Features of the structure and function of the root cover in plants

Every living creature has its own adaptations for a normal life, allowing to defend itself from a variety of troubles, from enemies to climatic adversities. Plants are no exception. For example, algae, to protect themselves from the force of the water flow and its speed, have specialized rhizoids - suckers, which are attached to the substrate and remain in place.

But the higher plants for this have roots of very different shapes and lengths. However, the underground organ itself also needs protection, because the soil is a rather tough habitat. In this he helps the root case, the features of the structure of which we will consider in this article.

Peculiarities of plant structure

From the most elementary school, every child knows the basic features of the device of the body of the higher plant. Of course, the inner content remains unexplored for many, except for specially interested people. However, the external organs know everything. It:

• Shoot, represented by the outer part: stem, leaf, flower (for angiosperms);
• The underground part formed by the root system.

Therefore, nothing unusual can be called here. The only difference between all representatives is the method of reproduction, and accordingly, the structure of the reproductive organs. In gymnosperms it is a cone with seeds, angiosperms have a flower with internal organs of reproduction, in spore - with sporangia.

However, the roots of plants are the same for all designated groups. They are his important underground part, performing a number of vital functions.

1. Like the anchor, the root fixes the plant in the soil.
2. It serves to absorb and carry the body of water and dissolved mineral substances in it.
3. In many species is the place of accumulation of additional nutrients.
4. Provides all representatives with positive geotropism (a special role in this is played by the tip of the root).
5. In some species it serves as an additional organ for the absorption of air or water oxygen.

Obviously, this organ is extremely important. It is known that if a plant in a transplant to damage the root system is strong enough, it will die or will be strong and long-term ill. This is due to the fact that the roots of plants are restored, like all other organs, but with extensive lesions begin to die.

Root of plants: species

Naturally, the underground organ of the plant must have such features of structure and development that allow it to be as hardy and resistant to mechanical damage. An important role in this is played by the root cover. However, before considering this body from the inside, we will analyze what it is outside.

All types of roots can be divided into three categories.

1. The main one is the central spine, which begins to grow first.
2. Lateral roots are branches that appear on the main with the course of life.
3. Pridatochnye - numerous hairs that form on the stem, which can have a variety of sizes: from thin and almost imperceptible to gigantic pillars.

Together they provide the whole plant with the above functions.

Types of roots

Types of roots - these are the modifications and unusual manifestations that occur in plants in nature. They are formed in order to adapt either to specific conditions of growth, or to win the competition for territory and mineral nutrition, water. There are several most common types.

1. Roots-props - subordinate, departing from the stem and self-fixing in the soil. Formed to further strengthen the extensive tree crown. Such plants are called banyans.
2. Root-hooks - serve to further strengthen the plant on the surface of some substrate. For example, ivy, wild grapes, beans, peas and others.
3. Suckers are the adaptations of plant-parasites and semi-parasites for penetration into the stems of the host with the purpose of sucking nutrients out of it. Their other name is Haustoria. Example: mistletoe, petrine cross, dodder and others.
4. Breathing roots. These are the side roots, which serve to absorb oxygen in conditions of plant growth in excess moisture. Example: mangroves, shallow willow, marsh cypress.
5. Air - the accessory roots, which perform the function of absorbing additional moisture from the air. Example: orchid and other epiphytes.
6. Tubers - growth under the ground of the lateral and accessory roots for the purpose of storing complex carbohydrates and other compounds. Example: potatoes.
7. Root crops are an underground organ, formed by the growth of the main root, which stores nutrients. Examples: carrots, radishes, beets and others.

Thus, we examined the parts of the root of the plant that can be seen with the naked eye, if it is released from the ground.

Root system of plants

All the indicated types of roots of each plant form a whole system. It is called the root one and there are two main types.

1. Uterine - pronounced lateral and accessory, can not see the main thing.
2. Rod - the central main root is expressed distinctly, and lateral and adnexal weakly.

Such types of root systems are characteristic of all angiosperms of the flora.

Features of the structure of the root of the plant (table)

Now let's look inside the plant to get to and study the root cover, the features of the structure that help the whole body. However, in addition to the root tip, there are other parts of it. To consider all the features of the structure of the root of the plant, the table will be very convenient.

Thus, we found out that the growth of plant roots starts from the calyptra and ends with a site with the primary crust. Now, let's take a closer look at the structure and functions of the very top of the underground part of these amazing creatures.

