Subsidiary farm. The importance of microelements in the life of plants

Plants and vegetables need nutrients to grow and develop. The ratio of nutrients is different for species, varieties, growing period and age of the plant.

❖ Nitrogen is the main biogenic element for vegetable plants, which is part of proteins and nucleic acids. The mineral forms of nitrogen that enter the plant go through a complex cycle of transformations, being included in the composition of organic acids. The process of nitrate reduction is catalyzed by enzymes and has several intermediate steps. The activity of reducing enzymes depends on magnesium and trace elements: molybdenum, copper, iron and manganese.

Nitrate nitrogen can accumulate in significant amounts, which is safe for plants, but the content of nitrates in vegetables above a certain level is harmful to humans.

Free ammonia in plants is in small quantities. This is due to the fact that it quickly interacts with the carbohydrates found in plants. The result of the interaction is the formation of primary amino acids. Excessive accumulation of ammonia, especially with a deficiency of carbohydrates, leads to poisoning of plants.

The quality of products depends on which of the nitrogen compounds are assimilated in large quantities. With enhanced ammonia nutrition, the reducing ability of the plant cell increases and there is a predominant accumulation of reducing compounds. With nitrate nutrition, the oxidative capacity of cell sap increases, more organic acids are formed.

Assimilation of ammonia and nitrate nitrogen by plants depends on the concentration of the nutrient solution, its reaction, the content of accompanying elements, the provision of plants with carbohydrates and biological features culture.

❖ Phosphorus is found in plants in much smaller quantities than nitrogen. It acts as a companion of nitrogen, with its deficiency in plants, the accumulation of nitrate forms of nitrogen increases. The largest number phosphorus is concentrated in the reproductive organs: 3-6 times more than in the vegetative.

Phosphorus is contained in DNA and RNA nucleic acids, which are carriers of hereditary information. Phosphorus compounds with proteins (phosphoroproteins) are the most important plant enzymes. Phosphorus entering the plant contributes to the accumulation of starch, sugars, coloring and aromatic substances, increases the keeping quality of fruits.

❖ Potassium regulates the water exchange of plants, the physical state of the colloids of the cytoplasm, its swelling and viscosity. Under the influence of potassium, the water-retaining capacity of the protoplasm increases, which reduces the risk of short-term wilting of plants with a lack of moisture. The presence of potassium in the plant cell ensures the normal course of oxidative processes, carbohydrate and nitrogen metabolism. The accumulation of potassium contributes to the activation metabolic processes plants. Potassium improves immunity, enhances the use of ammonia nitrogen in the synthesis of amino acids and protein. Potassium is characterized by high mobility - the outflow from older leaves to younger ones. In fact, the plant gets the opportunity to reuse potassium.

❖ Calcium plays important role in photosynthesis, the movement of carbohydrates in a plant. It is involved in the formation of cell membranes, causes watering and maintains the structure of cell organelles. The lack of calcium affects the development of the root system, the growth of leaves slows down, they die off. Calcium deficiency appears on young plants.

❖ Magnesium is part of the chlorophyll molecule and takes part in photosynthesis, and is also part of pectin and phytin. With a lack of magnesium, the content of chlorophyll in the leaves decreases, “marbling” appears. Magnesium and phosphorus are found in the growing parts of the plant. Magnesium accumulates in seeds. Magnesium is involved in the movement of phosphorus in plants. Activates enzymes. This element contributes to the accumulation essential oils and fats. With magnesium deficiency, oxidative processes increase, the activity of the peroxidase enzyme increases, the content of invert sugar and ascorbic acid decreases.

mineral nutrition plants

Plant nutrition consists in the absorption by them from the environment of substances necessary for life processes, as well as their distribution and use in metabolism. In the process of photosynthesis, plant organisms synthesize organic substances, some of which are used to build the organism itself, and some are used as an energy source. Organic matter contains various chemical elements entering plants from the soil. Most plants absorb water passively - by force, which was formed due to the difference between osmotic and turgor pressure. Plants that have adapted to existence on saline substrates use active water transport against the salt concentration gradient, consuming a significant part of the assimilation products for this. Because of this, they are always undersized. Plants absorb minerals by active absorption. However, plants are able not only to absorb minerals from the soil solution, but also to dissolve water-insoluble compounds. This is facilitated by organic acids secreted by the plant - malic, citric, etc.

Due to the difference in the concentration of the fields of the soil solution and the cytoplasm of the epiblema cells, osmosis - movement of the solvent from the soil to the hair cells. It is known that the concentration of substances in root cells increases from the periphery to the center (concentration gradient). As a result, water and substances dissolved in it move to the vessels of the central cylinder of the root, and root pressure arises, under the influence of which the solution moves towards the stem. In addition to root pressure (lower water pump), the movement of the solution through the vessels also supports the process of transpiration in the leaves (upper water pump). Under the action of a large force of adhesion of water molecules to each other, a kind of water columns are formed in the conducting system of the plant. Such columns begin in the root hairs, and end in the stomata of the leaves. By root pressure, water is, as it were, pumped into the xylem, and transpiration ensures its transport to the desired height.

The role of minerals in the life of plants in different periods of vegetation is determined by the method of water cultures. An aquatic culture is a plant grown without soil in vessels with aqueous solutions of mineral salts when air enters the solution (aeration of the solution). At the same time, they use different variants nutrient media, changing the content of components in them and comparing the nature of the vegetation of plants on these media with the vegetation of crops, for the cultivation of which standard set substances.

The movement of inorganic and organic substances along the root. The movement of water and substances dissolved in it in a plant occurs mainly in two ways: diffusion and flow. Diffusion of water and substances occurs along a concentration gradient, and flow movement along a gradient hydrostatic pressure. Water moves through the vessels, as through pipes, according to the general laws of hydrodynamics, and in parenchymal cells - by osmosis, and the movement of water in living cells is much more difficult.

At the root, the movement of water and substances dissolved in it begins with its absorption by root hairs. From the hairs to the xylem of the central cylinder, water enters through the cytoplasm of the living cells of the root cortex, as well as along the cell walls. In this way, water moves slowly and over a short distance. Finally, water and substances dissolved in it enter the xylem (xylem sap), and then the xylem sap moves through the xylem vessels due to root pressure. Organic substances can also move along the xylem of the root, for example, reserve substances of the root in spring.

