The regulator which retards ageing/senescence of plant parts is

Options

A. Cytokinin
B. Auxin
C. Gibberellin
D. Abscisic acid.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a regulator that slows down the aging process (senescence) in plant parts. This means we need to identify a plant hormone that has this specific effect.

2. **Reviewing the Options**: The options provided are:
- Cytokinin
- Auxin
- Gibberellin
- Abscisic acid

3. **Analyzing Each Option**:
- **Cytokinin**: This hormone is known to promote cell division and delay senescence in plant tissues. It helps maintain the health and productivity of plant parts by delaying the aging process.
- **Auxin**: Primarily involved in the elongation of roots and shoots, it does not specifically function to retard aging.
- **Gibberellin**: This hormone is associated with promoting stem elongation and flowering, but it does not directly influence senescence.
- **Abscisic Acid**: This hormone plays a role in seed maturation and stress responses, but it is not known for delaying aging.

4. **Identifying the Correct Answer**: Based on the analysis, cytokinin is the hormone that is known to retard aging in plant parts. It is associated with the Richmond-Lang effect, which helps in delaying the destruction of chlorophyll and promotes protein synthesis and nutrient mobilization.

5. **Conclusion**: Therefore, the correct answer to the question is **Cytokinin**.

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