Apical meristem cells are a division method. Apical meristem. Case. Primary root structure

The apical meristems are located at the apex of the shoot in the tissues of the growth cone, as well as at the tip of the root. Therefore, they are also called apical meristems. In the growth cone there are: tunic cells, from which the epidermis develops; the central meristematic zone, which is a reserve of educational cells for other zones; median meristem, generating core cells; peripheral zone, from the cells of which procambium is formed; and the main meristem, providing the formation of the primary cortex and parenchyma of the central cylinder.

At the root tip, the apical meristem is located in the division subzone. From the initial cells of this meristem, several groups of cells are formed: caliptrogen, characteristic of monocotyledons, whose cells generate the root cap; a dermatogen differentiating into an epiblem - the primary integumentary tissue of the root; the problem of the primary root cortex; pleroma used to build the central cylinder.

\u003e Intercalar meristems

Intercalar, or intercalary, meristems are primary in origin. They are the remains of the apical meristems and are localized in the basal part of the internodes and in the bases of the leaves. Their cells can be in an embryonic state for a long time and significantly lag behind in their development from adjacent cells of permanent tissues. Active cell division of intercalar meristems begins as the apical shoot slows down and ceases. For example, in wheat and other bluegrass with a shoot length of about 1 cm, the growth cone differentiates and instead of metameres of the vegetative part of the shoot, it produces metameres of a complex spike or other inflorescence. By this time, 4–6 aboveground internodes are formed on the shoot, in which subsequent growth in length is ensured by cell division of the intercalar meristem and extension of their derivatives. Thanks to the intercalary meristems, the leaf in angiosperms grows with its base after exiting the kidney.

\u003e Lateral meristems

Lateral or lateral meristems are located in the stem and root parallel to their surface and provide growth of plants in thickness.

Primary lateral meristems include procambium and pericycle. From the procambium, tissues of the conducting bundles of the stem are formed. If the procambium is laid in the growth cone in a continuous ring, then with subsequent development a stalk of a non-bundled type of structure is formed, as in flax. When a procambium is laid in separate cords in a circle, separate conducting bundles develop in the stem, as, for example, in wheat and other bluegrass ones.

Pericycle cells are functionally more diverse. Of them, the mechanical tissue of sclerenchyma is formed in the stem, and cambium and pellogen (cork cambium) can arise in the root. In addition, pericycle cells are involved in the formation of lateral roots.

Secondary lateral meristems are cambium and pellogen, which are formed either from the pericycle or from the cells of the main parenchyma; cambium may also arise from procambium. They are characteristic of the axial vegetative organs of dicotyledonous angiosperms and gymnosperms. Cambium provides the formation of secondary elements of conductive tissues and bundles, bast and wood. The pellogen generates the cells from which the cork and the phalloderm form. The laying of repeated layers of the phallogen in the bast leads to the formation of a crust in tree species.

\u003e Wound meristems

When injuring plants, the cells of the main parenchyma located next to the damaged area are dedifferentiated, i.e. acquire the ability to divide and generate a special tissue - wound, or traumatic, meristem, from the cells of which callus is first formed. Thus, this meristem is secondary in origin. When the cell walls of callus are soaked with suberin, a cork is formed. Callus and cork protect the injured area from pathogen damage.

\u003e Sporogenous tissue

The purpose of sporogenous tissues is the formation of spores. In flowering plants, they develop during the formation of a flower in anthers and ovaries of pistils. In developed anthers, sporogenous tissue is multicellular, and in the ovule is represented by only a few cells. The cells are large, thin-walled, mononuclear, with a diploid set of chromosomes, a large supply of nutrients in the cytoplasm.

In anthers, four haploid microspores are formed from each sporogenous cell as a result of meiosis. With subsequent mitotic division, pollen forms from microspores. In the ovule, in most angiosperms, the meiotic division of the sporogenous cell leads to the formation of four unequal cells. Of these, one develops into a haploid macrospore, the rest die off. Subsequent mitotic division of macrospores is the basis for the formation of an embryonic sac.

(from Greek Meristos - fissile) is the lateral tissue of plants, consisting of undifferentiated cells (meristematic cells), and is located in parts of plants where growth occurs.

Cytological features of meristems

Differentiated plant cells as a whole cannot divide or turn into cells of other types. Therefore, cell division in the meristems is necessary to provide new cells for the growth of other tissues, the formation of new organs and ensure the structure of the plant body. By function, the meristematic cells are similar to animal stem cells, do not differentiate or differentiate slightly, and are capable of continuous cell division. The meristematic cells are small, and the cytoplasm and nucleus completely fill the cell. Vacuoles are extremely small, and the cytoplasm does not contain differentiated plastids (chloroplasts or chromoplasts), although they are present in a rudimentary form (protoplastids). The meristematic cells are tightly packed, with almost no extracellular space. The cell wall is a very thin primary cell wall.

The physiological activity of meristems requires a balance between two antagonistic processes: the formation of new tissues and support for the renewal of the population of meristematic cells.

- forming plant tissue, from which all other tissues can form, meristematic cells for a long time retain the ability to divide with the formation of new non-specialized cells.

The meristem cells are flattened, small, densely located next to each other, without interclinics, the nucleus is located in the center of the cells, vacuoles are small, numerous, the cell membrane is primary, only plastid precursors are present.

The cytological features of the meristems are most typically expressed in the apical meristems. Cells are isodiametric polygons, not separated by intercellular spaces. Cell walls are thin, with a small content of cellulose. The cytoplasm is dense, the nucleus is large, located in the center. In the cytoplasm, a large number of ribosomes and mitochodria (there is an intensive synthesis of proteins and other substances). Numerous vacuoles are very small.

The cells of the lateral meristems are not the same in size and shape. This is due to the difference in the cells of permanent tissues, from which they are formed. So, for example, in the cambium is the parenchymal and prosenchymal cells. From the parenchymal initials, the parenchyma of the leading complexes is formed, from the prosenchymal - the leading elements themselves.

