USEFUL RADIATION
If the Lord God would do me the honor to ask
my opinion at the creation of the world, then I would tell him
advised to create it better, and most importantly - simpler
KING ALPHONSO OF CASTILE XIII CENTURY
Probably, each of us has repeatedly had the thought of how complex and ingeniously organized a living cell is. It seems to be thought out to the end and so perfect that it cannot be improved. In the process of evolution, options for optimal cell designs were reworked millions of times, and millions of options were rejected. The most developed, complete and perfect samples remained. But over the past decades, scientists have convincingly proven the possibility of improving plants and other organisms using ionizing radiation and radioactive isotopes.
In Paris, in the Jardepe do Plante district, there is a small house. It is the property of the National Museum of Natural History. On its wall there is a modest plaque, and on it is the inscription “In the laboratory of applied physics of the Museum, Henri Becquerel discovered radioactivity on March 1, 1896.” Three quarters of a century have passed since then. Did any of even the most perspicacious compatriots of Becquerel imagine that seventy years later radioactive isotopes would become widely used in agriculture, biology, and medicine? That labeled atoms will be reliable human assistants in solving the most pressing problems? And that, finally, with the help of penetrating radiation from certain radioactive isotopes it will be possible to increase grain yield?
Using ionizing radiation, it is indeed possible to change living organisms in the direction desired by humans
A few years ago in Moldova in the spring, you could see on the roads a van with the inscription on the back “Atom for the world.” This is not a simple truck, but a mobile irradiator for pre-sowing seed treatment. Its “atomic heart” is a large container with a gamma-active isotope of cesium. -137 On the eve of sowing, the van drives into the field. A truck with corn seeds drives up to it. The conveyor belt is turned on. The seeds are poured into a bunker with a radioactive cesium isotope. Completely isolated from direct contact with the isotope, the seeds are at the same time irradiated with gamma rays in the required dose. Continuous jet. The grain runs through the bunker. Then it gets onto another conveyor and is poured into bags on another vehicle. Pre-sowing irradiation of the seeds is completed. The seeds can be sown.
Why were corn seeds irradiated? Pre-sowing seed training is a method of increasing the yield of agricultural crops. With its help, you can speed up the ripening of plants and improve their beneficial qualities.
On the laboratory table there are ten pots with corn seedlings of various heights. Under the leftmost one there is a signature: “Control”, under each of the others there are numbers - 100, 300, 500, 800.. And so on up to 40,000. The laboratory journal records “Height of corn seedlings at different doses of radiation on the 13th day of the growing season.”
When seeds are irradiated at a dose of 100 and 300 roentgens, the height of the seedlings is the same as in the control group. When the irradiation dose is 500 roentgens, the plants are one and a half times higher than the control. But then, as the dose increases, the size of the seedlings decreases. At a dose of 8,000 roentgens, the plants appear dwarfs. At a dose of 40,000 they are barely visible.
A few pages later in the same laboratory journal there is a photograph pasted in. These are the roots of the same plants. Almost the same pattern. At a certain dose of gamma rays - a sharp increase in growth, and then a gradual decrease. At large doses, root growth is sharply inhibited.
First, experiments are carried out in laboratory conditions. Then the experiments are repeated in the field. Experiments in the field are like a dress rehearsal in a theater, like the last exam, after which the results of experimental research will be put into practice. Experimenters irradiated corn seeds of the Sterling and Voronezhskaya-76 varieties, which are grown in the Moscow region to produce silage. Experiments in field for three years showed that irradiation of seeds at a dose of 500 roentgens increases the yield of green mass of corn by 10-28 percent. Silage obtained from such plants contains more protein, fats, nitrogen-free substances, fiber, carbohydrates
What if you irradiate radish seeds?
On the experimenter’s table are two bunches of radishes of the same variety. The amount of radish in each bunch is the same, but the radish on the left is much thicker and meatier. In comparison, the radish on the right seems skinny. But the right bunch is an ordinary, so to speak, “normal” radish. The plump relative on the left is a radish grown from irradiated seeds. When the seeds of this variety are irradiated! gamma rays at a dose of 500 roentgens increased the yield by 37 percent! Harvesting 100 or 137 kg of radishes is a significant difference. And this is from the same number of seeds, on the same lands and with the same care. And the costs of irradiation are extremely low.
In other radish varieties - "Rubin", "Pink with a white tip", "Sax" - the yield increased when irradiated at a dose of 1000 roentgens. And the irradiated "Sax" was also juicier and ripened earlier than usual by 5-6 days. Pre-sowing irradiation seeds of "Rubin" not only increased the yield of root crops, but also increased the content of vitamin C in them. With the help of ionizing radiation in root crops, the content of vitamin A can also be increased. Thus, after irradiation of carrot seeds of the "Nantes" variety in a dose of 4000 roentgens, the yield of root crops in relation to to control increased by 26 percent, and the supply of carotene - a plant pigment that is converted into vitamin A in the human body - by 56.
What about corn? Irradiation of seeds at a dose of 500 roentgens increased the yield of green mass by up to 28 percent
The stimulating effect of pre-sowing irradiation of seeds has been proven for cucumbers, tomatoes, beets, cabbage, salut, potatoes, cotton, rye, barley...
Scientists noticed one peculiarity. The dose of ionizing radiation that causes the stimulation effect is different not only for different plant species, but even for different varieties of the same species. Moreover, it turned out to be not the same for the same variety sown in different geographical zones.
Thus, the stimulating dose of radiation for cucumbers of the “Nezhinskie” variety, sown in the Moscow region, is 300 roentgens, and to obtain the same result in Azerbaijan, a dose of about 2000-4000 roentgens was needed.
Let's take corn seeds. Lots of seeds. We irradiate them under the same conditions with a dose of gamma rays, which causes a stimulating effect. We will divide them into four equal groups - 1000 pieces in each. We will sow one group immediately after irradiation, the second - after a week, the third - after two, the fourth - after a month. Now we will wait patiently. The seeds have sprouted and the plants have begun to develop. But what is it? Plants sown immediately after irradiation develop faster than others. In seeds that were sown a week after irradiation, the stimulation effect was less pronounced. In seeds sown 2 weeks after radiation treatment, almost no acceleration in development was observed. Seeds kept after irradiation for a month germinated, but had no stimulating effect. This means that during storage some mysterious substance, some stimulant slowly disappeared.
What's the matter?
We are entering an area where facts are still friends with assumptions, where much has not yet been explored. It has been established that after irradiation, very active fragments of molecules are formed in the seeds, called Opie radicals, capable of entering into reactions unusual for a healthy organism. And it turned out that after irradiation of seeds, the number of radicals gradually decreases over time. Several days pass and the radicals disappear completely. The higher the temperature and humidity at which the seeds are stored, the faster the radicals disappear
What happens when seeds fall into moist, sun-warmed soil? The nutrients contained in the seeds begin to turn into soluble form and are transported to the embryo. In the so-called aleurone layer of the seed, oxidative processes are activated, and the production of energy-rich compounds begins. The embryo awakens, its cells swell and begin to divide. The processes of growth and development of seedlings begin. Cells begin to divide and need building material. The activity of many enzymes increases significantly as a result of irradiation. And when seeds are irradiated, oxidative processes begin to occur much more intensely. And this leads to faster development and acceleration of seed germination and germination. Plants become more powerful.
Not long ago, an article was published in the Courier magazine, which is published by the UN. It said that every third peasant in Africa actually worked for birds, rodents, insect pests and microparasites.
Naturally, it is difficult to vouch for the accuracy of these figures, but it is a fact that losses from pests are enormous.
Experts have calculated that agricultural pests destroy so much grain in a year that they could feed 100 million people.
How can ionizing radiation help agriculture in pest control?
You already know: different types of plants have different radiosensitivities, some are quite high. Insects, as a rule, are highly radioresistant. Among them there are even unique champions of radio resistance. For example, scorpions. But insect eggs and larvae turned out to be more radiosensitive. And insect reproductive cells are also more sensitive to radiation.
