modified plant roots. Modifications of plant organs. Histological structure of the root

When we hear the word "root", we imagine something deep underground, absorbing water. But this is not typical for every plant. There are roots that are in the air and are capable of photosynthesis. There are roots that create fancy "skirts" around trees. And it also happens that the plant generally does well without a root. In this lesson, we will learn what other roots are.

The main function of the root is the absorption of water and minerals.

On dry fields, the length of wheat roots reaches 2.5 m, and on moist fields - 0.5 m. But they are much thicker. The main condition is soil moisture.

In the tundra, the roots are located near the surface, and the plants themselves are stunted. This is due to the low nutritional value of the soil and the presence of permafrost. The roots of dwarf birch (see Fig. 1) reach 20 cm. But when the plant is placed in more favorable conditions, the size of the roots increases.

Rice. 1. Dwarf birch

Desert plants have very long roots, which is due to the deep location of groundwater. The length of the roots of the leafless barnyard (see Fig. 2) is 15 m. Plants without a developed root system are adapted to absorb moisture from fog with the help of stems and leaves.

Rice. 2. Leafless barnyard

Root development

In the spring, sow carrots, beets, turnips in the garden. Pull the seedlings out one at a time a week after germination. Consider and sketch the root system. Mark the date. Make an album of drawings that trace the development of root crops.

Radishes, beets (see Fig. 3), turnips, carrots store nutrients in enlarged roots. With the accumulation of reserve nutrients in them, they become fleshy. If these formations are edible for humans or animals, they are called root crops.

Rice. 3. Beetroot

The main root and the lower sections of the stem take part in the formation of root crops.

Root tubers (see Fig. 4) appear as a result of thickening of the lateral or adventitious roots. Developed in dahlia, chistyak, sweet potato, cassava.

Rice. 4. Sweet potato root tubers

retracting roots- roots that can be greatly shortened. They pull under the ground a bulb of onion, woodland, tulips, orchids, saffron. The roots have transverse wrinkles.

Do you know that…

Sugar is obtained from the roots of sugar beets.

The root system of corn grows to the sides of the stem by almost 2 meters, onions - by 60-70 cm.

The bulk of the roots of most plants grows at a depth of 15-18 cm.

The roots of carrots are about 7 times longer than the above-ground part of the plant.

Ivy develops trailing roots (see Fig. 5), with which the plant is attached to a support (rock, tree trunk).

Rice. 5. Ivy roots

Root vegetables and root tubers not should be confused with rhizomes and true tubers. Rhizomes and tubers are modifications of shoots that are not related to roots.

Rice. 6. Orchid

Some epiphytes have no roots at all - bulbous tillandsia (see Fig. 7).

Rice. 7. Tillandsia bulbous

respiratory roots(pneumatophores) - are formed in gymnosperms and angiosperms growing on marshy soil (river banks). For example, brittle willow (see Fig. 8), mangrove. Roots grow vertically upwards until they reach the surface of the soil. Through the intercellular spaces, air moves to the roots, which are deeper - in conditions of lack of oxygen.

Rice. 8. Brittle willow

stilted roots(see Fig. 9) - are formed on trunks and branches, serve as props. characteristic of tropical trees.

Rice. 9. Support roots

Plank roots (see Fig. 10) - vertical outgrowths of roots that abut against the trunk and support it. Formed in large trees. The height of the roots reaches 9 m.

Rice. 10. Plank roots

Columnar roots - grow from the horizontal branches of the tree down, support the crown of the tree (Indian banyan).

Rice. 11. White mistletoe

Rice. 12. Rattle

Bibliography

1. Biology. Bacteria, fungi, plants. Grade 6: textbook. for general education institutions / V.V. Beekeeper. - 14th ed., stereotype. - M.: Bustard, 2011. - 304 p.: ill.
2. Tikhonova E.T., Romanova N.I. Biology, 6. - M.: Russian word.
3. Isaeva T.A., Romanova N.I. Biology, 6. - M.: Russian word.

1. Biofile.ru ().
2. Festival of pedagogical ideas "Open Lesson" ().
3. Bsu.ru ().

Homework

1. Biology. Bacteria, fungi, plants. Grade 6: textbook. for general education institutions / V.V. Beekeeper. - 14th ed., stereotype. - M.: Bustard, 2011. - 304 p.: ill. - With. 106, tasks and questions 1, 4 ().
2. What are the root modifications?
3. What features of the root system of orchids do you know?
4. * Name at least 5 plants with modified roots growing in your area. Describe these changes.

