Q.
If a part of pith from the stem of a plant is used as an explant and cultured on nutrient medium, which of the following processes is responsible for the formation of an undifferentiated mass of cells called callus ?
The portion of pith taken as an explant comprises of parenchymatous cells (i.e., simple permanent tissue which have lost the capacity to divide). When such cells are cultured on solid culture media, the parenchymatous cells of pith become meristematic and start dividing resulting in a mass of undifferentiated cells called callus. This is an example of dedifferentiation. These cells may be made to divide in different manners in order to produce different organs so that the meristematic cells of callus may become permanent tissues by the process of redifferentiation. For example, treatment of certain hormones may lead to the differentiation of shoot buds or roots.