Phytohormones as the main regulatory system of plants. Abstract: Plant hormones. Plant growth inhibitors
Plant hormones are called phytohormones. Phytohormones are chemical compounds with the help of which the interaction of cells, tissues and organs is carried out and which in small quantities are necessary for the regulation of all life processes of plants. Plant hormones are low molecular weight compounds that are active in very low concentrations (10 -13 -10 -5 mol/l). They, as a rule, are formed in one part of the plant and transported to another, where they have a strong impact on the processes of growth and development of the plant organism.
Despite the variety of functions of certain hormones, they can be combined into two groups: stimulating hormones And hormone inhibitors. The most important stimulants include auxins, gibberellins and cytokinins, and inhibitors include abscisic acid and ethylene.
Auxins substances of indole nature are called: indolylacetic acid and its derivatives. The precursor to auxins in plants is one of the essential amino acids, tryptophan. The synthesis of auxin from tryptophan is under the control of other plant hormones - gibberellins (they activate synthesis) and ethylene (suppresses synthesis). Auxins are synthesized mainly in the apical systems (growth points) of the stem and root. They accumulate most of all in growing buds and leaves, pollen and developing seeds. Auxin has a strong influence on flowering, growth and ripening of plant fruits. Auxin contained in pollen is essential for the growth of the pollen tube and therefore for plant pollination. Transport of auxins in a plant occurs strictly polarly: down the stem from the tip of the shoot to the tip of the root - to the zone of its elongation. Auxin flows from the leaves also flow here. Auxin is one of the most ancient phytohormones. It is known that even primitive flagellated organisms have a regulatory chemical compound - serotonin, very similar in structure to auxin, which plays the role of an intracellular hormone. In highly organized animals, serotonin is one of the neurotransmitters. Auxins are used in plant growing to stimulate root formation in cuttings of trees, shrubs and herbaceous plants (currants, gooseberries, cherries, grapes, jasmine, roses, etc.), as well as to improve the fusion of scion and rootstock during grafting.
Gibberellins. The name of these phytohormones comes from the Latin name of the gibberella fungus from the class Marsupials (Gibberella fujikuroi). This mushroom produces hyberellic acid, which was discovered (in 1926) in Japan. Gibberellins are synthesized especially intensively in growing (apical 9-apical) stem buds of plants, in leaf chloroplasts, in developing seeds, and in the embryo of germinating seeds. The physiological functions of gibberellins are varied. They have a strong influence on the intensity of mitosis and cell elongation. Under the influence of gibberellins, the stem and leaves lengthen, and the flowers and inflorescences become larger. The grapes produce larger clusters.
Gibberellin has a powerful effect on plant flowering. It turned out that for plants to flower, a certain concentration of gibberellin in tissues is necessary. This concentration occurs either during long daylight hours or at low temperatures (during vernalization). Therefore, treatment with gibberellin accelerates the flowering of long-day plants: they can be “forced” to bloom even with short daylight hours.
Gibberellin has the strongest effect on the emergence of plants from a state of physiological dormancy. The seeds and tubers of many plants are dormant after harvesting and do not germinate even under favorable conditions of moisture, oxygen and heat. However, treatment with gibberellin causes their germination.
Gibberellin also awakens dormant buds of overwintering herbaceous and tree-shrub plants. Treatment with gibberellin allows, for example, to obtain flowering shoots of jasmine, lilac or lily of the valley in the middle of winter. This method in plant growing is called plant forcing.
High physiological activity of gibberellins manifests itself during the formation of juicy fruits. As it turned out, seeds developing after fertilization produce gibberellins necessary for growth and fruit formation. The lack of active gibberellins at this critical moment causes a delay in fruit growth. Additional treatment with gibberellin, on the contrary, promotes the formation of large seedless (parthenocarpic) fruits in tomato, grapes, peppers, citrus fruits, pome and stone fruit crops.
Cytokinins. Cytokinins are phytohormones, purine derivatives, which have a strong stimulating effect on plant growth and development. The main site of cytokinin synthesis is the apical meristem of roots. They are also formed in young leaves and buds, in developing fruits and seeds.
It is noteworthy that cytokinins are synthesized not only by plants, but also by some microorganisms associated with plants. Thus, nodule bacteria settle on the roots of leguminous plants. Their tissues are enriched with cytokinins and auxins, which leads to an influx of nutrients and the formation of nodules.
Cytokinins in plants stimulate cell division, accelerate the growth of cells in dicotyledonous (but not monocotyledonous) plants in length, and promote their differentiation. The physiological activity of cytokinins is based on enhancing the synthesis of DNA, protein, growth and development of chloroplasts and other cell organelles. Cytokinins stimulate the growth and development of shoots, but inhibit root growth. This is their difference from the action of auxins.
Like gibberellins, cytokinins have a high “awakening” ability: they bring seeds and tubers, dormant buds of trees and shrubs out of a state of deep dormancy, and increase the germination of seeds of peas, corn, barley and many other plants.
Cytokinins delay the aging of leaves, increase the supply of nutrients to tissues, due to which the structure of chloroplasts is restored, and the synthesis of chlorophyll, RNA and protein in them is enhanced. The intensity of photosynthesis increases.
Abscisic acid. If auxins, gibberellins and cytokinins are stimulators of plant growth and development, then abscisic acid is the most important plant inhibitor with a wide spectrum of action. Abscisic acid (ABA) is synthesized in almost all plant organs, especially in aging ones. ABA is an antagonist of stimulating hormones. Thus, the transition into dormancy of seeds, tubers, bulbs and buds is associated with an increase in the ABA content in them.
As it turns out, the plant responds to shortening daylight hours and the approach of winter by accelerating ABA synthesis. During this period, the content of this hormone increases in the wintering organs of perennial legumes and cereal grasses, and winter grains. At the same time, the activity of auxins, gibberellins and cytokinins is suppressed. This prevents excessive physiological activity of plants preparing for winter.
The aging of plants and the ripening of tomato, strawberry, pear, grape and other crops is associated with a significant concentration of ABA: the phytohormone accelerates the breakdown of proteins, nucleic acids, and photopigments.
As it turned out, abscisic acid is involved in such an important process as the regulation of stomata. When leaves are dehydrated, their ABA content rapidly increases. This causes the stomata to close, resulting in decreased transpiration.
The dynamic balance in plant cells between the inhibitory effect of ABA, on the one hand, and the stimulating effect of auxins, cytokinins and gibberellins, on the other hand, serves as a necessary condition for normal plant growth and development. A unique system of mutual inhibition of antagonist hormones is created, as a result of which the metabolism of the plant organism acquires the necessary stability.
Ethylene. The well-known ethylene gas is a hormonal factor in the plant organism. It is formed from the amino acid methionine in almost any plant organ, but the rate of its biosynthesis is still highest in aging leaves and ripening fruits. The physiological functions of ethylene in plants are diverse. Ethylene promotes tissue aging and thereby accelerates the fall of leaves and fruits. In case of local damage, the plant synthesizes the so-called “stress ethylene”, which promotes the rejection of damaged tissue. Ethylene increases the dormancy of seeds, tubers and bulbs, and also accelerates the ripening of fruits. Therefore, ethylene is used to accelerate the ripening of fruits, for which they are placed in specially hermetically sealed chambers filled with this gas.
