The following points highlight the four significances of callus culture. The significances are: 1. Source of Tissue for Plant Regeneration 2. Source of Chromosomal Variation (Somaclona) Variation) 3. Source of Secondary Metabolites 4. Source of Tissue for Cell Suspension Culture.
Significance # 1. Source of Tissue for Plant Regeneration:
Callus tissue is a good source of experimental tissue material from which whole plant can be regenerated by changing the nutrient and hormonal constituents in the culture medium. This kind of plant regeneration is known as organogenesis.
Again by manipulation of hormonal constituents in the medium the cells of calli can be transformed into embryonal mass and the whole plant can be regenerated from those somatic embryos, the process known as somatic embryogenesis.
Significance # 2. Source of Chromosomal Variation (Somaclona Variation):
Chromosomal variation may occur genetically or epigenetically in the cells of callus tissue. If the explant contains the meristematic tissue then ordinary diploid cell mass develops. But endoreduplication is a natural phenomenon in the cells of permanent tissue as they remain in mitotically blocked condition, as a result when these cells, are stimulated to divide the callus tissue may have such genetically variable cells.
By serial sub- culturing the number of diploid or polyploid cells may increase or decrease in number, and after prolonged sub-culturing only one karyotype get established. If the polyploid cells are mostly found in the callus then the polyploid plant can be obtained through the process of regeneration. Again if callus tissue is derived from the haploid cells (such as microspore) then the haploid plants can also be obtained.
Significance # 3. Source of Secondary Metabolites:
If any of the medicinally important secondary metabolite is available from certain type of tissue material of a particular plant then that tissue material may be used as explants to get the callus tissue.
The particular secondary metabolite can be obtained by extraction of that particular callus tissue. This process can reduce the time and expenditure as it does not need to have the whole plant cultivation and sacrificing it from extraction.
Significance # 4. Source of Tissue for Cell Suspension Culture:
When the callus tissue is of friable and soft type then the cell suspension culture can be initiated by culturing the callus tissue in liquid medium, continuously agitated by moving in rotatory shaker. More friable callus tissue is an ideal material for the dispersion of cells. As cell division occurs in the callus tissue the cells on the surface layer shed off and disperse in the medium.
Here also the produced secondary metabolite may leach out in the medium and can be obtained from the medium by distillation. Cell suspension culture is useful in the cell plating technique to develop single cell culture which is important in the production of mutant cell lines and exploitation of somaclonal variation.