Sieve tube element

in the plant, sieve elements are living cells. They are thick and circular and can be different colours.

At the interface between two sieve tube members in angiosperms are sieve plates, pores in the plant cell walls that facilitate the movement of liquid. Neighbouring each of the sieve tube elements is a minimum of one companion cell, connected by plasmodesmata (channels between the cells). Sieve tube members have no cell nucleus, ribosomes, or a vacuole, the nucleus and ribosomes of its companion cell(s) compensate for this. In leaves, these cells help in moving the sugar produced by photosynthesis in the mesophyll tissue into the sieve tube elements. Sieve tubes are mainly to transport sugars and nutrients up and down the plant.

Sieve cells are long, slender, conducting cells of the secondary phloem that do not form a constituent element of a sieve tube, but which are provided with relatively unspecialized sieve areas, especially in the tapering ends of the cells that overlap those of other sieve cells. They have a narrower diameter and are more elongated compared to sieve tube members, the other kind of sieve elements present in the phloem. Sieve cells are associated with albuminous cells, which lack starch, thus making it possible to differentiate them from phloem parenchyma.

The forest botanist Theodor Hartig was the first to discover and name these cells as "Siebfasern" (sieve fibres) and "Siebröhren" (sieve tubes) in 1837.

ee also

*Phloem
*Vascular tissue

External links

* [http://www.biologie.uni-hamburg.de/b-online/e06/06d.htm Comprehensive explanation of sieve elements] - University of Hamburg Department of Biology
* [http://www.botany.hawaii.edu/faculty/webb/BOT410/410Labs/LabsHTML-99/SecPhloem/LabSecPhloem-99.htm Introduction to secondary pholem tissue] by Dr. David T. Webb - University of Hawaii

References

*Katherine Esau (1969). "The Phloem" -in: Encyclopedia of Plant Anatomy. Gebrüder Borntraeger, Berlin, Stuttgart.
*Campbell, N. A. (1996) "Biology" (4th edition). Benjamin Cummings NY. ISBN 0-8053-1957-3
*Hartig, T. (1837) Vergleichende Untersuchungen über die Organisation des Stammes der einheimischen Waldbäume. Jahresber. Fortschr. Forstwiss. Forstl. Naturkd. 1:125-168


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