Function of leghemoglobin (a red pigment) in root nodules of leguminous plants is

Options

A. a) to regulate `O_(2)` supply in cells
B. b) to regulate `CO_(2)` supply in cells
C. c) to regulate production of phenolic compounds
D. d) to regulate the Mo supply in cells

Answer

### Step-by-Step Solution:

1. **Understanding Leghemoglobin**: Leghemoglobin is a red pigment found in the root nodules of leguminous plants. It is similar to hemoglobin found in blood and plays a crucial role in the plant's nitrogen-fixing process.

2. **Function of Leghemoglobin**: The primary function of leghemoglobin is to bind oxygen. In root nodules, it helps to maintain an optimal concentration of oxygen for the nitrogen-fixing bacteria (Rhizobia) that reside there.

3. **Oxygen Supply Regulation**: The presence of leghemoglobin allows the plant to regulate the supply of oxygen. This is important because while Rhizobia need oxygen for respiration, they also require a low concentration of free oxygen to effectively fix nitrogen.

4. **Conclusion**: Given the functions described, the correct answer to the question about the function of leghemoglobin in root nodules is that it regulates the oxygen supply.

5. **Final Answer**: Therefore, the correct option is **A) to regulate O2 supply**.