What are Sieve Tubes Members?

Sieve tubes members are usually shorter and wider than sieve cells, and are arranged end to end into the sieve tubes. Their sieve areas have larger sieve pores than do sieve cells, and are concentrated along the contacting end-walls of adjacent sieve tube members. These specializations allow solutes to move through sieve tubes faster than through sieve cells.

Mature sieve tubes lack the nuclei but contain living cytoplasm, but each sieve tube member is associated with at least one specialized cell called a companion cell, which regulates loading and unloading of carbohydrates from sieve tube members. These sieve tube members and the companion cells arise from the same cell, and are linked through a plasmodesmata.

Sieve tubes members also contain a proteinaceous substances called P-protein, along their longitudinal walls.