Textile- a group of cells that are structurally and functionally interconnected with each other, similar in origin, structure and performing certain functions in the body.
The tissues originated from higher plants in connection with reaching land and achieving the greatest specialization at angiosperms, in which up to 80 species are distinguished. The most important plant tissues:
Educational,
Integumentary,
Conductive,
Mechanical
Basic.
Fabrics can be simple and complex. Plain fabricsconsist of one type of cell (for example, collenchyma, meristem), andcomplex- from cells of different structure, performing, in addition to the main and additional features(epidermis, xylem, phloem, etc.).
Educational fabrics , or meristems, are embryonic tissues. Thanks to their long-lasting ability to divide (some cells divide throughout life), meristems participate in the formation of all permanent tissues and thereby form the plant, and also determine its long-term growth.
The cells of educational tissue are thin-walled, multifaceted, tightly closed, with dense cytoplasm, a large nucleus and very small vacuoles. They are capable of dividing in different directions.
According to the origin of meristems, there are primary and secondary. The primary meristem is the embryo of the seed, and in an adult plant it remains at the tip of the roots and tips of the shoots, which makes it possible for them to grow in length. Further growth of the root and stem in diameter (secondary growth) is ensured secondary meristems- cambium and phellogen. Based on their location in the plant body, apical (apical), lateral (lateral), intercalary (intercalary) and wound (traumatic) meristems are distinguished.
Integumentary tissues located on the surface of all plant organs. They perform a mainly protective function - they protect plants from mechanical damage, penetration of microorganisms, sudden temperature fluctuations, excessive evaporation, etc. Depending on their origin, three groups of integumentary tissues are distinguished - epidermis, periderm and crust.
Epidermis (epidermis, skin)- primary integumentary tissue located on the surface of leaves and young green shoots (Fig. 8.1). It consists of a single layer of living, tightly packed cells that do not have chloroplasts. The cell membranes are usually tortuous, which ensures their strong closure. The outer surface of the cells of this tissue is often covered with a cuticle or waxy coating, which is an additional protective device. The epidermis of leaves and green stems contains stomata that regulate transpiration and gas exchange in the plant.
Periderm- secondary integumentary tissue of stems and roots, replacing the epidermis in perennial (less often annual) plants (Fig. 8.2.). Its formation is associated with the activity of the secondary meristem - phellogen (cork cambium), the cells of which divide and differentiate in the centrifugal direction (outward) into the cork (phellema), and in the centripetal direction (inward) - into a layer of living parenchyma cells (phelloderm). Cork, phellogen and phelloderm make up the periderm.
Rice. 8.1. Leaf epidermis of various plants: a-chlorophytum; 6 - common ivy: in - fragrant geranium; G - white mulberry; 1- epidermal cells; 2 - stomatal guard cells; 3 - stomatal fissure.
Figure 8.2. Periderm of elderberry stem (a - cross section of a shoot, b - lentils): I-performing fabric; 2 - remnants of the epidermis; 3 -cork (phellema); 4 - phellogen; 5 - phelloderm.
The cells of the cork are impregnated with a fat-like substance - suberin - and do not allow water and air to pass through, so the contents of the cell die and it fills with air. The multilayer cork forms a kind of stem cover that reliably protects the plant from adverse influences. environment. For gas exchange and transpiration of living tissues lying under the plug, the latter has special formations - lentils; These are gaps in the plug filled with loosely arranged cells.
Crust formed in trees and shrubs to replace cork. In the deeper tissues of the cortex, new areas of phellogen are laid down, forming new layers of cork. As a result, the outer tissues are isolated from the central part of the stem, deformed and die. On the surface of the stem, a complex of dead tissues gradually forms, consisting of several layers of cork and dead sections of bark. A thick crust lasts longer reliable protection for a plant than a cork.
Conductive fabrics ensure the movement of water and dissolved in it nutrients by plant. There are two types of conductive tissue - xylem (wood) and phloem (bast).
