Why Is Collenchyma Essential for Plant Support?
Collenchyma cells are elongated and spindle-shaped. Their walls are slightly thickened with irregular thickness. The cell wall is weakly lignified, as a result, it can expand tangentially as well as radially after absorbing water. In the cold season, collenchyma cells die due to a lack of enough water for absorption and continuing their normal activity. They remain alive during the warm season and during winter. The collenchyma produces new cells that aid in elongating the plant's stem. Hence, they function as a supporting tissue, especially around the new growing part of the plant.
Collenchymas are usually found in monocot plants such as grasses and palms. In dicots, we can find them in the leaves of celery or lettuce. Collenchyma is not a primary tissue because it only develops from meristematic cells, for example, cambium and procambium. Collenchyma is usually found between the cortex of the stem and the endoderm of its vascular bundles.
Collenchyma Under Ground Tissues Category
Collenchyma falls under the 'ground tissues' category. Ground tissues are classified into three types based on their characteristics of cell walls. First, we will see those three types, and then we will be discussing the type' collenchyma'.
The Three Types of Ground Tissues are as follows –
Parenchyma – Parenchyma work as filler tissues in the plants' soft part, and they have thin primary walls. They remain alive after their maturation and are present in the pericycle, medullary rays, pith, and cortex in the primary root and stem.
Collenchyma – Collenchyma has thin walls with irregular thickness. They provide additional structural and mechanical support, especially around the new growing part of the plant.
Sclerenchyma – Sclerenchyma consists of thick and lignified secondary walls but dies after maturation. They provide the primary structural support to the plants.
Collenchyma Definition
As we have seen earlier, ground tissues are an integral part of the plants, and Collenchyma is one of the three. It consists of non-uniformly thickened elongated plant cell walls. Their role is to provide structural support to the growing leaves and shoots. The cell walls, irregularly thick, are made of pectin and cellulose, and they are usually living cells.
The reason behind the cell walls having an irregular thickness is the mechanical stress on the plant. The mechanical plant affects the consistency of these cell walls. The shaken plants' cell wall thickness (due to wind, etc.) is 40 to 100% more than that of the plants not shaken.
Background
Though Collenchyma is a natural and supporting tissue within the plants, it has not been exposed as far as its essential functions are concerned. Since it was first identified, it did not get scientific attention despite having a strong role in the plants' growth. It was always neglected because of commercially explained wood or fiber tissues.
Collenchyma has a superior functional property compared to Sclerenchyma. It plays a vital role during the organs' growth as it supports them while they are growing. This is because of the super flexibility of these tissues during the elongation of the plant organs. If one studies the collenchyma cell diagram, he can understand what Collenchyma is and why these tissues can exhibit flexibility during growth.
Collenchyma function may become rigid with the changes in the collenchyma cell wall composition. The information about Collenchyma molecular constitution and properties of its cell walls is still lacking. What is only known is the organographic and systematic distribution of Collenchyma.
Collenchyma Has Four Major Types
Tangential Collenchyma (Cells are thickened at the tangential face of the cell wall and arranged into lined up rows)
Lacunar Collenchyma (it has space within the cells)
Angular Collenchyma (intercellular contact points are thickened)
Annular Collenchyma (cells walls are thickened uniformly)
Vascular cambium, the outer growing tissues, consists of most of the collenchyma tissues. The integrity and structural support required to them is provided by the collenchyma tissues. For the first time, while describing the sticky matter on Bletia (Orchidaceae) pollen, 'Link' used the term collenchyma.
An essential characteristic of Collenchyma is, it is incredibly elastic. When the plant organ grows, these cells can expand to accommodate the growth. These tissues are mainly a part of the leaves and the cortex of the stem. They are exceptional structure support in many herbaceous plants. In plants with secondary growth, these tissues function only temporarily and get crushed due to the development of woody tissues.
Commonly found in the borders of veins in dicot leaves, Collenchyma forms angles of stem and ridges (e.g., strings in stalks of celery plants)
Collenchyma Tissue
Long living cells with varying cell wall thickness.
Contains cellulose, hemicelluloses, and pectic materials.
Gives flexibility to petiole, stems of young plants, leaf veins, support structure, and mechanism.
Found in young stems, under the epidermis, leaf veins, and petiole.
Also observed in avocado fruit hypodermis.
It May or may not contain a few chloroplasts.
May perform photosynthesis and store food.
Position in the Plant
Collenchyma supports the growing organs of many herbaceous and woody plants. They are found in the stems and leaves of fully grown herbaceous plants. The Collenchyma mainly occurs in the peripheral position of the petioles and stems. As a particular property, the spread of collenchyma cell walls is not even in all the plant positions.
