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Given the toxicity of trace metals, their concentration, speciation and bioavailability serve to induce various plant detoxification processes, which themselves are specific to several parameters like plant species, tissue type and developmental stage. In this study, Myriophyllum alterniflorum (or alternate watermilfoil) enzyme activities (ascorbate peroxidase, catalase, glutathione peroxidase and superoxide dismutase) from in vitro cultures was measured over 27 days in response to copper (Cu) or cadmium (Cd) stress. These enzymes are unique to reactive oxygen species (ROS) scavenging (mainly hydrogen peroxide H 2 O 2 and superoxide anion O 2 - ) and moreover showed specific or unspecific activity profiles, depending on the metal concentrations used. Our results suggest a higher-priority protection of chloroplasts during the initial days of exposure to both metals. At the same time, the increased catalase activity could indicate an H 2 O 2 diffusion in peroxisome in order to protect other organelles from ROS accumulation. However, as opposed to the Cd effects, high Cu concentrations appear to induce a "limited oxidative threshold" for some antioxidant enzymes, which could suggest an ion absorption competition between Cu 2+ and Fe 2+ . In spite of an overall analysis conducted of the scavenging processes occurring in plant cells, biochemical analyses still yielded relevant indications regarding the watermilfoil strategies used for ROS management., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Proline plays an important role in plant response to various environmental stresses. However, its involvement in mitigation of heavy metal stress in plants remains elusive. In this study, we examined the effectiveness of exogenous proline (10 and 20 mM) in alleviating cadmium induced inhibitory effects in young olive plants (Olea europaea L. cv. Chemlali) exposed to two Cd levels (10 and 30 mg CdCl2 kg(-1) soil). The Cd treatment induced substantial accumulation of Cd in both root and leaf tissues and a decrease in gas exchange, photosynthetic pigments contents, uptake of essential elements (Ca, Mg and K) and plant biomass. Furthermore, an elevation of antioxidant enzymes activities (superoxide dismutase, catalase, glutathione peroxydase) and proline content in association with relatively high amounts of hydrogen peroxide, thiobarbituric acid reactive substances and electrolyte leakage were observed. Interestingly, the application of exogenous proline alleviated the oxidative damage induced by Cd accumulation. In fact, Cd-stressed olive plants treated with proline showed an increase of antioxidant enzymes activities, photosynthetic activity, nutritional status, plant growth and oil content of olive fruit. Generally, it seems that proline supplementation alleviated the deleterious effects of young olive plants exposed to Cd stress., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The ability of exogenous compatible solutes, such as proline, to counteract cadmium (Cd) inhibitory effects in young date palm plants ( Phoenix dactylifera L. cv Deglet Nour) was investigated. Two-year-old date palm plants were subjected for five months at different Cd stress levels (0, 10 and 30 mg CdCl 2 kg −1 soil) whether supplied or not with exogenous proline (20 mM) added through the irrigation water. Different levels of Cd stress altered plant growth, gas exchanges and chlorophyll content as well as water status, but at different extent among them. In contrast, an increase of antioxidant enzymes activities of Cd-treated plants in association with high amounts of proline content, hydrogen peroxide (H 2 O 2 ), thiobarbituric acid reactive substances (TBARS) and electrolyte leakage (EL) were observed. Interestingly, exogenous proline mitigated the adverse effects of Cd on young date palm. Indeed, it alleviated the oxidative damage induced by Cd accumulation and established better levels of plant growth, water status and photosynthetic activity. Moreover, proline-treated plants showed high antioxidant enzymes activities (superoxide dismutase, catalase and glutathione peroxydase) in roots and leaves as compared to Cd-treated plants. [ABSTRACT FROM AUTHOR]

Fluoride (F) as one of the most toxic pollutants affecting the environment severely restricted plant growth and development. The Fluoride toxicity was studied in young olive plants ( Olea europaea L. cv Chemlali), which were irrigated for 5 months with increasing NaF concentration: 0 (control), 20, 40, and 80 mM NaF. The NaF application resulted in an increase of the F content in plant tissues with a higher level in roots compared to leaves. Olive plants treated with 20 or 40 mM NaF maintained their mineral status and activated their antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase). In fact, lipid peroxidation and electrolyte leakage were not affected in the plant leaves. However, olive plants treated with 80 mM NaF showed (i) the highest reduction of antioxidant enzyme activities and mineral contents, and (ii) an increase of oxidative stress markers such as hydrogen peroxide, thiobarbituric acid reactive substances and electrolyte leakage in both roots and leaves. [ABSTRACT FROM AUTHOR]