This review presents a comprehensive and systematic study of the field of plant biostimulants and considers the fundamental and innovative principles underlying this technology. The elucidation of the biological basis of biostimulant function is a prerequisite for the development of science-based biostimulant industry and sound regulations governing these compounds. The task of defining the biological basis of biostimulants as a class of compounds, however, is made more complex by the diverse sources of biostimulants present in the market, which include bacteria, fungi, seaweeds, higher plants, animals and humate-containing raw materials, and the wide diversity of industrial processes utilized in their preparation. To distinguish biostimulants from the existing legislative product categories we propose the following definition of a biostimulant as ‘a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds’. The definition provided here is important as it emphasizes the principle that biological function can be positively modulated through application of molecules, or mixtures of molecules, for which an explicit mode of action has not been defined. Given the difficulty in determining a ‘mode of action’ for a biostimulant, and recognizing the need for the market in biostimulants to attain legitimacy, we suggest that the focus of biostimulant research and validation should be upon proof of efficacy and safety and the determination of a broad mechanism of action, without a requirement for the determination of a specific mode of action. While there is a clear commercial imperative to rationalize biostimulants as a discrete class of products, there is also a compelling biological case for the science-based development of, and experimentation with biostimulants in the expectation that this may lead to the identification of novel biological molecules and phenomenon, pathways and processes, that would not have been discovered if the category of biostimulants did not exist, or was not considered legitimate.

Plant sugar transporters play an essential role in the organism’s productivity by carrying out carbohydrate transportation from source cells in the leaves to sink cells in the cortex. In addition, they aid in the regulation of a substantial part of the exchange of nutrients with microorganisms in the rhizosphere (bacteria and fungi), an activity essential to the formation of symbiotic relationships. This review pays special attention to carbohydrate nutrition during the development of arbuscular mycorrhiza (AM), a symbiosis of plants with fungi from the Glomeromycotina subdivision. This relationship results in the host plant receiving micronutrients from the mycosymbiont, mainly phosphorus, and the fungus receiving carbon assimilation products in return. While the efficient nutrient transport pathways in AM symbiosis are yet to be discovered, SWEET sugar transporters are one of the three key families of plant carbohydrate transporters. Specific AM symbiosis transporters can be identified among the SWEET proteins. The survey provides data on the study history, structure and localization, phylogeny and functions of the SWEET proteins. A high variability of both the SWEET proteins themselves and their functions is noted along with the fact that the same proteins may perform different functions in different plants. A special role is given to the SWEET transporters in AM development. SWEET transporters can also play a key role in abiotic stress tolerance, thus allowing plants to adapt to adverse environmental conditions. The development of knowledge about symbiotic systems will contribute to the creation of microbial preparations for use in agriculture in the Russian Federation.

Background: Investigations that are focused on arbuscular mycorrhizal fungus (AMF) biodiversity is still limited. The analysis of the AMF taxa in the North Caucasus, a temperate biodiversity hotspot, used to be limited to the genus level. This study aimed to define the AMF biodiversity at the species level in the North Caucasus biotopes. Methods: The molecular genetic identification of fungi was carried out with ITS1 and ITS2 regions as barcodes via sequencing using Illumina MiSeq, the analysis of phylogenetic trees for individual genera, and searches for operational taxonomic units (OTUs) with identification at the species level. Sequences from MaarjAM and NCBI GenBank were used as references. Results: We analyzed >10 million reads in soil samples for three biotopes to estimate fungal biodiversity. Briefly, 50 AMF species belonging to 20 genera were registered. The total number of the AM fungus OTUs for the “Subalpine Meadow” biotope was 171/131, that for “Forest” was 117/60, and that for “River Valley” was 296/221 based on ITS1/ITS2 data. The total number of the AM fungus species (except for virtual taxa) for the “Subalpine Meadow” biotope was 24/19, that for “Forest” was 22/13, and that for “River Valley” was 28/24 based on ITS1/ITS2 data. Greater AMF diversity, as well as number of OTUs and species, in comparison with that of forest biotopes, characterized valley biotopes (disturbed ecosystems; grasslands). The correlation coefficient between “Percentage of annual plants” and “Glomeromycota total reads” r = 0.76 and 0.81 for ITS1 and ITS2, respectively, and the correlation coefficient between “Percentage of annual plants” and “OTUs number (for total species)” was r = 0.67 and 0.77 for ITS1 and ITS2, respectively. Conclusion: High AMF biodiversity for the river valley can be associated with a higher percentage of annual plants in these biotopes and the active development of restorative successional processes.