Fertilizers. With each harvest, a certain part of the mineral substances is taken out of the soil, and it is gradually depleted. Stock necessary elements replenished with mineral (ammonium sulfate, urea, potassium chloride, superphosphate, phosphate rock; potassium, calcium and sodium nitrate, etc.) and organic (humus, peat, peat composts, green fertilizers, bird droppings) fertilizers, which in different form(powder, solution) used in different dates depending on the type of soil, its fertility and the needs of the plant. For example, nitrogen-containing fertilizers are applied before sowing or in early summer. During the period of fruit formation, plants need more phosphorus and potassium.

The amount of fertilizer to be applied to the soil is determined using chemical analysis soil. Both the excess of certain elements in the soil and their shortage can negatively affect crop yields. The timing of fertilizer application is determined taking into account their ability to dissolve in water. Hardly soluble (phosphate) and insoluble (organic) fertilizers are applied in the fall, so that by the action of soil organisms they decompose to water-soluble mineral compounds before spring and enter the soil with melt water. Fertilizers can be applied in certain phases of plant development as top dressing. It can be dry (powdered fertilizers are scattered) and wet (soluble fertilizers are applied to the soil).

Evaporation of water from leaves (transpiration)

Water coming from the soil through root system into the stem and leaves, moves along the intercellular spaces and evaporates through the stomata to the outside.

Transpiration promotes the entry of a new amount of water into the root and lifting it up the stem to the leaves. It is a means of adapting plants to the conditions of existence. Thanks to evaporation in the plant body, a constant balance of water in the cells is maintained. In addition, due to the direct movement and movement of water in the body of a plant, movement and exchange occur. nutrients between individual organs. Finally, this process is regulated temperature regime in the plant body. Evaporation of water by plants is regulated by stomata. With a high water content, the stomata open and transpiration increases, with a lack of water, when the plants wither, the stomata close and transpiration becomes more difficult. The supply of water to the leaves from the roots is provided by three forces: the suction force of the cells, the force of adhesion of water molecules in the conducting system, and root pressure.

The intensity of evaporation also depends on the growth conditions of the plant and its biological properties. Plants of arid places, as well as in dry weather, evaporate more water than in the conditions high humidity. Evaporation of water, except for stomata, is also regulated by protective formations on the skin of the leaf. These formations are the cuticle, wax coating, pubescence with different hairs. In succulent plants, the leaf has turned into thorns (cacti), and the stem performs its functions. Plants that grow in damp places have large leaf blades that do not have protective formations on the skin. shade plants evaporate less water than those that grow without shade. Plants evaporate a lot of water during dry winds and in the heat, much less - in calm cloudy weather.

The main role in the evaporation of water is played by stomata, and the entire surface of the leaf is partially involved in this process. Therefore, stomatal and cuticular transpiration is distinguished - through the surface of the cuticle, which covers the epidermis of the leaf. Cuticular transpiration is much less than stomatal.

Since transpiration occurs mainly through the stomata, where it penetrates and carbon dioxide for the course of the photosynthesis process, there is a relationship between the evaporation of water and the accumulation of dry matter in the plant. The amount of water that a plant evaporates to build 1 g of dry matter is called the transpiration coefficient. Its value depends on the growth conditions, species and varieties of plants.

With difficult evaporation, guttation is observed in plants - the release of water droplets through water stomata (hydathodes). This phenomenon in nature is observed in the morning, when the air is saturated with water vapor, or before rain. Hydathodes are a very active secretion structure. However, they are classified as excretory system only formally, since the product of excretion is water, and not excretory substances. The place of concentration of hydathodes is the edge of the leaf, mainly the tops of the teeth, where the conductive elements of the acidum end.

The biological adaptation of plants to protection from evaporation is leaf fall - the mass fall of leaves in the cold or hot periods of the year.

Mineral plant nutrition

For a normal life cycle of a plant organism, a certain group of nutrients is necessary, the functions of which in a plant cannot be replaced by other chemical elements.

These are: 1) organogens - C (45% dry weight); About (42%); H (6.5%); N (1.5%) - in the amount of 95%;

2) macronutrients (1 - 0.01%): P, S, K, Ca, Mg, Fe, Al, Si, Cl, Na;

3) trace elements (0.01 - 0.00001%): Mn, Cu, Zn, Co, Mo, B, I;

4) ultramicroelements (< 0,00001 %): Ag, Au, Pb, Ge….и др.

J. Liebig found that all of the listed elements are equivalent and the complete exclusion of any of them leads the plant to deep suffering and death, none of the listed elements can be replaced by another, even close in chemical properties. Macronutrients at a concentration of 200-300 mg/l in the nutrient solution do not yet have a harmful effect on the plant. Most trace elements at a concentration of 0.1-0.5 mg/l inhibit plant growth.

For the normal life of plants, there must be a certain ratio of various ions in environment. Pure solutions of any one cation are poisonous. Thus, when wheat seedlings were placed on pure solutions of KCL or CaCL 2, swelling first appeared on the roots, and then the roots died off. Mixed solutions of these salts did not have a toxic effect. The softening effect of one cation on the action of another cation is called ion antagonism. Antagonism of ions manifests itself both between different ions of the same valence, for example, between sodium and potassium ions, and between ions of different valences, for example, potassium and calcium. One of the reasons for the antagonism of ions is their effect on the hydration of cytoplasmic proteins. Divalent cations (calcium, magnesium) dehydrate colloids more strongly than monovalent cations (sodium, potassium). The next reason for antagonism of ions is their competition for the active centers of enzymes. Thus, the activity of some respiratory enzymes is inhibited by sodium ions, but their action is removed by the addition of potassium ions. In addition, ions can compete for binding with carriers during uptake. The action of one ion can also enhance the influence of another ion. This phenomenon is called synergy. So, under the influence of phosphorus, the positive effect of molybdenum increases.

The physiological significance of micro and macro elements

1. Are part of biologically important nutrients;

2. Participate in the creation of a certain ionic concentration and stabilization of macromolecules;

3. Participate in catalytic reactions, being part of or activating individual enzymes.

Nitrogen (N 2)

It is part of proteins, nucleic acids, membrane phospholipids, porphyrins (the basis of chlorophyll and cytochromes), numerous enzymes (including NAD and NADP) and many vitamins.

