It is necessary to study the adaptability of plant ontogenesis to environmental conditions as a result of their evolutionary development, protective and adaptive reactions of plants against damaging influences, to understand reversible and irreversible damage to plants, their tissues and organs.
Need to study biological basis cold resistance of plants, what physiological and biochemical changes occur in heat-loving plants at low positive temperatures and determine ways to increase the cold resistance of plants.
An important point when studying this topic is to determine the frost resistance of plants. It includes knowledge of the basics of freezing of plant cells and tissues, conditions and causes of plant freezing, hardening phases and methods of increasing frost resistance.
Of no small importance is the winter hardiness of plants, which is a complex property of plant resistance to unfavorable overwintering factors (damping off, soaking, bulging, ice crust, winter drought). What are the measures to prevent the death of winter and wintering crops and methods for determining the viability of plants in winter and early spring.
Heat resistance has a significant impact on plant productivity. It is necessary to find out the changes that occur in metabolism, in the growth and development of plants when exposed to maximum temperatures, and methods that increase the heat resistance of plants.
The combined effect of lack of moisture and high temperature on a plant determines its drought resistance. In this regard, it is necessary to study the features of water exchange in xerophytes and mesophytes, the physiological basis of this phenomenon in agricultural crops, determine methods for pre-sowing increase in drought resistance of plants, physiologically substantiate the selection of varieties for drought resistance and the need for irrigation of agricultural crops.
Attention should be paid to the salt tolerance of plants, the effect of salinity on plants and tolerance mechanisms, types of halophytes, salt tolerance of cultivated plants, possibilities for increasing the salt tolerance of plants.
Anthropogenic impact on the environment has determined the problem of combating harmful gaseous emissions from industry and transport, and the residual effects of substances used to control diseases, pests and weeds. In this regard, it is necessary to study the physiological and biochemical basis of plant resistance to these unfavorable conditions, the possibility of accumulation of toxic substances in crop products, and to understand the interaction of plants with atmospheric pollutants. To study plant resistance to infectious diseases.
2. Test tasks
2.1. Physiology and biochemistry of plant cells
What is the uniform distribution of solute molecules between solvent molecules called?
1) osmosis; 2) osmotic pressure; 3) chemical potential; 4) diffusion.
2. The cell membrane matrix consists of the following substances:
1) cellulose, hemicellulose; 2) pectin substances, cellulose; 3) starch, pectin substances; 4) hemicellulose, pectin substances, protein.
The flow of substances through a membrane at different rates is called
Forms of water in a cell?
1) gravity and film; 2) free and difficult to access; 3) free and bound; 4) connected and easily accessible.
5. According to the liquid-mosaic model of the structure of biological membranes, it is represented by:
1) a double layer of polar lipids is “stitched” with protein molecules; 2) a continuous bilayer of polar lipids; 3) a double layer of non-polar lipids is “stitched” with carbohydrate molecules; 4) two inner layers of lipids are limited on the outside by protein molecules.
What process will occur if you take a plasmolyzed cell and place it in clean water?
1) cytorrhiz; 2) plasmolysis; 3) hydrolysis; 4) deplasmolysis.
What is the name of the membrane that separates the cell membrane from the cytoplasm?
1) tonoplast; 2) mesoplasm; 3) endoplasmic reticulum;
4) plasmalemma.
8. What are colorless plastids called:
1) leukoplasts; 2) chloroplasts; 3) chromoplasts; 4) mitochondria.
In which plastids does the process of photosynthesis take place?
1) chloroplasts; 2) leukoplasts; 3) chromoplasts; 4) mitochondria.
What makes up the paraplast of a plant cell?
1) vacuole, cell membrane; 2) macroscopic structures; 3) nucleus, cytoplasm; 4) cell membrane, cytoplasm.
What is the process of separation of the cytoplasm from the cell membrane called?
1) plasmolysis; 2) deplasmolysis; 3) osmosis; 4) cytorhiz.
What is the movement of water from places of lesser negative potential to places of greater negative potential through a semi-permeable membrane called?
1) diffusion; 2) osmotic pressure; 3) osmosis; 4) osmotic potential.
What is the flow of substances through a membrane predominantly in one direction called?
1) selective permeability; 2) one-way permeability; 3) semi-permeability; 4) secretory.
In which cell organelles does protein synthesis occur?
1) ribosomes; 2) chloroplasts; 3) mitochondria; 4) Golgi complex.
The biological membranes of a plant cell include
1) phospholipids; 2) amino acids; 3) hemicellulose; 4) vitamins.
Which of the following substances would you classify as high-energy compounds?
1) proteins; 2) fats; 3) amino acids; 4) ATP, UTP, sugar phosphates.
What components make up the ATP molecule?
1) ribose, three phosphoric acid residues, adenine; 2) ribose, two phosphoric acid residues, adenine; 3) ribose, two phosphoric acid residues, uracil; 4) ribose, three phosphoric acid residues, uracil.
What cellular structures determine the possibility of various substances entering the cell and divide the cell into separate compartments?
1) membrane; 2) cell wall; 3) vacuole; 4) mitochondria.
What substances make up cell membranes?
1) carbohydrates, proteins, fats, nucleic acids; 2) cellulose, hemicellulose, pectin substances, lipids and proteins; 3) cellulose, carbohydrates, proteins, fats; 4) nucleic acids, amino acids, hemicellulose, ribose.
Define the concept of "osmosis"
1) this is a uniform distribution of solute molecules between solvent molecules; 2) this is the diffusion of water through a semi-permeable membrane caused by a difference in concentrations or a difference in chemical potentials; 3) this is the diffusion of water caused by a difference in concentrations or a difference in chemical potentials; 4) movement of water under the influence of osmotic pressure.
Define the concept of “diffusion”?
1) this is a process leading to a uniform distribution of solute and solvent molecules; 2) this is the uniform distribution of water through a semi-permeable membrane, caused by a difference in concentrations or a difference in chemical potentials; 3) selective permeability of cell membranes;
4) transition of the plant cell to a turgor state.
What substances are called enzymes?
1) these are substances of protein nature that have catalytic and regulatory properties; 2) these are substances of a non-protein nature that have catalytic and regulatory properties; 3) these are substances produced in the process of natural metabolism and exerting a regulatory effect in negligible quantities; 4) catalysts of lipid composition.
Enzyme inhibitors are substances that
1) inhibit the action of enzymes; 2) accelerate the action of enzymes; 3) destroy enzymes; 4) stimulate the formation of enzymes.
