This article may be expanded with text translated from the corresponding article in French. (February 2019) Click [show] for important translation instructions. View a machine-translated version of the French article. Machine translation like DeepL or Google Translate is a useful starting point for translations, but translators must revise errors as necessary and confirm that the translation is accurate, rather than simply copy-pasting machine-translated text into the English Wikipedia. Consider adding a topic to this template: there are already 5,099 articles in the main category, and specifying|topic= will aid in categorization. Do not translate text that appears unreliable or low-quality. If possible, verify the text with references provided in the foreign-language article. You must provide copyright attribution in the edit summary accompanying your translation by providing an interlanguage link to the source of your translation. A model attribution edit summary is Content in this edit is translated from the existing French Wikipedia article at [[:fr:Faisceau cribro-vasculaire]]; see its history for attribution. You should also add the template ((Translated|fr|Faisceau cribro-vasculaire)) to the talk page. For more guidance, see Wikipedia:Translation.
Types of Vascular bundles (blue: Xylem, green: Phloem, white: Cambium) A  concentric, periphloematic B  concentric, perixylematic C  radial with inner xylem, here with four xylem-poles, left closed, right open D  collateral closed E  collateral open F  bicollateral open
Types of Vascular bundles
(blue: Xylem, green: Phloem, white: Cambium)
A  concentric, periphloematic
B  concentric, perixylematic
C  radial with inner xylem, here with four xylem-poles, left closed, right open
D  collateral closed
E  collateral open
F  bicollateral open
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem
Detail of vascular bundle: closed, collateral vascular bundles of the stem axis of Zea mays
Detail of vascular bundle: closed, collateral vascular bundles of the stem axis of Zea mays
Vascular bundle in the leaf of Metasequoia glyptostroboides
Vascular bundle in the leaf of Metasequoia glyptostroboides
The vascular bundle of pine leaf showing xylem and phloem
The vascular bundle of pine leaf showing xylem and phloem

A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in the stem, 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. In addition, there is also a tissue between xylem and phloem which is the cambium.

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. Aphids and leaf hoppers feed 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: see stele.



Cross section of a leaf showing parts of a vascular bundle
Cross section of a leaf showing parts of a vascular bundle

Bundle-sheath cells

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, usually parenchyma. Loosely arranged mesophyll cells lie between the bundle sheath and the leaf surface. The Calvin cycle is confined to the chloroplasts of these bundle sheath cells in C4 plants. C2 plants also use a variation of this structure.[1]

References

  1. ^ 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.

Further reading