Introduction:
In this age of time, medicinal herbs are cycled in current therapeutics with leading success in fundamental health care. Some of medicinal plants do not produce usable seeds. In Orchids, very small seed size and the guild with mycorrhizal fungi is crucially demanded for germination of viable seed. Traditional propagation methods are very costly and time arresting. For the above told senses, the in vitro propagation methods, such as somatic embryogenesis serve a breakthrough for the production of uniform plants, provides a powerful tool for mass propagation in less time and season independent production. Moreover, this method provides gene bank maintenance of elite classes for germplasm conservation and exchange. Somatic embryogenesis (SE) is a science of inducing embryos from somatic cells, tissues or organs. Somatic embryos are basically bipolar structures having both apical and basal meristematic regions, which bears the potential of forming shoot and root, respectively. They can be convinced to germinate in tissue culture media by providing all required conditions. Somatic embryo productions were carried out independently and this concept was firstly described by Steward in 1958. SE helps in in vitro propagation and this has been reported in many medicinal plants. There are two types of SE, it can be direct or indirect. Differentiation occur directly from explant called as direct SE. It is just due to the presence of pre-embryonic determined cells (PEDC). Sometimes explants undergoes callus formation and then somatic embryo induction, this is defined as an indirect SE and caused by the presence of induced embryo-genic determined cells (IEDC)
A schematic representation of embryogenesis.
(A) Direct embryogenesis. (B) Indirect embryogenesis
SE phases:
Generally, somatic embryo develops from single cell. This cell undergoes cell divisions to form a group of meristematic cells. The constituent cells of this group continue to divide to give rise globular, heart shaped, torpedo shaped and cotyledonary stage.
Phase I (Development) – Somatic embryo develops from a group of meristematic cells undergoing through any above told shape and cotyledonary stage.
Phase II (Conversion) – Immediately after cotyledonary stage, somatic embryo germinates, this is the conversion phase. But most of the times plantlets obtained from immediate germination are weak.
Phase III (Maturation) – Instead of undergoing germination, somatic embryos undergo biochemical changes and become hardy.
Methodology
- Leaf petiole or root portions of 7-days seedlings (1 cm) can be used as explant.
- Considering aseptic technique, explants are placed individually on a semi-solid MS media. Cultures are incubated in the dark, for sufficient callus tissue formation.
- After 4 weeks of callus growth, cell suspension culture is to be initiated by transferring 0.2 gm. of callus tissue to a 250 ml of Erlenmeyer flask containing 20-25 ml of liquid medium of the same composition as used for callus growth (without agar). Flasks are placed on a horizontal gyratory shaker with 125-160 rpm at 25°C.
- Cell suspensions are sub-cultured every 4 weeks by transferring 5 ml to 65 ml of fresh liquid medium
- To induce somatic embryogenesis, portions of sieved cell suspension are transferred to 2, 4-D free liquid medium or cell suspension can be planted in semi-solid MS medium devoid of 2, 4-D. 6. After 3-4 weeks, the culture would contain numerous embryos in different stages of development.
- Somatic embryos can be placed on agar medium devoid of 2, 4-D for plantlet development.
- Plantlets are finally transferred to Jiffy pots or vermiculite for subsequent development.
SE Applications:
- Clonal propagation of genetically uniform plant material
- Elimination of viruses
- Synthesis of metabolite.
- In genetic transformation it provides source tissue
- Synthesis of artificial seeds.
- Generation of whole plants from single cells called protoplast.
Author:
Asad Riaz
Center of Agricultural Biochemistry and Biotechnology
University of Agriculture, Faisalabad.
Co-Authors:
Habib ur Rahman, Farah Kanwal, Aqsa Tahir & Iqra Khalid
Center of Agricultural Biochemistry and Biotechnology
University of Agriculture, Faisalabad
Contact.email. [email protected]
