Vascular bundle

Vascular bundle

A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues. Also, it is a vein in the leaf that contains conducting tissues.

The xylem typically lies with phloem positioned . In a stem or root this means that the xylem is closer to the centre of the stem or root while the phloem is closer to the exterior. In a leaf, the adaxial surface of the leaf will usually be the upper side, with the abaxial surface the lower side. This is why aphids are typically found on the underside of a leaf rather than on the top, since the sugars manufactured by the plant are transported by the phloem, which is closer to the lower surface.

The position of vascular bundles relative to each other may vary considerably: see stele.

Bundle-sheath cells

Bundle-sheath cells are contained in certain C4 plants. These plants use C4 carbon fixation to carry out photosynthesis when normal conditions for C3 plants aren't present (e.g. normal water levels, CO2 levels, heat, light).

Bundle-sheath cells are photosynthetic cells arranged into tightly packed sheaths around the veins of a leaf. They form a protective covering these leaf veins, and consist of one or more cell layers, usually parenchyma. Between the bundle sheath and the leaf surface are the more loosely arranged mesophyll cells. The Calvin cycle is confined to the chloroplasts of these bundle sheath cells.

External links

Vascular bundles pictured in cross section, by [http://botweb.uwsp.edu/anatomy/primaryxylem.htm Curtis, Lersten, and Nowak] ; and [http://www.sbs.utexas.edu/mauseth/weblab/webchap8phloem/chapter_8.htm Mauseth]

References

*Campbell, N. A. & Reece, J. B. (2005). Photosynthesis. "Biology" (7th ed.). San Francisco: Benjamin Cummings.


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Look at other dictionaries:

  • vascular bundle — n. Bot. an isolated unit of the conducting system of vascular plants, consisting of xylem and phloem, frequently with other interspersed cells or a sheath of thick walled cells …   English World dictionary

  • vascular bundle — noun a unit strand of the vascular system in stems and leaves of higher plants consisting essentially of xylem and phloem • Syn: ↑vascular strand, ↑fibrovascular bundle • Hypernyms: ↑vascular tissue • Hyponyms: ↑vein, ↑nervure …   Useful english dictionary

  • vascular bundle — Bot. a longitudinal arrangement of strands of xylem and phloem, and sometimes cambium, that forms the fluid conducting channels of vascular tissue in the rhizomes, stems, and leaf veins of vascular plants, the arrangement varying with the type of …   Universalium

  • vascular bundle — noun Date: 1842 a strand of specialized vascular tissue of higher plants consisting mostly of xylem and phloem …   New Collegiate Dictionary

  • vascular bundle — Strand of vascular tissue in a plant; composed of xylem and phloem …   Dictionary of molecular biology

  • vascular bundle — noun A strand of xylem, phloem, and their associated tissues within a eustele or atactostele. See Also: vascular tissue …   Wiktionary

  • vascular bundle — vas′cular bun′dle n. bot any of the strands of the conducting channels in vascular plants composed of xylem and phloem in various structural arrangements • Etymology: 1880–85 …   From formal English to slang

  • vascular bundle — A strand of tissue containing primary xylem and primary phloem (and procambium if present) and frequently enclosed by a bundle sheath of parenchyma or fibres …   Glossary of Biotechnology

  • vascular bundle — noun Botany a strand of conducting vessels in the stem or leaves of a plant, typically with phloem on the outside and xylem on the inside …   English new terms dictionary

  • vascular bundle — /væskjələ ˈbʌndl/ (say vaskyuhluh bundl) noun an aggregation of strands of specialised conductive and mechanical tissue in a plant …  

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