Xylem is the main water-conducting tissue of higher vascular plants, ensuring the movement of water with minerals dissolved in it from the roots to the leaves and other parts of the plant (ascending current). It also performs a supporting function. The xylem consists of tracheids and tracheae (vessels) (Fig. 8.3), wood parenchyma and mechanical tissue.
Tracheids They are narrow, highly elongated dead cells with pointed ends and lignified membranes. The penetration of solutions from one tracheid into another occurs by filtration through pores - recesses covered with a membrane. Liquid flows through the tracheids slowly, since the pore membrane prevents the movement of water. Tracheids are found in all higher plants, and in most horsetails, club mosses, ferns and gymnosperms they serve as the only conducting element of the xylem. Angiosperms have vessels along with tracheids.
Figure 8.3. Elements of xylem (a) and phloem (6): 1-5 - ringed, spiral, scalariform and porous (4, 5) trachea, respectively; 6 - ringed and porous tracheids; 7 - sieve tube with companion cell.
Trachea (vessels)- these are hollow tubes consisting of individual segments located one above the other. In the segments, through holes are formed on the transverse walls - perforations, or these walls are completely destroyed, due to which the speed of the flow of solutions through the vessels increases many times over. The shells of the vessels are impregnated with lignin and give the stem additional strength. Depending on the nature of the thickening of the membranes, tracheas are distinguished as ringed, spiral, scalariform, etc. (see Fig. 8.3).
Phloem conducts organic substances synthesized in the leaves to all plant organs (downward current). Like xylem, it is a complex tissue and consists of sieve tubes with companion cells (see Fig. 8.3), parenchyma and mechanical tissue. Sieve tubes are formed by living cells located one above the other. Their transverse walls are pierced with small holes, forming a kind of sieve. The cells of the sieve tubes are devoid of nuclei, but contain cytoplasm in the central part, strands of which pass through through holes in the transverse partitions into neighboring cells. Sieve tubes, like vessels, stretch along the entire length of the plant. Companion cells are connected to the segments of the sieve tubes by numerous plasmodesmata and, apparently, perform some of the functions lost by the sieve tubes (enzyme synthesis, ATP formation).
Xylem and phloem are in close interaction with each other and form special complex groups in plant organs - vascular bundles.
Mechanical fabrics ensure the strength of plant organs. They form a frame that supports all plant organs, resisting their fracture, compression, and rupture. The main characteristics of the structure of mechanical tissues, ensuring their strength and elasticity, are the powerful thickening and lignification of their membranes, close closure between cells, and the absence of perforations in the cell walls.
Mechanical tissues are most developed in the stem, where they are represented by bast and wood fibers. In roots, mechanical tissue is concentrated in the center of the organ.
Depending on the shape of the cells, their structure, physiological state and the method of thickening of the cell membranes, two types of mechanical tissue are distinguished: collenchyma and sclerenchyma (Fig. 8.4).
Rice. 8.4. Mechanical fabrics: a -angular collenchyma; 6- sclerenchyma; V -- sclereids from cherry plum fruits: 1 - cytoplasm, 2-thickened cell wall, 3 - pore tubules.
Collenchyma is represented by living parenchyma cells with unevenly thickened membranes, making them especially well adapted for strengthening young growing organs. Being primary, collenchyma cells easily stretch and practically do not interfere with the elongation of the part of the plant in which they are located. Collenchyma is usually located in separate strands or a continuous cylinder under the epidermis of the young stem and leaf petioles, and also borders the veins in dicotyledonous leaves. Sometimes collenchyma contains chloroplasts.
Sclerenchyma consists of elongated cells with uniformly thickened, often lignified membranes, the contents of which die in the early stages. The membranes of sclerenchyma cells have high strength, close to the strength of steel. This tissue is widely represented in the vegetative organs of land plants and forms their axial support.
There are two types of sclerenchyma cells: fibers and sclereids. Fibers- these are long thin cells, usually collected in strands or bundles (for example, bast or wood fibers). Sclereids - these are round, dead cells with very thick, lignified membranes. They form the seed coat, nut shells, seeds of cherries, plums, and apricots; they give the flesh of pears their characteristic coarse character.
