Synthetic Seeds or Artificial Seeds
Artificial seeds can be defined as artificial encapsulation of somatic embryos which has the ability to form a plant in-vitro or ex-vivo condition.
The coating material should have several qualities they are:
- It must be non-damaging to the embryos.
- The coating should be mild enough to protect the embryos and allow germination but it must be sufficiently durable for rough handling during manufacture, storage, transportation and planting.
- The coat must contain nutrients, growth regulators and other components necessary for germination.
- The quality of somatic embryo should be good enough, they all are of uniform stage with reversible arrested growth and with high rate of conversion to plantlets.
Two types of artificial seeds( encapsulated somatic embryos) are commonly produced they are
- Dessicated synthetic seeds
- Hydrated synthetic seeds
Dessiccated synthetic seeds
It involves encapsulation of somatic embryos followed by their desiccation.
Desiccated synthetic seeds can be prepared by fallowing methodology
a) Mix equal volumes of embryo suspension+polyyox (polyoxyethylene)
b) Suspension was dispensed on Teflon sheets( dried suspension sticks to glass plate).
c) Dried to wafers in laminar air flow hood for about 5 hours until the wafers get separated from Teflon plate.
- The polyox is readily soluble in water and dries to thin film. It does not support the growth of microorganism and is non toxic to the embryos.
- Embryo survival and conversion of seeds are determined by redissolving the wafers in embryogenic medium and culturing the re hydrated embryos.
- These types of artificial seeds can be only made in plants whose somatic embryos are desiccated-tolerant.
Hydrated synthetic seeds
They are produced in plant species which are sensitive to desiccation. Hydrated artificial seeds can be produced by encapsulating somatic embryos in hydrogel capsules. Several methods have been examined to produce hydrated artificial seeds of which Ca-alginate encapsulation has been the most widely used.
It can be prepared by fallowing steps:
a) Mix somatic embryos with sodium alginate
b) Drop the mixture using a pipette into 100mM of calcium chloride.
c) Ion exchange occurs and sodium ions are replaced by calcium ion foaming calcium alginate beads.
- In general three percent of sodium alginate upon complexation with 100 mM CaCl2.2H2O for half an hour gives optimum bead hardness and rigidity for the production of viable sythetic seeds.
- Sodium alginate droplets containing the somatic embryos when dropped into the CaCl2.2H2O solution form round and firm beads due to ion exchange between the Na+ in sodium alginate with Ca2+ in the CaCl2.2H2O solution.
- The hardness or rigidity of the capsule mainly depends upon the number of sodium ion exchanged with calcium ions.
-Hence, the concentration of the two gelling agents i,e sodium alginate and CaCl2.2H2O, and the complexing time should be optimized for the formation of the capsule with optimum bead hardness and rigidity.
Applications
- Speed up the clonal propagation of plants being bipolar in nature.
- Being single cell in origin, there is a possibility to automate large scale production of embryos in bioreactors and their field planting as synthetic seeds.
- The bipolar nature of embryos allows their direct development into complete plantlet without the need of a rooting stage as required for plant regeneration via organogenesis.
- It can also be used for the production of metabolites in species where embryos are the reservoir of important biochemical compounds.
- The production of artificial seeds using somatic embryos is an obvious choice for efficient transport and storage.
- The embryo culture technique is applied to overcome embryo abortion, seed dormancy and self-sterility in plants.
Limitations:
- Complete conversion into plantlets or poor germination of embryos is a major limitation of somatic embryogenesis in many plants
- Compared to other plant species active research on somatic embryogenesis involving forest trees has been very slow.
- The insufficient knowledge regarding controlling somatic embryogenesis, the synchrony of somatic embryo development and low frequency of true to type embryonic efficiency are responsible for its reduced commercial application.
- To obtain a complete conversion into plantlets it is necessary to provide optimum nutritive and environmental conditions.