The scheme for combating insect pests is simple. Through a bunker charged with a radioactive isotope, grain is passed through a conveyor. Over a certain period of time, it receives the dose of ionizing radiation necessary to kill the pests. Such grain, of course, is not used as planting material. But it is completely harmless for human nutrition. After irradiation the grain enters the storage facility - the dangerous pest no longer threatens it. The same techniques can be used to combat dry fruit pests - insects and their larvae, by irradiating “future compotes” with gamma rays in a dose of up to 50,000 roentgens. And in Canada, they proposed a method of radiation control of salmonella, infecting powdered eggs Do you know about the “sterile male” method? Scientists developed it relatively recently. Insects irradiated with ponting radiation during a certain period of growth are unable to give birth to offspring. “Sterile males” mate with normal females. However, the female does not produce offspring. The more males are sterilized, the greater the possibility that the females will not produce offspring. If there are many sterilized insects for several generations, then the offspring will be sharply reduced. In some countries, there is a dangerous pest - the so-called blowfly. It lays its eggs in brine of warm-blooded animals From the eggs, larvae develop, which cause disease and even death of livestock, wild animals and game. The blowfly causes great harm to the household. And then they decided to try the method of radiation sterilization on the blowfly. They built a “fly” factory where flies were bred and sterilized. Sterilized insects were released into the contaminated area. The result had an immediate effect. The disease and mortality of livestock decreased sharply. The costs of the “fly” factory not only paid off in the first year, but also brought a profit equal to the amount of costs. In the USA, on the island of Kurakoo, with an area of 435 square kilometers, about 2,000 sterile male blowflies were released per square kilometer. The blowfly on the island has been practically destroyed.
The idea of canning food arose a long time ago. Food was canned by the ancient Egyptians and the Indians. Probably the most ancient way to preserve food is by drying it in the sun. Over time, methods of canning have changed. Today, there is a refrigerator in almost every city apartment. But the most modern way of preserving food is to preserve it using penetrating radiation If, for example, fresh meat is irradiated with gamma rays at a dose of 100,000 rept-hep, then the period of its storage in the warehouse is extended five times. If irradiated meat is stored at a temperature of about zero degrees, then it is stored for several months without losing nutritional and taste quality With the help of radiation, the shelf life of fresh fish is extended. Irradiated fish in refrigerators retains its taste for up to 35 days. And without radiation treatment under the same storage conditions - 7 - 10 days.
Now they are looking for a way to preserve caviar, milk, fruits and seafood - crabs, oysters, shrimps using gamma rays
Irradiation of berries and fruits gives good results. Irradiated strawberries, stored in a refrigerator at a temperature of +4 degrees, did not lose either freshness or aroma for a long time. Even experienced tasters and experts could not determine which of the berries were irradiated in “preservative” doses. And champignon mushrooms ? They have excellent taste and can be grown artificially throughout the year. But during storage, the mushrooms quickly deteriorate, lose their freshness and taste, their heads and caps unfurl, like old mushrooms. Irradiated champignons during long-term storage looked as if they had just been freshly picked. brought from a greenhouse - the aging of the mushrooms was sharply slowed down, their caps were tightly curled, like those of young mushrooms.
Recently, a report appeared in the press about beam-preservation of flowers. The famous Dutch tulips, irradiated at a certain dose, placed in a bag inflated with carbon dioxide, are easy to transport and can be stored for a long time. It seemed as if they had just been picked from the garden, their petals were so fresh.
It is especially beneficial to use radiation to increase the shelf life of vegetables.
Potatoes have one serious drawback: during storage they sprout, the tubers shrink and lose their taste. Many scientists in various research institutes of our country began to work on the problem of radiation preservation of potatoes. Numerous experiments have shown that irradiation of tubers at a dose of 10,000 x-rays sharply slows down or stops the spring germination of potatoes and does not reduce their resistance to diseases. The taste of irradiated potatoes does not deteriorate. Experienced tasters did not find any changes in dishes prepared from such potatoes.
The problem of radiation preservation is being intensively studied all over the world. And this is natural. It brings too obvious economic benefits. Some radiation preservation methods have already been approved for practical use. Others have not yet left the walls of laboratories. And most importantly, many years of experiments are underway, which should prove: irradiated products are harmless to humans.
It is easier to experiment on plants than on animals. When working with seed irradiation, it is possible to conduct experiments on many thousands of biological objects at once. And therefore, statistics significantly help the scientist. And economically, such experience is much more profitable.
Has ionizing radiation been used for practical purposes in animal husbandry?
Animals are much more sensitive to the effects of penetrating radiation than plants. In our country, such an experiment was carried out at one of the modern poultry farms. During the incubation process, chicken eggs were irradiated for several hours at a dose of 1-2 roentgens. Such insignificant doses of radiation had a stimulating effect: the number of hatched chickens increased, and chickens from irradiated eggs had greater egg production.
Are the chickens “lucky” or is the stimulating effect of small doses of ionizing radiation a general pattern?
Probably, there are also general patterns hidden here. In any case, doctors all over the world have long recognized the healing effect of radon baths for humans.
So, ionizing radiation from radioactive isotopes can be reasonably used by humans and in agriculture. But the inquisitive reader probably already noticed that we were talking about external sources of penetrating rays. Typically, gamma rays emitted by radioactive cobalt. But there are a huge number of radioactive isotopes that emit, for example, “soft” beta rays, the energy of which is low. Radioactive carbon C" and radioactive sulfur B3®, the most biologically important elements, possess precisely such “soft” radiation. The energy of penetrating radiation of another biologically important isotope - radioactive phosphorus P3! is much higher, but it is also “softer” compared to “ hard" gamma rays of cobalt Co0.
The possibilities for using such “labeled” atoms in the national economy are also great. Let's give examples.
To defeat the enemy, you need to know him. To successfully combat dangerous agricultural pests and harmful insects, you need to thoroughly study their life.
Scientists have tagged dangerous insects such as locusts, malaria mosquitoes, and fruit flies with radioactive phosphorus. This method was used to determine the speed of locust flight and the range of its spread from the main breeding grounds; found out the length of flights of malaria mosquitoes. The fruit fly turned out to be a relative homebody. It was labeled with radioactive phosphorus and released in an orange grove. Under favorable conditions, fruit flies did not move more than a few hundred meters from their habitat.
The information obtained made it possible to outline the location of barrier zones and develop a system of defense and control of these insects.
Insecticides are poisons for insects, one of the modern ways to combat them. Let's introduce a radioactive label into these chemical compounds. The indicator allows you to immediately answer a number of important questions. How do these compounds behave in the body of insects, why are they poisonous to them? How to make them selective in action - not harmful to humans, plants and beneficial insects? Do poisons get into agricultural products? When do poisons lose their toxicity?
Experiments were carried out on our oldest friends - bees. For example, they fed a worker bee radioactive phosphorus, and it became marked. A counter of radioactive particles was placed in the hive. And now it was possible to establish how many times a day a worker bee flies to work, what is its working day and what is its flight speed. Or they did it differently. Sugar-sweetened solutions with radioactive phosphorus mixed in were placed on some field. Arrivals the bees naturally aimed at it. And then it was possible to accurately determine which fields are most popular among the bees. And hence the practical solutions that will help increase the production of tireless workers.
Radioactive isotopes are used in all studies of insect biochemistry and physiology. The significance of this work is clear. Having studied, for example, the activities of hormones and enzymes that control the development and behavior of beneficial insects, it will be possible to use insects in the interests of humans.
Scientists were amazed when they learned how quickly some biochemical processes occur in plants.
Several leaves of a plant were placed in a plexiglass box, a certain amount of carbon dioxide, radioactive in carbon, was introduced into it and the plant was left in sunlight. As a result of the processes of photosynthesis, carbon dioxide was absorbed, turned into organic matter and transported to various parts of the plant. At regular intervals, samples were taken and measured radioactivity And it turned out that the speed of movement of newly synthesized compounds with an ascending current is very significant: even in sunlight - 50-100 centimeters per minute. Previously, it was believed that all the carbon in organic substances is formed naturally from carbon dioxide in the air, although there are hundredths of it only relatively recently, with the help of labeled atoms, it was possible to prove that carbon dioxide and carbonic acid salts contained in the soil are intense.
Radioactive phosphorus can be used to tag insects and plants.
used by the plant. They are actively transported from roots to leaves. There, as a result of photosynthesis, carbohydrates are formed from them and organic substances are synthesized. And from here followed a practically important conclusion: to increase productivity, it is necessary to enrich the soil with carbon dioxide - add carbonic acid salts to the soil. You can also add so-called green fertilizers to the soil. For example, plow in perennial grasses. After about 20-30 days, the release of carbon dioxide begins, which continues throughout the summer.
Thus, the use of the radioactive tracer method turned out to be useful for the science of plant fertilizers.
What and how is it more profitable to feed plants? When? In what form should fertilizer be applied? How are they affected by climatic conditions? How are they transported in plants and where are they absorbed?
Phosphorus-labeled superphosphate, hydroxyapatite and other fertilizers were added to the soil. And it turned out that 2.5 months after planting, corn absorbed phosphorus best from tricalcium phosphate, worse from superphosphate, and even worse from hydroxyapatite. It was found that cotton especially needs phosphorus feeding at the age of 10-20 days and during flowering.
