Question

In callus culture, roots can be induced by the supply of:
A. Auxin
B. Cytokinin
C. Gibberellin
D. Ethylene

Answer 1

Auxin is one of the growth hormones. It regulates growth of the plant. Auxin is produced inside the root tips and helps in root initiation.

Complete answer:
To solve the question, we must first know about the various plant hormones and their functions.
Callus culture is a tissue culture technique in which an entire plant grows from a cell or a tissue in vitro, i.e. inside a test tube. The cell is kept in a nutrient-rich medium. Sufficient growth hormones are required for the root and shoot initiation.

Additional Information:
Cytokinin enhances the process of cell division, delays senescence and initiates flowering. It promotes germination.
Ethylene is known to break dormancy, inhibit root elongation and plays a vital role in the ripening of fruits.
Gibberellin aids in cell elongation. It induces parthenocarpy ( The process in which the fruit develops without fertilization). Auxin is used for the root initiation while cytokinin is used for the shoot initiation.

Hence, the correct answer to this question is auxin.

Note: Other uses of Auxins are:

Auxin is used for cell elongation.
Apical Dominance- Apical buds suppress the growth of the lateral buds. This phenomenon is known as apical dominance. So to initiate the growth of lateral buds, the apical buds are removed. This process can be reversed if auxin is applied to the apical buds.
Abscission-Abscission is the process by which the leaves, fruits, and flowers get detached from the main plant. When the concentration of auxin in the plants decreases abscission takes place. Auxin prevents abscission.
Auxin prevents flowering.
Auxin slows down the process of senescence (ageing).