Enzymes that catalyze the transfer of atomic groups, radicals and molecular residues belong to the class
What is the name of the substance with which the enzyme interacts to form a complex?
1) substrate; 2) isoenzyme; 3) coenzyme; 4) prosthetic group.
What class do enzymes that carry out redox reactions belong to?
1) lyases; 2) oxidoreductases; 3) transferases; 4) isomerases.
A. Climatic conditions. Unfavorable climatic conditions include high air humidity, sudden changes in temperature and atmospheric pressure. Despite the fact that sensitivity to these factors is individual, unfavorable climatic conditions generally negatively affect the course of allergic diseases, especially bronchial asthma.
B. Air pollution
1. Smog is formed during the combustion of liquid and solid natural fuels. The degree of air pollution from industrial smog is assessed by the content of carbon monoxide, suspended particles and sulfur dioxide. With severe air pollution, attacks of bronchial asthma become more frequent. This is due to the combined action of all components of industrial smog.
A. Carbon monoxide, even at its maximum concentration (about 120 mg/m3), recorded in the city during rush hours, does not worsen the indicators of external respiration function in both healthy people and patients with bronchial asthma.
b. Particulate matter, such as dust, smoke, and soot, when inhaled, can cause coughing and bronchospasm. In the presence particulate matter the adverse effects on the respiratory system of other air pollutants are enhanced.
V. The level of sulfur dioxide in atmospheric air usually does not exceed 1.95 mg/m3. It has been experimentally established that inhalation of air with a high concentration of sulfur dioxide (22-65 mg/m 3) causes bronchospasm and a decrease in the activity of the ciliated epithelium of the bronchi.
2. Photochemical smog consists of ozone (its content in photochemical smog usually exceeds 90%), nitrogen dioxide and other oxidants and is formed under the influence of ultraviolet radiation from hydrocarbons contained in exhaust gases. In low concentrations, photochemical smog has an irritating effect on the mucous membranes of the eyes and respiratory tract; in high concentrations, it leads to a decrease in vital capacity, FEV1 and impaired gas exchange. Nitrogen dioxide has a direct toxic effect on the lungs, and in smokers can lead to irreversible changes in the lungs.
B. Indoor air pollution. In buildings with closed ventilation systems, there is no influx of outside air, which leads to an increase in the concentration of pollutants in the air - smoke from coal and gas heaters of central air heating systems, fireplaces, household kerosene and electric heaters, as well as solvent vapors, such as formaldehyde, which is part of adhesive for flooring. Passively inhaled tobacco smoke causes breathing problems that are much more severe than previously thought, especially in young children.
D. Viruses and bacteria. There is no evidence that viruses and bacteria can cause allergic reactions. However, it is well known that they contribute to the development of allergic diseases and complicate their course. Thus, sinusitis can provoke bronchial asthma and at the same time become its complication.
Vitamin deficiency on low-calorie diets can reach catastrophic levels (50%-90%) and not only leads to illness, but to serious health problems. It follows that one of the most important unfavorable factors of low-calorie diets is micro- and macronutrient deficiency of vitamins and microelements. Despite the fact that there is an obvious relationship between a deficiency of B vitamins in the human body, the development of increased fatigue, as well as nervous disorders, this issue very little attention is paid.
The B vitamins, or vitamin B complex, include seven essential water-soluble vitamins. Their properties, as well as their effect on the human body, are very closely interrelated, so a lack of most of them in the human body can lead to the development of increased fatigue.
Types of anthropogenic pollution of the natural environment as a result of economic activity people are diverse. They cause chemical, physical, mechanical, acoustic, thermal, aromatic and visual changes in the quality of the natural environment that exceed established standards for harmful effects. As a result, a threat is created to the health of the population, as well as to the state of flora and fauna and accumulated material values.
Numerous anthropogenic environmental pollutants are always potentially dangerous to humans. Experimental and field studies have established that the ecopathogenic impact depends on the level and quality of the pollutant, its exposure - the so-called “dose - substance - time” effect. Changes in health status depend on people's age, their professional activity, initial level of health, as well as on individual behavioral orientation and social and hygienic living conditions.
1). Increased and decreased air temperature of fences.
Production premises are divided into: cold, having normal temperature and hot shops.
Particularly large heat releases occur in metallurgy.
(blast furnace, open-hearth and rolling shops), mechanical engineering (foundry, forging, thermal shops), textile industry (dying and drying shops), clothing industry (iron), bakeries, glass production, etc.
In a number of industries, work is carried out at low air temperatures. In breweries in basements at a temperature of +4-7°, in refrigerators - from 0 to -20°.
Many works are carried out in unheated premises (warehouses, elevators) or in the open air (construction workers, logging, timber rafting, quarries, open-pit mining of coal and ore, etc.).
2). High or low humidity.
It is found in laundries, dyeing shops of textile factories, chemical plants, etc. Particularly unfavorable conditions are created if the evaporating liquids heat up and boil.
3). Increased or decreased atmospheric pressure.
Associated with diver work, caisson work, aviation work and mining work.
4). Excessive noise and vibration.
5). Air dust level - industrial
6) . Industrial poisons.
Chemical methods are increasingly being introduced into various industries
industries - metallurgical, mechanical engineering, mining, etc. The chemical industry is developing rapidly. Insectofungicides are increasingly used in agriculture.
7. Bacterial contamination of the environment.
Calls occupational infections, spreading among
working in contact with one or another infectious agent. In some cases, the disease occurs as a result of contact of people with sick animals (animal technicians, veterinarians, etc.), in others - with infectious material: skin, animal hair, rags, bacterial cultures (tanner workers, recycling plant workers, microbiological laboratory workers etc.), thirdly - with sick people (medical personnel caring for infectious patients).
8. Radioactive contamination of the external environment, premises, tools, materials.
III. Failure to comply with general sanitary conditions in places of work. To them include:
1) insufficient area and cubic capacity of premises;
2) unsatisfactory heating and ventilation, what explains
cold and heat, uneven temperatures, etc.
3) irrationally arranged and insufficient natural and artificial lighting.
Systems heating, ventilation And conditioning air are designed to ensure standardized meteorological conditions and air purity in the workplace.
(slide No. 28) According to the method of organizing air exchange, ventilation can be general, local and combined.
General ventilation is used in cases where harmful substances are released in small quantities and evenly throughout the room.