Ethylene affects the generative organs of plants, in particular, it promotes a shift in the sex of dioecious plants towards the female side. This leads, for example, to a change in the ratio of female and male cucumber flowers and helps to increase its yield. Ethylene, as a gaseous compound, has high mobility in plant tissues. Therefore, quickly spreading throughout the plant, it has a regulatory effect on the work of other phytohormones, enhancing or, conversely, suppressing their physiological activity.
Thus, the hormonal system of plants is multicomponent. The ratio of activator hormones and inhibitor hormones naturally changes during the individual development of plants, as well as in response to changes in environmental factors. In this regard, phytohormones are extremely important for increasing plant resistance to unfavorable factors. The general pattern is as follows: in the case of stress, the role of inhibitor hormones (abscisic acid and ethylene) predominates, and when the plant exits the stressful state and transitions to normal life activity, the role of activator hormones (auxins, gibberellins and cytokinins) predominates.
Plant hormones, or phytohormones, are organic substances produced by plants that are different from nutrients and are usually formed not where their effect is manifested, but in other parts of the plant. These substances in small concentrations regulate plant growth and their physiological responses to various influences. In recent years, a number of phytohormones have been synthesized, and now they are used in agricultural production. They are used, in particular, for weed control and for producing seedless fruits.
A plant organism is not just a mass of cells growing and multiplying randomly; Plants, both morphologically and functionally, are highly organized forms. Phytohormones coordinate plant growth processes. This ability of hormones to regulate growth is especially clearly demonstrated in experiments with plant tissue cultures. If you isolate living cells from a plant that have retained the ability to divide, then in the presence of the necessary nutrients and hormones they will begin to actively grow. But if the correct ratio of various hormones is not exactly observed, then growth will be uncontrolled and we will get a cell mass resembling tumor tissue, i.e. completely devoid of the ability to differentiate and form structures. At the same time, by properly changing the ratio and concentration of hormones in the culture medium, the experimenter can grow a whole plant with roots, stem and all other organs from a single cell.
The chemical basis of the action of phytohormones in plant cells has not yet been sufficiently studied. It is currently believed that one of the points of application of their action is close to the gene and hormones stimulate the formation of specific messenger RNA here. This RNA, in turn, participates as an intermediary in the synthesis of specific enzymes - protein compounds that control biochemical and physiological processes.
Plant hormones were only discovered in the 1920s, so all information about them is relatively recent. However, back in 1880, Yu. Sachs and Charles Darwin came to the idea of the existence of such substances. Darwin, who studied the influence of light on plant growth, wrote in his book The Power of Movement in Plants: “When the seedlings are freely exposed to side light, some influence is transmitted from the upper to the lower part, causing the latter to bend". Speaking about the effect of gravity on the roots of a plant, he concluded that "only the tip (of the root) is sensitive to this influence and transmits some influence or stimulus to the neighboring parts, causing them to bend."
During the 1920s and 1930s, the hormone responsible for the reactions Darwin observed was isolated and identified as indolyl-3-acetic acid (IAA). This work was carried out in Holland by F. Vent, F. Kogl and A. Hagen-Smith. Around the same time, Japanese researcher E. Kurosawa studied substances that cause hypertrophied growth of rice. Now these substances are known as phytohormones gibberellins. Later, other researchers working with plant tissue and organ cultures discovered that crop growth was significantly accelerated if small amounts of coconut milk were added to them. The search for the factor causing this increased growth led to the discovery of hormones that were called cytokinins.
Main classes of plant hormones
Plant hormones can be grouped into several main classes, depending either on their chemical nature or on the effect they exert.
Auxins. Substances that stimulate plant cell elongation are collectively known as auxins. Auxins are produced and accumulated in high concentrations in the apical meristems (growth cones of the shoot and root), i.e. in those places where cells divide especially quickly. From here they move to other parts of the plant. Auxins applied to a cut stem accelerate the formation of roots in cuttings. However, in excessively large doses they suppress root formation. In general, the sensitivity to auxins in root tissues is much higher than in stem tissues, so the doses of these hormones that are most favorable for stem growth usually slow down root formation.
This difference in sensitivity explains why the tip of a horizontally lying shoot exhibits negative geotropism, i.e. bends upward, and the root tip has positive geotropism, i.e. bends towards the ground. When auxin accumulates on the underside of a stem under the influence of gravity, the cells on that underside stretch more than the cells on the upper side, and the growing tip of the stem bends upward. Auxin acts differently on the root. Accumulating on its lower side, it suppresses cell elongation here. In comparison, the cells on the upper side stretch more, and the root tip bends toward the ground.
Auxins are also responsible for phototropism - growth bending of organs in response to one-sided lighting. Since the breakdown of auxin in meristems appears to be somewhat accelerated by light, cells on the shaded side stretch more than those on the illuminated side, which causes the shoot tip to bend towards the light source.
The so-called apical dominance - a phenomenon in which the presence of an apical bud prevents the lateral buds from awakening - also depends on auxins. Research results suggest that auxins, in the concentration in which they accumulate in the apical bud, cause the tip of the stem to grow, and moving down the stem, they inhibit the growth of lateral buds. Trees in which apical dominance is sharply expressed, such as conifers, have a characteristic upward-pointing shape, unlike mature elm or maple trees.
After pollination has occurred, the ovary wall and receptacle grow rapidly; a large fleshy fruit is formed. The growth of the ovary is associated with cell elongation, a process in which auxins are involved. It is now known that some fruits can be obtained without pollination if auxin is applied at the appropriate time to some organ of the flower, for example on the stigma. This formation of fruits - without pollination - is called parthenocarpy. Parthenocarpic fruits are seedless.
Rows of specialized cells, the so-called, are formed on the stalk of ripened fruits or on the petiole of old leaves. separating layer. The connective tissue between the two rows of such cells gradually loosens, and the fruit or leaf is separated from the plant. This natural separation of fruits or leaves from the plant is called abscission; it is induced by changes in auxin concentration in the separating layer.
Of the natural auxins, indolyl-3-acetic acid (IAA) is the most widely distributed in plants. However, this natural auxin is used in agriculture much less frequently than synthetic auxins such as indolylbutyric acid, naphthylacetic acid and 2,4-dichlorophenoxyacetic acid (2,4-D). The fact is that IAA is continuously destroyed by plant enzymes, while synthetic compounds are not subject to enzymatic destruction, and therefore small doses can cause a noticeable and long-lasting effect.
