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#callus

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Plant tissue culture 3

Friable callus is mainly used to initiate:

Texture of callus determines suitability for liquid systems. Compact nodular callus consists of tightly packed cells cemented by calcium pectate, resistant to dispersal. Friable type arises when pectin methylesterase activity reduces middle lamella cohesion, producing crumbly masses of loosely associated, highly vacuolated cells with large intercellular air spaces. Upon transfer to agitated liquid Murashige-Skoog medium containing 2,4-D, these fragments break easily into single cells and small aggregates under 100 micrometer diameter, forming homogeneous suspension. Such suspensions exhibit exponential growth, uniform nutrient uptake, and amenability to sieving and plating for single-cell cloning. They serve as source for protoplast isolation and bioreactor inoculum. Compact embryogenic callus retains cohesion and yields poor suspensions. Hence friable callus is specifically maintained and multiplied to initiate cell suspension cultures essential for secondary metabolite production and large-scale propagation. Size distribution analysis via hemocytometer shows friable callus yields high proportion of viable small clusters. Sieving through 250 micrometer mesh enriches for embryogenic units initiating suspensions. Maintenance requires regular subculture of friable clumps to prevent compacting. This physical property exploited in scale-up for bioreactor inoculum and somatic embryogenesis induction protocols.

Ref: Murashige & Skoog 1962 friable callus; Street Plant Tissue 1977 suspension initiation; Dodds & Roberts Experiments 4th ed; NCBI NBK26844 cell suspensions texture importance.

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Plant tissue culture 1

Callus is best defined as:

Callus is unorganized proliferation of dedifferentiated parenchymatous cells produced in response to wounding or exogenous hormone application in vitro under sterile conditions. When explant such as leaf segment, stem internode, or cotyledon is placed on Murashige and Skoog medium supplemented with balanced auxin like 2,4-D and cytokinin BAP, mature cells dedifferentiate and divide mitotically forming amorphous mass of thin-walled, vacuolated, isodiametric cells lacking organized meristems, vascular pattern, or polarity initially. Callus growth reflects loss of positional information and continuous cell cycle driven by phytohormone signaling activating auxin response factors and cell cycle genes. It appears cream, friable, or compact depending on genotype and conditions and auxin concentration. Though disorganized, callus retains totipotency and can be induced to redifferentiate into shoots via high cytokinin or roots via high auxin, or embryos via somatic embryogenesis. Callus serves as platform for somaclonal variation generation, genetic transformation, secondary metabolite accumulation, and micropropagation cycles for mass production of uniform planting material.

Ref: Bhojwani SS & Razdan MK. Plant Tissue Culture – callus definition. George EF et al. Plant Propagation – unorganized mass

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