Imagine we want to study how plants grow in space or create plants with super resistance to diseases. But growing full plants can be slow, space-consuming, and hard to control. This is where callus culture come in.
They allow us to grow plant cells in a lab under controlled conditions, making it easier to understand plant growth and manipulate plants for research or agricultural purposes.
These techniques are at the core of plant biotechnology, helping us produce medicines, improve crops, and conserve endangered species.
Table of Contents
What is Callus Culture?
A callus is a mass of undifferentiated plant cells that grow on a solid medium, often initiated by wounding a plant or using specific plant hormones.
In callus culture, we take small pieces of plant tissue and grow them on a nutrient-rich medium in a lab. These cells multiply, forming a clump, which we can manipulate for further studies or regeneration into a full plant.
Explants tissue can be : roots, stem, leaves, flowers etc.
Factors important for the formation –
- Hormons – Auxin alone, Cytokinin alone or Both
- Genotype,
- Composition of nutrient medium,
- Physical growth factors (light etc.)
- Types of Sugar source (glucose or sucrose)
Different characteristics of callus
Callus tissue induced form different plant species may be different in structure and growth habit :
- White or colored
- Soft (watery) or hard
- Friable (easy to separate)
- Compact
Initiation and maintenance of Callus Culture
Starting a callus culture involves the following steps:
- Wash the seeds using water with few drop of detergent in a small vessel/container/beaker and shake.
- Submerge the seed into 70% alcohol for around 30-60 second and then discard the alcohol.
- Transfer the seeds to a flask or beaker containing 20-40% sodium hypochlorite for 15-20 min. Then rinse the seeds for 4-5 times with sterile distilled water.
- Transfer 2-3 seeds/flask on the surface of MS agar medium without growth regulators.
- Incubate the culture at 250C under photoperiod of 16 light (~1000 lux intensity) for 1-2 week.
- Collect the seedling aspectically (about 2 week old) and place them into sterile petri dish and prepare the explants.
- Excise shoot apex and inoculate them into nutrient medium (containing 1-2 mg/l Auxin)
- Incubate the cultures in dark at 250C for about 3-4 week.
- Check the growth and if require cut small pieces of callus and subculture on the same fresh medium.
Growth of Callus
Culturing of regularily new medium exhibit an S-shaped or sigmoid pattern of growth during each passae.
- Lag phase : cell prepare to divide
- Exponential phase : Highest cell division
- Linear phase: Slow division but increase cell expansion
- Deceleration phase : decrease division and elongation.
- Stationary phase : cell remain constant
Growth can be monitored by – Weigh measurements, color change or any irregularity, Mitotic index to reduce sample error.
Maintenance of Callus Culture
- Subculturing : Periodically transfer portions of callus tissue onto fresh nutrient media to promote continuous growth. Prevent overgrowth or browning by subculturing at optimal intervals.
- Monitoring: Regularly inspect cultures for contamination, changes in color, texture, and growth patterns.
- Adjustment of Growth Regulators : Modify concentrations of auxins and cytokinins in the medium to control growth and induce specific responses (e.g., organogenesis or embryogenesis)
Advantages of Callus Cultures
- Mass Production: Large quantities of undifferentiated cells can be generated quickly.
- Genetic Engineering: Callus tissue can be manipulated easily for introducing new genes, allowing the development of genetically modified plants with desirable traits (disease resistance, increased yield, etc.).
- Regeneration of Plants: Under the right hormonal conditions, a callus can regenerate into an entire plant, a process known as organogenesis.
- Conservation: Callus cultures help preserve rare and endangered plant species by allowing their propagation in vitro.
Limitations of Callus Cultures
- Loss of Differentiation: Over time, callus cells may lose their ability to differentiate into specific tissues (e.g., roots, shoots).
- High Contamination Risk: Cultures are prone to contamination by bacteria or fungi, especially during the transfer and sub-culturing steps.
- Cost: The setup and maintenance of sterile culture environments can be expensive.
Which hormones are used in tissue culture for callus induction?
The hormones used for callus induction in plant tissue culture are typically auxins (like 2,4-D) and cytokinins (like BAP). These can be used alone or in combination, depending on the specific needs of the culture.
What is callus culture in plant tissue culture?
Callus culture refers to the process of growing undifferentiated plant cells (callus) on a nutrient-rich medium under controlled lab conditions, often used for research, plant regeneration, or genetic modification.
How is the callus formed in the tissue culture technique?
Callus formation occurs when explants (like plant leaves, stems, or roots) are placed on a nutrient medium containing specific hormones, usually auxins and cytokinins. The plant cells respond by growing into a mass of undifferentiated cells known as callus.
What is the phenomenon that operates in the formation of root or shoot in a callus culture?
The phenomenon is called organogenesis, where specific hormones are adjusted to induce the formation of either roots (more auxins) or shoots (more cytokinins)
Increase amount of auxin in callus culture will promote which part of the plant tissue?
An increased amount of auxin in callus culture will promote root formation.
References
Pan Y, Li L, Xiao S, Chen Z, Sarsaiya S, Zhang S, ShangGuan Y, Liu H, Xu D. Callus growth kinetics and accumulation of secondary metabolites of Bletilla striata Rchb.f. using a callus suspension culture. PLoS One. 2020 Feb 19;15(2):e0220084. doi: 10.1371/journal.pone.0220084. PMID: 32074105; PMCID: PMC7029869.
Qahtan AA, Faisal M, Alatar AA, Abdel-Salam EM. Callus-Mediated High-Frequency Plant Regeneration, Phytochemical Profiling, Antioxidant Activity and Genetic Stability in Ruta chalepensis L. Plants (Basel). 2022 Jun 20;11(12):1614. doi: 10.3390/plants11121614. PMID: 35736765; PMCID: PMC9229613.
Lv S, Ding F, Zhang S, Nosov AM, Kitashov AV, Yang L. Induction and Suspension Culture of Panax japonicus Callus Tissue for the Production of Secondary Metabolic Active Substances. Plants (Basel). 2024 Sep 4;13(17):2480. doi: 10.3390/plants13172480. PMID: 39273964; PMCID: PMC11396918.