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.

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.

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.

Researchers have traditionally paid close attention to the problem of stress tolerance of agricultural plants. Spring wheat is highly sensitive to the action of various stress factors. Secondary metabolites play an important role in the formation of plants' stress tolerance. In this work, the composition and features of changes in the content of triterpenes and sterols in the roots and leaves of wheat seedlings of Triticum aestivum L. under the action of stress phytohormones-abscisic acid, methyl jasmonate, and salicylic acid are comprehensively studied using thin layer chromatography and chromatography-mass spectrometry. Significant changes were revealed in the triterpene and sterol components of wheat as well as in the level of transcripts of key genes of sterol biosynthesis. It was found that the leaves and roots of wheat seedlings exhibit different sensitivity to the action of phytohormones. The data obtained will help to decipher the role of membrane sterols in plant stress responses.

Autophagy is a highly conserved process of intracellular degradation of damaged, oxidized or excess macromolecules and organelles in eukaryotic cells. Under optimal conditions, the baseline level of autophagy is low. However, the activity of autophagic processes greatly increases in response to stress. In this paper, we analyzed the biochemical characteristics of autophagosomes that are formed in the wheat suspension culture cells in response to starvation and as a result of treatment with polyamine spermine. High activity of acid phosphatase and protease, the marker enzymes of lytic vesicles, and changes in the lipid composition were observed in the autophagosomes isolated from the sucrose-deficient cells. It was revealed that polyamine spermine can induce.utophagy, which was accompanied with the changes in the cellular redox status and the energy status of mitochondria. The spermine-induced autophagosomes were characterized by the high enzymatic activity of acid phosphatase and protease. The results obtained suggest the functional universality of the main biochemical markers of autophagosomes in plant cells.

Most crops are seriously threatened by various abiotic stressors. Biological membrane is a primary barrier protecting from stress factors and acting as a target that takes a hit on itself. An important component of membranes, on which the state of a plant membrane depends, its permeability to ions, microviscosity, and the activity of membrane-bound enzyme complexes, are lipids. The aim of this study was to study the lipid profile in the roots of wheat seedlings of Triticum aestivum L. with a directed alteration of the membrane state by specific agents: CaCl2 (1 mM) and beta-sitosterol (0.5 mM) that increase the membrane rigidity, as well as the channel former nystatin (0.1 mM) and detergent Triton X-100 (16 mu M) that increase the membrane permeability. It was found that stabilization of membranes by CaCl2 did not lead to changes in the lipid composition of wheat root cells, while the stability index and degree of membrane ordering increased. Saturation of membranes with beta-sitosterol also caused an increase in membrane stability and ordering of the lipid bilayer, which was accompanied by an increase in the content of sterols and monogalactosyl diacylglyceride and a decrease in the level of phosphatidylcholine and glycoceramides. The action of the channel former nystatin on intact seedlings did not affect the stability and orderliness of the membranes, despite a decrease in the total level of sterols in the cells of the roots of wheat. Damage of the root membranes by Triton X-100, which manifested itself in a significant increase in the electrolyte leakage and a decrease in the ordering of the bilayer, was accompanied by an increase in the proportion of terpenoids.