Beetroot is a modified root. Root systems. Root modifications. Differences in root systems

In most plants, the roots perform two main functions - support and soil nutrition, and have a normal structure. But in some plants, during the process of evolution, the roots have changed and began to perform additional functions.

The following root modifications are distinguished:

• Storage roots
• Aerial roots
  • Stilt roots
  • Board-shaped support roots
  • Epiphytic roots
  • Breathing roots
• Sucker roots
• Trailer roots
• Retracting roots

Storage roots

In some perennial plants, the storage function of the root becomes the main one. Such roots are called storage roots. The supply of nutrients allows the plant to survive the cold season. There are two types of storage roots - root vegetables and root cones.

Roots are formed due to the growth of the main root and the lower part of the stem. In some plants (beets, radishes, turnips), the bulk of reserve nutrients (starch, sugar, mineral salts, vitamins) are deposited in the stem part of the root crop, and the root itself is its lower part, on which lateral roots develop. In other plants (carrots, parsley), reserve nutrients are deposited in the root parenchyma. Root vegetables contain many vitamins, minerals and other nutrients and are of great economic importance. Many of them are eaten raw, boiled and stewed, they are dried and canned (carrots, beets, radishes, turnips, radishes, parsley). Juicy root vegetables are valuable food for domestic animals.

Root cones- These are the growths of lateral or adventitious roots in the fibrous root system. Root cones are formed by dahlia, sweet potato, chistyak, orchis and many other plants. Sometimes root cones are called root tubers.

Adventitious buds are formed on the root cones, which serve for vegetative propagation.

Aerial roots

Stilt roots

Stilt roots (support roots) are adventitious roots that grow down from the stem of a plant and serve to further strengthen it on the soil. In plants living in flooded and tidal zones, stilted roots lift the plants above the water and also perform a respiratory function. Stilt roots are formed in special plant communities of tropical forests - mangroves, as well as in some tropical trees and palms, and even in corn. An example of stilted roots is also a special life form of ficus - the banyan.

Board-shaped support roots

Unlike stilt roots, plank roots are lateral roots. Located at the very surface of the soil, or protruding above it, they form flat outgrowths that create additional support for the tree. Board-shaped roots are characteristic of large tropical trees.

Epiphytic roots

Epiphytes are plants that live on trees. The aerial roots of epiphytes hang freely in the air, absorbing moisture - rain or dew drops with a special covering tissue - velamen. Epiphytes include orchids that live in tropical forests.

Respiratory roots (pneumatophores)

Respiratory roots are formed in trees growing in flooded or oxygen-poor soils. They grow upward from underground lateral roots. The main function of respiratory roots is to supply oxygen to the underground parts of the plant. Oxygen penetrates through large lentils located on the respiratory roots.

Sucker roots (haustoria)

Some creeping plants, such as ivy, vanilla, and some ficus trees, have trailing roots. These are modified adventitious roots, with the help of which the plant can attach to any surface, even bare stones, and therefore bring leaves to the light.

Retracting roots

This modification of roots, such as retracting roots, is characteristic of many onions, woodlands, saffron (crocus), many orchids, aquatic plants, etc. Retracting roots, due to their special structure, can shorten by 10-70% and retract bulbs, corms, rhizomes, etc. .d underground, which protects plants from freezing in winter. Externally, the retracting roots are thick, with transverse striations.

It is difficult to overestimate the importance of the underground organ of plants. After all, it reliably holds even huge trees in the soil, provides them with water and a sufficient supply. Sometimes environmental conditions require the performance of additional functions. And then a modification of the root occurs.

Root and its structure

Based on their structural features, there are several types of roots. The main root acts as a rod. It is easy to distinguish from others. The plant always has one. Lateral roots extend from the main root. They are necessary to increase the surface area of ​​the soil to be able to absorb more moisture. The root system consisting of such roots is called taproot. Roots that grow directly from the shoot (the above-ground part of the plant) are called adventitious. Their bundle forms

Modifications of plant roots

The classic system makes it possible to perform only certain functions. For plants to survive in difficult conditions, root modification is necessary. Let's look at each of them in more detail.