Local ventilation is designed for suction harmful secretions in the places of their formation.
The combined system provides for the simultaneous operation of local and general ventilation.
(slide No. 29) Depending on the method of air movement ventilation can be natural or mechanical. With natural ventilation, air moves under the influence of natural factors: thermal pressure or wind. With mechanical ventilation, air is moved using fans, ejectors, etc. The combination of natural and artificial ventilation forms a mixed ventilation system.
(slide No. 30) Depending on the purpose of ventilation - supply (supply) of air into a room or removal (exhaust) of it from a room, ventilation is called supply and exhaust. When air is supplied and removed simultaneously, ventilation is called supply and exhaust ventilation.
With unorganized ventilation, air is supplied and removed from the room through leaks and pores in the external fences of buildings (infiltration), as well as through vents and windows that are opened without any system. Natural ventilation is considered organized if the directions of air flows and air exchange are regulated using special devices. A system of organized natural air exchange is called aeration.
Emergency ventilation represents self-installation and is of great importance for ensuring the safety of operation of explosion- and fire-hazardous industries and industries associated with the use harmful substances.
For automatic activation, emergency ventilation is blocked with automatic gas analyzers installed either at the value MPC harmful substances, or by a certain percentage of the lower concentration explosive limit (explosive mixtures). Remote start of emergency ventilation must be provided by trigger devices located at the entrance doors outside the premises. Emergency ventilation is always provided only with exhaust ventilation to prevent the flow of harmful substances into adjacent rooms.
To maintain air parameters within the limits that provide comfortable conditions in areas where people stay, it is also used conditioning. In general, air conditioning means heating or cooling, humidifying or drying air and cleaning it from dust. There are comfort air conditioning systems, which provide constant comfortable conditions for humans in the room, and technological air conditioning systems, designed to maintain the conditions required by the technological process in the production room.
Scheduled inspections and checks ventilation systems must be carried out in accordance with the schedule approved by the administration of the facility. Cleaning of ventilation systems must be carried out within a time limit established by instructions manual.
Lighting in industrial buildings and open areas can be carried out naturally and artificial light.
Artificial lighting comes in two systems: general and combined. In the latter case, local lighting is added to general lighting.
General lighting is designed to illuminate the entire room; it can be uniform or localized.
Local lighting is intended to illuminate only work surfaces.
It can be stationary or portable. The use of only local lighting in industrial premises is prohibited.
In addition to working lighting, the standards provide for the installation of emergency, security and duty lighting.
The impact of harmful and hazardous production factors and occupational hazards on a worker’s body can lead to the development occupational diseases.
(slide No. 32) There is no generally accepted and unified classification of occupational diseases, but the most rational is the classification based on etiological criteria, proposed by N.F. Izmerov in 1996 (Academician of the Russian Academy of Medical Sciences, Director of the Research Institute of Occupational Medicine). It includes 5 groups of diseases:
1. Diseases caused by exposure to chemical factors: acute and chronic intoxication; skin diseases (epidermosis, contact dermatitis, photodermatitis, onychia and paronychia, toxic mylanoderma, oil folliculitis; metal fever; fluoroplastic (Teflon) fever.
2. Diseases caused by exposure to industrial aerosols: chronic bronchitis (dust, toxic-dust), pneumoconiosis (silicosis, silicosis - asbestosis, talcosis, kaolinosis, anthracosis, berylliosis, byssinosis, pneumoconiosis of mixed etiology).
3. Diseases caused by exposure to physical factors: vibration disease; diseases associated with exposure to contact ultrasound; cataract; cochlear neuritis; diseases associated with exposure to non-ionizing radiation (vegetative-vascular dystonia, asthenic, astheno-vegetative, hypothalamic syndromes); local tissue damage from laser radiation (skin burns, damage to the cornea and retina); diseases associated with exposure to ionizing radiation (radiation sickness, local radiation injuries); diseases associated with exposure to high atmospheric pressure and its subsequent sudden changes (decompression sickness and its consequences); diseases associated with exposure to adverse weather conditions (overheating, chronic overheating), etc.
4. diseases associated with physical overload and overstrain of individual organs and systems: focal neuroses; diseases of the peripheral nervous system and musculoskeletal system (mono- and polyneuropathies, cervical and lumbosacral radiculitis, epicondylosis of the shoulder, bursitis, aseptic osteonecrosis); prolapse of the uterus and vaginal walls; pronounced varicose veins in the legs; diseases caused by overstrain of the vocal apparatus (chronic laryngitis, vasomotor monochorditis, vocal cord nodules, phonasthenia) and visual organs (progressive myopia); flat feet of loaders; emphysema of glassblowers and brass band musicians.
(slide No. 33)
(slide No. 34)
(slide No. 35)
Increased and decreased air temperature of fences.
Production facilities are divided into: cold, normal-temperature and hot workshops. Workshops with insignificant heat release include those in which heat release from equipment, materials, people and inhalation does not exceed 20 kcal per 1 m2 of room per hour. If the heat release exceeds the specified value, then the workshops are classified as hot. For hot workshops, heat transfer by radiation is of particular importance. the air temperature of working premises can reach 30-40° or even more.
In a number of industries, work is carried out at low air temperatures.
In breweries in basements at a temperature of +4-7°, in refrigerators - from 0 to -20°.
Many works are carried out in unheated premises (warehouses, elevators)
Or outdoors (construction workers, logging, timber rafting, quarries, open
development of coal and ore, etc.). What negatively affects the central nervous system, cardiovascular system.,
chronic diseases of the upper respiratory tract appear.
2. High or low humidity.
It is found in laundries, dyeing shops of textile factories, chemical plants, etc. of the body. Thus, in air saturated with moisture, at t = 35°, sweat production can reach 3.5 l/hour.
3. Increased or decreased atmospheric pressure.
Associated with diver work, caisson work, aviation work and mining work.
Combating the adverse effects of industrial microclimate carried out using
Technological,
Sanitary
Medical and preventive measures.
In the prevention of the harmful effects of high temperatures of infrared radiation, the leading role belongs to technological measures: replacement of old and introduction of new technological processes and equipment, automation and mechanization of processes, remote control.
The group of sanitary measures includes means of heat localization and thermal insulation, aimed at reducing the intensity of thermal radiation and heat release from equipment.