Instead, the cell walls get adjusted according to the expansion of the growing part of the plant; therefore, the cell walls of Collenchyma vary at different positions. E.g., it may be uniform immediately under the epidermis, but on the peripheral part, it can be thicker. This is to adjust the wall thickness while the growth of the epidermis takes place.
This naturally occurring mechanical efficiency has been neglected for many years now, and there has been no research on the cells' mechanism in the growing parts like leaves. At the same time, we all know that the new leaves are small and eventually grow big as they mature, and this happens due to this property of Collenchyma. But unfortunately, very negligible reports of research are available on this fantastic property.
Collenchyma is also associated with vascular bundles observed at the phloem side, xylem side, or surrounding. There is a suggestion from most of the researchers that only the plant's peripheral place be called Collenchyma.
Conclusion
Like we mentioned earlier, such fantastic functionality won't remain unattended for long, and yes, now there has been detailed compositional analysis of the Collenchyma being carried out. The molecular composition of the Collenchyma is being studied to understand what causes the structural support to the growing organs of the plants.
One should keep in mind that the fascinating functionality of this tissue is not limited to that; it has other huge implications like seedling growth, fruit softening, etc. Collenchyma cells provide mechanical support and elasticity to a growing plant organ. They develop in many herbaceous and woody plants. This tissue is present in the stems, veins of leaves, and petioles of fully-grown herbaceous plants.
The thickness of the cell walls varies according to the growth of the plant organ and is observed unevenly in different positions. Students of plant biology must understand the research on this tissue to help further it.
FAQs on Collenchyma: Definition, Types, and Functions
1. What is collenchyma tissue in simple terms?
Collenchyma is a type of simple permanent tissue found in plants. It is a living mechanical tissue, which means it provides structural support to the plant while its cells are still alive. Its most unique feature is its cell wall, which is unevenly thickened with deposits of pectin and cellulose, giving it both strength and flexibility.
2. What are the main functions of collenchyma in a plant?
Collenchyma has two primary functions in plants:
- Mechanical Support: It provides strength to young and growing parts of the plant, such as stems and leaves, helping them stay upright.
- Flexibility and Elasticity: It allows plant parts like leaf stalks (petioles) and young stems to bend without breaking, which is crucial for resisting wind and supporting growth.
3. Where is collenchyma tissue usually found in plants?
Collenchyma is strategically located in specific parts of the plant that need flexible support. You can typically find it:
- Just below the epidermis (the outer skin) in young dicot stems and leaf stalks.
- Along the veins of leaves, providing support to the leaf blade.
It is generally absent in roots and the stems of monocot plants.
4. What are the key differences between collenchyma, parenchyma, and sclerenchyma?
These three simple tissues are different in their structure and function:
- Collenchyma vs. Parenchyma: Collenchyma has unevenly thickened cell walls for flexible support, while parenchyma has thin, uniform cell walls and is mainly for storage and photosynthesis.
- Collenchyma vs. Sclerenchyma: Collenchyma consists of living cells with cellulose and pectin walls, providing flexible support. In contrast, sclerenchyma consists of dead cells with thick, rigid walls hardened by lignin, providing inflexible strength.
5. Why are the cell walls of collenchyma unevenly thickened?
The uneven thickening is the key to collenchyma's function. The extra deposits of pectin and cellulose at the corners or on certain walls make the tissue strong, but because the cells are alive and the walls aren't uniformly rigid (like in sclerenchyma), they can still stretch. This provides a perfect combination of strength and elasticity, allowing organs to grow and bend.
6. Can collenchyma cells perform photosynthesis?
While the primary role of collenchyma is support, some collenchyma cells that are located near the surface of a stem may contain a few chloroplasts. If they do, they can perform a small amount of photosynthesis. However, their main job is structural, and they are not as specialised for photosynthesis as chlorenchyma (a type of parenchyma tissue).
7. What are the different types of collenchyma?
Based on how the cell walls are thickened, collenchyma is classified into a few types. The three main types are:
- Angular Collenchyma: Thickening is most prominent at the corners where several cells meet.
- Lamellar Collenchyma: Thickening occurs mainly on the tangential walls (the inner and outer walls of the cell).
- Lacunar Collenchyma: Thickening occurs on the walls that face the intercellular spaces.
8. How does collenchyma support a plant part while it is still growing?
Because collenchyma cells are living and their walls are not hardened with lignin, they are plastic and can elongate. This means as a young stem or leaf grows longer, the collenchyma tissue can stretch along with it, providing continuous support without restricting growth. This is a key advantage over rigid tissues like sclerenchyma, which cannot stretch.