Synthetic auxins are widely used. They are used to enhance root formation in cuttings that otherwise take root poorly; for producing parthenocarpic fruits, for example, in tomatoes in greenhouses, where conditions make pollination difficult; in order to cause the fall of some flowers and ovaries in fruit trees (the preserved fruits with such “chemical thinning” turn out to be larger and better); to prevent pre-harvest fruit drop in citrus fruits and some pome trees, for example apple trees, i.e. to delay their natural fall. In high concentrations, synthetic auxins are used as herbicides to control certain weeds.
Gibberellins. Gibberellins are widely distributed in plants and regulate a number of functions. By 1965, 13 molecular forms of gibberellins had been identified, very similar chemically, but very different in their biological activity. Among synthetic gibberellins, the most commonly used is gibberellic acid, produced by the microbiological industry.
An important physiological effect of gibberellins is the acceleration of plant growth. For example, genetic dwarfism in plants is known, in which the internodes (the sections of the stem between the nodes from which leaves arise) are sharply shortened; as it turned out, this is due to the fact that in such plants the formation of gibberellins during metabolism is genetically blocked. If, however, gibberellins are introduced into them from the outside, then the plants will grow and develop normally.
Many biennial plants require a period of time in either low temperatures or short days, or sometimes both, in order to shoot and bloom. By treating such plants with gibberellic acid, they can be forced to bloom under conditions in which only vegetative growth is possible.
Like auxins, gibberellins can cause parthenocarpy. In California, they are regularly used to treat vineyards. As a result of this processing, the clusters are larger and better formed.
During seed germination, the interaction of gibberellins and auxins plays a decisive role. After the seed swells, gibberellins are synthesized in the embryo, which induce the synthesis of enzymes responsible for the formation of auxin. Gibberellins also accelerate the growth of the primary root of the embryo at a time when, under the influence of auxin, the seed coat is loosened and the embryo grows. The root emerges from the seed first, followed by the plant itself. High concentrations of auxin cause rapid elongation of the embryo stalk, and eventually the tip of the seedling breaks through the soil.
In addition to water and minerals coming from the soil, carbohydrates formed during photosynthesis, necessary as a source of energy and building proteins of protoplasm, a plant cell also requires some other chemical compounds for optimal growth. These, in particular, include organic compounds - hormones. The amount of hormones required is usually very small, and in most cases the hormones are synthesized in sufficient quantities by the plant itself.
Moreover, information must be exchanged between cells in the body. One group of cells “sends” the signal, the other receives it. A molecule of a chemical nature that has a signaling function is called a primary messenger. Among the wide range of primary messengers, plant hormones are also distinguished.
Signs that a substance is classified as a hormone:
The substance causes a specific physiological response; the peculiarity of plant hormones is that they launch large development programs not only of cells, but also at the level of tissues, organs, and the whole plant;
It is synthesized in the plant by one group of cells, and another group is responsible for it (the place of synthesis and the place of action are separated, i.e. the signal substance is transported). Any plant cell is potentially capable of producing hormones; As a rule, phytohormones are low-molecular compounds;
It plays virtually no role in the basic metabolism of the cell, and is used only for signaling purposes.
Acts in low concentration.
Primary messengers perceived by the cell specifically interact with many target molecules, in particular receptors. In order for a cell to respond to a stimulus, it is necessary to turn on the intracellular system of secondary messengers, which amplify the signal tens and hundreds of times. For example, one auxin molecule activates up to 10 4 protons.
Receptor detection criteria:
High selectivity and structural specificity for the hormone; the greater the physiological response, the higher the affinity;
The effect occurs at low concentrations of the hormone;
The kinetics of binding to the agonist is described by a saturation curve;
When interacting with the receptor, the chemical structure of the hormone should not change;
The interaction of the hormone with the receptor leads to the activation of the secondary messenger system.
Most of the second messenger systems studied in animals are also found in plants. These are phosphatidylinositol and adenylate and guanylate cyclase systems.
Receptors are usually localized in the plasmalemma, but can also be located in other cell compartments. The receptor is associated with secondary messengers. Signal transmission using second messengers activates phosphorylation/dephosphorylation processes, which leads to changes in metabolism and cytoskeletal function.
So, any hormone is a substance formed in small quantities in one part of the body and then transported to another part of the plant, where it has a corresponding effect. The distance over which the hormone is transported can be relatively large, for example, from the root to the leaf, from the latter to the bud, or it can be smaller - from the apical meristem to the cells below, or very small - within one cell.
Higher plants contain important classes of growth-regulating hormones, the main of which are: auxin, gibberellins, cytokinins, abscisic acid and ethylene.
Auxin synthesized by growing apical zones of stems, including young leaves. From the apex, auxin migrates to the elongation zone, where it specifically affects elongated growth. Natural auxin is a simple compound - indolyl-3-acetic acid (IAA).
IAA transport occurs polarly at a speed of 10-15 cm/h from the top of the shoots to the roots. The mechanism of polar transport is as follows: IAA penetrates passively together with H + into the apical end of the cell, and is actively secreted through the cell membrane at the basal end.
The physiological action of auxin is complex. Different tissues respond to the action of auxin by increasing growth, which is due to stimulation of cell elongation.
The attracting effect is that cells and tissues enriched with auxin become centers of attraction for substances. The role of auxin in stimulating the fall of leaves and flowers is associated with a noticeable decrease in its content in the leaves. This leads to aging of the leaves. Aging tissues produce ethylene, which acts on the separation zone (absidence zone).
Auxin itself delays the falling of leaves and flowers. There is evidence that auxin, in addition to participating in cell elongation and leaf fall, stimulates the processes of cell division. Auxins probably increase cambial activity. It is believed that auxins are involved in the differentiation of vascular tissue during the beginning of the growth process and in the formation of lateral roots. The transformation of the ovary into a fruit is another auxin-controlled process. Auxin plays a primary role in growth movements - tropisms and growths.
There are two mechanisms underlying the action of auxins: the rapid influence of auxins on the membrane system, where, due to the energy of ATP, the transport of hydrogen ions from the cytoplasm to the cell membrane is increased and the softening of the cell membrane is accelerated; the slow influence of auxins through the genomic system on the synthesis of proteins that determine cell growth.
The presence of both mechanisms is very likely, since auxin not only causes the release of protons, but also changes the microstructure of the cytoplasm (microtubules).
Gibberellins– phytohormones, mainly of the class of tetracyclic diterpenoids. All gibberellins are carboxylic acids, which is why they are called gibberellic acids. More than 110 different gibberellins (GAs) are known, many of which have no physiological activity in plants.
HAs are synthesized mainly in roots and leaves. They are transported passively through xylem and phloem flows. HAs, when applied to some plants, cause a strong elongation of the stem, and in some cases, a decrease in leaf surface. The most striking manifestation of their action is the rapid stimulation of peduncle elongation (shooting) and, in many cases, stimulation of flowering in long-day plants. In short-day plants, GCs probably have the opposite effect on flowering. The site of action of GC is the apical and intercalary meristems.
