Root, its functions. Main, lateral and adventitious roots, their origin

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Vegetative organs

Lecture 2. Root and root systems

The root is an axial organ with the ability to grow indefinitely and the property of positive geotropism. Root functions. The root performs several functions, let's dwell on the main ones:

Strengthening the plant in the soil and holding the aerial part of the plant;

Absorption of water and minerals;

Carrying out substances;

Can serve as a place of accumulation of spare nutrients;

Can serve as an organ vegetative propagation.

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Rice. Root types:

1 - the main root; 2 - adventitious roots; 3 - lateral roots

Root orphology . By origin, the roots are divided into main, lateral and adventitious (Fig.). The main root is the root that develops from the embryonic root. It is characterized by unlimited growth and positive geotropism. The main root has the most active apical meristem. Lateral roots - roots that develop on another root of any origin and are formations of the second and subsequent orders of branching. The formation of these roots begins with the division of cells of a special meristem - the pericycle, located at the periphery of the central cylinder of the root. P

Residual roots - roots that develop from stems, leaves, old roots. They appear due to the activity of secondary meristems. Young root zones. Zones of a young root are different parts of the root along the length, performing different functions and characterized by certain morphological features. In a young root, 4 zones are usually distinguished (Fig. 9): Division zone. The apex of the root, 1-2 mm long, is called the division zone. This is where the primary apical root meristem is located. Due to cell division in this zone, new cells are constantly being formed. The apical meristem of the root is protected by a root cap. It is formed by living cells constantly forming at the expense of the meristem. They often contain starch grains (provide positive geotropism). The outer cells produce mucus, which makes it easier for the root to move through the soil. Growth zone, or stretch. The length of the zone is several millimeters. In this zone, cell division is practically absent, the cells are maximally stretched due to the formation of vacuoles. Suction zone , or the zone of root hairs. The length of the zone is several centimeters. This is where differentiation and specialization of cells takes place. Here, the outer layer of the epiblema (rhizoderm) with root hairs, the layer of the primary cortex and the central cylinder are already distinguished. The root hair is a lateral outgrowth of the epiblel (rhizoderm) cell. Almost the entire cell is occupied by a vacuole surrounded by thin layer cytoplasm. The vacuole creates a high osmotic pressure, due to which water with dissolved salts is absorbed by the cell. The length of the root hairs is up to 8 mm. On average, from 100 to 300 root hairs are formed per 1 mm 2 of the root surface. As a result, the total area of ​​the absorption zone is greater than the surface area of ​​the aboveground organs (in a winter wheat plant, 130 times, for example). The surface of the root hairs smoothes and sticks to soil particles, which facilitates the flow of water and minerals into the plant. Absorption is also facilitated by the release of acids by the root hairs that dissolve mineral salts. Root hairs are short-lived, die off after 10-20 days. The dead (in the upper part of the zone) are replaced by new ones (in the lower part of the zone). Due to this, the suction zone is always at the same distance from the root tip, and always moves to new soil areas. Zone located above the suction zone . In this zone, water and mineral salts extracted from the soil move from the roots up to the stem and leaves. Here, due to the formation of lateral roots, branching of the root occurs. Primary and secondary root structure. The primary structure of the root is formed by primary meristems, which is characteristic of young roots of all plant groups. On a transverse section of the root in the suction zone, three parts can be distinguished: the epibleme, the primary cortex, and the central axial cylinder (stele) (Fig. 10). In ploons, horsetails, ferns and monocotyledonous plants persists throughout life. Epible, or skin - the primary integumentary tissue of the root. Consists of one row of tightly closed cells, in the absorption zone with outgrowths - root hairs. Primary cortex It is represented by three distinct layers from each other: the exoderm, the outer part of the primary cortex, is located directly under the epiblem. As the epibleme dies away, it turns out to be on the root surface and in this case plays the role of integumentary tissue: thickening and corking of the cell membranes occurs, and the death of the cell contents. Under the exoderm is the mesoderm, the main layer of cells of the primary cortex. Here, water moves into the axial cylinder of the root, nutrients accumulate. The innermost layer of the primary cortex is the endoderm, formed by one layer of cells. In dicotyledonous plants, the endoderm cells have thickenings on the radial walls (Caspari bands), impregnated with a fat-like substance impermeable to water - suberin. In monocotyledonous plants, horseshoe-shaped thickening of the cell walls form in the endoderm cells. Among them, there are living thin-walled cells - passage cells, which also have Caspari belts. Endoderm cells with the help of a living protoplast control the flow of water and minerals dissolved in it from the cortex to the central cylinder and back of organic matter. Central cylinder, axial cylinder, or stele ... The outer layer of the stele, adjacent to the endoderm, is called the pericycle. Its cells retain the ability to divide for a long time. Here, the lateral roots are laid. In the central part of the axial cylinder there is a vascular-fibrous bundle. Xylem forms a star, and phloem is located between its rays. The number of xylem rays is different - from two to several dozen. In dicotyledons up to five, in monocotyledons - five and more than five. In the very center of the cylinder, there may be elements of the xylem, sclerenchyma or thin-walled parenchyma.

Rice. ... Internal structure of the root.

A - primary and secondary structure of the root; B - internal structure the root of a monocotyledonous plant; B - the internal structure of the root of a dicotyledonous plant.

1 - epiblema; 2 - primary cortex; 3 - pericycle; 4 - phloem; 5 - xylem; 6 - cambium; 7 - stele; 8 - endoderm; 9 - passage cells of the endoderm.

Rice Secondary root structure. In dicotyledonous and gymnosperms, the primary structure of the root is not preserved for long. As a result of the activity of secondary meristems, the secondary structure of the root is formed. The process of secondary changes begins with the appearance of cambium interlayers between the phloem and xylem. Cambium arises from the poorly differentiated parenchyma of the central cylinder. Inside, it lays down elements of the secondary xylem (wood), outside the elements of the secondary phloem (bast). At first, the cambium interlayers are separated, then they close together, forming a continuous layer. When cambium cells divide, the radial symmetry characteristic of the primary structure of the root disappears, and cork cambium (phellogen) appears in the pericycle. It lays out the layers of cells of the secondary integumentary tissue - cork. The primary bark gradually dies off and sloughs off. TO

Rice. 11. Types of root systems.

Ornev systems . The root system is the collection of all the roots of a plant. The main root, lateral and adventitious roots are involved in the formation of the root system. By shape, there are 2 main types of root systems (Fig. 11): Core root system - a root system with a well-defined main root. Typical for dicotyledonous plants. Fibrous root system - a root system formed by lateral and adventitious roots. The main root grows poorly and stops growing early. Typical for monocotyledonous plants. Root physiology. The root has unlimited growth. It grows with the tip, on which the apical meristem is located. Take 3-4 day old bean seedlings, apply thin marks on the developing root with ink at a distance of 1 mm from each other and place them in a humid chamber. After a few days, you can find that the distance between the marks at the root tip has increased, while in higher areas of the root it does not change. This experience proves the apical growth of the root (Fig. 12). This fact is used in human practice. When transplanting seedlings of cultivated plants, carry out pick - removal of the root apex. This leads to the cessation of growth of the main root and causes increased development of the lateral roots. As a result, the suction area of ​​the root system is significantly increased, all roots are located in the upper most fertile soil layers, which leads to an increase in plant productivity.

Rice. ... Root growth.

A - root growth in length; B - root picking; B - the development of adventitious roots during hilling.

