Vol 70, No 2 (2023)

Nitric oxide is a universal signaling molecule involved in the modulation of metabolic activity during the normal growth and development of plants, and in the formation of their resistance to environmental stressors. The review presents key information that reflects the current state of the problem of the regulatory role of NO in plants. Brief information on physicochemical properties of NO, methods of its research, ways of biosynthesis and functional activity at different stages of plant development (germination, vegetative growth, flowering, root formation, symbiosis, mineral nutrition) are given.In addition, the appearance of the protective effects of NO under conditions of moisture deficiency is described, since disturbance of the water regime and dehydration of plants is observed under the influence of various abiotic stress factors, including drought, salinity, hypo- and hyperthermia. Particular attention is paid to the molecular mechanisms of NO-dependent signaling, which are implemented in plants at the genomic, proteomic and post-proteomic levels during multiple nitration reactions. Understanding the mechanisms of regulatory action of NO in normal and under stress is of important theoretical and applied importance in connection with the need for a fundamental justification of the possibility of practical use of NO in order to increase the stability and productivity of cultivated plants.

Unlike the natural photoperiod that includes the alternation of day and night in the diurnal cycle, continuous (24 h a day) lighting provides uninterrupted supply of light energy required for photosynthesis, permanently promotes photooxidative processes, implies continuous signaling to the photoreceptors, and desynchronizes the internal circadian biorhythms from the external light/dark cycle (circadian asynchrony). The leaves of many plant species grown under constinuous lighting are prone to characteristic and potentially lethal interveinal chlorosis and necrosis. The photodamage of plant leaves exposed to long photoperiods, including daily 24-h illumination was described more than 90 years ago, but the causes of this phenomenon are still not entirely clear. Biological bases underlying this phenomenon are theoretically and practically important, because growing plants under a 24-h photoperiod at a relatively low photon flux density is seemingly an effective way to save resources and increase plant productivity in greenhouses and plant factories with artificial lighting. This review of available literature compiles and evaluates the arguments both supporting and confronting the hypothesis that carbohydrate accumulation, specifically the hyperaccumulation of starch in leaves, is the main cause of photodamage to plants grown under continuous lighting or long photoperiods. The analysis of a large number of studies indicates that the accumulation of carbohydrates is neither the main nor the only cause of leaf injuries in plants grown under a 24-h photoperiod, although the role of this factor in photodamage cannot be ruled out. The appearance and development of photodamage under a 24-h photoperiod is presumably due to several simultaneously acting factors, such as photooxidation, stress-induced senescence, and circadian asynchrony. The contribution of individual factors to photodamage may vary substantially depending on environmental conditions and biological properties of the object (plant species and variety, plant age, and the stage of development).

Tomato Solanum lycopersicum L. is an important agricultural crop and, at the same time, a model for studying the ontogeny of the succulent fruit. The decisive role in the ripening of the fruit is played by abscisic acid, which is formed as a result of the oxidative cleavage of epoxycarotenoids 9-cis-epoxycarotenoid dioxygenases NCED. Gene-expression profiles of SlNCED1 and SlNCED2 and the content of carotenoids in fruits at different stages of development were determined in three varieties of tomato with different color of ripe fruit. It was shown that transcripts of both genes are present in all organs. Transcript level of SlNCED1 was approximately four to six times higher than the level of SlNCED2 transcripts; peak activity of SlNCED1 occurs in the late stages of ripening, while that of SlNCED2 is at the initial stage. Ripe fruits are characterized by the highest amount of carotenoids; lycopene was found only in the fruits of late stages in red-fruited varieties, the highest content of β-carotene was found in ripe fruits of the yellow-fruited variety. The precursor of abscisic acid, violaxanthin, is present only in the immature fruit; the other precursor, neoxanthin, decreases with ripening and is absent at the ripeness stage. In red-fruited varieties, a correlation was found between the level of SlNCED1 and SlNCED2 transcripts with the content of β-carotene. Findings suggest the coparticipation of SlNCED1 and SlNCED2 in the biosynthesis of abscisic acid during the development and ripening of tomato fruit. In this case, the key role belongs to the gene SlNCED1, the peak of activity of which falls on the stage of changing the color of the fruit. Lower levels of SINCED2 transcripts and its peak activity in the early stages of fruit development suggests a division of NCED functions between the two enzymes.

Currently, microalgae and cyanobacteria attract the attention of researchers as potential producers of various valuable substances. To increase the profitability of biotechnological processes using these organisms, it is necessary to select highly effective strains and choose the optimal conditions for their growth and maximum productivity. Growth optimization should be carried out, on the one hand, under intensive conditions, as close as possible to large-scale cultivation, and, on the other hand, in small volumes in order to be able to check many different parameters in parallel at minimal cost. In this paper, the authors present a description and characteristics of their laboratory system for intensive cultivation (LSIC—Laboratory System for Intensive Cultivation) with thermo-, light-, and gas regulation and the possibility of cultivation in four repetitions in eight different conditions, differing in light, temperature, and CO₂ concentration. As an example, the results of a number of experiments using the installation are also presented.

The regulation of glutamate dehydrogenase, an enzyme that is involved in both nitrogen and carbon metabolism, and also links between the tricarboxylic acid cycle and the γ-aminobutyric acid shunt, has been studied. It was found that oxygen deficiency-induced changes in glutamate dehydrogenase activity in maize leaves (Zea mays L.) are to increase its catalytic activity by more than twice. Differential expression of genes was studied by real-time PCR in GDH1 and GDH2, which encode the β- and α-subunits of glutamate dehydrogenase, respectively, in the maize genome. Decreased relative level of gene transcripts GDH2 was accompanied by an increase in the expression activity of the gene GDH1. This, in turn, presumably promoted the amination reaction of 2-oxoglutarate. In the promoter of the gene GDH2, the presence of two CpG islands 404 and 383 bp in size was found. Gene promoter GDH1 does not contain a single CpG island; however, 38% of the CpNpG and CpNpN sites of the total number of studied dinucleotides in its composition were found. To assess the influence of the degree of methylation of individual CpG dinucleotides that are part of the promoter regions of genes GDH1 and GDH2 on their expression under hypoxic conditions, a comparative analysis of the dynamics of the transcriptional activity of the genes of β- and α-subunits of glutamate dehydrogenase from the methyl status of their promoters was carried out. Inversely proportional superposition of changes in the methylation profile of gene promoters GDH1 and GDH2 and transformation of the level of expression of these genes shows their correlation. The data obtained as a result of methyl-specific PCR indicate that an increase in the proportion of methylated CpG dinucleotides leads to a decrease in the amount of mRNA of the gene GDH2, while a decrease in this value for the gene GDH1 causes the induction of its functioning. Methylation of promoter regions of glutamate dehydrogenase genes regulates their transcriptional activity in maize leaves in vivo under conditions of oxygen deficiency. Thus, the little data on the molecular mechanisms of regulation of the synthesis of glutamate dehydrogenase isoenzymes were supplemented by new results on the role of the degree of methylation of gene promoters GDH1 and GDH2 glutamate dehydrogenases in their differential expression during maize’s adaptation to hypoxia.