Every living creature has its own adaptations for a normal life, allowing you to defend yourself from a variety of troubles, from enemies to climatic adversities. Plants are no exception. For example, algae, in order to protect themselves from the force of the flow of water and its speed, have specialized rhizoids - suckers that attach to the substrate and remain in place.
But the higher plants for this have roots of very different shapes and lengths. However, at the same time, the underground organ itself also needs protection, because the soil is a fairly tough habitat. The root cap helps him in this, the structural features of which we will consider in this article.
Features of the structure of plants
From the very elementary school, every child knows the main features of the structure of the body of a higher plant. Of course, the inner content remains unexplored for many, except for those who are specially interested. However, the external organs know everything. This is:
- shoot, represented by the outer part: stem, leaf, flower (for angiosperms);
- 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, in angiosperms it is a flower with internal reproductive organs, in spores it is sporangia with spores.
However, the roots of plants are the same organ for all the indicated groups. They are its important underground part, which performs a number of vital functions.
- Like an anchor, the root anchors the plant in the soil.
- Serves for absorption and conduction of water and minerals dissolved in it through the body.
- In many species, it is a place of accumulation of additional nutrients.
- Provides positive geotropism for all representatives (the tip of the root plays a special role in this).
- In some species, it serves as an additional organ for absorbing oxygen from the air or water.
Obviously, this organ is extremely important. It is known that if a houseplant damages the root system strongly enough during transplantation, it will die or will be very and ill for a long time. This is due to the fact that the roots of plants are restored, like all other organs, but with extensive lesions they begin to die.
Root of plants: species
Naturally, the underground organ of a plant must have such structural and developmental features that allow it to be as hardy and resistant to mechanical stress as possible.damage. An important role in this is played by the root cap. However, before considering this organ from the inside, let's analyze what it is like from the outside.
All types of roots can be divided into three categories.
- Main - the central root, which begins to grow first.
- Lateral roots are branches that appear on the main one over the course of life.
- Adnexia - numerous hairs that form on the stem, which can have a variety of sizes: from thin and almost imperceptible to giant columnar supports.
Together they provide the entire plant with the above functions.
Types of roots
Types of roots are those modifications and their unusual manifestations that are found in plants in nature. They are formed in order to adapt either to specific growing conditions, or to win the competition for territory and mineral nutrition, water. There are several most common types.
- Supporting roots are adventitious, extending from the stem and self-fixing in the soil. Formed to further strengthen the extensive crown of the tree. Such plants are called banyans.
- Roots-tacks - serve to additionally strengthen the plant on the surface of some substrate. For example, ivy, wild grapes, beans, peas and others.
- Suckers are adaptations of parasitic and semi-parasitic plants to penetrate the host's stems in order to suck out nutrients from it. Their other names are haustoria. Example: mistletoe, petrov cross, dodder and others.
- Respiratory roots. These are lateral roots that serve to absorb oxygen in the conditions of plant growth in excess moisture. Example: mangrove, brittle willow, swamp cypress.
- Air - adventitious roots that perform the function of absorbing additional moisture from the air. Example: orchids and other epiphytes.
- Tubers - underground growth of lateral and adventitious roots in order to store complex carbohydrates and other compounds. Example: potatoes.
- Root crops - an underground organ, formed by the growth of the main root, which stores nutrients. Examples: carrots, radishes, beets and others.
Thus, we have examined the parts of the plant root that can be seen with the naked eye if it is released from the ground.
Root system of plants
All designated types of roots in each plant form a whole system. It is called root and comes in two main types.
- Fibrous - pronounced lateral and adnexal, the main thing is not visible.
- Rod - the central main root is distinctly expressed, and the lateral and adnexal roots are weak.
Such types of root systems are typical for all angiosperms of the flora.
Features of the structure of the plant root (table)
Now let's look inside the plant to get to and study the root cap, the structural features of which help the whole organism so much. However, apart from the top of the rootthere are other parts of it. To consider all the structural features of the plant root, the table will be very convenient.
| Part of the root | Building features | Function to run |
| Calyptra, or root cap | Details below. | Protection against mechanical damage (main) |
| Fission zone | Represented by small cells with dense cytoplasm and large nuclei. Division is constantly taking place, since it is here that the apical meristem is located, giving rise to all other cells and tissues of the root. The color of the zone when viewed is dark, slightly yellowish. The size is about one millimeter. | The main function is to ensure constant division and increase in the mass of undifferentiated cells, which will later go to different specializations. |
| Stretch (growth) zone | Represented by large cells with cell walls, lignified over time. While they are still soft, these structures store a lot of water, stretch and thereby push the root cap deeper into the ground. The size of this area is a few millimeters, when viewed it is transparent. | Stretching and moving the plant deep into the soil. |
| Zone of absorption, differentiation | Formed by mitochondria-rich cells that assemble into an epiblema or rhizoderm. This is an integumentary tissue lining the outside of the root hairs located in this area. They can be of different sizes and lengths. Some of them die off, but belownew ones are formed. This zone is several centimeters in size and is clearly visible. | Absorption of soil solution and water from the ground |
| Conference area | Represented by exoderm cells. This is the fabric that replaces the epibleme. Exoderm cells have thick walls, often lignified, and look like a cork. The root in this part is thinner, but durable, this area is the primary bark. When considering the transition from the epiblem to the exoderm, it is almost imperceptible, it is conditional. | Conveying nutrients (soil solution and water) from the absorption zone to the stem and leaves of the plant. |
Thus, we found out that the growth of plant roots begins with the calyptra and ends with the area with the primary bark. Now let's take a closer look at the structure and functions of the very top of the underground part of these amazing creatures.