Root uptake and movement of water and minerals. The absorption of water and minerals from the soil and movement to the terrestrial organs is one of the most important functions of the root. This function arose in plants in connection with landfall. The structure of the root is adapted to absorb water and nutrients from the soil. Water enters the plant body through the rhizoderm, the surface of which is greatly increased due to the presence of root hairs. In this zone, the root conductive system is formed in the root stele - xylem, which is necessary to ensure the ascending flow of water and minerals. The absorption of water and minerals by the plant occurs independently of each other, since these processes are based on different mechanisms of action. Water passes passively into the cells of the root, and minerals enter the cells of the root, mainly as a result of active transport, which comes with the expenditure of energy. V

Rice. Horizontal transport of water.

1 - root hair; 2 - apoplastic pathway; 3 - symplastic path; 4 - epiblema (rhizoderm); 5 - endoderm; 6 - pericycle; 7 - xylem vessels; 8 - primary cortex; 9 - plasmodesmata; 10 - Caspari belts.

Ode enters the plant mainly according to the law of osmosis. Root hairs have a huge vacuole with high osmotic potential, which ensures the flow of water from the soil solution into the root hair. Horizontal transport of substances. At the root, the horizontal movement of water and minerals is carried out in the following order: root hair, cells of the primary cortex (exoderm, mesoderm, endoderm), stele cells - pericycle, parenchyma of the axial cylinder, root vessels. Horizontal transport of water and minerals occurs along three paths (Fig. 14): the path through apoplastic , symplastic and vacuolar The apoplastic pathway includes all intercellular spaces and cell walls. This path is the main one for the transport of water and ions of inorganic substances. The path through the symplast is a system of protoplasts of cells connected by means of plasmodesmata. Serves for transportation of mineral and organic substances. Vacuolar pathway. Water passes from the vacuole to the vacuole through other components of adjacent cells (plasma membranes, cytoplasm and vacuole tonoplast). This route is used exclusively for the transport of water. Movement along the vacuolar pathway is negligible at the root; at the root, water moves along the apoplast to the endoderm. Here, its further advance is hindered by waterproof cell walls impregnated with suberin (Caspari belts). Therefore, water enters the stele through the symplast through the passage cells (water passes through the plasma membrane under the control of the cytoplasm of the passage cells of the endoderm). Due to this, the movement of water and minerals from the soil to the xylem is regulated. In the stele, water no longer meets resistance and enters the xylem conductive elements. Vertical transport of substances. The roots not only absorb water and minerals from the soil, but also supply them to the organs above the ground. The vertical movement of water occurs over dead cells that are unable to push water towards the leaves. The vertical transport of water and solutes is provided by the activity of the root itself and the leaves. The root is bottom end motor , which supplies water to the vessels of the stem under pressure, called root pressure. Root pressure refers to the force with which the root pumps water into the stem. Root pressure arises mainly as a result of an increase in the osmotic pressure in the root vessels over the osmotic pressure of the soil solution. It is a consequence of the active release of mineral and organic substances by the root cells into the vessels. The root pressure is usually 1-3 atm. The proof of the presence of root pressure is gutting and highlighting sap .Gutation is the release of water from an intact plant through the water stomata - hydatodes, which are located at the tips of the leaves. Pasoka is the liquid that comes out of the cut stem. Upper end motor , providing vertical transport of water - the suction force of the leaves. It occurs as a result of transpiration - the evaporation of water from the surface of the leaves. Continuous evaporation of water creates the opportunity for a new inflow of water to the leaves. The sucking force of leaves in trees can reach 15-20 atm. In xylem vessels, water moves in the form of continuous water threads. When moving upward, the water molecules adhere to each other (cohesion), which makes them move one after the other. In addition, water molecules are able to adhere to the walls of blood vessels (adhesion). Thus, the rise of water along the plant is carried out thanks to the upper and lower motors of the water current and the cohesion forces of water molecules in the vessels. The main driving force is transpiration. Modifications of the roots. Roots often perform other functions as well, with various root modifications occurring. Storage roots. The root often acts as a store of nutrients. Such roots are called storing roots. They differ from typical roots by the strong development of the storage parenchyma, which can be located in the primary (in monocots) or secondary bark, as well as in the wood or core (in dicots). Among the storage roots, root tubers and root crops are distinguished. Root tubers typical for both dicotyledonous and monocotyledonous plants, and are formed as a result of modification of lateral or adventitious roots (chistyak, orchis, lyubka). Due to their limited growth in length, they can have an oval, fusiform shape and do not branch. In most species of dicotyledonous and monocotyledonous plants, the tuber is only a part of the root, and for the rest of the length, the root has a typical structure and branches (sweet potato, dahlia, daylily). Root vegetable is formed mainly as a result of thickening of the main root, but the stem also takes part in its formation. Root crops are also typical for many cultivated vegetable, fodder and industrial biennial plants, and for wild herbaceous plants. perennial plants(chicory, dandelion, ginseng, horseradish). Most often, root crops are formed as a result of secondary thickening of the roots (carrots, parsnips, parsley, celery, turnips, radishes, radishes). In this case, storage tissue can develop both in the xylem and in the phloem. The pericycle can also take part in the thickening of the main root, forming additional cambial rings (in beets). Plants growing in swamps often form roots growing upward - respiratory roots , pneumatophores. In such roots, the air parenchyma is well developed. Thus, the roots of marsh plants receive a sufficient amount of oxygen.

Rice. ... Modifications of the roots.

Key terms and concepts

1. Root. 2. Main root, lateral and adventitious roots. 3. Primary structure of the root. 4. Secondary structure of the root. 5. Primary cortex. 6. Axial cylinder, root stele. 7. Caspari's belts. 8. Pericycle. 9. Root system. 10. Picking. 11. Apoplastic, symplastic transport routes. 12. Root pressure. 13. Guttation. 14. Pasoka. 15. Root crops. 16. Root tubers. 17. Respiratory roots. 18. Aerial roots, velamen. 19. Nodule bacteria.

Essential Review Questions

What is a root?

What roots are called main, adventitious, lateral?

What is the difference between the root systems of dicotyledonous and monocotyledonous plants?

Root zones.

Three layers of primary root bark?

Tissue of the axial cylinder of the root.

Routes of horizontal transport of substances along the root?

Lower and upper water current motors over the stem and leaves?

Modifications of the roots.

Root. Functions. Types of roots and root systems. Anatomical structure of the root. The mechanism of the entry of the soil solution into the root and its movement into the stem. Modifications of the roots. The role of mineral salts. The concept of hydroponics and aeroponics.

Higher plants, in contrast to lower ones, are characterized by the dismemberment of the body into organs that perform various functions. Distinguish between vegetative and generative organs of higher plants.

Vegetative organs - parts of the body of plants that perform the functions of nutrition and metabolism. Evolutionarily, they arose as a result of the complication of the body of plants when they came to land and the development of air and soil environments. Vegetative organs include the root, stem and leaf.

1. Root and root systems

The root is an axial organ of plants with radial symmetry, growing due to the apical meristem and not bearing leaves. The growth cone of the root is protected by a root cap.

The root system is the collection of roots of one plant. The shape and nature of the root system is determined by the ratio of growth and development of the main, lateral and adventitious roots. The main root develops from the embryonic root and has positive geotropism. Lateral roots appear on the main or adventitious roots as ramifications. They are characterized by transverse geotropism (diageotropism). Adventitious roots appear on stems, roots, and rarely on leaves. In the case when the main and lateral roots of the plant are well developed, a taproot system is formed, which may also contain adventitious roots. If the plant has a predominant development of adventitious roots, and the main root is invisible or absent, then a fibrous root system is formed.