Meristems are classified by their position in the plant:

Apical (apical).
Lateral (lateral).
Plug-in (intercalary).

And by origin:

primary
secondary.

Primary meristems are closely connected with the apical meristem and directly from them are formed, in particular, protoderm, the main meristem, and procambium. Protodermis - a single layer layer of poorly differentiated cells covering the apex from the outside, later on the epidermis is formed from it. A crust forms from the main meristem, and a central cylinder forms from the procambium, whose cells are elongated along the axis of the stem.

Secondary meristems arise from specialized cells of mature organs of plants and ensure their lateral growth (pellogen, pericycle, cambium). Tissues, formed from the primary meristem, are called primary, and with the secondary - secondary. Secondary meristems should also include the so-called traumatic meristems, which form at the sites of damage to the plant body and provide regeneration.

Among the listed types of meristems, the apical meristem appears first in ontogenesis, with which differentiation of all other tissues occurs. It is located on the tops (apex) of the stem and root and their lateral branches. A feature of the vital activity of a plant organism is, in particular, the preservation of generative activity in the apical meristems during the entire ontogenesis, therefore it is said that plants are capable of unlimited growth.

Apical meristem

Apical meristem - represented by a set of cells located on the tops of the main and lateral axes of the stem and root, due to which the organs grow in length.

The apical meristem is localized at the poles of the embryo - the tip of the root and kidney. Provides root growth and shoot length. The apical meristems are primary; they form a cone of root and shoot growth.

Lateral meristem

Lateral meristem (lateral) - cells are located along the axis of the organs, ensuring their growth in thickness. Lateral meristems can be both primary (procambium, pericycle) and secondary (cambium, pellogen).

The lateral meristem is located in a circle of axial organs, forming cylinders, in the cross sections they have the appearance of a ring.

The primary lateral meristems - procambium, pericycle - arise under the apex and are in direct connection with them.

Secondary lateral meristems - cambium and pellogen (cork cambium) - are formed later with the promerist or permanent tissues by their differentiation.

Lateral meristems provide thickening of the root and stem. Conducting tissues are formed from procambium and cambium, and the crust is formed from phallogen.

Fellogen (Russian. Fellogen) - secondary meristematic tissue - formed due to periclinal divisions of the cells of the pericycle and laid under the endoderm. Fellogen lays out the secondary integumentary tissue - the cork. The activity of the phallogen leads to the fact that the primary cortex, under the pressure of growing secondary tissues, is isolated from the central cylinder, dies and is separated.

Thus, in place of the primary, the secondary cortex is formed, which is a collection of tissues located outward from the cambium.

Intercalary meristem

Intercalar meristem (synonym - inserted meristem) - cells are located between areas of differentiated tissues, providing inserted growth.

The intercalary meristem, for example, is located in the nodes of cereals, at the base of the petioles, stamens. These are residual primary meristems. They come from the believing meristems, but their conversion to permanent tissue is delayed compared to other stem tissues. These delicate meristems are especially noticeable in cereals. In the case of the condition of the bread, they provide an increase in the stems due to uneven cell division from the lower and upper sides of the straws.

Wound, or traumatic meristem

Formed when injuring tissues and organs. Living cells surrounding the affected areas, become differentiated and begin to divide, that is, they turn into a secondary meristem. Wound meristems form calus - A dense tissue of whitish or yellowish color, consisting of parenchymal cells of different sizes, not arranged in order. Kalus cells have large nuclei and relatively thick cell walls. Kalus can give rise to any plant tissue or organ. A plug is formed on the periphery; callus cells may differentiate into other tissues. In Kalyusa, additional roots and buds can be laid. Kalyus occurs when plants are inoculated, provides growth of the scion and stock; at the heart of cuttings. Calus is also used to obtain a culture of isolated tissues.

MERISTEM OR FORMING FABRIC FABRICS

Cytoplasm. Chemical composition, physical condition, structure and properties. The entry of substances into the cell. Types of movement of the cytoplasm.

The cytoplasm is colorless, has a mucous consistency and contains various substances, including high-molecular compounds, for example, proteins, the presence of which determines the colloidal properties of the cytoplasm. The cytoplasm is the part of the protoplast enclosed between the plasmalemma and the nucleus. The basis of the cytoplasm is its matrix, or hyaloplasm, a complex, colorless, optically transparent colloidal system capable of reversible transitions from sol to gel.

In the cytoplasm of plant cells there are organoids: small bodies that perform special functions - plastids, Golgi complex, endoplasmic reticulum, mitochondria, etc. In the cytoplasm, most of the processes of cellular metabolism are carried out, excluding the synthesis of nucleic acids occurring in the nucleus. The cytoplasm is penetrated by membranes - the thinnest (4-10nm) films built mainly from phospholipids and lipoproteins. Membranes restrict the cytoplasm from the cell membrane and vacuole and within the cytoplasm form the endoplasmic reticulum (reticulum) - a system of small vacuoles and tubules that are connected to each other.

The most important property of the cytoplasm, associated primarily with the physicochemical characteristics of hyaloplasm, is its ability to move. In cells with one large vacuole, the movement is usually carried out in one direction (cyclosis) due to special organelles - microfilaments, which are threads of a special protein - actin. The driving hyaloplasm carries away plastids and mitochondria. Cellular juice in vacuoles is an aqueous solution of various substances: proteins, carbohydrates, pigments, organic acids, salts, alkaloids, etc. The concentration of substances in cellular juice is usually higher than the concentration of substances in the environment (soil, water bodies). The difference in concentrations to a certain extent makes it possible for water and soil solutions to enter the cell, which is to some extent explained by the phenomenon of osmosis. In the cell, the role of a semipermeable membrane is played by the cytoplasm. The boundary layers of the cytoplasm lining the membrane and cell vacuole are permeable only to water and some solutions, but impermeable to many substances dissolved in water. This property of the cytoplasm is called semi-permeability or selective permeability. Unlike the cytoplasm, the cell membrane is permeable to all solutions; it is impermeable only to solid particles. The entry of substances into the cell cannot be reduced only to osmotic phenomena, which are expressed in adult cells with well-developed vacuoles. In fact, this is a very complex process, due to many factors. The entire colloid system of the cytoplasm takes an active part in the absorption of substances. The intensity of movement depends on temperature, the degree of illumination, oxygen supply, etc.

