Synthetic Seeds
1Suman Sanadhya, 2 Abhilasha Sharma and 3Anubhuti Sharma
1,2,3 Rajasthan College of Agriculture, MPUAT, UDAIPUR-313001

Synthetic seed technology has become a promising method for germplasm propagation and preservation (Sharma et al., 2013). The original definition of an artificial seed, as given by Murashige (1978), was "an encapsulated single somatic embryo", i.e., a clonal product that could be handled and used as real seed for transport, storage and sowing and that, therefore, would eventually grow either in vitro or ex vitro, into a plantlet ("conversion"). Basic aims of this technology are to convert different micropropagules, mainly somatic embryo into artificial or synthetic seeds which can be grown in the field or greenhouse when required. Artificial seed production has been practiced for last several years with initial efforts made only with somatic embryos. It was "Kamada" who broadened the scope of the technique by suggesting a new definition of these somatic propagules (Kamada, 1985). Somatic embryo is bipolar structure with both apical and basal meristematic region which are capable of forming shoot and root respectively. There are various advantages of artificial seed such as better and clonal plants could be propagated similar to seed, preservation of rare plant species and more consistent and synchronized harvesting of important agricultural crops would become a reality, among many other possibilities (Ravi and Anand, 2012). Artificial seed technology can be very useful for the propagation of a number of vegetatively propagated plants, crop plants and hybrid varieties. Among crop plants this technique can be used for plants which do not multiply by true seeds or the seeds if available the prices are not affordable (Sharma et al., 2013). Micropropagation through artificial seeds may be commercially exploited on a large scale, generating millions of plants in a few days, and this may become a profitable multi-billion rupees industry in the near future. This technology would be feasible and even competitive economically with the traditional seed propagation.

NEED OF SYNTHETIC SEEDS

A seed is basically zygotic embryo with enhanced nutritive tissue and covered by several protective layers.
Zygotic embryo seeds are progeny of two parents, which are the result of sexual reproduction.
One major disadvantage of zygotic embryo seeds is that, we could not get true to type plants of the parents.( Ravi and Anand, 2012)
To overcome this problem, synthetic seed technology emerges as a promising tool for the production of synthetic seeds.

DEVELOPMENTAL STAGE OF SOMATIC EMBRYO

Somatic cell
Cell division
Globular embryo
Heart shape embryo
Torpedo shape embryo

TYPES OF SYNTHETIC SEED

DESSICATED: - Somatic embryo first hardened to withstand dessication and then encapsulated in a suitable coating material.

HYDRATED: - Somatic embryo enclosed in gels, which remain hydrated. Hydrated synseeds produced from plants where the somatic embryos cannot sustain the stress of dessication. Method used for encapsulation of synseeds is gel complexation via dropping technique.


GEL COMPLEXATION VIA DROPPING TECHNIQUE

The sodium alginate along with explants is allowed to drizzle through a pipette drop-by-drop into a solution of either CaCl2 or CaNO3. When the sodium alginate enters the calcium salt solution an ion exchange reaction takes-place whereby Ca2+ ions are replaced by Na+ ions and forms a gelled calcium alginate around the somatic embryos which looks like beads in appearance. A number of other gelling agents besides alginate have been successfully used such as potassium alginate, agar, guar-gum, carboxy methyl cellulose, sodium pectate, carrageen an etc. Sodium alginate is widely and most commonly used as a gelling agent because of following reasons: Easy complexation ability with calcium solution, Moderate viscosity, No toxic for propagules, Quick gelation, Cheaper material, Biocompatible and non damaging ions.

POTENTIAL USES

Propagation: - Large scale monoculture of rare, endangered, genetically engineered elite genotypes.
Conservation: - Cost-effective approach for ex situ germplasm conservation.
Analytical tool: - Comparative study aid for zygotic embryogeny, study of somaclonal variation and seed coat formation studies etc.
Transport: - Direct green house and field delivery and germplasm exchange between countries without obligations from quarantine department etc.

REFERENCES

1. Kamada, H. (1985). Artificial seed. In Practical Technology on the Mass Production clonal Plants. Tanaka R. (Ed.), 48 CM publisher. Tokyo, Japan.
2. Murashige T. (1978) The impact of plant tissue culture on agriculture. In: Thorpe TA, editor. Frontiers of plant tissue culture. International Association for Plant Tissue Culture. Alberta, Canada: University of Calgary. p. 15-26.
3. Ravi and Anand. 2012. Production and applications of artificial seeds: A review. International Res. J. Biol. Sci. 1(5): 74-78.
4. Sharma, S., Shahzad, A. and Silva, J. 2013. Synseed technology- A complete synthesis. Biotechnol. Adv. 31: 186-207.

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