Root functions:

Absorption of water with dissolved mineral salts from the soil. The suction function is performed by root hairs (or mycorrhizae) located in the suction zone.

Anchoring the plant in the soil.

Synthesis of products of primary and secondary metabolism.

The biosynthesis of secondary metabolites (alkaloids, hormones and other biologically active substances) is carried out.

Root pressure and transpiration ensure the transport of aqueous solutions of mineral substances through the vessels of the root xylem (ascending current), to the leaves and reproductive organs.

Reserve nutrients (starch, inulin) are deposited in the roots.

Growth substances are synthesized in the meristematic zones, which are necessary for the growth and development of the aboveground parts of the plant.

They carry out symbiosis with soil microorganisms - bacteria and fungi.

Provide vegetative propagation.

In some plants (monstera, philodendron) they function as a respiratory organ.

Modifications of the roots. Very often the roots perform special functions, and in this regard, they undergo changes or metamorphoses. Root metamorphoses are hereditary.

Retracting (contractile) roots at bulbous plants serve to immerse the bulbs in the soil.

Storing the roots are thickened and strongly parenchymalized. Due to the accumulation of reserve substances, they acquire onion, conical, tuberous, and other forms. Storage roots include 1) roots in biennial plants. Their formation involves not only the root, but also the stem (carrots, turnips, beets). 2) root tubers - thickening of adventitious roots. They are also called root cones(dahlia, sweet potato, cleanser). Essential for the early appearance of large flowers.

Roots - attachments have climbing plants (ivy).

Aerial roots typical for epiphytes (orchids). They provide the plant with the absorption of water and minerals from moist air.

Respiratory the roots are of plants growing on waterlogged soils. These roots rise above the soil surface and supply the underground parts of the plant with air.

Stilted roots are formed in trees growing in the littoral of tropical seas (mangroves). Strengthens plants in shaky ground.

Mycorrhiza- symbiosis of the roots of higher plants with soil fungi.

Nodules - tumor-like growths of the root bark as a result of symbiosis with nodule bacteria.

Columnar roots (roots - supports) are laid as adventitious on the horizontal branches of the tree, reaching the soil, grow, supporting the crown. Indian banyan tree.

In some perennial plants, adventitious buds are laid in the root tissues, which later develop into terrestrial shoots. These shoots are called root suckers, and plants - root suckers(aspen –Populustremula, raspberry –Rubusidaeus, sow thistle –Sonchusarvensis, etc.).

Anatomical structure of the root.

In a young root, 4 zones are usually distinguished in the longitudinal direction:

Division zone 1 - 2 mm. It is represented by the tip of the growing cone, where active cell division occurs. Consists of cells of the apical meristem, and is covered with a root cap. It has a protective function. Upon contact with the soil, the cells of the root cap are destroyed with the formation of a mucous membrane. It (root cap) is restored due to the primary meristem, and in cereals - due to a special meristem - caliptrogen.

Stretch zone is a few mm. Cell division is practically absent. The cells are stretched as much as possible due to the formation of vacuoles.

Suction zone is a few centimeters. Differentiation and specialization of cells takes place in it. Distinguish between integumentary tissue - epibleme with root hairs. The cells of the epiblema (rhizoderm) are alive, with a thin cellulose wall. Long outgrowths are formed from some cells - root hairs. Their function is the absorption of aqueous solutions by the entire surface of the outer walls. Therefore, the hair length is 0.15 - 8 mm. On average, from 100 to 300 root hairs are formed per 1 mm 2 of the root surface. They die off after 10 to 20 days. play a mechanical (supporting) role - they serve as a support for the root tip.

Zone stretches up to the root collar and is most the length of the root. In this zone, there is an intensive branching of the main root and the appearance of lateral roots.

The transverse structure of the root.

On a cross section in the absorption zone in dicotyledonous plants, and in monocotyledons - and in the conduction zone, three main parts are distinguished: the integumentary absorption tissue, the primary cortex and the central axial cylinder.

The integumentary and absorptive tissue - the rhizoderma performs integumentary, absorptive, and also, partially, support functions. It is represented by one layer of epibleme cells.

The primary root bark is the most powerfully developed. Consists of exoderm, mesoderm = parenchyma of the primary cortex and endoderm. Exoderm cells are polygonal, tightly adjacent to each other, arranged in several rows. Their cell walls are impregnated with suberin (suberinization) and lignin (lignification). Suberin ensures that the cells are impermeable to water and gases. Lignin gives it strength. The water and mineral salts absorbed by the rhizoderm pass through the thin-walled cells of the exoderm = passage cells. They are located under the root hairs. As the cells of the rhizoderm die off, the ectoderm can also perform the integumentary function.

The mesoderm is located under the ectoderm and consists of living parenchymal cells. They perform a storage function, as well as the function of carrying water and salts dissolved in it from the root hairs into the central axial cylinder.

The inner single-row layer of the primary cortex is represented by endoderm. Endoderm with Caspari bands and endoderm with horseshoe-shaped thickenings are distinguished.

Endoderm with Caspari belts is the initial stage of endoderm formation, in which only the radial walls of its cells are thickened due to their impregnation with lignin and suberin.

In monocotyledonous plants, the cells of the endoderm are further saturated with suberin on the cell walls. As a result, only the outer cell wall remains unthickened. Among these cells, cells with thin cellulose membranes are observed. These are access cells. They are usually located opposite the xylem rays of the radial-type beam.

It is believed that endoderm is a hydraulic barrier, promoting the movement of minerals and water from the primary cortex into the central axial cylinder, and preventing their return flow.

The central axial cylinder consists of a single-row pericycle and a radial vascular fibrous bundle. The pericycle is capable of meristematic activity. It forms lateral roots. The vascular fibrous bundle is the conducting system of the root. In the root of dicotyledonous plants, the radial bundle consists of 1 - 5 xylem rays. Monocots have 6 or more xylem rays. The roots do not have a core.

In monocotyledonous plants, the structure of the root during the life of the plant does not undergo significant changes.

For dicotyledonous plants at the border of the suction zone and the zone of strengthening (holding), there is a transition from primary to secondary structure root. The process of secondary changes begins with the appearance of cambium interlayers under the areas of the primary phloem, inward from it. Cambium arises from the poorly differentiated parenchyma of the central cylinder (stele).

Between the rays of the primary xylem from the procambium cells (lateral meristem), cambium arcs are formed, closing on the pericycle. The pericycle partly forms cambium and phellogen. The cambial areas arising from the pericycle form only parenchymal cells of the medullary rays. Cambium cells deposit secondary xylem towards the center, and secondary phloem outwards. As a result of the activity of the cambium, open collateral vascular-fibrous bundles are formed between the rays of the primary xylem, the number of which is equal to the number of rays of the primary xylem.

At the site of the pericycle, a cork cambium (phellogen) is laid, giving rise to the peridermis, a secondary integumentary tissue. The plug insulates the primary cortex from the central axial cylinder. The bark dies off and is discarded. The peridermis becomes the covering tissue. And the root is actually represented by the central axial cylinder. In the very center of the axial cylinder, the rays of the primary xylem are preserved, between them there are vascular-fibrous bundles. The complex of tissues outside of the cambium is called the secondary cortex. That. the root of the secondary structure consists of xylem, cambium, secondary cortex, and cork.

Absorption and transport of water and minerals by the root.

Absorption of water from the soil and delivery to terrestrial organs is one of the most important functions of the root, which has arisen in connection with going to land.