With the help of labeled atoms, the role of microelements - cobalt, manganese, zinc, copper - in the life of plants was determined. It is enough, for example, to add 1-3 kilograms of boron per hectare of arable land to the soil, and the yield of clover will increase sharply. Manganese increases the yield of sugar beets, copper sulfate increases the yield of grain on peat soils.
Once, at a lecture on radiation biochemistry, a student from the Faculty of Biology at Moscow University approached me. She complained that in our time the impossibility of a miracle has been proven. “There was some hope,” she said, “when reports appeared in the press about the existence of “Bigfoot” or the assumption that it was not the Tunguska meteorite that fell to Earth, but a spaceship from unknown planets of an unearthly civilization. So no to you! Meticulous scientists quickly proved that this cannot be.”
But didn't researchers find a small miracle when they discovered that individual trees in a forest can exchange nutrients with each other through fused roots? In an oak grove, radioactive potassium bromide introduced into a tree was found in five nearby oak trees after 3 days!
Chemical compounds labeled with radioactive carbon, phosphorus, and sulfur are especially often used. And of course, microelements and compounds such as potassium, sodium, iron... But you need to have a good understanding of the research problem in order to choose the right radioisotope. For example, the half-life of radioactive carbon C is about 6000 years. This radioisotope is too “young” for studying geological processes , but it is indispensable for studying metabolic processes in animals.
Using radioactive carbon, you can find out what nutritional conditions are necessary to achieve maximum animal productivity or how nutritious feed is digested and what needs to be introduced into the diet of cows to increase milk yield.
Without a good theory there can be no good practice. The possibilities of the method of radioactive isotopes for solving the most complex theoretical questions of biochemistry, physiology, and biophysics are limitless. A scientist in one working day will not have time to read even the headlines of articles and studies that talk about the use of radioactive isotopes for various biological purposes Even specialists are often surprised by studies that use labeled atoms.
Sometimes complex biological problems are solved simply. Sometimes it’s the other way around: a seemingly simple biological phenomenon is deciphered through many years of painstaking work
For example, from what component, simplest parts is cow’s milk formed and in what tissues?
The question sounds simple, but answering it required the efforts of many dozens of scientists over many years.
Three quarters of a century ago, only a few people knew about the existence of radioactive isotopes. Today, “useful radiation” has become the property of millions of people. Albert Einstein said: “The phenomena of radioactivity are the most revolutionary force in technological progress since prehistoric man discovered fire.”
Evgeny Romantsev. "Born by an Atom"
EFFECT OF RADIATION ON PLANTS Our planet is constantly bombarded by an incalculable number of particles invisible to the eye, coming from the depths of the Universe. When these particles enter any substance, they cause the formation of ions 1 in it, therefore they are called ionizing, and the entire flow of such particles falling on the Earth is called ionizing radiation (radiation). Under artificial conditions, ionizing radiation is obtained during the operation of the well-known X-ray machine, as well as in nuclear reactors, where atoms are bombarded with neutrons.
The Universe around us contains colossal sources of ionizing radiation. These are the so-called “hot stars”. An example of such a star is our Sun, which is a natural atomic reactor. It constantly undergoes decay processes with the release of enormous amounts of energy in the form of alpha, beta, gamma, x-rays 2, neutron and proton particles. Scientists have come up with interesting ways to detect the path taken by ionizing particles. One of them is that highly humidified air is pumped into a cloud chamber - a small metal box with a glass lid and bottom. An ionizing particle flying through the chamber causes the formation of water droplets along its path, since the air atoms ionized by the particle become condensation centers. This makes the particle's path visible and can be photographed. Another way is even simpler. Flying particles leave a mark on the photographic plate,
Path formation scheme
ionizing particle in
Wilson chamber.
Emulsion method for detecting the path of ionizing particles.
Coated with a thick layer of special emulsion. Thus, the particles themselves photograph their path or the place of collision with other particles. The number of ions formed per 1 micron of particle travel, as well as the energy that the particle loses along its path, serves as an important indicator for each type of ionizing particle.
The difference in the action of neutrons ( A) and X-rays (b) for barley seedlings: in the frames - non-irradiated plants, outside the frames - seedlings with a gradual increase in the radiation dose.
Numerous experiments have shown that ionization density is of great importance for determining the biological reaction when irradiating animals and plants. For example, beta
1 An ion is the part of a molecule that carries an electrical charge.
2 Alpha, beta, gamma, X-rays are different types of radiation.
particles stimulate plant growth, but alpha particles do not have such an effect. Look at the picture, which shows the effect of two types of radiation on barley seedlings - X-rays and neutrons. If, under the influence of neutrons, the height of the seedlings uniformly decreases with increasing irradiation dose, then under the influence of X-rays, the seedlings react differently. It has now been clarified that, despite many common features inherent in ionizing particles, the nature of the changes they cause largely depends on the type of ionizing radiation, the duration of irradiation, the number of particles per second entering the plant, and, finally, on the phase of plant development.
The amount of ionizing radiation is measured in special units called roentgens in honor of the famous scientist Roentgen, abbreviated as R.
HUNTERS FOR... ONE PERCENT
After the discovery of ionizing radiation, radiobiologists discovered that irradiation causes various changes in plant cells and tissues. Thus, under the influence of large doses of radiation, the shape and color of leaves and flowers changes, and growth is suppressed. At the same time, it was noted that medium and low doses of radiation, on the contrary, help accelerate plant growth. Such stimulation increases the yield of many crops, reduces ripening time, increases the sugar content of fruits, etc.
Each plant is sensitive to ionizing radiation in its own way. This sensitivity varies depending on the developmental phase. For example, to increase productivity and enhance the growth of wheat and barley, their seedlings are irradiated with X-rays at 400-750 R. If we take dry seeds of these crops, they require a 10-30 times higher dose of radiation. When dry wheat seeds were irradiated, small, dwarf plants appeared along with giant plants. At the same time, the ears of the giants were large, but loose, while the ears of the dwarfs were very valuable for breeding purposes - dense and compact.
Thus, the changes that occur in plants when their seeds or seedlings are irradiated may be useful to plant breeders. It is possible to select forms that are characterized by high yield, straw strength, increased protein content in seeds, and the size of grains and fruits. When these new forms are crossed with each other, plants will be obtained that will have many valuable properties and characteristics. True, out of one hundred percent of the changes that occur in plants, only one percent turns out to be valuable to breeders. Hundreds of researchers around the world irradiate plants in the hope of getting that coveted one percent. When luck comes, the researcher is rewarded with varieties and forms of plants with unusually valuable properties.
Radiobiology has given researchers a new method of loosening hereditary properties, obtaining dramatically changed plants,
Various forms of ears of winter wheat that appeared after irradiation of seeds with gamma rays and fast neutrons: 1 - original variety; 2- 18 - hereditarily modified ears. (From the work of V. F. Mozhaeva, V. V. Khvostova and G. D. Lapchenko.)
ranging from useless deformities to plants with such amazing properties that they could not be obtained at all in any other way. True, this required a lot of work.
Anyone who thinks that the plant breeder’s selection work is just pollination of flowers is very mistaken.
DO YOU NEED A CONCRETE WALL WHEN GROWING PEAS AND APPLES
If you ask a similar question to a person unfamiliar with the successes and achievements of radiobiology, he will probably shrug his shoulders in bewilderment.
But these days such amazing fields exist. Moreover, they are not only fenced at times by a high concrete wall, but also surrounded by two rows of barbed wire and equipped with shields with a menacing inscription: “Danger to life! Radioactivity!" This is a gamma field. It received this name because it contains a source that emits gamma rays.
How is this field structured? A radioactive source is installed in the middle of a large fenced area. It is a two-meter column, on top of which in a special tube there is radioactive cobalt emitting gamma rays - Co 60. Various crops are planted on the field in a radial direction, from seedlings to mature plants: wheat, rye, barley, peas, vetch, black currants and other shrubs, as well as apple trees and pears of various ages. All these plants are irradiated for a long time, receiving different doses of radiation. It was in this gamma field that scientists managed, for example, to obtain high-yielding barley with strong straw and disease-resistant. In apple trees irradiated in the field, the size and color of the fruits, etc., changed.
Ionizing radiation is now also used in floriculture. Irradiation of tulips and hyacinths gave very interesting results - flowers appeared with unusual colors and with changed petals.
But why a concrete wall, barbed wire and billboards with menacing inscriptions? The fact is that radioactive radiation is dangerous to human life, and therefore all safety measures are taken at the gamma field. When researchers come to the field at the end of the year to collect plant material, fruits and seeds, the cobalt source is automatically closed with lead shields and, using a special device, is lowered into a deep underground well - a steel pipe filled with mineral oil. In this form, it is not dangerous to researchers.
