Synthetic Seeds and their Uses
Authors: *Pawan Kumar, Ritu Choudhary, Chhagan Lal, Sheetal Raj Sharma
Ph.D. Scholar, Rajasthan Agriculture Research Institute
Durgapura, Jaipur
*Corresponds - mailto:pawanchoudhary2@gmail.com


Plant propagation using artificial or synthetic seeds make a promising technique for propagation of transgenic plants, non-flowering plants, polyploidy with elite traits and plant lines with problems in seed propagation. These bypass the recombination breeding and can bring the advancement of biotechnology to the doorsteps of the farmers in a cost effective manners.


Synthetic seed and somatic embryo:

Somatic embryo enclosed in suitable gel (sodium alginates) is called synthetic seed and somatic embryo is bipolar structure with both apical and basal meristematic regions, which are capable of forming shoot and root, respectively. A plant derived from a somatic embryo is sometimes referred to as an 'embling'

Need for synthetic seed production technology:

Micro propagation technique will ensure abundant supply of the desired plant species. in some crops seed production is not feasible because of minute seed size, presence of reduced endosperm and the requirement of seed with micorrhizal fungi association for germination (eg. orchid) and also in some seedless varieties in crops like grapes, watermelon ete. some of them can be propagated by vegetative means but in vivo propagation is expensive and time consuming. Artificial seed production technology is considered as effective and efficient alternate method of propagation in several crops.

Artificial seed technology involves the production of tissue culture derived somatic embryos encased in protective coating. Artificial seeds have also been referred as synthetic seed and would also be a channel for new plant lines produced through biotechnological advances to be delivered directly to the green house and field. This technology is a high volume, low cost effective production technologies. high volume propagation potential of somatic embryos combined with formation of synthetic seed for low cost delivery would open new ways for clonal propagation in several commercially important crop species.

Somatic embryo v/s zygotic embryo and their application:

Somatic embryos are similar to zygotic embryos found in seeds and possess many of their useful features, including ability to develop into complete plant but differ in that they develop from somatic cells. Natural seed develops as a result of a sexual process in cross-pollinating species. it is not genetically identical to one single parents. in contrast, somatic embryo develops from somatic cells and does not involve sexual recombination and bypasses genetic recombination and selection inheritant in conventional breeding program.

Basic requirement for production of artificial seed:

One pre-requisite for the application of synthetic seed technology in micro-propagation is the production of high-quality; vigorous somatic embryos that can produce plant with frequencies comparable to natural seeds. The characteristic lack of developmental synchrony in embryogenic system multi-step procedures for guiding somatic embryos through maturation. Synchronized embryoid development is required for efficient production of synthetic seeds.

Procedures for production of synthetic seed:

Establish somatic embryogenesis
       ↓
Mature somatic embryos
       ↓
Synchronize and singulate somatic embryos
       ↓
Mass production of somatic embryos
       ↓
Standardization of encapsulation
       ↓
Standardization of artificial endosperm
       ↓
Mass production of synthetic seeds
       ↓
Green housing and field planting
Gelling agents used for encapsulation:

Several gels like agar, alginate, poly co2133, guar gum, sodium pectate, tragacanth gum, carboxy methyl cellulose, carrageenan etc. were tested for artificial seed production, out of which alginate encapsulation was found to be more suitable and practicable for artificial seed production. Alginate hydrogel is frequently selected as a matrix for artificial seed because of its moderate viscosity and low spinnability of solution, low toxicity for somatic embryos and quick gellation, low cost and bio-compatibility characteristics. The use of agar as gel matrix was deliberately avoided as it is considered inferior to alginates with respect to storage. Alginate was chosen because it enhances capsule formation and also the rigidity of alginate beads provide better protection (than agar) to the encased somatic embryos against mechanical injury.

Artificial endosperm:

Somatic embryo lack seed coat (Testa) and endosperm that provide protection and nutrition for zygotic embryos in developing seeds. To augment these deficiencies addition of nutrients and growth regulators to the encapsulation matrix is desired. Which serve as artificial endosperm. Addition of nutrient and growth regulatos to the encapsulation matrix results in increase in efficiency of germination and viability of encapsulated somatic embryos. these somatic embryos can be stored for a longer period of time even upto 6 months without losing viability, especially when stored at 4oC.

Utilization of Artificial seed:

Synthetic seed can be used for specific purpose, non seed producing plants, ornamental plants or propagation of polyploid plants with elite's plants. The artificial seed system can also be employed in the propagation of male and female sterile plants for hybrid seed production. cryo preserved artificial seed may also be used for germplasm conservation in recalcitrant crop plants. Transgenic plants which require special growth facilities may also be preserved using through somatic embryos.

Artificial seed produced in tissue culture are free from pathogens and saving time and other resources. Thus, another advantage is the transport of pathogen free prop gules across the internationals boarders avoiding bulk transportation of plants, quartine and spread of diseases.

Artificial seed production technologies can be used for zygotic embryogeny, production of large number of identicles embryos, determination of role of endosperm in embryo development and germination, study of seed coat formation and study of somaclonal variation.

Applicability and feasibility of artificial seed production technology:

In order to be useful, synthetic seed must either reduce production cost or increase crop value. Considering a combination of factors, including improvement of the existing embryogenic system, relative cost of seed as well as specific application for synthetic seed allows judgement of relative need for a given crop. For examples, synthetic seed of seedless watermelon would actually cost less than conventional seed, providing a benefit at the outset of crop production. The benefit that could be conferred by the use of synthetic seed would be very great. Value added aspect that would increase crop worth are numerous and include cloning of elite genotypes, such as genetically engineered verities, that cannot produce seed.

References:
1. K. Redenbaugh, (edi.), Synthetic seed, CRC Press, Boca Raton, 1993
2. J. A. Fujii, D.T. Slade, K. Redenbaugh and K. A. Walker, Artificial seed for plant propagation, Tends in biotechnology, 5: 335-339, 1987
3. T. Senaratna, Artificial seeds, Biotechnology Advances, 10: 379-392, 1992



About Author / Additional Info:
I am persuing Ph.D. in Plant Breeding and Genetics at RARI,Durgapura Jaipur