Question

Which of the following statements is true regarding callus formation in tissue culture?

• A. Callus formation takes place after the formation of a plantlet
• B. The cells of an explant divide meiotically to form a callus
• C. The callus formed gradually grows into a new plant without any special treatment
• D. The formation of callus requires the presence of growth hormones in the culture media

Answer 1

The correct option is D The formation of callus requires the presence of growth hormones in the culture media

Tissue culture is the technique of growing plant cells, tissues or organs in a sterile culture medium under controlled environmental conditions.

Callus is a mass of unorganized, undifferentiated and totipotent (the ability of a cell to develop into an entire organism) parenchymatous cells formed during the process of growing plants from vegetative parts of plants.

When auxins and cytokinins (growth hormones) are added to the culture media at intermediate concentrations, the cells of the explant are induced to undergo de-differentiation (losing their specialised character and become meristematic again).

These cells actively divide to form the callus by repeated mitotic divisions of the cells of the explant (plant parts, tissues or organs being cultured) when it grows within an aseptic culture media.

The callus can now be induced to develop into a plantlet through morphological changes (morphogenesis) to form specific plant organs (organogenesis). When the callus is treated with additional cytokinins, its cells undergo division as well as differentiation into tissues that form the shoot.

The young shoot is then treated with auxins to induce root formation. A tiny shoot with roots at its base is called the plantlet which when placed in a field, can grow into an entire plant.