Main fabric, or parenchyma, consists of living, usually thin-walled cells that form the basis of organs (hence the name tissue). It houses mechanical, conductive and other permanent tissues. The main tissue performs a number of functions, and therefore they distinguish between assimilation (chlorenchyma), storage, pneumatic (aerenchyma) and aquiferous parenchyma (Fig. 8.5).
Figure 8.5. Parenchymal tissues: 1-3 - chlorophyll-bearing (columnar, spongy and folded, respectively); 4-storage (cells with starch grains); 5 - pneumatic, or aerenchyma.
Cells assimilation tissues contain chloroplasts and perform the function of photosynthesis. The bulk of this tissue is concentrated in the leaves, a smaller part in young green stems.
In cells storing proteins, carbohydrates and other substances are deposited in the parenchyma. It is well developed in the stems of woody plants, in roots, tubers, bulbs, fruits and seeds. Plants of desert habitats (cacti) and salt marshes have aquifer parenchyma, which serves to accumulate water (for example, large specimens of cacti from the genus Carnegia contain up to 2-3 thousand liters of water in their tissues). Aquatic and marsh plants develop a special type of basic tissue - pneumatic parenchyma, or aerenchyma. Aerenchyma cells form large air-bearing intercellular spaces, through which air is delivered to those parts of the plant whose connection with the atmosphere is difficult
Onion scales under a microscope
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The concept of “plant tissue”. Fabric types
It is characteristic of most multicellular organisms that during their development, cells begin to differ in structure and the functions they perform. This phenomenon is called differentiation in science. As a result of this process, tissues of multicellular organisms are formed.
Higher plants and most multicellular animals have several types of developed tissues. But multicellular algae, fungi and sponges do not have such tissues or they are poorly differentiated. In plants, all types of tissues, without exception, are formed from educational tissue. The tissues of multicellular plants are divided into educational, integumentary, basic, conductive, and mechanical. Let's look at their structure and functions in more detail.
Educational fabrics
Educational tissues (or meristem) consist of cells capable of division. They are the ones that give rise to all other types of cells. Cells of educational tissues are distinguished by a large nucleus and thin elastic walls with a small cellulose content.
According to the location in the plant, the meristem can be: apical, lateral and intercalary. Apical meristem located at the top of the shoot or root. It ensures the growth of these organs in length. Lateral meristem (cambium) is located in the middle of perennial roots and shoots, covering their central part in the form of a cylinder. It is responsible for the growth of the plant in thickness. Inserted meristem located at the base of the internodes of the stem of some plants (for example, cereals). Just like the apical one, it ensures the growth of the shoot in length. At the same time, such growth is called intercalary, because it occurs as a result of elongation of internodes.
Integumentary tissues
Integumentary tissues are located on the surface of plant organs. They separate internal tissues from the external environment, protect them from the adverse effects of the environment and various damages. Integumentary tissues can consist of different cells, including living or dead. There are main types of integumentary tissues: epidermis (skin) and periderm.
Peel (epidermis or epidermis) this is the primary integumentary tissue. It is represented by one layer of small, thick-walled, tightly closed cells, devoid of chloroplasts. The membranes of epidermal cells fit tightly to each other. This is achieved due to the fact that usually the membranes of these cells are tortuous. The top of the skin may be covered with a layer of waxy substance – cuticle. This is a natural adaptation that prevents the plant from excessive evaporation of water. In addition, the surface of the skin may often be covered with hairs. of various structures. Their functions depend on their structure and location (in nettle – protection, root hairs – plant nutrition). The skin contains special formations - stomata. They provide communication between the plant and the atmosphere (gas exchange and transpiration).
Note 1
U perennial plants the epidermis is replaced by secondary integumentary tissue - periderm (plug) . The thickened cell walls are saturated with a fat-like substance, after which they become impenetrable to water and air. A plug (corky substance) is formed. Small humps - lentils - form on the surface of the cork. Gas exchange and transpiration occur through them.
Conductive fabrics
Plants have two types of conducting tissues that provide ascending and descending transport of substances. These tissues are called xylem and phloem.