With a lack of nitrogen in the environment, plant growth is inhibited, the formation of lateral shoots is weakened, small leaves and pale green color of the leaves are observed due to the destruction of chlorophyll.

Despite the presence in atmospheric air 78% N 2 (410 5 t), such molecular nitrogen is not absorbed by higher plants (the nitrogen molecule (NN) is chemically inert; to break its three covalent bonds in chemical process ammonia synthesis requires catalysts, high temperature and pressure) and can be converted into a form accessible to them only due to the activity of nitrogen-fixing microorganisms. Of the lithospheric reserves of nitrogen (1810 15 tons), only its minimum part is concentrated in the soil, of which only 0.5 - 2% is directly available to plants: - these are NH 4 + and NO 3 - ions formed as a result of mineralization of organic nitrogen of plant plants by bacteria and animal residues and humus. Namely, processes:

1. ammonification(conversion of organic nitrogen to NH 4 +);

2. Nitrification(oxidation of NH 4 + to NO 3 -);

3. Denitrification(anaerobic reduction of NO 3 - to N 2)

Molecular nitrogen fixation ( N 2)

Chemical binding of molecular nitrogen in the form of NH 4 + or NO 3 - is carried out either as a result of electrical discharges in the atmosphere, or in the presence of a catalyst at a temperature of more than 500 0 C and an atmospheric pressure of about 35 MPa.

Biological binding of atmospheric molecular nitrogen is carried out by nitrogen-fixing microorganisms. They are:

1. free-living(p. Azotobacter, Beijrinckia - aerobic and p. Clostridium - anaerobic);

2. *symbiotic(R. Rhizobium, which forms nodules on the roots of leguminous plants, and some actinomycetes).

*Infection of the host plant symbiotic bacteria begins with the penetration of the bacterium into the cell of the root hair, migration to the cells of the cortex and intensive division of infected cells, which leads to the formation of nodules on the roots. At the same time, the bacteria themselves become bacteroids, which are 40 times larger than the original bacterium. The main role in the process of nitrogen fixation belongs to the enzyme nitrogenase . The enzyme consists of two components: a higher molecular weight Fe-Mo protein (Mr = 200-250,000, 2 Mo molecules, 30 Fe molecules and 22 S molecules) and an Fe-protein (Mr = 50-70,000, 4 Fe molecules and 4 molecules S). The Fe-Mo protein serves to bind and reduce molecular nitrogen, and the Fe-protein serves as a source of electrons for the reduction of the Fe-Mo protein, which it receives from ferredoxin. The whole complex works only in the presence of ATP hydrolysis and the protective action of the protein legoglobin (synthesized by host cells and protects nitrogenase from oxygen).

The resulting NH 4 + binds to keto acids, forming amino acids that are transported to the cells of the host plant.

Nitrate reduction and ammonia assimilation pathways

Since in organic compounds only ammonium nitrogen is included, nitrate ions NO 3 - absorbed by the root must be reduced in cells to ammonia. This is done in two stages:

1. Reduction of nitrate to nitrite, catalyzed by nitrate reductase (in the cytoplasm); NO 3 - ---2 e---- NO 2 -

2. Reduction of nitrite to ammonia catalyzed by nitrite reductase (in chloroplasts). NO 2 - ---- 6e --- NH 4 +

Ammonia, formed during the reduction of nitrates or in the process of molecular nitrogen fixation, is further absorbed by plants with the formation of various amino acids. First of all, the NH 4 + acceptor is α-ketoglutaric acid, which, under the action of glutamate dehydrogenase turns into glutamate.

1. Study of the effect on the intensity of physiological processes when they are excluded from the nutrient medium.

2. The study of the specific role of individual trace elements, mainly their participation in certain enzymatic reactions.

The second biochemical approach proved to be more effective.

Iron was the first trace element, the need for which was discovered by Gries in 1843-1844.

The need for other trace elements - boron, manganese, copper, zinc and molybdenum, for higher plants was established only in the 20s and 30s of the 20th century. The establishment of their necessity was facilitated by the discovery of the causes of many plant diseases not caused by fungal and bacterial infection - sugar beet heart rot, gray leaf spot, bronze disease, etc. All these diseases were the result of a physiological disorder caused by a lack of one or another microelement, and the disease was eliminated, as soon as the plant's need for the missing element was satisfied.

These elements play an exceptional role in metabolism. They combine with organic substances, especially proteins, many times increase their catalytic activity. So, for example, iron in the composition of a complex hemin complex in combination with a specific protein increases the catalytic activity against the activity of the iron ion by 1010 times.

Boron, aluminum, cobalt, manganese, zinc and copper increase the drought resistance of plants. And in this case, the effect of microelements is due to the influence on the colloid-biochemical properties of protoplasm (increased hydrophilicity and water-retaining capacity of colloids). Trace elements also enhance the movement of plastic substances from the leaves to the generative organs.

Significant shifts are caused by some trace elements in the speed of passing through the stages of development. It has been established that soaking wheat seeds in solutions of Cu, Zn, Mo, B salts significantly accelerates the passage of the vernalization stage by plants, while solutions of Fe and Mn did not have a positive effect or retarded development.

The influence of each of the elements depends on the concentration: it affects the subsequent growth aboveground organs and roots are not the same. Thus, Cu and Mo stimulate the growth of the stem and roots, while Mn and Ni - only the stem, and B and Sr - only the root.

The treatment of Cu seeds had a strong positive effect on the drought resistance of cotton plants. This effect is due to an increase in the water-retaining capacity and sucking power of the leaf parenchyma cells, a change in the anatomical structure of the leaves towards xerophyte, etc. A similar effect was observed on winter wheat when seeds were treated with B, Cu, Mo, Co, P, and K salts. The passage of the light stage was accelerated under the influence of B, Co, Mo, Mn, Zn, Cu, and Al. Interestingly, this was observed only on long-day plants (winter wheat, oats) and did not appear on short-day plants (perilla).

Ya. V. Peive, M. Ya. Shkolnik, M. V. Katalymov, B. A. Yagodin and others made a great contribution to the solution of issues related to the nutrition of plants with microelements.

