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The below mentioned article provides a study note on totipotency.
Cellular Totipotency:
Though Haberlandt was able to culture isolated cells but failed to induce division in vitro. The culture of embryogenic tissue by Hannig (1904) and root-tip culture by Kotte and Robbins (1922) helped in solving the problems of cell divisions in in vitro conditions. During the period of 1934-1954, the main focus was the development of callus from different kind of explants.
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The two main aspects of plant tissue culture are:
1. Multiplication of a single cell in vitro.
2. Development of a whole plant from proliferated tissue of this cell.
Various experimental studies on single cell culture and cell suspension culture; development of cell mass and then induction of somatic embryogenesis from carrot suspension culture contributed to the establishment of the concept of totipotency of somatic cells under experimental conditions.
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The technique of cloning isolated single cells in vitro has demonstrated the fact that somatic cells, under appropriate conditions, can differentiate to a whole plant. This potential of a cell to grow and develop a multicellular or multiorganed higher organism is termed as cellular totipotency.
In plant tissue culture, more often an explant (an excised piece of differentiated tissue or organ) is used to initiate their growth in culture. The non-dividing differentiated quiescent cells of the explant, when grown on a medium, first undergo changes to achieve the meristematic state.
The phenomenon of mature cells reverting to a meristematic state and forming undifferentiated callus tissue is termed as dedifferentiation. The ability of the component cells of the callus to differentiate into a whole plant or a plant organ is termed as re-differentiation.
These two phenomena of dedifferentiation and re-differentiation are the inherent property of plant cell i.e., the potential lies within the genes which remain inactive in differentiated tissues or organs and are able to express only under adequate cultural conditions (Fig. 16.1).
In animals, the differentiation is irreversible. This is in contrast to plants where even highly mature or differentiated cells have the ability to regress to a meristematic state as long as they are viable. Tissue culture techniques offer an excellent opportunity to study factors responsible for differentiation of cells. These factors control cellular totipotency through cytological, histological and organogenic differentiation.
