Nitrate reductase enzyme:

Options

A. Reduces `NO_(2)^(-)`
B. oxidise `NO_(2)`
C. Reduces `NO_(3)^(-)`
D. oxidises `NO_(3)`

Answer

### Step-by-Step Solution:

1. **Understanding Nitrate Reductase**:
- Nitrate reductase is an enzyme that plays a crucial role in the nitrogen assimilation process in plants. It catalyzes the reduction of nitrate (NO3-) to nitrite (NO2-).

2. **Location of Action**:
- The reduction of nitrate to nitrite occurs in the cytosol of plant cells. This is the first step in the process of nitrogen assimilation.

3. **The Reaction**:
- The reaction facilitated by nitrate reductase can be summarized as:
\[ \text{Nitrate (NO}_3^-\text{) } \xrightarrow{\text{Nitrate Reductase}} \text{Nitrite (NO}_2^-\text{)} \]

4. **Further Reduction**:
- After the formation of nitrite, it is further reduced to ammonia (NH3) in the chloroplasts or plastids of the roots. This step involves a different enzyme called nitrite reductase.

5. **Summary of the Process**:
- The overall process of nitrate reduction involves two main steps:
- Step 1: Nitrate (NO3-) is reduced to nitrite (NO2-) by nitrate reductase in the cytosol.
- Step 2: Nitrite (NO2-) is further reduced to ammonia (NH3) by nitrite reductase in the chloroplasts.

6. **Conclusion**:
- The key enzyme in the first step of this process is nitrate reductase, which is essential for the conversion of nitrate to nitrite.