what is callus in tissue culture
Callus in tissue culture is an unorganized, actively dividing mass of undifferentiated plant cells that forms from an explant (a piece of plant tissue) when it is grown on a nutrient medium with specific plant hormones under sterile conditions.
What is callus in tissue culture?
In plant tissue culture, callus is usually a soft, whitish to green, amorphous lump of cells that does not yet look like any normal plant organ (no clear roots, stems, or leaves).
It arises when plant cells at a wound site or in an explant start dividing in an unorganized way in response to growth regulators like auxins and cytokinins added to the culture medium.
Key points:
- Callus is a mass of undifferentiated or disorganized parenchyma cells.
- It is induced in vitro from explants such as leaf, stem, or root pieces placed on nutrient agar medium.
- Hormone balance (auxin/cytokinin ratio) largely controls whether callus forms and how it behaves.
Why is callus important in tissue culture?
Callus is central to many plant biotechnology techniques because its cells are often totipotent , meaning each cell can potentially regenerate into a whole plant under the right conditions.
Uses of callus in tissue culture:
- Plant regeneration and micropropagation (regenerating whole plants from a small tissue piece).
- Genetic transformation experiments (introducing new genes into callus, then regenerating plants).
- Production of valuable secondary metabolites in vitro (e.g., medicinal compounds) using callus or derived cell suspensions.
- Studying cell differentiation, somaclonal variation, and plant development pathways.
Types and characteristics of callus
In practice, different kinds of callus can appear depending on plant species, medium, and culture conditions.
Common types:
- Friable callus: Soft, crumbly, easily broken into small pieces, ideal for liquid cell suspension culture.
- Compact callus: Harder, densely packed cells, often used for organogenesis and plant regeneration.
- Nodular callus: Contains small organized nodules resembling meristems, often a good sign for shoot or embryo formation.
Typical features:
- Color can range from white or cream to green, yellow, or brown, influenced by species, age, and medium.
- Texture may be soft and watery or hard and dry, which can correlate with regeneration potential.
Quick FAQ style recap
- Simple definition (exam style):
Callus in tissue culture is an unorganized, actively dividing mass of undifferentiated plant cells produced from an explant on artificial nutrient medium containing plant growth regulators.
- Where does it come from?
Usually from wound sites or cut surfaces of explants like leaf discs, stem segments, or root pieces cultured in vitro.
- Why do we induce callus first?
Because once callus is formed, we can redirect it (by changing hormones and conditions) to form shoots, roots, or somatic embryos and regenerate complete plants.
TL;DR: In plant tissue culture, callus is the unorganized, undifferentiated cell mass you first grow from an explant on hormone- containing medium, which then serves as the starting material for regenerating whole plants or producing useful compounds.