WHAT IS RADIO STIMULATION
Immediately after the discovery of ionizing particles, scientists discovered that large doses of radiation are harmful to plants, while small doses, on the contrary, stimulate them. The stimulating effect of ionizing radiation (radiostimulation) means that plants are better
A - schematic plan of the gamma field; B- type of irradiated plants in gamma-field plots.
develop, they accumulate more chlorophyll, the main pigment necessary for photosynthesis. They become stronger and better withstand unfavorable climatic conditions. Stimulation affects not only plants, but also their seeds. For example, under the influence of low doses of radiation, plant yields increased. If you take seeds from these plants and sow them next year, they will also produce an increased yield. Currently, much work is being done to clarify the reasons that lead to radiostimulation. There is reason to believe that the main reason for radiostimulation is that very rapid cell division occurs in the tissues of irradiated plants, associated with the accelerated formation of deoxyribonucleic acid in the cell nuclei.
True, some scientists explain radiostimulation simply by the chemical effect of radioactive substances or impurities contained in them. Other researchers did not receive radio stimulation at all in their experiments. Thus, there is still a lot of work to be done to clarify all the changes that ionizing radiation causes when exposed to a living organism.
In connection with experiments on plant irradiation, interesting phenomena were discovered. In the same pots, the scientists grew irradiated and non-irradiated cucumber and radish seedlings. It turned out that when grown together, not only irradiated but also non-irradiated plants slow down their growth! This means that irradiated plants affect non-irradiated ones.
Inhibition of the growth of non-irradiated plants when grown together with irradiated ones is observed when the latter are exposed to doses of 150 R(for beans), 2-5 thousand. R(for cucumbers and radishes). When plants are irradiated with large doses (50 thousand R) they no longer inhibit the growth of non-irradiated plants grown next to them. Scientists do not yet know why this happens. But there is no doubt that the solution to the mystery is close.
The study of the effect of ionizing radiation on the movements made by plant leaves turned out to be interesting. Probably, few people know that plant leaves make certain movements - they rise and fall and can even turn around their axis, as if twisting. True, it is quite difficult to see this, because the movements are very slow. But if the plants
Schematic representation of the position of plant leaves at different times of the day: a - leaf movement under normal conditions; b- leaf movement after irradiation.
By taking photographs throughout the day at certain intervals and then viewing the film, the movement of the leaves becomes clearly visible. The perilla oleifera plant was irradiated with gamma rays. At doses of 5 thousand. R the movement of its leaves was weakened at doses of 50 thousand. R became barely noticeable, and at doses of 100 thousand. R stopped completely. Plant growth stops, but there are no other external signs of damage. They remain green and viable.
Scientists immediately try to put any data obtained as a result of painstaking research work at the service of man. We have already said that irradiation
Diagram of an industrial installation for irradiating food products with radioactive cobalt: 1 - pool for loading the emitter; 2 - a trench through which the radiation source is transmitted to the working pool; 3 - pool for storing the radiation source in an inoperative state; 4 - cassettes with radioactive cobalt; 5 - a basket with irradiated products moving on a chain conveyor; 6 - chain conveyor; 7 - rotary sprockets; 8 - place for loading baskets with products. Bottom left - non-irradiated potatoes, right - irradiated.
It stops plant growth. This property is now used for storing agricultural products: onions, potatoes, etc. Potato tubers, as is known, begin the germination process after a 5-6-month dormant period. If timely measures are not taken, the tuber will disappear. And this is where radiobiology comes to the aid of business executives, skillfully using the biological effect of ionizing radiation. A source of gamma rays is installed in potato storage facilities - a steel tube containing radioactive cobalt (similar to how it is described for a gamma field, only with a lower radiation intensity). Irradiation leads to the fact that potato tubers do not germinate and are preserved for a long time, and they do not lose their taste and nutritional properties.
There is another important area of application of ionizing radiation. It is very important that the products we receive are largely free of germs. For this purpose, products are sterilized using ionizing radiation. At the same time, fruits, for example, spoil less and go on sale fresh, as if they had just been picked from the branch.
This is how the achievements of science serve people and make their work easier.
PLANTS AND MAGNET
More than 100 years ago, the famous English scientist M. Faraday showed that all substances have magnetic properties, only they are expressed to varying degrees.
These properties are most pronounced in iron, cobalt, nickel and some alloys; for other substances they are so weak that they can be installed and measured only with the help of a special device called a magnetic torsion balance.
It is quite easy to verify that the magnetic field also affects the plant. Let's take a dry barberry leaf and hang it between the poles of a strong electromagnet, closer to one of them. When we then turn on or off the current flowing through the electromagnet coil, we will see how the sheet shudders and is pulled into the gap or, conversely, is pushed out of it (see figure on page 119).
If any substances are attracted to the region of the strongest magnetic field, they are called paramagnetic; if pushed out, they are called diamagnetic.
It turned out that the magnetic properties of a plant object largely depend on how much water it contains. A dry apple, for example, is always diamagnetic, but a raw apple can be either diamagnetic or paramagnetic.
The magnetic field can be homogeneous or inhomogeneous. In the first case, the intensity does not change within the field volume being studied, and in the second - at different points of this
When a very strong magnetic field is turned on, the barberry leaf shudders and is pulled into the gap between the poles.
The fields are different. In a non-uniform field, paramagnetic substances are attracted to the point of greatest field strength, and diamagnetic substances are repelled. This reaction of substances to a non-uniform magnetic field is a magneto-mechanical reaction. English scientists studied this reaction in the root tips of watercress seedlings placed in a strong, non-uniform magnetic field. Under a microscope, they saw how the starch grains present in the cell, under the influence of a magnetic field, shifted in the protoplasm of the cell in the area of least unevenness and field strength. Under the influence of irritation caused by their pressure, this part of the cell slowed down its growth. Moreover, the tip of the root, as if trying to escape the magnetic field, began to bend in the same direction.
Scientists called the reaction to a non-uniform magnetic field described by us magnetotropic, and the phenomenon itself - magnetotropism.
Well, what happens if the magnetic field is uniform within the boundaries of the object under study? Russian scientists became interested in this issue. They showed that a constant magnetic field affects biocurrents and biochemical reactions in the cell.
The multilateral effect of a magnetic field on a plant cell is expressed in the fact that with different orientations of the cell in the magnetic field, the speed of movement of the protoplasm and the particles and organelles of the cell in it changes differently. (Organelles are parts of the cell that perform various vital functions.) It is theoretically calculated that in 75 cases the magnetic field should inhibit the movement of protoplasm; In fact, scientists have established that it is inhibited in 79 cases.
The cell is especially sensitive to the action of the magnetic field during division and growth. Therefore, the most susceptible to a magnetic field are the young, intensively growing parts of plants - the root tip and the first leaf of cereals, the so-called coleoptile.
The effect of a constant magnetic field on the growth of the root system in plants is now most well studied. It is known that the tip of the root of many plants, such as peas, makes small oscillatory movements relative to its axis during growth. As experiments show, in a strong magnetic field (10 thousand oersteds1) these movements are significantly disrupted: rotational movements appear, the angles of deviation of the root tip from the axis increase. For a long time, scientists in their experiments observed how the growth of the root in such a field slowed down both in length and thickness. Large magnetic fields also had an effect on plant respiration, for example: pea seedlings placed in a magnetic field of 10 thousand oersteds reduced the release of carbon dioxide by almost 25%.
But it is still wrong to think that only a strong magnetic field has a noticeable effect on the plant. Often everything happens quite the opposite. For example, observing the root of a wheat seedling with a horizontal microscope 2 at magnetic field strengths of 60 and 1600 oersteds, one can see that in the first case the field stimulates root growth, and in the second it does not affect it at all. The question quite naturally arises: what is the lower limit of magnetic field strength that can cause a reaction on the part of the plant?
For a long time, there was an assumption in science that the earth's magnetic field is not indifferent to plant growth. And just recently, in 1960, Soviet plant physiologists A.V. Krylov and G.A. Tarakanova were able to show how germinating seeds of corn and wheat of certain varieties react to orientation relative to the poles of the Earth’s magnetic field. Thus, they established that when planting the embryo facing the south
1 Oersted is a unit of magnetic field strength. One oersted is a field strength that is approximately 2 times stronger than the strength of the earth's magnetic field in the Moscow region.
2 A microscope is called horizontal because its tube and the entire magnifying system are located in a horizontal plane. It is used to study the growth rate of stem tips or roots.
Schematic representation of the root system of wheat variety Kharkov, oriented along the earth's magnetic meridian (it does not coincide with the geographic meridian) in the north-south direction: 1 - side view; 2 - top view.
