Zygotic Seed

 Somatic Embryogenesis:

Somatic embryos are treated as seeds if they fulfill all the conditions of a seed. Different scientists work on it they apply different allegations to it so, that we can apply the idea of Murashige. Scientists give two different gels agarose, gel right, or phytagel. These chemicals can be used in gel formation during protein or DNA analysis.

To start, scientists take microtiter plates having small wells or PCR plates. In this plate, they take agarose and melt it in distilled water. They do not solidify agarose at room temperature when the temperature of agarose is 35 to 40 degree range (near polymerization on gel formation). They add somatic embryos in gel when polymerization is complete somatic embryos are packed in gel.

Drawback:

• Agarose, gel right, or phytagel do not maintain their property for a long period. So, this is not the best technique. Agarose remains at room temperature for 48 hours after it is dry.

After this scientists try to find an alternative to this so, that they can synthesize the synthetic seed and the gel that can maintain itself for long-term storage and also have nutrients for growing embryos.

Synthetic seed

For this purpose, scientists used different chemicals like Sodium alginate (2^o/^o sodium solution) for the best synthetic seed production. To make the best synthetic embryos from callus or explant place them in suspension culture (liquid MS medium or distilled water) and centrifuge it at 100 to 150 rpm gradually shake it. Somatic embryos are separated from it.

Take forceps and pick a somatic embryo from it. Take 2 Percent sodium alginate solution in a beaker. In another beaker take (CaCl₂ or Ca (NO₃) Calcium nitrate solution. On one hand, take the somatic embryo with the help of forceps, and on the other hand, take sodium alginate drop from the micropipette.

Press the micropipette in such a way that a drop of sodium alginate falls on the somatic embryo. So, the drop accumulates around the embryo like a drop of water fell on something.

With the help of forceps the embryo is placed in Ca (NO₃) solution. In 4 to 5 minutes or a maximum of 10 minutes 2 percent sodium alginate drop reacts with calcium nitrate ultimately drop is converted into a gel-like structure.

After 5 to 10 minutes place it out from the calcium nitrate solution then place it on blotting paper and dry it at room temperature. In the centrifuge machine agitate the somatic embryos so, that the extra moisture in the somatic embryos is absorbed (decicate or dehydrate embryos). If the embryos are not dehydrated water in embryos destroys the sodium alginate conc. which is also in small quantity.

Storage of synthetic seed for a long time:

Synthetic seed can be used for a long time then mixed sodium alginate with MS-medium rather than mixing sodium alginate with water. Then drop of sodium alginate falls on somatic embryos and is placed in a Ca (NO₃)₂ solution. So, after 10 minutes synthetic seed is formed to resemble with zygotic seed.

(In-vitro Condition) The somatic embryo is used to regenerate a plant in a test tube.

(In-vivo Condition) For some time you do not have an In-vitro facility. So, you have to make gel completion around somatic embryos form simply grow it in a pot. So, the synthetic seed is used to make plants. For this purpose sterilized sand or a mixture of soil and sand for growing plants.

Difference between Zygotic seed and Synthetic Seed:

Zygotic Seed	Synthetic Seed
1. Dormancy time or dormancy break is involved.	There is no dormancy.
2. It is natural. It is formed after fertilization.	There is no fertilization. It is artificial.
3. Gametes formation is involved.	No gametes formation is involved.
4. There is variation in zygotic seed.	True two type seed is formed.

 

Why do we make Somatic Embryos/ Synthetic Seed?

1.   For long-term storage, desiccation is required.

2.   Coating by hydrated gel or by agarose gel.

3.  We can also form somatic embryos without desiccation during it is coating.

Types of Synthetic Seed:

Based on quality, there are four types of synthetic seed.

1.     Un-coated desiccated somatic seed:

The simple somatic embryo in which we use desiccation, coating of hydrated gel sodium alginate, and Ca (NO₃) is used.

2.     Coated desiccated seed:

In this, we use MS-medium instead of water during coating.

3.     Encapsulated Coated Hydrated embryo:

In this type there is no desiccation is used.

4.     Encoated hydrated Embryos:

For long-term use, we use these embryos.

Importance of Synthetic Seed:

1. When we use zygotic seed we do not attain a uniform crop and we do not assure about our yield of the crop.

For example:

In the case of sugarcane if we use zygotic seed we do not know about several sugarcane, the size of sugarcane. So, then we use vegetative propagation. In vegetative propagation, we make pieces of sugarcane. This is difficult so, you can make or take a small portion of any plant from the somatic embryo and then you can form a synthetic seed. These are true two types of plants.

2. Its transportation is very easy.

For example:

Some crops like potatoes are imported from Holand in Pakistan and their transportation is very costly due to the high weight of potatoes. In the case of synthetic seeds, we can transport millions of synthetic seeds in a small box very easily with a small transportation cost.

3. In micro-propagation, we require the hardening of plants. In synthetic seed formation, we do not require hardening we directly germinate seed in a pot.

4. Zygotic seed is available in a specific season e.g. Wheat seed is available in May and April. Synthetic seeds can be formed during the whole year or around the clock. There is no dormancy in synthetic seed.

5. There is no endosperm, cotyledon, or testa in synthetic seed. The somatic embryo is directly formed from somatic cells. While a zygotic cell embryo is formed after fertilization. We understand the importance of cotyledon and testa by a comparative study of both synthetic seeds (do not contain testa) and zygotic seeds (contain testa).

Testa:

The protective covering around the zygotic embryo is called the Testa.