Xylem consists of tracheids and tracheae (vessels). It is responsible for the transport of water and substances dissolved in it from the roots of the plant to other organs (ascending transport). Tracheids are elongated dead cells. Their shells have become woody. Transport occurs by filtration through pores. Tracheas look like hollow tubes, consisting of individual segments on top of each other. Their shells are impregnated with lignin.
Phloem consists of sieve tubes. These are living cells through which organic substances are transported (downward flow).
Vessels, tracheids and sieve tubes, together with the main and mechanical tissues, form vascular-fibrous bundles (for example, veins in a leaf). Plants can also have laticifers - elongated conducting cells through which juice (latex) of orange or milky white color moves - dandelion, celandine, hevea.
Mechanical fabrics
Mechanical tissues give plants strength and flexibility. They perform a supporting function in the plant body. They are represented by bast and wood fibers. These tissues consist of living and dead cells that have an elongated shape and unevenly thickened cell walls. Depending on the structure of cells, their shape and condition, thickening of cell membranes, two types of mechanical tissue are distinguished: collenchyma and sclerenchyma.
Collenchyma consists of living cells and is located under the epidermis of a young shoot. It may contain chloroplasts and take part in photosynthesis.
Sclerenchyma consists of dead, woody cells. Sclerenchyma can be part of not only shoots, but also seed coats, nut shells, and fruit seeds.
Main fabric
The main tissue (parenchyma) consists mainly of living cells with large intercellular spaces. Parenchyma fills the spaces between other types of cells. Depending on the structural features of the main tissue and the functions performed, it comes in several varieties: photosynthetic (contains chloroplasts and is found mainly in leaves), storage (in fruits, roots, in the core of the plant). Cacti and aloe have very developed water-storing parenchyma.
Note 2
The main thing to note is that the structure of tissue cells is closely related to the functions that the cells of this tissue perform.
Plant tissues: Meristem, Parenchyma and Integument
There are the following types of plant tissues: educational (meristem), integumentary, basic (parenchyma), conductive, mechanical and excretory. Simple tissues consist of cells that are identical in shape and function. These are educational, basic, mechanical tissues. Complex tissues are made up of cells that vary in shape and function. For example, integumentary, conductive. In the process of evolution, the most advanced tissues were formed in angiosperms.
Educational or Meristem(from Greek meristos– divisible). The cells are living, thin-walled, have thin cell walls with a small amount of cellulose, with a large nucleus, and often divide. They give rise to almost all cells of other tissue types and ensure plant growth throughout its life. With each division, one of the newly formed cells remains meristematic, and the second turns into a cell of some tissue. Division is regulated by phytohormones.
Types of educational fabrics
Based on their location, apical, intercalary and lateral meristems are distinguished. Apical (apical ) is located in the root division zone and the growth cone at the shoot apex. It ensures their growth in length. It is laid in the body of the embryo. Each lateral shoot and lateral root develops its own apical meristem.
Lateral located inside the stem or root, covering their central part. Ensures the growth of these organs in thickness. For example, cambium is found mainly in trees, sometimes in herbaceous plants.
Intercalary (intercalary) found at the base of the stem internodes in some plants (cereals, horsetails) and provides intercalary growth. This meristem ceases to exist and turns into permanent tissues when the growth of the stem or leaf ends.
There are also primary And secondary meristems. Primary The meristem develops in the embryo and determines the growth and development of the seedling. It is formed at the tops of the embryonic root and stalk. Secondary is formed from the primary one and is formed later. Secondary meristems provide secondary growth in thickness of the stem and root (cambium and phellogen). The cork cambium arises from the cells of the main tissue or epidermis. Among the secondary meristems there are wound, which gives rise to special protective tissue in places of damage.
Ground tissue or parenchyma(from Greek parenchyma- poured nearby). It makes up the majority of all plant organs. It fills the gaps between conductive and mechanical tissues and is present in all organs. The parenchyma consists of living cells with relatively thin walls. They may have large gaps - intercellular spaces . Individual parenchyma cells can perform secretory function. Under certain conditions, parenchyma cells can restore the ability to divide and form a cork cambium, etc.