Treatment with HA brings the seeds and tubers of some plants out of dormancy. Exogenously introduced HA eliminates the need for vernalization and stratification in biennial plants in those seeds for which stratification is necessary. HAs cause parthenocarpy: for this, flowers must be sprayed with a HA solution. Auxin can also cause parthenocarpy, but GCs are more active. In tissues treated with HA, the IAA content increases. It is believed that the physiological basis of dwarfism in most plants is a violation of gibberellosis metabolism, which leads to a lack of endogenous gibberellins.
Auxins and gibberellins represent two potent classes of regulators. However, they are not able to regulate the course of the growth process in ontogenesis.
Cytokinins. None of the previous hormones can affect the greening process of isolated leaves or the formation of buds in tissue culture. These properties are possessed by cytokinins, which got their name because of their ability to stimulate cytokinesis (cell division). Cytokinin is found in some bacteria, algae, fungi and insects. The main site of cytokinin synthesis is the roots; However, recently, evidence has been obtained that the synthesis of cytokinins can also occur in seeds. From roots, cytokinins are passively transported to ground organs along the xylem.
The role of cytokinins in the processes of cell division is associated with the stimulation of DNA replication and the regulation of transitions from previous phases to the mitotic phase. There is evidence of the effect of cytokinin on the transport of K +, H +, Ca 2+.
Ethylene(CH 2 = CH 2) – aging hormone (hormonal gas-like factor). It has long been known that one rotten apple in a barrel spoils all the others. As it turned out, a rotten apple produces a volatile substance - ethylene, which produces a destructive effect in healthy fruits. The fact that the effect of ethylene can be removed by increasing the concentration of CO 2 in the environment underlies the practical method of storing apples and other fruits.
Ethylene causes the formation of an apical bend in many etiolated seedlings; The effect of light on bend straightening is due to the fact that light inhibits the formation of ethylene. Ethylene can influence geotropism and other auxin-mediated responses (eg, inhibition of lateral bud growth). Ethylene inhibits the polar transport of auxin, enhances the processes of aging, leaf and fruit abscission, eliminates apical dominance, and also accelerates fruit ripening.
Abscisic acid (ABA) is a natural hormonal growth inhibitor of terpenoid nature.
ABA is synthesized mainly in leaves, as well as in the root cap. The movement of ABA in plants occurs in both the basipetal and acropetal directions as part of xylem and phloem sap.
As we have already noted, in most cases ABA inhibits plant growth. This hormone often acts as an antagonist of IAA, cytokinin and gibberellins.
ABA inhibits seed germination and bud growth, and promotes leaf fall associated with leaf aging. ABA accelerates the breakdown of nucleic acids, proteins and chlorophyll. In some cases, ABA is an activator: it stimulates the development of parthenocarpy in roses, elongation of the cucumber hypocotyl, and the formation of roots in bean cuttings. ABA is formed in high quantities under stress (under the influence of various unfavorable environmental factors). Especially a lot of it is formed during water stress in the leaves. The action of ABA in this case is due to its influence on the functioning of the H + pump, causing the outflow of K + ions from the guard cells, as a result of which the stomata close and thereby prevent the danger of drying out. ABA can also play a signaling role during water deficiency.
Thus, ABA is a broad-spectrum inhibitor that affects the processes of dormancy, growth, stomatal movement, geotropism, and the entry of substances into the cell.
Fusicoccin was discovered as a toxin secreted by a pathogenic fungus Phusicoccum amygdale. Widely distributed in nature. More than 15 compounds of this group are now known. In addition to fungi, they are found in the cells of algae, higher plants (bryophytes, pteridophytes, flowering plants) and even animals.
By chemical nature, fusicoccin is a terpenoid and in flowering plants it is a diterpene - C 36 H 56 O 12. Fusicoccin is similar in action to auxin. It stimulates the elongation of cells of roots, stems, coleoptiles, leaves, and even more actively than IAA, as well as the germination of seeds (for example, wheat). Fusicoccin causes stomatal opening in the presence and absence of light (ABA antagonist). This is due to the activation of proton ATPase and potassium channels. In addition, fusicoccin stimulates the transport of calcium, chlorine, glucose, amino acids into the cell, as well as respiration and root formation.
Fusicoccin has anti-stress functions. It increases seed germination at high and low temperatures, excess moisture, and salinity. Soaking seeds in a solution of fusicoccin, as well as spraying it during the tillering phase of winter wheat, rye and barley, increases their frost resistance due to better development of the photosynthetic apparatus in the treated plants and the accumulation of more sugars in their cells. Fusicoccin protects rice plants during salinity and increases the resistance of potato tubers to certain diseases.
The group of phytohormones also includes jasmine and salicylic acids, as well as other hormonal compounds discovered in plants in recent years. FA and its methyl ester can control the processes of fruit ripening, root growth, tendril bending, production of viable pollen, and plant resistance to insects and pathogens. Jasmine acid and its methyl ester can be synthesized during mechanical damage from linolenic acid, which is formed during the breakdown of cell membrane phospholipids. Jasmine acid is transported to undamaged areas through the phloem, and its ethyl ester, as a volatile compound, acts through the air on neighboring plants, “informing” them about the attack of pathogens. The FA content in plant tissues increases with mechanical stimulation: changes in turgor pressure due to water deficiency, movement of tendrils, and interaction of root hairs with soil particles. Activation of FA synthesis in response to a number of mechanical stimuli occurs with the participation of the Ca-calmodulin signal transduction pathway. The concentration of FAs is highest in zones of cell division, young buds, flowers, pericarp tissues, and in the hypocotyl hook of leguminous plants. FA reduces chlorophyll content and leads to chlorosis.
The concentration of jasmine acid in plant tissues increases sharply with mechanical damage or exposure to elicitors that can induce a hypersensitivity reaction (HSR). The latter is one of the most effective ways to protect plant organisms from damage, since rapid local death of infected plant cells along with the pathogen occurs, which ensures the stability of the entire plant. The synthesis of jasmonates is triggered when the plant is wounded, for example, in the process of being eaten by phytophages.
Jasmine acid activates the expression of a number of genes, the products of which are produced in response to stress factors such as mechanical tissue damage and infection by pathogens. These include, for example, thionins, extensins, enzymes involved in the synthesis of a number of phenolic compounds and phytoalexins. Therefore, treating plants with jasmine acid dramatically increases their resistance to damage. Jasmine acid is one of the factors inducing plant immunity to repeated infections.
Salicylic acid also provides the plant with resistance to damage caused by various pathogens. SA synthesis plays a decisive role in the hypersensitivity reaction, as well as in the prolonged systemic resistance of plants to a wide range of infections.
The formation of large quantities of hydrogen peroxide is also the reason for the activation of the synthesis of phytohormones - salicylic and jasmine acids.
Increasing the content of salicylic acid enhances the microwave reaction, since salicylate is an inhibitor of catalase, an enzyme that breaks down hydrogen peroxide. That is, hydrogen peroxide, activating the synthesis of salicylic acid, promotes an even greater accumulation of reactive oxygen species and causes an increase in the microwave reaction. As the microwave reaction decays, salicylic acid is converted into a bound form, interacting with glucose and forming glycosides. It is salicylic acid and the formation of its conjugants that are the key elements not only in the microwave reaction, but also in the formation of systemic acquired immunity of the plant. Thus, during the microwave reaction in the plant, immunity to repeated infections also occurs.