Roots, in addition to their main functions, often perform other functions. In this case, the so-called metamorphosis of the roots occurs. Metamorphoses are evolutionary modifications of the form and structure of organs.

Let's consider them in more detail.

1. Symbiosis of roots with soil fungi.

Phenomenon symbiosis roots of higher plants with soil fungi is widespread in nature.

The ends of the roots can either be braided from the surface with fungal hyphae, or the fungal hyphae can be contained in the root cortex. Such a phenomenon is called mycorrhiza , literal translation - " mushroom root ". Mycorrhiza can be external (ectotrophic), internal (endotrophic), or external-internal.

Ectotrophic (external) mycorrhiza can replace root hairs in a plant. In this case, root hairs often simply do not develop. External and internal mycorrhiza occurs in woody and shrubby plants (for example, birch, maple, oak, hazel, etc.).

Internal mycorrhiza is often found in various types of herbaceous and woody plants (for example, these are most types of cereals, onions, walnuts, grapes, etc.). There are types of families that cannot exist without mycorrhiza (heather, wintergreen and orchids).

What are the manifestations of the symbiotic relationship between autotrophic plants and fungi? Autotrophic plants supply the fungal symbiont with soluble carbohydrates available to them. The fungal symbiont, in turn, provides the plant with important minerals. For example, a nitrogen-fixing fungal symbiont supplies the plant with nitrogen compounds, ferments and converts sparingly soluble reserve nutrients to glucose. Excess glucose increases the absorption activity of the roots.

2. Symbiosis of roots with bacteria.

In addition to mycorrhiza ( mycosymbiotrophy ), which is often found in nature, there is another symbiosis that is not as common as the first. This is a symbiosis of plant roots with bacteria ( bacteriosymbiotrophy ).

Most often in leguminous plants, but sometimes in some other plants, parenchymal growths , which are also called nodules . Inside these nodules are many nodule bacteria. The peculiarity of these bacteria is that they can fix atmospheric nitrogen in the form of compounds that are absorbed by plants. For example, legume clover and alfalfa can accumulate 150-300 kg/ha of nitrogen in their nodules. Therefore, in agriculture, legumes are often planted in order to enrich the soil with nitrogen.

3. Storage roots.

In the roots of any plants, as a rule, reserve nutrients such as sugar, starch, inulin, etc. are deposited in some quantities. But there are cases when this storage function is hypertrophied and comes to the fore. The roots thicken and become fleshy.

Such modified tap roots that perform the function of storage are called " root crops ". Most often, this structure is found in biennials. For example, these are carrots, beets, turnips, radishes, etc. Part of the stem, the hypocotyl (or hypocotyl knee), also takes part in the formation of these root crops.

Root crops in the picture: 1 - swede; 2 - Egyptian beets; 3 - beetroot variety Mammut; 4 - carrots; c - cotyledons; hp - hypocotyl; gk - main root.

In some plant species, there are so-called root cones, which are strongly thickened adventitious roots. These are, for example, dahlia, lyubka, chistyak, etc. Numerous transitions occur between root cones and "root crops".

4. Retractor or contractile roots.

There are some types of plants in which the root is sharply reduced in the longitudinal direction at its base. For example, this happens in bulbous plants.
Often found in angiosperms retracting roots , which provide a snug fit to the ground sockets (dandelion, plantain, etc.).
Due to the underground position of the root neck and vertical rhizome, the deepening of the tubers in the soil is ensured. Those. retracting roots enable the shoots to choose the most favorable depth in the soil. In adverse climatic conditions, for example in the Arctic, retracting roots help flower buds and renewal buds survive the difficult winter period.

Many tropical plants are epiphytes aerial roots . For example, such roots are found in plants of the orchid family, aronnikovyh and bromeliads. These plants have what is called aerenchyma. This is a special loose air-bearing tissue of thin-walled parenchymal cells, from which jumpers are formed between large air cavities. Thanks to aerenchyma, these plants are able to absorb atmospheric moisture.

In the tropics, on marshy soils, trees often form respiratory roots or pneumatophores. These respiratory roots rise up (note that this is negative geotropism!) above the surface of the waterlogged soil to supply air to the underground organs of the plant through a system of holes.

In the mangroves growing in the tidal zone of tropical seas, there are trees with the so-called stilted roots . These adventitious roots are highly branched and grow down, making the trees stable on shaky ground.

