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Heavy metal pollution is one of the major agronomic challenges. Tungsten (W) exposure leads to its accumulation in plants, which in turn reduces plant growth, inhibits photosynthesis and induces oxidative damage. In addition, the predicted increase in CO2 could boost plant growth under both optimal and heavy metal stress conditions. The aim of the present study was to investigate the effect of W on growth, photosynthetic parameters, oxidative stress and redox status in rye plants under ambient and elevated (eCO2) levels. To this end, rye plants were grown under the following conditions: ambient CO2 (aCO2, 420 ppm), elevated CO2 (eCO2, 720 ppm), W stress (350 mg kg−1 soil) and W+eCO2. W stress induced significant (p < 0.05) decreases in growth and photosynthesis, increases in oxidative damages (lipid peroxidation) and the antioxidant defense system, i.e., ascorbate (ASC), reduced glutathione (GSH), GSH reductase (GR), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), ASC peroxide (APX) and dehydroascorbate reductase (DHAR). On the other hand, eCO2 decreased W uptake and improved photosynthesis, which sequentially improved plant growth. The obtained results showed that eCO2 can decrease the phytotoxicity risks of W in rye plants. This positive impact of eCO2 on reducing the negative effects of soil W was related to their ability to enhance plant photosynthesis, which in turn provided energy and a carbon source for scavenging the reactive oxygen species (ROS) accumulation caused by soil W stress. [ABSTRACT FROM AUTHOR]

Increases in atmospheric CO2 is known to promote plant growth under heavy metals stress conditions. However, vanadium (V) stress mitigating the impact of eCO2 as well as the physiological and biochemical bases of this stress mitigation have not been well studied. To this end, this study investigated the growth, photosynthetic parameters, oxidative damages antioxidants, and antioxidants enzymes in wheat plants grown under ambient (420 PPM) and high eCO2 (720 ppm) levels. Exposing wheat plants to higher V increased its accumulation in plants which consequentially inhibited plant growth and induced oxidative damage. An increase in antioxidant and detoxification defense systems was observed but it was not enough to reduce V stress toxicity. On the other hand, wheat growth was improved as a result of reduced V uptake and toxicity on photosynthesis under eCO2. To reduce V uptake, wheat accumulated citric acid, and oxalic acid in soil preferentially under both treatments but to more extend under V and eCO2. Additionally, improved photosynthesis induced high carbon availability that was directed to produce chelating proteins (metallothioneins, phytochelatin) and antioxidants (phenolics, flavonoids, total antioxidant capacity). This study advances our knowledge of the processes behind the variations in the physiological and biochemical responses of the wheat crop under V and eCO2 conditions. [ABSTRACT FROM AUTHOR]

Through metabolic analysis, the present research seeks to reveal the defense mechanisms activated by a heavy metals-resistant plant, Sesuvium portulacastrum L. In this regard, shifting metabolisms in this plant were investigated in different heavy metals-contaminated experimental sites, which were 50, 100, 500, 1000, and 5000 m away from a man-fabricated sewage dumping lake, with a wide range of pollutant concentrations. Heavy metals contaminations in contaminated soil and their impact on mineral composition and microbial population were also investigated. The significant findings to emerge from this research were the modifications of nitrogen and carbon metabolisms in plant tissues to cope with heavy metal toxicity. Increased plant amylase enzymes activity in contaminated soils increased starch degradation to soluble sugars as a mechanism to mitigate stress impact. Furthermore, increased activity of sucrose phosphate synthase in contaminated plants led to more accumulation of sucrose. Moreover, no change in the content of sucrose hydrolyzing enzymes (vacuolar invertase and cytosolic invertase) in the contaminated sites can suggest the translocation of sucrose from shoot to root under stress. Similarly, although this study demonstrated a high level of malate in plants exposed to stress, caution must be applied in suggesting a strong link between organic acids and the activation of defense mechanisms in plants, since other key organic acids were not affected by stress. Therefore, activation of other defense mechanisms, especially antioxidant defense molecules including alpha and beta tocopherols, showed a greater role in protecting plants from heavy metals stress. Moreover, the increment in the content of some amino acids (e.g., glycine, alanine, glutamate, arginine, and ornithine) in plants under metal toxicity can be attributed to a high level of stress tolerance. Moreover, strategies in the excitation of the synthesis of the unsaturated fatty acids (oleic and palmitoleic) were involved in enhancing stress tolerance, which was unexpectedly associated with an increase in the accumulation of palmitic and stearic (saturated fatty acids). Taken together, it can be concluded that these multiple mechanisms were involved in the response to stress which may be cooperative and complementary with each other in inducing resistance to the plants. [ABSTRACT FROM AUTHOR]

Propiconazole (PCZ), a triazole broad spectrum fungicide has been frequently detected in agricultural water webs. This emerging contaminant imposes a serious toxic impact on soil and aquatic microbiota. Thus, we aimed to investigate the potential of the microalgae as PCZ phycoremediator. To this end, its toxicity, degradation and detoxification mechanisms by Scenedesmus obliquus and Nostoc muscorum were studied. Over a week, both species were exposed to mild (5 mg/L) and high (10 mg/L) PCZ concentrations. Results showed a dose-dependent accumulation of PCZ typically higher in S. obliquus than in N. muscorum. Moreover, S. obliquus degraded PCZ into a less toxic environmental product; 1-[2-(2,4-dichlorophenyl)− 4-(hydroxypropyl)− 1,3-dioxolan-2ylmethyl]− 1,2,4-triazole and 1-(2,4-dichlorophenyl)− 2-(1,2,4-triazol-1-yl) ethanone. The metabolic pathway assumed cellular dehydroxylation and side chain breakdown in S. obliquus. The high PCZ dose significantly decreased cell growth, chlorophyll a content and inhibited photosynthesis activity and machinery (PEPC and RuBisCo) in both species but, to lesser extend in S. obliquus. Additionally, the exposure to high concentration of PCZ caused a serious oxidative damage especially in N. muscorum. This damage is evident by increased lipid peroxidation, H 2 O 2 level, protein oxidation and NADPH oxidase activity. The two species experienced differential antioxidant and detoxification mechanisms using glutathione-S-transferases, phytochelatins and metalothionine to alleviate PCZ-oxidative stress. This study represented S. obliquus as an efficient PCZ phycoremediator and provided new data on the PCZ toxicity, environmental fate and risk of PCZ to aquatic environment. [Display omitted] • S. obliquus accumulated considerable level of propiconazole (PCZ). • PCZ was detoxified and decomposed by S. obliquus to less-hazardous compounds. • PCZ inhibited photosynthesis & evoked oxidative damage, especially in N. muscorum • Antioxidants induction in S. obliquus explained its resistance to PCZ. • S. obliquus is introduced as a PCZ phycoremediator. [ABSTRACT FROM AUTHOR]