In very young cells, the cytoplasm fills almost their entire cavity. As the cell grows, small vacuoles appear in the cytoplasm, filled with cell juice, which is an aqueous solution of various organic substances. Subsequently, with further cell growth, vacuoles increase in size and, merging, often form one large central vacuole, pushing the cytoplasm to the cell membrane. In such cells, all organelles are located in a thin walled layer of the cytoplasm. Sometimes the nucleus remains in the center of the cell. In this case, the cytoplasm, which forms a nuclear pocket around it, is connected to the wall layer by thin cytoplasmic strands.

Chloroplasts lining the upper wall are located in the cytoplasm layer. They are almost rounded or slightly oval bodies. Occasionally, plastids can be stuck in the middle.

The concept of tissue. Classification of tissues. The difference between permanent and educational tissues.

In most terrestrial plants, body cells are unequal in their functions, structure and origin. This heterogeneity arose and consolidated, in the process of adaptation of plants to differences in air and soil environments. Cell systems, structurally and functionally similar to each other and usually having a common origin, are called weavers. Tissues are found in almost all higher plants. Only some of the bryophytes (liverworts) do not have them. Algae and scarlet (lower plants), as a rule, also do not have developed tissues.

Complexes of cells similar in function, and for the most part in structure, having the same origin and a certain localization in the plant body, are called tissues.

The distribution of tissues in plant organs and their structure are closely related to the performance of certain physiological functions by them.

Tissues consisting of one type of cell are called simple, while those consisting of different types of cells are called complex or complex. There are various classifications of tissues, but they are all rather arbitrary. Plant tissues are divided into several groups depending on the main function:

1) meristems, or educational tissues (tissues consisting of living thin-walled, intensively dividing cells);

a) apical (apical) meristims (located on the tops of the stems and at the ends of the roots) cause the growth of these organs in length;

b) lateral measures - cambium and fellogen (cambium provides thickening of the stem and root. Fellogen forms a cork)

2) integumentary (protect the internal tissues of plants from the direct influence of the external environment, regulate evaporation and gas exchange)

a) epidermis;

b) cork;

3) conductive (ensure the conduct of water, soil solutions and assimilation products produced by leaves. Conductive tissues of origin can be primary and secondary.);

a) xelima or wood fabric (water-conducting fabric)

b) phloem or bast (tissue conducting organic matter formed by the plant during photosynthesis);

4) mechanical (determine the strength of the plant);

a) colenchyma (consists of a parenchyma or several elongated cells with unevenly thickened cellulose walls);

b) sclerenchyma (cells have uniformly thickened lignified walls);

1) fiber;

2) sclerids;

5) core (consisting of homogeneous parenchymal cells that fill the space between other tissues);

6) secretory, or excretory (containing waste products).

Only cells of meristematic tissues are capable of division. Cells of other tissues, as a rule, are not capable of division, and their number increases due to the activity of the corresponding meristems. Such fabrics are called permanent. Permanent tissues arise from meristems as a result of cell differentiation. Differentiation consists in the fact that during the individual development of an organism (ontogenesis), qualitative differences arise between initially homogeneous cells, while the structure and functional properties of cells change. Differentiation is usually irreversible. Substances that act as hormones influence its course.

MERISTEM OR FORMING FABRIC FABRICS

Meristems (from the Greek. "Meristos" - divisible), or educational tissue, have the ability to divide and form new cells. Due to the meristems, all other tissues are formed and a long (throughout life) plant growth is carried out. In animals, there are no meristems, which explains the limited period of their growth. Meristem cells are characterized by high metabolic activity. Some meristem cells, called initial, are retained at the embryonic stage of development throughout the life of the plant, while others gradually differentiate and turn into cells of various permanent tissues. The initial meristem cell can fundamentally give rise to any cell in the body. The body of land plants is a derivative of relatively few initial cells.

Primary meristems have meristematic activity, i.e., are capable of division initially. In some cases, the ability to actively divide can again arise in cells that have already almost lost this property. Such "newly" arisen meristems are called secondary.

In the body of the plant, the meristems occupy a different position, which allows them to be classified. According to the position in the plant, apical, or apical (from lat. "Apex" - top), lateral, or lateral (from lat. "Latus" - lateral), and intercalar meristems are distinguished.

Apical meristems are located on the tops of the axial organs of the plant and provide body growth in length, and lateral ones - mainly growth in thickness. Each shoot and root, as well as the germinal root, kidney of the embryo have an apical meristem. Apical meristems are primary and form cones of root and shoot growth (Fig. 1).

Lateral meristems are located parallel to the lateral surfaces of the axial organs, forming a kind of cylinders, in the cross sections having the appearance of rings. Some of them are primary. The primary meristems are Procambius and the pericycle; the secondary are cambium and pellogen.

Intercalar, or intercalary, meristems are often primary and persist as separate sections in zones of active growth (for example, at the bases of the internodes, at the bases of leaf petioles).

There are also wound meristems. They are formed in places of damage to tissues and organs and give rise to callus - a special tissue consisting of homogeneous parenchymal cells that cover the site of damage. The callus-educational ability of plants is used in gardening when propagated by cuttings and grafts. The more callus formation is, the greater is the guarantee of rootstock growth with scion and rooting of cuttings. The formation of callus is a necessary condition for the culture of plant tissues on artificial media.

Apical meristem cells are more or less isodiametric in size and multifaceted in shape. There are no intercellular spaces between them, the membranes are thin, contain little cellulose. The cell cavity is filled with a dense cytoplasm with a relatively large nucleus, which occupies a central position. Vacuoles are numerous, small, but usually not visible under a light microscope. Ergastic substances are usually absent. Plastid and mitochondria are few and small.