The most interesting and spectacular stilted roots include supporting roots powerful branches of ficus-banyan. Numerous adventitious roots of the banyan also grow down, as can be seen in the figure. Below, they strongly thicken, take root, while developing their own root system. As a result of this, one single banyan tree can grow into a whole "grove", and at the same time occupy an area of ​​​​up to 500 m 2.

Support plank roots often found in large tropical rainforest trees. In my opinion, they are no less interesting than stilted roots. The tree trunks of the first tier of the rainforest can reach gigantic sizes, while their root system is superficial. These giants need to stay in the soil (which is practically non-existent) during frequent storms and downpours. And the roots of ordinary structure could never anchor such plants in such conditions. Therefore, in such trees, special vertical outgrowths develop on the roots creeping along the surface of the soil. These outgrowths, like boards, are adjacent to the tree trunk. At the first stage, the plank-like roots are round in cross section, but then a strong unilateral secondary growth gradually occurs. The height of such plank roots In a tropical rainforest can easily exceed the height of a person.

8. Attachment roots.

Adnexal attachment roots often found on the stems of various root-climbing vines. These include, for example, ivy. The ends of these clothespin roots are densely covered with suction hairs that secrete mucus. Thanks to this mucus, they stick very firmly to their support. Attachment roots firmly hold plants, penetrating into various irregularities or cracks in a tree, wall, rock, or some other support.

Ivy has trailing roots

- these are the vegetative organs of higher plants that are underground and carry out water with dissolved minerals to the above-ground organs of plants (stem, leaves, flowers). The main function of the root is to anchor the plant in the soil.

Types of roots: main, lateral and adventitious. main root grows from a seed, it is most powerfully developed and grows vertically down. Lateral roots depart from the main and branch many times. adventitious roots formed on stems and leaves, never depart from the main.

The totality of all the roots of a plant is called - root system. There are two types of root systems - rod and fibrous. AT pivotal the main root is strongly expressed in the root system. It is usually found in dicotyledonous plants. fibrous consists only of adventitious and lateral roots, the main root is not expressed. Fibrous root systems have monocots and some dicots.

Roots in the root system differ in appearance, age and function. The thinnest and youngest roots perform mainly the functions of growth, water absorption and nutrient absorption. Older and thicker roots are fixed in the soil, conduct moisture and nutrients to the ground organs of the plant.

Modified roots ( types of metamorphoses ):

Common storage roots are roots(carrots, beets, parsley. Starch, sugar, etc. are deposited in root crops.

root cones(root tubers) - storing adventitious roots in dahlia, sweet potato, chistyak, etc.

Attachment roots have climbing plants (ivy).

retracting roots(in bulbous plants) serve to immerse the bulb in the soil.

aerial roots are formed in plants that settle on other plants (epiphytes), for example, orchids. They provide the plant with absorption of water and minerals from the moist air.

respiratory roots have plants that grow in waterlogged soils, such as the American swamp cypress. These roots rise above the soil surface and supply the underground parts of the plant with air, which is absorbed through special holes.

stilted roots are formed in trees that grow in the littoral of tropical seas (mangroves). The roots are strongly branched and strengthen the plant in unsteady ground.

supporting roots- move away from the crown and reach the soil (banyan tree).

sucker roots- grow into the organs of other plants and absorb water and minerals from them (dodder).

Mycorrhiza- this is a symbiosis of the roots of higher plants and soil fungi. Plants supply fungi with soluble carbohydrates, while fungi supply minerals to the plant.

Symbiosis between nitrogen-fixing bacteria and the roots of leguminous plants (nodule bacteria) is also a modification of the roots. Bacteria fix atmospheric nitrogen and convert it into compounds that are absorbed by plants.

Formation of the root system:

1. pinching - remove the tip of the root, more lateral roots develop
2. hilling - the base of the shoot is covered with earth, adventitious roots grow

Root structure.

1. Division zone. The root grows in length due to the apical point of growth. It consists of an educational tissue, the cells of which are capable of constant division. The growth point is covered with a root cap. The root cap is formed by living cells, which are exfoliated and replaced by new ones due to the growth point cells. The root cap protects the growing point from mechanical damage. This zone of the root is called the division zone.

