Collenchyma Tissue in Plants

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 – 

1. 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.

2. Collenchyma – Collenchyma has thin walls with irregular thickness. They provide additional structural and mechanical support, especially around the new growing part of the plant.

3. 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.