Roots

Everyone remembers the fairy tale about tops and roots. Such root modifications as root vegetables are an example of tasty and juicy roots. Carrots, radishes, turnips, beets... It is impossible to imagine even one day without the presence of these healthy and tasty products in our diet.

They are the result of thickening of the main root of the taproot system. In order to survive the cold autumn and winter and form seeds, the plant stores water and minerals underground. And people use juicy root vegetables for food.

Root tubers

What is a modification of the root can also be considered using the example of root tubers. This is also thickening of the roots. But not the main one, but the adventitious roots of the fibrous system. As a result, the underground beam becomes powerful and heavy due to a significant supply of water. It is found in dahlia, asparagus, cinquefoil, and sweet potato.

An additional function of root tubers is vegetative propagation. This is possible due to the presence of accessory buds on these modifications, which are often also called root cones.

Aerial roots

The conditions of growth and modification of roots are inextricably linked. grow in conditions of high humidity. Such plants do not need to get moisture from the soil, since there is enough of it in the air. For example, an orchid grows directly on tree trunks from which aerial roots hang. Absorbing water directly from the air, they provide the plant with this necessary substance with the help of aerial (respiratory) roots. Ficus, Crassula, Monstera are indoor plants that also form aerial roots. For their normal development, sufficient air humidification in the room is necessary.

Support roots

A modification of the root is also a support root. The name itself speaks volumes about the functions it performs. Indeed, strong adventitious roots, like artificial fastenings, hold the shoot. They are often seen in corn. The shoot of this plant with fruits is quite weighty. And the fibrous one has rather superficial roots that are not able to hold the plant during strong gusts of wind. This is where a special device comes to the rescue - support roots.

Many people have seen people on stilts in the circus, but in nature you can find plants on such devices. Stilt roots look like supports, but grow downward from the shoot. In the mangroves of tropical forests, they additionally perform the function of absorbing moisture from the air. They seem to lift plants in the ebb and flow zone above the water, ensuring their normal functioning.

Trailer roots

The well-known ivy can occupy any surface. Even a vertical rock will not be a particular obstacle for him. It acquired this ability due to the presence of adventitious roots-trailers, capable of attaching to any surface.

Everyone knows that boletus grows under birch, and boletus grows under aspen. But not everyone knows why this is so. The fact is that the roots of some plants coexist mutually beneficially with fungi. This symbiosis is good for everyone. Mushrooms receive organic substances from the tree, which they cannot produce on their own because they are incapable of photosynthesis. And trees, with the help of mushrooms, are provided with water and a solution of inorganic substances.

Modification of the root helps the plant survive in conditions of deficiency or excess moisture, better stay in the soil, attach to the support and remain viable for a long time, giving an excellent harvest.

Man has long learned to use them in his activities. Root vegetables containing large amounts of valuable vitamins and minerals are used as food. And not only raw, but also boiled, fried and canned. Forage varieties of beets and turnips are grown for livestock. Sugar is obtained from a special type of beet by processing. But in parsley it is not the bitter root that is valued, but the juicy and healing leaves of the shoot. This is how, by changing, the roots benefit not only plant, but also animal organisms and humans.

The root of a plant has many functions. The most important of them for the life of the plant are the retention of the plant in the soil and the absorption of water with dissolved minerals. In addition to the above-mentioned roots, they also perform a number of other functions, which is why their structure changes. Due to metamorphosis, the modified root loses its similarity with a regular root.

Root vegetable

In some biennial plants (turnips, parsley, carrots), the root is transformed into a root vegetable, which is a thickened adventitious root. The main root and the lower part of the stem take part in the formation of the root crop. In the structure of the root crop, the main place belongs to the storage tissue.
Depending on the structure of the root, there are three types of root vegetables: carrot, beet and radish.

1. Carrot-type root vegetables - vegetables with an elongated root shape, which can be cylindrical, conical, elongated conical, spindle-shaped and blunt or sharp at the end. Root crops of this type have a clearly demarcated bark (phloem) and a core (xylem). Between them is the cork cambium. The top of the root crop is covered with natural periderm. In terms of composition and amount of nutrients, the bark is more valuable than the pith. Root vegetables of this type include carrots, parsley, celery, and parsnips.

