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. These cells are closely associated with sieve tube elements, providing them with essential support and enabling efficient transport through the plant's vascular system. Their close relationship allows for the regulation of nutrient flow and communication between the sieve elements and the surrounding tissues.

5 Must Know Facts For Your Next Test

1. Companion cells are derived from the same mother cell as sieve tube elements during development, ensuring their functional relationship.
2. These cells contain numerous mitochondria, which provide the energy necessary for active transport of nutrients into sieve tube elements.
3. Companion cells help maintain the pressure gradient needed for effective nutrient flow in phloem through a process called translocation.
4. They also play a role in loading and unloading sugars at various points in the plant, adapting to its metabolic needs.
5. Companion cells can communicate with each other and sieve tube elements via plasmodesmata, allowing for rapid signaling and nutrient exchange.

Review Questions

• How do companion cells support the function of sieve tube elements in nutrient transport?
  • Companion cells support sieve tube elements by providing them with necessary proteins and energy. They are equipped with many mitochondria, supplying ATP for active transport, which is essential for moving sugars into sieve tubes. This relationship ensures that sieve tube elements can effectively carry out their primary role in transporting nutrients throughout the plant.
• Discuss the significance of companion cells in maintaining the overall health of a plant's vascular system.
  • Companion cells are vital for maintaining the health of a plant's vascular system by ensuring efficient nutrient transport. Their ability to load and unload sugars as needed allows plants to adapt to changing metabolic demands. By actively regulating nutrient flow, companion cells help sustain growth and development, especially during times of high energy demand such as flowering or fruiting.
• Evaluate how disruptions in companion cell function could impact a plant's ability to thrive under varying environmental conditions.
  • Disruptions in companion cell function can severely affect a plant's ability to thrive, particularly under stress conditions like drought or nutrient deficiency. If companion cells cannot efficiently load or unload sugars, it can lead to reduced energy availability for growth processes. This dysfunction could hinder overall plant health, making it less resilient to environmental challenges and limiting its reproductive success or survival.

Related terms

Sieve tube elements: The elongated cells in the phloem that transport sugars and nutrients throughout the plant, functioning alongside companion cells.

Phloem: The vascular tissue responsible for the transport of organic nutrients, particularly sugars produced during photosynthesis, from leaves to other parts of the plant.

Xylem: The vascular tissue responsible for the transport of water and minerals from the roots to the rest of the plant.