Integumentary tissues protect the plant from adverse environmental influences: solar overheating, excessive evaporation, sudden changes in air temperature, drying wind, mechanical impact, from the penetration of pathogenic fungi and bacteria into the plant, etc. Like other permanent tissues, integumentary tissues are formed from meristems during ontogenesis. There are primary and secondary integumentary
tissues that are respectively formed as a result of differentiation of cells of the primary and secondary meristems. Thus, the primary integumentary tissues include the skin, or epidermis, and epiblema, and the secondary tissues include the periderm (cork, cork cambium and phelloderm).
Peel or epidermis, covers all organs of annual plants, young green shoots of perennial woody plants of the current growing season, above-ground herbaceous parts of plants (leaves, stems and flowers). The epidermis most often consists of a single layer of tightly packed cells without intercellular space. It is easily removable and is a thin transparent film. Epidermis - living tissue, consists of a wall layer of protoplast with leukoplasts and a nucleus, a large vacuole that occupies almost the entire cell. The cell wall is mainly cellulose. The outer wall of the epidermal cells is thicker, the lateral and internal ones are thin. The outer wall of the skin of cereals, sedges, and horsetails can be impregnated with silica; crystals of calcium oxalate are sometimes found in dracaenas; polysaccharides in the form of mucus are sometimes found in seeds. May be deposited on the outer surface of the cell walls of some plants. suberins And cutins. Cell walls impregnated with suberin (suberization) are impermeable to water, vapors and gases. The side and inner walls of the cells have pores. The main function of the epidermis is the regulation of gas exchange and transpiration, carried out mainly through the stomata. Water and inorganic substances penetrate through the pores. Epidermis of some aquatic plants participates in photosynthesis; some desert plants store water in it.
Epidermal cells different plants unequal in shape and size. In many monocotyledonous plants, the cells are elongated; in most dicotyledonous plants, they have sinuous side walls, which increases the density of their adhesion to each other (Fig. 21). Epidermis of the upper and lower parts the leaf also differs in its structure: for example, on the underside of the leaf in the epidermis there are a larger number of stomata, and on the upper side there are much fewer of them; on the leaves of aquatic plants with leaves floating on the surface (water lily, water lily), stomata are present only on the upper side of the leaf, and in plants completely submerged in water there are no stomata.
Stomata- high specialized education epidermis, consist of two guard cells and a slit-like formation between them - the stomatal fissure (Fig. 21, A). Crescent-shaped guard cells regulate the size of the stomatal fissure; the gap can open and close depending on the turgor pressure in the guard cells, the carbon dioxide content in the atmosphere and other factors. Thus, during the day, when stomatal cells participate in photosynthesis, turgor pressure in stomatal
cells are high, the stomatal fissure is open, at night, on the contrary, it is closed. Similar phenomenon observed in dry times and when leaves wither, it is associated with the adaptation of stomata to store moisture inside the plant. Many species growing in areas with excessive moisture, especially in humid tropical forests, there are stomata through which water is released. The stomata are named hydathodes. Water in the form of droplets is released out and drips from the leaves. This also happens with some indoor plants (Monstera, Philodendron and other aroids) when atmospheric pressure usually before it rains. The “crying” of a plant is a kind of weather predictor and is scientifically called guttation. Hydathodes are located along the edge of the leaf; they do not have an opening or closing mechanism.
The epidermis of many plants has protective devices against unfavorable conditions: hairs, cuticle, waxy coating, etc.
Hairs (trichomes)- peculiar outgrowths of the epidermis, they can cover the entire plant or some of its parts. Hairs can be living or dead. The hairs help reduce moisture evaporation; in addition, they protect the plant from overheating, being eaten by animals, and from sudden temperature fluctuations.
Therefore, plants of arid - arid regions, high mountains, and subpolar regions are most often covered with hairs. globe, as well as plants from weedy habitats.
Hairs are unicellular and multicellular (Fig. 22). Single-celled hairs are presented in the form of papillae. Papillae are found on the petals of many flowers, giving them a velvety feel (tagetis, pansy). Single-celled hairs may be simple (on the underside of many fruit crops) and are usually dead. Single-celled hairs can be branched (shepherd's purse). More often, the hairs are multicellular, differing in structure: linear (potato leaves), bushy-branched (mullein), scaly and stellate-squamous (representatives of the Sucker family), massive (tufts of hairs from plants of the Lamiaceae family). There are glandular hairs in which essential substances (labiaceae and umbelliferous plants), pungent substances (nettle), etc. can accumulate (Fig. 23). The stinging hairs of nettle are impregnated with silica and are very brittle. Having broken off, the sharp edges of the hair injure the skin, the contents of the hair are poured onto the wound - formic acid, which irritates the skin. Stinging hairs of nettles, thorns of roses, blackberries, thorns on the fruits of umbrellas, datura, chestnut, etc. - peculiar outgrowths called Emergents, V
in the formation of which, in addition to epidermal cells, deeper layers of cells take part.