Effective means of reducing heat generation are:
covering heated surfaces and steam and gas pipelines with heat-insulating materials (glass wool, asbestos mastic, asbothermite, etc.); equipment sealing; the use of reflective, heat-absorbing and heat-removing screens; arrangement of ventilation systems; use of personal protective equipment.
Medical and preventive measures include: organizing a rational regime of work and rest; ensuring drinking regime; increasing resistance to high temperatures through the use of pharmacological agents (taking dibazole, ascorbic acid, glucose), inhaling oxygen; undergoing pre-employment and periodic medical examinations.
Measures to prevent the adverse effects of cold should include heat retention - prevention of cooling of production premises, selection of rational work and rest regimes, use of personal protective equipment, as well as measures to increase protective forces body.
4. Excessive noise and vibration.
Noise is one of the most common environmental factors. Some technological processes (for example, testing automobile engines, working on weaving machines, riveting, cutting and trimming castings, cleaning castings in drums, stamping, etc.) are accompanied by sharp noise, which has an adverse effect not only on the hearing organ, but also on the nervous system worker. Noise as an external factor inhibits the body's immune reactions and reduces the body's protective functions.
The specific impact of noise manifests itself in a significant impairment of the function of the hearing organ. The following form A disorder of the function of the hearing organ is occupational hearing loss - a persistent decrease in sensitivity to various tones and whispered speech.
Prevention of noise illness should also be carried out comprehensively:
A change in production technology, combined with possible automation of production and the removal of humans from the production environment.
The use of devices on mechanisms that reduce noise intensity, as well as its frequency response.
Isolation of one workplace from another.
Correct device foundations for noise-generating machines.
All surfaces of a noisy room (walls, ceiling, etc.) must be lined with sound-absorbing material.
6. Working hours - after every hour of work there is a 10-minute break, which should be carried out in a specially equipped room that has a positive effect on a person’s emotional status. The room temperature is not lower than 18°C.
Personal protective equipment: from the simplest (earplugs) to the installation of noise-insulating booths.
At each workplace, depending on the accuracy of the work performed, a maximum permissible noise intensity level is set, and depending on the frequency characteristics, an octave band is established.
Plants in the process of growth and development are exposed to unfavorable environmental factors, which include temperature fluctuations, drought, excessive moisture, soil salinity, etc. If these factors act on plants within the tolerance zone and this effect is short-lived, then no significant disturbances are observed structure and physiological functions of plants, which is due to the ability of organisms to maintain a relatively stable state under changing conditions, that is, to maintain homeostasis. If changes in external factors are large enough (go beyond the tolerance zone), occur quickly enough and last long enough, then these factors are irritants. A stimulus is any external influence that has reached a threshold strength. The ability of living structures to respond to stimuli is called irritability. The presence of the property of irritability allows cells to adapt to the environment and thereby protect and preserve their life. That is why C. Bernard called irritability “the first engine of the vital functions of the living.”
In their natural habitat, plants are exposed to constantly changing factors: biological (viruses, bacteria, fungi, competition with other plants, influence of animals, etc.); chemical (water, nutrients, hormones, gases, herbicides, insecticides, fungicides, etc.); physical (illumination, temperature, radiation, mechanical factors, etc.) One of the distinctive features of the environment in which a plant develops is its instability. The development of a plant is adapted not to any one environmental factor, but to a certain combination, set of conditions.
It should be borne in mind that in some cases, damage to the body caused by factors of a physical nature is mediated by chemical agents that arise in the plant when a physical factor acts on it. The action is associated with mediators of a chemical nature ionizing radiation, high temperature and a number of other physical factors. According to their physiological significance, environmental factors are divided into adequate and inadequate. Adequate- these are natural factors accompanying a species in the process of its evolution, to the perception of which it is adapted and the sensitivity to which these organisms are very high. Inadequate- these are artificial factors that could not take part in the formation of the species and for the perception of which cells are not specially adapted. In this regard, reactions to inadequate factors, even if they act in small doses, can lead to damage to cells and tissues.
The effect of a factor can be long-term (for example, atmospheric drought, prolonged exposure of plants to salinity conditions, etc.) or a sharp increase in the intensity of unfavorable factors occurs in a relatively short period of time (for example, dry winds, a sharp drop in temperature, etc.). Responses to the chronic effect of the factor and to stressful conditions are different.
To live and function normally, a cell must clearly respond to signals from the external environment. The ability of organisms to respond appropriately to external stimuli, to signals from outside, should be considered as necessary condition adaptation of cells to the environment. To perceive external signals, the cell has a set of necessary receptors, in most cases built into the plasma membrane or located in the protoplasm. Cells perceive signals that are of a physical, chemical and biological nature from the external environment or from neighboring cells and convert them into various intracellular biochemical processes. The ability of cellular structures to perceive and respond to certain signals and their volumes largely depends on the competence of the cell.
Cell competence- its ability to react in a certain way to an external inducer is determined by the presence of receptor molecules and their compliance with environmental factors. In addition, a competent cell has a certain potential to respond to various external influences. The competence of resistant cells is determined by their compliance internal structure and combinations of external conditions. When the intensity of environmental factors changes, changes in the structural organization and metabolic processes in the cell occur at a certain speed and direction, corresponding to these conditions.
In a multicellular organism, cells different types at different points in time they reach a state of competence to respond to certain environmental factors. After a cell becomes competent and responds to a certain stimulus, it changes its state and begins to exhibit new competence (either perceives other signals, or the same signals, but in a different volume). Temporary mechanisms of competence are based on the oscillatory behavior of regulatory systems and the plasticity of intracellular metabolism. Consequently, the competence of a cell is determined by the number, location, structure of receptors and the potential of response to an inducing influence. Receptors are specific cell structures of protein or non-protein nature (lectins, photoreceptors, chemoreceptors, mechanoreceptors, hormonal receptors).
The membrane, with the help of its receptors, “analyzes” and “qualitatively evaluates” chemical and physical environmental factors and recodes signals from the external environment into a language understandable to intracellular processes. The binding of an irritant to a receptor is accompanied by conformational changes in receptor molecules, which transmit the signal to the next authority in the language of conformational rearrangements. Subsequent signal transformations depend on the nature of the cells and the properties of the stimulus.
