Alleviation of silver toxicity by calcium chloride (CaCl2) in Lemna gibba L

The effects of solubility of silver nanoparticles, accumulation, and toxicity to the aquatic plant Lemna minor

The use of silver nanoparticles (AgNPs) in commercial products has increased due to their antibacterial properties and their impacts on the environment must be investigated. This scenario has motivated the conduction of this study, which relates different factors that affect the toxicity of AgNPs to the aquatic plant Lemna minor such as size, accumulation, concentration, and dissolution of AgNPs. To this end, synthesized AgNPs measuring 30, 85, and 110 nm were added into the culture medium to observe toxicity for 30 days. The mapping by SEM showed that the smallest AgNPs can translocate from roots to leaves due to its mobility and internalization. As predicted by the Ostwald equation, the solubility for 30-nm AgNPs increased almost 3 times at the end of 30 days, while for 85 and 110 nm size nanoparticles, after 7 days, the solubility decreased due to "Ostwald ripening" process. Plant mortality was assessed and, after 1 month, the size of 30 nm was the most toxic with negative growth in all studied concentrations, with 60% mortality in the worst case. The concentration of 50 μg mL^-1 was toxic in all sizes with negative growth in the period. Therefore, the investigation of AgNPs' toxicity needs to consider a different factor to better understand their effects on aquatic plants and the environment.

Physiological and biochemical effect of silver on the aquatic plant Lemna gibba L.: Evaluation of commercially available product containing colloidal silver

This paper aims to evaluate the effects of a product containing colloidal silver in the aquatic environment, using duckweed Lemna gibba as a model plant. Therefore, growth parameters, photosynthetic pigments content and protein content as physiological indices were evaluated. Changes in the content of non-enzymatic antioxidants and activity of several antioxidant enzymes, alongside with the accumulation of hydrogen peroxide and lipid peroxidation end-products were assessed to explore the potential of colloidal silver to induce oxidative stress. The commercially available colloidal silver product contained a primary soluble form of silver. The treatment with colloidal silver resulted in significant physiological and biochemical changes in L. gibba plants and a consequent reduction of growth. Accumulation of silver caused altered nutrient balance in the plants as well as a significant decrease in photosynthetic pigments content and protein concentration. The antioxidative response of L. gibba plants to treatment with colloidal silver was inadequate to protect the plants from oxidative stress caused by metal accumulation. Silver caused concentration-dependent and time-dependent hydrogen peroxide accumulation as well as the elevation of lipid peroxidation levels in L. gibba plants. The use of commercially available products containing colloidal silver, and consequent accumulation of silver, both ionic and nanoparticle form in the environment, represents a potential source of toxicity to primary producers in the aquatic ecosystem.

Alleviating effects of calcium on cobalt toxicity in two barley genotypes differing in cobalt tolerance

Cobalt (Co) contamination in soils is becoming a severe issue in environment safety and crop production. Calcium (Ca)^, as a macro-nutrient element, shows the antagonism with many divalent heavy metals and the capacity of alleviating oxidative stress in plants. In this study, the protective role of Ca in alleviating Co stress was hydroponically investigated using two barley genotypes differing in Co toxicity tolerance. Barley seedlings exposed to 100µM Co showed the significant reduction in growth and photosynthetic rate, and the dramatic increase in the contents of reactive oxygen species (ROS), malondialdehyde (MDA), reduced glutathione (GSH) and oxidized glutathione (GSSG), and the activities of anti-oxidative enzymes, with Ea52 (Co-sensitive) being much more affected than Yan66 (Co-tolerant). Addition of Ca in growth medium alleviated Co toxicity by reducing Co uptake and enhancing the antioxidant capacity. The effect of Ca in alleviating Co toxicity was much greater in Yan66 than in Ea52. The results indicate that the alleviation of Co toxicity in barley plants by Ca is attributed to the reduced Co uptake and enhanced antioxidant capacity.