Companion cells

Definition

Companion cells are specialized cells found in the phloem of flowering plants that play a crucial role in the transport of sugars and other organic nutrients. They are closely associated with sieve tube elements, facilitating the loading and unloading of these substances. Companion cells help maintain the metabolic functions necessary for the sieve tubes to operate efficiently, ensuring that the plant's vascular system can effectively distribute nutrients throughout its tissues.

5 Must Know Facts For Your Next Test

1. Companion cells are derived from the same parent cell as sieve tube elements during development, which explains their close relationship.
2. They contain many mitochondria, indicating their high metabolic activity required to support sieve tube function.
3. Companion cells facilitate the active transport of sugars into the sieve tubes through specialized proteins and energy expenditure.
4. They also help maintain turgor pressure in sieve tubes, which is essential for effective nutrient flow throughout the phloem.
5. Companion cells can communicate with sieve tube elements via plasmodesmata, allowing for coordinated transport and sharing of resources.

Review Questions

• How do companion cells support the function of sieve tube elements in the phloem?
  • Companion cells play a vital role in supporting sieve tube elements by facilitating the loading and unloading of sugars and nutrients. They possess high metabolic activity, providing the necessary energy and molecular machinery to actively transport these substances into the sieve tubes. Additionally, companion cells help maintain turgor pressure within the sieve tubes, which is crucial for efficient nutrient transport throughout the plant.
• Discuss the importance of plasmodesmata in the relationship between companion cells and sieve tube elements.
  • Plasmodesmata serve as critical connections between companion cells and sieve tube elements, enabling direct communication and resource sharing. These channels allow for the passage of small molecules and ions, which is essential for coordinating nutrient transport. This connection ensures that companion cells can quickly respond to changes in nutrient availability or demand, optimizing the efficiency of phloem transport.
• Evaluate how companion cell structure relates to their function in phloem tissue and overall plant health.
  • The structure of companion cells is intricately linked to their function in phloem tissue. Their abundance of mitochondria supports high metabolic rates necessary for active transport processes, ensuring efficient sugar loading into sieve tubes. This structural adaptation enables plants to rapidly respond to varying energy needs, directly influencing overall plant health by maintaining effective nutrient distribution. A disruption in companion cell function could lead to decreased nutrient flow, impacting growth and vitality.

Related terms

sieve tube elements: Sieve tube elements are the main conductive cells in phloem, responsible for transporting sugars and other nutrients from sources to sinks in the plant.

phloem: Phloem is a type of vascular tissue in plants that transports organic compounds, particularly sucrose, from photosynthetic tissues to non-photosynthetic parts.

plasmodesmata: Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, allowing for transport and communication between neighboring cells, including companion cells and sieve tube elements.