The standard reaction of membranes to external stimuli is depolarization- loss of charge or change in the sign of charge, resulting in an action potential and changes in the properties of membrane components. High amplitude action potentials can be produced by temperature, light, electrical stimulation, and certain chemicals. In the absence of stimuli, the plant cell has a negative resting potential (from - 50 to - 200 mV), protoplasm is charged negatively with respect to the outer surface. The reason for this is the uneven distribution of ions: there are more Cl - and K + ions inside the cell than outside, but less Ca 2+. The uneven distribution of ions, manifested in the form of membrane potential, is apparently due to the action of membrane ion pumps (transporters), ion channels and different mobility of ions in the membrane. In response to prolonged stimulation, the membrane depolarizes and then gradually recharges. A potential of the opposite sign arises, an action potential, which can temporarily completely compensate for the resting potential or cause the appearance of a potential with the opposite sign. The action potential first develops with the release of Cl - from the cell and the entry of Ca 2+ into the cell. Then a slower process begins - the release of K + ions from the cell, as a result the action potential is removed and the resting potential is restored, first with a different distribution of ions than before stimulation. Then the original distribution of ions is restored with the participation of carriers (K + and Cl - enter the cell, and Ca 2+ outside). Regardless of the nature of the stimulus, the action potential has a biphasic character. However, under the influence of various agents, action potential parameters such as amplitude, wavelength, and response time may change. It has been established that all plants are capable of generating an action potential under certain conditions. The latent period of the action potential in plants ranges from fractions to hundreds of seconds, and its value can reach 100 - 150 mV. In the multinucleated alga Nitella, a high-amplitude action potential can be caused by temperature, light, etc. In an insectivorous plant (sundew) and mimosa, a mechanical stimulus perceived by specialized sensitive hairs leads to a change in turgor pressure in the cells, and as a result, in one case, slams a trap, and in the other the leaves are falling off. The action potential generated in effector cells is similar in its parameters to that observed in neuromuscular systems. The propagating action potentials of plants and animals have much in common, but in plants they occur more slowly. Velocity of action potential propagation in mimosa 4 cm/s, for most plants 0.08 - 0.5 cm/s.
The electrical potential appears to be involved in the transport of environmental signals and the initiation of intracellular processes. For example, sudden changes in living conditions in the root zone induce a single impulse, which, reaching the leaves, causes an increase in gas exchange and acceleration of the transport of assimilates along the conducting bundles. In case of severe irritation of the shoot tips (0.5 M KCl, cold water etc.) a single pulse accelerates the absorption of potassium and phosphorus by the roots. These data indicate the existence of rapid electrical communication between individual cells and tissues in plants.
Currently, attempts are being made to identify the molecular basis of signal perception and the entire associated sequence of events associated with the amplification and transformation of these signals through a system of intermediaries.
It is known that calcium increases the resistance of plants to various stresses (high and low temperatures, anaerobiosis, decreased pH, disease). D. Marme and his colleagues conducted detailed studies of the possible functioning of calcium as a second messenger in plant cells. They showed that the distribution of Ca 2+ in maize coleotyl cells depends on light: upon illumination, the concentration of free calcium in the cell cytosol increased, which was accompanied by an increase in NAD kinase activity.
Obviously, calcium, as a secondary messenger, perceives the information of the primary signal (light) and thus regulates biochemical processes (in particular, the activity of NAD kinase).
The concentration of free Ca 2+ in the cytoplasm of plant and animal cells is low (10 -8 - 10 -6 M). In intracellular structures (mitochondria, endoplasmic reticulum), the concentration of free Ca 2+ ions exceeds 10 -3 M. In animal cells, such a difference in calcium concentration is maintained by membrane Ca 2+ -ATPases, the Na + /Ca 2+ exchange system, and, possibly, the Ca 2+ transport system of mitochondria. In plant cells, when an action potential occurs or when membranes are depolarized, Ca 2+ enters the cell from the outside and (or) is released from intracellular reservoirs (ER cisterns, mitochondria, vacuoles). The works of a number of researchers have shown that Ca 2+ -ATPase, localized in plasma membranes, exchanges Ca 2+ for protons (Ca 2+ /H + -antiport). In the plasmalemma of cells there are voltage-gated calcium channels that open when the membrane is depolarized. The ER also contains calcium channels, similar to the channels of plasma membranes, and the movement of Ca2+ in them is directed from the ER cisterns to the cytosol. In addition, Ca 2+ -ATPase was found in the ER membranes of plant cells, transporting calcium from the cytosol to the intracellular depot (ER cisterns). The concentration of free calcium in the stroma of chloroplasts is low, but it increases with light. A significant portion of Ca 2+ is contained in plant cell walls (in the form of nectates, carbonates, sulfates) and in vacuoles (in the form of oxalate).
Changes in the concentration of Ca 2+ in the cytosol of cells play a significant role in the mechanisms of protoplasm movement, cell division, and the secretory activity of some plant tissues.
Thus, calcium, coming from the external environment or released from intracellular compartments, acts as an intracellular mediator that induces a number of physiological processes.
Plant cell calcium can bind to calmodulin and other Ca 2+ -binding proteins. Calmodulin is a low molecular weight protein (Mm 16700) with a high content of acidic amino acids. It has four regions with high affinity for Ca 2+ . Calmodulin is found in mitochondria, chloroplasts, microsomes and cell walls. The cytosolic fraction contains a significant amount of this protein (90%). Activated by Ca 2+ (10 -6 M), calmodulin regulates the activity of Ca 2+ -ATPase, NAD kinase, NAD oxidoreductase, protein kinases, and lipases.
Many reactions induced by photochrome far red (F730) are also controlled by calcium ions. C. Po (Ronx) suggests the following sequence of events after the absorption of red light quanta by plant cells: formation of F 730 from F 660 →increasing concentration of calcium ions in the cytoplasm of cells →binding of calcium ions by calmodulin and the direct effect of increased concentrations of Ca 2+ on cell functions →binding activated calmodulin with enzymes dependent on it and activation of these proteins.
Therefore, plant cells have mechanisms to maintain a certain level of free calcium ions in the cytosol and to function as Ca 2+ as a second messenger in the regulation of metabolism.
c-AMP is considered as another signaling system. In animal organisms, cyclic nucleotides (c-AMP, c-GMP) play a very significant role in the system of intracellular regulation. The adenylate cyclase enzyme system is responsible for the synthesis of a relatively simple nucleotide - cyclic adenosine monophosphate (c-AMP), which can activate many intracellular enzymes. In its structure, c-AMP is close to ATP. It is formed from ATP by separating two phosphate groups and then closing the remaining phosphate group into a ring (hence the name cyclic AMP). This reaction is catalyzed by adenylate cyclase, which is located on the inner surface of the membranes and works in the presence of phospholipids and magnesium ions.
