Collenchyma tissue is a term given by a scientist named Schleiden in the year 1839. It is a kind of simple permanent supportive tissue that confers mechanical strength to the plant. The collenchyma cells appear as elongated cells with the non-uniform thickened cell wall. It originates by the modification of parenchyma tissue into the cells comprising thickened cell wall due to the deposition of cellulose, hemicellulose and pectin like substances.
It exists under the epidermis layer of stem, leaves, petiole etc. and may or may not contain chloroplast. Collenchyma tissues are of many types, based on location and cell arrangement.
Content: Collenchyma Tissue
Collenchyma tissue can define as the simple permanent tissue that comprises axially elongated cells with the non-uniform and thickened cell wall (composed of pectin, cellulose and hemicellulose). These are sometimes associated with vascular bundles and generally located in the hypodermis layer (underneath the epidermis). Collenchyma cells are devoid of hydrophobic components. It only gives mechanical strength to the plant when the cells are at turgid state. These are having a prominent nucleus with developed cell organelles, and comprising a compact cell arrangement.
The collenchymatous tissue shows the following features:
- These are living cell with living protoplasm, having axially elongated cells.
- The cell wall is thickened towards the cell’s corner as a result of pectin, cellulose and hemicellulose deposition. Sometimes tannin also deposits in the cell wall.
- Unlike sclerenchyma tissue, collenchyma cell comprises a non-lignified cell wall.
- The collenchyma cell is usually having a compact cell arrangement with little or no intercellular space.
- The collenchyma cells have varying cell shapes and sizes.
- Generally, the collenchymatous tissue is absent in monocots and the region of root.
- Collenchyma tissue predominantly exists just below the epidermis of dicotyledonous stems, leaves etc.
- The tissue is elastic or extensible, which gives flexibility to the stems in bending without breakage.
Types of Collenchyma Tissue
The collenchyma tissue can classify into many types depending upon the pattern of wall thickening and cell arrangement, and their location.
Based on cell wall thickening
Angular collenchyma: These are polygonal in shape. The thickening pattern of the cell wall is towards the corner. The extra-wall material deposits on the vertical walls where cells meet. It has a compact cell arrangement with no intercellular space.
Example: Petioles of Cucurbita in the hypodermis layer.
Annular collenchyma: These consist of cells that appear circular and contain invariably thickened cell wall.
Lamellar collenchyma: It also refers as “Plate or tangential collenchyma” where the cells are longitudinally elongated. The thickening pattern of the cell wall restricts to the tangential walls. The cells are having a compact cell arrangement or arranged in the tangential rows with no intercellular space.
Example: Stem of Sambucus in the hypodermis layer.
Lacunar collenchyma: It also refers as “Tubular collenchyma” where the cells appear spherical or oval in shape. The thickening pattern of the cell wall is towards the direct contact of intercellular spaces.
Example: Petioles of Salvia, Malvia etc. in the hypodermis layer.
Based on the location
Peripheral collenchyma: In this type, the collenchyma cells are located below the outermost epidermis layer and are concentrated by one or more layers of parenchyma cell. It further subdivides into two kinds:
Continuous: In this kind, the collenchyma cells appear as a continuous layer.
Strand: In this kind, the cells appear as the discrete axial strands concentrated from one another by the parenchyma cells.
Fascicular collenchyma: In this type, the collenchyma cells are located in distinct regions with respect to the vascular bundles. Depending on the different locations, the fascicular collenchyma further subdivides into the following three kinds:
Supracribal: This type of collenchyma tissue encircles the vascular bundle towards the phloem side.
Infraxylary: This type of collenchyma tissue encircles the vascular bundle towards the xylem side.
Circumfascicular: This type of collenchyma tissue fully encircles the vascular bundle.
Structure of Collenchyma tissue
Both the cell shape and size of collenchyma cells vary considerably depending on various factors like plant age, plant type etc. The length of the cell is approximately 2.5 mm. The shape ranges from small spherical or polyhedral cells to long, tubular-like cells with narrow ends. Collenchyma cell is living in nature and having vacuolated protoplast. Chloroplasts rarely present inside the collenchyma cell. Primary pit fields are also observable under the microscopic study. Collenchyma cell either contains small or leaves no intercellular space.
The cell wall is unevenly thickened, and the concentration of pectin and hemicellulose is higher than that of cellulose. The composition of collenchyma cell wall mainly includes 45% of pectin, 35% of hemicellulose and 20% of cellulose. A scientist named Anderson in the year 1927 reported that the cell wall consists of firmly packed, interspersed cellulose with pectin lamellae. In addition to these two, some scientists have reported the presence of hemicellulose in addition to cellulose and pectin.
Cellulose is a polysaccharide which exists as linear insoluble microfibrils. Pectin is also a polysaccharide which is a glue-like substance that abundantly occurs at the time of primary cell wall thickening. Hemicellulose includes xylans, mannans etc. whose function is to provide cell rigidity in combination with cellulose.
Collenchyma tissue performs the following tasks:
- Collenchyma cell induces rigorousness to the rising parts like stems, leaves etc. of the plant.
- It also permits growth and elongation of the plant parts.
- The cells of collenchyma tissue have the capability of sclerification, where the cell wall can modify to withstand bending stresses.
- Collenchyma tissue prevents contravention of the stem against wind and other environmental stresses.
- It improves the tensile strength of the plant body.
- Collenchyma cells confer elasticity in different parts like stem, petiole etc.
The collenchyma cell is a supporting tissue whose cell wall material is irregularly distributed due to which it has an uneven cell wall thickenings, and characteristically found in stems, leaves etc. of dicotyledonous plants. Therefore, after reading this article, we can conclude that the collenchyma tissue has three primary features like the presence of a living protoplast, thickened cell wall and axially elongated cells.