Boron is one of the most important trace elements for plants. Its average content is 0.0001%, or 0.1 mg per 1 kg of dry weight. Boron is most needed by dicotyledonous plants. A significant content of boron was found in the flowers, especially in the stigma and styles. In the cell, most of this trace element is concentrated in the cell walls. Boron enhances the growth of pollen tubes, pollen germination, increases the number of flowers and fruits. Without it, seed maturation is disrupted. Boron reduces the activity of some respiratory enzymes, affects carbohydrate, protein and nucleic metabolism.

Boron absorption strongly depends on pH, and its distribution throughout the plant occurs mainly with the transpiration current. The need for boron for plants has been established for a very long time, but it is still unclear how its functions are realized: in what specific reactions it is included and what is the mechanism of its participation in individual processes.

The role of boron is far from being sufficiently elucidated. This is due to the fact that boron, unlike most other trace elements, is not part of any enzyme and is not an enzyme activator. Of great importance for the implementation of the function of boron is its ability to give complex compounds. Complexes with boric acid form simple sugars, polysaccharides, alcohols, phenolic compounds, etc. In this regard, it can be assumed that boron affects the rate of enzymatic reactions through the substrates on which enzymes act.

A lack of boron causes a number of diseases: sugar beet heart rot, internal black spot of table beet and rutabaga, cauliflower head browning disease, death of spikelets in wheat and even the entire rudimentary ear in barley, yellowing of alfalfa, etc. It has been established that under the influence of boron the series physiological processes: the water content of the plasma increases, the absorption of cations and especially calcium increases, and the absorption of anions decreases.

Also, with a lack of boron, the synthesis, transformation and transport of carbohydrates, the formation reproductive organs, fertilization and fruiting. Boron is necessary for plants during the entire period of their development. It cannot be reutilized, and therefore, during boron starvation, first of all

growth cones die off - the most typical symptom of boron deficiency. Anatomical studies indicate the cessation of cell division in the meristem. At the same time, significant disturbances in the normal arrangement of the elements of the phloem and xylem are detected, up to the complete loss of conductivity by these tissues. This is the reason for the disturbances in the movement of plastic substances and, above all, sugars from the leaves to the axial and reserve organs of plants found during boron starvation.

Crops most sensitive to boron deficiency: sugar and fodder beet, rapeseed, legumes, alfalfa, vegetables, apple, grapes.

In higher plants, the average magnesium content is 0.02%. Especially a lot of magnesium in plants short day- corn, millet, sorghum, hemp, as well as in potatoes, beets, tobacco and legumes. A lot of it accumulates in young cells and growing tissues, as well as in generative organs and storage tissues. In caryopses, magnesium accumulates in the embryo, where its level is several times higher than the content in the endosperm and peel. The accumulation of magnesium in young tissues is facilitated by its relatively high mobility in plants, which leads to its secondary use (reutilization) from aging tissues. The movement of magnesium is carried out both in the xylem and in the phloem.

The chloroplast contains 15% Mg 2+ of the leaf, up to 6% of it can be in the composition of chlorophyll. With magnesium deficiency (starvation), the proportion of Mg 2+ in the pigment can even reach 50% of the total content in the leaf. This function of magnesium is unique: no other element can replace it in chlorophyll. Magnesium is necessary for the synthesis of protoporphyrin 9, the direct precursor of chlorophyll.

Magnesium maintains the structure of ribosomes by binding RNA and protein. The large and small subunits of ribosomes associate together only in the presence of magnesium. Hence, protein synthesis does not occur with a lack of magnesium, and even more so in its absence. Magnesium is an activator of many enzymes. An important feature magnesium is that it binds the enzyme to the substrate in a chelate bond.

Magnesium is part of phytin (organophosphate), a reserve organic substance. Responsible for energy transport, activates the enzyme, which is a catalyst for the participation of CO 2 in the process of photosynthesis.

Magnesium is essential for many enzymes in the Krebs cycle and glycolysis. It is also required for the work of enzymes of lactic acid and alcoholic fermentation.

Magnesium enhances the synthesis of essential oils, rubber, vitamins A and C.

With an increase in the degree of magnesium supply in plants, the content of organic and inorganic forms of phosphorus compounds increases. This effect is probably associated with the role of magnesium in the activation of enzymes involved in the metabolism of phosphorus.

The process of magnesium intake into plants may depend on the degree of provision of plants with other cations. So, with a high content of potassium or ammonium in the soil or nutrient solution, the level of magnesium, especially in the vegetative parts of plants, decreases. In fruits, the amount of magnesium does not change or may even increase. Conversely, when the level of potassium or ammonium in the nutrient medium is low, the magnesium content in the plant increases. Calcium and manganese also act as competitors in the uptake of magnesium by plants.

Plants experience a lack of magnesium in mostly non-sandy soils. Poor in magnesium and calcium, rich in gray soils; chernozems occupy an intermediate position. When the pH of the soil solution decreases, magnesium enters the plants in smaller quantities.

Magnesium deficiency leads to a decrease in the phosphorus content in plants, even if phosphates are present in sufficient quantities in the nutrient substrate, especially since phosphorus is transported throughout the plant mainly in organic form. Therefore, magnesium deficiency will inhibit the formation of organophosphorus compounds and, accordingly, the distribution of phosphorus in the plant body.

With a lack of magnesium, the formation of plastids is disrupted: the chloroplast matrix becomes clear, the grana stick together. Spots and stripes of light green appear between the green veins, and then yellow color. The edges of the leaf blades become yellow, orange, red or dark red, and this "marble" color of the leaves, along with chlorosis, serves hallmark lack of magnesium. At later stages of magnesium starvation, light yellow and whitish stripes are also observed on young leaves, indicating the destruction of chloroplasts in them, and then carotenoids, and the leaf zones adjacent to the vessels remain green longer. Subsequently, chlorosis and necrosis develop, affecting primarily the tops of the leaves.

Signs of magnesium deficiency first appear on old leaves, and then spread to young leaves and plant organs. High and prolonged illumination exacerbates the symptoms of magnesium deficiency.

Magnesium sensitive crops: sugar beets, potatoes, hops, grapes, nuts, greenhouse crops.