Root tip
There are several names that denote this part of the underground organ. So, the synonyms are as follows:
- caliptra, from lat. calyptra;
- root cap;
- root tip;
- calyptrogen;
- root tip.
However, whatever the name, the functions of the root cap in plants remain unchanged. In general, this area is a slightly thickened formation at the very tip of the spine underground. In a microscope, it is seen as a cap put on top to protect delicate tissues from soil particles. The dimensions of the caliptra are small, only 0.2 mm. Only in such modified structures asrespiratory roots, it reaches several millimeters.
The main function of the root cap is also determined by the appearance - naturally, this is protection against mechanical damage. However, she is not the only one.
What cells are in the root cap?
Root cap cells of two types. The first part is external. They are elongated, elongated and growing formations, tightly adjacent to each other. Therefore, intercellular spaces are practically absent. The life of these cells is very short and is only 4 to 9 days. During this time, they should have time to grow and split.
Therefore, the processes of mitosis at the root tip occur constantly. The origin of calyptra cells is usual - from the apical meristem, located immediately above the cap. The cell walls of these structures are quite thin, non-lignified.
During life, these cells are exfoliated, dying, secrete a mixture of polysaccharides - mucus. Therefore, the function of the root cap is to provide a protective mucous coating to the top of the underground organ for its safe passage between soil particles.
Due to the slime of the calyptra, the firm earthy structures stick to the spine and make it easier to slide down. However, these are not the only cells that form the cap.
There are also cells by which the calyptra is formed in its central part - the columella. These are starch grains, or amyloplasts. They are byorigin of plastid derivatives that do not have chlorophyll. That is, initially they were separate organisms that learned to live in symbiosis with more highly organized beings and gradually became indispensable internal structural cells for them.
Amyloplasts are cells that accumulate large grains of starch polysaccharide inside themselves. Outside, they are rounded, adjoining each other as tightly as the structures of the calyptra discussed above.
Another function of the root cap is associated with them, which we will discuss below. Note also that the starch in amyloplasts can serve as an additional source of energy for the plant, if environmental conditions require it.
Functions of the root cap in plants
One of them, the main one, we have already identified. Let's repeat it again and add those that have not been mentioned yet.
Functions of the root cap in plants:
- The outer layer of calyptra cells secretes a polysaccharide mucus, which serves to facilitate root penetration into the soil.
- The same slimy cap keeps the plant from drying out.
- The cells of the columella (the central part of the calyptra) contain starch grains, being due to this statoliths and performing the functions of georeception for the root. Because of this, he always has positive geotropism.
Experiments have shown that if a calyptra is removed from a plant, its growth in length will stop. However, it will not die, but will begin to actively develop lateral and adventitious roots, expanding the soil capture area.in width. This property is used by gardeners and gardeners when growing crops.
Obviously, the functions of the root cap in plants are extremely important. After all, each lateral or adventitious root also has a caliptra at its top. Otherwise, the plant would have died when the cap was removed from the central axial root. There are exceptions. These are those types of plants whose roots are completely devoid of designated structures. Examples: water chestnut, duckweed, vodokras. It is clear that these are mainly aquatic representatives of the plant world.
Function of amyloplasts
We have already said that there is a root cap function associated with amyloplasts. They accumulate grains of starch and turn into real statoliths. This is practically the same as the statocysts (otoliths) in the mammalian inner ear. They play an important role in the sense of balance.
Amyloplast statoliths do the same. Thanks to them, the plant "feels" the location of the earth's radius and always grows according to it, that is, it is guided by the force of gravity. This feature was first established by Thomas Knight in 1806, who conducted a series of confirmatory experiments. Also, this phenomenon is commonly called plant geotropism.
Geotropism
Geotropism, or gravitropism, is usually called the feature of plants and their parts to grow only in the direction of the earth's radius. This means that if, for example, you let the seeds germinate in their normal state, and then turn the pot on its side, then after a while the tipthe root will also make a bend and begin to grow down to the new position.
What is the significance of the root cap in this phenomenon? It is the amyloplasts of the calyptra that allow the root to have positive geotropism, that is, it always grows downward. While the stems, on the contrary, have negative geotropism, since their growth is carried out upwards.
It is thanks to this phenomenon that all plants suffering from bad weather and fallen to the ground with their stems, after natural phenomena (thunderstorms, hail, heavy rain, wind), are able to restore their previous state again in a short period of time.