Top of the root

There are several names that designate this part of the subterranean organ. So, the synonyms are as follows:

• Calipta, from the lat. Calyptra;
• Root cover;
• Apex of the root;
• Caliptrogen;
• Tip of the root.

However, whatever the name, the functions of the root cover in plants remain unchanged. In general, this area is a slightly thickened formation at the very tip of the rootlet under the ground. In a microscope, it is seen as a cap, put on top to protect the delicate tissues from soil particles. Dimensions of the calipers are small, only 0.2 mm. Only in such modified structures as the respiratory roots, it reaches several millimeters.

External appearance determines the main function of the root cover - naturally, this is protection from mechanical damage. However, it is not the only one.

What are the cells in the root case?

Root cage cells are of two types. The first part is external. They are oblong, elongated, and growing formations, closely adjacent to each other. Therefore, the intercellular spaces are practically absent. The life of these cells is very short and is only 4 to 9 days. During this time they must grow and divide.

Therefore, the processes of mitosis at the tip of the root occur constantly. The origin of calyptra cells is usual - from the apical meristem, located just above the case. The cell walls of these structures are rather thin, non-woody.

During life, these cells sluschyvayutsya, dying, secrete a mixture of polysaccharides - mucus. Therefore, the function of the root cap is to provide a protective mucous coating of the apex of the subterranean organ for its safe advancement between soil particles.

Thanks to the mucus of the calipers, the solid earth structures adhere to the spine and facilitate its sliding downward. However, these are not the only cells by which the case is formed.

There are also cells with which the calipter is formed in its central part - the columella. These are starch grains, or amyloplasts. They are derived from derivatives of plastids that do not have chlorophyll. That is, originally were separate organisms that learned to live in symbiosis with more highly organized beings and gradually became irreplaceable internal structural cells for them.

Amyloplastes are cells that accumulate large grains of starch polysaccharide. Outside they are rounded, adjoining each other as tightly as the above-mentioned structures of the calipter.

Another function of the root cap is related to them, which we will discuss below. Note also that starch in amyloplast can serve as an additional source of energy for the plant, if environmental conditions so require.

Root canopy functions in plants

One of them, the main one, we have already identified. Repeat it once more and add those that have not been mentioned yet.

Functions of the root cover in plants:

1. The outer layer of the calyte cells secrete polysaccharide mucus, which serves to facilitate the movement of the root deep into the soil.
2. This same mucous membrane allows the plant to avoid drying out.
3. The cells of the columella (the central part of the caliphra) contain starch grains, which, due to this, are statoliths and perform georeception functions for the root. Thanks to this, he always has positive geotropism.

Experiments have shown that if a plant is removed from the calipter, its growth will cease in length. However, it will not perish, but will actively develop lateral and accessory roots, expanding the range of soil capture in width. This property is used by gardeners and truck farmers in the cultivation of crops.

Obviously, the functions of the root sheath of plants are extremely important. After all, each lateral or accessory root also has a calipter on its apex. Otherwise, the plant would have died if the cap is removed from the central axial root. There are exceptions. These are species of plants whose roots are completely devoid of the designated structures. Examples: water chestnut, duckweed, water-color. It is clear that this is mainly water representatives of the plant world.

Function of amyloplasts

We have already said that there is a function of the root cap associated with amyloplasts. They accumulate starch grains and become real statoliths. This is practically the same as statocysts (otoliths) in the inner ear of mammals. They play an important role in the sense of balance.

The statoliths of amyloplasts are also engaged in this. Thanks to them, the plant "feels" the location of the earth's radius and grows always according to it, that is, it is guided by the force of gravity. This feature was first established by Thomas Knight in 1806, which conducted a series of confirmatory experiments. Also, this phenomenon is called plant aerootropism.

Geotropism

Geotropism, or gravitropism, it is customary to call the feature of plants and their parts to grow only in the direction of the earth's radius. This means that if, for example, the seeds are allowed to germinate in the normal state, and then turn the pot on its side, then after some time the root tip will also make a bend and begin to grow downward, taking into account the new position.

What is the significance of the root case in this phenomenon? It is the amyloplasts of the calyptra that allow the root to have a positive geotropism, that is, it always grows downward. While the stems, on the other hand, have negative geotropism, since their growth is upward.

Due to this phenomenon, all plants suffering from bad weather and piled on the ground with stems, after natural phenomena (thunderstorms, hail, heavy rain, wind), are able to restore the old state again in a short period of time.