2. Beet-type root vegetables - vegetables with round, round-flat, oval or elongated root vegetables. Represented by table beet and sugar beet. Only table beets are used as a vegetable crop. The root vegetable has dark red flesh with rings of lighter toga, which is due to the alternation of xylem (light rings) and phloem (dark rings) tissues. The smaller the proportion of xylem, the higher the nutritional value of beets.

3. Rare root vegetables - vegetables with rounded, turnip-shaped, elongated-conical root crops. A feature of their internal structure is the radial arrangement of secondary xylem, phloem and parenchyma tissue. The cambium layer is located directly below the periderm. Root vegetables of this type include radishes, radishes, rutabaga and turnips.
Root vegetables of all types are characterized by common morphological characteristics: a head in the upper part with leaf petioles and buds at the base, a root body (the main edible part) and a root tip (the main one), and beet-type root vegetables have lateral roots. In other root vegetables, thin lateral roots are easily torn off during harvesting and, as a rule, are absent.
The peculiarity of all root vegetables is their ability to heal mechanical damage by suberinization of cells, as well as their easy digestibility. The most easily withered root vegetables are carrots and radishes; the least susceptible are beets, radishes, turnips and rutabaga.

Root tubers (root cones)

Many angiosperms have root tubers (or root cones) on their roots. Their origin is associated with thickening of adventitious and lateral roots. Root tubers are a reservoir of nutrients. They are also used for vegetative propagation of plants.
The most famous of the plants with a typical root tuber is the dahlia. Swollen root cones extend from one point - the base of the old stem. These modified roots provide the plant with nutrients. During the growth period, they grow their own thin roots, which extract water and nutrients from the soil. Plants with root cones are propagated by separate cones with a bud (eye) at the end (dahlia, eremurus, clivia, buttercup).

Cling roots, stilt roots, aerial roots, board-shaped roots, sucker roots

Ivy. Photo: Harry Knight

Roots-holds- peculiar adventitious roots that allow the plant to easily attach to any support. Such roots are found in ivy and other climbing plants.
An amazing phenomenon in nature is stilted roots, which serve as a support for the plant. Such roots have the ability to withstand heavy loads due to the presence of mechanical tissues in all sections. They are found in plants of the genus Pandaus, growing on oceanic islands in the tropics, where strong hurricane winds prevail.

Aerial (breathing) roots found in tropical trees that grow in oxygen-depleted soils and freshwater tropical swamps. These are lateral roots located above the ground. Thanks to aerial roots, oxygen and water are absorbed by the plant from the air in conditions of high humidity. Thus, the respiratory roots provide the function of additional breathing.

Board-shaped roots - These are vertical above-ground roots characteristic of large trees growing in tropical rain forests. They develop at the base of the trunk, look like boards adjacent to the trunk, providing the plant with additional support.

Mycorrhiza

Mycorrhiza is a symbiosis of the roots of higher plants with fungal hyphae. This cohabitation is beneficial for both organisms, since the fungus receives ready-made organic substances from the plant, and the plant absorbs water and minerals from the fungus. Mycorrhiza is often found on the roots of higher plants, especially woody ones. You can think of fungal hyphae intertwined with thick tree roots as root hairs, since their functions are similar.
Most perennial plants have mycorrhizae. It is assumed that mycorrhiza is one of the factors that contributed to the progress of flowering plants. Plants that feed on mycorrhizal fungi are called mycotrophic.

There are two main types of mycorrhiza: ectotrophic and endotrophic. The hyphae of ectotrophic mycorrhiza cover the root only from the outside, sometimes penetrating into the intercellular spaces of the bark parenchyma. Ectomycorrhiza is common in many woody plants (pine, birch, oak, beech, etc.), as well as a number of herbaceous agricultural plants, especially cereals. The fungus settles on the sprouted root of the seed and in its further development, especially in the tillering phase, provides abundant soil nutrition for the plant.
Endotrophic mycorrhiza is more common. It is characteristic of most flowering plants. Endomycorrhiza does not form a fungal sheath around the root, root hairs do not die, but hyphae penetrate the root and penetrate into the cells of the bark parenchyma.