Epiblema (rhizoderm)- primary single-layer integumentary tissue of the root. It is formed from the outer cells of the apical meristem of the root near the root cap. The epiblema covers the young root endings. Through it, water and mineral nutrition of the plant from the soil is carried out. Since a certain amount of energy is expended on root nutrition, epiblema contains many mitochondria. Epiblema cells are thin-walled, with more viscous cytoplasm, and lack stomata and cuticle. The epiblema is short-lived and is constantly renewed through mitotic divisions.
Periderm- a complex multilayer complex of secondary integumentary tissue (cork, cork cambium, or phellogen, and phelloderm) of the stems and roots of perennial dicotyledonous plants and gymnosperms, which are capable of continuously thickening. To a lesser extent, periderm is found in monocots and annual plants. By the autumn of the first year of life, the shoots become lignified, which is noticeable by a change in their color from green to brown-gray, i.e. there was a change from the epidermis to the periderm, capable of withstanding unfavourable conditions winter period. The periderm is based on the secondary meristem - phellogen (cork cambium), formed in the cells of the main parenchyma lying under the epidermis. Phellogen has weak meristematic activity. It forms cells in two directions: outward - cells traffic jams, inside - living cells phelloderms, and there are much more cork cells than phelloderm cells (Fig. 24). The plug consists of dead cells filled with air, they are elongated,
They fit tightly together, there are no pores, their walls are impregnated with suberin, the cells are air- and water-tight. Cork cells are brown or yellowish color, which depends on the presence of resinous or tannin substances in the cells (cork oak, Sakhalin velvet). White color Birch cork is caused by betulin. Cork is a good insulating material, does not conduct heat, electricity or sound, and is used to seal bottles, etc. A thick layer of cork has cork oak, types of velvet, and cork elm. Cork oak grows in Mediterranean countries. A layer of cork about 10 cm thick is removed from cork oak plantations approximately every 10 years. In Russia, in deciduous forests Far East and about. Amur velvet and Sakhalin velvet grow on Sakhalin, but their cork thickness does not exceed 6-7 cm.
Lentils- “ventilation” holes in the cork to ensure gas and water exchange between living, deeper plant tissues and external environment. Externally, lentils are similar to lentil seeds, which is why they got their name. As a rule, lenticels are laid to replace stomata. The shapes and sizes of lentils are different. Thus, in birch, the lentil has a narrow transverse stripe up to 15 cm long. However, in quantitative terms, there are much fewer lentils than stomata. Lentils are round, thin-walled, chlorophyll-free cells with intercellular spaces that lift the skin and break it. This layer of loose, slightly suberized parenchyma cells that make up the lentil is called fulfilling tissue (Fig. 25).
Crust- a powerful integumentary complex of dead outer cells of the periderm. It forms on perennial shoots and roots of woody plants. The crust has a cracked and uneven shape. It protects tree trunks from mechanical damage, ground fires, low temperatures, sunburn, penetration of pathogenic fungi and bacteria. The crust grows due to the growth of new layers of periderm underneath it. In tree and shrub plants, the crust appears (for example, in pine) on
8 - 10th, and for oak - at 25 - 30th year of life. The bark is part of the bark of trees. On the outside, it constantly peels off, throwing off all kinds of spores of fungi and lichens.
The integumentary tissue is the skin (epidermis) and cork. Living skin cells cover the tissue or organ in one continuous layer. On top, the epidermal cells are covered with cuticle, thin film from fat-like substances, often have pubescence.
Cork is multi-layered dead tissue. The membranes of its cells are thickened and saturated with a substance similar in composition to fats. After the contents die, the cell cavities are filled with air, resinous or tannin substances. The functions of integumentary tissues are to protect organs from evaporation, drying, cooling, and various damage.
Mechanical tissue consists of dead cells with thickened membranes. Most cells are shaped like long fibers. However, there are also those in which the length is approximately equal to the width. Their shells are even thicker than those of fibers. These are stony cells that give hardness to the pits of cherries, apricots, nut shells, etc.
