Vessel element

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SEM image (top) and Transmission Light Microscope image (bottom) of vessel elements in Oak

A vessel element or vessel member (also called a xylem vessel)

conifers. Vessel elements are the main feature distinguishing the "hardwood" of angiosperms from the "softwood" of conifers
.

Anatomy

Xylem is the tissue in vascular plants that conducts water (and substances dissolved in it) upwards from the roots to the shoots. Two kinds of cell are involved in xylem transport: tracheids and vessel elements.[2][3][4] Vessel elements are the building blocks of vessels, the conducting pathways that constitute the major part of the water transporting system in flowering plants. Vessels form an efficient system for transporting water (including necessary minerals) from the root to the leaves and other parts of the plant.

Stained Xylem Vessel in Red/Orange (x400 magnification)

In secondary xylem – the xylem that is produced as a stem thickens rather than when it first appears – a vessel element originates from the vascular cambium. A long cell, oriented along the axis of the stem, called a "fusiform initial", divides along its length forming new vessel elements. The cell wall of a vessel element becomes strongly "lignified", i.e. it develops reinforcing material made of lignin. The side walls of a vessel element have pits: more or less circular regions in contact with neighbouring cells. Tracheids also have pits, but only vessel elements have openings at both ends that connect individual vessel elements to form a continuous tubular vessel. These end openings are called perforations or perforation plates. They have a variety of shapes: the most common are the simple perforation (a simple opening) and the scalariform perforation (several elongated openings in a ladder-like design). Other types include the foraminate perforation plate (several round openings) and the reticulate perforation plate (a net-like pattern, with many openings).

At maturity, the protoplast – the living material of the cell – dies and disappears, but the lignified cell walls persist. A vessel element is then a dead cell, but one that still has a function, and is still being protected by surrounding living cells.

Evolutionary significance

The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the flowering plants. It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal

Amborellaceae, Trochodendraceae, and Winteraceae), described by Arthur Cronquist as "primitively vesselless". Cronquist considered the vessels of Gnetum
to be convergent with those of angiosperms.

Vessel-like cells have also been found in the xylem of

Gigantopteridales
. In these cases, it is generally agreed that the vessels evolved independently. It is possible that vessels may have appeared more than once among the angiosperms as well.

See also

References

  1. ^ "Vessel | plant anatomy". Encyclopedia Britannica. Retrieved 2021-03-30.
  2. ^ "Vessels vs Tracheids, Similarities and Differences". Easy Biology Class. 2016-12-12. Retrieved 2021-12-31.
  3. PMID 17472568
    .
  4. ^ "Xylem vessel". Biology Online. 2019-10-07. Retrieved 2021-12-31.

Further references

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