The cells of the lateral meristems are different in size and shape. They approximately correspond to the cells of those permanent tissues, which subsequently arise from them. So, in the cambium there are both parenchymal and prosenchymal initials. The parenchyma of conductive tissues is formed from the parenchymal initials, and the conductive elements from the prosenchymal initials.

Fig. 1. The apical meristem of the escape of Elodea. A is a longitudinal section; 5 - growth cone (appearance and longitudinal section); B - cells of the primary meristem;

G - parenchymal cell of the formed sheet:

1 ~ growth cone, 2 - leaf primordium, 3 - axillary tubercle

Zones of the root. Features of the morphological structure of each zone in connection with the functions performed. Root growth in length and thickness.

Along with the shoot, the root is the main organ of a higher plant, which typically performs the function of mineral and water nutrition. Another important root function, closely related to the main one, is fixing, plants in the soil.

Different parts of the root perform different functions and are characterized by certain morphological features. These parts are called zones (Fig. 2). The root tip is always covered from the outside with a root cover protecting the apical meristem. The cells of the root cap produce mucus covering the root surface. Thanks to the mucus, friction against the soil is reduced, and its particles adhere easily to the root ends and root hairs.

The root cap consists of living parenchymal cells that arise in most monocotyledons from a special meristem called caliptrogen, and in dicotyledons and gymnosperms from the apical meristem of the root tip. Aquatic plants usually have no root cap.

Under the cover there is a division zone, represented by the meristematic apex of the root, its apex. As a result of the activity of the apical meristem, all other zones and tissues of the root are formed.

Dividing cells are concentrated in a division zone measuring about 1 mm. This part of the root differs noticeably from other zones with its yellowish coloration. Following the division zone, there is a stretch (growth) zone. It is also small in length (several millimeters), is distinguished by a light color and, as it were, transparent. The cells of the growth zone practically do not divide, but are able to stretch in the longitudinal direction, pushing the root ending into the depths of the soil. They are characterized by high turgor, which contributes to the active spreading of soil particles. Within the growth zone, differentiation of primary conductive tissues occurs.

The end of the growth zone is noticeable by the appearance of numerous root hairs on the epiblem. Root hairs are located in the suction zone, the function of which is clear from its name. At the root, it occupies a section from a few millimeters to several centimeters. In contrast to the growth zone, sections of this zone are no longer displaced with respect to soil particles. Young roots absorb the bulk of water and salt solutions in the absorption zone using root hairs.

Root hairs appear in the form of small papillae - outgrowths of epiblema cells. Hair growth occurs at its apex. The shell of the root hair stretches quickly. After a certain time, the root hair dies. The duration of his life does not exceed 10-20 days.

MERISTEM OR FORMING FABRIC FABRICS

Cytoplasm. Chemical composition, physical condition, structure and properties. The entry of substances into the cell. Types of movement of the cytoplasm.

Chloroplasts lining the upper wall are located in the cytoplasm layer. They are almost rounded or slightly oval bodies. Occasionally, plastids can be stuck in the middle.

The concept of tissue. Classification of tissues. The difference between permanent and educational tissues.

In most terrestrial plants, body cells are unequal in their functions, structure and origin. This heterogeneity arose and consolidated, in the process of adaptation of plants to differences in air and soil environments. Cell systems, structurally and functionally similar to each other and usually having a common origin, are called weavers. Tissues are found in almost all higher plants. Only some of the bryophytes (liverworts) do not have them. Algae and scarlet (lower plants), as a rule, also do not have developed tissues.

Complexes of cells similar in function, and for the most part in structure, having the same origin and a certain localization in the plant body, are called tissues.

The distribution of tissues in plant organs and their structure are closely related to the performance of certain physiological functions by them.

1) meristems, or educational tissues (tissues consisting of living thin-walled, intensively dividing cells);

a) apical (apical) meristims (located on the tops of the stems and at the ends of the roots) cause the growth of these organs in length;

b) lateral measures - cambium and fellogen (cambium provides thickening of the stem and root. Fellogen forms a cork)

2) integumentary (protect the internal tissues of plants from the direct influence of the external environment, regulate evaporation and gas exchange)

a) epidermis;

b) cork;

3) conductive (ensure the conduct of water, soil solutions and assimilation products produced by leaves. Conductive tissues of origin can be primary and secondary.);

a) xelima or wood fabric (water-conducting fabric)

b) phloem or bast (tissue conducting organic matter formed by the plant during photosynthesis);

4) mechanical (determine the strength of the plant);

a) colenchyma (consists of a parenchyma or several elongated cells with unevenly thickened cellulose walls);

b) sclerenchyma (cells have uniformly thickened lignified walls);

1) fiber;

2) sclerides;

5) core (consisting of homogeneous parenchymal cells that fill the space between other tissues);

6) secretory, or excretory (containing waste products).

Only cells of meristematic tissues are capable of division. Cells of other tissues, as a rule, are not capable of division, and their number increases due to the activity of the corresponding meristems. Such fabrics are called permanent. Permanent tissues arise from meristems as a result of cell differentiation. Differentiation consists in the fact that during the individual development of an organism (ontogenesis), qualitative differences arise between initially homogeneous cells, while the structure and functional properties of cells change. Differentiation is usually irreversible. Substances that act as hormones influence its course.

MERISTEM OR FORMING FABRIC FABRICS

Primary meristems possess meristematic activity, i.e., are capable of division initially. In some cases, the ability to actively divide can again arise in cells that have already almost lost this property. Such "newly" arisen meristems are called secondary.

Apical meristems located on the tops of the axial organs of the plant and provide body growth in length, and lateral - mainly growth in thickness. Each shoot and root, as well as the germinal root, kidney of the embryo have an apical meristem. Apical meristems are primary and form cones of root and shoot growth (Fig. 1).

Lateral meristems They are located parallel to the lateral surfaces of the axial organs, forming a kind of cylinders, in the form of rings on transverse sections. Some of them are primary. Primary meristems are procambia and pericyclesecondary - cambium and fellogen.

