BIOINORGANIC AND BIOORGANIC CHEMISTRY - M.V. Yatskov - 2014

III. NATURAL CATALYSTS, REGULATORS AND STIMULANTS OF BIOCHEMICAL PROCESSES

3.3. Plant Growth and Development Regulators

Plant HORMONES were discovered in the early 20th century and were named phytohormones or plant growth stimulants.

Phytohormones are organic, relatively low-molecular-weight endogenous compounds that facilitate communication between Cells, Tissues, and Organs, and are required in small quantities for the execution and regulation of physiological processes. All phytohormones share the following General characteristics:

1. First and foremost, they are low-molecular-weight compounds of a non-protein nature.

2. Phytohormones are present in tissues in a free, physiologically active state and at very low concentrations.

3. They diffuse freely from one Cell to another, enabling them to interact with various Cells and Tissues of the plant.

4. Phytohormones trigger and regulate entire physiological processes, such as Cell Division, ROOT formation, flowering, and others. Their General mechanism of action is based on interacting with regulatory substances in the membrane and directly with regulatory Proteins that ensure Gene function.

To date, about 5,000 compounds (of chemical, microbial, and plant origin) exhibiting regulatory activity have been discovered and studied, yet only about 50 are used in global practice. This indicates that their large-scale production and application are only just beginning.

Plant growth regulators are classified into:

stimulants - substances that directly promote the growth of seeds and plants;

defoliants - substances that induce premature leaf drop;

desiccants - substances that remove excess flowers and Ovaries;

retardants - substances that increase stem stiffness and lodging resistance in plants.

The most widespread Applications in domestic crop production have been found in preparations of natural origin, produced by cultivating microscopic Fungi under artificial conditions, as well as BIOLOGICALLY ACTIVE SUBSTANCES derived from The Root System of ginseng and other medicinal plants.

It is known that one of the primary Mechanisms of action of natural plant growth regulators (phytohormones) is the modification of cellular genome functioning, the acceleration of membrane transport processes, and the enhancement of the uptake of specific metabolites and nutrients into cells. Simultaneously, under their influence, The activity of the H⁺-pump and transport processes is enhanced, METABOLISM/31.html">Transcription processes are accelerated, and the synthesis of essential Biomacromolecules, such as RNA and proteins, is activated. All these molecular-level reactions form the basis for the intensification of physiological processes and cell division, and consequently, the integrated GROWTH AND DEVELOPMENT of plants.

The most common stimulants belong to three classes of Organic compounds: indolecarboxylic acids, kinins, and Gibberellins.

Indolecarboxylic acids include heteroauxin and its derivatives, meaning they are nitrogen-containing heterocyclic compounds.

Kinins comprise a series of unsaturated alcohols of the adenine group. Among synthetic analogues, the best known are kinetin (6-furfurylaminopurine) and auxin.

The most effective results are achieved through the combined use of two groups: gibberellins and kinins.

Gibberellins are isolated from certain fungi, with gibberellic acid being the most prominent among them.

The main component of most growth regulators is a balanced complex of natural growth substances—phytohormones of cytokinin and gibberellin origin, CARBOHYDRATES, Amino Acids, Fatty acids, and Trace Elements.

Modern plant growth regulators are natural or synthetic compounds used to treat plants in order to initiate changes in their life processes, improve the quality of plant material, increase crop yields, and facilitate harvesting and storage. The Use of growth regulators induces metabolic shifts similar to those caused by external environmental factors (day length, Temperature, etc.), which is crucially important under the conditions of low moisture availability in the southern steppe of Ukraine, where Water scarcity severely limits metabolic processes. In other words, growth regulators are not nutrients, but rather controlling factors for PLANT GROWTH AND Development.

The Role of auxin in plant physiological activity is vast and multifaceted. It participates in the Regulation of Cell division, elongation, and differentiation. Some authors believe that auxin's function is to create the conditions necessary for DNA Replication, thereby stimulating the synthesis of RNA and proteins. Auxin is also capable of influencing Photosynthesis, the Synthesis of Secondary metabolites, and the Transport of Assimilates and minerals throughout the plant.

