The role of Fe-nano particles in scarlet sage responses to heavy metals stress

Metal-based-oxide nanoparticles assisted the in vitro culture growth of Populus alba as micronutrients: essential metabolic processes and genetic stability

The present study evaluates the in vitro culture growth rate of Populus alba upon using nano metal-based-oxides such as hematite (Fe₂O₃ NPs), zinc oxide (ZnO NPs), and manganese oxide (Mn₂O₃ NPs) nanoparticles as analogues of three primary micronutrients such as iron (Fe), zinc (Zn), and manganese (Mn), which exist in soil as micronutrients. Herein, the in vitro culture growth rate was investigated using three different concentrations (i.e., 20, 40, and 60 mg L^-1) of as-prepared metal oxide nanoparticles compared to the control. In addition, the as-prepared nanoparticles have been prepared via the co-precipitation method. Furthermore, the physicochemical properties were investigated using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and dynamic light scattering techniques. Overall, a significant difference in the biomass production-related parameters such as fresh weight, shoot length, and root length was observed compared to the control upon the treatment with micronutrient-based nano-metal-oxides (i.e., Mn₂O₃ > Fe₂O₃ > ZnO NPs, respectively). In addition, a significant increase in the root number of Populus alba plants upon their treatment with ZnO NPs was observed compared to other prepared nano-metal-oxides and the control. Also, a remarkable increase in the chlorophyll index was monitored upon the treatment with Fe₂O₃ NPs rather than the other commonly used Mn₂O₃ and ZnO NPs, respectively. Moreover, RAPD-PCR bioassays were applied, and the actual six primers showed a genetic variation percentage of 34.17%, indicating that Populus alba is highly genetically stable even in highly contaminated soil. As a result, our findings suggest an idea that indicates the ability to enhance the in vitro culture growth rate of Populus alba plants using metal oxide nanoparticles as analogous to essential micronutrients.

Effects of urease-producing bacteria and eggshell on physiological characteristics and Cd accumulation of pakchoi (Brassica chinensis L.) plants

Soil cadmium (Cd) contamination resulting from anthropogenic activity poses severe threats to food safety and human health. In this study, a pot experiment was performed to evaluate the possibility of using urease-producing bacterium UR21 and eggshell (ES) waste for improving the physiological characteristics and reducing Cd accumulation of pakchoi (Brassica chinensis L.) plants. UR21 has siderophore and IAA production ability. The application of UR21 and ES individually or in combination could improve the root and shoot length, and fresh and dry weight of pakchoi plants under Cd stress. In Cd + ES + UR21-treated plants, the dry weight of shoot and root were increased by 61.54% and 72.73%, respectively. The chlorophyll a, chlorophyll b, and carotenoid content were increased by 52.19%, 42.95%, and 95.56% in Cd + ES + UR21-treated plants. Meanwhile, the H₂O₂ and MDA content were decreased while the SOD and POD activity were increased, and an increase of soluble protein level in pakchoi plants was observed under Cd + ES + UR21 treatment. Importantly, eggshell and UR21 alone or in combination induced a decline of Cd content in pakchoi plants, especially that Cd + ES + UR21 treatment decreased Cd content in shoot and root by 26.96% and 42.91%, respectively. Meanwhile, the soil urease and sucrase activities were enhanced. Generally, the combined application of ureolytic bacteria UR21 and eggshell exhibited better effects than applied them individually in terms of alleviating Cd toxicity in pakchoi plants. Our findings may give a unique perspective for an eco-friendly and sustainable strategy to remediate heavy metal-polluted soils.

Combined Role of Fe Nanoparticles (Fe NPs) and Staphylococcus aureus L. in the Alleviation of Chromium Stress in Rice Plants

Chromium (Cr) is a toxic heavy metal whose high concentration in soil badly affects plant growth, photosynthesis, and overall yield. Metal-derived nano-particles and metal-resistant bacteria can strengthen the plant defense system against different abiotic stresses; however, little is known about the use of nanoparticles in conjunction with bacteria. This study examined the combined effect of Fe nanoparticles (Fe NPs) and a chromium-resistant bacterium Staphylococcus aureus, on rice plants grown on chromium saturated medium. Chromium stress reduced rice growth, biomass, and chlorophyll contents by causing oxidative damage leading to overproduction of electrolyte leakage, hydrogen peroxide, and malondialdehyde. Fe NPs significantly improved plant growth, biomass, yield, and photosynthetic activity by enhancing the chlorophyll contents and alleviating oxidative damage. Application of Fe NPs also reduced the uptake and accumulation of Cr in the plants by increasing the bioavailability of micronutrients to the plant. The Fe NPs decreased oxidative damage and enhanced the enzymatic and non-enzymatic activity in the plant to withstand Cr stress compared to the plants without Fe NPs treatments. The inoculation of rice plants with the chromium-resistant bacteria S. aureus further enhanced the positive impact of Fe NPs by transforming the toxic form of chromium (Cr⁶⁺) into a less toxic form of chromium (Cr³⁺). The bacterial inoculation reduced Cr uptake by plants through adsorption of Cr ions, resulting in decreased chromium ion bioavailability. At chromium level 100 mg/kg, the foliar application of Fe NPs from 0 to 20 mg/L increased the total chlorophyll contents from 2.8 to 3.9. The application of S. aureus further enhanced the chlorophyll contents from 4.4 to 5.4, respectively. The current study suggested that combining Fe NPs and S. aureus could be a viable strategy for reducing Cr toxicity and accumulation in rice plants and most likely other plants.