In the composition of compounds containing heme (all cytochromes, catalase, peroxidase), and in non-heme form (iron-sulfur centers), iron takes part in the functioning of the main redox systems of photosynthesis and respiration. Together with molybdenum, iron is involved in the reduction of nitrates and in the fixation of molecular nitrogen by nodule bacteria, being a part of nitrate reductase and nitrogenase. Iron also catalyzes the initial steps in the synthesis of chlorophyll. Therefore, the insufficient supply of iron to plants under waterlogged conditions and on carbonate soils leads to a decrease in the intensity of respiration and photosynthesis and is expressed in yellowing of the leaves (chlorosis) and their rapid fall. If iron becomes unavailable for vegetative plants, then chlorosis appears only on newly developing organs. Consequently, iron is firmly bound in cells and is not able to move from old tissues to young ones. Iron is also necessary for colorless plants - fungi and bacteria, so its role is not limited to participation in the formation of chlorophyll.

In cereal crops, chlorosis appears as alternating yellow and green stripes along the leaf. In some cases, iron deficiency can cause the death of young shoots.

Iron deficiency also causes changes in root morphology, inducing the growth of root hairs that profusely cover the root surface. This promotes better contact with the soil and soil solution, increasing iron uptake.

Along with iron in catalytically active compounds, plant tissues can include this element in reserve substances. One of them is the protein ferritin, which contains non-heme iron. Iron can account for about 23% of the dry weight of ferritin. Ferritin is present in large amounts in plastids.

Crops sensitive to iron deficiency: corn, legumes, potatoes, cabbage, tomatoes, grapes, fruit and citrus fruits, ornamental crops.

For the first time, Bertrand (1897) drew attention to the need for manganese in plants. Its average content is 0.001% or 1 mg per 1 kg of dry tissue mass. It enters the cells in the form of Mn 2+ ions. Manganese accumulates in leaves. The participation of ions of this metal in the release of oxygen (photodecomposition of water) and the reduction of CO 2 during photosynthesis has been established. Manganese helps to increase the content of sugars and their outflow from the leaves. Manganese ions activate enzymes that catalyze the reactions of the Krebs cycle (malic acid dehydrogenase, citric acid, oxaloacetic acid decarboxylase, etc.). in this regard, it is clear great importance manganese for the process of respiration, especially its aerobic phase.

The importance of manganese for the normal course of the exchange of nitrogenous compounds is great. Manganese takes part in the process of reduction of nitrates to ammonia. This process goes through steps catalyzed by a number of enzymes, of which two (hydroxylamine reductase and nitrite reductase) are manganese dependent, so that manganese-deficient plants cannot use nitrate as a source of nitrogen nutrition.

Manganese activates the enzymes involved in the oxidation of the most important phytohormone - auxin.

This element plays a specific role in maintaining the structure of chloroplasts. In the absence of manganese, chlorophyll rapidly degrades in the presence of light.

Despite the significant content of manganese in the soil, most of it is difficult for plants to access, especially on soils with a neutral pH value.

Manganese is responsible for the oxidation of iron in the plant body to non-toxic compounds. It is a necessary component of the synthesis of vitamin C. It intensifies the accumulation of sugar in sugar beet roots and protein in grain crops. Responsible for the process of nitrogen assimilation. It is an activator of photosynthesis after freezing of plants.

A symptom of a disease caused by a lack of manganese is, first of all, the appearance of chlorotic spots between the leaf veins. Cereals develop elongated strips of chlorotic tissue gray color, then a narrow zone of weakened turgor appears, as a result of which the leaf blade hangs down. With a sharp deficiency of manganese, these symptoms extend to the stem. Affected leaves with the development of the disease turn brown and die.

The gray spot disease is widespread on humus-rich soils that have an alkaline reaction. This disease affects cereals, especially oats, wheat, rye, and corn.

In plants with reticulated leaf venation, with a lack of manganese, chlorotic spots appear scattered over the leaf, to a greater extent on the lower leaves than on the upper ones.

In beets, manganese deficiency causes a disease known as spotted jaundice. Yellow chlorotic areas appear on the leaves, then the edges of the leaves curl up.

In peas with a lack of manganese, seed spot develops. This disease is expressed in the appearance of brown and black spots or even cavities on pea seeds. internal surfaces cotyledons.

Chlorosis also develops at a very high content of manganese, in this case manganese oxidizes iron into an insoluble oxide form and chlorosis develops already from a lack of iron. Excess iron causes symptoms of manganese deficiency. The most favorable ratios of iron and manganese for better growth plants and general health 2:1.

Crops sensitive to manganese deficiency: cereals (wheat, barley, oats), corn, peas, soybeans, potatoes, sugar beets, cherries, citrus fruits.

The content of zinc in aboveground parts legumes and cereals is 15 - 60 mg per 1 kg of dry weight. An increased concentration is noted in the leaves, reproductive organs and growth cones, the highest - in the seeds. Zinc enters the plant in the form of the Zn 2+ cation, having a multilateral effect on metabolism. It is necessary for the functioning of a number of glycolysis enzymes. The role of zinc is also important in the formation of the amino acid tryptophan. It is with this that the influence of zinc on the synthesis of proteins, as well as the phytohormone of indoleacetic acid (auxin), the precursor of which is tryptophan, is connected. Top dressing with zinc helps to increase the content of auxins in tissues and activates their growth. Zinc plays an important role in DNA and RNA metabolism, protein synthesis and cell division. It is an enzyme activator, prevents premature cell aging. Helps to increase heat, drought and frost resistance of plants. Zinc has long been considered as a stimulant, and only by the 30s. of the last century, the absolute necessity of this element for all higher plants was established. Zinc deficiency disease is widespread among fruit trees. With zinc deficiency, instead of normally elongated shoots with well-developed leaves, diseased plants form in spring a rosette of small, crowded, hard leaves. Different fruit disease It is indicated in different ways: small-leaved, rosette disease, spotted chlorosis, jaundice. Zinc is involved in redox processes, it is associated with the transformation of compounds containing a sulfhydryl group. The lack of zinc causes the suppression of carbohydrate metabolism processes, since the lack of zinc has the greatest effect on plants rich in carbohydrates. Also, with zinc deficiency in plants, phosphorus metabolism is disturbed: phosphorus accumulates in the root system, its transport to aboveground organs is delayed, the conversion of phosphorus into organic forms slows down - the content of inorganic phosphates increases several times, the content of phosphorus in the composition of nucleotides, lipids and nucleic acids decreases. In addition, the rate of cell division is suppressed by 2-3 times, which leads to morphological changes in the leaves, impaired cell elongation and tissue differentiation.

