A plant growth regulator which stimulates the closure of stomata is

Options

A. cytokinin
B. gibberellin
C. ethylene
D. abscisic acid

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a plant growth regulator that stimulates the closure of stomata. Stomata are small openings on the surfaces of leaves that allow for gas exchange and transpiration.

2. **Identifying the Options**: The options provided are cytokinin, zyberlin, ethylene, and abscisic acid. We need to analyze each of these hormones to determine which one is responsible for stomatal closure.

3. **Analyzing Cytokinin**: Cytokinins are known for promoting cell division and delaying senescence (aging) in plants. They do not play a role in stomatal closure.

4. **Analyzing Zyberlin**: Zyberlin is primarily involved in promoting growth, particularly in increasing internodal length and aiding in seed germination. It does not influence stomatal closure.

5. **Analyzing Ethylene**: Ethylene is a hormone that is mainly responsible for the ripening of fruits and promoting senescence. It also increases the rate of respiration but does not directly cause stomatal closure.

6. **Analyzing Abscisic Acid**: Abscisic acid (ABA) is known as the stress hormone in plants. It plays a crucial role in response to water stress by stimulating the closure of stomata to reduce water loss through transpiration.

7. **Conclusion**: Based on the analysis, the plant growth regulator that stimulates the closure of stomata is **abscisic acid**.

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