Which primary hormone causing abscission of leaves is

Options

A. IAA
B. Ethylene
C. ABA
D. Cytokinin

Answer

**Step-by-Step Solution:**

1. **Understanding Abscission**: Abscission refers to the process of leaf fall in plants. It is a natural process that occurs in response to various environmental and physiological factors.

2. **Role of Plant Hormones**: Plant hormones, also known as phytohormones, are chemical substances that regulate various physiological activities in plants, including growth, development, and responses to stress.

3. **Types of Plant Hormones**: Plant hormones can be categorized into two main types based on their functions:
- **Growth Promoters**: These hormones promote growth and development. Examples include auxins, gibberellins, and cytokinins.
- **Growth Inhibitors**: These hormones inhibit growth and are often produced in response to stress. Examples include abscisic acid (ABA) and ethylene.

4. **Identifying the Hormones Involved in Abscission**: Among the growth inhibitors, abscisic acid (ABA) and ethylene are significant. ABA is known as the stress hormone and is involved in various stress responses, including dormancy and abscission. Ethylene, on the other hand, is primarily responsible for the abscission of leaves.

5. **Conclusion**: The primary hormone responsible for the abscission of leaves is ethylene. It plays a crucial role in the leaf fall process by signaling the cells in the abscission zone to break down, leading to the detachment of leaves from the plant.

**Final Answer**: The primary hormone causing abscission of leaves is ethylene.

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