Practical Application of Somatic Embryogenesis
The potential applications and importance of in vitro somatic embryogenesis and organogenesis are more or less similar.
i) Clonal Propagation:
Since both the growth of embryogenic cells and subsequent development of somatic embryos can be carried out in liquid medium, it is possible to combine somatic embryogenesis with engineering technology to create large-scale mechanical or automated culture systems. Such systems are capable of producing propagules repetitively with labour input. In this process of repetitive somatic embryogenesis is initiated where by somatic embryos proliferate from the previously existing somatic embryo in order to produce clones.
ii) Raising Somaclonal Variants in Tree Species:
Embryos formed directly from pro-embryogenic determined cells ( PEDCs) appear to produce relatively uniform clonal material, whereas the indirect pathway involving induced embryogenic determined cells (IEDCs) generates a high frequency of Somaclonal variants. Mutation during adventive embryogenesis may give rise to a mutant embryo which on germination would form a new strain of plant. For clonal propagation of tree species, somatic embryogenesis from nucellar cells may offer only rapid means or obtaining juvenile plants equivalent to seedlings with parental genotype.
iii) Synthesis of Artificial Seeds:
Artificial seeds are the living seeds like structures which are made experientially by a technique where somatic embryoids derive d from plant tissue culture are encapsulated by a hydrogel and such encapsulated embryoids behave like a true seeds if grown in soil and can be used as a substitute for natural seeds.
Several Steps are Followed for Making Artificial Seeds:
1. Establishment of callus culture
2. Induction of somatic embryogenesis in callus culture.
3. Maturation of somatic embryos
4. Encapsulation of somatic embryos
Maturation of somatic embryos means completion of embryo development throught some stages. Initially, embryo develops as globular shaped stage, the heart-shaped stage and finally torpedo-shaped stage. In the final stage embryo attains maturity and develops the opposite poles for shoot and root development at two extremities. This embryo then starts to germinate and produces plantlets.
Two types of artificial seeds have developed, namely, , hydrated and desiccated Redenbergh et.al. (1986) developed artificial seeds by mixing somatic embryos of alfalfa, celery and cauliflower with sodium alginate , followed dropping into a solution of calcium chloride to form calcium- alginate beads. About 29-55% embryos encapsulated with this hydrogel germinated and formed seedlings in vitro. Kim and Janick (1989) applied synthetic seeds coats to clumps of carrot somatic embryos to develop desiccated artificial seed. They mixed equal volumes of embryo suspenion and 5% solution of polythene oxide, a water soluble resin, which subsequently dried to further achieved by embryo a ‘ hardening ‘ treatment with 12% sucrose or 10-6 MABA, followed by chilling at inoculum density.
Another delivery system for somatic embryos for obtaining transgenic plant is fluid drilling. Embryos are suspended in a viscous- carrier gel which extrudes into the soil. The primary problem in fluid –drilling is that the sucrose level necessary to permit conversion also promotes rapid growth of contaminating micro-organisms in a non-aseptic system.
iv) Source of Regenerable Protoplast System:
Embryogenic callus, suspension cultures, and somatic embryos have been employed as source of protoplast isolation for a range of species. Cells or tissues in these system have demonstrated the potentiality to regeneration in culture and therefore, yield protoplast that are capable to forming whole plants.
v) Genetic Transformation:
Repetitive embryos originate from single epidermal or sub epidermal cells which can readily be exposed to Agrobacterium. Thus the transformation technique applied to primary somatic embryos. Repetitive embryogenesis is also ideally suited to particle gun-mediated genetic transformation. Instead or recycling on Agrobacterium to mediate the transfer of genes into plant cells, the particle gun literally shoots DNA that has been precipitated onto particles of a heavy metals, into the plant cells. Embryogenic suspension cultures of the cotton and soybean, initiated cell lines following each firing of the gun. The transformed cell lines can then the induced to form an unlimited number of transformed somatic embryos through repetive embryogenesis.
vi) Synthetic of Metabolites:
The repetitive embryogenesis system is of potential use in the synthesis of metabolites such as pharmaceuticals and oils. Borage contains high level of Y-Linoleic acid, used as precursor of post-glandins or in the treatment of atopic eczema. Somatic embryos of borage also produce this metabolite but through repetitive somatic embryogenesis a continuous supply of Y-lenolenic acid is ensured. Which otherwise would be limited to the growing season in the zygotic embryos. The same principle can be applied for production in vitro of industrial lubricant from jojoba and leo-palmitostearin from cacao.