Q.How is 'somatic hybridization' carried out ? Mention one example of a somatic hybrid.
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Start your 14-day free trial to unlock the full solution →Somatic hybridization fuses protoplasts from two different plant species to create a hybrid cell that regenerates into a complete plant; a classic example is Pomato (potato + tomato).
The concept behind somatic hybridization
Sexual reproduction has natural barriers—two species often cannot cross-breed because their gametes are incompatible or their chromosomes refuse to pair. Somatic hybridization bypasses sexual reproduction entirely by fusing ordinary body cells (somatic cells) from two different plants. The technique exploits the remarkable totipotency of plant cells: a single somatic cell, if given the right conditions, can regenerate into a whole organism.
The key insight is that once you strip away the rigid cell walls, the naked protoplasts (cells without walls) can be induced to merge, pooling the genetic material of both parents into one hybrid cell. This hybrid then grows into a plant carrying traits from both species—something sexual crossing could never achieve.
Step-by-step procedure
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Isolation of protoplasts
Treat leaf tissue or other plant parts with cell-wall-degrading enzymes—typically cellulase and pectinase. These enzymes digest the cellulose and pectin, releasing protoplasts (spherical cells bounded only by the plasma membrane). The protoplasts are then washed and suspended in an isotonic solution to prevent bursting.
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Fusion of protoplasts
Mix protoplasts from the two parent species and induce fusion using one of these methods:
- Chemical fusion: Polyethylene glycol (PEG) in high concentration destabilizes the membranes, causing adjacent protoplasts to fuse.
- Electrofusion: Brief electric pulses align the protoplasts and create transient pores in their membranes, allowing cytoplasmic continuity and fusion.
Not every protoplast fuses; you get a mixture of unfused cells, self-fused (homokaryons), and heterokaryon hybrids (the desired product containing nuclei from both parents).
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Selection of hybrid cells
Use selective culture media or genetic markers to identify and isolate true heterokaryons. For instance, if one parent is resistant to antibiotic A and the other to antibiotic B, only hybrid cells survive on medium containing both A and B.
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Culture and regeneration
Plate the selected hybrid protoplasts on nutrient medium supplemented with plant hormones (auxins and cytokinins). The protoplasts first regenerate their cell walls, then divide to form callus (an undifferentiated mass). With the right hormone balance, the callus differentiates into shoots and roots, eventually forming a complete plantlet.
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Hardening and transfer
Acclimatize the regenerated hybrid plant to soil conditions. The resulting somatic hybrid carries the combined genome of both parents—often tetraploid or aneuploid because both diploid nuclear genomes are retained.
Protoplast fusion is especially powerful for overcoming sexual incompatibility between species that belong to different genera or even families, something conventional breeding cannot do.
Example of a somatic hybrid …
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