In plants, complexes of conducting cells and mechanical tissue fibers are often found. Such complexes are called vascular-fibrous, or conductive, bundles. They stretch along the root, stem, leaf petioles, and form a network of leaf veins. The main parts of the bundle of most flowering plants are two zones - wood (xylem) and phloem (phloem). The woody part of the bundle consists of vessels and trachea ides and adjacent wood parenchyma cells. The bast part of the bundle consists of sieve tubes with companion cells and bast parenchyma. Around these zones of the beam there are cells of mechanical tissue, which significantly strengthen it.
Vascular bundles begin to form in the growth cone at the apexes of the stem and root and the primary meristematic tissue - the procambium. It does not function in the plant for long. After some time, the division of its cells stops, and they either all turn into elements of xylem and phloem, or a number of procambial cells remain between the phloem and xylem, which become a secondary meristem - the cambium. The cambium cells divide parallel to the plant surface and the tuft can grow through the formation of secondary phloem and xylem.
Tufts with a cambium are called open, while those without a cambium are called closed. The ability to form certain bundles - characteristic plants. Thus, monocots are characterized by closed vascular bundles, while dicots are characterized by open ones.
In every organ flowering plant the combination of fabrics is different. The differentiation of plant cells into tissues and organs is a major aromorphosis that ensures adaptation to living conditions on land.
They are located on the border with the external environment. Most consist of tightly packed living cells, less often dead cells.
Perform a barrier role, protecting internal organs from drying out and damage.
Integumentary tissue is a barrier to the penetration of pathogenic microorganisms. It was formed in the process of evolution at the moment when plants emerged from aquatic environment to land. It arises from meristems.
What primary integumentary tissues are distinguished?
Primary integumentary tissues are distinguished:
1. Primary - epidermis and epiblema
2. Secondary - periderm (cork), formed from phellogen
3. Tertiary - rhytide or crust.
Epidermis and its main features:
Epidermis: leaves and young shoots are covered like fur with a homogeneous primary integumentary tissue - the epidermis. It arises from the cone of growth of the tunica. The outer surface of epidermal cells is often covered with a layer of cuticle. It can reach considerable thickness.
There are no intercellular spaces, the cells are tightly closed. Main function epidermis regulation of gas exchange and transpiration, i.e. evaporation of water by the plant. They occur through the stomata, but can also partially occur through the cuticle. The shape of epidermal cells is different. There is one large vacuole inside the cell.
Typically, epidermal cells are colorless, but sometimes, especially in the cells of flower fruits, they can be colored. In some plants, under the epidermis there is a special tissue - the hypodermis (in pine needles).
Performs mechanical function and protects against evaporation.
Epidermal derivatives:
Stomata- highly specialized formations of the epidermis consist of two guard cells and a stomatal fissure. The walls of the guard cells are not evenly thickened.
The abdominal ones (near the slit) are thicker than the removable ones. The gap can expand and contract, regulating transpiration and gas exchange. Beneath it lies the respiratory or air cavity, surrounded by leaf pulp cells. The epidermal cells adjacent to the guard cells are called secondary or near-stomatal. Together they form the stomatal apparatus.
The stomatal type depends on the structure of the stomatal apparatus. Their study was called stomatography (“stoma” - from the Greek stomata). The data can be used in plant taxonomy and pharmacognosy for microdiagnostics of medicinal plant materials.
Stomatal types:
1. Anomocytic type - (anomos - disorderly). Side cells do not differ from other epidermal cells and are characteristic of all groups higher plants, excluding conifers.
2. Diacitic type - there are only two subsidiary cells, the common wall of which is at right angles to the guard cells (Labiaceae).
3. Paracytic type - (pair - side by side). Cork cells are located parallel to the guard cells and stomatal fissure (ferns, horsetails, a number of flowering plants).
4. Anisocytic type - (anisos - unequal) guard cells are surrounded by three subsidiary cells, one of which is noticeably larger or smaller than the others (only in flowering plants).
5. Tetracytic type - (tetra - four) guard cells surrounded by four subsidiary cells (monocots).
6. Encyclocytic type - (cyclos - wheel). The subsidiary cells form a narrow ring around the guard cells (ferns).
7. Actinocyte type - (actis - ray). Side cells radiate away from the guard cells. This type of cell is found only in flowering plants.
The hairs lining the stomata are called stomatal crypts. The number of stomata on a leaf varies greatly from 10-20 to 200-300 per 1 sq. mm. The mechanism of their operation is very complex and depends on temperature, light, and water. They make up 1-2% of the leaf area.
What are epidermal trichomes?
The hairs on the epidermis are called trichomes. They are divided into covering and glandular. Glandulars are derivatives of secretory tissues. The coverts are usually located on the same side as the stomata. Trichomes are outgrowths of epidermal cells that vary in shape, structure and function.