Water enters the plants through the rhizoderm, in the absorption zone, the surface of which is increased due to the presence of root hairs. In this zone of the root, xylem is formed, which provides an upward flow of water and minerals.

The plant absorbs water and minerals independently of each other, because these processes are based on different mechanisms of action. Water enters the root cells passively, thanks to osmosis. In the root hair there is a huge vacuole with cell sap. Its osmotic potential ensures the flow of water from the soil solution into the root hair.

Mineral substances enter the root cells mainly as a result of active transport. Their absorption is facilitated by the release of various organic acids by the root, which convert inorganic compounds into a form available for absorption.

At the root, the horizontal movement of water and minerals occurs in the following sequence: root hair, cells of the parenchyma of the cortex, endoderm, pericycle, parenchyma of the axial cylinder, root vessels. Horizontal transport of water and minerals occurs in three ways:

Pathway through the apoplast (a system consisting of intercellular spaces and cell walls). Main for the transport of water and ions of inorganic substances.

Pathway through the symplast (a system of protoplasts of cells, connected by means of plasmodesmata). Carries out the transport of mineral and organic substances.

Vacuolar pathway - movement from vacuole to vacuole through other components of adjacent cells (plasma membranes, cytoplasm, vacuole tonoplast). Applicable exclusively for water transport. It is insignificant for the root.

At the root, water moves along the apoplast to the endoderm. Here, its further advancement is impeded by the Caspari belts, therefore, further water enters the stele along the symplast through the passage cells of the endoderm. This path switching ensures the regulation of the movement of water and minerals from the soil to the xylem. In the stele, water does not meet resistance and enters the xylem conducting vessels.

The vertical transport of water goes through dead cells, so the movement of water is provided by the activity of the root and leaves. The root supplies water to the vessels of the stem under pressure called root pressure. It arises as a result of the fact that the osmotic pressure in the root vessels exceeds the osmotic pressure of the soil solution due to the active release of mineral and organic substances by the root cells into the vessels. Its value is 1 - 3 atm.

The evidence of root pressure is the “cry of the plant” and gutation.

"Crying plant" - the release of fluid from the cut stem.

Gutation is the release of water from an intact plant through the tips of the leaves when it is in a humid atmosphere or intensively absorbs water and minerals from the soil.

The upper force of water movement is the suction force of the leaves, provided by transpiration. Transpiration - evaporation of water from the surface of the leaves. The sucking force of leaves in trees can reach 15 - 20 atm.

In xylem vessels, water moves in the form of continuous water threads. There are adhesion forces (cohesion) between the water molecules, which makes them move one after the other. The adhesion of water molecules to the walls of blood vessels (adhesion) provides an ascending capillary flow of water. The main driving force is transpiration.

For the normal development of the plant, the roots must be provided with moisture, fresh air and the necessary mineral salts. All these plants are obtained from the soil, which is the top fertile layer of the earth.

To increase the fertility of the soil, various fertilizers are introduced into it. Fertilizing during plant growth is called top dressing.

There are two main groups of fertilizers:

Mineral fertilizers: nitrogen (nitrate, urea, ammonium sulfate), phosphoric (superphosphate), potassium (potassium chloride, ash). Complete fertilizers contain nitrogen, phosphorus and potassium.

Organic fertilizers - substances of organic origin (manure, bird droppings, peat, humus).

Nitrogen fertilizers dissolve well in water and promote plant growth. They are introduced into the soil before sowing. For the ripening of fruits, the growth of roots, bulbs and tubers, phosphorus and potassium fertilizers are needed. Phosphate fertilizers are poorly soluble in water. They are brought in in the fall, along with the manure. Phosphorus and potassium increase the cold hardiness of plants.

Plants in greenhouses can be grown without soil, in an aquatic environment that contains all the elements, necessary for the plant... This method is called hydroponics.

There is also a method of aeroponics - aerial culture - when the root system is in the air and is periodically irrigated with a nutrient solution.

Root functions. The root is the main organ of the higher plant. The functions of the roots are as follows:

They suck up water and mineral salts dissolved in it from the soil, transport them up the stem, leaves and reproductive organs. The suction function is performed by root hairs (or mycorrhiza) located in the suction zone.

Due to its high strength, the plant is fixed in the soil.

1. During the interaction of water, ions of mineral salts and products of photosynthesis, the products of primary and secondary metabolism are synthesized.
2. Under the action of root pressure and transpiration, ions of aqueous solutions of mineral substances and organic substances move along the vessels of the root xylem along the ascending current into the stem and leaves.
3. Nutrients (starch, inulin, etc.) are stored in the roots.
4. In the roots, the biosynthesis of secondary metabolites (alkaloids, hormones, and other biologically active substances) is carried out.
5. Growth substances synthesized in the meristematic zones of the roots (gibberellins, etc.) are necessary for the growth and development of the aerial parts of the plant.
6. Due to the roots, symbiosis is carried out with soil microorganisms - bacteria and fungi.
7. With the help of roots, vegetative propagation of many plants occurs.

10. Some roots function as a respiratory organ (monstera, philodendron, etc.).

11. The roots of a number of plants function as "stilted" roots (ficus banyan, pandanus, etc.).

12. The root is capable of metamorphosis (thickening of the main root forms "root crops" in carrots, parsley, etc.; thickenings of lateral or adventitious roots form root tubers in dahlias, peanuts, peel, etc., shortening of roots in bulbous plants).

The root is an axial organ, usually cylindrical in shape, with radial symmetry, with geotropism. It grows as long as the apical meristem is preserved, covered with a root cap. On the root, unlike the shoot, leaves are never formed, but, like the shoot, the root branches, forming root system.

A root system is a collection of roots from a single plant. The nature of the root system depends on the ratio of the growth of the main, lateral and adventitious roots.

^ Types of roots and root systems. In the embryo of the seed, all the organs of the plant are in their infancy. The main, or first, root develops from embryonic root. The main root is located at the center of the entire root system, the stem serves as an extension of the root, and together they form a first-order axis. The area on the border between the main root and the stem is called root collar. This transition from stem to root is noticeable by the different thickness of the stem and root: the stem is thicker than the root. The section of the stem from the root collar to the first embryonic leaves - the cotyledons are called hypocotal knee or hypocotyl... From the main root, lateral roots of successive orders extend to the sides. Such a root system is called pivotal, in many dicotyledonous plants, it is capable of branching. A branched root system is a type of tap root system. Lateral branching of the root is characterized by the fact that new roots are laid at some distance from the apex and are formed endogenously - in the internal tissues of the parent root of the previous order due to the activity of the pericycle. The more the lateral roots move away from the main root, the larger the plant nutrition area, therefore there are special agrotechnical techniques that enhance the ability of the main root to form lateral roots, for example, pinching or dive of the main root by l / 3 of its length. After diving for some time, the main root stops growing in length, while the lateral roots grow intensively.

In dicotyledonous plants, the main root, as a rule, persists throughout life, in monocotyledons, the embryonic root dies off quickly, the main root does not develop, and form from the base of the shoot clauses roots that also have branches of the first, second, etc. orders. Such a root system is called fibrous. The adventitious roots, like the lateral ones, are laid endogenously. They can form on stems and leaves. The ability of plants to develop adventitious roots is widely used in plant growing during vegetative propagation of plants (propagation by stem and leaf cuttings). Overground stem cuttings willow, poplar, maple, black currant and others are propagated; leafy cuttings - uzambara violet, or saintpaulia, some types of begonias. Underground cuttings of modified shoots (rhizomes) are propagated by many medicinal plants, for example, lily of the valley, kupenu officinalis, etc. Some plants form many adventitious roots when hilling the lower part of the stem (potatoes, cabbage, corn, etc.), thereby creating additional nutrition.

