Tissue System in Plants: Tissue is a collection of cells that perform a certain function. Plant cells, like those of other organisms, are organised into tissues. These tissues might be simple (containing only one cell type) or complex (containing multiple cell types). Plant tissues are divided into plant tissue systems, with their own set of functions. The plant tissue system is formed by plant cells that support and protect a plant. This article provides all the major details about the tissue system in Plants. Read on to know more about The Tissue System in Plants.

Tissue System in Plants

The structural and functional tissue systems of plants are known as plant tissue systems. The tissue system is the arrangement of different tissues in plants. These systems are large groups of tissues that share some characteristics. The epidermal tissue system, the ground tissue system, and the vascular tissue system are the three types of tissue systems. The cell proliferative activity of the shoot or root apical meristems is the origin of all three tissue systems, and each contains a small number of specialised cell types that carry out certain functions that are required for the plant’s growth and survival.

Fig: Tissue Systems in Plants

Epidermal Tissue System

The plant’s epidermal tissue system is the outermost covering. Protoderm is the origin of the epidermal tissue system. In vascular plants, a protoderm is a thin outer layer of meristematic tissue that gives rise to the epidermal tissue system. The epidermis, stomata, and epidermal outgrowths constitute the epidermal system.

a) Epidermis: The epidermis is made up of a single layer of parenchymatous cells that are closely packed together. The cells are living, and cytoplasm can be seen as a thin layer beneath the cell wall. The nucleus is situated on the periphery. A huge central vacuole is located within the cytoplasm. There are small, colourless plastids present. Epidermal cells have a tabular shape and are closely packed together without any intercellular spaces. They have thick primary cell walls and a special cuticle with an outer waxy layer that resists evaporative water loss on their exterior surface. The cuticle protects against mechanical injuries and prevents loss during the winter. It can be thought of as the “skin” of the plant. Its function is to cover and protect the plant, as well as to regulate gas exchange and water flow.
In secondary growth, the periderm, commonly known as bark, takes the place of the epidermis. In contrast to the epidermis, which is singlelayered, the periderm is multilayered. Cork cells (phellem), phelloderm, and phellogen make up the phellogen (cork cambium). Cork cells are nonliving cells that protect and insulate the plant by covering the outside of stems and roots. The periderm defends the plant from diseases and harm, as well as prevents excessive water loss and provides insulation.

b) Stomata: Stomata are small pores or openings found in the epidermis of leaves. They are composed of two specialised Kidney-shaped epidermal cells known as guard cells that regulate the diameter of the pore by controlling its opening and closing, thus regulating the take up of carbon dioxide and the release of oxygen and water. They are absent in the epidermis of the root. Stomata control the process of transpiration and gaseous exchange between internal tissues and the surrounding environment.

Fig: Stomata

c) Epidermal appendages: There are two types of epidermal appendages: trichomes and emergences.

(i)Trichomes: Trichomes are hair-like structures that develop on the epidermal. Trichomes can be found on any part of the plant. They can be temporary or long-lasting. They can either stay alive or die. They are multicellular structures with branched or unbranched branches. Cellulose is used to make their walls. Trichomes have a protoplast that is heavily vacuolated. The cuticle covers the walls. They aid in the reduction of transpiration, the increase of solar reflectance, and the storage of chemicals that protect the leaves from herbivore predation.

Root hairs: They are unicellular or multicellular epidermal cell outgrowths. They assist in the absorption of water and minerals. They also hold soil particles and play an important role in the plant’s anchoring.

Aerial hairs: They are unicellular or multicellular appendages that are covered by a cuticle layer. The hair is thickened with cellulose.

Stinging hairs: They are hollow hairs with siliceous tips that contain a highly irritant and inflammatory liquid containing histamine, serotonin, formic acid, tartaric acid, and oxalic acid. It is injected into the skin of animals that are rubbing against each other.

Glandular hairs: These glandular hairs produce essential oils and play a role in the odour of the plants.