Intercalary or insertion meristems are more often primary and remain as separate sites in zones of active growth (for example, at the bases of the internodes, at the bases of leaf petioles).

There are also wound meristems. They are formed in places of damage to tissues and organs and give rise to callus - a special tissue consisting of homogeneous parenchymal cells that cover the site of damage The callus-educational ability of plants is used in gardening practice when propagated by cuttings and grafts. The more callus formation is, the greater is the guarantee of rootstock growth with scion and rooting of cuttings. The formation of callus is a necessary condition for the culture of plant tissues on artificial media.

Fig. 1. The apical meristem of the escape of Elodea. BUT - longitudinal section; 5 - growth cone (appearance and longitudinal section); IN - primary meristem cells;

G - parenchymal cell of the formed leaf:

1 ~ growth cone, 2 - leaf primordium, 3 - axillary tubercle

Zones of the root. Features of the morphological structure of each zone in connection with the functions performed. Root growth in length and thickness.

Different parts of the root perform different functions and are characterized by certain morphological features. These parts are called zones (fig. 2). The root tip is always covered from the outside with a root cover protecting the apical meristem. The cells of the root cap produce mucus covering the root surface. Thanks to the mucus, friction against the soil is reduced, and its particles adhere easily to the root ends and root hairs.

Root case consists of living parenchymal cells that arise in most monocotyledons from a special meristem, called caliptrogen, and in dicotyledons and gymnosperms, from the apical meristem of the root tip. Aquatic plants usually have no root cap.

Under the cover is located division area represented by the meristematic apex of the root, its apex. As a result of the activity of the apical meristem, all other zones and tissues of the root are formed.

Above the absorption zone, where the root hairs disappear, the conduction zone begins. The structure of this zone in different parts of it is not the same. On this part of the root, water and salt solutions absorbed by the root hairs are transported to the overlying sections of the plant. The areas of the conduction zone occupy a fixed position relative to the soil, not shifting relative to them. Despite the fixed position in space of specific sections of the absorption and conducting zones, these zones are shifted due to apical growth. As a result of this, the suction apparatus is constantly moving in the soil.

Within the same root system, there are roots that perform different functions. Most plants differ in growth and sucking endings. Growth endings are more durable, relatively powerful, quickly lengthen and advance deep into the soil. Sucking endings are short-lived, occur in large numbers on the growth roots

and lengthen slowly. Modified trees and shrubs skeletal and semi-skeletal roots on which short-lived root lobes arise, bearing many sucking endings.

Fig. 2 General view (BUT) and a longitudinal section (5) of the root end (outline). 1- root cover; 11 - growth and extension zone; /// - zone of root hairs, or zone of absorption; IV- beginning of the holding zone (lateral roots are also laid in this zone):

1 - the laid lateral root, 2 - root hairs on the epiblema, 3 - epiblem Per - exoderm, 4 - primary bark

5 - endoderm, 6 - pericycle, 7 - axial cylinder

Environmental factors and processes of growth and development. Phytohormones. Photoperiodism. Environmental factors and processes of growth and development.

External factors, or environmental factors, also have a noticeable effect on growth and development. Consider here the most important factors - light, heat and moisture. Light has a profound effect on the external structure of plants, and its effect is diverse. Light affects respiration and seed germination, the formation of rhizomes and tubers, the formation of flowers, leaf fall, the transition of the kidneys to a dormant state. Plants grown in the absence of light (etiolated plants) overtake plants grown in the light in growth. Intense lighting often enhances the differentiation process.

Each plant has its own temperature optimum growthand development. Temperature minimums for growth and development, on average, lie in the range of 5 -15 ° C, optimums - at 25 - 35 ° FROM, maximums are in the range of 45 - 55 ° С. Low and high temperatures can disturb the dormancy of seeds, buds and make it possible for them to germinate and bloom. The formation of flowers is a transition from a vegetative state to a generative one. Induction, i.e., the acceleration of this process by cold, is called vernalization. Without the process of vernalization, many plants (beets, turnips, celery, winter cereals) are not capable of flowering.

The availability of water is of great importance for growth, especially in the stretching phase. Lack of water entails small cell formation, and therefore, growth retardation.

Phytohormones are chemical factors produced in extremely small quantities, but capable of producing a significant physiological effect. Phytohormones produced in one part of the plant are transported to another part, causing corresponding changes there, depending on the gene model of the receptive cell.

Three classes of phytohormones are known, acting primarily as stimulants: auxins, gibberellins and cytokinins. Two classes of hormones - abscisic acid and ethylene - have a mainly inhibitory effect. The mechanism of action of various hormones varies.

Many processes of metabolism, growth, development and movement are subject to rhythmic fluctuations. Sometimes these fluctuations follow the change of day and night (circadian rhythms) sometimes associated with the length of the day (photoperiodism). An example of rhythmic movements is the nightly closing of flowers, the lowering and longitudinal folding of leaves opened and raised in the daytime. These movements are associated with uneven turgor. In many cases, these processes are controlled by an internal chronometric system - physiological hours apparently existing in all eukaryotic organisms. In plants, the most important function of the physiological clock is to record the length of the day and at the same time the season, which determines the transition to flowering or preparation for winter rest (photoperiodism).

Species growing in the north (north of 60 ° N) should be predominantly long-day, since their short growing season coincides with the long day. In middle latitudes (35-40 ° N), plants are found as long day like that short day. Here, spring or autumn blooming species belong to short-day ones, and blooming at the height of summer - to long-day ones.

The photoperiod is of great importance for the nature of the distribution of plants. In the process of natural selection, species genetically consolidated information on the day length of their habitats and on the optimal timing of the onset of flowering. Even in plants that grow vegetatively, the day length determines the relationship between seasonal changes and the accumulation of reserve substances. Species indifferent to the length of the day are potential osmopolitans. This also includes species that bloom from early spring to late autumn. Other species cannot go beyond the geographical latitude that determines their ability to bloom at the appropriate length of the day. Photoperiodism is also important in practical terms, since it determines the possibility of moving the southern plants to the north, and the north to the south.

