In the sieve tubes pressure gradient is maintained with the help of

Options

A. Phloem fibres
B. Phloem parenchyma
C. Sieve cells
D. Companion cells

Answer

### Step-by-Step Solution:

1. **Understanding Sieve Tubes**:
- Sieve tubes are essential components of the phloem tissue in plants. They are responsible for the transport of nutrients, particularly sugars, throughout the plant.

2. **Identifying the Role of Companion Cells**:
- Companion cells are specialized cells that are closely associated with sieve tube elements. They play a crucial role in the functioning of sieve tubes.

3. **Pressure Gradient Maintenance**:
- The pressure gradient in sieve tubes is vital for the movement of sap. This gradient is primarily maintained through the activity of companion cells. They assist in loading and unloading carbohydrates into the sieve tubes, which helps in creating and maintaining the necessary pressure for transport.

4. **Excluding Other Options**:
- Other components of the phloem, such as phloem fibers and phloem parenchyma, do not play a significant role in maintaining the pressure gradient. Phloem fibers provide structural support, while phloem parenchyma mainly serves as storage.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the pressure gradient in the sieve tubes is maintained with the help of **companion cells**.