Callus (cell biology)

Light_callus_PV_5-30_gameto_callus_forming_5_x19.TIF

== Callus (cell biology) ==

A callus in cell biology refers to a mass of unorganized plant cells that are often formed in response to plant tissue culture techniques. Callus formation is a crucial step in plant regeneration and genetic engineering.

Formation

Callus formation typically occurs when plant explants (small pieces of plant tissue) are placed on a nutrient-rich culture medium containing plant hormones such as auxins and cytokinins. The balance of these hormones influences the type of growth that occurs. High auxin to cytokinin ratios generally promote root formation, while high cytokinin to auxin ratios promote shoot formation. An intermediate balance often leads to callus formation.

Applications

Callus cultures are widely used in plant biotechnology for various purposes:

• **Micropropagation**: Callus can be induced to form shoots and roots, leading to the production of whole plants.
• **Genetic transformation**: Callus tissues are often used as targets for gene transfer techniques, such as Agrobacterium tumefaciens-mediated transformation or biolistics.
• **Somatic embryogenesis**: Callus can differentiate into somatic embryos, which can then develop into complete plants.

Types of Callus

Callus can be classified based on its texture and appearance:

• **Friable callus**: Loose and crumbly, often used in suspension cultures.
• **Compact callus**: Dense and hard, typically used for organogenesis.

Challenges

One of the main challenges in working with callus cultures is maintaining their totipotency, the ability to differentiate into any cell type. Over time, callus tissues can become genetically unstable or lose their regenerative capacity.

See also

• Plant tissue culture
• Totipotency
• Somatic embryogenesis
• Micropropagation
• Genetic engineering