Seeds germinate faster towards the Earth's magnetic pole. The root system of such a seedling develops much more intensively than that of a seed that, when planted, was facing the north magnetic pole of the Earth. Thus, it can be considered proven that the plant not only reacts to the Earth’s magnetic field, the intensity of which in our latitudes is 0.5 oersted, but also distinguishes the direction of the earth’s magnetic field lines.
Canadian scientists have established that adult wheat plants of the Kharkov variety place their root system in the soil along a north-south line. According to other authors, the roots of some varieties of sugar beets are located along the west-east line. This means that plants respond differently to the Earth's magnetic field and that the nature of this response is a genetic trait. It is too early to say what explains this reaction and what its significance is for the plant world. Scientists have just begun to work in this direction. In some cases, the reaction of choosing a certain direction or preferential growth towards one pole was also observed in an artificial magnetic field. In 1958, the results of the work of scientists who observed the growth of bean roots in a magnetic field were published. If the tip of the root of this plant was directed towards the northern end of the magnetic field, then the field had no effect on its growth. On the contrary, the orientation of the root apex towards the south magnetic pole inhibited root growth.
These observations once again confirmed the importance of further studying the reaction of plants to the poles of a magnet, which, apparently, varies from plant to plant.
Why is it necessary to study the effect of a magnetic field on plants?
The magnetic field is one of the constantly present environmental factors. However, it is safe to say that this is also one of the least studied factors in terms of its influence on plants, animals and humans. When, with the further exploration of outer space and the development of technology, human life for some period of time will take place in magnetic fields thousands of times stronger than the earth’s, he should already know how the field acts on biological objects, including plants (see Art. . "Space biology"). But even the “small” earth’s magnetic field can be of practical interest to him in the field of agriculture.
The roots of some varieties of sugar beets are located along the west-east line: 1 - top view, 2 - side view.
Production. If it turns out that the location of the root systems of some agricultural plants is largely determined by the Earth’s magnetic field, then, apparently, we will have to take this factor into account both when applying fertilizers and when breeding new varieties.
HOW PLANTS COMBAT DROUGHT AND SOIL SALINIZATION
The climate on the vast territory of our Motherland is very diverse. In the North in winter, frosts reach 60° or more, and in the deserts of Central Asia in the summer the temperature in the shade is over 50°. In the area of Batumi on the Black Sea coast, about 2000 falls mm precipitation per year, and in the deserts of Turkmenistan it falls a little more than 100 mm, i.e. 20 times less.
In most regions of Central Asia, agriculture is impossible without irrigation. Agricultural plants here suffer from drought, that is, they are damaged by a lack of water in the soil and by too dry and hot air.
At the same time, in deserts there are many wild plants that have adapted to these harsh conditions and grow and develop well. It helps them to endure severe drought and successfully fight it
Many steppe plants obtain water through their root system, which goes deep into the soil: on the left - the root of falcaria; on the right is sage root.
Veronica incana root.
a number of properties, or, as biologists say, adaptations. These properties in desert plants did not arise immediately, but over a very long time.
Many thousands of generations have changed, many of the emerging species have died. Only those plant species survived that, under the influence of environmental conditions, through the process of natural selection, developed properties that helped them fight drought.
Plants that tolerate drought well are found not only in deserts, but also in steppes. In the steppes there is more precipitation (300-350 mm per year), but in summer there is almost always, even for a short period of time, drought. Plants that tolerate drought well are called xerophytes (from the Greek words “xeros” - dry and “phyton” - plant). In what ways do xerophytes fight drought?
The most interesting xerophytes are cacti, inhabitants of the deserts of North and Central America. Cacti are well known to us; they are bred by indoor plant lovers. Academician N.A. Maksimov successfully called cacti “hoarding” plants. Indeed, during the rainy season, cacti store water in their stems, absorbing it through a highly branched root system that lies shallow in the soil. Their leaves changed and became thorny. Cacti are covered with thick cuticles and use water very sparingly. At the same time, they are resistant to high temperatures. Many cacti can tolerate heating of their tissues up to 62° and even slightly higher without much harm. These are the most heat-tolerant flowering plants on Earth.
In addition to cacti that store water in their stems, there are plants that store water in their leaves. These include the well-known houseplant aloe. It grows wild in the South African deserts. In the middle zone of our country, a small plant called sedum, blooming with golden-yellow flowers, grows on sandy soil.
The leaves of sedum are fleshy, with reserves of water that the plant uses in the absence of rain.
Many shrubs and small trees in the deserts of Central Asia obtain water using a root system that goes deep into the soil.
Among the browned vegetation of the sun-scorched clayey Central Asian desert, bright green bushes with very small leaves and a mass of thorns stand out. This is camel thorn, or yantak, as the local population calls it. The tissues of camel thorn contain a lot of sugar, but only the unpretentious camel feeds on it. Even the donkey refuses to eat it. Why does camel thorn thrive when most other desert plants die from drought? The fact is that the long thorn root reaches the groundwater - to the depth
10-20 m. When they were digging the Suez Canal, a camel thorn root was found in one place at a depth of 33 m. That is why the thorn does not lack water. By evaporating water, it cools its tissues and can withstand high air temperatures.
In our steppes there is a small plant from the umbrella family - falcaria (cutter). Just like camel thorn, falcaria is supplied with water through the root system, penetrating the soil 5-6 m.
Plants have other ways of dealing with drought. In the sandy deserts of the Middle
Falkaria.
In Asia there are twig-shaped juzgun (calligonum) bushes. Its leaves have grown together with the stems. The leaf surface of juzgun is smaller than that of other plants, and therefore the evaporation of water is small.
In the Western Siberian steppe, a small bluish plant attracts attention - Veronica incana. Its stem and leaves are covered with hairs. These hairs quickly die and fill with air. The air is bad
Annual desert ephemera.
It allows heat to pass through, and therefore Veronica Incana is not so heated by the sun's rays. In addition, Veronica tolerates drying out relatively easily. It can lose up to 60% of its water content and still survive a drought. Gray wormwood has the same properties.
In the steppes, during and after rain, you can notice small dark green lumps of blue-green nostok algae on the soil surface. When there is no rain, the nostok dries out, becoming a small dry brownish-gray crust that is difficult to notice. In this form, nostok tolerates drought, and grows and develops after rain and in the fall.
In the clay deserts of Central Asia in early spring, the soil is almost completely covered with ephemerals (from the Greek word “ephemeros” - one-day) - plants from various families: cereals, cruciferous plants, poppy plants, etc. These plants fight drought as
would overtake it: they have very rapid development. In spring, there is moisture in the desert soil and the air temperature is moderate. Ephemera use this and quickly finish their growth and de-drinking. In 5-6 weeks they manage to bloom and produce seeds, which will lie in dry soil until next spring.
In addition to annual ephemerals, there are also perennial ephemerals in the desert. Ephemeroids include tulips growing in steppes and deserts, sand sedge and a number of other plants. They survive drought by producing rhizomes, tubers and bulbs. All these parts of plants are located in the soil and are protected from water loss by special covers. Ephemeroids, like ephemerals, manage to bear offspring (seeds) in the spring. When drought comes, they are no longer afraid of it.
Do not think that xerophytes are found only in steppes and deserts. They exist in the middle zone, and even in the northern part of our Union. In a white-moss pine forest, on a hot summer day, dried bushes of lichen - the so-called reindeer moss, or reindeer moss - crunch underfoot. Like almost all lichens, moss tolerates drying out well, and after rain begins to grow again.
No less interesting than xerophytes is the group of halophyte plants (from the Greek word “hals” - salt). They grow on saline soil: along the coasts of the seas or in arid climates (in the zone of steppes, semi-deserts and deserts). In an arid climate, water evaporates strongly from the soil surface, and the salts dissolved in it (table salt, sodium sulfate, soda, etc.) rise to the top with the water and remain in the soil. This is how salt marshes are formed, on which only halophytes can grow. Usually in the very center of the salt marsh, where the salinity is most severe, there are no plants at all, but only “bleaching” of salts. Is it around?
Halophyte Soleros: 1 - general view; 2 - twig; 3 - cross section of a branch.
Soleros develops better on saline soil. In the vessel on the left the soil is non-saline; in the vessel on the right - salted. Plants were planted at the same time.
Plants not adapted to salinity develop poorly in salty soil. In both vessels, cotton was sown at the same time: in the vessel on the left the soil is non-saline, in the vessel on the right it is saline.