Crops particularly sensitive to zinc deficiency: corn, soybeans, beans, hops, potatoes, flax, green vegetables, grapes, apple and pear, citrus fruits.

The highest content of molybdenum is typical for legumes (0.5 - 20 mg per 1 kg of dry weight), cereals contain from 0.2 to 2.0 mg of molybdenum per 1 kg of dry weight. It enters plants as an anion MoO 4 2- and is concentrated in young, growing organs. It is more in leaves than in roots and stems, and in the leaf it is concentrated mainly in chloroplasts.

Molybdenum takes part in the reduction of nitrates, being part of nitrate reductase, and is also a component active center nitrogenases of bacteroids that fix atmospheric nitrogen in nodules of legumes.

Helps to increase the content of chlorophyll, carbohydrates, carotene, ascorbic acid and proteins.

Molybdenum is a part of more than 20 enzymes, while performing not only a catalytic, but also a structural function.

With a lack of Mo, a large amount of nitrates accumulate in the tissues, nodules do not develop on the roots of legumes, plant growth is inhibited, and leaf blades are deformed. Molybdenum, like iron, is necessary for the biosynthesis of legoglobin (leghemoglobin), an oxygen carrier protein in legume nodules. With a deficiency, the nodules become yellow or gray, while their normal color is red.

With a lack of molybdenum, the content of ascorbic acid drops sharply, and disturbances in the phosphorus metabolism of plants are observed.

In plants that are deficient in molybdenum, light spots appear on the leaves, buds may die, fruits and tubers crack.

Plant growth is inhibited and due to a violation of the synthesis of chlorophyll, the plants look pale green. These signs are similar to those of a nitrogen deficiency.

Crops sensitive to molybdenum deficiency: cereals, legumes, sugar beet, tomatoes, cabbage, alfalfa.

As part of different types plants, more than 60 elements were found, of which, in addition to those noted above, sodium, silicon, chlorine, cobalt, copper, and aluminum are also considered by some authors as necessary.

located in a plant silicon impregnates cell walls and makes them hard and resistant to insect damage and protects cells from fungal infection. Silicon is also essential for the growth of diatoms.

Chlorine considered to be an enzyme stimulant. Importance chlorine is for green photosynthetic plants. There is information about the effect of chlorine on nitrogen metabolism. Concentrating in the plant in vacuoles, chlorides can perform an osmoregulatory function. Chlorine deficiency is rare and occurs only in very alkaline soils.

Action aluminum regarded as a catalyst. In addition, with some excess accumulation of aluminum in the plant, the color of the flowers changes. Thus, for example, under the influence of the accumulation of aluminum in the Hydrangea plant, normally red or white flowers change to blue or purple.

Sodium accumulates in plants in significant quantities, but does not play a significant role in their life, since it can be completely excluded from the nutrient solution. However, for halophytes, plants in saline areas, the presence of sodium favors growth.

Content cobalt averages 0.00002%. Especially cobalt is needed leguminous plants, as it participates in the fixation of atmospheric nitrogen. Cobalt is part of cobalamin (vitamin B12 and its derivatives), which is synthesized by bacteria in the nodules of leguminous plants, as well as in the composition of enzymes in nitrogen-fixing organisms involved in the synthesis of methionine, DNA and bacterial cell division. With cobalt deficiency, leghemoglobin synthesis is suppressed, protein synthesis is reduced, and the size of bacteroids is reduced. This speaks in favor of the need for cobalt. The need for cobalt for higher plants that are not capable of nitrogen fixation has been established. The influence of cobalt on the functioning of the photosynthetic apparatus, protein synthesis, its relationship with auxin metabolism is shown. The difficulty in resolving the issue of the need for cobalt for all plants lies in the fact that the need for it is extremely small.

Copper activates the formation of proteins and B vitamins. Like zinc, it activates the enzyme and prevents premature aging of plant cells. It takes part in the metabolism of proteins and carbohydrates in the plant. Significantly increases the plant's immunity to fungal and bacterial diseases. This element is very small in sandy and peaty soils. Copper deficiency manifests itself in persistent wilt top leaves, even with good moisture supply, until they fall off. There is a death of the edges of young leaves, followed by their chlorosis and twisting; the release of pollen grains slows down, as a result of which the pollination of plants decreases. There is a significant decrease in crop yield (if there are no visual signs of trace element deficiency); lodging can be observed in cereal crops; at fruit crops drooping branches and crowns can be observed.

Plants are able to absorb from the environment in larger or smaller quantities almost all elements of the periodic table. Meanwhile, for the normal life cycle of a plant organism, only a certain group of basic nutritional elements is necessary, the functions of which in the plant cannot be replaced by other chemical elements. This group includes the following 19 elements:

Among these main nutrients, only 16 are actually mineral, since C, H and O enter plants mainly in the form of CO 2, O 2 and H 2 O. The elements Na, Si, and Co are given in brackets, since their necessity for all higher plants has not yet been established. Sodium is absorbed in relatively high amounts by some species of the family. Chenopodiaceae (Chenopodiaceae), in particular beets, as well as species adapted to salinity conditions, and in this case is necessary. The same is true for silicon, which is found in especially large quantities in the straw of cereals; for rice, it is an essential element.

The first four elements - C, H. O, N - are called organogenes. Carbon averages 45% of the dry mass of tissues, oxygen - 42, hydrogen - 6.5 and nitrogen - 1.5. and all together - 95%. The remaining 5% are ash substances: P, S, K, Ca, Mg, Pe, A1, Si, Na, etc. O mineral composition plants are usually judged by the analysis of the ash remaining after the combustion of plant organic matter. The content of mineral elements (or their oxides) in a plant is usually expressed as a percentage of the dry matter mass or as a percentage of the ash mass. The ash substances listed above are macronutrients.

Elements that are present in tissues at concentrations of 0.001 % and below from the dry weight of tissues, called microelementtami. Some of them play an important role in metabolism (Mg, Cu, Zn, Co, Mo, B, C1).