Systemin– a polypeptide hormone discovered in plants in 1991, consisting of 18 amino acids. Unlike previously known hormones, it triggers systems that protect plants from pathogens and increases resistance to diseases.
An important component of plant defense reactions are enzyme inhibitors involved in the processes of food digestion by insects. The most studied of these are inhibitors of proteolytic enzymes (proteases), which break down proteins during digestion. Insects that feed on plants containing protease inhibitors have a sharp decline in growth and development, since their diet lacks free amino acids. Protease inhibitors usually appear in plants in response to damage. The expression of genes encoding protease inhibitors is induced by mechanical damage to plants and is directly controlled by two phytohormones: a small peptide of 18 amino acids, systemin and jasminic acid.
It has been shown that the synthesis of protease inhibitors is the result of a number of events.
At the first stage of plant damage by insects, systemin is synthesized, the first peptide hormone found in plants. Systemin is then transported through the phloem to undamaged areas of the plant, where it interacts with receptors and initiates the synthesis of another hormone, jasmine acid, which in turn activates the expression of genes encoding the synthesis of protease inhibitors. In this case, the regulation of the expression of some “protective” genes by systemin can be carried out together with other hormones, for example, ABA, ethylene, jasmine acid.
Other hormones have also been identified in plants, in particular phytosulfokines, which are involved in the regulation of cell division and other growth processes in plants. These are small peptides consisting of 4-5 amino acids.
In recent years, brassinosteroids (BS) and prostaglandins (PG) have been classified as growth regulators exhibiting hormonal activity in plants.
Non-hormonal growth regulators. The functions of the main types of phytohormones-stimulators (auxins, gibberellins, cytokinins) and their antagonists - phytohormones-inhibitors (ABA and ethylene) - are realized in the plant cell under the direct influence of non-hormonal factors. The latter include substances that enhance the effect of phytohormones (vitamins, phenolic compounds (protectors and synergists), phytohormone imitators).
The discovery of phytohormones predetermined the prerequisites for the creation of the chemical bases of growth substances. In general, all natural and synthetic compounds involved in the regulation of growth and development are united under the general name growth and development regulators. These include organic compounds that are different from nutrients, but cause stimulation or inhibition of growth and development.
Natural growth stimulants.Vitamins– non-hormonal regulators synthesized in plants in microquantities. They perform catalytic functions and enhance growth processes activated by phytohormones. Phenolic protectors of phytohormones– endogenous compounds that prevent the destruction or immobilization of regulatory compounds. These include phenolic compounds such as phenolcarboxylic acids (caffeic acid, ferulic acid, synapic acid), which protect auxins such as IAA from destruction. Thus, protectors are direct regulators of phytohormone metabolites, i.e. regulators of phytohormone metabolism. Phenolic synergists– substances that are not independently involved in growth regulation, but activate the function of phytohormones. As already noted, neither protectors nor synergists have an independent hormonal effect. This is how they differ from hormone mimics, i.e. organic compounds of bacterial, fungal or plant origin that exhibit the effect of one or more plant hormones in biotests.
Natural growth inhibitors. Compounds of non-hormonal nature represent an independent class of regulators in plants. This includes a number of phenolic derivatives (paracoumaric acid, phloridzin, etc.), as well as terpenoid compounds (portulal, cucurbitacin, batatazines, etc.).
Synthetic growth regulators. In recent years, a number of synthetic regulators, in particular synthetic inhibitors, have been developed. The latter compounds comprise several groups that have specific functions, for example:
1. Retordants , suppressing stem growth (chlorocholine chloride, phosphon, etc.);
2. Antiauxins , inhibiting the movement of IAA and its analogues throughout the plant.
3. Herbicides – synthetic drugs that kill plants. General herbicides are being considered that destroy all vegetation, while selective herbicides are used to control weeds in monocultures. When herbicides act, polarity is first disrupted, shoots thicken, epinasties appear, leaves fall, pathological morphoses occur, which leads to the death of the plant.
Chemical analogues of natural inhibitors. These are synthetic compounds, analogues of ethylene, phenolic inhibitors, coumarins and ABA, which have a powerful herbicidal or defoliating effect.
In recent years, drugs that enhance the flowering of fruit crops (alar) and cause defoliation and stunted stem growth (ethrel, hydrel) have become widespread.
Chemical analogues of natural growth stimulants. These are regulators that activate special phases of plant growth and ontogenesis. These include, for example, synthetic analogues of auxins (a-naphthylacetic, idolylbutyric, 2,4-dichlorophenoxyacetic acids). Growth stimulants are used to activate root formation, tissue culture growth, and prevent fruit drop.
Growth regulators, or phytohormones.
The growth and development of plants is impossible without specific substances - growth regulators, or phytohormones. . These substances are responsible for the life of plants from the moment the seed germinates until the plant dies completely.
Phytohormones are produced in plants in small quantities (in concentrations starting from 10 -5 mol/l), but they perform signaling functions - they control the processes of growth and development of the entire plant. They are synthesized in one of the organs - roots, young leaves, apical bud of a shoot - and move to certain places where they trigger vital processes. These are kind of messengers - messengers (from the English. " message“-“message”, “message”), transmitting gene commands: to grow, bloom, form fruits, shed leaves, grow old, die...
There are five main groups of classical hormones: auxins, gibberellins, cytokinins, ethylene, abscisins. Other substances are often added to this list: brassinosteroids, jasmine acid, salicylic acid, some phenolic compounds, etc. Each class includes both stimulants and inhibitors of various functions, and they often work in pairs, determining the final effect on plant growth .
You can influence the ratio of hormones (hormonal balance) to obtain a certain result. For this purpose, in ornamental gardening and agriculture, synthetic hormones are used - analogues of natural ones, treating plants with them. Synthetic hormones are pesticides and are produced as industrial drugs in agrochemical plants.
Auxins are formed in the tips of roots and shoots. They stimulate root formation, as well as active growth of the main shoot, moving along the stem.
Gibberellin is called a growth hormone - it is responsible for stem growth and is formed mainly in the leaves of plants and sometimes in the roots.
Cytokinin regulates the initiation and growth of buds, which leads to the growth of lateral shoots. It is formed mainly in the roots of plants.
Ethylene slows down growth and is responsible for fruit ripening, and also causes leaf drop, preparing plants for winter. It is called the aging hormone. It is formed in the tissues of the meristem - growth zones.
Abscisic acid- helps overcome water deficiency (water stress) during drought and frost - regulates water balance, turns on protective mechanisms and inhibits excessive plant growth. During dormant periods or as plants age, it becomes more and more in the buds, tubers and other dormant organs.
Epibrassinolide regulates the functioning of all phytohormones and is formed in all plant organs. It is called the hormone of hormones. This is a multifunctional phytohormone – it is a growth regulator, helps overcome stress and improves plant immunity.
