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Vascular bundle

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Bundle-sheath cells:
– Photosynthetic cells form a protective covering around leaf veins.
– Consist of one or more layers of parenchyma cells.
– Mesophyll cells are loosely arranged between bundle sheath and leaf surface.
– Calvin cycle occurs in chloroplasts of bundle sheath cells in C plants.
– C plants utilize a variation of this structure.

– Sage, Rowan F.; Khoshravesh, Roxana; Sage, Tammy L. (2014).
– Published in the Journal of Experimental Botany.
– Focuses on the evolution from proto-Kranz to C4 Kranz for C4 photosynthesis.

Further reading:
– Campbell, N. A. & Reece, J. B. (2005).
– Book titled “Photosynthesis” in the 7th edition of Biology.
– Published by Benjamin Cummings in San Francisco.

Vascular bundle:
– Part of the transport system in vascular plants.
– Contains xylem, phloem, and supporting/protective tissues.
– Cambium is the tissue between xylem and phloem.
– Xylem is closer to the stem/root axis; phloem is closer to the exterior.
– Phloem transports sugars synthesized by the plant with sunlight.

Types of vascular bundles:
– Concentric periphloematic, concentric perixylematic, radial with inner xylem.
– Collateral closed and collateral open.
– Bicollateral open.
– Vascular bundles include xylem, phloem, and cambium.
– Vascular bundles vary in position relative to each other.

Cross section of a leaf:
– Shows parts of a vascular bundle.
– Includes both phloem and xylem.
– Vascular bundles are essential for transport in plants.
– The adaxial surface of a leaf is usually the upper side.
– The abaxial surface of a leaf is typically the lower side.

Vascular bundle (Wikipedia)

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.

Types of Vascular bundles
(black: 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
Detail of vascular bundle: closed, collateral vascular bundles of the stem axis of Zea mays
Vascular bundle in the leaf of Metasequoia glyptostroboides
The vascular bundle of pine leaf showing xylem and phloem

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
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