There are two types of plant tissue: meristematic and permanent. Meristematic tissue cells can divide throughout a plant’s life. When the cells mature and lose their dividing ability, they quickly differentiate and transform into permanent tissue. This permanent tissue further differentiates, giving rise to ground, vascular, and dermal tissues.
What is Dermal Tissue
Dermal tissue is a type of permanent tissue that covers the outermost layer of the young plant parts, including leaves, roots, stems, flowers, fruits, and seeds. It is composed of a single layer of closely packed cells called the epidermis. It mediates most of the interactions between a plant and its environment. As certain plant parts undergo secondary growth, that is, become woody, this layer gets replaced by periderm or bark. Unlike epidermis, periderm is multilayered.
The dermal tissue is composed of the following cell types:
1. Pavement cells
The outer region of the epidermis layer is made up of pavement cells. These are the most commonly occurring epidermal cells, lacking any characteristic shape. Under the influence of the cell cytoskeleton and some specific cellular proteins, the morphology of pavement cells varies from organ to organ, or in between different plant species.
For instance, in dicot leaves, the shape resembles interlocking jigsaw puzzle pieces to form a sturdy layer, providing mechanical strength to the leaves. On the contrary, the pavement cells found in the stem and various elongated plant organs have a rectangular shape with a long axis that is parallel to the direction of expansion of the stem, or that organ.
- Form a protective layer for the cells lying underneath.
- Prevent excess water loss.
- Keep the inner layers of cells in place.
- Help maintain the internal temperature.
- Resist the intrusion of any outside particles or pathogen.
- Keep the stomata apart by providing tension on both sides. There is at least one pavement cell between each stoma.
The outer surface of epidermal cells has a waxy coating called the cuticle. It is made up of cutin, a polymerized ester of fatty acids. Being waxy, it acts as a water-repellent, adds shine, and helps reflect excess sunlight. The thickness of this coating largely depends on the type and location of the plant.
- Protects plants against drought, extreme temperatures, UV radiation, chemical attack, mechanical injuries, and pathogen or pest infection.
3. Guard cells and stomata
Another component of the epidermis, the guard cells, are two bean-shaped, chlorophyll-containing cells surrounding each stoma. Unlike pavement cells, these cells have a definitive shape. However, the spatial arrangement of these cells depends not only on size but also on the shape of the air-space below them.
Depending on the concentration of water vapor, sugars and ions, these guard cells become turgid or flaccid, thus aiding in the opening or closing of the stomatal pore. When water enters the guard cell, they become turgid, thus closing the stoma and vice versa. The closing and opening of these stomatal pores also regulate the gaseous exchange in and out of the leaves during respiration and photosynthesis.
- Regulate the closing and opening of stomata, thus aiding in gaseous exchange.
- Help in photosynthesis.
Trichomes, also known as epidermal hairs, are tiny hair-like structures or spikey outgrowths located on the outermost region of the epidermis. The epidermis of petals forms a variation of trichomes called conical cells. Root hairs, which are extensions of root epidermal cells, increase the surface area of the root, greatly contributing to the absorption of water and minerals.
- Aid in better water and nutrient absorption.
- Protect plants from predators and pathogens by either trapping or poisoning them.
- Shield inner tissues of leaves.
Functions: What Does it Do
- Protects internal tissues from any mechanical shock or injury.
- Minimizes water loss, keeping plants from drying out.
- Controls the process of gaseous exchange during transpiration, photosynthesis, and respiration.
- Secretes metabolic compounds.
- Helps in the absorption of water and essential minerals.
- Protects plants from predators and parasitic attacks.
Ans: The cuticle of the dermal tissue, being a waxy material prevents the loss of water to the environment. Also, sensing the moisture content and temperature of the surroundings, the guard cells regulate the opening and closing of stomata, thus keeping the water level in check.
Article was last reviewed on Monday, May 2, 2022