Question

Two hormones required for a callus to differentiate are

• A. Auxin and cytokinin
• B. Auxin and Abscisic acid
• C. Ethylene and Auxin
• D. Cytokinin and gibberellin

Hint:

The Skoog-Miller model of hormonal control remains a fundamental principle used in plant tissue culture to regenerate complete, transgenic plants from transformed cell lines.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Plant tissue culture relies on totipotency, which is the inherent ability of plant cells to regenerate into complete plants.
Differentiating an unorganized mass of cells (callus) into organized shoots or roots (organogenesis) is controlled by plant growth regulators.

Step 2: Detailed Explanation:
In 1957, Folke Skoog and Carlos Miller published a landmark discovery showing that organogenesis in plant tissue culture is controlled by the ratio of two plant hormones: Auxin and Cytokinin.
By adjusting the relative concentrations of these two hormones in the growth medium, researchers can control plant differentiation:
- High Auxin to Cytokinin ratio: This hormonal balance promotes root development (rhizogenesis) from the callus.
- High Cytokinin to Auxin ratio: This hormonal balance promotes shoot development (caulogenesis) from the callus.
- Balanced Auxin and Cytokinin ratio: This hormonal balance promotes continuous, unorganized cell division, maintaining callus growth without differentiation.
The other hormones listed (abscisic acid, ethylene, gibberellin) play secondary roles in seed dormancy, senescence, and stem elongation, but are not the primary regulators of callus differentiation.

Step 3: Final Answer:
The two hormones required for a callus to differentiate are auxin and cytokinin, corresponding to option (A).