During their life cycle, plants constantly respond to environmental changes. Abiotic stressors affect the photosynthetic and respiratory processes of plants. Reactive oxygen species (ROS) are produced during aerobic metabolism and play an important role as regulatory mediators in signaling processes, activating the plant’s protective response to abiotic stress and restoring “oxidation-reduction homeostasis”. Cells develop normally if the rates of ROS production and the ability to neutralize them are balanced. To implement oxidation-reduction signaling, this balance must be disrupted either by an increase in ROS concentration or a decrease in the activity of one or more antioxidant systems. Under abiotic stress, plants accumulate excessive amounts of ROS, and if the ROS content exceeds the threshold amount dangerous for living organisms, it can lead to damage to all major cellular components. Adaptive resistance of plants to abiotic stressors depends on a set of mechanisms of adaptation to them. The accumulation of ROS in the cell depends on the type of abiotic stress, the strength of its impact on the plant, the duration of its impact, and the recovery period. The aim of this review is to provide a general understanding of the processes occurring during ROS homeostasis in plants, oxidation-reduction processes in cellular compartments in response to abiotic stress, and the participation of ROS in signaling processes activating adaptation processes to abiotic stress.

The high salinity of soil salts limits plant growth. Wheat is sensitive to toxic levels of mineral salts. Salinity leads to the accumulation of toxic ions in all organs of wheat. Depending on the level of ion accumulation, wheat is defined as salt stress-tolerant or -sensitive. The wheat variety Zolotaya accumulated Cl⁻ and Na⁺ ions to a greater extent than the Orenburgskaya 22 variety. The accumulation of toxic ions was accompanied by an increase in ROS and an increase in damage to root tissues up to 80% in the Zolotaya variety. The formation of autophagosomes is considered a defense mechanism against abiotic stresses in plants. At a concentration of 150 mM NaCl, an increase in the expression level of TOR, which is a negative regulator of the formation of autophagosomes, occurred. The level of TOR expression in the Zolotaya variety was 2.8 times higher in the roots and 3.8 times higher in the leaves than in the Orenburgskaya 22 variety. Under the action of salinity, homeostasis was disturbed in the root cells and ROS production accumulated. In the unstable variety Zolotaya, ROS was found in the cap zone and the root meristem in contrast to the resistant variety Orenburgskaya 22 in which ROS production was found only in the cap zone. Accumulation of ROS production triggered autophagy and PCD. PCD markers revealed DNA breaks in the nuclei and metaphase chromosomes, cells with a surface location of phosphatidylserine, and the release of cytochrome c into the cytoplasm, which indicates a mitochondrial pathway for the death of part of the root cells during salinity. Based on electron microscopy data, mitophagy induction was revealed in wheat root and leaf cells under saline conditions.

Various stressors lead to an increase in ROS and damage to plant tissues. Plants have a powerful antioxidant system (AOS), which allows them to neutralize excess ROS. We detected an intense fluorescent glow of ROS in the cells of the cap, meristem, and elongation zones in the roots of wheat Triticum aestivum (Orenburgskaya 22 variety) and Triticum durum (Zolotaya variety). An increase in ROS was accompanied by DNA breaks in the nuclei of wheat root cells, the release of cytochrome c from mitochondria into the cytoplasm, and the translocation of phosphatidylserine into the outer layer of the plasma membrane under salt stress and hypoxia. The different resistances of the two wheat varieties to different abiotic stresses were revealed. The soft wheat variety Orenburgskaya 22 showed high resistance to salt stress but sensitivity to hypoxia, and the durum wheat variety Zolotaya showed tolerance to hypoxia but high sensitivity to salt stress. Different activations of AOS components (GSH, MnSOD, Cu/ZnSOD, CAT, PX, GPX, and GST) were revealed in different wheat genotypes. The basis for the tolerance of the Zolotaya variety to hypoxia is the high content of glutathione (GSH) and the activation of glutathione-dependent enzymes. One of the mechanisms of high resistance to salt stress in the Orenburgskaya 22 variety is a decrease in the level of ROS as a result of the increased activity of the MnSOD and Cu/ZnSOD genes. Identifying the mechanisms of plant tolerance to abiotic stress is the most important task for improving breeding varieties of agricultural plants and increasing their yield.

During their life cycle, plants constantly respond to environmental changes. Abiotic stressors affect the photosynthetic and respiratory processes of plants. Reactive oxygen species (ROS) are produced during aerobic metabolism and play an important role as regulatory mediators in signaling processes, activating the plant's protective response to abiotic stress and restoring "oxidation-reduction homeostasis". Cells develop normally if the rates of ROS production and the ability to neutralize them are balanced. To implement oxidation-reduction signaling, this balance must be disrupted either by an increase in ROS concentration or a decrease in the activity of one or more antioxidant systems. Under abiotic stress, plants accumulate excessive amounts of ROS and if the ROS content exceeds the threshold amount dangerous for living organisms, it can lead to damage to all major cellular components. Adaptive resistance of plants to abiotic stressors depends on a set of mechanisms of adaptation to them. The accumulation of ROS in the cell depends on the type of abiotic stress, the strength of its impact on the plant, the duration of its impact and the recovery period. The aim of this review is to provide a general understanding of the processes occurring during ROS homeostasis in plants, oxidation-reduction processes in cellular compartments in response to abiotic stress and the participation of ROS in signaling processes activating adaptation processes to abiotic stress.

The toxicity of high concentrations of sodium chloride creates significant difficulties in realizing the productivity potential of wheat. The development of effective test systems for the identification and selection of resistant genotypes is an urgent task given the global increase in soil salinity in agricultural land. To identify the characteristics of the plant’s reaction to the toxic effect of sodium chloride, wheat genotypes with different resistance to ionic toxicity (the Orenburgskaya 10 and Orenburgskaya 22 varieties) were used. In model experiments, we used fluorescence, light-optical and electron microscopy to characterize the structural and functional features of the cells of the roots of wheat seedlings, and cytological markers suitable for creating a test system for the early diagnosis of the sensitivity of wheat genotypes to sodium chloride were established. The response of the plants to the effects of sodium chloride was assessed by changes in biometric data, respiration rate, peculiarities in the accumulation of reactive oxygen species (ROS) and mitochondrial staining, and the quantitative assessment of coleoptile cell viability as putative sensitivity markers. In the sodium chloride-sensitive genotype (Orenburgskaya 10), toxic effects resulted in oxidative damage in the root cells, while in the resistant genotype (Orenburgskaya 22), oxidative damage to the cells was minimal. A high level of expression of mitochondrial superoxide dismutase (MnSOD) was found in the roots of the Orenburgskaya 22 variety. The identification and functional analysis of cytological and molecular markers provide the basis for further studies of the resistance of wheat to sodium chloride stress.

Like phytohormones, peptide hormones participate in many cellular processes, participate in intercellular communications, and are involved in signal transmission. The system of intercellular communications based on peptide–receptor interactions plays a critical role in the development and functioning of plants. One of the most important molecules are reactive oxygen species (ROS). ROS participate in signaling processes and intercellular communications, including the development of the root system. ROS are recognized as active regulators of cell division and differentiation, which depend on the oxidation–reduction balance. The stem cell niche and the size of the root meristem are maintained by the intercellular interactions and signaling networks of peptide hormone and ROS. Therefore, peptides and ROS can interact with each other both directly and indirectly and function as regulators of cellular processes. Peptides and ROS regulate cell division and stem cell differentiation through a negative feedback mechanism. In this review, we focused on the molecular mechanisms regulating the development of the main root, lateral roots, and nodules, in which peptides and ROS participate.