All phytohormones directly interact with each other.
Growth regulators used in crop production have different effects on the hormonal status of the plant.
One of the best drugs that is very convenient to work with is Zircon, which has auxin, cytokinin and gibberellin activity, which leads to the activation of growth processes, especially the root system, an increase in leaf surface and, accordingly, to an increase in the process of photosynthesis and the absorption of mineral nutrition elements. At the same time, it prolongs the fruiting process of berry and vegetable crops (strawberries, raspberries, cucumbers, tomatoes, etc.), and in ornamental crops the flowering period, flower size and brightness of color increase.
Knowing the nature of the action of a phytohormone, you can expect one or another result of the action and choose the right drug.
For example, the drug heteroauxin has only auxin activity and stimulates root formation and growth of the aerial parts.
But Epin-Extra and Zircon are multi-purpose drugs, since they increase the activity of various hormones responsible for the growth of roots, the main stem and side shoots, flowering, and increase resistance to adverse environmental factors. Therefore, the use of such multifaceted drugs is more profitable.
It should be borne in mind that growth regulators are used in very small quantities, and exceeding the norm of their consumption can lead to the opposite effect - for example, instead of stimulating growth inhibition. In order not to harm the plant, it is better to give less than more.
Auxin group drugs.
Heteroauxin– active ingredient IAA (indolyl 3-acetic acid), used:
— to accelerate root formation and for rooting cuttings of ornamental and fruit crops. Green cuttings soaked in 0.002% solution(0.2 g/10 l) for 10-16 hours.
— before planting, the roots of fruit plant seedlings are immersed in a solution of 0.1-0.2 g/10 l for 1 hour.
— to stimulate the growth of the root system in the spring (during the budding phase) and autumn (during the fall of leaves), the tree trunk circles of fruit and berry crops are watered with a 0.002% solution at the rate of 5 l/bush or 5 - 10 l/tree.
— to improve the germination of bulbs and tubers of flower crops, soak before planting in a 0.01% solution (0.1 g/l) for 16-24 hours.
Kornevin– active ingredient IMC (4-(indol-3-yl) butyric acid).
IBA is a synthetic analogue of heteroauxin, but persists longer in plants and is a more powerful growth stimulator.
Kornevin is used:
— to improve root formation and rooting of cuttings of fruit and ornamental crops by dusting the cut of cuttings (10-20 g/100 cuttings).
— to increase the survival rate of seedlings, before planting, soak the roots in a 0.1% solution (1 g/l) for 6 hours, the consumption of the working solution is 100 liters per 100 plants, and also water the plants at the root immediately after planting and after 10 days.
It is important to note that heteroauxin and rootin act at temperatures above +15 0 C, so water for their solutions should ideally have a temperature of +20 0 C.
Group drugs gibberellins.
Ovary, Bud, Gibbersib - The active substance of gibberellic acids is sodium salts.
It is known that gibberellin, by stimulating shoot formation, inhibits root growth, and auxin, by stimulating root formation, inhibits shoot growth. Thus, interacting with each other, they ensure the harmonious growth and development of both the root system and its above-ground part.
Ovary applies:
— to preserve ovaries on fruit and berry crops,
— accelerating ripening, increasing yield and product quality.
Spraying of currants and raspberries is carried out in the phase of budding and green ovaries, and pears, cherries and plums - in the phase of mass flowering and again after the petals fall, garden strawberries - in the phase of the beginning of the appearance of peduncles and again after 7 days. The solution concentration is 0.2%.
A drug Epin – Extra, active substance epibrassinolide.
Epin-Extra has broad biological activity, has an anti-stress effect on plants, and reduces the impact of adverse natural factors (frost, drought, etc.). Along with this, it has a growth-regulating and growth-stimulating effect, as it activates auxin and cytokinin activity.
Treatment with Epin increases the resistance of a number of crops to fungal diseases, reduces the entry of heavy metal salts, radionuclides, and nitrates into plants, increases the frost resistance of plants to spring and summer frosts, improves the ripening of wood and thus increases its resistance to temperature changes in the autumn-winter period.
Epin-Extra is used:
- to increase germination when soaking seeds of any plants and flower bulbs,
- before planting flower seedlings in open ground or the day after planting them,
— before the onset of frosts, during them or immediately after them for the treatment of fruits and berries, ornamental and other crops (the consumption rate of the drug is 1 ml per 5 liters of water). This ensures the safety of plants and a good harvest.
- for better fruit set and increased productivity of fruit trees - during budding and again in the flowering or petal fall phase (consumption 2ml/5l). This helps preserve the ovaries, reduce the incidence of disease, and increase resistance to temperature and humidity changes.
— for awakening in the spring of coniferous trees and shrubs planted the previous autumn or winter (consumption rate 1 ml/10 l).
— to overcome the consequences of winter sunburn of coniferous plants.
Drug Zircon, active ingredient hydroxycinnamic acids .
Hydroxycinnamic acids included in the drug are natural compounds that are constantly consumed by humans with food in concentrations that often exceed their concentration in the drug. They are quickly absorbed by plants and decomposed by soil and water microorganisms.
Zircon activates chlorophyll synthesis, growth and root formation processes. He shows indirect antifungal and antibacterial action and immediate antivirus activity.
The drug is recommended for enhancing growth processes, increasing seed germination, accelerating flowering, increasing yield, and reducing disease incidence. Zircon has a stronger stimulating effect on root formation and rooting than IAA, and increases drought resistance of crops.
Zircon is applied:
- to increase the germination of seeds, as well as corms when soaking (for 6-8 hours),
— to increase the resistance of plants to pathogens of fungal diseases,
— in severe drought and heat to relieve stress and improve the well-being of plants,
- when planting plants to improve root formation and increase survival rate (I usually soak bare roots for half an hour before planting or soak a container plant ball in a zircon solution; then water the plant every other day after planting).
— to overcome the consequences of winter sunburn of coniferous plants,
— when working with pesticides to remove their negative effects on plants (I always add 1 ml of Zircon per 10 liters of solution to a solution with pesticides).
- to increase fruit set and, accordingly, their yield during the budding period, especially stone fruits. For example, spraying cherries during budding with a zircon solution (0.5 and 1.0 ml per 1 liter of water) increased fruit set by 10–37% depending on the variety, and berry picking by 2-3 times.
Silicon-containing preparations.
Siliplant. Silicon-containing fertilizer Siliplant has recently appeared on sale, which in addition to silicon (7.5-7.8%) contains a number of microelements (Fe, Cu, Zn, Mg, Mn, Mo, B).
The effect of silicon on plants is multifaceted. It is found in all plants and takes an active part in many metabolic processes. Silicon is part of the cell wall and its strength depends on its content. It has long been noted that plants with a high silicon content are less affected by diseases and pests, and they are more resistant to adverse weather conditions.
Many silicon compounds have fungicidal activity and increase plant disease resistance.
