Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays).

Introduction: The increasing use of cerium nanoparticles (CeO2-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals. Methods: The present investigation was conducted to evaluate the effect of CeO2-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO2-10 nm-NPs/kg-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured. Results and discussion: The NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO2-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO2-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy.

Zn alleviated salt toxicity in Solanum lycopersicum L. seedlings by reducing Na+ transfer, improving gas exchange, defense system and Zn contents.

Soil secondary salinization is a serious menace that has significant influence on the sustainability of agriculture and threatens food security around the world. Zinc (Zn) as an essential plant nutrient associated with many physio-biochemical processes in plants and improve resistance against various abiotic stresses. The role of Zn in acclimation of Solanum lycopersicum L. challenged with salt stress is miserly understood. A hydroponic study was performed with two tomato varieties (Riogrande and Sungold) exposed to the salinity stress (0 mM and 160 mM NaCl) under two Zn concentrations (15 µM and 30 µM ZnSO4). The results revealed that salt stress exerted strongly negative impacts on root and shoot length, fresh and dry biomass, plant water relations, membrane stability, chlorophyll contents, Na+/K+ ratio along with inferior gas exchange attributes and activities of antioxidant enzymes. Moreover, Riogrande was found to be more resistant to salinity stress than Sungold. However, Zn supply significantly alleviated the hazardous effects of salinity by altering compatible solutes accumulation, photosynthetic activity, water relation, soluble sugar contents and providing antioxidant defense against salt stress. The salinity + Zn2 treatment more obviously enhanced RWC (19.0%), MSI (30.8%), SPAD value (17.8%), and activities of SOD (31.7%), POD (28.5%), APX (64.5%) and CAT (23.3%) in Riogrande than Sungold, compared with the corresponding salinity treatment alone. In addition, salinity + Zn2 treatment significantly (P > 0.05) ameliorated salinity stress due to the depreciation in Na+/K+ ratio by 63.3% and 40.8%, Na+ ion relocation from root to shoot by 10.4% and 6.4%, and thereby significantly reduced Na+ ion accumulation by 47.4% and 16.3% in the leaves of Riogrande and Sungold respectively, compared to the salinity treatment alone. Therefore, it was obvious that 30 µM Zn concentration was more effective to induce resistance against salinity stress than 15 µM Zn concentration. Conclusively, it can be reported that exogenous Zn application helps tomato plant to combat adverse saline conditions by modulating photosynthetic and antioxidant capacity along with reduced Na+ uptake at the root surface of tomato plant.

Combined application of citric acid and 5-aminolevulinic acid improved biomass, photosynthesis and gas exchange attributes of sunflower (Helianthus annuus L.) grown on chromium contaminated soil.

Phytoremediation is an important technique to remove heavy metals from contaminated soils due to its efficiency and cost-effectiveness. The present study was conducted to assess the synergistic role of 5-aminolevulinic acid (ALA) and citric acid (CA) in improving the phyto-extraction of chromium (Cr) by sunflower. Sunflower plants were grown in soil, spiked with different concentrations of Cr (0, 5, 10, 20 mg kg-1). Various concentrations of 5-ALA (0, 10, 20 mg L-1) and CA (0, 2.5, 5 mM) were applied exogenously at juvenile stage. A significant decrease was observed in biomass and agronomic traits of sunflower under Cr stress alone. Further, Cr toxicity significantly decreased the plant growth, soluble proteins and photosynthetic pigments. However, exogenously applied ALA and CA significantly improved the plants' physiological as well as agronomic attributes by lowering the production of reactive oxygen species and reducing electrolyte leakage. Moreover, Cr uptake was increased with increasing concentration of Cr in spiked soil, which was further enhanced by combined application of ALA and CA.