(ii) Emergences: They are multicellular epidermal outgrowths. Emergence is illustrated by prickles. They are stiff and sharp outgrowths. They protect the plant from grazing animals and excessive transpiration.

Functions of Epidermal Tissue System

1. The epidermis protects the plant’s internal organs.
2. The epidermis reduces transpiration.
3. Stomata help in gas exchange, water and mineral uptake, and water vapour escape.
4. Photosynthesis is carried out by epidermal cells with chloroplasts.
5. Trichomes are also helpful for seed and fruit dispersal.
6. Root hairs soil absorb water and mineral salts from the soil.

Ground Tissue System

The ground meristems form the ground tissue systems. They make up a large portion of the plant’s body. Except for epidermal and vascular tissues, it comprises all the plant’s tissues. This layer comprises simple permanent tissues such as parenchyma, collenchyma, and sclerenchyma. Hypodermis, cortex, endodermis, pericycle, medullary rays, and pith are some of its components.

Palisade and spongy mesophyll cells, which are made up of parenchymatous cells, are found in the ground tissue system of leaves.

1. Hypodermis: The hypodermis is located beneath the epidermis. It is multilayered, with one, two, or a few layers of collenchymatous cells (in dicots) that are continuous or discontinuous and sclerenchymatous cells (in monocots).
2. Cortex: Cortex is the ground tissue that surrounds the centre cylinder and is found beneath the epidermis. With or without chloroplasts, Parenchymatous cells make up this type of cell. In addition to parenchyma, the cortex can have collenchyma, sclerenchyma, and sclereids. Starch, tannins, crystals, and other typical secretions are all found in cortical cells.
3. Endodermis: The innermost layer of the cortex is the endodermis. Due to the presence of starch, it is also known as a starch sheath. It consists of barrel-shaped cells without intercellular space. The cells of the endodermis are living. The radial and internal walls of the endodermal cell are thickened; a band of lignin or suberin known as Casparian strip is sometimes found on every cell’s radial and transverse wall.
4. Pericycle: In dicots, the pericycle is a single or multilayered layer that lies between the endodermis and the vascular bundles. The pericycle in roots is made up of parenchyma cells. Sclerenchymatous and parenchymatous cells make up this tissue. During secondary growth, these cells initiate the formation of lateral roots and vascular cambium. It always appears as a thin cylinder of tissue enclosing the vascular bundles and pith completely.
5. Medullary rays: Medullary rays are strips of parenchyma that run between the dicot stem’s vascular bundles. These are places that aren’t vascular. They are used to distinguish between xylem and phloem bundles. The apical meristem is where they originate from. They act as a connection between the pericycle and the pith. Some of the parenchyma cells of the medullary rays become meristematic and give rise to interfascicular cambium in dicots.
6. Pith: The medulla is another name for pith. It forms the central section of the stem and root. The inner portion of the ground or fundamental tissue system is referred to as pith. The dicot stem pith is mainly parenchymatous, while monocot stem pith is sclerenchymatous, in certain pith cells tannins and crystals are present. It contains intercellular space. Medullary or pith rays are pith extensions in the shape of narrow parenchymatous strips. Vascular bundles are distributed scattered throughout the ground tissue of monocot stems, and pith is not distinguishable. The pith is scant or absent in dicot roots, whereas it is extensively developed in monocot roots.

Functions of Ground tissue system

1. Ground tissue makes up the majority of the plant’s mass and fills the spaces between the dermal and vascular tissues.
2. It gives the plant support or mechanical strength.
3. It can also store food in the form of starch in some circumstances.
4. There are spaces for gaseous exchange between the cortex and the atmosphere.
5. Organic molecules are synthesised by ground tissues.
6. Sclerenchyma cells are hollow with thick walls that help to support the ground tissue.