The use of silicon-containing compounds has a positive effect on crop yield and product quality(for example, it increases the sugar content of grapes), increases the winter hardiness of crops.
Siliplant is good when treating plants with pesticides, since it increases their effectiveness and increases the period of protective action. Siliplant forms a porous film that fixes pesticides on the surface of plants and reduces their losses. Silicon allows you to reduce the rate of pesticide consumption by 20-40%, as it enhances the absorption and movement of pesticides inside plants.
Silicon reduces the negative effects of pesticides on plants, as well as high and low temperatures.
Treatment of perennial plants with Siliplant promotes better wintering for them.
When spraying lawns with Siliplant, their resistance to trampling.
The working concentration of Siliplant is 0.1-0.3%.
Lysenko's theory
Any plant organism, in order to produce offspring, is forced to go through its own specific developmental phases, which strictly depend on environmental conditions.
Vernalization - a period of exposure to low positive temperatures in order to produce a crop.
Photoperiodism - adaptation to a certain length of day and night. Depending on this, plants are divided into short-day (less than 11 hours) - corn, sorghum, pumpkin, pepper, cotton, and long-day (winter grains, potatoes, flax, legumes, more than 12 hours).
TOPIC: "PHYTOHORMONES"
As mediators in physiological processes, they convert specific environmental signals into biochemical information. Plant hormones are translated from Greek. phyto - plant, hormone - moving. These are low molecular weight organic compounds that are produced in micro quantities by the plant itself to control its own plants. The interaction of cells, tissues and organs to trigger and regulate physiological and morphological programs during ontogenesis. Phytohormones are compounds through which interaction in the plant body occurs between all biochemical reactions occurring in the plant body and environmental factors.
All phytohormones are divided into two groups:
Stimulating - cytokinins (CK), auxins (IAA), gibberellins (GK 1, GK 3, etc.), brassinosteroids (brassinolides)
Inhibitory - abcisic acid (ABA) and ethylene.
All classes of phytohormones are named by their representative.
General features of phytohormones- low-molecular substances, their effect is manifested in very small doses (1 mol/g of a narrow substance), synthesized in individual parts of plants. They are able to spread to other parts of the body, forming a hormonal field, and regulate major morphological and physiological processes; exogenous phytohormones can affect the plant if the tissues and organs are competent to them. This occurs only when the content of endogenous phytohormone is currently low.
In agricultural practice, analogues of natural compounds are very widely used. In the list of approved drugs they are collected in a separate section - Growth regulators .
They are used for:
1. Increasing seed germination
2. Improved root formation
3. Increased sustainability
4. Prevent fruit drop
5. Acceleration of fruit ripening
6. To relieve phytotoxic stress from the use of plant protection products
7. From lodging of crops
8. Suppression of growth processes
9. acceleration of flowering processes
10. increasing plant resistance to adverse conditions
Some drugs have fungicidal properties, but their main biological effect on the plant is to raise the immune status of the body.
Plant growth regulators (PGR) act effectively against saprophytes, which prefer weakened plants and tissues, against insects by thickening the leaf blade (succinic acid on melons) - Larvae of the 1st instar are not able to use this food substrate - increasing or decreasing the sugar content in the leaves, the more As a result, they become an unfavorable food substrate. Shifts the development phases of the host plant.
Auxins- substances of indolic nature, which are produced by the growing tips (apixes) of stems and roots. Auxin was discovered before other hormones. The chemical formula was deciphered in 1934 by Keglem (indolyl - three vinegars). The principles of the physiological activity of the auxin group were developed in the works of Kholodny and Vent, who are considered the founders of the doctrine of plant hormones.
The source for the formation of auxins is the essential amino acid tryptophan. It, in turn, is synthesized from schimomic acid, which occurs during respiration.
Physiological manifestations of the action of auxins:
1) Activates the growth of coleoptile segments 2) Stimulates the formation of roots and cuttings 3) Causes parthenocarpy in fruits 4) Causes tropism 5) Delays the abscission of leaves and ovaries 6) Has the ability to attract water and nutrients 7) removes apical dominance 8) Maximum content them in leaves, soils, pollen, etc.
Auxins induce the work of the hydrogen pump and activate the work of tRNA. Auxins increase the rate of respiration, thereby increasing the growth rate. It moves strictly polarly from the tops to the roots. The formation of auxins depends on the supply of nitrogen. In some cases, synthetic analogues of auxins acted even more actively on plants than IAA itself. have not found practical application in the field of growth regulators and herbicides. Auxins are predominantly formed in the stem meristems; they are most actively synthesized in the apex of the main shoot and root, as well as in young leaves.
Gibberellins- were discovered much later than auxins, when studying rice diseases. They are tetracyclic carboxylic acids. More than 70 species of gibberellins have been identified. The most common and studied is GA 3 (gibberellic acid). This acid is mainly formed in leaves (in plastids). They are formed from mevalonic acid, synthesized from acetyl coasin A. Their participation in the regulation of many physiological processes in plants has been established: accelerating cell division, increasing elongation, increasing metotic activity, changing the size and shape of leaves, and sometimes their number. In cereals, gibberellins cause the transition of plants to flowering, affect the formation of fruits, the chlorophyll content in leaves, the intensity of plant transpiration, their nucleic acid metabolism and other physiological processes.
Developing seeds are a source of endogenous gibberellins necessary for growth and fruit formation.
Gibberellins are synthesized especially intensively in growing apical stem buds of plants, chloroplasts of leaves and developing seeds.
Cytokinins- were discovered in 1955 by Miller and Skoog, since their presence in the nutrient medium caused the cells of the isolated tobacco core to begin dividing into something called kinetin (from the word kinesis - division). The active substance was isolated in crystalline form and it was determined that it was furfural aminopurine. Other exogenous drugs were synthesized that had higher biological activity than kinetin itself. All substances were combined into a group under the general name - cytokinins.
Although cytokinins were discovered as substances that stimulate cell division, their physiological effect is not limited to this. It has now been established that cytokinins are involved in the regulation of cell division, growth, and differentiation, as well as in the formation and regulation of metabolic processes. Cytokinins have also been found to delay the aging of leaves, increase plant resistance, influence the movement of substances throughout the plant, stimulate seed germination, etc. The main site of cytokinin synthesis is the apical meristem of roots. They are also formed in young leaves and buds, developing fruits and seeds.
ABK- according to its chemical structure it is a terpenoid. There are two ways of ABA synthesis in the plant body - as a result of the degradation of carotenoids, or through the Krebs cycle, namely through acetyl coasin A and mevalonic acid. One of the most active endogenous inhibitors, therefore it plays an important role in ensuring a state of dormancy, in the regulation of the processes of aging and organ loss, in reactions to damaging effects, the onset of a state of dormancy in buds, tubers, seeds, accompanied by a noticeable decrease in ABA content. ABA is responsible for the closure of stomata, which allows water to be conserved under unfavorable conditions. Processing leaves of wheat, barley, etc. synthetic ABA leads to the closure of stomata. ABA is also responsible for suppressing root growth and their geotropic response; the inhibitor is found in the root cap, which exhibits increased sensitivity to both light and gravity. ABA can be synthesized in all plant organs, especially in old ones.
