Practice question

Somaclonal variation denotes phenotypic and genetic variability observed among plants regenerated from somatic cells in tissue culture, term introduced by Larkin and Scowcroft 1981 to describe variation in clones derived from same explant. Unlike seed derived variation, somaclonal variation originates from stress imposed by in vitro environment high concentrations of synthetic auxins especially 2,4-D, rapid cell cycles, oxidative burst from autoclaved medium components, and epigenetic reprogramming during dedifferentiation redifferentiation. Underlying mechanisms include point mutations due to error prone DNA repair, transposable element mobilization such as activation of Tos17 retrotransposon in rice callus, chromosome aberrations aneuploidy polyploidy translocations due to spindle failures, and altered DNA methylation patterns affecting gene expression without sequence change. Phenotypically manifests as changes in plant height, leaf shape, flowering time, yield components, disease resistance or metabolite profile. While undesirable when clonal fidelity required for micropropagation of elite genotypes, variation is exploited as source of novel useful traits generating new cultivars like sugarcane with Fiji disease resistance and tomato high lycopene lines selected from tissue culture derived population without transgenic intervention.