Vascular Tissue System

The vascular tissue system is made up of xylem and phloem, which are complex tissues. Vascular bundles are conducting strands made up of xylem and phloem. Procambium and apical meristems give rise to vascular bundles. Tracheids, trachea, xylem fibres, and xylem parenchyma constitute xylem. Sieve tubes, companion cells, phloem parenchyma, and phloem fibres comprise phloem. The primary function of the xylem is to transport water and materials throughout the plant. The primary function of phloem is to transfer food materials throughout the plant.

A portion of procambium in gymnosperms and dicotyledons’ stems is undifferentiated and stays meristematic, known as cambium. It’s found in the vascular bundles that connect the phloem and xylem. Cambium cells have thin walls, hence a vascular bundle with cambium is called an open vascular bundle. A closed vascular bundle refers to a vascular bundle that lacks cambium. Cambium cells have thin walls.

Three types of vascular bundles are recognised based on the arrangement of phloem and xylem. These are radial, conjoint, and concentric.

(i) Radial vascular bundles: In radial vascular bundles, xylem and phloem strands are arranged on alternate radii. These are the most basic types. These are mostly found in angiosperm roots.

(ii) Conjoint vascular bundles: Xylem and phloem form a bundle, with xylem in the centre and phloem on the periphery. Conjoint bundles are divided into two categories.
a. Collateral: Xylem and phloem are on the same radius, with the xylem closer to the centre and phloem towards the periphery. On one side of the xylem strand, phloem can be found. In the dicot stem, cambium exists between the xylem and the phloem, forming collateral open vascular bundles. In monocot stems, there is no cambium between the xylem and the phloem forming collateral closed vascular bundles.

b. Bicollateral: Phloem strands are present on both the outer and inner sides of the xylem in a bicollateral bundle. Cucurbitaceae members are known for having such bundles. These bundles are never closed.

(iii) Concentric vascular bundles: One tissue is entirely encompassed by the other in this form of vascular bundle. These bundles are usually tied together. Amphivasal and Amphicribral are the two types.
a. Amphivasal: Xylem surrounds the phloem in this form of vascular bundle, as shown in Dracaena.
b. Amphicribral: Phloem surrounds the xylem in this kind, as seen in Ferns.

Fig: Different types of vascular bundles

Functions of Vascular tissue system

1. Conduction of water and nutrients takes place from the roots to the leaves.
2. Translocation of prepared carbohydrates from the leaves to the plant’s various storage organs and growing regions.

Summary

The arrangement of tissues in a plant is called a tissue system. The epidermal tissue system, the ground tissue system, and the vascular tissue system are the three types of tissue systems. The plant’s epidermal tissue system is the outermost covering. Protoderm is the origin of the epidermal tissue system. The epidermis, stomata, and epidermal outgrowths constitute the epidermal system. The ground meristems form the ground tissue systems. They make up a large portion of the plant’s body. Simple permanent tissues such as parenchyma, collenchyma, and sclerenchyma comprise this layer. Hypodermis, cortex, endodermis, pericycle, medullary rays, and pith are some of its components. The vascular tissue system comprises the xylem and phloem, which are complex tissues. Vascular bundles are conducting strands made up of xylem and phloem. Procambium and apical meristems give rise to vascular bundles.

Frequently Asked Questions (FAQs) on The Tissue System

Q.1. What are the three types of plant tissue systems?
Ans: The three types of plant tissue systems are epidermal tissue, ground tissue, and vascular tissue.

Q.2. What do you mean by stomata?
Ans: Stomata are small pores or openings found in the epidermis of leaves.

Q.3. What are medullary rays?
Ans: Medullary rays are strips of parenchyma that run between the dicot stem’s vascular bundles.

Q.4. What are the functions of the ground tissue system in plants?
Ans: The ground tissue system performs many functions. Two major functions are:
1. It gives the plant support or mechanical strength.
2. It can also store food in the form of starch in some circumstances.

Q.5. What are the most important functions of the vascular tissue system in plants?
Ans:
1. Conduction of water and nutrients takes place from the roots to the leaves.
2. Translocation of prepared carbohydrates from the leaves to the plant’s various storage organs and growing regions.

Learn about the Internal Structure of Leaf here

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