The acitvity of sieve tubes is remotely controlled by the nucleus of

Options

A. Phloem parenchyma
B. Companion cells
C. Phloem fibers
D. Both phloem parenchyma and phloem fidres

Answer

To solve the question regarding the activity of sieve tubes being remotely controlled by the nucleus of which cell type, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Sieve Tubes**: Sieve tubes are specialized structures in the phloem of flowering plants responsible for the transport of nutrients, particularly sugars. They are long, tube-like structures that are arranged longitudinally.

**Hint**: Remember that sieve tubes are part of the phloem tissue and are involved in the transport of organic substances.

2. **Identify Companion Cells**: Companion cells are closely associated with sieve tubes. They are living cells that provide metabolic support to sieve tubes. Each sieve tube element is typically accompanied by one or more companion cells.

**Hint**: Think about the relationship between sieve tubes and companion cells; they work together in the phloem.

3. **Examine the Structure of Sieve Tubes**: Mature sieve tubes lack a nucleus and have a peripheral cytoplasm. This means that they cannot control their own activities.

**Hint**: Consider the implications of sieve tubes lacking a nucleus; who then controls their functions?

4. **Role of Companion Cells**: Since sieve tubes do not have a nucleus, their activities are regulated by the nucleus of the companion cells. The companion cells provide the necessary proteins and other molecules that the sieve tubes need to function.

**Hint**: Focus on the role of companion cells in supporting sieve tube function.

5. **Evaluate the Options**: Now, looking at the options provided:
- Phloem parenchyma
- Companion cell
- Phloem fibers
- Both phloem parenchyma and phloem fibers

The correct answer is the second option: **Companion cell**, as it is the nucleus of the companion cell that controls the activity of the sieve tubes.

**Hint**: Eliminate options that do not directly relate to the control of sieve tube activity.

### Final Answer:
The activity of sieve tubes is remotely controlled by the nucleus of the **companion cell**.