Ageing of leaves is promoted by

Options

A. Ethylene
B. Abscisic acid
C. Cytokinins
D. Auxin.

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks which substance promotes the aging of leaves.

2. **Understand the Options**: The options provided are:
- Ethylene
- Abscisic Acid
- Cytokinins
- Auxins

3. **Analyze Each Option**:
- **Ethylene**: This hormone is known for promoting the ripening of fruits. While it does have effects on aging, it is more associated with fruit maturation rather than leaf aging.
- **Abscisic Acid (ABA)**: This is a plant hormone that acts primarily as a growth inhibitor. It promotes dormancy in seeds and buds, closes stomata to reduce transpiration, and is known to promote leaf senescence (aging) and abscission (the dropping of leaves).
- **Cytokinins**: These hormones promote cell division and are known to delay the aging of leaves, which makes them an incorrect choice for this question.
- **Auxins**: These hormones are responsible for cell elongation and differentiation, promoting growth in shoots and roots. They do not promote leaf aging.

4. **Conclusion**: Based on the analysis, the hormone that promotes the aging of leaves is **Abscisic Acid**.

5. **Final Answer**: The correct answer is **Abscisic Acid**.

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