Comparative analysis of reactions of the antioxidant system of barley seedlings to abiotic stresses of various nature

In the context of modern climate change and anthropogenic soil pollution, the study of the mechanisms of stress resistance of agricultural crops is an urgent task. The purpose of this study was a comprehensive analysis of the reactions of the antioxidant system of barley seedlings (Hordeum vulgare L.) to the effects of key abiotic stressors: drought, low (4 °C) and high (35 °C) temperatures, as well as the toxic effects of copper sulfate (cuso₄). The work assessed physiological and biochemical parameters, including the concentration of low molecular weight antioxidants (NMAO), peroxidase activity and the level of malonic dialdehyde (MDA) as a marker of oxidative damage to lipids. It has been established that different stresses induce qualitatively different responses of the antioxidant system. Drought caused a sharp (more than 5-fold) increase in the NMAO pool, while heat shock led to its depletion (at least 9.9 micrograms/g·eq) and a compensatory increase in peroxidase activity (up to 83.2 micromol/ min·g), which was combined with a maximum level of MDA (3.1 micrograms/g). Cold stress and low doses of copper activated both protective links, while high concentrations of CUSO₄ caused decompensation with suppression of enzymatic activity. It has been shown that the most profound cell damage is associated with heat stress and copper toxicosis, which disrupt antioxidant protection. Based on the calculated coefficients (K1=NMAO/MDA, K2=Peroxidase/ The dominant protection strategies have been identified: non—enzymatic - in case of drought and enzymatic — in case of temperature shocks. The results of the work are important for predicting the stability of cereals in adverse conditions.