Stomatal closure in response to leaf stress is mediated by

Options

A. IAA
B. IBA
C. ABA
D. 2,4-D

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks which hormone mediates stomatal closure in response to leaf stress. Stomata are small openings on the leaf surface that regulate gas exchange and water loss.

2. **Identifying the Hormones**: The options given are IAA (Indole-3 Acetic Acid), IBA (Indole Butyric Acid), ABA (Abscisic Acid), and 2,4-D (2,4-Dichlorophenoxyacetic Acid).

3. **Analyzing IAA and IBA**:
- IAA and IBA are both types of auxins, which are plant hormones primarily involved in growth processes such as apical dominance, xylem differentiation, and parthenocarpy.
- They are not known to play a significant role in stomatal closure.

4. **Analyzing 2,4-D**:
- 2,4-D is a synthetic auxin and, like IAA and IBA, is not responsible for stomatal closure. It is mainly used as a herbicide.

5. **Analyzing ABA**:
- ABA stands for Abscisic Acid, which is known as a stress hormone.
- It plays a crucial role in plant responses to stress, particularly water stress. When plants experience water stress, ABA is produced to help the plant conserve water.

6. **Mechanism of Stomatal Closure**:
- When ABA levels increase, it triggers the closure of stomata. This reduces transpiration (the loss of water vapor from the plant), helping the plant retain water during stressful conditions.

7. **Conclusion**:
- Based on the analysis, the hormone responsible for stomatal closure in response to leaf stress is ABA (Abscisic Acid).

**Final Answer**: The hormone responsible for stomatal closure in response to leaf stress is ABA (Abscisic Acid).

---