The content of one or another element in plant tissues is not constant and can change greatly under the influence of environmental factors. For example. Al, Ni, F and others can accumulate in plants to toxic levels. Among the higher plants, there are species that differ sharply in the content in the tissues of such elements as Na, as already mentioned, and Ca, in connection with which the plant groups of natriophiles are distinguished. , calciumphiles(most legumes, including beans, beans, clover), calcium phobes (lupine, white-bearded, sorrel, etc.). These specific features are due to the nature of soils in the places of origin and habitat of species, a certain genetically fixed role that rocked elements play in plant metabolism.

The leaves are the richest in mineral elements, in which ash can be from 2 to 15% of the dry matter mass. The minimum ash content (0.4-1%) was found in tree trunks.

Nitrogen . For plants, nitrogen is a deficient element. If some microorganisms are able to assimilate atmospheric nitrogen, then plants can only use mineral nitrogen, and animals can only use nitrogen of organic origin, and even then not any. For example, urea is not directly absorbed by the animal body. While animals are quite wasteful of nitrogen, releasing uric acid. urea and other nitrogen-containing substances, plants almost do not emit nitrogenous compounds as waste products, and where possible, nitrogenous compounds are replaced by nitrogen-free substances. For example, in plants, the polyaccharides of cell membranes do not include hekeosamines characteristic of mucopolysaccharides of animals and chitin of arthropods and fungi.

With a lack of nitrogen in the habitat, plant growth is inhibited, the formation of lateral shoots and tillering in cereals is weakened, and small-leaved leaves are observed. At the same time, the branching of the roots decreases, but the ratio of the mass of the roots and the aerial part can increase. One of the early manifestations of nitrogen deficiency is the pale green color of the leaves, caused by a weakening of the synthesis of chlorophyll. Prolonged nitrogen starvation leads to the hydrolysis of proteins and the destruction of chlorophyll, primarily in the lower, older leaves and the outflow of soluble nitrogen compounds to younger leaves and growth buds. Due to the destruction of chlorophyll, the color of the lower leaves, depending on the type of plant, acquires yellow-orange or red tones, and with a pronounced nitrogen deficiency, necrosis, drying and tissue death may occur. Nitrogen starvation leads to a reduction in the period of vegetative growth and earlier seed ripening.

Phosphorus like nitrogen, essential element plant nutrition. It is absorbed by them in the form of higher oxide PO 4 ~ and does not change, being included in organic compounds. In plant tissues, the concentration of phosphorus is 0.2-1.3% of the dry mass of the plant. Phosphorus reserves in the arable layer of the soil are relatively small, about 2.3-4.4 t / ha (in terms of P 2 O 5). Of this amount, 2 / s falls on the mineral salts of orthophosphoric acid (H 3 PO 4), and " / s ~~ on organic compounds containing phosphorus (organic residues, humus, phytate, etc.). Phytates make up up to half of the organic phosphorus of the soil . Most of phosphorus compounds are slightly soluble in soil solution. This, on the one hand, reduces the loss of phosphorus from the soil due to leaching, but, on the other hand, limits the possibilities for its use by plants. The main natural source of phosphorus in the arable layer is the weathering of the soil-forming rock, where it is found mainly in the form of apatites ZСа 3 (PO 4) 2 CaP 2 and others. Trisubstituted phosphoric salts of calcium and magnesium and salts of iron and aluminum sesquioxides (FePO 4. A1PO 4 in acidic soils) are slightly soluble and inaccessible to plants. Two-substituted and especially one-substituted salts of calcium and magnesium, especially salts of monovalent cations and free phosphoric acid, are soluble in water and are used by plants as the main source of phosphorus in the soil solution.

Sulfur is one of the main nutrients necessary for the life of the plant. It enters them mainly in the form of sulfate. Its content in plant tissues is relatively low and amounts to 2-1.0% based on dry weight. The need for sulfur is high in plants rich in proteins, such as legumes (alfalfa, clover), but it is especially pronounced in representatives of the cruciferous family, which synthesize oils in large quantities.

Insufficient supply of sulfur to plants inhibits the synthesis of sulfur-containing amino acids and proteins, reduces photosynthesis and the growth rate of plants, especially the aerial parts. In acute cases, the formation of chloroplasts is disrupted and their disintegration is possible. Symptoms of sulfur deficiency - blanching and yellowing of the leaves - are similar to signs of a lack of nitrogen, but first appear in the youngest foxes and ewes. This shows that the outflow of sulfur from older leaves cannot compensate for the insufficient supply of sulfur to plants through lint.

Potassium - one of the most essential elements of the mineral nutrition of plants, the content in tissues averages 0.5-1.2% based on dry weight. For a long time, ash served as the main source of potassium, which was reflected in the name of the element (derived from the word - crucible ash). The content of potassium in the cell is 100-1000 times higher than its level in the external environment. It is much more in tissues than other cations.

The reserves of potassium in the soil are 8-40 times greater than the content of phosphorus, and nitrogen - 5-50 times. In the soil, potassium can be in the following forms: as part of the crystal lattice of minerals, in the exchange and non-exchange state in colloidal particles, as part of crop residues and microorganisms, in the form of mineral salts of the soil solution.

The best source of nutrition are soluble potassium salts (0.5 - 2% of the gross reserves in the soil). As the mobile forms of potassium are consumed, its reserves in the soil can be replenished at the expense of exchangeable forms, and when the latter decrease, at the expense of non-exchangeable, fixed forms of potassium. Alternate drying and moistening of the soil, as well as the activity of the root system of plants and microorganisms, contribute to the transition of potassium into accessible forms.

In plants, potassium is concentrated in the greatest amount in young, growing tissues characterized by a high level of metabolism: meristems, cambium, young leaves, shoots, buds. In cells, potassium is present mainly in ionic form, it is not part of organic compounds, has high mobility and is therefore easily regulated. The movement of potassium from old to young leaves is facilitated by sodium, which can replace it in the tissues of plants that have stopped growing.

