Each living creature has its own adaptations for a normal life, allowing you to protect yourself from a variety of troubles, from enemies to climatic adversities. Plants are no exception. For example, algae, to protect themselves from the strength of the flow of water and its speed, have specialized rhizoids - suckers that attach to the substrate and remain in place.
But 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. In this, the root cover helps him, the structural features of which we will consider in this article.
Plant structure features
From the very elementary school, every child knows the basic features of the body structure of a higher plant. Of course, the inner content remains unexplored for many, except for specially interested people. However, external organs know everything. It:
- 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, this is a cone with seeds, in angiosperms, a flower with internal reproductive organs, and in spores, sporangia with spores.
However, the roots of plants are the same organ for all designated groups. They are its important underground part that performs a number of vital functions.
- Like an anchor, the root fixes the plant in the soil.
- Serves for the absorption and passage through the body of water and minerals dissolved in it.
- In many species, it is the site of accumulation of additional nutrients.
- It provides all representatives with positive geotropism (the root tip plays a special role in this).
- In some species, it serves as an additional organ for the absorption of oxygen in air or water.
Obviously, this organ is extremely important. It is known that if a houseplant suffers damage to the root system during a transplant, it will die or be seriously and permanently 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.
Plant Root: Species
Naturally, the underground organ of the plant should have such structural and developmental features that allow it to be as hardy and resistant to mechanical damage as possible. An important role in this is played by the root cap. However, before considering this organ from the inside, we will analyze what it is like from the outside.
All kinds of roots can be divided into three categories.
- The main one is the central root, which begins to grow first.
- Lateral roots are branches that appear on the main one over the course of life.
- Adnexal - numerous hairs that form on the stem, which can have a variety of sizes: from thin and almost invisible to giant pillar-shaped supports.
Together, they provide the entire plant with the performance of the above functions.
Types of roots
Types of roots are those modifications and their unusual manifestations that occur in plants in nature. They are formed in order to adapt either to the specific conditions of growth, or to win in the competition for territory and mineral nutrition, water. There are several of the most common types.
- Roots-props - subordinate, extending from the stem and self-fixing in the soil. Formed with the aim of further strengthening the vast crown of the tree. Such plants are commonly called banyan trees.
- Roots-hooks - serve to further strengthen the plant on the surface of a substrate. For example, ivy, wild grapes, beans, peas and others.
- Suckers are the adaptations of parasitic and semi-parasitic plants to penetrate the stems of the host in order to suck out nutrients from it. Their other name is haustoria. Example: mistletoe, peter cross, dodder and others.
- Respiratory roots. These are the lateral roots, which serve to absorb oxygen in conditions of plant growth in excess moisture. Example: mangroves, fragile willow, bog cypress.
- Air - accessory roots, which perform the function of absorbing additional moisture from the air. Example: orchid and other epiphytes.
- Tubers - underground growth of lateral and accessory roots in order to store complex carbohydrates and other compounds. Example: potatoes.
- Root crops - an underground organ that is formed by the growth of the main root, which stores nutrients. Examples: carrots, radishes, beets and others.
Thus, we examined the parts of the plant root that can be seen with the naked eye if you release it from the ground.
Root system of plants
All designated root types of each plant form a whole system. It is called the root and is of two main types.
- Fibrous - lateral and subordinate are expressed, the main is not visible.
- Stem - the central main root is distinct, and the lateral and subordinate are weak.
These types of root systems are characteristic of all angiosperms of the flora.
Features of the structure of the plant root (table)
Now let's look inside the plant in order to get to and study the root cap, the structural features of which so help the whole body. However, besides the apex of the root, there are other parts of it. To consider all the structural features of the root of the plant, the table will be very convenient.
| Root part | Structural features | Function to be performed |
| Caliptra, or root case | Below we consider in more detail. | Protection against mechanical damage (basic) |
| Division area | It is represented by small cells having a dense cytoplasm and large nuclei. Division is constantly occurring, 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. Size is about one millimeter. | The main function is to ensure continuous division and increase in the mass of undifferentiated cells, which in the future will go to different specializations. |
| Stretch Zone | It is represented by large cells with cell walls, eventually lignifying. While they are still soft, these structures store a lot of water, stretch, and thereby push the root cover deeper into the ground. The size of this section is a few millimeters; when viewed, it is transparent. | Stretching and moving the plant deep into the soil. |
| Zone of absorption, differentiation | It is formed by mitochondria-rich cells that assemble into the epiblema or rhizoderm. This is the integumentary tissue lining the root hairs located on this site from the outside. They can be of different sizes and lengths. Some of them die off, but new ones are formed below. In size, this zone is several centimeters, is clearly visible. | Absorption of soil solution and water from the earth |
| Holding area | Presented by exoderm cells. This is the fabric replacing the epiblem. Exoderm cells have thick walls, often lignify, look like corks. The root in this part is thinner, but strong, this site is the primary bark. When considering the transition from the epiblema to the exoderm is almost imperceptible, it is conditional. | Conducting nutrients (soil solution and water) from the absorption zone into the stem and leaves of the plant. |
Thus, we found that the growth of plant roots begins with a caliper and ends with a site with a primary bark. Now we will examine in more detail the structure and functions of the very top of the underground part of these amazing creatures.
