A gene cluster of nod and fix factors control the establishment and function of biological nitrogen fixation system in leguminous roots. One of the following is not a function of nod gene, i.e.,

Options

A. Root hair formation
B. Production of leghaemoglobin
C. Synthesis of nitrogenase
D. Curvature of rood hair tip

Answer

To solve the question regarding the functions of the nod gene in the biological nitrogen fixation system in leguminous roots, we will analyze the options provided and identify which one does not correspond to the functions of the nod gene.

### Step-by-Step Solution:

1. **Understanding the Role of Nod Genes**:
- Nod genes are crucial in the establishment of symbiotic relationships between leguminous plants and Rhizobium bacteria. They encode proteins that modify nodulation factors, which are signaling molecules produced by Rhizobium.

2. **Functions of Nod Genes**:
- The primary functions of nod genes include:
- **Root Hair Formation**: Nod genes are responsible for the curling of root hairs, which facilitates the entry of Rhizobium bacteria into the plant roots.
- **Formation of Infectious Threads**: After the root hairs curl, an infectious thread is formed that allows bacteria to penetrate deeper into the plant tissues.
- **Nodule Formation**: The division of cortical cells leads to the formation of nodules, where nitrogen fixation occurs.

3. **Analyzing the Options**:
- The options provided are:
1. Root hair formation
2. Production of leghemoglobin
3. Synthesis of nitrogenase
4. Curvature of root hair tip

4. **Identifying the Incorrect Function**:
- **Root Hair Formation**: This is a function of the nod gene.
- **Production of Leghemoglobin**: While leghemoglobin is important for protecting nitrogenase from oxygen, its production is not directly a function of the nod gene but rather a result of the nodule formation process.
- **Synthesis of Nitrogenase**: Nitrogenase is an enzyme present in Rhizobium and is not synthesized by the nod gene.
- **Curvature of Root Hair Tip**: This is also a function of the nod gene.

5. **Conclusion**:
- The option that is **not a function of the nod gene** is **3. Synthesis of nitrogenase**. This enzyme is already present in Rhizobium and is not produced by the nod genes.

### Final Answer:
**The correct option is 3. Synthesis of nitrogenase.**