Epiphytic tropical orchids and some other plants have so-called aerial roots. They are covered with a multi-layered epiblema called velamen. Velamen sometimes performs a photosynthetic function, and later can participate in the absorption of atmospheric moisture, forming a dead spongy hygroscopic root cover.
Without mycorrhiza, the mycelium of symbiotic fungi can exist in the soil for a certain time, but will never form fruiting bodies. Therefore, under artificial conditions it is impossible to obtain fruiting bodies of porcini mushrooms, russula mushrooms, fly agaric mushrooms - all of them are mycorrhiza-formers, and without a certain tree species they will not bear fruit. In turn, a plant without its fungal symbionts develops poorly, slowly, is easily susceptible to diseases and may even die.

Mycorrhiza is of great importance in tropical rain forests. Due to the strong leaching regime (daily precipitation), these forests are practically devoid of soil (all nutrients are washed out of the soil). Plants are faced with an acute problem of nutrition. At the same time, there is a lot of fresh organic matter: fallen branches, leaves, fruits, seeds. But this organic matter is inaccessible to higher plants, and they come into close contact with saprotrophic fungi. Thus, the main source of minerals under these conditions is not the soil, but soil fungi. Minerals enter the root directly from the hyphae of mycorrhizal fungi, which is why rain forest plants have a shallow root system. How effectively mycorrhiza works can be judged by the fact that tropical rain forests are the most productive communities on Earth; the maximum possible biomass develops here.

Bacterial nodules

Plants can also coexist mutually beneficially with nitrogen-fixing bacteria. This is how bacterial nodules appear on the roots of higher plants - modified lateral roots that have adaptations for symbiosis with bacteria. Through root hairs, bacteria enter young roots and provoke the formation of nodules. The role of these bacteria is that they convert nitrogen from the air into mineral form so that it becomes available for absorption by plants. Plants provide protection for bacteria from competing species of soil bacteria. Bacteria also feed on substances from the roots of higher plants. The appearance of nodule bacteria has been recorded, mainly on the roots of plants from the legume family. Therefore, legume seeds are enriched with protein, and in agriculture, representatives of this family are used in crop rotation to enrich the soil with nitrogen.

You will learn about the root systems of plants and their functions, and about the consequences of the roots performing functions that are unusual for them.

Roots are needed to absorb substances. And also for what?

The root system is the entire collection of plant roots. The appearance of root systems depends on the growing conditions and how the plant adapts to these conditions (Fig. 77).

The roots of some plants are located only in the surface layer of soil, several centimeters thick (Fig. 77, e). Thus, the surface roots of some types of cacti reach a depth of up to 30 m. They are able to quickly collect dew from a large area, because in the desert there is water, you falling in the morning, it does not penetrate deep into the soil and quickly evaporates. In tropical rainforest trees, surface roots have time to capture minerals formed during the very rapid decomposition of dead plant parts. However, the roots usually reach greater depths. Thus, in barley and winter rapeseed they deepen to almost 3 m, in grapevine - up to 16 m. Some desert plants, in order to reach aquifers in the soil, deepen their roots to 30-50 m.

Aerial roots are adapted to exist in the air* They are characteristic of most orchids and other inhabitants of tropical rainforests (Fig. 81\au indoor plants - for Monstera. Aerial roots absorb water during precipitation not with root hairs, but with special spongy tissue.

Respiratory roots (Fig. 82) develop in plants in waterlogged habitats, where there is not enough air in the soil to ensure respiration of the root system. In such plants, part of the roots protrudes above the surface and ensures gas exchange. For example, in swamp cypress, the respiratory roots have the form of cones more than 1 m high.

Supporting roots (Fig. 83) develop at the base of the trunks of tall plants where it is necessary to ensure plant stability. Thus, thanks to plank-shaped supporting roots, gigantic tropical trees, whose root systems are superficial, do not fall. In our fields, supporting roots can be seen in corn.

