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The aftereffects of copper ions (100 and 300 μM) on the organ size, the content of stress markers (hydro-gen peroxide, lipid peroxidation - LPO) and components of the antioxidant status (superoxide dismutase - SOD and guaiacol peroxidase - GPO) were studied in the roots, stem, and leaves of Nicotiana tabacum L. It was shown that tobacco plants were sensitive to long-term exposure to 100 and 300 μM Cu2+. Both concentrations inhibited root growth, while shoot length and thickness, and leaf area decreased only in the case of pretreatment with 300 μM Cu2+. So, the growth of aboveground organs was suppressed signifi-cantly less than the root. The level of lipid peroxidation and the content of hydrogen peroxide in the roots under these conditions were also higher, which indicates a stronger stress, compared to stem and leaf. The activity of antioxidant enzymes SOD and GPO in roots and aboveground organs specifically changed de-pending on the concentration of copper ions and the type of organ. In the roots, there was a decrease in SOD activity and an increase in the activity of GPO under pretreatment with 300 μM Cu2+, compared to the control and 100 μM Cu2+, while in stem and leaves the activity of enzymes decreased. The data ob-tained indicate incomplete plant recovery under the aftereffect of copper ions.

The present work aims to study the responses (seed germination, root and hypocotyl size, hydrogen peroxide concentration, lipid peroxidation products, and peroxidase activity) of Zinnia elegans Jacq. seedlings to different concentrations of Cu2+ (25, 50, 100 and 200 µM). At low Cu2+ content (25–50 µM) seed germination, biomass of seedlings, and hypocotyl length did not change, but root length decreased. Under 100–200 µM Cu2+, a decrease was revealed in seed germination percentage, root and hypocotyl length, and the biomass in 8-days plants. An increase in hydrogen peroxide concentration and lipid peroxidation products, induction of apoplastic and cytosolic guaiacol peroxidase (GPOX) activity were observed in the root tissues under 50–200 µM Cu2+. The negative effects were less pronounced in the hypocotyl tissues: increase of lipid peroxidation was noted under 200 µM Cu2+, and hydrogen peroxide under 100 and 200 µM Cu2+; the activity of peroxidases did not change compared to control. Thus, the root was more sensitive to the excess of copper ions. A specific increase in the activity of apoplastic and cytosolic GPOX in root tissues can be considered as a biochemical marker for the selection of resistant forms of plants at the early stages of development.

The symptoms of copper ion toxicity are well studied, but there is limited information on the mechanisms of plant recovery after stress. The paper deals with the recovery of growth in Zinnia elegans Jacq., treated with 50 and 100 µM Cu2+ for 15 days, then cultivated in normal condition for 30 days. After the recovery period the length of shoot, anatomical changes of root, hypocotyl and stem (first internode) were investigated. It was shown that the copper ions induced a decrease of plant length during stress period. After stress relief for 30 days, the length of hypocotyl and stem of Cu-treated plants increased compared to control. The diameter of root was bigger due to the increase in thickness of cortex and stele. The changes were less noticeable in shoot tissues. The diameter of hypocotyl positively correlates with the thickness of stele. Same effect of copper was observed in stem only in plants, previously treated with 100 µM. The diameter of cortex and metaxylem cells increased in all analyzed organs. No significant differences were found in cell wall thickness of metaxylem cells. The recovery of Z. elegans growth after cooper treatment occurred due to the expansion of cortex and metaxylem cells.

