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Somatic fusion

life science Maturity 9-11 Next article →

Somatic fusion, also known as protoplast fusion, is a method of genetic modification. It involves joining two distinct plant species together to create a new hybrid. This hybrid is called a somatic hybrid. These new plants possess characteristics from both original parents. This process is a powerful tool in biotechnology. It allows scientists to overcome natural barriers that prevent different species from breeding sexually.

Protoplast fusion
Protoplast fusion

The process for plant cells follows a specific four-step sequence. First, scientists use an enzyme called cellulase to remove the cell wall. This leaves behind a single cell known as a protoplast. Next, the protoplasts are joined together. This can be done through chemical treatment or an electric shock called electrofusion. When the nuclei of the cells join, the resulting structure is called a heterokaryon. Third, scientists use hormones to induce the formation of a new cell wall. Finally, the cells grow into clumps called calluses. These calluses eventually develop into plantlets and then into full somatic hybrid plants.

Different organisms require different methods during this process. For example, moss protoplasts behave differently than seed plants. Moss protoplasts do not require phytohormones for regeneration. They also do not form a callus. Instead, regenerating moss protoplasts act like germinating moss spores. While seed plants often use electric shocks, moss protoplast fusion can be initiated using polyethylene glycol, or PEG. Other substances like calcium ions at a high pH can also be used, though results vary by organism.

Somatic fusion was first introduced by Carlson and his colleagues. They conducted their initial work using a plant called Nicotiana glauca. Since that discovery, the technology has expanded to many different species. Scientists have successfully fused various plants, such as oats with maize. They have also performed fusions between different types of Brassica. Some researchers have even fused Torenia fournieri with Torenia flava. These successes demonstrate the wide range of botanical possibilities.

A major use for this technology is improving agriculture. For instance, the crop potato, Solanum tuberosum, suffers from a viral disease. This disease is spread by an aphid vector and reduces crop yields. Scientists can fuse this potato with Solanum brevidens. This is a wild potato that does not bear tubers but is resistant to the disease. The resulting hybrid contains the chromosomes of both plants. It is similar to polyploid plants, which have multiple sets of chromosomes. Another famous example is the Pomato. This is a hybrid created by fusing a potato with a tomato. The Pomato exhibits characteristics from both parent plants.

Beyond plants, somatic fusion is used in human and animal cell research. Scientists often fuse human fibrocytes or leucocytes with mouse cell lines. Spontaneous fusion between these species occurs at a very low rate of 10 to 6. To increase this, researchers add inactivated Sendai virus or PEG. These agents adhere to the plasma membranes to facilitate fusion. This is used for chromosome mapping. If a specific trait appears only when a human chromosome is present, scientists can locate the gene on that chromosome.

Protoplast fusion
Protoplast fusion

This method is also vital for medical research and studying cell behavior. It helps scientists investigate how cells divide and how genes are expressed. It can also be used to study malignant transformations or viral replication. One important application is the production of monoclonal antibodies. This is achieved by creating a hybridoma. A hybridoma is a cell formed by fusing an antibody-producing lymphocyte with an immortalized cell.

Protoplast fusion
Protoplast fusion

To isolate these specific hybrid cells, scientists use a selective medium called HAT medium. This medium contains hypoxanthine, aminopterin, and thymidine. The aminopterin blocks the biosynthesis of purines and pyrimidines. However, hybrid cells can survive by using a salvage pathway. This pathway recycles these necessary components. To ensure only hybrids grow, scientists use cells with specific enzyme deficiencies. For example, they might use human cells lacking the HGPRT enzyme and mouse cells lacking the TK enzyme. The resulting hybrid will have both functional enzymes and will be the only cell type able to multiply on the HAT medium.

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