The action of exogenous factors can manifest itself through cyclic nucleotides. In particular, G. Mohr and his colleagues showed that activation of phytochrome by red light is accompanied by a twofold increase in the level of c-AMP in etiolated white mustard seedlings. The influence of environmental factors is directed at the membrane. The adenylate cyclase system begins to function (Fig. 1), cyclic nucleotides are synthesized, which change the structural and functional state of chromatin, the matrix activity of DNA, and the intensity of the new formation of enzyme proteins. In 1971, T. Langan showed a possible connection between c-AMP and the regulation of genome activity. It has been shown that c-AMP stimulates the phosphorylation of histones by histone kinase drugs, which leads to the activation of RNA synthesis on the DNA template. In addition, c-AMP acts as an allosteric effector on protein kinases that catalyze modification reactions such as phosphorylation of nuclear, cytoplasmic, and membrane-bound proteins. Currently, a protein has been isolated and purified that exhibits affinity for both c-AMP and cytokinins. In this regard, it is believed that there is a certain connection between cyclic nucleotides and phytohormones.
Thus, c-AMP is apparently a “second messenger” in the chain of events from the reception of environmental signals to changes in the activity of the hormonal, enzymatic and genetic apparatus of the cell. The connection of phytochrome with the synthesis of c-AMP explains the multifaceted influence of this pigment on various parts of metabolism, including the synthesis of RNA and protein.
Japanese researchers have shown that carrot culture cells synthesize phytoalexins in response to fungal infection. The authors believe that this response is mediated by another signaling system - phosphatidylinositol, which includes calmodulin-dependent processes. The presence of a system of phosphorylated inosigols has been established in plant cells. Inositol 1,4,5-trisphosphate (ITP) causes the release of Ca 2+ from intracellular compartments. ITP, together with calcium, is involved in transmitting signals from outside to inside the cell (Fig. 1). The external signal binds to the receptor, which, through a series of intermediate compounds, activates phosphodiesterase (PDE). This enzyme breaks down phosphatidylinositol 1,4,5-triphosphate (PITP), resulting in the formation of inositol 1,4,5-triphosphate and diacylglycerol. ITP is soluble in water, so it diffuses into the cytoplasm and causes the release of calcium from the ER, mitochondria and other compartments. The released Ca 2+ activates calmodulin-dependent protein kinase, which phosphorylates intracellular proteins and causes a change in the speed and direction of metabolic processes.
In general, the cell signaling system consists of receptors that perceive the signal and are functionally associated with receptors of second messengers (Ca 2+, calmodulin, c-AMP, ITP, protein kinase). These intracellular messengers serve to amplify and transmit the perceived signal and trigger metabolic processes.
Protein kinase activity is found in almost all cells and tissues of animal organisms. Enzymes similar in a number of properties to protein kinases. From animal organisms, found in the cells of wheat and pumpkin and in acorn sprouts. IN recent years In the literature, information appeared about the presence of Ca 2+ phospholipid-dependent protein kinases in plant cells. They are found in the plasma membrane fraction of pea root cells and in the cytosolic fraction obtained from hypocotels and pumpkin stems. Protein kinases are enzymes that phosphorylate proteins at strictly defined groups of serine, threonine and tyrosine. The addition of phosphate leads to a change in the structure of the protein molecule and its functional activity. Structural, transport and regulatory proteins are subject to phosphorylation. Protein kinase is activated by calcium (10 -6 -3.10 -7 M), phospholipids (phosphatidylserine) and diacylglycerol (Table 1).
Regulation of protein kinase activity may vary depending on the quality of the perceived signal and functional features fabrics. It may or may not depend on cyclic nucleotides and be sensitive or insensitive to calmodulin and calcium. Activated protein kinase transfers a phosphate group from ATP to proteins, which in turn activate other enzymes. The biological meaning of this enzyme activation cascade is that, like cascade amplifiers used in radio engineering, it repeatedly amplifies the initial signal, which induces a whole complex of protective and adaptive reactions. As a result, the synthesis of adaptive proteins (for example, stress proteins), protective compounds (proline, polyamines, oligo- and polysaccharides, etc.) is turned on, changes are detected at the level of membrane structures (their lipid and protein complex changes), protective systems arise on the structural and metabolic level, and then morphostructural changes follow.
For example, for light to have its physiological effect on a plant, it must be absorbed by a receptor (phytochrome or other pigments). One of the reactions under the control of phytochrome is the curling of mimosa leaves at nightfall. The entire process is completed in 5 minutes - this time is too short to allow control at the transcription level. This fact, as well as the fact that some amount of phytochrome is tightly bound to membranes, led to the assumption that the primary effect of phytochrome is reduced to changing the properties of the membrane. The pigment molecule that has absorbed the light quantum goes into an excited state, interacts with the cell membrane and causes a change in its conformation. A change in the state of the membrane in one place can spread to other parts of it. As a result, the permeability of the membrane, its charge, and the activity of enzymes associated with it will change. All this, in turn, may cause changes in the overall metabolic pathways of the cell. Slow reactions in response to changes in phytochrome state may be associated with the process of gene transcription. Pigments involved in the photoregulation of plant morphogenesis, when excited by light, have a direct effect on the plant gene apparatus, converting potentially active genes into active ones and thereby promoting the formation of new messenger RNAs and the biosynthesis of hitherto “forbidden” proteins.
The cell receptor apparatus is a dynamic and, apparently, highly selective system that provides both communication between cells and the external environment and regulation of their functional activity. The specificity of receptor systems in accordance with cellular specialization determines the possibility of implementing a response characteristic of a given type of cell to the action of various environmental factors.
The action of any unfavorable extreme factor causes a number of protective and adaptive reactions. The nature of the responses largely depends on the intensity of the acting factor. At low intensity, a normal response is observed (i.e., strengthening or weakening of intracellular physiological processes). With a significant intensity of the active factor, the body begins to protect itself from adverse effects and for this purpose mobilizes all its available potencies. At the same time, new properties may appear in the body that were absent before the action of this factor.
