O sclerenchyma it is a tissue composed of cells with thick and lignified secondary walls. Together with the colenchyma, it acts assuring support for the plant. It can occur in any part of the plant, being common in areas that are no longer in the elongation phase.
This tissue is formed by cells that are dead at maturity, with regular thickened walls. Its walls are composed of cellulose, hemicellulose, pectic substances and lignin. The term sclerenchyma is derived from Skleros, a word of Greek origin that means hard. Its name is a reference to the fact that its cells are very resistant.
O sclerenchyma is composed of two main cell types: the sclereids and fibers.
Sclereids vary in shapes and sizes. They have a reduced size, when compared to fibers, and can be found in groups or isolated. They can be isodiametric (all diameters are equal), elongated or branched. Its walls are very thick and dotted with simple punctuations.
The sclereids are classified according to their form into: brachisclereids (stone cells), macrosclereids, osteosclereids, astrosclereids and trichosclereids.
At brachisclereids they are sclereids with a more isodiametric shape. They are responsible for the texture of the pear and for those regions of the apple banana that we say are “stoned”.
At macrosclereids they are more elongated sclereids and are common in legume seeds such as pea.
At osteosclereids, as the name itself reveals, have a bone shape (columnar with the extremity dilated). They are also common in legume seeds such as soybeans.
Astrosclereids have a star shape and are found, for example, in the Nymphaea, a genus of aquatic plants.
Trichosclereids have a shape similar to trichomes and may have ramifications. They are common in olive leaves.
Fibers, unlike sclereids, have a more elongated shape and are not branched. Its size can range from 0.5 to 70 millimeters depending on the species. Its ends are tapered and its walls are thickened. They often appear in association, forming cords and bundles, but they also occur in isolation. Some fibers may have live protoplasm at maturity.
According to their location, they can be called xylematic or extra-xylematic. Xylematics are those that occur together with the xylem, while extraxylemmatics are those present in regions outside the xylem.
Some fibers are economically important, such as hemp and flax. Some of these fibers are taken from the stem and others from leaves.
by Vanessa dos Santos
Graduated in Biology
Source: Brazil School - https://brasilescola.uol.com.br/biologia/esclerenquima.htm
