Mature sieve tubes do not have nucleus but they are living and metabolically active . The cell which is associated with sieve tube is :

Options

A. Companion cell
B. Phloem parenchyma
C. Transfer cells
D. Transfusion tissue

Answer

To answer the question, "Mature sieve tubes do not have a nucleus but they are living and metabolically active. The cell which is associated with the sieve tube is:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Sieve Tubes**:
- Sieve tubes are specialized structures in the phloem of flowering plants responsible for the transport of nutrients, particularly sugars.
- Mature sieve tube elements lack a nucleus and some organelles, which raises the question of how they remain metabolically active.

2. **Identifying Associated Cells**:
- To support the sieve tubes, there are specific cells that are functionally associated with them. These cells provide the necessary metabolic support.
- The options given are: companion cell, phloem parenchyma, transfer cells, and transfusion cells.

3. **Role of Companion Cells**:
- Companion cells are closely associated with sieve tube elements. They have a nucleus and are metabolically active.
- They help in the loading and unloading of sugars into the sieve tubes and maintain the function of the sieve tubes.

4. **Connection Between Cells**:
- Companion cells are connected to sieve tube elements through plasmodesmata, which are small channels that allow for the transport of substances between the two cell types.
- This connection is crucial for the survival and function of the sieve tubes since they lack a nucleus.

5. **Conclusion**:
- Given that companion cells are the primary cells associated with sieve tubes, providing them with metabolic support, the correct answer to the question is **companion cells**.

### Final Answer:
The cell which is associated with the sieve tube is **companion cell**.