Neck vegetation spots, where there is less salt, settles the most salt-loving plant in the world - saltwort. The appearance of the saltwort is unusual. This is a small annual herbaceous plant, with a height of 10 to 30 cm. It consists of individual segments, thick and fleshy. Each such segment represents a stem fused with a leaf. Saltweed accumulates salts inside its tissues. When there are too many salts in the tissue, individual segments fall off. This is how the saltwort protects itself from excess salts inside its body. Side by side with the saltwort grows sweda, which has a stem and thick fleshy leaves. It is less resistant to soil salinity than saltwort. Kermek, which has a basal rosette, combats salinity in a slightly different way.
Introduction
Bibliography
INTRODUCTION
During the radioactive decay of nuclei, α-, β- and γ-rays are emitted, which have ionization ability. The irradiated medium is partially ionized by the absorbed rays. These rays interact with the atoms of the irradiated substance, which leads to the excitation of atoms and the ejection of individual electrons from their electron shells. As a result, the atom turns into a positively charged ion (primary ionization). The knocked-out electrons, in turn, themselves interact with oncoming atoms, causing secondary ionization. The electrons, having spent all their energy, “stick” to neutral atoms, forming negatively charged ions. The number of pairs of ions created in a substance by ionizing rays per unit path length is called specific ionization, and the distance traveled by the ionizing particle from the place of its formation to the place where the energy of motion is lost is called run length.
The ionizing ability of different rays is not the same. It is highest for alpha rays. Beta rays cause less ionization of matter. Gamma rays have the lowest ionization ability. The penetrating ability is highest for gamma rays, and the lowest for alpha rays.
Not all substances absorb rays equally. Lead, concrete and water have a high absorption capacity, which are most often used for protection against ionizing radiation.
1 Factors determining the response of plants to irradiation
The degree of damage to tissues and the plant organism as a whole depends on many factors, which can be divided into three main groups: genetic, physiological and environmental conditions. Genetic factors include species and varietal characteristics of a plant organism, which are mainly determined by cytogenetic indicators (size of the nucleus, chromosomes and amount of DNA). Cytogenetic characteristics - the size of the nuclei, the number and structure of chromosomes - determine the radioresistance of plants, which is closely dependent on the volume of cell nuclei. Physiological factors include phases and stages of plant development at the start of irradiation, growth rate and metabolism of the plant organism. Environmental factors include weather and climatic conditions during the irradiation period, conditions of mineral nutrition of plants, etc.
The volume of the cell nucleus reflects the DNA content in it, and there is a relationship between the sensitivity of plants to radiation and the amount of DNA in the nuclei of their cells. Since the ionization number inside the nucleus is proportional to its volume, the larger the volume of the nucleus, the more chromosome damage will occur per unit dose. However, there is no inverse proportional relationship between the lethal dose and nuclear volume. This is due to the fact that the number and structure of chromosomes in plant cells of different species is not the same. Therefore, a more accurate indicator of radiosensitivity is the nuclear volume per chromosome, i.e., the ratio of the nuclear volume in interphase to the number of chromosomes in somatic cells (briefly called chromosome volume). On a logarithmic scale, this dependence is expressed as a straight line with a slope equal to 1, i.e., there is a linear relationship between these characteristics (Fig.).
Radiosensitivity of various plants under chronic irradiation (according to A. Sparrow)
Dependence of radiosensitivity of woody (a) and herbaceous (b) plants on the volume of interphase chromosomes (according to Sparrow, 1965): 1-acute irradiation (exposure in P); 2 - chronic radiation (exposure in R/day)
It follows from this that the product of two quantities - the dose (or dose rate) and the volume of the chromosome for a given degree of radiation damage - is a constant value, i.e., with a constant average ionization number in each chromosome, the same probability of damage to the genetic material of the cell appears. This means that for radiation damage to plant cells, it is not so much the value of the specific absorbed dose (for example, per 1 g of tissue) that is important, but rather the amount of radiation energy absorbed by the nuclear apparatus. The inverse proportionality of isoeffective doses to the size of the chromosomal apparatus means that the average amount of energy adsorbed by chromosomes at the exposures necessary to cause a given effect is approximately constant within each plant group, i.e., for trees and grasses. Isoeffective dose- a dose that has the same (similar) effect.
The resistance of plants to irradiation is also influenced by the degree of ploidy of plant organisms. Diploid species are more sensitive. Doses damaging polyploid species are higher. Polyploid species are resistant to radiation damage and other unfavorable factors because they have an excess of DNA.
Of the physiological factors, the radiosensitivity of plants is influenced by the growth rate, i.e., the rate of cell division. During acute irradiation, the dependence of radiosensitivity on the rate of division obeys the Bergonier-Tribondo law: plants have greater radiosensitivity at the stage of the most intensive growth; slowly growing plants or their individual tissues are more resistant to radiation than plants or tissues with accelerated growth. With chronic irradiation, an inverse relationship appears: the higher the growth rate, the less the plants are inhibited. This is due to the intensity of cell division. Rapidly dividing cells accumulate a smaller dose during one act of the cell cycle and, therefore, are less damaged. Such cells are more able to withstand radiation without significant functional impairment. Therefore, when irradiated at sublethal doses, any factor that increases the duration of mitosis or meiosis should enhance radiation damage, causing an increase in the frequency of radiation-induced chromosomal rearrangements and a stronger inhibition of growth rate.
Criterion for the effect of ionizing radiation on plants. Since radiosensitivity is a complex, complex phenomenon, determined by many factors, we should dwell on the assessment methods and criteria by which the degree of radiosensitivity of plants is judged. Typically, such criteria are used: suppression of mitotic activity during cell division, the percentage of damaged cells in the first mitosis, the number of chromosomal aberrations per cell, the percentage of seed germination, depression in plant growth and development, radiomorphosis, the percentage of chlorophyll mutations, plant survival and ultimately the result is a seed harvest. For practical assessment of the decrease in plant productivity from exposure to radiation, the last two criteria are usually used: plant survival and their yield.
Quantitative assessment of plant radiosensitivity according to the survival criterion is established by the LD50 indicator (or LD50, LD100). This is the dose value at which 50% (or 70, 100%) of all irradiated individuals die. The LD50 indicator can also be used to assess crop losses as a result of radiation damage to plants. In this case, it shows at what dose of radiation to plants their yield is reduced by 50%.
Radiosensitivity of plants at different periods of their development. During the process of growth and development, the radiosensitivity of plants changes significantly. This is due to the fact that during different periods of ontogenesis, plants differ not only in their morphological structure, but also in the different quality of cells and tissues, as well as in the physiological, biochemical processes characteristic of each period.
When plants are acutely irradiated during different periods of ontogenesis, they react differently depending on the stage of organogenesis at the start of irradiation (Fig.). Radiation causes damage to those organs in plants and a displacement of those processes that are formed and occur during the period of exposure. Depending on the magnitude of the radiation dose, these changes can be either stimulating or damaging.
Radiation damage to plants to one degree or another affects all organs and all functional systems of the body. The most sensitive “critical organs”, damage to which determines the development and result of radiation damage to plants, are meristematic and embryonic tissues. The qualitative nature of the response of plants to their irradiation depends on the biological specificity of the morphophysiological state of plants during the period of accumulation of the main radiation dose.
Fluctuations in plant radioresistance during ontogenesis (Batygin, Potapova, 1969)
In terms of damage to the main shoot, all crops show the greatest sensitivity to the effects of radiation in the first period of the growing season (stages I and III of organogenesis). Irradiation of plants during these periods inhibits growth processes and disrupts the mutual consistency of physiological functions that determine shape-forming processes. At irradiation doses exceeding their critical values for a particular crop (LD70), in all cases the death of the main shoot of cereal plants is observed.
If plants are exposed to irradiation at the early stages of organogenesis (I and V), additional shoots are formed, which, under favorable seasonal conditions, manage to reach maturity and produce a harvest that compensates, to one degree or another, for the losses associated with the death of the main shoot. Irradiation of plants at the VI stage of organogenesis - during the formation of pollen mother cells (meiosis) - can lead to significant sterility and loss of grain yield. A critical dose of radiation (for example, 3 kR for wheat, barley and peas) during this period causes complete sterility of the inflorescences of the main shoots. Additional tillering or branching shoots that develop in these plants at a relatively late time do not have time to complete their development cycle and cannot compensate for the loss of yield from the main shoots.
When plants are irradiated at the same VI stage of organogenesis during the formation of mononuclear pollen grains, the resistance to the action of ionizing radiation in plants increases significantly. For example, when wheat is irradiated with a dose of 3 kR during the period of meiosis, the grain yield is practically zero, while when plants are irradiated during the formation of mononuclear pollen, a 50% reduction in yield is observed. At subsequent stages of organogenesis, plant resistance to radiation increases even more. Irradiation of plants during flowering, embryogenesis and grain filling at the same doses does not cause a noticeable decrease in their productivity. Consequently, the most sensitive periods include seed germination and the transition of plants from a vegetative state to a generative state, when fruiting organs are formed. These periods are characterized by increased metabolic activity and high rates of cell division. Plants are most resistant to radiation during the period of ripening and during the period of physiological dormancy of seeds (table). Cereal crops are more radiosensitive during the booting, tillering and heading phases.