Back in 1900, the Indian physicist and plant physiologist Jagdish Chandra Bose came to the conclusion about the commonality of responses in animals and plants. Ideas about the uniformity of responses of organisms to environmental conditions were developed in the works of D. N. Nasonov and V. Ya. Aleksandrov. It was postulated that the response of the cell's protoplasm to environmental conditions is monotonous. It is expressed in the fact that in response to influences in the protoplasm of plant and animal cells, the same changes always occur in the following sequence: 1) the degree of dispersion of the protoplasm decreases; 2) the permeability of protoplasm increases; 3) denature proteins; 4) paranecrotic changes in the nucleus occur; 5) protoplasm coagulates.
These same-type, monotonous changes that appear with any damage can completely disappear after eliminating the altering agent, if its effect has not gone too far. The nonspecificity of these signs is expressed in the fact that they accompany in different ways damage and are observed in any tissue cells and single-celled organisms. This complex of nonspecific physicochemical signs of damage was called paranecrotic, and the state of cells in which they develop a complex of paranecrotic changes was called paranecrosis (paranecrosis - “near” or “near” death). The meaning of this name is that the reactions that occur in the cell during irritation and damage are similar. Subsequently, the ideas of D. N. Nasonov and V. Ya. Alexandrov were developed in the works of the Canadian physiologist G. Selye. He introduced the concept of stress into the field of medicine, but it also became widely used in plant physiology. G. Selye gives the following definition of this concept: “Stress is a nonspecific response of the body to any demand placed on it.” Stress in the understanding of phytophysiologists is a certain disorder caused by unfavorable conditions.
Changes in the permeability of cell membranes appear to be the primary link in the response. Permeability - the ability of cells and tissues to absorb or exchange substances with environment. Membrane permeability can change both under the influence of internal conditions (in the processes of seed germination, plant growth and aging of cells and tissues), and under the influence of various environmental factors (phytopathogens, temperature and light conditions, anaerobiosis, excess heavy metals, etc.) . Significant changes in the permeability of plant cell membranes are detected under the influence of abiotic environmental factors. In 4-5-day-old seedlings of wheat, beans and cotton, immersed in solutions of sodium chloride, sulfate and sodium carbonate salts, there is a significant increase in the permeability of root membranes and an increased release of amino acids, organic acids and inorganic ions into the external solution. The permeability of plant tissues changes sharply at elevated environmental temperatures (45°C). There is numerous data in the literature that directly or indirectly indicates the existence of a certain connection between the permeability of plant cell membranes and the frost and cold resistance of plants. According to P. Nobel, the permeability of the membranes of chloroplasts of plants not tolerant to cold (tomatoes, beans) at low temperatures increased sharply, while the resistant ones (peas, spinach) did not change. The above suggests that changes in the permeability of cell membranes are a common, primary link in the nonspecific mechanisms of the plant organism’s response to external influences. It has now been proven that the permeability of plant tissues can be used as an indicator of plant resistance to adverse environmental conditions.
The question arises: is plant resistance to drought, frost, and salinity determined by one general mechanism, or are these mechanisms specific in each case? The plant organism responds to any impact with a whole complex of protective and adaptive reactions, consisting of both general (nonspecific) and specific processes. The work of B.P. Strogonov shows that the process of adaptation of plants to sulfate and chloride salinity proceeds differently. For example, transpiration in plants increases under sulfate salinity, and decreases under chloride salinity.
Some researchers believe that resistance to various extreme factors is based on nonspecific (same type) reactions (V. Ya. Aleksandrov, G. V. Udovenko). V. Ya. Aleksandrov interprets his large material on the influence of temperature on animal and plant organisms from the standpoint of a nonspecific reaction of organisms to the action of elevated temperatures. Others associate resistance with reactions of a specific nature (N. A. Maksimov, P. A. Genkel)). P. A. Genkel believes that the plant’s response to unfavorable conditions is complex. During the adaptation process, protective-adaptive reactions of both nonspecific and specific nature are deployed.
Yu. A. Urmantsev interprets the question of the specificity and nonspecificity of plant responses as follows. “Plant responses to various unfavorable conditions, at least in some cases, can appear in the form of specific implementations of the same pattern.” In particular, curves describing the dependence of certain plant functions on the action of one or another unfavorable factor, as a rule, have the same “bell” shape. However, when analyzing these curves, it is noted that these forms differ significantly in their amplitudes and heights. If we proceed from the concept of a single plant resistance, then for all plant functions and all unfavorable conditions, researchers would receive the same “bell” with the same parameters (amplitudes, heights). Apparently, the specificity of response reactions manifests itself as an integral part of general, similar protective-adaptive reactions. The specificity of responses is a feature of the manifestation of the general.
The concept that plant responses to unfavorable environmental conditions proceed in the same way developed mainly in the study of damage and death of plants. The idea that the response is more complex and consists of both nonspecific and specific reactions arose from the study of adaptive changes, where specific plant responses come to the fore. At a certain (small) dose of exposure to an unfavorable factor, when adaptive changes are possible, specific reactions are observed along with non-specific ones. When the impact measure is increased (factor×time), the body begins to protect itself from adverse effects and mobilizes all the means available to it. In the latter case, we may not detect specificity in the responses. I. N. Andreeva and G. M. Grineva studied the effect of elevated temperature and anaerobiosis on the submicroscopic structure of mitochondria. The submicroscopic patterns observed as a result of the influence of these factors differed sharply from each other. When corn roots are exposed to high temperature (45°C), mitochondria swell, matrix clears, vesiculates, and the number of cristae decreases. Under the influence of anaerobiosis, ribbon-shaped and twisted cristae are detected, their volume increases, they become denser, their vesiculation and increase in number are observed. With increasing exposure (at the end of the exposure), the morphological patterns of damage become closer: a high degree of mitochondrial swelling is observed, a complete absence of the matrix, and a small number of cristae-vesicles are preserved. Under the influence of both factors, the mitochondria were eventually destroyed. The phosphorylating activity of mitochondria was maintained at low doses of temperature and anaerobiosis, and with severe damage, complete uncoupling of oxidation and phosphorylation was observed.
The ratio of specific and nonspecific responses largely depends on the duration of the active factor. With short-term exposure to the factor in a high dose, mainly nonspecific responses are observed. For example, we use a similar gesture to withdraw our hand after touching a hot, cold, or sharp object. With prolonged exposure to a stress factor, a greater number of metabolic links are activated, some of which have specific features for of a given organism. The gradual, prolonged action of a stressor leads to the inclusion of specialized adaptation processes, which provide a system of reliable functioning of intracellular processes under extreme conditions.
