Apical hook formation in dicot seedlings initiated by

Options

A. auxin
B. gibberellin
C. cytokinin
D. ethylene

Answer

### Step-by-Step Solution:

1. **Understanding Apical Hook Formation**:
- Apical hook formation is a phenomenon observed in dicot seedlings where the shoot tip bends downwards, forming a hook. This structure helps protect the delicate apical meristem as the seedling emerges from the soil.

2. **Identifying the Role of Phytohormones**:
- Several phytohormones are involved in plant growth and development, including auxins, gibberellins, cytokinins, and ethylene. Each hormone has a specific role in plant processes.

3. **Analyzing Each Option**:
- **Option 1: Auxin**:
- Auxins are known for promoting apical dominance and elongation of stems but are not primarily responsible for apical hook formation.
- **Option 2: Gibberellin**:
- Gibberellins are involved in seed germination and stem elongation, but they do not initiate apical hook formation.
- **Option 3: Cytokinin**:
- Cytokinins promote cell division and are not directly involved in the formation of the apical hook.
- **Option 4: Ethylene**:
- Ethylene is the correct answer as it plays a crucial role in the formation of the apical hook in dicot seedlings. It causes differential growth, leading to the bending of the stem.

4. **Conclusion**:
- The apical hook formation in dicot seedlings is initiated by ethylene, which helps protect the apical meristem during the emergence of the seedling from the soil.

### Final Answer:
- The correct answer is **Ethylene** (Option 4).

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