In the process of obtaining transgenic plants suitable for phytoremediation of heavy metal-contaminated soils, a synthetic pseudophytochelatin gene coding for a phytochelatin analog Met(GluCys)₆Gly was de novo designed and cloned. Contrary to natural enzymatically synthesized phytochelatins, this peptide can be made by a template synthesis. A construct carrying the gene in question under the control of the viral constitutive 35S promoter was made on the basis of a binary vector pCAMBIA 1305.1. This construct was used to express the pseudophytochelatin gene in the model transgenic tobacco plants (Nicotiana tabacum L.), and the above plants acquired additional resistance to various cadmium concentrations.

Plant responses to cadmium, whose accumulation may cause various disturbances in metabolic processes, can be represented as a multicomponent integrative response model (in particular, as a gan-shaped response) [1]. In view of this, it is reasonable to use a complex approach to analyzing plant responses to cadmium, which may include studies of plant adaptation, cadmium accumulation, and detoxication. The goal of this work was to study plant responses to cadmium and its accumulation in plants. The study included characterizing the resistance of plants by changes in the proportion of linear sizes and weight; determination of the degree of hydration, phytohormone balance, and the content of free amino acids; establishing the mechanisms of occurrence of chromosome rearrangements on the basis of analysis of the distribution of chromosome aberrations in cells and the aberration index under exposure to cadmium; and assessment of the retaining ability and barrier function of roots during cadmium entry into sprouts. The study was performed with the cibol ( Allium fistulosum L.) cultivars Gribovskii and Russkii zimnii; the spring wheat ( Triticum aestivum L.) cultivars Zhnitsa, Irmenka, and Omskaya-35; the maize ( Zea mays L.) cultivar Zhemchug; and the rice ( Oryza sativa L.) cultivar Rapan. Seeds were sterilized with 70% ethanol. Seedlings were grown in Petri dishes on filter paper wetter with water in a constant-temperature cabinet at 24‐27 ° C. Aligned 48-h-old seedlings were incubated with cadmium acetate for 18, 36, and 54 h (cibol); 24, 48, 72, 96, and 120 h (maize and wheat); and 1, 24, and 48 h (rice). In addition, wheat seeds were allowed to germinate at 24 ° C for 24 h, placed on cork rafts with 4-mm holes, and grown in vessels filled with cadmium acetate for 14 days. During the entire experiment, solutions were aerated and their volume was maintained constant by adding distilled water. Distilled water was used as a control. The resistance index was determined by the ratio between the plant weight in the presence of cadmium and in the control [2]. We studied the effect of cadmium on the intensity of division of apical meristematic cells, the nucleolus characteristics, the level of chromosome aberrations in root meristematic cells (by metaphase and anaphase methods), the content of phytohormones (abscisic acid (ABA), indolylacetic acid (IAA), and cytokinins by enzyme immunoassay), as well as the content of free amino acids by ionexchange chromatography. The content of cadmium was determined by the Experiments were performed in quadruplicate and repeated at least five times. The statistical significance of differences between variants was estimated by Student’s t test. In the presence of cadmium at concentrations of 100, 10, and 1 mg/l, the resistance index of wheat was 0.75, 0.98, and 0.92 (Zhnitsa); 0.69, 1.03, and 1.05 (Omskaya-35); and 0.73, 0.88, and 1.05 (Irmenka), respectively. At these concentrations, the sprout/root ratio obtained after determination of linear sizes was 0.70, 1.31, 0.72, and 0.70 (Zhnitsa); 0.51, 1.06, 0.51, and 0.61 (Omskaya-35); and 0.63, 1.41, 0.70, and 0.60 (Irmenka), respectively. In the presence of 100 mg/l cadmium, the degree of hydration of plants significantly decreased: by 45% (Zhnitsa), 41% (Irmenka), and 41% (Omskaya-35). At concentrations of 10 and 1 mg/l, cadmium had no effect on the degree of hydration. The potential of wheat resistance to cadmium determined at early developmental stages in the Barsukova medium varied from very low (0.21) to very high (1.2) [2]. Thus, we did not reveal significant genotypic differences in plant responses to cadmium at the concentrations used.

The growth regulator Stifun at all concentrations tested (0.033, 0.33, 3.3, and 33 mg/L) affected the hormonal status of wheat seedlings ( Triticum aestivumL., cv. Zhnitsa) and stimulated plant...