Different Types of Sclerenchyma – Fibres and Sclereids
Just like concrete provides support to a building, a form of plant tissue called sclerenchyma comprises cells with thick cell walls provide support to the plants. There are no spaces between the cells. Sclerenchyma is present in the coating of seeds and nuts, as well as in the region surrounding the vascular tissues in some stems and leaves. These lignin-based cell walls give the tissue its complicated, stiff structure. Lignin is a complex, insoluble substance. Typically, the cells of sclerenchyma tissue are dead and devoid of chloroplasts. Plant stems and leaves include this tissue, which serves as structural support. There are different types of sclerenchyma in plants.
Also read another one on plant anatomy- Difference between wood of Gymnosperms and Dicots (Soft Wood vs Hard Wood) – My Biology Dictionary
Types of sclerenchyma
To begin with, different kinds of plants have different types of sclerenchyma:
1) Fibrous sclerenchyma: The cells that make up this kind of sclerenchyma are long and thin, and they are aligned parallel to one another. They provide sturdiness and support and are located in the stems and leaves of plants.
2) Sclereid sclerenchyma: These small, thick cells are distributed radially in the sclerenchyma of this kind. They are in charge of offering assistance and avoiding water loss, and they are located in plant roots.
Function of Sclerenchyma
- The primary purpose of the sclerenchyma is to support the plant’s structural integrity. Plant stems and leaves have this type of tissue, which contributes to the shape and rigidity of the tissue.
- Sclerenchyma is a type of plant cell specifically specialized to provide structural support to the plant.
- Sclerenchyma cells typically have an extremely elongated shape and have a very thick, robust cell wall.
As a result, sclerenchyma cells can assist the plant in a number of ways, including helping to keep it upright, giving the stem and leaves stiffness, and aiding in the storage of nutrients.
Location of Sclerenchyma
The secondary xylem and secondary phloem contain sclerenchyma, a form of plant tissue. It is made up of cells with thickened cell walls, and these cells are in charge of giving the plant support. Sclerenchyma cells can be found in a variety of places on a plant, but they are commonly found in the stem, leaves, and fruit. All this depends on the role and types of sclerenchyma being focussed.
Plant cells of the sclerenchyma type have a very thick cell wall. The two hardy, long-lasting substances cellulose and lignin are used to create this cell wall. Sclerenchyma cells are strong, rigid structures thanks to the cell wall. They are therefore perfect for providing plants’ structural support. Plant stems and leaves are the primary locations of sclerenchyma cells. They contribute to the strong structure and support that plants have.
Structure of Sclerenchyma
Plant tissue known as sclerenchyma comprises cells with thickened secondary cell walls. Lignin and other hard substances are used to create these walls, which give sclerenchyma tissues their exceptional stiffness and strength.
Sclerenchyma tissue’s primary job is to support the plant’s other tissues and organs. The sclerenchyma cells’ strong walls aid in maintaining the plant’s upright posture and healthy operation. Sclerenchyma cells play a significant role in the metabolism of the plant as they have the capacity to store both nutrients and water. Depending on types of sclerenchyma, a variety of structural features are seen in these cells.
Fibres are substantially elongated cells with interlocking long, tapering ends that give a plant the most support possible. Nearly every part of the plant body, including the stem, the roots, and the vascular bundles in leaves, contains them, and they frequently appear as bundles or strands. Numerous of these fibres, such as seed hairs, leaf fibres, and bast fibres, are crucial raw materials for textiles and other woven goods.
Types of Fibers
In angiosperms, the fibres are found in the stem as the outermost strands or tangential plates of the major phloem. They have been divided into two types based on where they are found in plants: xylary (intraxylary) and extraxylary fibres. The fibres found in the xylem are known as intraxylary or xylary fibres.
- Surface fibres are present on fruit walls and seed coats.
- Xylary fibres, also known as wood fibres, are connected to the xylem.
- Extraxylary fibres, also known as blast fibres, are present in association with the cortex, pericycles, and phloem.
