Which of the following hormone is produced in the root cells by the rhizobium bacteria?

Options

A. cytokinin
B. Auxin
C. Gibberellin
D. Ethylene

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks which hormone is produced in the root cells by rhizobium bacteria.

2. **Identifying the Role of Rhizobium:**
Rhizobium bacteria form a symbiotic relationship with legume plants. They are known for their ability to fix nitrogen, which is essential for plant growth.

3. **Formation of Nodules:**
In this symbiotic relationship, rhizobium bacteria induce the formation of root nodules in legume plants. These nodules provide a suitable environment for the bacteria to convert atmospheric nitrogen into a form that the plant can utilize (ammonium).

4. **Hormonal Influence:**
The leguminous plants respond to the presence of rhizobium by producing certain hormones. Among the options given (cytokinin, auxin, gibberellin, ethylene), we need to identify which one is specifically produced in response to rhizobium.

5. **Role of Cytokinin:**
Cytokinin is known to play a crucial role in the differentiation of nodules. It is an endogenous plant hormone that helps in orchestrating the signaling events necessary for rhizobial colonization of the root cortex.

6. **Conclusion:**
Based on the information, the hormone produced in the root cells by rhizobium bacteria is **cytokinin**.

**Final Answer:** Cytokinin

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