Forms of epidermal trichomes:
They have the form of hairs (covering or glandular, which will be considered as part of excretory tissues), scales, etc. The functions of most types of trichomes are unclear. Covering trichomes can be unicellular (in apple trees), multicellular unbranched (in potatoes) or branched (in mullein), star-shaped (in oleaster)
A little about hairs...
Hairs able to stay alive for a long time. But often the protoplasts in them die off, and the hairs fill with air. Such hairs protect the plant from strong solar insolation, excessive evaporation and temperature fluctuations.
Many alpine plants (edelweiss) are distinguished by strong pubescence. Some dead hairs, such as those covering cotton seeds, reach a length of 55 mm and are widely used in the textile industry. Trichomes protect the plant from insects
The thicker the pubescence, the less often insects use it as food or for laying eggs; insects and their larvae are pinned on the hooked trichomes.
Outgrowths on the epidermis are called emergents - these are stinging hairs of nettles, thorns of roses, raspberries, blackberries, thorns on the fruits of dope and chestnut.
The epidermis functions, as a rule, for one year; usually by autumn it is replaced by a cork.
Epiblem: not rarely called rhizoderm. It arises from a dermatogen, through which water and mineral salts are absorbed from the soil. This is the hair-bearing layer in the absorptive zone of the cortex. Root hairs are not formed in all cells of the epidermis of the cortex, but through special trichoblasts.
The main function of the epiblema is absorption, selective absorption from the soil of water with mineral nutrition elements dissolved in it. Through the epiblema, a number of substances are released, for example, acids, which act on the substrate and transform it.
The cytological features of the epiblema are related to its functions. These are thin-walled cells, lacking a cuticle, with viscous cytoplasm, with a large number mitochondria (active absorption of substances occurs with the expenditure of energy).
The absorbing surface of the epiblema increases 10 times or more due to the formation of root hairs. A root hair is a cell outgrowth 1...2 (3) mm long.
During education root hair the outer wall of the cell protrudes, the nucleus moves to its growing end, where it is located in the wall cytoplasm. There are also numerous dictyosomes Golgi apparatus, producing substances for building cell wall. The central vacuole occupies most cells. The lifespan of epiblema cells is up to 15...20
Let's talk about secondary integumentary tissues...
What is the periderm?
Periderm(cork or phellem) - (from the Greek “peri” - around and “derma” - skin).
Continuous multilayer secondary integumentary tissue of the stems and roots of multilayer plants.
Formed from phellogen, which arises from the cells of the main parenchyma lying under the epidermis. During the formation of the periderm, phellem cells are deposited outside, and living parenchyma-shaped cells - phelloderm - are deposited inside. The cork consists of tabular, initially living, then dead cells, devoid of intercellular spaces.
Their shell is impregnated with suberin. The cells are air-plug and waterproof. It forms a protective case that protects living tissues from water loss. In cork oak and Amur velvet, a thick layer of cork is formed. It is used as a capping material.
From the very beginning, lenticels are formed in the periderm - holes covered with loose tissue. The stem is “ventilated” through them; they look like small tubercles on the surface of young shoots. The structure of lentils is used in the diagnosis of plant materials.
Tertiary integumentary tissue….
The crust is...
In perennial axial organs of plants, several periderms develop. Gradually they die off and form a powerful integumentary complex - a crust or “rhythid”. It forms on the trunks of perennial trees and on the roots.
How does the crust form?
Several periderms develop on the trunks, each subsequent one being laid deeper than the previous one. Living tissues enclosed between the layers of cork die, and a covering complex - a crust - is formed.
The crust consists of several layers of cork and dead tissue enclosed between them.
Types of crusts formed:
If the formation of periderms does not occur along the entire circumference of the trunk, but in separate semi-arcs, then the crust is formed in irregular pieces. This crust is called scaly and is formed in most plants.
A ring-shaped crust is formed if each newly emerging periderm encircles the trunk, periodically cutting off cylindrical sections of the bark (for example, in grapes).
The crust is not capable of stretching, so as the trunk thickens, cracks appear in it. At the bottom of the cracks in the inner periderm there are lenticels that ensure gas exchange.
Also plays a protective role: protects against burns, abrupt changes temperature, cold, illness.
Educational tissues (meristems)
Educational tissues in the body of plants are located in different places, so they are divided into the following groups (Figure 0;1).
1. Apical (apical) meristems located at the tops, or apices, of axial organs - stem, root. With the help of these meristems, the vegetative organs of plants grow in length.
2. Lateral meristems characteristic of axial organs. There they are arranged concentrically, in the form of a coupling.
3. Intercalary, or intercalary, meristems originate from apical meristems. These are groups of cells that are not yet able to reproduce, but have embarked on the path of differentiation. There are no initial cells among them, but many are specialized.