In higher spore plants (lyes, horsetails, ferns), the main root does not arise at all, they only form adventitious roots extending from the rhizome. In many dicotyledonous herbaceous rhizome plants, the main root often dies off and the system of adventitious roots extending from the rhizomes prevails (runny, nettle, creeping buttercup, etc.).

In terms of the depth of penetration into the soil, the first place belongs to the tap root system: the record depth of penetration of roots, according to some information, reaches 120 m! However, the fibrous root system, having mainly superficial roots, contributes to the creation of a sod cover and prevents soil erosion.

The total length of the roots in the root system is different, some roots reach several tens or even hundreds of kilometers. For example, in wheat, the length of all root hairs reaches 20 km, and in winter rye, the total length of roots of the first, second and third orders is over 180 km, and with the addition of roots of the fourth order - 623 km. Despite the fact that the root grows throughout its life, its growth is limited by the influence of the roots of other plants.

The degree of development of root systems on different soils in different natural zones is not the same. So, in the sandy deserts, where deep groundwater, the roots of some plants go down to a depth of 40 m or more (Selin cereal, acupressure prosopis from the Legume family, etc.). Semi-desert ephemeral plants have superficial the root system, which is adapted to the rapid absorption of early spring moisture, which is sufficient for the rapid passage of all phases of the vegetation of plants. On clayey, poorly aerated podzols of the taiga forest zone, the root system of plants is 90% concentrated in the surface layer of the soil (10-15 cm), the plants have “nourishing roots” (European spruce). For example, saxaul has roots in different time years use moisture from different horizons.

Very important factor in the distribution of the root system - moisture. The direction of the roots goes in the direction of higher humidity, however, in water and in waterlogged soil, the roots branch much weaker.

The degree of development of root systems, the depth of root penetration and other plastic characteristics of the root depend on external conditions and at the same time are hereditarily assigned to each plant species.

^ Zones of young root. In a young root, there are: 1) a division zone covered by a root cap; 2) a zone of cell stretching, or a growth zone; 3) the zone of suction, or the zone of root hairs; 4) conductive zone.

^ Division zone represents the tip of the root, covered on the outside root cap, protecting the apical, or apical, meristem. The young root tip is slippery to the touch due to mucus secreted by the cells. As the root grows in length, the mucus reduces the friction of the root tip against the soil. According to Academician V.L. Komarov, the root cap "digs the ground", it protects the dividing cells of the meristem from mechanical damage, and also controls positive geotropism the root itself, that is, it promotes the growth of the root and its penetration into the depths of the soil. The root cap consists of living parenchymal cells in which starch grains are present. There is a division zone under the cover, or root cone, represented by the primary educational tissue (meristem). As a result of active division of the root apical meristem, all other root zones and tissues are formed. The division zone of a young root is only 1 mm long. Outwardly, it differs from other zones in yellow.

^ Stretch zone, or growth zone, with a length of several millimeters, it is outwardly transparent, consists of cells that are practically non-dividing, but stretching in the longitudinal direction. The cells increase in size, vacuoles appear in them. The cells are characterized by high turgor. In the stretch zone, differentiation of primary conductive tissues occurs and permanent root tissues begin to form.

Above the stretch zone is located suction zone. Its length is 5 - 20 mm. The suction zone is represented by root hairs - outgrowths of epidermal cells. With the help of root hairs, water and salt solutions are absorbed from the soil. The more numerous the root hairs, the larger the suction surface of the root. About 400 root hairs can be located per 1 mm at the root surface. Root hairs are short-lived, live 10 - 20 days, after which they die off. The length of the root hairs in different plants from 0.5 - 1.0 cm.Young root hairs are formed above the stretch zone, and die off above the absorption zone, therefore the zone of root hairs constantly moves as the root grows and the plant is able to absorb water and nutrients dissolved in it from different soil horizons ...

Above the suction zone begins the zone of conduction, or the zone of lateral roots. The water and salt solutions absorbed by the root are transported through the vessels of the wood up to the aboveground parts of the plant.

There are no sharp boundaries between the root zones, but a gradual transition is observed.

6. Metamorphosis of the root. Their biological significance... Mycorrhiza. Most plants in the same root system have distinctly different growth and sucking endings. Growth ends are usually more powerful, quickly elongate and move deeper into the soil. The stretch zone in them is well expressed, and the apical meristems work vigorously. Sucking endings, which appear in large numbers on growth roots, lengthen slowly, and their apical meristems almost stop working. The sucking ends seem to stop in the soil and intensively "suck" it.

Have woody plants distinguish between thick skeletal and semi-skeletal roots on which short-lived root lobes... The root lobes, which are continuously replacing each other, include growth and sucking endings.

If the roots perform special functions, their structure changes. A sharp, hereditarily fixed organ modification caused by a change in functions is called metamorphosis... Root modifications are very diverse.

The roots of many plants form a symbiosis with the hyphae of soil fungi, called mycorrhiza("Mushroom root"). Mycorrhiza forms on sucking roots in the absorption zone. The fungal component makes it easier for the roots to obtain water and mineral elements from the soil, often fungal hyphae replace root hairs. In turn, the fungus receives carbohydrates and other nutrients from the plant. There are two main types of mycorrhiza. Hyphae ectotrophic mycorrhiza form a cover that envelops the root from the outside. Ectomycorrhiza is widespread in trees and shrubs. Endotrophic mycorrhiza occurs mainly in herbaceous plants. Endomycorrhiza is located inside the root, hyphae are introduced into the cells of the crustal parenchyma. Mycotrophic nutrition is very widespread. Some plants, for example orchids, cannot exist at all without symbiosis with fungi.

Special formations arise on the roots of legumes - nodules in which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Some of the substances synthesized in nodules are assimilated by plants, bacteria, in turn, use substances in the roots. This symbiosis has great importance for Agriculture... Legumes are rich in protein due to their additional nitrogen source. They provide valuable food and feed products and enrich the soil with nitrogenous substances.

Very widespread storing roots. They are usually thickened and heavily parenchyma. Strongly thickened adventitious roots are called root cones, or root tubers(dahlia, some orchids). Many, more often biennial, plants with a taproot system develop a formation called root vegetable... Both the main root and Bottom part stem. In carrots, almost the entire root crop is made up of the root, in turnips, the root forms only the lowest part of the root crop ( rice. 4.12).

Root crops of cultivated plants have arisen as a result of long-term selection. In root crops, the storage parenchyma is highly developed and mechanical tissues have disappeared. In carrots, parsley, and other umbelliferae, the parenchyma is strongly developed in the phloem; in turnips, radishes and other crucifers, in the xylem. In beets, reserve substances are deposited in the parenchyma formed by the activity of several additional layers of cambium ( rice. 4.12).

Many bulbous and rhizome plants form retractors, or contractile roots ( rice. 4.13, 1). They can shorten and retract the shoot into the soil to the optimum depth during summer drought or winter frost. Retracting roots have thickened bases with transverse rugosity.

Respiratory roots, or pneumatophores (rice. 4.13, 2) are formed in some tropical woody plants living in conditions of lack of oxygen (taxodium, or marsh cypress; mangrove plants living along the marshy shores of the ocean coasts). Pneumatophores grow vertically upward and protrude above the soil surface. Through a system of holes in these roots associated with aerenchyma, air enters the underwater organs.