A root crop is a modification formed as a result of thickening and accumulation of nutrients in three organs of a young plant at once - the main root, the subcotyledon and the base of the main shoot. Root vegetables allow the plant to survive in unfavorable conditions. People have long used root vegetables for food and developed many different cultivated varieties: beets, carrots. parsley, celery, radishes and radishes.

A sign of the root part of the root crop is the lateral roots arranged in rows.

The neck, formed by the thickened hypocotyledon, has a smooth surface. And on the head of the root crop (the thickened base of the main shoot) there are scars of dead leaves (Fig. 84).

All three parts are almost equally developed in the celery root crop (Fig. 85.a). But in carrots (Fig. 85, b) and parsley, the root crop has a very small head, the smooth neck is visible above the soil surface, and the main part is formed by a thickened root. In radish (Fig. 85.c), almost all of its smooth root is a thickened subcotyledon. Therefore, radish seeds cannot be sown deep - the harvest will be of poor quality.

conclusions

1. The roots of a plant form a root system, the structure of which depends on the growth conditions of the plant.

2. The performance of a certain specific function by the root leads to its modifications.

3. A modified root can be an integral part of a root crop, in the formation of which the hypocotyledon and the main shoot also participate.

Terms and concepts that are important to know

Root system, root modifications, root tubers, sucking roots, aerial roots, respiratory roots, supporting roots, root vegetables.

Control questions

1. What is the root system?

2. What are root modifications?

3. What root modifications do you know, how do they differ from typical plant roots in structure and function?

4. How does a root vegetable differ from a root tuber?

Tasks

Put the table in order: establish correspondences between the names of plants, their root modifications and their functions. Write rows of three numbers in a notebook.

Various environmental conditions require the organisms living there to develop certain adaptive mechanisms. In other words, plants, animals, birds and other living beings living in difficult conditions are forced to adapt to the environment not only at the behavioral, but also at the biological level.

Thus, the plant modifies the structure of the root system, leaves or shoots depending on conditions. This part will highlight root modifications.

Differences in root systems

The most common difference in the root system is its length, that is, the depth of penetration of the root into the soil. In dry areas, the roots of wheat, for example, can reach more than two meters deep to draw water from deep in the soil.

The same root system is found in desert plants (for example, leafless barnacle), the roots of which penetrate the soil more than 15 m. On more irrigated plants, the roots are dense, but not longer than 50 cm.

The same is observed in plants living in permafrost conditions (for example, the roots of a dwarf birch are only 20 cm long). In areas requiring more careful adaptation, the roots changed more and acquired a number of new functions.

Modification of roots

Firstly, these are clinging roots, or trailing roots, with which the plant hooks onto any vertical support, in particular, a tree trunk or wall, grows upward and brings the leaves closer to the light.

The most common representative is ivy. Its function is to provide the plant with greater survival among higher representatives.

The next type is a root crop: the growth of the main root and sometimes even lower sections of the stem. The main function is to store nutrients in the root crop. Examples include carrots, turnips, beets, radishes and others.

A similar modification is called root tubers. Here the lateral and adventitious roots are already growing and thickening. This type of roots is observed in dahlia, sweet potato, and chistyak. The fourth modification of the root is the appearance of nodules, a symbiosis of roots with nodule nitrogen-fixing bacteria. Nodules look like thickenings on the root of a plant (most often legumes or alders).

Sometimes the plant forms freely hanging aerial roots. For example, this is an orchid that lives on tree trunks in tropical forests. This root system allows it to absorb rainwater in the absence of direct access to it.

Another type of roots located outside the soil are respiratory ones. These are processes of lateral roots with especially developed air tissue, growing vertically upward. They are found in marsh plants such as cypress or brittle willow. The function is to provide the plant with an influx of oxygen through the intercellular spaces.

Also, some roots can serve as supports (that is, support). They are otherwise called adventitious roots or stilt roots. It is also an adaptation of tropical plants (such as the banyan tree).

The roots of many aquatic plants, taking root in the ground, lose root hairs.

And the roots of parasitic plants simply penetrate the body of the host plant (for example, mistletoe).