4. Wound meristems provide restoration of the damaged part of the body. Regeneration begins with dedifferentiation, that is, the reverse development from specialized cells to meristematic ones. They turn into phellogen, which forms traffic jam covering the surface of the wound. Dedifferentiated cells, dividing, can form loose parenchymal tissue - callus. Under certain conditions, plant organs are formed from it.
Integumentary tissues
They act as a boundary barrier, separating underlying tissues from the environment. The primary integument of a plant consists only of living cells. Secondary and tertiary integuments are mainly made of dead cells with thick cell walls.
Main functions of integumentary tissues:
· protecting the plant from drying out;
· protection from harmful microorganisms;
· protection from sunburn;
· protection from mechanical damage;
regulation of metabolism between the plant and environment;
· perception of irritation.
Primary integumentary tissue - epidermis, epidermis . Consists of living cells. Formed from apical meristems. Covers young growing stems and leaves.
The epidermis was formed in plants in connection with their exit from the aquatic habitat onto land in order to prevent them from drying out. Except for the stomata, all epidermal cells are tightly connected to each other. The outer walls of the main cells are thicker than the others. The entire surface is covered with a layer of cutin and plant waxes. This layer is called cuticle(skin). It is absent on growing roots and underwater parts of plants. When it dries out, the permeability of the cuticle is significantly weakened.
Except main cells, there are others in the epidermis, in particular hairs, or trichomes. They are unicellular and multicellular (Fig. 2). Functionally, they increase the surface of the epidermis, for example, in the root growth zone, serve as mechanical protection, cling to support, and reduce water loss. A number of plants have glandular hairs, for example, nettle.
Only higher plants have epidermis stomata, which regulate the exchange of water and gases. If there is no cuticle, then there is no need for stomata. Stomata are a group of cells that form stomatal apparatus, which consists of two guard cells and adjacent epidermal cells - side cells. They are different from the main epidermal cells (Fig.3 ). Guard cells differ from the surrounding cells in the shape and presence of a large number of chloroplasts and unevenly thickened walls. Those facing each other are thicker than the others (Fig.4) . Forms between guard cells stomatal fissure which leads to substomatal space, called substomatal cavity. Guard cells have high photosynthetic activity. They contain a large number of storage starch and numerous mitochondria.
The number and distribution of stomata and types of stomatal apparatus vary widely among various plants. Modern bryophytes lack stomata. Photosynthesis is carried out by the gametophytic generation, and sporophytes independent existence are not capable.
Typically, stomata are located on the underside of the leaf. Those floating on water surface plants - on the upper surface. In cereal leaves, stomata are often distributed evenly on both sides. Such leaves are illuminated relatively evenly. On 1mm2 surface there can be from 100 to 700 stomata.
Secondary integumentary tissue (periderm). This tissue replaces the epidermis when green color annual shoots change to brown. It is multilayered and consists of a central layer of cambial cells - phellogen. Phellogen cells, dividing, lay out a layer phellems, and inside - phelloderma(Fig. 5).
Fellema, or cork. First it consists of living thin-walled cells. Over time, their walls become saturated with suberin and plant waxes and die. The contents of the cell are filled with air.
Functions of the phellem:
· prevents moisture loss;
· protects the plant from mechanical damage;
· protects against pathogenic microorganisms;
· provides thermal insulation, since the cells are filled with air.
Phellogen cells, located in the epidermis itself, the underlying subepidermal layer, less often in the deep layers of the primary cortex, are the generating basis of the primary cortex.
The cork layer is not constant. There are gaps in it that communicate with the intercellular spaces located nearby. In this case, small tubercles form on the surface - lentils, which connect the intercellular spaces with atmospheric air (Fig.6,7).
In autumn, phellogen under the lentils deposits a layer of suberized cells, which greatly reduces transpiration, but does not completely eliminate it. In spring, this layer is destroyed from the inside. On the light birch bark, the lenticels are clearly visible in the form of dark lines.
Tertiary covering tissue (crust), It is also characteristic only of woody forms of plants.
Phellogen is repeatedly laid down in the deeper layers of the cortex. The tissues that are outside of it die over time, forming a crust. Its cells are dead and incapable of stretching. However, living cells located deeper are dividing, which leads to an increase in the transverse size of the trunk. Over time, the outer layer of the crust breaks. The time for such a gap to occur is quite constant value for specific plants. In an apple tree this happens in the seventh year of life, in a hornbeam - in the fiftieth. In some species this does not happen at all. The main function of the crust is protection against mechanical and thermal damage.