Phloem of angiosperms differ from that of other vascular plants by the presence of Companion cells.

Companion cells are specialized parenchyma cells that are closely associated with sieve tube elements in the phloem of angiosperms. They play a crucial role in the functioning of the phloem and are absent in the phloem of other vascular plants such as gymnosperms.

Function of Companion Cells:
Companion cells are involved in maintaining the metabolic functions of sieve tube elements. They provide essential materials and energy to sieve tube elements, which are responsible for the long-distance transport of organic nutrients in plants. Some of the key functions of companion cells include:

1. Loading of sugars: Companion cells actively transport sugars, such as sucrose, into the sieve tube elements through plasmodesmata. This loading process is energy-dependent and allows for the movement of sugars from source tissues (such as leaves) to sink tissues (such as roots or developing fruits).

2. Protein synthesis: Companion cells have a high concentration of ribosomes, which are responsible for protein synthesis. They produce proteins that are needed for the proper functioning of sieve tube elements.

3. Cellular communication: Companion cells are connected to sieve tube elements through numerous plasmodesmata. These channels allow for the exchange of ions, nutrients, and signaling molecules between companion cells and sieve tube elements. This communication is essential for coordinating the activities of the phloem and ensuring efficient nutrient transport.

4. Metabolic support: Companion cells provide metabolic support to sieve tube elements by supplying them with energy-rich molecules, such as ATP, and other essential nutrients. This support is crucial for maintaining the high metabolic activity required for long-distance nutrient transport.

5. Defense: Companion cells are also involved in plant defense mechanisms against pathogens and pests. They can produce antimicrobial compounds and participate in the systemic response of the plant to pathogens.

Conclusion:
The presence of companion cells in the phloem of angiosperms is a unique feature that distinguishes them from other vascular plants. These specialized cells play a vital role in loading sugars, protein synthesis, cellular communication, metabolic support, and defense mechanisms. Their presence ensures efficient long-distance transport of organic nutrients in angiosperms.