What is synthetic seed technology?

Did you know that you can also develop artificial seeds using synthetic seed technology?

This technology is an important application of plant tissue culture. Several developments in scientific research have proved that we can now develop artificial seeds using different plant materials. In most cases, these seeds function and even look like true seeds.

But how did this technology came to light? It was the famous scientist Murashige who first came up with the concept of artificial seeds and called them “synthetic seeds”. He defined a single seed as an encapsulated single somatic embryo.

Among various plant tissue culture methods, somatic embryogenesis is a popular one where you can form an embryo from any somatic cell of the plant. This further led to an increase in demand for artificial seeds and synthetic seed technology was developed.

If you want to read more about somatic embryogenesis or what are the important factors to successfully develop somatic embryos, then do have a look at our recent articles on  "Somatic embryogenesis for plant tissue culture" and "Factors affecting somatic embryogenesis".

But for now, let us delve deeper into the concept of synthetic seeds:

What is a synthetic seed?

Synthetic seeds are artificially encapsulated plant propagation material. This material could be somatic embryos, shoot buds, cell aggregates, or any other tissue that we can use as a seed for propagation. Synthetic seed technology primarily involves encapsulating somatic embryos in a protective coating. These seeds have the potential to develop into a whole plant in vitro as well as ex vitro conditions. They retain this potential even after storage.

One of the interesting facts to note here is that these synthetic seeds need not only a protective covering to resemble a true seed, but also supplementary nutritive material. This nutritive material may include growth nutrients, plant growth-promoting microorganisms, or other biological components that facilitate better embryo-to-plant development. With this addition, you can ensure better growth and development of synthetic seeds.

Why there is a need for synthetic seeds?

So you might be wondering why do we need to use synthetic seeds technology? What is the reason to develop this method even though we can continue with just somatic embryos?

First of all, synthetic seed technology is not only available for use with somatic embryogenesis. But it has also been there for other micropropagation methods, such as organogenesis and the enhanced axillary bud proliferation system. All these techniques facilitate the large-scale multiplication of plant species. And we will discuss these methods in detail in the coming articles!

However, coming back to our question: why is there a need for such seeds? One of the reasons is that this technology can help in improving characteristics in the new embryos and hence can be beneficial for longer duration storage. For instance, these embryos and plant propagules are prone to weed infestations as well as pathogen infections that can affect their ability to survive. Therefore, adding herbicides or biological pesticides along with nutritive material provides resistance against weeds and even pests for the initial growth phase. Thus, facilitating better growth and development.

Another important reason is to prevent the desiccation of somatic embryos or plant propagules in the natural environment. Hence, to prevent these outcomes, protective coatings are suggested for somatic embryos or propagules.

They are also important for some seedless plant species or varieties, for instance, grapes where it is hard to have successful propagation via seeds.

Types of synthetic seeds

There are two types of synthetic seeds available for production:

1. Desiccated synthetic seeds

These seeds are produced by encapsulating multiple somatic embryos along with the process of desiccation. The process of desiccation involves completely removing the moisture content from these seeds. To form the protective coating on somatic embryos or propagules, we use polyoxyethylene (Polyox) as encapsulating material. This material prevents the growth of microorganisms and is non-toxic to embryos.

The process of desiccation either takes place slowly over a period of 1 to 2 weeks in decreasing humidity environment or by simply leaving them on the bench overnight to dry. However, desiccated seeds are beneficial only for those plant species where somatic embryos are tolerant to desiccation.

2. Hydrated synthetic seeds

These seeds are produced by encapsulating the somatic embryos in hydrogel capsules. They are more suitable for plant species where somatic embryos are recalcitrant and show sensitivity to desiccation. The most common method to form hydrated seeds is by using calcium-alginate encapsulation. 

Advantages of synthetic seeds

Let us now discuss some of the major advantages this technique offers:

• This method is for large scale productions.
• It maintains genetic uniformity for a high number of generations. Most plant tissue culture methods fail to maintain genetic uniformity for longer durations.
• According to literature, the costs of producing a plant using this technology is low.
• It facilitates rapid multiplication of plants.
• One of the biggest merit of this method is direct delivery of plant parts (protected with viable coating) to the field.
• These seeds have potential for short and medium term storage without losing viability.
• As compared to plantlets, it is easy to handle and tranport synthetic seeds.

Disadvantages

Though this technology sounds promising, it has some demerits as well. Let us discuss them briefly:

• Somatic embryos have low survival rates for most plant species, which also limits the value of synthetic seeds.
• There are not many protocols available to produce propagules from different plant parts using plant tissue culture methods. Hence less useful material available for producing synthetic seeds.
• In some cases, inefficient maturation of somatic embryos leads to poor germination and hence poor growth and development.
• According to scientists, somatic embryos from some plants species are not capable of germinating out of the capsule or coating. Hence, they are not able to form normal plants rapidly.
• The concentration of coating material is also a limiting factor for producing synthetic seeds. It should have nutrient supplementing materials for facilitating germination and growth.
• When the shape of synthetic seeds is not matching the farm machinery then it is hard to use them for transplantation. Hence, seeds should be transplantable.
• One of the major problems these seeds face is quick drying out of capsules. You need to store them in a humid environment and coat them with hydrophobic materials to prevent drying.

Synthetic seeds have promising applications. There is intensive research and development going on around the world for producing such seeds, especially for important crops. They can be transported easily from one country to another without any quarantine obligations. Hence, these seeds can definitely be an innovative way to increase global food production in the coming years.

We hope this article provides you a better understanding of the synthetic seed technology used in plant tissue culture. For more interesting articles, keep checking our space!

By Nancy Bhatia | 22-July-2021

References

• Bajaj, Y. P. S. (1995). Somatic Embryogenesis and Its Applications for Crop Improvement. Somatic Embryogenesis and Synthetic Seed I, 105–125. DOI:10.1007/978-3-662-03091-2_8.
• Bhojwani S. S. and Razdan M. K. (1983). Plant Tissue Culture: Theory and Practice. Elsevier publications.
• Hussein, S., Ibrahim, R., Ling Pick Kiong, A. (2006). Somatic Embryogenesis: An Alternative Method for in vitro Micropropagation. Iranian Journal of Biotechnology, 4(3), 156-161.
• Zimmerman Lynn J. (1993). Somatic Embryogenesis: A Model for Early Development in Higher Plants. The Plant Cell, 5, 1411-1423.
• Faisal, M., & Alatar, A. A. (Eds.). (2019). Synthetic Seeds. DOI:10.1007/978-3-030-24631-0