The nature of a specific reaction to stress indicates the nature of the damaging factor, and in the case of a nonspecific reaction, it is difficult to guess the nature of the acting signal. Nonspecific reactions are observed more often than specific ones. An example of a specific reaction is signs of acute deficiency (or excess) of plant nutrients.
It is important to note that plant responses to various factors are oscillatory. Thus, the data obtained by P. S. Belikov show that when exposed to high temperature, the viscosity of the cytoplasm first decreases and then increases. The speed of movement of the cytoplasm and the release of substances from the cell also change in waves: at first, an intensification of these processes is observed, then their speed slows down. Depending on the strength of the damaging effect, the nature of these oscillations changes: amplitude, wavelength, time of onset of the triggering response. According to V. Ya. Aleksandrov, the oscillatory nature of physiological processes in cells under the influence of stimuli reflects the complex nature of responses, which have different directions. Some of these reactions are destructive in nature, while others are aimed at preserving intracellular structures and processes.
It can be assumed that a specific response to the action of extreme factors is controlled by genetic mechanisms through the work of the protein synthesizing apparatus. The nonspecific response, apparently, is not associated with genetic control and is based on the physiological plasticity of the organism (plasticity of membrane components, changes in the structure and activity of intracellular proteins, etc.). The ratio of specificity and nonspecificity in resistance may vary depending on the biological characteristics of the object. As an example, consider two biological objects. Cucumber as a species was formed in tropical conditions; Its natural distribution range includes individual areas Central Asia, characterized by slight fluctuations in temperature and other environmental factors. When exposed to extreme (low) temperatures, to maintain the viability of these plants, specific responses are mainly triggered, which are determined by the genetic potential of the species. Stable factors in the regions of Central Asia did not ensure the formation of metabolic plasticity in this plant organism.
In contrast to cucumber, the formation of the genus Triticum occurred against the background of noticeable fluctuations in environmental temperature and other factors. The distribution area of wheat includes vast territories from the Arctic Circle to the southern reaches of Australia, America and Africa. Wheat is well adapted to mountain conditions and grows at an altitude of 4 thousand. m above sea level. It can be assumed that for wheat, the key to widespread distribution is a well-developed specific response system, supported by mechanisms of nonspecific resistance. Evolution in wheat proceeded according to the development of mechanisms of lability of membrane components, plasticity of regulatory mechanisms, mobility of the structure and function of intracellular proteins, which allows wheat to have a wide distribution area.
In all cases, it is impossible to draw a sharp line between specific and nonspecific reactions. The apparent nonspecificity of physiological, biochemical and other signs of damage is not absolute; here, apparently, we should rather talk about the similarity of phenomena than about their identity, since against the background of reactions of the same type it is usually possible to notice specific features. Apparently, the combination of the specific and non-specific nature of the responses lies in the possibility of the response of living systems and their development in evolution.
When studying resistance processes, cases of simultaneous resistance to two or more types are sometimes observed. P. A. Genkel, analyzing a number of similar facts, formulated the concept of conjugate stability, which can be positive or negative. A good example of conjugate resistance is the increase in heat and salt tolerance in millet variety Kremovy, which was treated with 1/40 before sowing M CaCl2. In this case, positive conjugate stability appears. Treatments with CaCl 2 cause an increase in the viscosity of protoplasm and a decrease in the intensity of metabolism, which contributes to greater heat and salt resistance of plants. Examples of positive and negative conjugate stability are given in the works of A. Kashlan. Tobacco grown in vegetation experiments was subjected to pre-sowing hardening against drought. An increase in drought resistance and, at the same time, sulfate resistance in plants and a decrease in chloride resistance were found. More detailed analysis showed that the improvement in growth and productivity under sulfate salinity in plants hardened to drought is associated not with an increase in sulfate resistance, but with their increased heat resistance, since control non-hardened plants greatly reduce their heat resistance under sulfate salinity of the soil. Under chloride salinity, a decrease in chloride resistance in drought-hardened plants is associated with their increased metabolism, greater salt absorption and a more developed root system (larger volume and surface area of root absorption).
The repeatedly noted similarity in plant responses to unfavorable environmental factors, such as cold and heat, and the presence of positive conjugate resistance led to the conclusion that plant resistance to various extreme conditions can be controlled by the same endogenous factors. The similarity of responses can be explained by the existence of a wide range of nonspecific adaptive reactions and the fact that a specific response to exogenous influences such as cold and heat is associated with a system of induced protein synthesis, i.e., it is carried out according to a single type of genetic regulation of physiological processes. The similarity of plant responses to temperature, water and salt stress is determined, apparently, by the fact that under these conditions a water deficit is created in the cells, which can be eliminated using the same type of protective and adaptive processes (increased synthesis of water, etc.).
In addition to the concept of conjugate stability, P. A. Genkel introduced the concept of convergent stability. Convergence is the observed similarity of different organisms caused by the same conditions of existence - the same selection pressure. There are two types of convergent stability: 1) typical convergence, when the stability of different organisms is due to the same conditions of existence; 2) atypical, when different conditions lead to the same result. An example of an atypical convergence is the high heat resistance of tree species in winter, associated with their dehydration and the accumulation of lipids on the surface of the protoplast.
In addition, there are cases of divergent atypical convergent resistance, when the same impact leads to a different result.
For all organisms at different levels of organization, it is possible to identify some similar characteristic features in their response to external influences. These include: 1) the ability to respond to the action of stimuli by turning on signaling systems that receive the signal, amplify it and trigger response physiological and biochemical processes; 2) the ability to combine in responses nonspecific signs, largely independent of the nature of the influencing factor, with specific signs characteristic of a given factor. The source of specific responses is the heterogeneous dismemberment of systems, the source of nonspecificity is the interconnectedness of its parts, the cooperativity of their relationships. Under the influence of irritants, damage occurs, resulting in disruption of the structure and function of the cell. Excitation processes lead to activation of cell vital processes. As a result of this, the action of subsequent stimuli begins to be perceived by the cell with less force, and hardening appears. Against the background of hardening, restoration occurs - reparation of the original functions and structures.
In higher terrestrial plants, strong contact with the environment under conditions of a sedentary lifestyle necessitates the development of active adaptive reactions, improving the methods of their adaptation to a constantly changing, heterogeneous habitat. The study of protective reactions is necessary to resolve issues related to the introduction and selection of plants, as well as to develop methods for artificially increasing the resistance of cells and organisms to biotic and abiotic environmental factors.