Somaclonal Variation, Micropropagation and Tissue Culture -

We described the different media used for cell/tissue culture, and also discussed culture of individual differentiated cells. However, in plant tissue culture experiments, unless single cell cultures are absolutely necessary, more often we use explants (pieces of differentiated tissues) to initiate their growth in culture.

This is also necessary to obtain callus from which single cell cultures are derived. During the last few decades, even for development of new crops or for improvement in the characteristics of existing crops (e.g. to obtain disease free crop, etc.), the techniques of tissue culture in combination with genetic manipulation have become important tools.

These two phenomenons of dedifferentiation and redifferentiation are inherent in the capacity described as cellular totipotency, a property found only in plant cells and not in animal cells.In other words, while a differentiated plant cell retains its capacity to give rise to a whole plant, an animal cell loses this capacity of regeneration after differentiation.

Although, generally a callus phase is involved before the cells can undergo redifferentiation leading to regeneration of a whole plant, but rarely the dedifferentiated cells can give rise to whole plants directly without an intermediate callus phase. These aspects of tissue culture and its application in clonal propagation and in the general on of hereditary variation called somaclonal variation.