In some plants, to maintain shoots in the air, additional supporting roots. They move away from the horizontal branches of the crown and, having reached the surface of the soil, branch intensively, turning into columnar formations that support the crown of the tree ( columnar banyan roots) ( rice. 4.15, 2). Stilted the roots extend from the lower portions of the stem, giving the stem stability. They are formed in plants of mangrove thickets, plant communities that develop on tropical oceans inundated during high tide ( rice. 4.15, 3), as well as in corn ( rice. 4.15, 1). Ficus rubbery forms board-like roots. Unlike columnar and stilted, they are not adventitious in origin, but lateral roots.

Rice. 4.15. ^ Supporting roots: 1 - stilted corn roots; 2 - pillar-like roots of a banyan tree; 3 - stilted roots of rhizophora ( etc- tide zone; from- low tide zone; silt- the surface of the muddy bottom).

Escape concept. Morphological dissection of the shoot. Nodes and inter-wedges. Apical shoot growth. The structure and activity of the cone is growing. A shoot is a stem with leaves and buds located on it.

Areas of the stem where leaves develop called knots.
Stem sections between two nearest nodes called internodes.
The angle between the sheet and the above internode called the leaf axil.
An axillary bud is formed in the leaf axil. The escape consists of repeating sections - metamers.
One metamere includes internode, node, leaf, and axillary bud. A shoot is a complex consisting of a stem and leaves. The primary shoot is laid in the embryo, where it is represented by the kidney. The bud consists of an embryonic stem - an epicotyl, an apical meristem, and one or more leaf primordia (leaf primordia). When the seed germinates, the stem lengthens. New leaf primordia develop from the apical meristem, from leaf primordia leaves develop, and in axils of leaves kidney primordia are formed. This development algorithm can be repeated many times during the formation of the plant shoot system.

In a formed shoot, nodes are distinguished - part of the shoot, where the leaf is connected to the stem; internodes - part of the shoot between the nodes, usually part of the stem; leaf axils - the angle between the leaf and the ascending part of the stem.

The buds are also part of the shoot. This is, first of all, the apical bud, which represents the growth cone of the shoot. V axils of leaves in seed plants, axillary or lateral buds are formed. If they develop one above the other (honeysuckle, Walnut, Robinia, etc.) are called serial. If the buds develop in the leaf axils next to each other (plums, cereals, etc.), then they are called collateral. The kidneys can form endogenously in the internode region. These kidneys are called adventitious kidneys.

Trees and shrubs of cold and temperate climates develop overwintering or dormant buds, which are often called eyes. From these buds, new shoots develop next year. The outer leaves of these buds usually develop into bud scales, which protect the inner parts of the bud from damage.

Hibernating, or dormant buds are formed in perennial herbs, on those organs that do not die off for the winter, i.e. on rhizomes, at the base of stems, etc. These buds are called renewal buds. From them aerial shoots develop in spring.

All of the above buds are called vegetative. Such kidneys consist of an apex, rudimentary nodes, rudimentary internodes, leaf primordia, above which kidney primordia can develop, and rudimentary leaves.

From a kidney that does not have renal primordia, a simple or unbranched the escape... Branching develops from a kidney with renal primordia the escape.

In addition, seed plants also have generative buds. These are flower buds and buds that give rise to gymnosperm cones. They differ from vegetative outward appearance... In addition to the apex, rudimentary internodes and rudimentary nodes, such buds have primordia, which give rise to parts of a flower or parts of cones. At the buds that give rise to inflorescences, flowering primordia are formed.

Finally, there are the so-called mixed buds, from which leafy shoots with flowers are formed.

The morphological characteristics of the shoot implies a description of the structure of nodes, internodes, buds. The type of leaf arrangement must be indicated. In most plants, it is alternate - there is one leaf at the node, but it can be opposite or whorled. Specific type Layout forms a sheet mosaic that makes the best use of space to ensure even illumination of the sheet.

The division of leaves into three categories is also associated with the process of growth and development of the shoot: lower leaves, middle leaves, apical, or upper leaves. In the morphological description of leaves, the middle leaves are usually described, but a complete morphological description requires separate description of all categories of leaves, because even middle leaves differences on one shoot. This phenomenon is called heterophyllia or variegation.

Apical shoot growth - the growth of the shoot in length due to the modification of the growth cone, initiation and growth of rudimentary leaves at its base. In the process of modification, the growth cone increases in length, becomes more complex and changes its shape.

Bud... This is a rudimentary escape. It consists of a meristematic axis ending with a growth cone (rudimentary stem) and leaf primordia (rudimentary leaves), that is, from a series of rudimentary metameres. The differentiated leaves located below cover the growth cone and primordia. This is how the vegetative kidney works. In a vegetative-reproductive bud, the growth cone has been transformed into an embryonic flower or embryonic inflorescence. Reproductive (flower) buds consist only of a rudimentary flower or inflorescence and do not have the rudiments of photosynthesizing leaves.

13. Metamorphosed shoots.

Their appearance is often associated with the performance of the functions of a container for spare products, the transfer of unfavorable conditions of the year, and vegetative reproduction.

Rhizome- This is a perennial underground shoot with a horizontal, ascending or vertical direction of growth, performing the functions of accumulation of spare products, renewal, vegetative reproduction. The rhizome has reduced leaves in the form of scales, buds, adventitious roots. Spare products accumulate in the stem part. Growth and branching occurs in the same way as in a normal shoot. The rhizome is distinguished from the root by the presence of leaves and the absence of a root cap at the apex. The rhizome can be long and thin (wheatgrass) or short and thick. Aerial buds are formed annually from the apical and axillary buds. annual shoots... The old parts of the rhizome gradually die off. Plants with horizontal long rhizomes forming many aerial shoots quickly occupy a large area, and if these are weeds (wheatgrass), then the fight against them is rather difficult. Such plants are used to fix sands (spikelet, aristida). In meadow growing, cereals with long horizontal rhizomes are called rhizome (bent grass, bluegrass), and with short ones - bushy (timothy, whiteus). Rhizomes are found mainly in perennial herbaceous plants, but sometimes in shrubs (euonymus) and shrubs (lingonberry, blueberry).

Tuber- This is a thickened part of the shoot, a container for spare products. Tubers are aboveground and underground.

Aerial tuber is a thickening of the main (kohlrabi) or lateral (tropical orchid) shoot and bears normal leaves.

Underground tuber- Thickening of the hypocotyl (cyclamen) or short-lived underground shoot - stolon (potato). The leaves on the underground tuber are reduced, in their axils there are buds, called eyes.

Overground stolon- This is a short-lived creeping shoot that serves for distribution (seizure of territory) and vegetative reproduction. It has long internodes and green leaves. Adventitious roots are formed on the nodes, and a shortened shoot (rosette) from the apical bud is formed, which, after the death of the stolon, continues to exist independently. The overground stolon is growing for sympodialia. Aboveground stolons, which have lost the function of photosynthesis and perform mainly the function of vegetative reproduction, are sometimes called whiskers (strawberries).

Bulb- This is a shortened stem (bottom), bearing numerous, closely spaced leaves and adventitious roots. There is a kidney at the top of the bottom. In many plants (onion, tulip, hyacinth, etc.), an aerial shoot is formed from this bud, and a new bulb is formed from the lateral axillary bud. The outer scales are in most cases dry, filmy and perform a protective function, the inner ones are fleshy, filled with spare products. The shape of the bulb is spherical, ovoid, flattened, etc.

Corm outwardly similar to an onion, but all its leaf scales are dry, and spare products are deposited in the stem part (saffron, gladiolus).