The physiological activity of Cytokinins, much like that of Auxins, is polyfunctional. Cell division stimulation is the primary property of cytokinins. Numerous experiments on a wide range of plant subjects have clearly demonstrated the role of cytokinins as stimulators of cell division. In 1957, The Influence of cytokinins on cell growth was discovered. The activation of cell growth by cytokinins is closely linked to profound Structural and Biochemical changes within the cells: RNA and Protein Synthesis is intensified, the synthesis of numerous Enzymes is enhanced, chloroplast growth and division are stimulated, and The formation of the intracellular membrane system is promoted. Cytokinins play a vital role in increasing Plant resistance to adverse environmental factors, such as extreme temperature fluctuations, drought, high salt concentrations, chemical toxicity, and fungal and viral infections.

Regarding the mechanisms of cytokinin action, it has been established that they activate protein synthesis by enhancing the influx of metabolites required for Protein and RNA synthesis.

Gibberellins stimulate the activity of various plant microsystems. Alongside stimulating stem elongation, they enhance the growth of pedicels and pollen tubes, promote an increase in the size of flowers and inflorescences as well as the number of flower-bearing shoots, activate hydrolytic and several Other Enzymes, prolong the juvenile period, and induce flowering in long-day plants under short-day conditions, among other effects.

According to the Sanitary and hygienic Classification, novel growth regulators are classified as non-toxic substances. They exert a positive effect on plants by increasing germination energy and plant development, and they are rapidly degraded by soil microorganisms and plant cells.

The peat-manure fertilizer "Tonak", produced from peat and cattle manure, has also proven effective. It contains 1.6-1.8% N, 0.4-0.5% P₂O₅, and 0.4-0.5% K₂O. The peat-litter fertilizer "Konkurent" is just as effective as the aforementioned product. Its base consists of peat and poultry manure, containing 0.7% N, 0.6% P₂O₅, and 0.6% K₂O. This fertilizer helps increase humus content and improves the yields of vegetable, berry, and melon crops, while fostering The production of ecologically clean, high-quality produce. It is applied at a rate of 1 kg/m² with mandatory incorporation to a depth of 10-15 cm.

The peat-mineral fertilizer "Germafos", which is 2 to 3 times more effective than manure, also deserves attention. The addition of phosphorus and lime to its composition enhances the activity of microorganisms that decompose peat. These fertilizers are manufactured by the "Ukrtertorf" concern. In terms of effectiveness, such fertilizers approach the quality of manure and make it possible to rapidly reclaim poor and eroded soils: by increasing the humus content and nutrient levels, one can stably obtain high yields and significant profits. Other types of peat-based fertilizers are also available.

Of particular value is the growth stimulator Humate (potassium or sodium), which is a product of the interaction between peat and an aqueous solution of KOH or NaOH. When applied to the soil, it activates the vital activity of microorganisms that synthesize biologically active substances, facilitating better nutrient uptake and stimulating the synthesis of proteins, carbohydrates, and Vitamins. Furthermore, Humate accelerates crop ripening and enhances both yield and quality.

In addressing Structure/149.html">The problem of pulling the agro-industrial complex out of crisis, a crucial role belongs to the Introduction of next-generation plant growth regulators into agriculture, which are unparalleled globally in terms of their efficacy, ecological, and technological indicators. Scientific research and practical experience indicate that domestic biostimulants are capable of increasing the yield of major field crops by 10-30%.

Over the past decades, 53 biostimulants and 14 plant growth regulators have been approved for use in Ukraine. Modern biostimulating products require very low application rates, amounting to tens of grams or milligrams per ton of seeds or per hectare of crops.

One variety of plant growth and development biostimulants is "Vermistim", produced from vermicompost. It is a highly humified liquid substance containing humates, fulvic acids, amino acids, vitamins, natural phytohormones, micro- and macroelements, spores of soil microorganisms, and bacteriostatic proteins—components lacking in most other stimulators. It is used both for seed Treatment at a rate of 8-10 L/ha and for root and foliar feeding. Vermistim boosts plant Immunity to various diseases, frosts, and droughts, reduces the levels of nitrates, nitrites, heavy metals, and radionuclides, and improves taste qualities. Its positive effect is also reflected in the intensive growth of the root system.