The survival of winter crops when irradiated in the autumn-winter-spring period increases noticeably when winter crops are sown at the earliest established dates. This is obviously explained by the fact that irradiated plants, going into winter stronger, in a state of full tillering, turn out to be more resistant to the effects of radiation.
A similar pattern of reduction in grain yield when plants are irradiated at different phases of development was also obtained for other crops. Grain legumes are most radiosensitive during the budding period. The most dramatic reduction in the yield of vegetable crops (cabbage, beets, carrots) and potatoes is observed when exposed to ionizing radiation during the germination period.
All grain crops have maximum radiosensitivity in the booting phase. Depending on the biological characteristics of plants, some differences are observed. Thus, oats exhibit maximum radiosensitivity at the end of the booting phase and during the period of panicle emergence.
Decrease in grain yield of winter grain crops (wheat, rye, barley) depending on plant irradiation with γ-rays at different phases of plant development, % of non-irradiated control
The negative effect of external γ-irradiation has less effect on the productivity of grain crops when they are irradiated in the tillering phase. When plants are partially damaged, increased tillering occurs and, in general, the reduction in yield is compensated by the formation of secondary tillering shoots. Irradiation of grain crops during milk ripeness does not cause a noticeable increase in the sterility of ears.
2 The effect of external ionizing radiation on the body
2.1 Options for possible radiation exposure
Sources of ionizing radiation (radionuclides) can be located outside the body and (or) inside it. If animals are exposed to radiation from the outside, then they talk about external irradiation, and the impact of ionizing radiation on organs and tissues from incorporated radionuclides is called internal irradiation. In real conditions, various options for both external and internal exposure are most often possible. These types of influences are called combined radiation injuries.
The external radiation dose is formed mainly due to the effect of γ-radiation; α- and β-radiation do not make a significant contribution to the total external irradiation of animals, since they are mainly absorbed by air or the epidermis of the skin. Radiation damage to the skin by β-particles is possible mainly when keeping livestock in open areas at the time of fallout of radioactive products of a nuclear explosion or other radioactive fallout.
The nature of external irradiation of animals may vary over time. Various options are possible one-time irradiation, where animals are exposed to radiation for a short period of time. In radiobiology, exposure to radiation for no more than 4 days is considered to be a single exposure. In all cases where animals are exposed to external irradiation intermittently (they may vary in duration), there is fractionated (intermittent) irradiation. With continuous long-term exposure to ionizing radiation on the animal body, they speak of prolonged irradiation.
Highlight the general (total) irradiation in which the entire body is exposed to radiation. This type of exposure occurs, for example, when animals live in areas contaminated with radioactive substances. In addition, under the conditions of special radiobiological studies, it can be carried out local irradiation, when one or another part of the body is exposed to radiation! With the same radiation dose, the most severe consequences are observed with general radiation. For example, when the entire body of animals is irradiated at a dose of 1500 R, almost 100% of their death is observed, while irradiation of a limited area of the body (head, limbs, thyroid gland, etc.) does not cause any serious consequences. In what follows, only the consequences of general external irradiation of animals are considered.
2.2 Effect of ionizing radiation on immunity
Low doses of radiation do not appear to have a noticeable effect on immunity. When animals are irradiated with sublethal and lethal doses, there is a sharp decrease in the body's resistance to infection, which is due to a number of factors, among which the most important role is played by: a sharp increase in the permeability of biological barriers (skin, respiratory tract, gastrointestinal tract, etc.), inhibition of the bactericidal properties of the skin , blood serum and tissues, a decrease in the concentration of lysozyme in saliva and blood, a sharp decrease in the number of leukocytes in the bloodstream, inhibition of the phagocytic system, unfavorable changes in the biological properties of microbes that constantly inhabit the body - an increase in their biochemical activity, increased pathogenic properties, increased resistance and etc.
Irradiation of animals in sublethal and lethal doses leads to the fact that a huge number of bacteria enter the blood and tissues from large microbial reservoirs (intestines, respiratory tract, skin)! In this case, a period of sterility is conventionally distinguished (its duration is one day), during which practically no microbes are detected in the tissues; the period of contamination of regional lymph nodes (usually coincides with the latent period); the bacteremic period (its duration is 4-7 days), which is characterized by the appearance of microbes in the blood and tissues, and, finally, the period of decompensation of protective mechanisms, during which there is a sharp increase in the number of microbes in organs, tissues and blood (this period occurs in a few days until the animals die).
Under the influence of large doses of radiation, causing partial or complete death of all irradiated animals, the body becomes defenseless against both endogenous (saprophytic) microflora and exogenous infections. It is believed that during the height of acute radiation sickness, both natural and artificial immunity are greatly weakened. However, there is data indicating a more favorable outcome of acute radiation sickness in animals that were immunized before exposure to ionizing radiation. At the same time, it has been experimentally established that vaccination of irradiated animals aggravates the course of acute radiation sickness, and for this reason it is contraindicated until the disease has resolved. On the contrary, several weeks after irradiation at sublethal doses, the production of antibodies is gradually restored, and therefore, already 1-2 months after radiation exposure, vaccination is quite acceptable.
2.3 Timing of death of animals after exposure to radiation in lethal doses
With a single irradiation of farm animals in doses that cause an extremely severe degree of acute radiation sickness (more than 1000 R), they usually die within the first week after radiation exposure. In all other cases, lethal outcomes of acute radiation sickness are most often observed within 30 days after exposure.1! Moreover, after a single irradiation, most of the animals die between the 15th and 28th days (Fig.); with fractionated irradiation with lethal doses, the death of animals occurs within two months after radiation exposure (Fig.).
As a rule, young animals die earlier after irradiation at lethal doses: animal mortality is usually observed on the 13-18th day. All age groups of animals irradiated at lethal doses are characterized by earlier death at the highest doses of radiation exposure (Fig.). However, this phenomenon can be regarded more as a trend than a pattern, since there is quite a lot of experimental data on the early stages of death of animals when irradiated with relatively low doses of radiation.
Mortality of sheep after external γ - irradiation with lethal doses (Peich et al., 1968)
Mortality of goats exposed to fractionated x-ray irradiation (Tylor et al., 1971)
It should be borne in mind that with fractionated irradiation, the timing of death of animals depends primarily on the dose rate. Thus, with daily irradiation of donkeys at a dose of 400 R, all animals died between the 5th and 10th days. In experiments where the daily radiation dose was 50 and 25 R, the average life expectancy after the onset of radiation exposure was 30 and 63 days, respectively. In addition, life expectancy is greatly influenced by the species characteristics of animals. With fractionated daily irradiation of pigs at a dose of 50 R, their average life expectancy was 205 days, which was 6.4 times higher than the average life expectancy of donkeys under the same conditions of radiation exposure.
Mortality of cows at various times after γ-irradiation (Brown et al., 1961)
2.4 Economically useful qualities of animals exposed to ionizing radiation
In principle, all farm animals exposed to ionizing radiation can be divided into two categories. The first category includes animals that have received lethal doses of radiation. Their lifespan from the moment of irradiation is relatively short, but in some situations the productivity of fatally affected animals may be of some interest.
The milk production of cows in the first 10-12 days after radiation exposure changes slightly, and then drops sharply, and already 2 days before the death of the animals, lactation completely stops. The meat productivity of animals, which is usually characterized by the dynamics of live weight, also changes slightly: the decrease in body weight in fatally affected animals (if it occurs), as a rule, does not exceed 5-10%. Egg laying in laying hens exposed to lethal doses of radiation stops within the next 5-7 days. There is no need to talk about the wool productivity of lethally affected sheep, since they experience intense hair removal 7-10 days after radiation exposure.
In animals that survive irradiation at lethal or sublethal doses (the second category), productivity decreases for a short time. For example, when cows were irradiated 60 days before calving at a dose of 400 R, their milk production during the first 10-12 weeks was 5-10% lower than the control. After repeated irradiation at a dose of 350 R 18 weeks after the start of lactation, milk yield decreased by 16% during the first week after irradiation, by 8% by the 5th week, and by the 6th week milk production 
The productivity of irradiated cows returned to normal. It can be tentatively assumed that irradiation of cows in doses that can cause partial death of the dairy herd leads to a decrease in milk yield as a whole during lactation by an average of 5-8%.