Thorns have different origins - from the shoot (apple, pear, blackthorn, hawthorn, gleditsia, citrus), leaf (barberry) or parts of it: rachis (astragalus), stipules (white acacia), part of the plate (Compositae). Spines are characteristic of plants in hot, dry habitats.

Antennae are formed from a shoot (grapes), a leaf or its parts: rachis and several leaves (peas), a plate (rank.), stipules (sarsaparilla). They are used to attach to the support.

Phyloclades- These are flat, leafy shoots located in the axils of reduced leaves. Flowers are formed on them. They are found in plants mainly in arid habitats (butcher, phyllanthus). Fishing apparatus- modified leaves characteristic of insectivorous plants (sundew, flycatcher). They are in the form of jugs, urns, bubbles, or slamming and rolling plates. Small insects, getting into them, die, dissolve with the help of enzymes and are consumed by plants as mainly an additional source of minerals.

There are no leaves on the root, no chloroplasts in the root cells.

In addition to the main root, many plants have numerous adventitious roots. The collection of all the roots of a plant is called the root system. In the case when the main root is slightly pronounced, and the adventitious roots are pronounced significantly, the root system is called fibrous. If the main root is pronounced significantly, the root system is called taproot.

Some plants deposit reserve nutrients at the root, such formations are called root crops.

Basic functions of the root

1. Support (fixing the plant in the substrate);
2. Absorption, conduction of water and minerals;
3. Supply of nutrients;
4. Interaction with the roots of other plants, fungi, microorganisms that live in the soil (mycorrhiza, legume nodules).
5. Synthesis of biologically active substances

In many plants, the roots have special functions (aerial roots, sucker roots).

Root origin

The body of the first plants to emerge on land had not yet been dismembered into shoots and roots. It consisted of branches, some of which rose vertically, while others pressed against the soil and absorbed water and nutrients. Despite the primitive structure, these plants were provided with water and nutrients, as they were small in size and lived near water.

In the course of further evolution, some branches began to deepen into the soil and gave rise to roots adapted to more perfect soil nutrition. This was accompanied by a deep restructuring of their structure and the emergence of specialized tissues. Root formation was a major evolutionary advance that allowed plants to colonize drier soils and form large shoots that were lifted up into the light. For example, bryophytes have no true roots, their vegetative body small size- up to 30 cm, mosses live in humid places. In ferns, real roots appear, this leads to an increase in the size of the vegetative body and to the flowering of this group in the Carboniferous period.

Modifications and specialization of roots

The roots of some buildings have a tendency to metamorphosis.

Root modifications:

1. Root vegetable- a modified juicy root. The main root and the lower part of the stem are involved in the formation of the root crop. Most root plants are biennial.
2. Root tubers(root cones) are formed as a result of thickening of the lateral and adventitious roots.
3. Hook roots- a kind of adventitious roots. With the help of these roots, the plant "sticks" to any support.
4. Stilted roots- play the role of a support.
5. Aerial roots- lateral roots, growing downward. Absorb rainwater and oxygen from the air. Formed in many tropical plants in high humidity conditions.
6. Mycorrhiza- cohabitation of the roots of higher plants with fungal hyphae. With this mutually beneficial cohabitation, called symbiosis, the plant receives water from the fungus with nutrients dissolved in it, and the fungus receives organic substances. Mycorrhiza is characteristic of the roots of many higher plants, especially woody ones. Fungal hyphae, braiding thick lignified roots of trees and shrubs, act as root hairs.
7. Bacterial nodules on the roots of higher plants- cohabitation of higher plants with nitrogen-fixing bacteria - are modified lateral roots adapted to symbiosis with bacteria. The bacteria penetrate through the root hairs into the young roots and cause them to form nodules. In this symbiotic cohabitation, bacteria convert the nitrogen in the air into a mineral form available to plants. And plants, in turn, provide bacteria with a special habitat in which there is no competition with other types of soil bacteria. The bacteria also use substances found in the roots of the higher plant. More often than others, bacterial nodules are formed on the roots of plants of the legume family. Due to this feature, the seeds of legumes are rich in protein, and members of the family are widely used in crop rotation to enrich the soil with nitrogen.
8. Storing roots- Root crops consist mainly of storing basic tissue (turnips, carrots, parsley).
9. Respiratory roots- at tropical plants- perform the function of additional breathing.

Features of the structure of the roots

The collection of roots of one plant is called the root system.

Root systems include roots of different nature.

Distinguish:

• main root,
• lateral roots,
• adventitious roots.

The main root develops from the embryonic root. Lateral roots appear on any root as a lateral ram. The adventitious roots are formed by the shoot and its parts.

Types of root systems

In the tap root system, the main root is highly developed and clearly visible among other roots (typical for dicots). In the fibrous root system on early stages development, the main root, formed by the embryonic root, dies off, and the root system is made up of adventitious roots (characteristic of monocots). The core root system usually penetrates the soil deeper than the fibrous root system, however, the fibrous root system better braids adjacent soil particles, especially in its upper fertile layer. The branched root system is dominated by equally developed main and several lateral roots (in tree species, strawberries).

Zones of young root termination

Different parts of the root perform different functions and differ in appearance. These parts are called zones.

The root tip is always covered from the outside with a root cap that protects the delicate cells of the meristem. The cover consists of living cells that are constantly being renewed. The cells of the root cap secrete mucus, which covers the surface of the young root. Thanks to the mucus, friction against the soil is reduced, its particles easily adhere to the root ends and root hairs. In rare cases, the roots lack a root cap ( aquatic plants). Under the cap is the division zone, represented by the educational tissue - the meristem.

The cells of the division zone are thin-walled and filled with cytoplasm; there are no vacuoles. The division zone can be distinguished on a living root by its yellowish color, its length is about 1 mm. Following the division zone, there is a stretch zone. It is also small in length, only a few millimeters, stands out with a light color and, as it were, transparent. The cells of the growth zone no longer divide, but they are able to stretch in the longitudinal direction, pushing the root end deep into the soil. Within the growth zone, cells are divided into tissues.

The end of the growth zone is clearly visible by the appearance of numerous root hairs. Root hairs are located in the suction zone, the function of which is clear from its name. Its length is from several millimeters to several centimeters. Unlike the growth zone, the sections of this zone no longer move relative to the soil particles. Young roots absorb the bulk of water and nutrients with the help of root hairs.

Root hairs appear as small papillae - cell outgrowths. After a certain time, the root hair dies off. Its life span does not exceed 10-20 days.

Above the suction zone, where root hairs disappear, the conduction zone begins. Through this part of the root, water and solutions of mineral salts absorbed by the root hairs are transported to the higher parts of the plant.

Anatomical structure of the root

In order to get acquainted with the system of absorption and movement of water along the root, it is necessary to consider the internal structure of the root. In the growth zone, cells begin to differentiate into tissues, and in the zone of absorption and conduction, conductive tissues are formed, which ensure the rise of nutrient solutions into the aerial part of the plant.

Already at the very beginning of the root growth zone, the mass of cells differentiates into three zones: rhizoderm, cortex and axial cylinder.

Rhizoderma- integumentary tissue, which covers the outside of the young root endings. It contains root hairs and participates in absorption processes. In the suction zone, the rhizoderm passively or actively absorbs the elements of mineral nutrition, spending energy in the latter case. In this regard, the cells of the rhizoderm are rich in mitochondria.

Velamen, like rhizoderm, belongs to the primary integumentary tissues and originates from the surface layer of the apical meristem of the root. Consists of hollow cells with thin, corky membranes.

