Question

Apical dominance is mainly caused by:

• A. Cytokinin
• B. Gibberellin
• C. Auxin
• D. Ethylene Correct Answer: (C) Auxin

Hint:

To easily remember this for your botanical exams, associate Auxin with the Apex! Since Auxin is made at the Apex, it rules over the rest of the plant stem, enforcing Apical dominance. If you want a plant to grow wide instead of tall, chop the apex off to break the spell!

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
In many vascular plants, the growing terminal apex (the absolute top shoot tip) exerts a powerful inhibitory control over the development of lateral or axillary buds located further down the stem. This physiological phenomenon is called apical dominance. Because the main central stem grows much faster and suppresses the side branches, the plant takes on a tall, conical, Christmas-tree-like structural shape.

Step 2: Detailed Explanation:
Let's look at the hormonal mechanism that drives this process: 1. The terminal shoot apical meristem actively synthesizes high concentrations of the plant hormone Auxin (primarily Indole-3-acetic acid, or IAA). 2. Due to gravity and specialized cellular transport proteins, this auxin flows downward along the main stem axis. 3. The continuous downward flow of auxin triggers specific biochemical pathways that actively suppress the growth of axillary buds, keeping them dormant. 4. If a gardener trims away the terminal tip (decapitation), the primary source of auxin is removed. With auxin levels dropped, the lateral buds are released from dormancy and begin dividing rapidly, causing the plant to grow bushy and dense. Therefore, apical dominance is directly maintained by auxin. This matches option (C).

Step 3: Final Answer:
Apical dominance is mainly caused by Auxin.