Interactive effects of mercuric oxide nanoparticles and future climate CO2 on maize plant.

So far, the phytotoxic hazards of nano-sized mercuric oxide (HgO-NPs) are not investigated. Herein, the phytotoxicity of fully characterized HgO-NPs (100 mg/kg soil), prepared by coprecipitation method, on maize grown under ambient (aCO2, 410 ppm) and elevated CO2 (eCO2, 620 ppm) was investigated. Regardless of CO2 concentration, HgO-NPs treatment increased Hg levels in maize organs. HgO-NPs induced severe oxidative stress in aCO2 grown plants as indicated by reduced growth and photosynthesis and accumulation of reactive oxygen species (ROS), through photorespiration and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activities, and lipid and protein oxidation products. Although HgO-NPs increased molecular (polyphenols, flavonoids, tocopherols) and enzymatic (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione peroxidase) antioxidants in shoots of aCO2 plants, but this failed to fight the eruption of increased ROS. On contrary, eCO2 treatment mitigated the HgO-NPs impact by promoting photosynthesis and reducing the Hg-induced ROS production. Moreover, eCO2 promoted ROS detoxification via molecular antioxidants overproduction, enhanced superoxide dismutase, catalase and peroxidases activities, and modulation of reduced ascorbate/oxidized ascorbate and reduced glutathione/oxidized glutathione homeostasis. The combined HgO-NPs + eCO2 treatment also enhanced the glutathione-S-transferase activity. This study suggests that HgO-NPs cause severe phytotoxic hazards and this effect will be less detrimental under future CO2 climate.

Silicon dioxide nanoparticles ameliorate the phytotoxic hazards of aluminum in maize grown on acidic soil.

Aluminum (Al) toxicity is a major constraint for crop production in acid soils. Therefore, looking for sustainable solutions to increase plant tolerance to Al toxicity is needed. Although several studies addressed the potential utilization of silica or silicon dioxide nanoparticles (SNPs) to ameliorate heavy metal phytotoxicity, the exact mechanisms underlying SNPs-induced stress tolerance are still unknown. The current study investigated how SNPs could mitigate Al toxicity in maize plants grown on acidic soil. The impact of Al alone or in combination with SNPs on Al accumulation and detoxification, plant growth, photosynthetic C assimilation and redox homeostasis has been investigated. Al accumulation in stressed-maize organs reduced their growth, decreased photosynthesis related parameters and increased production of reactive oxygen species, through induced NADPH oxidase and photorespiration activities, and cell damage. These effects were more pronounced in roots than in leaves. SNPs ameliorated Al toxicity at growth, physiological and oxidative damage levels. Co-application of SNPs significantly reduced the activities of the photorespiratory enzymes and NADPH oxidase. It stimulated the antioxidant defense systems at enzymatic (superoxide dismutase, catalase, ascorbate and glutathione peroxidases) and non-enzymatic (ascorbate, glutathione, polyphenols, flavonoids, tocopherols, and FRAP) levels. Moreover, SNPs increased organic acids accumulation and metal detoxification (i.e. glutathione-S-transferase activity) in roots, as a protective mechanism against Al toxicity. The SNPs induced-protective mechanisms was dependent on the applied Al concentration and acted in organ-specific manner. Overall, the current study suggests the promising application of SNPs as an innovative approach to mitigate Al phytotoxicity in acidic soils and provides a comprehensive view of the cellular and biochemical mechanisms underlying this mitigation capacity.