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Description of the presentation ROOT AND ROOT SYSTEMS 1. Functions and evolutionary by slides

ROOT AND ROOT SYSTEMS 1. Functions and evolutionary origin of the root. 2. The primary structure of the root. 3. Secondary root changes. 4. Formation of lateral and adventitious roots. Root systems... 5. Specialization and modification of roots.

The root is an axial organ with radial symmetry and growing in length indefinitely due to the activity of the apical meristem. Leaves never appear on the root, and the apical meristem is always covered with a cap. The main function of the root is to absorb water and minerals, that is, to provide soil nutrition for the plant. In addition to the named main function, the roots also perform other functions: they strengthen the plant in the soil, make it possible to grow vertically and carry shoots up; secondary synthesis of various substances (amino acids, alkaloids, phytohormones, etc.) occurs in the roots; storage substances can be deposited in the roots; the roots interact with the roots of other plants, soil microorganisms and fungi.

The roots arose from the bodies of rhinophytes spread over the soil surface. In the course of evolution, some branches of these bodies began to deepen into the soil and gave rise to roots.

The roots are adapted to better soil nutrition. The emergence of roots was accompanied by a deep restructuring of their entire structure. Specialized fabrics arose in them. The function of absorbing substances from the soil began to be performed by the young endings of the roots. They keep living cells on the surface. These cells formed the most important functionally root tissue - rhizoderm.

The function of absorbing substances from the soil began to be performed by the young endings of the roots. They keep living cells on the surface. These cells formed the most important functionally root tissue - rhizoderm. Further, in the process of evolution, there was an increase in the absorbing surface of the root due to three factors: 1) abundant branching and the formation of a large number of suction ends; 2) the constant growth of roots and the movement of the suction ends to new areas of the soil; 3) the formation of root hairs.

Since root growth occurs in dense soil, its apical meristem must be protected. The protection of the apical meristem from damage was ensured by the appearance of a root cap. The emergence of roots was caused by the increasing dryness of the climate. The onset of a drier climate caused terrestrial plants to attach to the substrate and absorb water and nutrients from it. However, in the course of evolution, the root structure of different types plants changed less than the stem. This is due to the fact that the conditions in the soil environment are more stable than in the air. Therefore, the root is considered a more "conservative" organ, although it appeared much later than the shoot. Root formation is an important aromorphosis of plants. Thanks to him, the plants were able to master drier soils and form large, upward shoots.

Root cap amyloplast response to gravity. The movement of statoliths plays an important role in creating phytohormone gradients that ensure vertical root growth.

The structure of the root of a wheat seedling (Triticum aestivum): A - a diagram of the structure of the root; B - differentiation of rhizoderm and exoderm cells. 1 - conduction zone, 2 - suction zone, 3 - stretch zone, 4 - division zone, 5 - root hair, 6 - root cap.

Cross section of the root (a - monocotyledonous, b - dicotyledonous plant)

The primary cortex arises from the peribleme. Its main mass is made up of living parenchymal cells with thin membranes. A system of intercellular spaces is formed between them, elongated along the root axis. Gases (CO 2) circulate through the intercellular spaces. Gases are necessary to maintain an intensive metabolism in the cells of the cortex and rhizoderm. Vigorous metabolism in the cells of the cortex is necessary for the performance of a number of important functions: 1) the cells of the cortex supply the rhizoderm with plastic substances and are themselves involved in the absorption and conduction of substances; 2) various substances are synthesized in the cortex, which are then transferred to other tissues; 3) reserve substances accumulate in the cells of the cortex; 4) the bark often contains hyphae of fungi that form mycorrhiza.

Endoderm cells go through three stages of development. In the suction zone, endoderm is in the first stage. Caspari belts are formed in the middle of the radial walls of its cells. Caspari belts block the movement of substances through the cell membranes, that is, along the apoplast. The second stage can be observed in the lateral root zone. Moreover, with inside a thin suberin plate appears in the cell membrane. However, the endoderm is still free to pass solutions, since individual passage cells with thin walls remain in it. The third stage of development and development of endoderm can be observed in the zone of the roots of monocots. The inner and radial walls of its cells are greatly thickened. On transverse sections, such cells have a horseshoe shape. There are no access cells. The thick-walled endoderm protects the conductive tissue and increases the strength of the root.

Caspari's belt is a waterproof barrier that forces water to leave the apoplast and rush through the endoderm cell membranes into the symplast

Water flow from the soil to the root: water can move along the apoplast and symplast until it reaches the endoderm. Further movement along the apoplast is impossible.

Various types of structure of the central cylinder of the root (primary structure): A-diarch, B-triarch, C-tetrarch, D-polyarch. Types A-B characteristic of dicotyledons, G - in many monocots. 1 - area of ​​the primary cortex, 2 - primary phloem, 3 - primary xylem.

It is possible to distinguish 4 stages of the transition of the root from the primary structure to the secondary one: 1) the appearance of a cambium between the areas of the primary phloem and xylem; 2) the formation of phellogen by the pericycle; 3) shedding the primary cortex; 4) change of the radial arrangement of the conducting tissues by the collateral one.

Transition from the primary structure of the root to the secondary 1 - primary phloem, 2 - primary xylem, 3 - cambium, 4 - pericycle, 5 - endoderm, 6 - mesoderm, 7 - rhizoderm, 8 - exoderm, 9 - secondary xylem, 10 - secondary phloem , 11 - secondary cortex, 12 - phellogen, 13 - fella.

Scheme of primary differentiation of conductive tissues in pea root 1 - centripetal differentiation of xylem, 2 - epidermis, 3 - primary cortex, 4 - endoderm, 5 - first differentiated xylem elements, 6 - undifferentiated xylem elements, 7 - first differentiated phloem elements, 9 - apical meristem, 10-root cap.

Secondary root changes in monocots. The overwhelming majority of monocotyledonous plants retain the primary structure of the root until the end of life. However, in this case, many elements of the root are lignified. In arboreal monocots (palms, dracaena, yucca), a meristem layer appears in the root bark from the cells of the parenchyma or from the pericycle. Rows of closed conducting beams are formed from it. Following this series of vascular bundles in the peripheral part of the parenchyma of the primary cortex, a new layer of educational tissue appears. This layer of the meristem gives rise to a new series of conducting bundles. Thus, the thickening of the root occurs.

Adventitious roots appear on various plant organs - on stems, leaves and roots. The adventitious roots that have arisen on the stem are called stem-like roots, and those that have arisen on the root are called corner-like ones. Lateral and adventitious roots are of endogenous origin, that is, they are laid in internal tissues.

The laying of the lateral root begins with the division of pericycle cells. In this case, a meristematic tubercle forms on the surface of the stele. After a series of cell divisions of the meristematic tubercle, a lateral root appears. It has its own apical meristem and cap. The lateral root bud grows, breaks through the primary cortex of the maternal root and moves outward. Usually, lateral roots arise against the xylem elements. Therefore, they are arranged in regular longitudinal rows along the root. They appear in the absorption zone or somewhat higher. The lateral roots are laid acropetally, that is, from the base of the root to its apex.

The adventitious roots are usually laid in tissues capable of meristematic activity: in the pericycle, cambium, phellogen. Endogenous formation of lateral (and adventitious) roots is adaptive. If branching took place in the apex, then the movement of the root in the soil would be difficult.

Dichotomous branching in the root system of Lycopodium clavatum 1 - isotomic dichotomous branching of the thinnest roots

Mycorrhiza: A - ectotrophic mycorrhiza of oak, B, C - endotrophic mycorrhiza of the orchis. Lupine root nodules