Industrial production of 13 biostimulating products based on the developments of the "Interdepartmental Scientific and Technical Center 'Agrobiotech'" has been organized in Ukraine. Ukrainian plant growth regulators created within the framework of the Ministry of Industrial Policy's sectoral program include: Biolan, Biosil, Biomas, Radostym, Agrostimulin, Zeastimulin, Betastimulin, Charkou, Lucis, Treptolem, Ivin, and Poteitin. Biolan and Radostym have been approved for use in organic agriculture.

Between 1999 and 2008, our specialists tested over 60 physiologically active substances and developed advanced technologies for applying growth regulators to sunflower and soybean crops. The primary techniques include pre-sowing seed treatment and crop spraying during the 4-6 pairs of true leaves growth phase. Applying these technological Methods makes it possible to increase the yield of the aforementioned agricultural crops by 2 to 6 dt/ha.

In 2010, Seed Trade Company LLC registered new organic biostimulants based on plant amino acids, "Fertigrain Start" and "Fertigrain Foliar", intended for use on cereal and other field crops.

The biostimulant "Fertigrain Start" is designed for pre-sowing treatment of field crop seeds (cereal grains, oats, rice, corn, sunflowers, rapeseed, soybeans, peas), as well as pre-planting treatment of potato tubers. The product is applied directly to the seeds via dressing, including co-application with fungicidal and insecticidal seed dressings. The optimal application rate is 1 L per ton of seeds with a working solution consumption of 10 L/t.

Pre-sowing seed treatment with "Fertigrain Start" ensures a high germination percentage, reducing The amount of unsprouted seeds. Winter crops better withstand the vagaries of winter and resume vegetation earlier. The tillering coefficient and the number of productive stalks increase significantly, as do the number of grains per ear and the average grain weight.

Plant growth regulators are natural or synthetic compounds capable of inducing metabolic changes in plant organisms, thereby directing their growth and development. They act as a unique form of doping that intensifies RNA and Protein synthesis. They enhance immune resistance and resistance to viral, bacterial, and fungal diseases, while mitigating the NEGATIVE IMPACT OF pesticides.

English biochemists were the first to propose animal growth-stimulating hormones. For the rapid growth of young calves and piglets, Somatostatin is used—a natural antagonist of the somatotropic (growth) hormone that blocks its synthesis, allowing the somatotropic hormone to act more rapidly and energetically, thereby doubling the growth rate.

The problem of protecting plants and animals from pests arose long ago. Today, over 70,000 different insect species are known to cause harm to humans, animals, and agriculture; consequently, chemical intervention against pests has been and remains a pressing issue. Currently, about 3,000 chemical compounds are used to protect plants and animals. Another pressing challenge in modern agricultural production is The Development of technologies that enhance yields while remaining ecologically safe for the ENVIRONMENT AND HUMAN health. Such technologies include the development and Implementation of scientifically grounded and ecologically safe methods for controlling weeds and pests, alongside plant growth regulators collectively known as pesticides.

Pesticides are chemical agents used to protect plants and animals from pests, diseases, and weeds. Pesticides are divided into 6 groups depending on the organisms they affect.

Bactericides are agents for combating harmful Bacteria.

Herbicides are chemical agents for weed control.

Insecticides are chemical agents used to destroy harmful plant insects as well as parasitic insects that transmit various diseases.

Repellents are agents that protect animals, humans, and plants from attacks by harmful insects by driving them away.

Fungicides are agents used to combat fungal infections and plant diseases.

Chemosterilants are substances that reduce or entirely destroy the reproductive capacity of harmful insects.