Class III peroxidases (EC 1.11.1.7) have use a wide range of substrates and perform numerous functions, including synthesis of monolignols, lignin precursors. The activity and tissue localization of cationic guaiacol (GPOX) and anionic benzidine peroxidases (BPOX) were studied in the first internode of zinnia plants of different ages. The lignin in cross sections of plant tissues was stained by phloroglucinol-HClTthe lignin content was determined by Klason. Enzyme activity and the H2O2 amount were determined spectrophotometrically. The hypocotyl grew for 40 days and the lignin content for 60 days. In 20-days-old plants, lignin was detected in protoxylem, and in 60-days-old—in sclerenchyma, protoxylem, and metaxylem. Enzyme histochemistry revealed that BPOX was localized in endoderm, phloem, and protoxylem, while GPOX—in the metaxylem and sclerenchyma. A moderate increase in GPOX activity during internode growth was shown. In contrast, BPOX activity was high at the initial growth stage, and declined to the 60th day. Thus, the most intense lignification in mechanical tissue and xylem occurred during the period from 20 to 40 days of plant growth. BPOX is likely involved in the process at the early stages of growth, while GPOX is responsible for sclerenchyma and metaxylem lignification at the later stages.

A small family of ARGOS genes encodes transmembrane proteins that act as negative regulators of ethylene signaling. Recent studies show that ARGOS genes are involved in the regulation of plant growth under the influence of stress factors. However, the role of ARGOS genes in this process is poorly known. Thereby, our goal was to determine the expression profile of these genes in Arabidopsis thaliana and Nicotiana tabacum in response to phytohormone treatment and stress factors. We discovered that expression of the AtARGOS and AtARGOS-LIKE genes of A. thaliana is regulated by ethylene and depends on environmental conditions. The highest expression level of the NtARGOS-LIKE1 gene of tobacco (NtARL1) was observed in blooming flowers and young organs. It was induced by auxins, ethylene, ABA, methyl jasmonate as well as hypothermia, drought, salinity and heat stresses. To evaluate the impact of ARGOS genes on plant growth under stress, we created transgenic tobacco plants with constitutive expression of the AtARGOS-LIKE gene of A. thaliana (AtARL), controlled by a strong Dahlia mosaic virus promoter. Overexpression of the AtARL gene contributed to an increase in the volume and quantity of mesophyll cells in the leaves of tobacco under normal conditions, and also to an improvement in root growth under salinity, cold and cadmium treatment. The AtARL transgene produced a positive effect on shoot growth when exposed to drought and high salinity, and a negative effect under cold stress. Accordingly, genes of the ARGOS family can be recommended as targets for genetic engineering and genome editing in order to enhance productivity and stress tolerance of economically important plants.

The study was focused on the responses of tobacco plants to salt stress. The changes in antioxidant enzymes, photosynthetic pigments, anatomy traits in root and stem tissues under the impact of different concentration of NaCl (25 and 50 mM L−1) were investigated. It was shown that low and high concentrations of NaCl differently effected on plant growth, and root and stem anatomy. The salt stress activated antioxidant enzymes (CAT, GPX, APX), and increased chlorophyll and carotenoid content. In roots salt stress causes the increase of total and cortex diameter and cell wall thickness in xylem tissues. The same NaCl concentrations cause stronger changes in roots than in shoots.

The adaptation of plants to an excess of heavy metals in the environment and their recovery after elimination of the stressor is of interest in connection with the large-scale pollution of ecosystems and their remediation. This study is aimed at the aftereffect of copper ions (100 and 300 μM) in plants of Nicotiana tabacum L. The level of plant stress markers (concentration of hydrogen peroxide, activity of class III peroxidases – benzidine and guaiacol, their isoforms) during the recovery period after the removal of copper ions from the environment was evaluated in pretreatment by copper ions of different concentration and the use of control plants. During the recovery period, the concentration of hydrogen peroxide in plant organs (root, stem, and leaves) was high compared to the control. The responses of the roots and shoots under the aftereffect of the stressor were different. The activity of cytosolic guaiacol peroxidase and cell wall-bound peroxidases in root tissues increased according to the increase in Н2О2. In plants pretreated with a lower copper concentration, the activity of cell wall-bound peroxidases in the stem and cytosolic and cell wall-bound benzidine peroxidases in leaves increased. In contrast, pretreatment with a high copper concentration led to a decrease in the activity of peroxidases during the period of plant recovery. Thus, plant organs differed in the content of H2O2 and the activity of class III peroxidases localized in different compartments (apoplast and cytosol) and in their ability to recover after the removal of the stressor