Lichens are extremophilic symbiotic associations possessing phenomenal resistance to abiotic stress-factors. In this regard, melanization of thalli in response to UV is one of the mechanisms protecting lichens from excessive insolation. However, microstructure and biochemical properties of the melanized thalli are still poorly investigated. In the present study, morphological, nanomechanical, and physiological, and biochemical traits of naturally melanized thalli of the Cetraria islandica (L.) Ach. lichen were examined. In the upper cortex of its thallus, the nature of the pigment layer was verified using typical qualitative reactions for melanins. It was found that melanization leads to changes in microstructure of the upper cortex of the mycobiont, in particular, thickening of the cell walls and extension of the interhyphal space. The melanized and pale (nonmelanized) thalli were found to differ from each other in their nanomechanical properties, including the parameters of adhesion and rigidity. This implies the possible formation of complex associates of melanin with cell wall components in the melanized mycobiont. In addition, higher antioxidant activity and lower respiratory activity were found in the melanized thalli of C. islandica in comparison with the pale thalli. Presumably, the found modifications in the microstructure and nanomechanical, physiological, and biochemical properties of thalli occurring in the course of melanization make lichens more resistant to intense insolation.

The ability of plants to adapt to unfavorable living conditions is a necessary condition for the survival of plants, the preservation of the genotype, and the maintenance of flora diversity. A promising approach to solving the problem of increasing plant resistance is to study the mechanisms of stress resistance of “extremophiles”, including mosses, higher nonvascular plants. The relative simplicity of their anatomical structure and ability to survive in unfavorable environmental conditions make these evolutionarily ancient plants ideal models for studying adaptation mechanisms. It is known that the functional activity of the photosynthetic apparatus can change dynamically under the influence of stress factors. In this work, we conducted a study of stress-induced changes in the content of carotenoids in the forest moss Hylocomium splendens Hedw. under temperature stress conditions. We have identified the main carotenoids of H. splendens moss. It has been established that the relative content of lutein, β-carotene, and zeaxanthin increased under the influence of negative and elevated temperatures, while the total content of carotenoids decreased under temperature stress. It was shown that 1 h of exposure to unfavorable temperatures led to a significant decrease in nonphotochemical quenching of chlorophyll fluorescence a, with stronger changes observed when exposed to negative temperatures. Transcript level analysis of HsLUT1, one of the key genes for lutein biosynthesis, showed a significant increase of four to five times under temperature stress. Thus, our data revealed that changes in the expression of the carotenoid biosynthesis gene are accompanied by changes in their content under temperature stress. The data obtained expand our knowledge of resistance mechanisms in bryophytes and will contribute to the understanding of evolutionary changes in stress resistance in higher plants.

Currently, special attention is paid to the study of the mechanisms of stress resistance of extremophile organisms that can survive in extreme conditions. Such organisms include lichens, which are symbiotic associations of fungi and algae and/or cyanobacteria. The high stress resistance of lichens is due to the presence of a wide range of biologically active metabolites, including sterols. It is known that lichens have a diverse and unique sterol composition, different from that of fungi and algae. Sterol-mediated biochemical mechanisms of stress resistance in lichens have not been fully studied and not systematized. Temperature stress is quite common for lichens, which often grow in unfavorable conditions. It is known that dry lichen thalli are able to withstand temperature changes over large ranges, while hydrated thalli are much more sensitive to unfavorable temperatures. In this work, stress-induced changes in respiratory activity and membrane stability index (MSI), as well as the sterol profile of hydrated lichen thalli, of Peltigera canina (L.) Willd. under the influence of elevated (+40°С) and low (–20°С) temperatures was investigated. It was shown that unfavorable temperatures caused a suppression of respiration rate and a decrease in the MSI of lichen thalli. Chromatomass spectrometric analysis showed the presence of P. canina ergosterol, dehydroergosterol, episterol, lichesterol, and fungisterol. Under the influence of both stress factors, there was a decrease in the level of ergosterol and an increase in the proportion of episterol. Under cold stress conditions, the proportion of dehydroergosterol also increased, the proportion of lichesterol decreased, and the relative content of the more saturated sterol fungisterol remained at the control level. It can be assumed that stress-induced changes in the sterol profile of lichens under low-temperature exposure create an optimal balance of sterols in membranes, which provides conditions for the deployment of a successful strategy leading to the adaptation of the lichen to the action of a stressor.