Root apex
There are several names that designate this part of the underground organ. So, the synonyms are as follows:
- caliptra, from lat. calyptra;
- root cap;
- root apex;
- caliptrogen;
- tip of the root.
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 root under the ground. In a microscope, it is seen as a cap worn on top to protect delicate tissues from soil particles. The size of the caliper is small, only 0.2 mm. Only in such modified structures as respiratory roots does it reach several millimeters.
The main function of the root cap is determined by the appearance - of course, this is protection against mechanical damage. However, she is not the only one.
What cells are in the root case?
Root cap cells are of two types. The first part is the outdoor. 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 lasts only from 4 to 9 days. During this time, they must have time to grow and split.
Therefore, mitosis processes at the tip of the root occur continuously. The origin of the caliper 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 desquamated, dying, secrete a mixture of polysaccharides - mucus. Therefore, the function of the root cap is to provide a protective mucous coating of the top of the underground organ for its safe movement between the soil particles.
Thanks to the mucus of the caliper, solid earthen structures adhere to the spine and facilitate its sliding down. However, these are not the only cells that form the cap.
There are also cells with which the caliptra is formed in its central part - columella. These are starch grains, or amyloplasts. They are plastid derivatives by origin 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 irreplaceable internal structural cells for them.
Amyloplasts are cells that accumulate large grains of starch polysaccharide inside themselves. Outside, they are rounded, adjacent to each other as tightly as the caliper structures discussed above.
Another function of the root cap is associated with them, which we will discuss below. We also note that starch in amyloplasts can serve as an additional source of energy for the plant, if environmental conditions so require.
The functions of the root cap in plants
One of them, the main one, we have already identified. Repeat it again and add those that have not yet been mentioned.
The functions of the root cap in plants:
- The outer layer of the caliper cells secrete polysaccharide mucus, which serves to facilitate the movement of the root deeper into the soil.
- The same mucus cover allows the plant to avoid drying out.
- Columella cells (the central part of the caliper) contain starchy grains, being due to this statoliths and performing georeception functions for the root. Thanks to this, he always has positive geotropism.
Experiments have shown that if a caliper is removed from a plant, then its growth in length will cease. However, it will not die, but will begin to actively develop lateral and additional roots, expanding the wide range of soil capture. 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 side or subordinate root also has a caliper at its apex. Otherwise, the plant would die if the cap was removed from the central axial root. There are exceptions. These are plant species whose roots are completely devoid of the indicated structures. Examples: hazelnut, duckweed, water-red. It is clear that these are mainly aquatic representatives of the plant world.
Amyloplast function
We have already said that there is a function of the root cap associated with amyloplasts. They accumulate starch grains and turn into real statoliths. This is practically the same as the statocysts (otoliths) in the inner ear of mammals. They play an important role in the sense of balance.
Amyloplast statoliths also do this. Thanks to them, the plant "feels" the location of the earth's radius and always grows according to it, that is, it focuses on the force of gravity. This feature was first established by Thomas Knight in 1806, who conducted a series of confirmatory experiments. Also, a similar phenomenon is commonly called plant geotropism.
Geotropism
Geotropism, or gravitropism, is called a feature of plants and their parts to grow only in the direction of the earth's radius. This means that if, for example, let the seeds germinate in the usual state, and then turn the pot over on its side, then after a while the tip of the root will also bend and begin to grow down, taking into account the new position.
What is the significance of the root cap in this phenomenon? It is the amyloplasts of the caliper that allow the root to have positive geotropism, that is, always grow down. While the stems, on the contrary, have negative geotropism, since their growth is carried up.
It is thanks to this phenomenon that all plants suffering from bad weather and felled by stems to the ground, after natural phenomena (thunderstorms, hail, heavy rain, wind), are able to restore their previous state again in a short period of time.