Protoplast Fusion is defined as the process of bringing about a fusion between protoplasts of two unrelated species of plants or animals. It is also known as somatic hybridization or parasexual hybridization because in this only somatic cells participate and it does not involve sexual fusion. In this technique, the naked cells after the removal of their cell walls by the use of enzymes are called protoplasts. The protoplasts of two cells from different species are brought in contact with each other to fuse in the presence of culture medium containing PEG factor (polyethylene glycol factor). The fusion product is called heterokaryon which is shifted to another culture medium having the differentiating capacity and after differentiation, the new hybrid is produced.
In 1965, it was for the first time, two scientists, H.Harris and J.F.Walkins of Oxford succeeded in making the cells from different animal species (mouse and man) to fuse to form hybrid cells. This was a revolutionary step in the world of genetics whereby crossing between unrelated cells from different animal species. But so far, we do not have any example of hybrid animals produced in this way because the animal cells fail to differentiate under culture conditions. But in the case of plants, we have two examples of interspecific hybrids, between two different species of tobacco and petunia. Recently, the fusion of plant protoplast and animal protoplast has been reported. Most interesting is the fusion between human cells and carrot protoplasts. It will be a most wonderful event if the plant components of this hybrid bring about differentiation.
The protoplast fusion technique is a new tool in the plant breeders. It is hoped that it will open up the possibility of overcoming the sexual barriers and of mixing and reassorting the genetic elements of incompatible and sexually isolated organisms. It has provided a field for the genetic manipulation of plants. For example- a fusion between green and a non-green cell to introduce the effect of autotrophic nutrition in heterotrophic plants.
Uses of Protoplast Fusion:
Somatic hybridization is the production of hybrids which are useful for introducing genes for male sterility and herbicidal resistance.
It produces genetic variability even in vegetatively propagated plants.
It produces rare hybrids which are rich in quality, food and economic products.
It overcomes the natural process of sexual barrier and it fuses the genetic elements of sexually isolated organisms.