Cellular totipotency is the inherent potentiality of a plant cell to give rise to a whole plant, a capacity that is retained even after a cell has undergone final differentiation in the plant body. It refers to the ability of many cells to retain the full genetic potential characteristic of the mature organism from which any of the cells were obtained, and thus enable the cell to regenerate the organism’s tissues and organs under favorable conditions.
The process of specializing cells’ functions is called cell differentiation . It is accompanied by morphogenesis, the change of the cells’ morphology. Differentiation is done by turning on certain genes and turning off some others at a certain time. Therefore, for a highly differentiated cell to grow into a full plant, the differentiation process has to be reversed (called dedifferentiation) and repeated again (called redifferentiation). Theoretically, all living cells can revert to an undifferential status through this process. However, the more differentiated a cell has been, the more difficult it will be to induce its dedifferentiation.
When a piece of differentiated tissue from a plant is cultured on a nutrient medium, the mature and non-dividing cells undergo dedifferentiation to transform into meristematic cells. These dividing cells of callus then redifferentiate to form an entire plant if provided with suitable nutritional and hormonal requirements. Practically, the younger or the less differentiated a cell is, the easier to culture it into a full plant. The ease of fulfilling the cell totipotency also varies tissue by tissue, genotype by genotype and species by species. Tissue culture techniques offer an excellent opportunity to study the factors that elicit the totipotentiality of cells, and allow the investigation of factors controlling cytological and histological differentiation.