Companion cell

Definition

A companion cell is a specialized type of plant cell found in the phloem tissue that works closely with sieve tube elements to facilitate the transport of nutrients, particularly sugars. These cells play a critical role in loading and unloading sugars into the sieve tubes, which are responsible for transporting these essential compounds throughout the plant. Companion cells are living cells that maintain the functionality of the sieve elements, which are largely devoid of organelles.

5 Must Know Facts For Your Next Test

1. Companion cells are derived from the same mother cell as sieve tube elements during development and are usually located adjacent to them.
2. These cells are rich in mitochondria and other organelles, providing the necessary energy and metabolic support for the active transport of sugars into the sieve tubes.
3. Companion cells utilize plasmodesmata to communicate and transfer materials directly to sieve tube elements, facilitating efficient nutrient transport.
4. In many plants, companion cells have specialized types called 'transfer cells' which have wall ingrowths to enhance their surface area for better nutrient absorption.
5. The functionality of companion cells is essential for plant growth and development, as they ensure that the phloem can efficiently distribute carbohydrates produced during photosynthesis.

Review Questions

• How do companion cells support the function of sieve tube elements in phloem tissue?
  • Companion cells support sieve tube elements by providing metabolic support and facilitating the loading and unloading of sugars. They contain numerous organelles, including mitochondria, which supply the energy needed for active transport processes. This partnership ensures that sieve tube elements can effectively transport nutrients throughout the plant, even though they lack many cellular components themselves.
• Discuss the role of plasmodesmata in the interaction between companion cells and sieve tube elements.
  • Plasmodesmata serve as vital connections between companion cells and sieve tube elements, allowing for direct communication and material exchange. These microscopic channels enable the movement of sugars and signaling molecules from companion cells to sieve tubes, which is crucial for maintaining nutrient flow within the phloem. This intercellular connectivity ensures that both types of cells can function efficiently together in nutrient transport.
• Evaluate how abnormalities in companion cell function might impact overall plant health and growth.
  • If companion cells experience dysfunction or abnormalities, it could severely disrupt the loading and unloading processes of sugars into sieve tube elements. This could lead to inadequate distribution of carbohydrates, causing stunted growth and poor development across various plant tissues. The resulting nutrient deficiency could compromise photosynthesis efficiency and reduce the plant's ability to respond to environmental stressors, ultimately threatening its survival.

Related terms

sieve tube element:

A long, cylindrical cell in the phloem that transports sugars and other organic nutrients throughout the plant.

phloem:

The vascular tissue in plants responsible for the transport of nutrients, primarily sugars, from leaves to other parts of the plant.

plasmodesmata:

Microscopic channels that connect plant cells, allowing for the transport of substances and communication between cells.