Synthetic seeds or artificial seeds are the living-seed like structure derived from somatic embryoids (or, somatic embryos) in-vitro culture after encapsulation by a hydrogel. The preserved embryoids are called synthetic seeds.
Synthetic seeds or artificial seeds are the living-seed like structure derived from somatic embryoids (or, somatic embryos) in vitro culture after encapsulation by a hydrogel. The preserved embryoids are called synthetic seeds.
Father of synthetic seeds in India is Bapat who worked on sandalwood and Morus alba in1980.
The general procedure is as followed:
- Induction of somatic embryogenesis
- Maturation of somatic embryos
- Encapsulation of somatic embryos (synthetic seeds)
- Evaluation of embryoid and plant conversion
- Planting in fields/green house
- It could be preserved for long time at lower temperature
- Rooting, hardening and conversion steps are waved off as these seeds can directly be sowed in the fields like natural seeds
- For the development of hybrid plants which have unstable genotypes or show seed sterility. In case that the seeds become sterile, the immature embryo from the seed can be rescued (called as embryo rescue) and then can be encapsulated artificially with appropriate growth medium to allow its maturation and desiccation for its germination.
- Germplasm conservation
- For various research and analysis purposes like studying the role of endosperm, etc
- To produce large number of the clones of elite species at the cheaper cost
- To supply adjuvant like plant growth regulators, pesticides, etc
Since, synthetic seeds lack endosperm which provide nutrient to the embryo in the natural seed. Therefore, addition of various nutrients is preferred in the gelling matrix.
Preparation of synthetic seeds:
For preparation seeds need to be encapsulated. This can be done using various water soluble hydrogels like alginate, gel rite, carboxy methyl cellulose, locust bean gum, sodium alginate with gelatin. However, alginate based encapsulation was found to be best.
Encapsulation can be done in two ways:
In this method, somatic embryos are mixed with 2% sodium alginate solution prepared in MS medium. However if the sodium alginate is purchased from an Indian based company the add 4% sodium alginate.
Then these encapsulated beads are then added as drops into a calcium nitrate solution (100mM) and then they were kept for around 20-30 minutes after which embryos are completely gelled by calcium alginate.. Then these gelled embryos are rinsed with water and then can be used as synthetic seeds.
This method has been used Redenbaugh et al. (1986) for alfalfa somatic embryos encapsulation.
However, in place of calcium nitrate, calcium chloride can also be used with by product of encapsulation as sodium chloride.
Gelling with sodium alginate is not done since sodium is toxic for cells.
In this, embryos are mixed with temperature dependent gel like gel rite where cells get gelled as the temperature is lowered.
However, the synthetic seeds obtained by above methods cannot be used directly into the fields because:
- They are very fragile
- Their nutrients will be attacked by the micro flora present in the soil which will starve the embryo to death
So, to prevent above problems, one or two more coatings of alginate are given and also, certain antibiotics, insecticides, pesticides, etc are added to prevent the microbial attack on the nutrient medium.
However, these seeds can’t be used for soil transfer as they show very poor germination efficiency. For example: a lettuce plant showed the efficiency of just 2% and is the only plant which was tried in the field.
Even, the green houses the efficiency is not very high, only around 10-20%. For example: 7% for alfalfa and 10% for celerly.
The reason that the factors like genes involved in regulating the dormancy, desiccation, development of seeds is not yet clearly known.
So, such seeds are mainly used for germplasm conservation and do not need liquid nitrogen for their storage. For example: Srinivas et al (2002) showed the successful germplasm conservation of a rice variety for 1 year at 8° C. however, when tried with direct soil transfer the synthetic seeds efficiency was found to be just 0.1%.