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Background: Cadmium (Cd) is one of the most dangerous environmental pollutants. Plant damage caused by oxidative stress during long-term Cd accumulation is well documented, while the primary response to Cd uptake is poorly understood. Objective: We assess the short-term injury and the primary reaction of the antioxidant system to the rapid accumulation of Cd in tobacco leaves. Methods: Leaf rosettes of the 5-week-old plants without roots were exposed to 100, 500 and 5000 μM Cd chloride for 2 and 12 hours. Cd accumulation, oxidation levels of proteins and lipids, content of reduced (Asc) and oxidized (DHA) ascorbate and activity of CAT, APX and POD were determined. Results: An accumulation of Cd in high concentration, but only a relatively small increase in the oxidation of proteins and lipids was found in the leaves after 2 hours of treatment. These effects were transient and disappeared after 12 hours. No visible damage to plants was observed. After 12 hours, the total ascorbate content (Asc + DHA) decreased by 18%, remained unchanged or increased by 85% after the application of 100, 500 and 5000 µM Cd chloride. The increase in the ascorbate pool, which should be considered as a component of the protective response, was caused by the accumulation of DHA. The activity of APX and POD remained unchanged, while that of CAT decreased, indicating that antioxidant enzymes activation is not involved in the primary response to Cd. Conclusions: The primary generation of ROS induced by Cd does not appear to be a deleterious manifestation of Cd toxicity, but rather a component of stress signaling that causes activation of the protective response. Uptake of Cd caused severe damage to the plant after long-term, but not after short-term treatment, suggesting that the damage is the result of secondary effects of Cd toxicity.

High temperature negatively affects the plants. In particular, under the heat stress he production of reactive oxygen species increases in the plant cell. It leads to the development of oxidative stress. The formation of carbonyl groups in proteins is a marker of oxidative damage of plant cells. Plants have a defense system that consists of soluble carbohydrates such as sucrose and glucose and antioxidant enzymes, including catalase. Carbohydrates have protective mechanisms and can activate different signaling pathways with following changes in gene expression. Despite the data available, information on the effects of sucrose and glucose on the oxidative modification of proteins under heat stress is insufficient. The aim of our work was to study the role of sucrose and glucose for the carbonyl groups content in cat2cat3 knockout plants of A. thaliana under heat stress. We used 7-week-old Arabidopsis thaliana plants of wild-type and knockout cat2cat3 line, which lacks the expression of two catalase genes – cat2 and cat3. Plants were grown under 16-hour light day at a temperature of + 20°C and an illumination of 2.5 kL. Heat treatment was performed on a water bath in glass flasks with 15-20 leaves which were incubated in 1 mm potassium phosphate buffer without carbohydrates and with addition of sucrose or glucose (1% final concentration) during 2 and 4 hours at the +37°C and +44° C. The content of carbonyl groups and total protein was determined photometrically. It has been shown that intact knockout cat2cat3 plants have a higher content of carbonyl groups, which indicates chronic oxidative stress. Addition of exogenous sucrose or glucose to the incubation buffer had a protective effect during 4 hours of stress. Carbonyl groups formation in wild type decreased under the +37ºС and +44ºС, while in the cat2сat3 line only under the moderate (+37ºС) heat stress. In the knockout mutant alternative ways of defense are exhausted under +44ºC.

An increase in the Earth's average temperature has a negative effect on the development, growth and productivity of cultivated plants. One of the main metabolic damages caused by exposure to elevated temperatures is excessive production of reactive oxygen species (ROS). ROS, accumulating in chloroplasts, cause significant damage to the photosynthetic apparatus of plants, destroying the chloroplast membrane and damaging pigments. Carbohydrates play a key role in the regulation of the processes of photosynthesis, respiration, seed germination, flowering and aging of plants. Carbohydrates are chemical signaling and sensitive molecules that receive a specific signal under normal conditions and under the influence of stress factors. The aim of our work was to study the effect of exogenous sucrose and glucose on the content of photosynthetic pigments in A. thaliana plants under the influence of heat stress. Two lines of arabidopsiswere used for research: wild-type plants and cat2cat3 knockout line with lacking isoforms of catalase, the main antioxidant enzyme. The plants were grown under conditions of 16-hour daylight at a constant temperature of + 28º C, air humidity of 70% and illumination of 2.5 kL. Treatment was perfomed in the dark for 2 and 4 hours at temperatures of +37 (moderate stress) and +44°C (severe stress treatment). Contorl Plants were incubated in a potassium-phosphate buffer without the addition of sucrose and glucose at a temperature of +20° C. It was shown that the content of chlorophyll a, b and carotenoids in intact plants of the wild type and the knockout line was the same. Under the influence of heat stress, the content of the studied pigments in the presence of sucrose did not change in both lines. During heat stress in the presence of glucose, changes were noted during the 4-hour stress. It was shown that in the control plants incubated at room temperature in the presence of glucose, the content of chlorophyll a and carotenoids increased in wild type. Upon severe heat stress (+44°С), a decrease in the pigment content was jbserved. The data obtained indicate that in conditions of 4 hours of heat stress, exogenous glucose is involved in the plant cell stress response. No changes in the content of chlorophyll and carotenoids were observed in knockout line cat2cat3.