2. Stretch zone, or growth. Here the cells grow and acquire a certain shape and size.

3. Suction zone. In it, differentiation of cells into tissues is observed. The suction zone outside carries an integumentary tissue, each cell of which forms root hair. With the help of root hairs, soil solutions of water and minerals are also absorbed. The shell of the root hair cells is thin - this facilitates absorption. Almost the entire cell of the root hair is occupied by a large vacuole, and the nucleus is located at the top of the hair. As the root grows, the root hairs die and the suction zone re-forms.

4. Zone holding. Its function is the transport of water and minerals to the aboveground organs of the plant and the transport of organic substances from the stem to the root.

To thicken the root, the cambium is used, which is laid in the conduction zone. Cambium ensures the growth of the root in thickness.

The suction zone consists of conductive, mechanical and base tissues. Through the vessels of wood, the transport of water and minerals flows to the above-ground organs of plants - this is an upward current. Through the sieve tubes of the bast, organic matter flows from the leaves and stem to the root - this is a downward current.

The root absorbs water and minerals from the soil with the help of root hairs. Water enters the root hair by osmosis. When the osmotic pressure in the root vessels exceeds the osmotic pressure of the soil solution, root pressure develops. Root pressure, along with evaporation, is involved in the movement of water in the plant body.

In natural biogeocenoses, the content of the elements necessary for the plant in the soil is maintained at a relatively constant level due to the circulation of substances. In agrocenoses, a person takes part of the mineral substances from the soil along with the harvest. Therefore, fertilizers must be applied to the soil of agricultural land.

fertilizers divided into organic and mineral.

organic fertilizers : manure, peat, bird droppings, peat composts, etc. - contain all nutrients necessary for plants. When organic fertilizers are applied, microorganisms - bacteria, fungi - enter the soil. They decompose organic residues and increase soil fertility.

Mineral fertilizers are nitrogen, potassium, phosphorus. Nitrogen fertilizers contain nitrogen in the form of nitrates. These include various nitrates (potassium, sodium, etc.), ammonium chloride, urea. Plants need nitrogen for the normal formation of vegetative organs. Potash fertilizers - potassium chloride, potassium sulfate affect the growth of roots, tubers, bulbs. Phosphate fertilizers - superphosphate, phosphate rock, etc. accelerate the ripening of fruits. Phosphorus and potassium increase the cold resistance of plants.

Root breath occurs as a result of the diffusion of oxygen from the soil into the tissues. For air to penetrate the soil, it must be constantly loosened. Loosening also contributes to the preservation of moisture in the soil, which is why it is called "dry irrigation".

Fill out an application for preparation for the exam in biology or chemistry

Short form of feedback

1. Root crop- a strongly thickened main root and part of the stem, serves for the accumulation of nutrients (beets, carrots) and vegetative propagation.

2. Root tubers- thickened lateral or adventitious roots, also serve as a place for the deposition of nutrients (dahlias, orchis) and for vegetative propagation.

3. Retracting roots- lateral roots are found in bulbous plants. They are able to shrink along, due to which the bulb or rhizome is drawn deeper into the soil (liliaceae).

4. Roots trailers- Adventitious roots are formed on the stem and serve to attach it to a support (ivy).

6. Aerial roots Many plants form epiphytes. These roots are adventitious in origin. They serve to absorb moisture from the air and respiration (orchids).

7. Stilted roots- Adventitious roots are formed in the lower part of the trunks and diverge cone-shaped to the sides, lifting the trunk above the water in flood zones (mangroves), or play the role of a backup (corn, Bengal ficus, banyan tree), additionally supply oxygen.

8. Respiratory roots arise on the roots of some woody plants growing on heavily waterlogged soils, in the form of outgrowths on the roots protruding above the soil surface. They serve to supply oxygen to the roots (brittle willow).

9. Assimilation Roots adapted for photosynthesis (tropical orchids. Water chestnut).

10. Root offspring- ground shoots (aspen).

11.Support board-shaped- modified lateral roots provide additional support (poplar, elm, beech).

The root is a vegetative organ of a plant with positive geotropism (growing in the direction of gravity), having a cylindrical shape and radial symmetry. As long as there is an apical (apical) meristem at the root tip, the root is capable of growth. The key difference between a root and a shoot is that the apical meristem is protected by a root cap that covers it. Remember also that leaves can never be found on the root. The main functions of the root:

• Support function - fixes the plant in the soil (anchoring)
• Absorption of water and minerals dissolved in it from the soil solution
• Synthesis of organic substances - in the cells of the root, compounds important for the plant are formed (alkaloids, hormones, amino acids)
• Storage of nutrients - the root accumulates starch, oils
• Vegetative propagation - can be carried out by parts of the root

Sometimes adventitious buds are laid on the roots - this is the name of the buds that are laid outside the typical places for the development of the kidneys (outside the leaf axil and the top of the shoot). Shoots sprout from them, often called root shoots or root offspring.

