Leghaemoglobin is produced in response to

Options

A. respiration
B. fatty acid oxidation
C. photosynthesis
D. `N_(2)`-fixation.

Explanation

### Step-by-Step Solution:

1. **Understanding Leghaemoglobin**: Leghaemoglobin (Lb) is a red-pink pigment found in the root nodules of leguminous plants. It plays a crucial role in the process of nitrogen fixation.

2. **Identifying the Stimulus**: Leghaemoglobin is produced in response to the presence of Rhizobium bacteria. These bacteria infect the root hairs of leguminous plants, leading to the formation of root nodules.

3. **Function of Leghaemoglobin**: The primary function of leghaemoglobin is to regulate oxygen levels within the root nodules. It binds to oxygen, thereby creating an anaerobic environment.

4. **Importance of Anaerobic Environment**: The anaerobic conditions are essential for the functioning of the enzyme nitrogenase, which is responsible for the conversion of atmospheric nitrogen (N₂) into a form that plants can use (ammonia, NH₃).

5. **Conclusion**: Therefore, leghaemoglobin is produced specifically in response to nitrogen fixation, which is the process facilitated by Rhizobium bacteria in leguminous plants.

### Final Answer:
Leghaemoglobin is produced in response to nitrogen fixation.

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