Senescence in leaves can be delayed by applying on them :

Options

A. Indole acetic acid
B. GA
C. Kinetin
D. Ethylene

Answer

To solve the question regarding how senescence in leaves can be delayed, we will analyze the role of different plant hormones and identify which one is effective in delaying leaf aging.

### Step-by-Step Solution:

1. **Understanding Senescence**:
- Senescence refers to the process of aging in plants, particularly in leaves, leading to their eventual death. It is a natural process but can be influenced by various factors, including hormones.

2. **Identifying Plant Hormones**:
- The question mentions several plant hormones: Indole Acetic Acid (IAA), Gibberellic Acid, Kinetin, and Ethylene. We need to evaluate their roles in plant growth and senescence.

3. **Role of Indole Acetic Acid (IAA)**:
- IAA is an auxin that primarily promotes cell division and elongation. While it plays a significant role in growth, it is not specifically known for delaying senescence.

4. **Role of Gibberellic Acid**:
- Gibberellic Acid is mainly involved in processes like seed germination and stem elongation. It does not have a direct role in delaying leaf senescence.

5. **Role of Kinetin**:
- Kinetin is a type of cytokinin. Cytokinins are known to promote cell division and growth. They also play a crucial role in delaying senescence by promoting nutrient and water uptake in leaves. This hormone helps in maintaining the vitality of leaves by preventing the formation of the abscission zone, which is responsible for leaf aging.

6. **Role of Ethylene**:
- Ethylene is a hormone that promotes fruit ripening and can actually accelerate senescence in leaves. Therefore, it is not effective in delaying senescence.

7. **Conclusion**:
- Among the hormones listed, Kinetin (cytokinin) is the most effective in delaying senescence in leaves. It works by preventing the formation of the abscission zone, allowing leaves to continue receiving nutrients and water.

### Final Answer:
Senescence in leaves can be delayed by applying **Kinetin** (a cytokinin).

---