CONSCIOUSNESS. Inflorescence definition. Classification. Structural features of cimoid inflorescences. Examples. The biological significance of inflorescences.

Flowers can be arranged singly or in groups. In those cases when they are arranged in groups, inflorescences are formed. An inflorescence can be defined as part of a win, shoot or a system of modified shoots carrying flowers.

Inflorescences are usually more or less limited from the vegetative part of the plant.

The biological meaning of the occurrence of inflorescences is in the increasing probability of pollination of flowers of both anemophilous and entomophilous plants. There is no doubt that an insect will visit much more flowers per unit of time if they are collected in inflorescences. In addition, flowers collected in inflorescences are more visible among green leaves than single flowers. Many drooping inflorescences easily swing under the influence of air movement, thereby contributing to the dispersion of pollen.

Inflorescences are characteristic of the vast majority of flowering plants. Inflorescences are usually grouped near the upper part of the plant at the ends of branches, but sometimes, especially in tropical trees, arise on trunks and thick branches. This phenomenon is known as caulifloria (from lat. "caulis" - a stalk, "flos" - a flower). An example is the chocolate tree. (Theobrota sasao). It is believed that in tropical rainforests, caulifloria makes flowers more accessible to pollinating insects.

Inflorescences are laid inside flower or mixed buds. In many plants (elderberry, lilac, hyacinth, etc.) the inflorescence arises as a whole as a result of the activity of one meristem.

Any inflorescence has a main axis, or an axis of inflorescence, and lateral axes that can be branched to various degrees or unbranched. Their final branches - pedicels - carry flowers. The axes of the inflorescence are divided into nodes and internodes. At the nodes of the axes of the inflorescence are leaves and bracts (Fig. 3).

The inflorescence carries modified or unchanged leaves. Strongly modified leaves are called bractsor brothers. An inflorescence bearing unchanged assimilating leaves is frisky that is, derogatory. At bracteous inflorescences in the nodes are bracts. Sometimes, due to the complete reduction of bracts, the inflorescence becomes ebracteous. He has no bracts. Inflorescences can be sharply separated from the vegetative part or (especially in the case of frontal inflorescences) this border is not clearly expressed.

An accurate characterization of inflorescences is necessary in many cases, including when analyzing the morphological characteristics of medicinal plants. Therefore, the classification of inflorescences is given considerable attention.

Inflorescences, in which the lateral axes branch, are called complex. In simple inflorescences, the lateral axes are not branched and are pedicels. In a complex inflorescence, the lateral axes are private or partial inflorescences.

There is an opinion that complex inflorescences are an older type. In many cases, simple inflorescences arose in the process of “depletion” of complex ones, which is associated with a reduction in their lateral axes. It is believed that single flowers in the axils of the leaves or on the tops of the shoots also arose as a result of extreme reduction of different types of inflorescences. The main axis may end with an apical flower; in this case, the inflorescence is limited in growth and is called closed.

At open inflorescences, the main axis has unlimited growth and flowers are located on the side of the morphological apex. In complex inflorescences, the top and side axes may end with apical flowers, or all of them have unlimited growth.

In bisexual plants, inflorescences carry bisexual flowers, but in monoecious and dioecious inflorescences, they can also be staminate, variegated, and polygamous. In the latter case, stamen, pistillate, and bisexual flowers occur simultaneously.

The classification of inflorescences can be carried out on the basis of branching characteristics of the final partial inflorescences. In accordance with this, the inflorescences are divided into two main types: botrioid and cimoid. In botryoid inflorescences (from the Greek. "Botrion" - brush) the nature of branching is monopodial. Tsimoid inflorescences (from the Greek “kyuma” - a wave in a special order of flowering) are necessarily characterized by sympodial branching of partial inflorescences.

Fig. 3. The structure of the inflorescence:

1 - main axis, 2 - lateral axis (paracladia), 3 - nodes 4 - internodes 5 - bracts, 6 - pedicels, 7 - flowers

. Fig. 4. Types of inflorescences BUT - simple botrioid:

1-brush, 2 - ear, 3 - an ear 4 - simple umbrella, 5 - head, 6 - basket, 7 - shield (4. 5, 6 - with a shortened main axis, others - with an elongated one);

B - complex botrioid. Whisk and its derivatives: 1 - panicle, 2 - complex shield, 3 - an antibody;

In - complex botrioid. Complex brush and its derivatives:

1 - triple brush, 2 - double brush, 3 - double spike 4 - double umbrella

CYMOID COMPLETIONS

This is an extensive group of inflorescences, as common as the botrioid ones. Among the cymoid inflorescences, two main types are distinguished: cymoids and thyres. Cymoids, as a rule, are simplified thyres. In all cymoid inflorescences, partial inflorescences are formed due to sympodial branching.

There are three types of cymoids: monochasia, dichasia and pleochasis. At monohaziev under the flower completing the main axis, only one partial inflorescence develops, or in the simplest cases a single flower. In accordance with the features of the branching of partial inflorescences of the monochasia type, it is customary to isolate curl, curl and clew. Monochasia is quite common in some buttercups, in particular in caustic buttercup (Rapipsi lus aceris). Partial inflorescences in the form of a curl are found in most representatives of the borage family. From the main axis dichasia under its final flower, two partial inflorescences, and in the simplest cases, two flowers, depart. Simple, double, triple dichasias, etc. are possible. Dichasia is found in a number of cloves, for example, species of the genus Asterisk (Stellaria)

Pleochasia characterized by a structure in which under the flower completing the main axis, three or more partial inflorescences (or flowers) develop. In principle, double, triple, etc. pleochasias are possible (Fig. 5). For the kind of euphorbia (Airhorbibut) from the family of euphorbia is characterized by a special type of cimoid inflorescence, called cyatium. Tsiatiy consists of an apical pistillate flower and five stamens resulting from extreme reduction of five stamen partial inflorescences. Cytium is surrounded by a wrapper consisting of leaves of reduced partial inflorescences. Thiers are arranged more complicated than cymoids. These are branched inflorescences, and the degree of branching decreases from the base to the apex. The main axis of the thyrsus grows monopodially, but the partial inflorescences of one order or another are cymoids.