Ethylene. It was first discovered by the Russian scientist D.N. Nelyubov in 1901. Ethylene is an unsaturated hydrocarbon. The functions of ethylene are diverse. Ethylene has been noted to be involved in cell aging and has the ability to inhibit stem growth. The participation of ethylene in the process of fruit ripening is used in ethyl chambers. Ethylene is formed in any plant organ. The highest rate of biosynthesis of this phytohormone is in aging fruits.
Brassinolides- were isolated in 1949 from rapeseed pollen. They have a sharp growth-regulating effect. Brassinolides have been shown to regulate cell division and elongation. Treatment with brassinolides increases plant resistance to unfavorable conditions.
Practical application of PGR (plant growth regulators):
1. RRR is used when there is a lack of endogenous phytohormones, especially during transitional moments of ontogenesis.
2. PRR is used when plant tissues are susceptible; they are susceptible only in the presence of receptor proteins that are able to recognize phytohormones.
3. The effect of PPP can provide tangible results when providing plants with mineral nutrition elements.
4. The action of all hormones depends very strictly on concentration.
Phytohormones have not received economically significant practical distribution. However, the idea of their use as endogenous regulators of plant growth and development ultimately led to the creation of synthetic drugs with a similar effect. Currently, more than 5 thousand compounds have been discovered that have a growth-regulating effect.
Synthetic growth regulators are widely used in crop production. With their help, it is possible to control life processes and achieve the realization of capabilities inherent in the plant organism, but not manifested in specific conditions. The action of these substances is strictly limited by the capabilities of the plant genotype. Exogenous growth regulators only help the plant to better reveal its inherited life potential, which under these conditions, for a number of reasons, remains unrealized. They are obtained by chemical and microbiological methods.
TOPIC: "PLANT RESISTANCE TO ABIOTIC ENVIRONMENTAL FACTORS"
Biological systems are characterized by the ability to combine resistance to changing environmental conditions (relative stability) - homeostasis - and fluidity (ability to adapt). Unfavorable environmental conditions cause stress in plants.
Stress - the state of the body when it deviates from the norm.
Types of stress:
1. physical (mechanical damage, drought, excess moisture, lack of moisture); 2. Chemical; 3. Biotic;
All this causes non-specific effects:
Primary nonspecific stress processes:
1. Membrane permeability increases;
2. The flow of calcium ions into the cytoplasm increases;
3. Shift the pH of the environment to the acidic side;
4. Increase in cytoplasmic viscosity;
5. Enhanced oxygen absorption;
6. Increased consumption of ATP;
7. Synthesis of stress proteins;
8. Increased synthesis of phytohormones;
Winter hardiness - In winter, plants die, the root system breaks, and an ice crust forms.
Getting wet - lack of oxygen
Low temperature -...
Cold resistance - symptoms: leaf wilting, necrotic spots, membrane damage, permeability increases, properties of chloroplasts and mitochondria change sharply, ATP synthesis is disrupted, the Krebs Cycle is disrupted, salt tolerance is disrupted
Salt resistance- mechanisms that trigger metabolic reactions are capable of neutralizing the effect of salts. One of these mechanisms is the synthesis of the amino acid proline, which is capable of normalizing osmotic pressure in the cell. This amino acid stabilizes the structure of nucleic acids.
The transport of ions from the environment into the cell is regulated by increasing the protective functions of membranes.
In order to transfer water into the intercellular spaces: 1) the plant increases the concentration of cell sap; 2) reduces cell volume; 3) shifts the pH of the medium in one direction or another;
Hardening - physiological adaptation of the body to unfavorably low temperatures produced under the influence of the external environment. Not all plants are capable of hardening - it depends on the species and origin.
If woody plants by winter have not produced an outflow of assimilates into the root system and have not completed growth, they die at low temperatures in winter and cannot vegetate in spring.
Hardening takes place in two stages:
1) in the light at low positive temperatures: during the day about +10, at night +2 0 C. Growth stops, sucrose and polysaccharides are consumed, temperature reduces the breakdown of these substances during respiration, sucrose accumulates in the cytoplasm, cell sap, chloroplasts, The concentration of cell sap increases and the freezing point decreases.
2) Without light at a temperature of about 0 0 C. For herbaceous plants, this phase can also take place under snow. During this period, specific proteins, phospholipids, unsaturated fatty acids are formed, and ATP accumulates. As a result of hardening, lipids are formed not in the cells, but in the intercellular spaces.
Heat resistance - most plants begin to suffer at temperatures of +35 0 C +45 0 C. Cacti begin to suffer at +60 0 C. Fungi, algae, bacteria at +70 0 C.
High temperature causes damage to membranes and proteins, the work of enzymes is inhibited, N 2 and poisons accumulate, and therefore the death of the plant organism occurs.
The process of photosynthesis is especially sensitive. The process slows down at +35 0 C, the work of phytohormones is inhibited, and growth is inhibited.
Frost resistance - the trait of frost resistance is genetically fixed, but manifests itself under certain environmental conditions. The destructive effect of frost depends on the water content of the tissue. Unlike high temperatures, death is caused not by the coagulation of proteins, but by the formation of ice.
Drought resistance - drought is a long period without rain, which is accompanied by a drop in relative humidity and high temperature.
Distinguish between drought atmospheric (low relative humidity - less than 30%) and soil (lack of available water in the soil). With a lack of water - temporary wilting and deep wilting. Temporary - easily tolerated by the plant, most often the cause is atmospheric drought. Long-term - all physiological processes are disrupted. With prolonged wilting, the concentration of cells increases. juice, membrane permeability increases, the viscosity of the cytoplasm increases, the work of enzymes and proteins slows down, DNA synthesis stops, the intensity of respiration and photosynthesis processes decreases, and ABA accumulates. In relation to water, plants are divided into four groups: hydrophytic, hygrophytic, mesophytic and xerophytic. In relation to drought, xerophytic plants are divided into groups: ephemeral (avoid drought), false xerophytes store moisture (succulents, Crassula), transpirate water to a limited extent, and have a shallow but widespread root system. Hemoxerophytes - plants adapted for obtaining water. High concentration of cell sap and deep root system. Poikiloxerophytes - during periods of drought they fall into suspended animation.
The main specific characteristic for individual species and varieties is the ability to tolerate a lack of water without a sharp decrease in growth processes and yield. This is determined by the stability of the cytoplasm and especially the membranes, mitochondria and chloroplasts; stability of enzymatic systems;
The plant organism has 3 weak points: ETC of respiration, photosynthesis, nitrogen metabolism.
In 1904, the Russian physiologist Zelensky established: the higher the leaf, the more active is transpiration and photosynthesis, and that the anatomical structure of the leaf depends on the layering. The smaller the cells, the smaller the size of the stomata. All this received Zelensky’s pattern.