In plant cells, about 80% of potassium is contained in vacuoles. It makes up the bulk of the cell sap cations. Therefore, potassium can be washed out of plants by rains, especially from old leaves. A small part of this cation (about 1%) is strongly associated with mitochondrial and chloroplast proteins. Potassium stabilizes the structure of these organelles. During potassium starvation, the lamellar-tranular structure of chloroplasts is disturbed and the membrane structures of mitochondria are disorganized. Up to 20% of the potassium of the cell is adsorbed on the colloids of the cytoplasm. In the light, the bond strength of potassium with colloids is higher than in the dark. At night, even the release of potassium through the root system of plants can be observed.

Potassium serves as the main progivoion to neutralize the negative charges of inorganic and organic anions. It is the presence of potassium that largely determines the colloid-chemical properties of the cytoplasm, which significantly affects almost all processes in the cell. Potassium contributes to maintaining the state of hydration of the colloids of the cytoplasm, regulating its water-retaining capacity. An increase in the hydration of proteins and the water-holding capacity of the cytoplasm increases the resistance of plants to drought and frost.

Calcium . The total calcium content in different plant species is 5-30 mg per 1 g of dry weight. Races of genius in relation to calcium are divided into three groups: calciumphiles, calciumphobs and neutral types. A lot of calcium contains legumes, buckwheat, sunflower, potatoes, cabbage, hemp, much less - cereals, flax, sugar beets. In the tissues of dicot plants, this element, as a rule, is greater than in monocots.

Calcium accumulates in old organs and tissues. This is due to the fact that its transport is carried out through the xylem and reutilization is difficult. With aging of cells or a decrease in their physiological activity, calcium from the cytoplasm moves to the vacuole and is deposited in the form of insoluble salts of oxalic, citric and other acids. The resulting crystalline inclusions impede the mobility and the possibility of reusing this cat. Calcium performs a variety of functions in the metabolism of cells and the body as a whole. They are associated with its influence on the structure of membranes, ion flows through them and bioelectrical phenomena, on rearrangements of the cytoskeleton, the processes of polarization of cells and tissues, etc. Calcium activates a number of enzymatic cell systems: dehydrogenases (glutamate dehydrogenase, malate dehydrogenase, glucose-6-phosphate dehydrogenase. ), amylase, adenylate and arginine kinases, lipases, phosphatases. In this case, calcium can promote the aggregation of protein subunits, serve as a bridge between the enzyme and the substrate, and affect the state of the allosteric center of the enzyme. Excess calcium in ionic form inhibits oxidative phosphorylation and photophosphorylation of the ion.

Young meristematic tissues and the root system are the first to suffer from a lack of calcium. Dividing cells do not form new cell walls and result in multinucleated cells characteristic of calcium-deficient meristems. The formation of lateral roots and root hairs stops, root growth slows down. Lack of calcium leads to swelling of pectic substances, which causes cell walls and cell destruction. As a result, the roots, leaves, individual sections of the stem are sewn up and die. The tips and edges of the leaves turn white at first 1. and then blacken, leaf blades and curl. Necrotic areas on fruits, storage and vascular tissues.

Magnesium. In terms of content in plants, magnesium ranks fourth after potassium, nitrogen and calcium. In higher plants, its average content in the calculated dry weight is 0.02 - 3.1%; in algae, 3.0 - 3.5%. I especially like it in short-day plants - corn, millet, sorghum, hemp, as well as in potatoes, beets, tobacco and legumes. 1 kg of fresh leaves contains 300-800 mg of magnesium, of which 30-80 mg (i.e. 1/10 part) is part of chlorophyll. There is especially a lot of magnesium in young cells and growing tissues, as well as in generative organs and storage tissues. In caryopses, magnesium accumulates in the germ, where its level is several times higher than the content in the endosperm and peel (for corn, respectively, 1.6, 0.04 and 0.19% of dry weight).

The action of magnesium on other areas of metabolism is most often associated with its ability to regulate the work of enzymes and its significance for a number of enzymes is unique. Magnesium deficiency leads to a decrease in the phosphorus content in plants, even if phosphates are present in sufficient quantities in the nutrient substrate, especially since phosphorus is transported throughout the plant mainly in organic form. Therefore, magnesium deficiency will inhibit the formation of organophosphorus compounds and, accordingly, the distribution of phosphorus in the plant body. With a lack of magnesium, the formation of plastids is disrupted: the chloroplast matrix becomes clear, the grana stick together. Stroma lamellae break and do not form a single structure; instead, many vesicles appear. With magnesium starvation, spots and stripes of light green, and then yellow, appear between the green veins. The edges of the leaf blades become yellow, orange, red or dark red, and this "marble" color of the leaves, along with chlorosis, is a characteristic sign of a lack of magnesium. At later stages of magnesium starvation, light yellow and whitish stripes are also observed on young leaves, indicating the destruction of the chloroplast in them, and then of carotenoids, and the leaf zones adjacent to the vessels remain green longer. Subsequently, chlorosis and necrosis develop, affecting primarily the tops of the leaves.

Iron . The average content of iron in plants is 0.02-0.08%. As part of compounds containing heme (all cytochromes, catalase, and in non-heme form, iron takes part in the functioning of the main redox systems of photosynthesis and respiration. Together with molybdenum, iron participates in the reduction of nitrates and the fixation of molecular nitrogen by nodule bacteria, being part of nitrate reductase and nitrogenase Iron also catalyzes the initial stages of chlorophyll synthesis (the formation of 8-aminolevulinic acid and progoporphyrins).Therefore, insufficient iron supply to plants under waterlogged conditions and on carbonate soils leads to a decrease in the intensity of respiration and photosynthesis and is expressed in yellowing of the leaves (chlorosis) and their rapid fall .

Silicon found in all plants. Especially a lot of it in the cell walls. Plants that accumulate silicon have strong stems. A lack of silicon can retard the growth of cereals (corn, oats, barley) and dicotyledonous plants (cucumbers, tomatoes, tobacco, beans). The exclusion of silicon during the reproductive stage causes a decrease in the number of seeds, while the number of mature seeds decreases. In the absence of silicon in the nutrient medium, the ultrastructure of cell organelles is disturbed.

Aluminum also refers to macronutrients that only some plants need. It is assumed that it is of great importance in the metabolism of hydrophytes. It is interesting to note that ferns and tea concentrate this cation. With a lack of aluminum, chlorosis is observed in the tea leaf, but high concentrations are toxic to plants. In high doses, aluminum binds to phosphorus in cells, which ultimately leads to phosphorus starvation of plants.