Various classifications of thyrses are possible. The thyres, the main axis of which ends with a flower, are called closed, otherwise they are considered open. Depending on the degree of branching of the lateral axes, pleiotirs in which cymoids are located on the axes of the third and higher orders; dieters in which the cymoids are located on the axes of the second order, and monotiers in which cimoids are located directly on the main axis of the inflorescence (see Fig. 4).

The outward similarity of thyres with a brush, spike, earring, umbrella or head allows us to talk about racemose, spike, scapular, umbellate, cephalic thyres, etc. etc. As a result of reduction, cymoids arise - inflorescences similar in appearance to botryoid ones, and even single flowers.

Thyres are very common in plants. For example, thyrsus - horse chestnut inflorescence (Aessilus hippocastanum), another example of tiers is mullein inflorescence (Verbascum) from the Norichen family. Thyres of various types are inflorescences of all labiaceae. The birch inflorescence is an ear-ringed tiers.

USE OF FLOWERS AND FLOWERS

Flowers have a variety of practical uses. Very often, beauty determines their decorative use and aesthetic impact on humans. Plants with flowers of attractive color, shape or smell are widely cultivated in a variety of artificially bred varieties. For example, about 25 thousand varieties of roses, about 4 thousand varieties of tulips, 12 thousand varieties of daffodils, etc. are known. Special societies of amateurs and collectors of tulips, lilies, orchids, roses have been established. In Russia and abroad, there are companies specializing in the cultivation and sale of flowering plants. The culture of decorative onion monocotyledons (tulips, hyacinths) in the Netherlands is especially highly placed. Orchids are grown commercially in Singapore and several countries in Southeast Asia. Cut flowers are widely used in the form of bouquets, garlands, wreaths, etc. In Japan, the art of making bouquets is called ikebana.

Many flowers contain aromatic essential oils. One of the most famous rose oil in Europe, obtained from the petals of terry forms of a damask rose (Rosa damascena), roses metropolitan (Rosa centifolia) and some other species, used in perfumes and partly in medicine. In medicine, many flowers of various plants are used. Especially popular are chamomile flowers (Matrisaributrthoutitbut), linden flowers (Tilibut withrdbuttbut), marigold flowers, or marigolds (Ca1epdu1a aboutfficipalis), buds of sophora japanese (Sturhhalfwaybiut japonicum) - a source of industrial production of vitamin P (routine), etc.

A number of flowers are used to flavor wines and Tobaccos. Of these, sweet clover is especially known. (Melilabouttus aboutfficinalis), whose flowers containing coumarin are added to many varieties of tobacco. Food colors are obtained from the flowers of the already mentioned medicinal marigolds, stigmas of cultivated saffron (FROMrosus sbuttivus) and safflower dyeing (Sarthamus tinctorius). Green buds of caper prickly (Sarahris spinosa) marinate as a spicy seasoning. A valuable spice is the buds of syzygium fragrant (Syzygium butrotatisit). They are known as cloves, which is associated with the form of dried buds. In the tropics, many large flowers are used as a vegetable. Quite widely used in this quality are flower buds of some types of bananas. (Musa). Nectar of flowers serves as a source of different varieties of honey. The most valuable honey plants are different types of linden, tansy tansy. (Rhacelibuttapasetifolia) and buckwheat edible (Fbutgyellingrum ess1eptum). In recent decades, medicine from plant pollen has begun to be used in medicine.

Fig. 4. Aggregate inflorescences:

1 - panicle of umbrellas, 2 - panicle of baskets, 3 - basket guard 4 - basket brush 5- ear of baskets

Fig. 5. Tsimoid inflorescences. BUT - cymoids:

1 -3 - monochasia: / - "elementary" monochasia, 2 - gyrus, 3-curl, 4- double curl 5-6- dichasia: 5-dichasia, 6-triple dichasia, 7-8- pleiochasia: 7-pleiochasia, 8- double pleiochasia;

B - tearse example

The anatomical structure of root crops (modifications of the root), such as radish, carrots and beets. Features of the structure and location of tissues in root crops.

Along with the functions of absorption and conduct, the roots perform the function of a reserve of nutrients, which sometimes accumulate in very large quantities. These are the roots of some biennial dicotyledonous plants (carrots, parsley, turnips, radishes, beets, etc.) that form root crops.

In addition to the root, the root crop includes a submucosal knee (hypocotyl), as well as the lower part of the shoot morphologically. In different "root crops" these organs are developed and thickened to varying degrees. So, in carrots, parsley, some varieties of radish and sugar beets, most of the "root crop" is formed by the main root; in turnips, table beet varieties and others - the base of the stem and hypocotyl, and the root itself represents only the lowermost part of the “root crop”, bearing side roots.

Spare substances deposited in the “root crop” in the first year of the plant’s life, the next year are spent on the development of flower-bearing shoots, fruits and seeds.

Nutrients accumulate in living parenchymal cells with thin, non-lignified walls. Cells are rich in cellular juice, so root vegetables are always juicy.

Substances can be deposited: 1) mainly in the woody (xelim) parenchyma (radish, turnip and other cruciferous); 2) in woody and especially in bast (phloem) parenchyma (carrots, parsley and other umbrella); 3) in a parenchyma formed by the activity of several additional cambiums (beets).

Carrot Root (Daucus sativus (Hoffm.) Roehl.)

In the cross section, which has not yet been treated with reagents, two zones are clearly distinguishable: the inner, rather narrow, light yellow (secondary xylem) and the outer, wider, orange (secondary phloem). The bulk of starch, soluble sugars, and other nutrients is concentrated in the phloem. The orange color is due to the presence of chromoplasts with carotene crystals in its cells. The phloem and xylem are separated by a light cambial zone, which is often torn, and conductive tissues are separated from each other.