Currently, special attention is paid to the study of the mechanisms of stress resistance of extremophile organisms that can survive in extreme conditions. Such organisms include lichens, which are symbiotic associations of fungi and algae and/or cyanobacteria. The high stress resistance of lichens is due to the presence of a wide range of biologically active metabolites, including sterols. It is known that lichens have a diverse and unique sterol composition, different from that of fungi and algae. Sterol-mediated biochemical mechanisms of stress resistance in lichens have not been fully studied and not systematized. Temperature stress is quite common for lichens, which often grow in unfavorable conditions. It is known that dry lichen thalli are able to withstand temperature changes over large ranges, while hydrated thalli are much more sensitive to unfavorable temperatures. In this work, stress-induced changes in respiratory activity and membrane stability index (MSI), as well as the sterol profile of hydrated lichen thalli, of Peltigera canina (L.) Willd. under the influence of elevated (+40°С) and low (–20°С) temperatures was investigated. It was shown that unfavorable temperatures caused a suppression of respiration rate and a decrease in the MSI of lichen thalli. Chromatomass spectrometric analysis showed the presence of P. canina ergosterol, dehydroergosterol, episterol, lichesterol, and fungisterol. Under the influence of both stress factors, there was a decrease in the level of ergosterol and an increase in the proportion of episterol. Under cold stress conditions, the proportion of dehydroergosterol also increased, the proportion of lichesterol decreased, and the relative content of the more saturated sterol fungisterol remained at the control level. It can be assumed that stress-induced changes in the sterol profile of lichens under low-temperature exposure create an optimal balance of sterols in membranes, which provides conditions for the deployment of a successful strategy leading to the adaptation of the lichen to the action of a stressor.

Mosses are an attractive model for studying the mechanisms of plant adaptation to unfavorable environmental conditions. There is little information in the literature on the pigment composition and its role in stress resistance of mosses, although this topic is quite widely covered for higher vascular plants. Unfavorable environmental temperature is one stress factors with the strongest effect on plants, since photosynthesis, the main energy-supplying producing process in plants, is sensitive to temperature and often inhibited before other cellular functions are impaired. Chlorophyll is known to play a central role in the process of photosynthesis. In this regard, the aim of the present work was to study the response of the moss Hylocomium splendens Hedw. to temperature stress. The chlorophyll content and chlorophyll a fluorescence parameters in H. splendens shoots were investigated. Results showed that both elevated and negative temperatures decreased the content of chlorophyll a significantly, while, on the contrary, the content of chlorophyll b increased. It is interesting to note that the decrease in chlorophyll a under temperature stress was accompanied by an increase in the content of pheophytin a. The content of chlorophylls in the post-stress period did not recover to the control level. Temperature stress did not affect the maximum photochemical efficiency of photosynthesis, but the rate of electron transfer significantly decreased under the influence of low temperature. Thus, significant changes in the pigment composition of chlorophylls are not always accompanied by changes in fluorescence parameters to the same extent.