Xylary fibres are also known as wood fibres and are of the following types:
a) Libriform fibres
b) Fibre tracheids
c) Septate fibres
d) Mucilage fibres
The type of pits found on the walls of these libriform and fibre tracheids determines how they are categorized. Fibre-tracheids are shorter and have bordered pits, whereas libriform fibres are longer and have plain pits (the Latin word liber indicates inner bark).
After the secondary wall is deposited, septa or cross-wall formation occurs in the phloem or xylem fibre of dicot species, which causes the fibre to be divided into two or more compartments. These fibres are referred to as septate fibres.
The deepest secondary wall layers of some fibres are made up of gelatinous layers (G layers), which contain large concentrations of cellulose but lack the lignin that sets them apart from the outer secondary wall layers. Because cellulose is present, the G layer becomes hygroscopic and expands by absorbing a lot of water. It may also obstruct the cell lumen, and as it dries, it pulls away from the rest of the wall. They are also known as mucilage fibre or reaction fibre.
Extraxylary fibres are located outside the xylem and these are of three types:
a) Phloem fibres: Phloem fibre, also referred to as bast fibre, begins in the early stages of primary phloem but takes on the role of fibre once its original function, namely conduction, has ended. This type of fibre is also referred to as primary phloem fibre or protophloem fibre.
b) Pericyclic or perivascular fibre: As in Aristolochia and Cucurbita, perivascular fibres are extraxylary fibres found in the stems of dicots and situated at the edges of vascular bundles inside the innermost cortical layer.
The fibre of the monocot, whether or not it is connected to the vascular bundles, is likewise a part of extraxylary fibres. They frequently have thick cell walls, and the amount of lignin deposited on the cell walls varies.
c) Cortical fibre: Extraxylary fibres known as the cortex, such as those found in barley, are located in the stem. The plant body’s mechanical strength comes from cortical fibre. The fibres produced by monocots are mostly made from leaves, and because of their hard, stiff nature, they are also known as hard or leaf fibres
Sclereids have a wide range of shapes and can be found in the periderm, cortex, pith, xylem, and phloem of plants, among other tissues. They make up the tough outer layer of many seeds and the hard shell of nuts, and they are also found in leaves and fruits. Sclereids, which are also known as stone cells, are what give Guavas and Pears their coarse feel.
Types of sclereids
Depending upon the basis of size and shape of sclereids, they have been classified into five main groups:
Often known as stone cells are isodiametric sclereids. These are isodiametric or elongated cells. They are particularly distributed widely in cells of the cortex, phloem, and pith of the stem. Brachysclereids are also found in the flesh of food.
Star-shaped sclereids dicot leaves and gymnosperms; Astrosclereids are formed when the central body of a cell sprouts arms or lobes that resemble the points of a star. They can be discovered on the adaxial leaf surface of N. cristata and eudicot leaves.
Osteosclereids have a columnar shape, but their ends expand to the point that it resembles a bone. Some plants have osteosclereids that are evenly distributed on the adaxial leaf surface, such as Nymphaea nouchali, Phillyrea latifolia, Hakia, and Osmenthus.
Rod-like sclereids found in the bark and seed coat of leguminous plants, are elongated and rod-like, creating a palisade-like epidermal layer in the seed coats of legumes. They are fully developed in the Malus sylvestris exocarp area.
Tricosclereids are thin-walled sclereids resembling hairs with branches. They are found on
the adaxial surface of leaves of Olea europea and Banana leaves.
Functions of Sclereids:
Sclereids provide mechanical strengths and plays important role in guiding light within mesophyll. They are responsible for the gritty texture found in some fruits like Pear.
Diagrams of sclereids types- apical meristem (miamioh.edu)
Difference between fibres and sclereids
|Fibres are extended.||Sclereids are extensive.|
|They have end walls that taper||Their end walls are blunt.|
|Fibres do not branch.||Sclereids may have branches.|
|Oblique pits.||Tubular pits.|
For instance, xylem and bast fibres.
Macrosclereids and osteosclerosis are two examples.
To conclude, the plant greatly relies on sclerenchyma tissue for mechanical support. A plant can have the different types of sclerenchyma as discussed in the article. Keep reading for other types of permanent tissues!