O phloem it is an important tissue related to the conduction of sap produced in the plant's body. This means that it is through this tissue that substances such as water, sucrose, amino acids, nucleic acids, vitamins and inorganic ions are transported. Along with xylem, phloem is considered an important conducting tissue.
→ What are the main characteristics of the phloem?
Phloem is a complex tissue formed by different cell types that guarantee the conduction of substances. The primary phloem originates from the activity of the procambium, and the secondary phloem originates from the activity of a lateral meristem, called cambium. Both the primary and secondary phloem are formed by the same cell types.
Among the cells found in the phloem, we can mention the crimped elements, which are the most specialized cells in the phloem. Also, we can't forget the parenchymal cells specialized, fibers and sclereids.
crimped elements
The crimped elements can be of two types: sieve cells and sieve tube elements.
These two cells have in common the fact that they have screened areas, places where there are pores that allow the communication of the protoplasts in the longitudinal and lateral directions. Furthermore, they are cells that have a live protoplast and no nucleus when they become mature.At riddled they are long cells with crimped areas on all their walls, and their pores are generally the same size. You vessel elements, in turn, are shorter cells, but with specialized areas on their end walls and sometimes on the side walls called crimped plates, which have larger diameter pores. These end walls communicate with other vessel elements, forming the sieve tube. On the side walls of these elements, there are crimped areas.
Crimped cells are normally found in pteridophytes and gymnosperms. The sieve tube elements, in turn, are cells found exclusively in angiosperms.
Companion and albuminous cells
Among the parenchymal cells found in the phloem, the companion cells and albuminous cells.The companion cells are located next to the elements of the sieved tube and present themselves in close association. It is believed that these cells are capable of directing some activities of the elements in the sieve tube. Albumin cells, in turn, are associated with cells riddled in gymnosperms.
→ Where is the phloem located?
The phloem, being responsible for conducting substances, is found in all organs of the plant. In the primary roots, it forms strands that alternate with the xylem. On the other hand, in roots with secondary structure and in the stem, the phloem normally presents itself more externally to the xylem. In the sheets, the phloem faces the underside.
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/biologia/o-que-e-floema.htm