In a section treated with phloroglucinol and hydrochloric acid, even with a small magnification of the microscope, one can find two very short, narrow, usually converging in the center of the cortex root of the tracheal elements of primary xelima, colored in red. From the outer ends of each of the strands of this diarchic xylem to the periphery of the slice, large-cell primary rays depart. Between them, on either side of the primary xylem, is the secondary xylem, intersected by numerous secondary rays (Fig. 6). The bulk of xylem consists of thin-walled parenchymal cells. There are few vessels in the root of carrots. They stand out sharply against the general background of colorless parenchyma, as they have thickened lignified walls. The vessels are located singly or collected three to seven in groups. In the inner, oldest sections of the secondary xelema, they constitute discontinuous radial bands. Parenchymal cells periodically divide in different directions, therefore, in the thick roots, all elements are strongly displaced.

The cambial zone is usually wide, its cells are small, compressed in the radial direction.

The phloem consists mainly of parenchymal elements. Among them are small groups of sieve tubes with accompanying cells and schizogenic essential oil channels. On the cut, rays from very large cells are clearly visible. Periodic divisions of parenchymal cells cause a significant growth of the phloem in thickness. The outer part of the phloem borders on a zone of several (6–7) rows of large parenchymal cells, which arose, probably, as a result of cell divisions of the phalloderm. In this zone, the oil channels are visible. The root is covered with a thin layer of cork.

Radish Root (Raphanus sativus L.)

Unlike carrots, radish root thickening occurs mainly due to the strong growth of secondary xelima. The secondary phloem, compared with the powerful xylem, is very poorly developed.

In the center of the cross-section (Fig. 7) there are small vessels of the diarchic primary xylem. From each of its ends, crossing in the radial direction the central cylinder, depart along one wide primary parenchymal ray.

Stocking root tissue is represented by secondary xylem, the bulk of which is composed of thin-walled cells of the heavy and radiation parenchyma; its cells contain starch and rich cell juice. A few wide-lumenal vessels are collected two to six in short radial chains, expanding to the periphery. Near the cambium, vessels are usually surrounded by a small number of mechanical elements with slightly thickened, sometimes lignified walls.

The cambial zone consists of small tabular cells with dense cytoplasmic contents. Outside, it is surrounded by a narrow ring of the secondary phloem, in which, as in the xylem, wide secondary rays are noticeable. Radially elongated groups of sieve tubes with accompanying cells are surrounded by a parenchyma. Towards the end of the growing season, strands of short fibers are detected in the secondary phloem. Their slightly thickened lignified walls have few simple pores. Around the phloem is a thin layer of parenchymal cells - derivatives of the pericycle and the felloderm. The root is covered with a brown cork.

Beet root (Beta vulgaris L.)

On the transverse section of the root, alternating concentric rings of more or less intensely stained tissues are noteworthy (Fig. 8).

The initial stages of thickening of the beet root are similar to the thickening of the roots of carrots and radishes, but in the future its growth in thickness occurs in a peculiar way.

The root of the seedling in the phase of cotyledonary leaves has a primary structure. A radial conducting beam with a diarchic primary xylem is surrounded by a single-layer recycle. With the appearance of the first true leaf in the plant, the cambium begins to function, which lies between the primary xylem and the phloem. As a result of its activity, on the 12-15th day of the seedling's life, a single bundle consisting of secondary xylems and phloem is formed on both sides of the primary xylem in the center of the root. The primary phloem, strongly obliterated by this time, is pushed to the periphery. Secondary xylem consists of vessels with lignified walls and a small number of parenchymal cells. Between the bundles of secondary tissues pass wide rays. The activity of this primary cambium soon ends and further thickening of the root continues due to additional cambium, which arise successively one after the other with the direct participation of the pericycle, dividing mainly by tangential partitions, form a multilayer meristematic tissue, which is located on the cross section of the ring. In the peripheral part of this ring, the phallogen is laid, the cells of the middle part differentiate into parenchymal elements, and the first additional cambium forms from the inner row of cells, forming a new zone of meristimatic cells. The outer row of cells in this zone will subsequently function as a second-complement cambium. The inner cells of the meristematic zone, dividing, lay out thin-walled parenchyma cells and small groups of secondary phloem cells outward, inward - large cells of the perenchyma, and immediately below the phloem sections - xelema elements.

Thus, as a result of the activity of the first additional cambium, a wide ring of parenchymal tissue appears with small collateral bundles immersed in it. The phloem consists of several sieve tubes with accompanying cells and parenchyma cells, xylem - from a small number of porous vessels surrounded by mechanical elements, and xylem parenchyma (Fig. 8, B).

Soon cells of the second additional cambium begin to divide, forming the next meristimatic zone. Its outer cells differentiate into the third additional cambium, and the inner cells form the second ring of conductive bundles and the inter-beam parenchyma. The third additional cambium, in turn, is involved in the formation of the fourth additional ambium and the third ring of conductive beams, etc.

The activity of additional cambiums explains the presence of several (8 or more) concentric rings on the cross section of the root, consisting of small conductive bundles and an abundant parenchyma, in the thin-walled cells of which sucrose and other nutrients accumulate. Table beet varieties in the parenchymal cells have a lot of anthocyanin. The more removed the additional cambium from the center root, the weaker their activity. Therefore, the width of the concentric rings, the number and size of the conductive beams are reduced to the periphery The youngest outer rings can be represented only by narrow layers of weakly differentiated or even meristimatic cells.

The intensity of the secondary thickening of the beet root is closely related to the development of the leaf apparatus. It was established that the number of concentric layers depends on the number of leaves in the root rosette.

The activity of additional cambia ends early, and further thickening of the root occurs due to division and proliferation of parenchymal cells.

Outside the root there is a thin layer of small cell parenchymal tissue surrounded by a dark brown cork.