Vascular bundle
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(black: Xylem, green: Phloem, white: Cambium)
Aconcentric, periphloematic
Bconcentric, perixylematic
Cradial with inner xylem, here with four xylem-poles, left closed, right open
Dcollateral closed
Ecollateral open
Fbicollateral open
Avascular bundleis a part of the transport system invascular plants.The transport itself happens in thestem,which exists in two forms:xylemandphloem.Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues. In addition, there is also a tissue between xylem and phloem which is thecambium.
The xylem typically lies towards the axis (adaxial) with phloem positioned away from the axis (abaxial). 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.
The sugars synthesized by the plant with sun light are transported by the phloem, which is closer to the lower surface.Aphidsandleaf hoppersfeed off of these sugars by tapping into the phloem. This is why aphids and leaf hoppers are typically found on the underside of a leaf rather than on the top. The position of vascular bundles relative to each other may vary considerably: seestele.
Bundle-sheath cells
[edit]The bundle-sheath cells are the photosynthetic cells arranged into a tightly packed sheath around the vein of a leaf. It forms a protective covering on leaf vein, and consist of one or more cell layers, usuallyparenchyma.Loosely arrangedmesophyllcells lie between the bundle sheath and the leaf surface. TheCalvin cycleis confined to thechloroplastsof these bundle sheath cells inC4plants.C2plantsalso use a variation of this structure.[1]
References
[edit]- ^Sage, Rowan F.; Khoshravesh, Roxana; Sage, Tammy L. (1 July 2014)."From proto-Kranz to C4 Kranz: building the bridge to C4 photosynthesis".Journal of Experimental Botany.65(13): 3341–3356.doi:10.1093/jxb/eru180.PMID24803502.
Further reading
[edit]- Campbell, N. A. & Reece, J. B. (2005). Photosynthesis.Biology(7th ed.). San Francisco: Benjamin Cummings.
External links
[edit]- Curtis, Lersten, and Nowakcross section of a vascular bundle
- Mausethanother cross section of a vascular bundle
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