Epidermal Tissue System: Its Functions and Tissue in Plant

The epidermal tissue system includes several differentiated cell types including epidermal cells, guard cells, subsidiary cells, and epidermal hairs (trichomes). The epidermis tissue system performs numerous functions: such as preventing water loss, regulating gas exchange, secreting metabolic substances, and absorbing water and mineral nutrients

Tissue System

The body structure of all other developed plants is complex. Similar cells are living together and form a group. It is a group of cells together to perform a specific function, that is, plants have different groups of cells for different forms, which are called tissues.

Sachs (1875) divided the tissues into three systems on the basis of the division of labor in higher-class plants, each system consisting of one tissue or consisting of different tissues. Their function and origin are the same. Tissues are formed by meristems.

1. Epidermal Tissue System
2. Ground Tissue System
3. Vascular Tissue System

Epidermal Tissue System

A group of tissues, no matter how dissimilar they may be, having a similar position and function, is called the epidermal tissue system. The epidermal tissue system is referred to as, the ‘dermal tissue system’. It is the outermost layer of plants. This System consists of the epidermis, stomata, and epidermal outgrowths.

Epidermis

This tissue is made up of epidermal cells and covers all the exposed parts of the plants except the stomatal and stomatal openings. The epidermis is in the form of a continuous layer. The shape and size of the cells are different, due to the cells being adjacent to each other, there are no intercellular spaces. Generally, the epidermis is of one layer (uniseriate), but in many plants, it is multiseriate, such as the Banyan tree. Its cells are made of living parenchyma, in which a large vacuole is found. This vacuole is filled with colorless celli-sap. Chloroplasts are also found in some epidermis. Sometimes these cells have mucilage, and the outer walls are thick due to cutinization and suburbanization. This (cystolith) and silica are also found. the inner and radial of cells. Protects and prevents excess transpiration.

In the leaves of many monocotyledonous plants, some cells of the epidermis are large, thin-walled and these are called bulliform (bubble-like) cells. Many vacuoles are found in these. It is hygroscopic and controls the opening and folding of leaves; as in plants of the Poaceae family.

The guard cells are surrounded by other cells of the epidermis. Their size is often different from other cells of the epidermis. These are called accessory cells or subsidiary cells. The main function of stomata is to exchange gases between the plant and the atmosphere.

The outermost layer of the root is called the epiblema or piliferous layer. Unicellular root hairs emerge from it, which do the work of absorption of water and mineral salts from the soil. Stomata and cuticles are not found in the rhizome.

Stomata

Stomata are found in the aerial parts of leaves and plants. Each stoma is surrounded by two crescent-shaped or kidney-shaped guard cells. The inner wall of guard cells is thick and the outer wall is thin. The guard cells are alive and contain chloroplasts. The guard cells control the opening and closing of the stomata. The guard cells also perform the function of food preparation due to chloroplasts. Due to this, the solution inside it becomes more concentrated, and due to this cells become swollen by absorbing water from the neighboring cells by endosmosis. Due to this, these cells become turgid i.e. due to filling with water, they spread outwards and stomata open. At night the sugar in the cell-sap of these cells is converted into starch. Starch being insoluble in water, the viscosity of the cell membrane in the guard cells is less than in the cells of the neighboring epidermis, thus they lose water by exosmosis and become flaccid. it goes In this way the stomata get closed.

The guard cells are surrounded by other cells of the epidermis. Their size is often different from other cells of the epidermis. These are called accessory cells or subsidiary cells. The main function of the stomata is to exchange gases between the plant and the atmosphere.

Water evaporates through the stomata. Thus the plants get rid of excessive water. And in summer the plants get coolness. The stomata are more numerous in the lower epidermis of the dorsiventral leaves. Their number is relatively less in the upper epidermis. In isobilateral leaves, stomata are equal on both sides. Dorsal leaves are found in dicot plants and isosceles leaves are found in monocot plants. In floating leaves, stomata are found only in the upper epidermis. Like water lilies. Water Stomata are absent in submerged leaves. Like Hydrilla. Sunken stomata are found in desert plants.

The following are the types of leaves based on the presence of stomata:

• Astomatic: Stomata are absent in this type of leaf. These are often found in submerged plants, such as Hydrilla and Velisleria, etc.
• Hypostomatic: In this type of leaf stomata are mostly found on the lower side of the leaf. For example the leaves of dicotyledons.
• Epistomatic: In this type of leaf stomata are found on the upper surface of the leaf. The leaves float on the surface of the water, like a lotus.
• Amphistomatic: In this type of leaf almost equal number of stomata are found on both surfaces, like wheat, maize, etc. (all monocotyledonous plants)

Epidermal Appendages

Epidermal outgrowths are growths that appear on the epidermis. There are different varieties depending on the location of the epidermal appendages, which are as follows:

• Root hairs
• Trichomes
• Prickles

Root Hairs

Unicellular outgrowths from the root epidermis or epiblema are known as root hairs. They also help in the absorption of water and minerals from the soil as well as in anchoring.

Trichomes

Many plants develop hairs or trichomes on the epidermis. These may be rigid or soft, unicellular or multicellular branches. These follicles reduce excessive transpiration and protect the plants. Hairs are found on all parts of plants. The role of hair is important in the classification of plants. Following are some of the main types of follicles

• Branched: They are found in the form of stars, scales, etc.
• Unbranched: In these, all the cells are in a single line; Like a tomato
• Nonglandular hair – Non Glandular hair can be unicellular or multicellular, branching or unbranched, stellate or T shaped. These trap air on the surface of the leaves, reducing water loss through transpiration and protecting against extremely hot or cold temperatures.
• Glandular hairs are multicellular in nature and release various compounds like mucilage, salt, honey, and so on. Glandular hairs can also function as digestive, aromatic, or stinging glands.
• Collectors are glandular trichomes that are either unicellular or multicellular and exude a sticky material. Some trichomes have been adapted to function as bladders for water storage.

Prickles

These are stiffed multicellular epidermal outgrowth. Priclkes are plucked out easily. Prickles help the plant form herbivorous animals. In rose plants prickles are present.

Functions of Epidermal Tissue System

1. The main function of the epidermis is to protect the inner tissues from injury, heat, cold, and attacks by parasites, fungi, bacteria, etc.
2. Cuticles, wax, follicles, scales, etc. are found on the epidermis. These prevent excessive evaporation from the plants.
3. The epidermis acts as a storage of water in desert plants.
4. Sometimes the epidermis performs the functions of photosynthesis and secretion.
5. Helps in exchange for gas due to stomata.
6. Works for absorption of water and mineral salts by root hairs in the root.

FAQs on Epidermal Tissue system

Q: What is the most important function of trichomes?

Answer:

The epidermal cells have hair-like structures referred to as trichomes. These hairs or trichomes support in protecting the plant from sunlight and outer injuries.

Q: What are the stomata?

Answer:

Stomata are cell structures in the epidermis of tree leaves and needles that help plants exchange carbon dioxide and water with the atmosphere.

Q: What is the function of the epidermal tissue system in plants?

Answer:

The main function of the epidermis is to protect the inner tissues from injury, heat, cold, and attacks by parasites, fungi, bacteria, etc.

Q: Describe guard cells?

Answer:

Guard cells are kidney-shaped cells that surround the stomata. They regulate the opening and closing of the stomata.