Types of main fabric
There are: assimilation, storage, air-bearing, aquiferous parenchyma.
Assimilation , or chlorophyll-bearing (chlorenchyma) . Photosynthesis occurs in it. Consists of living cells containing chloroplasts. It is found in green plant organs, mainly in leaves. In the leaves it is also called mesophyll .
Storage . Found in all plant organs (stem, root, rhizome, etc.). Sometimes it forms separate layers. The storage parenchyma consists of colorless cells with a large number of inclusions. Leukoplasts are located in the cells, and sometimes chromoplasts are located in the parenchyma of flowers and fruits. Storage substances - carbohydrates, proteins, fats.
Airborne , or aerenchyma (from Greek aer- air). This tissue has large intercellular spaces filled with air. Performs the functions of gas exchange and transfer of gases to different tissues. Characteristic mainly of aquatic plants.
Aquifer . The cells have vacuoles that help retain moisture. Characteristic of plants that grow in dry places.
They separate plant organs from the external environment. The main function is to protect plants from its adverse effects. There are primary (epidermis, or skin) and secondary.
Epidermis
Epidermis (from Greek epi- above, above and dermis– skin) consists of one or several layers of colorless living cells. Formed from the apical (apical) meristem. The cells adhere tightly to one another. They retain the ability to divide for some time. Their outer wall is thickened and can be impregnated with minerals. In horsetails, for example, silicon dioxide (Si0 2) is deposited. From the outside, the epidermis is covered with a layer cuticles (from lat. cuticula– skin), which is a secretion product of epidermal cells and consists of a lipoprotein substance cutina and pectin polysaccharide. Sometimes the epidermis is covered with a layer of wax of varying thickness. The cuticle prevents intense evaporation of water through its surface, therefore it is especially well developed in plants that grow in arid climates.
Epidermal cells lack chloroplasts, but contain leucoplasts. Chloroplasts contain special cells of the epidermis - stomatal guard cells . Stomata are surrounded supporting cells . Guard cells are bean-shaped and surround stomatal slits . Below the gap is a large cavity called respiratory . It is surrounded by leaf mesophyll cells. Stomata are located mainly on the leaves, sometimes on the stem.
The walls of the guard cells are thickened unevenly. Those walls that form the stomatal fissure are significantly thicker compared to others. The size of the gap can be adjusted depending on the intensity of photosynthesis processes. When exposed to sunlight, photosynthesis occurs intensively in the chloroplasts of guard cells. Saturation of cells with photosynthetic products (starch, sugars) leads to the active entry of potassium ions into the cell, as a result of which the concentration of cell sap increases. There is a difference in the concentrations of the cell sap of supporting and guard cells. Water from the supporting cells enters the guard cells, which leads to an increase in their volume and an increase in turgor. The guard cells acquire a pronounced bean-shaped shape and the stomatal fissure opens. When the light intensity decreases, the formation of sugars and starch in the guard cells decreases. No potassium ions are supplied. The concentration of cell sap in guard cells decreases compared to supporting cells. Water leaves the guard cells by osmosis, and turgor decreases, which leads to the closure of the stomatal fissure.
Stomatal cells are located on the underside of leaves. In aquatic plants whose leaves float, stomata are located on the outer surface of the leaf. The main functions of stomata are gas exchange and transpiration (evaporation of water).
Often single- or multicellular hairs develop from the epidermis. They have a diverse structure and perform different functions (protect the plant from overheating, from being eaten by animals, perform a secretory function), and can be alive or dead.
The integumentary tissue of the root absorptive zone has root hairs and is called epiblema , or rhizoderm (from Greek riz'– root). Root hairs absorb water and minerals.