All these pesticides must meet specific requirements, namely:

- while highly toxic to specific pests, the pesticide should have low toxicity (LD>1000 mg/kg) for humans, animals, plants, beneficial insects, and microorganisms;

- the persistence of the chemical in natural conditions should not be excessively high (the degradation half-life should not exceed 6 months);

- special attention must be paid to the potential impact of pesticides on the gene pool of humans, animals, beneficial insects, and plants, as well as their potential carcinogenicity.

Herbicides

Herbicides are classified by their mode of action into two groups: total (non-selective) herbicides, which destroy all types of plants, and selective herbicides, which eliminate specific plant species. These two groups are further subdivided into contact and systemic herbicides.

Contact herbicides are those that act upon direct contact of the chemical with the above-ground PARTS OF THE plant. Systemic herbicides affect the plant from the inside, entering it via soil solution or through direct contact with the preparation.

Total herbicides include substances used for soil sterilization, such as NaCl and borax. Kerosene can also be classified here, as it destroys all vegetation without sterilizing the soil. The second group comprises derivatives of aryloxycarboxylic acids, the most widely known being

2,4-dichlorophenoxyacetic acid (2,4-D) or 2-methyl-4-chlorophenoxyacetic acid (2-MCPA), which exhibit herbicidal activity at concentrations >0.01%, while at concentrations <0.001% they are used as plant growth stimulants. At high concentrations, these substances can be used as total herbicides. Esters of these acids are also employed.

Another Class of herbicides includes triazine compounds, first discovered back in 1955. A representative example of this group is 2-chloro-4,6-diethylaminosymtriazine (simazine, propazine, etc.). These substances have low toxicity to warm-blooded animals and do not affect most cultivated crops (carrots, cabbage, tomatoes, cucumbers), yet they effectively eliminate weeds. Therefore, they are classified as selective herbicides.

In 1980, urea-group herbicides were patented for the first time, such as "Glean", whose chemical name is chlorsulfuron.

Currently, There are many other developments from both foreign and domestic manufacturers. Among domestic products, the most well-known herbicides are "Prima", "Puma", etc.

Insecticides

Like herbicides, insecticides are classified by their mode of action into contact and systemic types. Contact insecticides kill insects upon touching their external organs or cuticle. Systemic insecticides are absorbed by plants and make the plant tissues toxic to insects. Among contact insecticides, the most famous is DDT (4,4-dichlorodiphenyltrichloroethane), discovered back in 1948, for which Müller was awarded the Nobel Prize. Its main advantages were manufacturing availability and low cost. However, it was banned as early as 1980 because polychlorinated compounds are extremely persistent, decompose very slowly in natural environments, and bioaccumulate in living organisms; furthermore, insects develop resistance to the chemical. Another group of insecticides is pyrethrins, which are analogs of the natural insecticide pyrethrum extracted from chamomile. They do not induce resistance and are non-toxic to warm-blooded animals, though they have poor storage stability.

Additionally, widely known insecticides include "Rotenone" (methyl bromide), fluorine compounds, and nicotine, though they are rarely used nowadays due to their accumulation in the soil. Currently, synthetic organic compounds such as organophosphorus agents, organosulfur agents, carbamates, and others are most frequently used. Their common drawback (especially for organophosphorus compounds) is toxicity to plants and warm-blooded animals; therefore, replacing phosphorus with sulfur reduces the toxicity of these preparations. All these compounds are eventually deactivated in nature through Hydrolysis and oxidation-reduction reactions occurring in the soil.

Among systemic insecticides, the most well-known are esters and amides of dithiophosphoric acid, such as phosphamid, anthio, etc. They are also deactivated by the hydrolysis of their ester groups, and their metabolism period does not exceed 3 weeks.

Fungicides

Fungicides are generally used more for the Prevention of plant diseases than for their treatment. Most commonly, these are inorganic sulfur- and copper-containing substances, of which the best-known is "Bordeaux mixture"—a blend of slaked lime and copper sulfate.

Among organic substances, formaldehyde is used, though it is toxic and therefore not widely applied. Synthetic organic fungicides—such as dithiocarbamates and streptomycin-type Antibiotics—are used much more frequently.

These fungicides have low toxicity and are successfully used to combat fungal diseases.