Hormone responsible for senescence

Options

A. ABA
B. Auxin
C. GA
D. Cytokinin

Answer

### Step-by-Step Solution:

1. **Understanding Senescence**:
- Senescence refers to the process of aging in plants. It can be triggered by various factors, including stress and the natural aging process.

2. **Identifying Plant Hormones**:
- The question provides four options: ABA (Abscisic Acid), Auxin, Gibberellic Acid (GA), and Cytokinin. We need to determine which of these hormones is primarily responsible for senescence.

3. **Analyzing Gibberellic Acid (GA)**:
- Gibberellic Acid is a plant hormone that promotes growth by stimulating cell division and elongation, particularly in stems and leaves. It does not play a significant role in the aging process, making it an incorrect option.

4. **Analyzing Cytokinin**:
- Cytokinins are known for promoting cell division and delaying senescence in plants. Therefore, they are also not responsible for inducing senescence, ruling them out as the correct answer.

5. **Analyzing Auxin**:
- Auxins are involved in various growth processes, including stem and root elongation. Similar to GA and Cytokinin, Auxin does not induce senescence, making it an incorrect choice.

6. **Identifying Abscisic Acid (ABA)**:
- Abscisic Acid (ABA) is known to induce senescence. It does this by increasing the biosynthesis of ethylene, a hormone that promotes leaf senescence. Additionally, ABA levels rise in response to both biotic and abiotic stress, further activating the signaling pathways that lead to senescence.

7. **Conclusion**:
- Based on the analysis, the hormone responsible for senescence in plants is Abscisic Acid (ABA).

### Final Answer:
The hormone responsible for senescence in plants is **Abscisic Acid (ABA)**.

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