Secondary covering tissue
It mainly includes cork And bark . Secondary integumentary tissue replaces the epidermis or occurs in the deep layers of the cortex. In autumn, the green color of the shoots is replaced by brown. From some of the cells of the main tissue, which are part of the cortex and restore the ability to divide, a layer of secondary meristem is formed - cork cambium or phellogen . It produces outward traffic jam - a layer of cells that have thickened walls, saturated with a fatty substance, become impermeable to gases and water, the contents of which die. The cork cells are rectangular in shape, tightly adjacent to one another, and arranged in rows. Cork preserves internal living cells from loss of moisture, sudden temperature fluctuations, and penetration of microorganisms. So that living cells can breathe under the plug and remove remaining moisture, phellogen under the stomata deposits living parenchyma cells with large intercellular spaces that break the epidermis and form lentils . Lentils are clearly visible on the surface of the bark of trees and bushes. They are unable to open and close. In winter they are clogged with a special substance.
The cork cambium remains active throughout the life of the plant and forms new cork layers. The upper layers of the bark are constantly peeling off. Inside the plant, the cork cambium produces living ground tissue cells.
Due to the repeated formation of layers of cork and the death of living cells between them, a characteristic of trees is formed. bark , which also includes the lower layers of cells.
Cells do not exist in isolation. They are connected to each other by plates consisting mainly of protopectin. These plates, together with the cell membranes, make up plant tissue.
The following types of fabrics are distinguished:
♦ integumentary;
♦ parenchymal;
♦ mechanical;
♦ conductive;
♦ educational.
Cover tissues protect fruits and vegetables from adverse external influences; mechanical damage, pathogenic microorganisms, agricultural pests, meteorological factors.
There are two types of integumentary tissue: epidermis (skin) and peridermis (cork).
The epidermis is a single-row integumentary tissue made up of elongated cells.
Characteristic feature The epidermis is the presence of a cuticle formed by a fat-like substance called cutin and waxes.
The cuticle enhances the protective properties of the epidermis, so removing wax deposits and damaging the cuticle causes rapid spoilage of fruits and vegetables.
The cuticle is different different types fruits and vegetables by structure, thickness and composition. These factors affect the shelf life of fruits and vegetables.
The thicker it is and the more densely it covers the epidermal cells, the less possibility of microorganisms penetrating inside and wetting with water.
Epidermal cells also contain vacuoles, nuclei, and some chloroplasts, which give color to fruits and vegetables.
Sometimes epidermal cells grow to form hairs covered with a cuticle. Then the fruits and vegetables have pubescence (peaches, gooseberries, apricots, etc.).
On the surface of the epidermis there are stomata - tiny openings through which gas exchange occurs between the internal tissues and external environment.
The epidermis covers mainly ground fruits and some vegetables - onions, garlic, tomatoes, peppers, etc.
The periderm is a secondary integumentary tissue consisting of several rows of tightly packed cells. Periderm cells are impregnated with suberin, which provides good protective properties.
Tubers and root vegetables are covered with periderm. Since they grow in soil, they need effective protection from mechanical pressure exerted by soil, stones, from microorganisms and pests inhabiting the soil.
Parenchymal tissues are the main tissues that form the pulp of fruits and vegetables.
Mechanical tissues are tissues that give density to plant organs.
The cells of these tissues are thick-walled, have a somewhat elongated shape, and contain pectin substances, chlorophyll, starch, and polyphenols.
Mechanical tissues can be observed in the form of veins on leaves, giving them strength, in lignified root vegetables (beets), in the form of stony cells in the pulp of fruits (pears, quince) and vegetables (horseradish).
An increased content of mechanical tissues, for example, stony cells, is undesirable, as it worsens the consistency of the pulp.
Conductive tissues communicate between different organs and tissues. Without this, metabolism is impossible.
They consist of prosenchymal cells of considerable length and are represented by three types: trachea, tracheids - conduct solutions of mineral substances, and sieve tubes - conduct solutions of organic substances.
The combination of tracheas, tracheids, and mechanical tissues forms wood and is called xylem, and sieve tubes with parenchymal and mechanical tissues form phloem.
The xylem and phloem are most pronounced in root crops such as carrots.
Conductive tissues have a significant impact on the consumer properties and shelf life of fruits.
A highly developed conductive tissue with a large number of mechanical tissues gives the pulp a rough, cartilaginous or woody (overgrown root crops, bigaro cherries) consistency.
Educational tissues serve to form permanent tissues.