Which hormone brings about stomatal closure during severe drought conditions?

Answer

**Step-by-Step Solution:**

1. **Understanding Plant Hormones**: There are several types of hormones in plants, each with specific functions. The main hormones include ethylene, gibberellins, cytokinins, abscisic acid, and auxins.

2. **Analyzing Each Hormone**:
- **Ethylene**: This hormone is primarily involved in the ripening of fruits, opening of flowers, and other growth processes. It does not play a role in stomatal closure.
- **Gibberellins**: These hormones are known for their role in promoting stem elongation, seed germination, and flowering. They do not cause stomatal closure.
- **Cytokinins**: These hormones are involved in cell division and growth, particularly in roots and shoots. They do not influence stomatal closure.
- **Auxins**: These hormones promote the growth of plant cells and are involved in processes like apical dominance. They do not directly cause stomatal closure.
- **Abscisic Acid (ABA)**: This hormone is crucial during stress conditions, particularly drought. It helps in the closure of stomata to reduce water loss.

3. **Conclusion**: After analyzing the functions of the various plant hormones, it is clear that abscisic acid is the hormone responsible for inducing stomatal closure during severe drought conditions.

**Final Answer**: Abscisic acid (ABA) is the hormone that brings about stomatal closure during severe drought conditions.

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