Phloem is a part of the vascular tissue in plants that transports the organic nutrients produced during photosynthesis, such as sugar, amino acids, and hormones, from the leaves to other parts of the plant. It is composed of two primary types of cells: sieve tubes and companion cells.
Sieve tubes are elongated cells that form the main transport pathway in the phloem. They are connected end-to-end, forming sieve tubes as the primary conducting tissue. The sieve plates, which are pores in the cell walls, allow the transport of the nutrients from one cell to another. The sieve tube elements lack nuclei, ribosomes, and other organelles, which makes sense since they are primarily transportation vessels.
Companion cells, on the other hand, assist the sieve tubes in their function. These cells are connected to the sieve tubes by thin, cytoplasmic strands and perform various functions related to phloem translocation. Companion cells transport sugars and other nutrients into the sieve tubes, help maintain the sieve elements’ metabolism, and aid in the defense of phloem-feeding insects and diseases.
An essential characteristic of phloem is its ability to move substances in different directions. This occurs because of the presence of bidirectional transporters, which can move nutrients up and down the sieve tubes.
Phloem plays a significant role in plant growth and development. The organic molecules transported by phloem are essential for growth, the formation of roots and fruits, and for the plant’s response to various stresses such as pathogen attack, drought, or high salinity. Without phloem, the plants would not be able to transport essential nutrients to other cells and would have a hard time surviving.
In conclusion, phloem is a crucial component of the plant’s transport system, and its function is essential for the growth and development of plants. Understanding the structure and function of phloem can help us develop new ways to improve plant growth, disease resistance, and productivity.#16#