Extremophile organisms can survive under extreme conditions through tolerance mechanisms. Such organisms include lichens, which are symbiotic associations of fungi and algae and/or cyanobacteria. Among other factors, the high stress tolerance of lichens can be attributed to their ability to synthesize a wide range of metabolites, including chemically diverse lipid compounds. Despite their obvious relevance, the biochemical mechanisms of stress tolerance in lichens that are mediated by changes in the lipid profile remain understudied. Peltigerous lichens constitute a separate division of lichens characterized by high growth rates and metabolic activity indices. Taking into account the temperate climate in which these lichens grow, it can be assumed that they may be highly sensitive to temperature fluctuations. These factors led to the choice of Peltigera canina, epigeic lichen, as the subject matter of this study. The present work examined stress-induced changes in the redox status of P. canina, as well as changes in its lipid composition at an elevated temperature (40 °С). The exposure of hydrated lichen thalli to an unfavorable temperature led to an increase in the level of hydrogen peroxide, phenoloxidase activity, and lipid peroxidation, which constitutes an important part of stress response in lichen. The stress-induced changes in the redox status of lichen thalli stimulated an increase in lipophilic antioxidant agents: a dramatic increase in the level of α-tocopherol and an increase in carotenoids, specifically β-carotene. Thus, the accumulation of lipophilic antioxidants constitutes an important part of the lipid-mediated stress response of P. canina to temperature elevation.

Exposure of plants to biotic and abiotic stress agents causes changes in the composition and content of metabolites of different chemical nature, including lipophilic compounds. One of the ways to simulate a stress situation is plant treatment with exogenous phytohormones. This work deals with investigation of organ specificity of composition of lipophilic compounds and changes in their content in wheat Triticum aestivum L. seedlings treated with exogenous stress hormones: abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA). It was found that roots and leaves of wheat seedlings have identical composition of lipophilic compounds but their content considerably differed. In the leaves, the quantity of hydrocarbons, including squalene, as well as triterpenes, sterols, and phosphatidyl choline, was much greater than in the roots. In the leaves, glycoceramides of type 1 containing a FA residue with α-hydroxyl group predominated; on the contrary, glycoceramides of type 2 whose FA residues lack α-hydroxyl group prevailed in the roots. Moreover, lipid extracts from the leaves contain lipophilic pigments (chlorophylls a and b and carotenoids) and hydrophobic phenolic compounds in the form of hydroxycinnamic acids. Treatment with stress phytohormones brings about considerable changes in growth characteristics, the rate of photosynthesis, and the profile of lipophilic compounds in wheat seedlings depending on the plant organ and the chemical nature of the phytohormone. In the case of ABA and MeJA, the growth of roots and leaves was suppressed, the level of nonphotochemical quenching rose, and the content of photosynthetic pigments changed. An unexpected effect was observed upon treatment with MeJA that raised the level of cholesterol and phosphatidyl serine. SA was notable for organ-specific changes in the content of products of mevalonate pathway, triterpenes, and sterols. Thus, the simulation of stress conditions by means of treatment of wheat seedlings with exogenous phytohormones strongly affected the composition of lipophilic compounds. Specific changes in lipid composition induced by hormones may contribute to adaptive structural transformations of cellular membranes, whereas changes in the content of hydrophobic phenolic metabolites and photosynthetic pigments may reinforce antioxidant defense of plants under stress conditions.

Peroxidases are widespread in animal and plant tissues, wherein they perform a variety of functions. Peroxidases have a broad specificity for substrates of various chemical structures. Along with hydrogen peroxide, phenolic compounds, and toxic compounds of aromatic nature, nitrogen-containing compounds are substrates for peroxidases. This work is devoted to the study of the role of wheat extracellular peroxidases in the metabolism of nitrogen-containing compounds. It has been shown that partially purified isozymes differing in peroxidase activity are involved in the metabolism of nitrogen-containing compounds. The formation of primary and secondary phenoxyl radicals during the combined oxidation of chlorogenic acid, nitrite, and H2O2 was demonstrated. With cooxidation with purified isoenzymes p˗coumaric acid and nitrite, the formation of 4˗hydroxy˗3˗nitrocinnamic acid was revealed. It is assumed that the same isoforms can participate both in the oxidation of nitrite with the formation of nitrophenol and in the reduction of nitrate. The participation of plant peroxidases in nitrogen metabolism can be represented as a set of reactions for the reduction and/or oxidation of nitrogen of different oxidation states with the formation of active intermediates.

