Question

Which plant hormone is mainly responsible for apical dominance?

• A. Cytokinin
• B. Gibberellin
• C. Abscisic acid
• D. Auxin

Hint:

Removal of the apical bud reduces auxin levels and allows lateral buds to grow.

Answer 1

The Correct Option is D

Let's discuss the role of plant hormones and understand which one is mainly responsible for apical dominance.

Apical dominance is a phenomenon where the main, central stem of a plant grows more strongly than other side stems or branches. This occurs due to the influence of plant hormones that regulate growth patterns.

The major plant hormones involved in growth and development are:

• Cytokinin: This hormone promotes cell division and growth in plant shoots and leaves, and can delay leaf senescence. It tends to promote growth in branches.
• Gibberellin: It promotes stem elongation, seed germination, and flowering but is not primarily associated with apical dominance.
• Abscisic acid: This hormone is mainly involved in stress responses, such as closing the stomata during drought, and doesn't play a significant role in apical dominance.
• Auxin: This hormone is primarily responsible for promoting cell elongation and is found in higher concentrations at the apical bud. It suppresses the growth of lateral (side) buds, maintaining apical dominance.

Conclusion: The hormone Auxin is mainly responsible for apical dominance. It is produced in the apical bud and inhibits the growth of lateral buds, thus ensuring that the central stem grows predominant over other potential shoots.

Answer 2

Step 1: Understanding apical dominance.
Apical dominance is a phenomenon in plants where the growth of lateral (side) buds is inhibited by the presence of the apical (terminal) bud. This ensures that the plant grows vertically rather than branching excessively.
Step 2: Role of plant hormones.
Plant hormones regulate growth and development. Different hormones control different physiological processes such as cell elongation, dormancy, and branching.
Step 3: Hormone responsible for apical dominance.
Auxin is produced in the apical bud and is transported downward through the stem. High concentrations of auxin suppress the growth of lateral buds, thereby maintaining apical dominance.
Step 4: Analyzing the options.
(A) Cytokinin: Cytokinins promote lateral bud growth and counteract apical dominance.
(B) Gibberellin: Gibberellins mainly promote stem elongation and seed germination.
(C) Abscisic acid: Abscisic acid is associated with dormancy and stress responses.
(D) Auxin: Correct — Auxin inhibits lateral bud growth and maintains apical dominance.
Step 5: Conclusion.
The plant hormone mainly responsible for apical dominance is auxin.