Complex metabolic reactions in plants are explained by the special structure of their body parts: root, stem, leaves, called vegetative organs. They are responsible for the processes of photosynthesis, transpiration, osmosis. In this work, we will study the structure and functions of such plant elements as root hairs. These are important structures that determine the absorption of water and mineral s alts from the soil.
Root - the vegetative organ of seed plants
The underground part of gymnosperms and flowering plants is represented by two types of root system: taproot and fibrous. They consist of the main, lateral, adventitious (in monocotyledonous plants) roots and a large number of small structures called root hairs.
These are outgrowths represented by single cells of the epiblema (rhizoderm). They are called trichoblasts. Being a support and performing the functions of storing organic substances, absorption and reproduction (the so-called root offspring of cherries, willows),the root is indirectly involved in such metabolic processes as transpiration, respiration, photosynthesis.
Suction area
The main root has a complex anatomical structure, and its various parts perform diverse functions. In this regard, they are called zones. Based on the function of the root hairs (above the stretch area included in the growth zone), an accumulation of outgrowths of the integumentary tissue is located. This area is called the suction zone. It is from one to three centimeters. This area can contain from 200 to 1500 or more elongated epiblema cells. They do not live long: from several hours to 20 days, and then die off. Simultaneously, new structures are formed from the rhizoderm. The root hair cell, in contact with the soil, is capable of absorbing water molecules and dissolved s alts from it in the form of sodium, chlorine, magnesium ions, acid residues of nitrate, nitrite and phosphate acids.
Epibleme and features of its structure
This plant tissue belongs to the group of primary meristems. By participating in division, its cells provide the formation of such elements as root hairs. This occurs in the outer layer of the educational tissue of the root - phellogen. The rhizoderm formed during the growing season dies off. In its place, young periderm cells are formed - a secondary integumentary tissue that is incapable of absorbing soil solutions. A new root hair, whose function is the absorption of water and mineral s alts, is formed from the overlying part of the epiblema.
Root hair functions
These structures are formed from protrusions of the rhizoderm and are single cells of the primary meristem capable of absorbing soil solution. Over time, they stretch, and the cell membrane becomes able to pass both hypotonic and highly concentrated s alt solutions inside. When mineral fertilizers are applied, for example, nitrogen and potassium fertilizers, the content of ammonium, potassium, and nitrate ions increases in the soil. This happens in the spring as this is the best time to apply this type of fertilizer. The soil solution containing the above types of ions penetrates into the trichoblast cytoplasm by passive diffusion.
Autumn application of phosphate fertilizers, which require more time to dissolve, causes absorption of ions of acidic residues of phosphate and metaphosphoric acids by root hairs. With the beginning of sap flow in late February - early March, almost the entire volume of rhizodermal cells is filled with vacuoles, the nucleus is displaced to the top of the root hair. The cell itself is capable of secreting molecules of organic acids: oxalic, malic. They dissolve humus particles, enhancing the absorption process. The formation of root hairs occurs quite quickly. Despite their short lifespan, they are able to absorb large volumes of soil solution. For example, in a woody plant, the suction area is about 120 to 640 m22.
What are trichoblasts
Earlier, we studied the features of the structure and functions of the primary tissueplant covers. It consists of a single layer of cells and is called an epiblema, located on young lateral roots growing from the main or adventitious roots. Root hairs are outgrowths of the integumentary tissue, which are highly elongated structures. It must be remembered that all epiblema cells are pluripotent, that is, capable of forming root hairs. But they are formed only from trichoblasts - protrusions of the epiblema, which look like microscopic tubercles.
The integumentary tissue responsible for the formation of trichoblasts has cytological structural features: for example, its cells lack a cuticle and a thick cellulose wall. The cytoplasm contains a large number of organelles that synthesize ATP molecules - mitochondria. They are necessary, since the absorption of water and mineral s alts requires energy. Trichoblasts also do not have stomata - elements of the integumentary tissue responsible for the processes of plant respiration and transpiration - the evaporation of water.
How s alt solutions penetrate plant roots
Trichoblast and the root hair formed from it, the function of which is the absorption of water and mineral s alts from the soil, can be considered an osmotic system. The absence of a rigid cell wall and the elasticity of the membrane promotes the transport of molecules from the external environment to the cytoplasm. In special root hair organelles - vacuoles, hypertonic solutions of glucose, fructose, malic, citric and oxalic acids accumulate.
Both the membrane and the tonoplast of the cell have a selectivesemipermeability. Therefore, the soil solution, being less concentrated than the cell sap, penetrates into the root hair according to the laws of osmosis. The water potential of the solutions coming from the soil is higher than this indicator in the tonoplast, and the osmotic potential is lower. Water and mineral s alts are transported from the root hair cell to the xylem. This is a conductive tissue that forms the vessels of plants - the trachea or tracheids. Through them, the soil solution moves up the stem to the leaves and other parts of the plant.
The pick and its meaning
To increase the suction area of the root system, you need to increase the number of lateral roots. Their epiblema containing trichoblasts will form additional root hairs. For this, a mechanical method of plucking the root tip is used, which destroys the division zone located above the root cap. It's called picking. This technique stimulates the growth of the lateral parts, on which a large number of root hairs develop. In this case, the growth of the main root in length stops. The large area of the suction zone has a positive effect on the growth and development of the plant, increasing its yield and vitality.
In this article, we studied the structural features of the root absorption zone of angiosperms, and also found out what function the root hair developing from the epiblema performs.