Other adverse effects have also been reported in surviving animals exposed to semi-lethal doses (or near them). Thus, after double irradiation of pigs (480 rad + 460 rad after 4 months), a decrease in weight gain was noted: 2 years after radiation exposure, irradiated animals had a body weight 45 kg lower than control pigs. The life expectancy of pigs is reduced by an average of 3% for every 100 rad of external irradiation of animals (Fig.). When White Leghorn chickens were irradiated at a dose of 800 R (the mortality rate of chickens was on average 20%), a noticeable decrease in egg production was observed (Fig.).
Radiation doses that cause acute radiation sickness of mild or moderate severity usually do not significantly affect the productivity of farm animals. For example, after external γ-irradiation at a dose of 240 R over the next 40 weeks, bulls had a body weight gain of 131 kg (118 kg in the control group). Pigs exposed to chronic irradiation at doses of 360-610 R (dose rate 1.4 R/h) had a fairly high average daily gain (500-540 g) during the entire irradiation period and the next 90 days of the experiment and did not differ in this indicator from control groups (approximately 470 g). A similar picture was observed with fractionated irradiation of pigs at a dose of 50 R/day. There was no decrease in egg laying in chickens after irradiation at a dose of 400 R, and at a dose of 600 R, egg laying decreased by approximately 20% only in the first decade after exposure.
Thus, when farm animals are irradiated in the sublethal dose range, no significant changes in their productive qualities are observed (if, of course, the animals are provided with normal living conditions and are provided with appropriate diets). When animals are irradiated with absolutely lethal doses, productivity decreases, but the quality of livestock products remains quite high. When animals are fed products obtained from sheep and cows fatally affected by radiation for a long time, no pathological changes are observed either in those consuming these products or in their offspring. However, when using products from radiation-affected animals for food, it is recommended to carry out particularly careful bacteriological studies and appropriate culinary processing.
2.5 Animal reproductive abilities
The gonads of animals are highly sensitive to the action of ionizing radiation. When males are irradiated with sublethal doses, radiation damage occurs to the seminiferous epithelium in the seminiferous tubules, as well as spermatogonia and spermatocytes; mature and formed sperm are considered radioresistant. High doses of radiation cause almost complete destruction of the spermatic epithelium and subsequent attenuation of sperm production, while irradiation of males with medium and low doses initially leads to a decrease in spermatogenesis, and then its gradual recovery is noted (Fig.). A decrease in the volume of ejaculate, a decrease in the concentration and mobility of sperm in the ejaculate, the appearance of a large number of ugly sperm, a decrease in the biological usefulness of sperm and its fertilizing ability are very characteristic. In addition, the weight of the testes decreases: when boars were γ-irradiated at a dose of 400 R, the weight of the testicles decreased by 30%, and when cockerels were irradiated at a dose of 500 R, it decreased by 3 times compared to the weight of the testes in control cockerels.
External influence γ - irradiation of chickens in a dose of 800 R on the egg production of surviving chickens (Maloniy, Mrats, 1969)
Sperm production of boars exposed to external γ-irradiation in sublethal doses (Paque et al., 1962).
Irradiation at a dose of 400 R in some boars causes long-term infertility (boar No. 5)
If the radiation doses are not too high, then over time there is a partial or complete restoration of reproductive function in males. In experiments on rams, for example, it was found that when irradiated at a dose of 100 R, the quality of sperm is restored after 4 months, and at a dose of 430 R - only after 12 months. Note that a similar restoration of sperm quality in irradiated boars and bulls was observed after 5 months, i.e. approximately twice as fast as in rams.
Ionizing radiation also affects the reproductive function of females. In irradiated animals, all types of cells of the functioning ovary (especially primary and secondary follicles, mature eggs) are damaged and partially die, and astral cycles are disrupted. It should, however, be borne in mind that soon after irradiation (even with moderate lethal doses), the reproductive function of females is restored and they can bear viable offspring. For example, there was no decrease in fertility in adult cows exposed to radiation twice (with a break of 2 years) at doses of 400 R.
The most severe consequences are observed when animals are exposed to ionizing radiation during their prenatal development. Most of the embryos die in the preimplantation period, i.e. during the period when the developing fertilized egg has not yet been introduced into the thickness of the uterine mucosa (in sheep and pigs - in the first 13, in cows - in the first 15 days after fertilization), or undergoes resorption (resorption) immediately after implantation. When pregnant animals are irradiated during the period of main organogenesis (in sheep - on the 17th-19th day, in pigs - on the 15th-18th day, in cows - on the 22nd-27th day) even with relatively low doses of radiation exposure (200- 300 R) in many cases, embryo resorption is possible, and surviving embryos experience growth retardation, developmental defects, increased neonatal mortality, and reduced life expectancy. For example, when pregnant females were irradiated on the 12-14th day of pregnancy at a dose of 400 R, cases of fused toes of the fore and hind limbs in the offspring were observed. When animals are irradiated in later stages of pregnancy, the radiosensitivity of the fetus decreases somewhat.
When studying the effects of ionizing radiation on the body during intrauterine development, an exceptionally high sensitivity of the fetal reproductive system to the effects of radiation was discovered. With chronic irradiation of sows during 108 days of pregnancy (γ-irradiation doses from 1 to 20 rad/day, daily irradiation duration of 22 hours), pregnancy in animals proceeded normally, the general condition of sows, the number of live piglets in the litter and their postpartum viability did not differ from the same indicators in control groups of animals. However, even when pregnant sows are irradiated at a dose of 1 rad/day, newborn piglets show a significant decrease in the total number of germ cells (in animals of both sexes). Thus, in boletus, the number of gonocytes (primary precursors of germ cells) was only 3% of the control, and in females, the number of surviving oocytes was equal to 7% of the oocytes of control pigs. Irradiation during the uterine period caused a decrease in sperm production (by 83%), an increase in the number of defective sperm from 2.8% (control) to 11.4 °/o, which resulted in infertility in 4 out of 10 boars. Despite a significant decrease in the number of primary and growing follicles in irradiated pigs, their reproductive abilities in the first litter were the same as in control animals, but upon repeated mating, infertility was established in 4 of 23 sows. Irradiation of pregnant sows at a dose of 0.25 rad/day has virtually no effect on the reproductive function of the offspring.
Bibliography
1. Annenkov B.N., Yudinneva E.V. Fundamentals of agricultural radiology. - M.: Agropromizdat, 1991. - 287 p.: ill.
2. Starkov V.D., Migunov V.I. Radiation ecology. Tyumen: FGU IPP "Tyumen", 2003, 304 p.
In general, plants are more resistant to radiation exposure than birds and mammals. Irradiation in small doses can stimulate the vital activity of plants - Figure 3 - seed germination, intensity of root growth, accumulation of green mass, etc. It should be noted that the dose curve shown in this figure is certainly repeated in experiments regarding a wide variety of plant properties for doses of radiation exposure , causing inhibition of processes. With regard to stimulation, the dose characteristics of the processes are not so obvious. In many cases, the manifestation of stimulation on living objects is not observed.
Figure 3 - Dependence of the number of sprouted eyes of a potato variety on the irradiation dose
Large doses (200 - 400 Gy) cause a decrease in plant survival, the appearance of deformities, mutations, and the occurrence of tumors. Disturbances in the growth and development of plants during irradiation are largely associated with changes in metabolism and the appearance of primary radiotoxins, which in small quantities stimulate vital activity, and in large quantities suppress and disrupt it. Thus, washing irradiated seeds within 24 hours after irradiation reduces the inhibitory effect by 50-70%.
In plants, radiation sickness occurs under the influence of various types of ionizing radiation. The most dangerous are alpha particles and neutrons, which disrupt nucleic acid, carbohydrate and fat metabolism in plants. Roots and young tissues are very sensitive to irradiation. A common symptom of radiation sickness is growth retardation. For example, in young plants of wheat, beans, corn and others, growth retardation is observed 20-30 hours after irradiation with a dose of more than 4 Gy. At the same time, various researchers have shown that irradiation of air-dried seeds of many crops with doses of 3-15 Gy not only does not lead to inhibition of plant growth and development, but, on the contrary, helps to accelerate many biochemical processes. This was expressed in accelerated development and increased productivity.
Species, varietal and individual intravarietal differences in the radiosensitivity of plants have been established. For example, symptoms of radiation sickness in tradescantia occur when it is irradiated with a dose of 40 r, in gladiolus - 6000 r. The lethal dose of radiation for most higher plants is 2000-3000 r (absorbed dose is about 20-30 Gy), and for lower plants, such as yeast, 30,000 r (300 Gy). Radiation sickness also increases the susceptibility of plants to infectious diseases. Affected plants cannot be used for food or livestock feed, as they can cause radiation sickness in humans and animals. Methods for protecting plants from radiation sickness have not been sufficiently developed.