Hormone antagonist to gibberellins is

Options

A. IAA
B. ABA
C. Zeatin
D. Ethylene.

Answer

**Step-by-Step Solution:**

1. **Understanding Gibberellins**: Gibberellins, specifically gibberellic acid (GA), are plant hormones produced in the embryo and young leaves. They play a crucial role in promoting growth and delaying senescence (aging) in plants.

2. **Identifying Antagonistic Hormones**: To find the hormone that acts as an antagonist to gibberellins, we need to look for a hormone that has opposing effects on plant growth.

3. **Introduction to Abscisic Acid (ABA)**: Abscisic acid (ABA) is a naturally occurring growth inhibitor found in a variety of plants. It is synthesized in the leaves and is known to promote senescence and cause the fall of leaves.

4. **Contrasting Effects of Gibberellins and ABA**: Gibberellins are known to break seed dormancy and promote growth, while ABA induces dormancy in seeds and promotes leaf senescence. This makes ABA an antagonist to gibberellins due to their opposing functions.

5. **Evaluating Other Hormones**: Other hormones like Indole-3-acetic acid (IAA), cytokinins (like zeatin), and ethylene do not serve as antagonists to gibberellins. IAA is an auxin that promotes growth, zeatin is a growth hormone, and ethylene is a gaseous hormone that also promotes ripening and senescence but is not directly antagonistic to gibberellins.

6. **Conclusion**: Based on the understanding of the roles of these hormones, the correct answer to the question of which hormone acts as an antagonist to gibberellins is **Abscisic Acid (ABA)**.

**Final Answer**: The hormone antagonist to gibberellins is **Abscisic Acid (ABA)**.

---