Sieve tubes | definition of Sieve tubes by Medical dictionary
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sieve tube a series of long cells (sieve cells) lying end to end forming a tube, found in the PHLOEM of ANGIOSPERMS. Each sieve cell loses its nucleus when mature, but maintains the cytoplasm, which is continuous from one cell to another and crosses the cell boundaries via perforations in the wall called sieve plates. Associated with the sieve tube are modified PARENCHYMA cells each with a cytoplasm, nucleus and many MITOCHONDRIA, called companion cells. It is considered that the companion cells may regulate TRANSLOCATION of materials within sieve tubes since there are cytoplasmic connections between the sieve cells, and the companion cells and the sieve cells are anucleate.
References in periodicals archive
In addition, after exposure to low temperature stress, the internal water in vessels and sieve tubes
in the Zhengmai 9023 tillering node froze, resulting in their rupture.
When wounding of the phloem occurs, the sieve tubes apparently synthesize a polysaccharide called callose, which plugs the sieve plate and reduces the flow.
These veins unload water through terminal vessels and load sugars through terminal sieve tubes for transport to other parts of the plant.