Одним из ключевых факторов устойчивости лишайников к неблагоприятным условиям являются редокс-ферменты, которые участвуют в образовании меланина, защитного пигмента, синтезируемого микобионтом.В талломах лишайника Lobaria pulmonaria (L.) Hoffm.(Лобария легочная) с разной степенью меланизации выявлена активность лакказы, пероксидазы и тирозиназы.Определены изоэлектрические точки и молекулярные массы отдельных изоформ лакказы и тирозиназы.Изоферментный спектр этих ферментов в немеланизированных и меланизированных талломах лишайника L. pulmonaria не различался.Частичная очистка осажденных белков L. pulmonaria с помощью анионообменной хроматографии выявила пики активности лакказы и тирозиназы.Результаты 2Dэлектрофоретического разделения белков обнаружили две мажорные изоформы ферментов: 120 кДа с pI 6,6 и 60 кДа с pI 5,9, которые визуализировались при окрашивании гелей субстратами как лакказы, так и тирозиназы.Высказывается предположение, что в лишайнике L. pulmonaria L-DOPA не только является предшественником в реакции образования меланина с участием тирозиназы, но также может быть метаболизирован пероксидазами и лакказами.Обсуждается роль этих ферментов в синтезе меланина, а также генерации активных форм кислорода, участвующих в защите лишайников от патогенов и абиотических стрессоров.

Nitrate reductase (NR) and peroxidase (POX) are important enzymes involved in the metabolism of reactive oxygen (ROS) and nitrogen species in leaves of wheat (Triticum aestivum L.) seedlings. It has been confirmed that NR activity in wheat leaves depends on the light conditions and the presence of nitrates during the cultivation of the seedlings, and it is regulated by the molybdenum cofactor and phosphorylation. In the present study, confocal microscopy and EPR spectroscopy studies showed that the addition of nitrite, a product of NR, increased the level of nitric oxide (NO). This increase was prevented by the addition of sodium azide, an inhibitor of NR. The results suggest that in wheat leaves one of the key functions of NR is the formation of the signaling NO molecule. Cultivation of green plants under conditions of prolonged (4 days) darkness, a strong stress factor for photosynthesizing cells, decreased the activity of NR. Moreover, darkness induced significant elevation of the POX activity that was prevented by the addition of nitrate to the growth medium. It is proposed that the changes in light conditions result in the competition between nitrate- and ROS-metabolizing activities of POX in leaves, and a possible interaction between NR and POX controls the levels of NO and ROS in the leaf tissue.

The effect of salicylic acid on the content of soluble proteins and individual polypeptides in Tatar buckwheat Fagopyrum tataricum calluses differing in ability for morphogenesis was studied. Changes in the protein composition of the calluses cultivated in the dark and in the light indicated the higher sensitivity of the non-morphogenic callus. Different response of callus cultures to salicylic acid and conditions of cultivation (light, darkness) is suggested to be associated with the antioxidant defense system, which is, in particular, characterized by the hydrogen peroxide content in the calluses. Salicylic acid increased the H2O2 content in non-morphogenic calluses more strongly than in morphogenic calluses, and the difference was more significant for the calluses cultivated in the light.

The content of soluble proteins and individual polypeptides was studied in calluses of buckwheat Fagopyrum tataricum (L.) Gaertn with different morphogenic potential. The morphogenic callus had a higher content of soluble proteins and cyclic pattern of changes in this index during passaging, which seems to be due to formation of proembryogenic cell complexes. Comparison of the protein patterns of the calluses demonstrated differences in composition and content of individual components. Morphogenic (35 and 73 kDa) and non-morphogenic callus-specific polypeptides (16 and 62 kDa) have been revealed.

An indirect somatic embryogenesis via the development of proembryogenic cell complexes (PECC) was observed in the in vitro cultured hypocotyl explants of 4–5-day-old buckwheat ( Fagopyrum esculentum Moench.) seedlings. PECC development was shown to depend on culturing conditions, including 2,4-D concentration and the period of explant exposure to 2,4-D, sucrose concentration, and explant density. The culturing protocol was designed to ensure the development of buckwheat somatic embryos in two-month period. The cytogenetic analysis demonstrated that this protocol did not affect the chromosome numbers in the regenerated plants.