• Symbiosis with bacteria, fungi

Nodule (nitrogen-fixing) bacteria are combined on the roots into special formations - nodules. These bacteria are able to convert atmospheric nitrogen (molecular substance) into nitrogen-containing complex substances that are absorbed by plants. With the mycelium of fungi, the root forms a symbiosis, which is called mycorrhiza (or fungus root).

Root system and origin of roots

The root system is made up of all the roots of a plant. It provides reliable anchoring of the plant in the soil. There are three main types of plants:

• Tap root system

Well expressed, developed main root, stands out from the rest of the roots. Lateral and adventitious roots are not distinguished, they occupy a subordinate position in relation to the main one. It is typical for dicotyledonous plants: clover, medicinal dandelion, burdock.

• fibrous root system

The main root is not developed or quickly dies off, adventitious roots growing from the shoot predominate. Roots are equivalent to each other. The fibrous system is characteristic of most monocotyledonous plants: onion, cereals, large plantain, caustic buttercup.

• Mixed root system

You can distinguish the main root, it stands out in size. However, multiple adventitious and lateral roots are well developed. A mixed root system is typical for strawberries, strawberries.

Root zones are a reflection of its growth and development. I always tell my students that imagination is the most important thing. Imagine a root growing deep into the soil. He faces many problems and tasks that root zones help to solve. As it grows deeper, the root zones replace each other in the direction of growth. So, what are the zones of the roots?

• Breeding zone (division)

This zone is represented by small, rapidly dividing cells of the apical (apical) meristem located at the top of the growth cone. Such young cells are especially vulnerable, therefore, in order to protect the breeding zone, it covers the root cap. Its cells constantly die from contact with the soil, forming a mucous membrane that promotes root growth deep into the soil and reduces friction on the soil.

The root cap in cereal plants is formed from meristematic cells, the totality of which is called calyptrogen. Dicotyledonous plants have a dermatocalyptrogen, from which, in addition to the root cap, a protoderm develops, from which the rhizoderm (epiblema) further differentiates.

• Growth zone (stretching)

In this zone, the divided "young cells - grow up", gain cytoplasmic mass, increase in size. It is due to their growth that the root division zone is pushed deep into the soil, which ensures root growth.

• Suction zone

Here, cell differentiation occurs, the main types of tissues are formed. Rhizoderm cells (epiblema) form root hairs - a hair-like outgrowth. It is important to note that the root hair is an outgrowth of a single cell. However, there are a lot of cells, and together all their root hairs significantly increase the root absorption area. Growing into the soil, root hairs perform one of the most important functions of the root - the absorption of water and mineral salts dissolved in it from the soil solution. The length of the suction zone is 1-1.5 cm.

• Venue

As the root grows deep into the soil, the root hairs fall off, the once active suction zone now becomes another extremely important zone - conduction. In terms of length, the root conduction zone surpasses all others: it stretches up to the root collar - the place where the root passes into the stem, reaches tens of centimeters.

Dive (dive) of the root

This is the removal of the top of the main root along with the breeding zone. Thus, gardeners stop the growth of the main root and stimulate the development of lateral and adventitious roots, the root system is branched, and the plant gives a good harvest.

In the roots, the process of respiration takes place, just as in other organs. For normal growth and development, fresh air containing oxygen must be supplied to the root. With a poor soil structure, its saturation with water leads to a real oxygen starvation of the roots - asphyxia, and not all plants are resistant to this phenomenon. There are species that do not tolerate flooding at all and require good soil aeration - pedunculate oak, beech.

Note for yourself the importance of aerating the roots of the plant by looking at the following experiment. With the help of a pear on the left side of the picture, air is pumped into the water, partially dissolving in water - the roots receive oxygen, the plant develops. On the right, root respiration is difficult, plant development is slowed down, and if root asphyxia continues, the plant will die.

Root modifications

© Bellevich Yury Sergeevich 2018-2020

This article was written by Yury Sergeevich Bellevich and is his intellectual property. Copying, distribution (including by copying to other sites and resources on the Internet) or any other use of information and objects without the prior consent of the copyright holder is punishable by law. To obtain the materials of the article and permission to use them, please contact