Damaged sieve tubes are sealed by deposition of

Options

A. pectin
B. callose
C. suberin
D. lignin

Answer

To answer the question "Damaged sieve tubes are sealed by deposition of," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Sieve Tubes**: Sieve tubes are part of the phloem in plants and are responsible for the transport of nutrients, particularly sugars. When they are damaged, it is crucial for the plant to seal these tubes to prevent loss of nutrients.

2. **Identifying the Sealing Mechanism**: The sealing of damaged sieve tubes involves a specific substance that is deposited at the site of damage. This substance must effectively block the pores of the sieve plates to stop the flow of sap.

3. **Recognizing the Substance**: The deposition that seals the damaged sieve tubes is known as "callose." Callose is a carbohydrate that is produced by the plant in response to injury.

4. **Formation of Callose**: At the end of the growing season, callose is deposited on the sieve plates. This process helps to block the pores of the sieve tubes, effectively sealing them off and preventing the transport of nutrients.

5. **Reopening of Sieve Tubes**: When the growing season resumes, the callose can dissolve, allowing the pores to reopen and resuming the transport of nutrients.

6. **Conclusion**: Therefore, the correct answer to the question is that damaged sieve tubes are sealed by the deposition of callose.

### Final Answer:
Damaged sieve tubes are sealed by the deposition of **callose**.