Phloem Parenchyma Cells and Companion Cells

Phloem is a complex tissue responsible for the transport of organic nutrients such as sugars, amino acids, and hormones from the leaves to the other parts of the plant. Phloem consists of four types of cells - sieve tube elements, companion cells, phloem parenchyma, and phloem fibres.

Among these, the companion cells and phloem parenchyma cells are specialised parenchymatous cells that are closely associated with the sieve tube elements. Let's understand each of these cells in detail:

Companion Cells:
- Companion cells are specialised parenchymatous cells that are closely associated with the sieve tube elements.
- They are responsible for maintaining the metabolic and physiological functions of the sieve tube elements, as these cells lack nuclei and other organelles.
- Companion cells are typically small, elongated cells with a dense cytoplasm and numerous mitochondria.
- They are connected to the sieve tube elements by plasmodesmata, which allows for the exchange of nutrients and other substances.
- Companion cells play a crucial role in the loading and unloading of sugars in the sieve tube elements, as they are involved in the synthesis, transport, and storage of sugars.

Phloem Parenchyma:
- Phloem parenchyma is another type of specialised parenchymatous cell that is closely associated with the sieve tube elements.
- They are typically thin-walled, elongated cells with a large central vacuole and a dense cytoplasm.
- Phloem parenchyma cells are involved in the storage and transport of organic nutrients such as sugars and amino acids, and they also play a role in the defence mechanism of the plant.
- These cells are connected to the sieve tube elements by plasmodesmata, which allows for the exchange of nutrients and other substances.

In summary, both companion cells and phloem parenchyma cells are specialised parenchymatous cells that are closely associated with the sieve tube elements. They play a crucial role in the transport and storage of organic nutrients in the phloem tissue.