise to small meristems with cells densely filled with protoplasm and strikingly large nuclei. The development of an organ is monopolar.
There are three ways of organogenesis which are from the callus culture, from an explant, and from the axillary bud.
The process in which plant organs are derived from a calli mass in the explant is called indirect organogenesis.
Indirect organogenesis has been used to produce transgenic plants in two ways which are as follows:
A plant can be regenerated from a transformed callus.
The initial explant is transformed, and the callus and shoots are developed from the modified explants.
Direct organogenesis is a process in which direct buds or shoots from tissues are produced with no intervening callus stage. Direct organogenesis has been used to propagate plants with improved multiplication rates thus reducing operational costs. It has also been used to produce more transgenic plants and most importantly, it has been used for clonal propagation since it ensures the production of uniform planting material without genetic variation.
Embryogenesis involves the development of an embryo from a zygote or a somatic cell. Somatic embryogenesis is the process in which somatic cells differentiate into somatic embryos. It is an artificial process in which an embryo or plant is obtained from one somatic cell. Somatic embryos are formed from the cells of plants, which do not take part in embryo development.
In this process, one cell or a cluster of cells drive the developmental route, which results in the reproducible regeneration of non-zygotic embryos, which can germinate for the formation of an entire plant.
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.
In direct somatic embryogenesis, embryos are formed directly from a cell or small group of cells without an intervening callus production and it is a rare event in tissue culture.
Indirect somatic embryogenesis is a process in which a callus is first produced from the explant, and then embryos are formed from the callus tissue or a cell suspension culture.
It speeds up clonal propagation.
It is very quick and easy to scale up in liquid cultures.
It aids in artificial seed production.
It also helps in physiological study.
Transformation of economically important plant species is enabled by it.
Poor germination of embryos
Low frequency of embryo production
Plantlets are weaker
May create unwanted genetic variation
Plantlets are weaker
Plants that arise from somatic embryogenesis are called emblings.
Somatic embryogenesis completely bypasses recombination however, variations are significantly seen in the embryos.
Somatic embryogenesis can be split into four stages:
In the first phase, embryogenic masses initiate from vegetative cells or tissues.
In the second phase, embryogenic cell lines are maintained and developed.
The third phase involves somatic embryo formation and maturation.
In the final stage, the somatic embryos are converted into viable plantlets.
1. What are the factors affecting somatic embryogenesis?
Genotype and type of explant, nitrogen source, characters of explant, environmental factors, and polyamines are some of the factors affecting somatic embryogenesis.
2. What factors affect organogenesis?
The factors affecting organogenesis are temperature, source, and sex of the explant, culture medium, size of the explant, and various environmental conditions.
3. What are the different steps in somatic embryogenesis?
There are four different steps involved in the process of somatic embryogenesis which are induction, maintenance, development, and regeneration.