Root System Architecture, Copper Uptake and Tissue Distribution in Soybean (Glycine max (L.) Merr.) Grown in Copper Oxide Nanoparticle (CuONP)-Amended Soil and Implications for Human Nutrition

Abstract

Understanding the potential uptake and biodistribution of engineered nanoparticles (ENPs) in soil-grown plants is imperative for realistic toxicity and risk assessment considering the oral intake of edibles by humans. Herein, growing N-fixing symbiont (Bradyrhizobium japonicum) inoculated soybean (Glycine max (L.) Merr.) for a full lifecycle of 120 days, we assessed the potential influence of particle size (25, 50, and 250 nm) and concentration (0, 50, 100, 200, and 500 mg/kg soil) of Copper oxide nanoparticles (CuONPs) on: (1) root system architecture, (2) soil physicochemical attributes at the soil–root interface, and (3) Cu transport and accumulation in root, stem, leaf, and seed in soybean, and compared them with the soluble Cu2+ ions and water-only controls. Finally, we performed a comparative assessment of total seed Cu levels in soybean with other valuable food sources for Cu intake and discussed potential human health implications. Results showed particle size- and concentration-dependent influence of CuONPs on Cu uptake and distribution in root, stem, leaf, and seed. Alterations in root architecture (root biomass, length, volume, and area) were dependent on the Cu compound types, Cu concentrations, and their interactions. Concentration–response relationships for all three sizes of CuONPs and Cu2+ ions were found to be linear. Furthermore, CuONPs and Cu2+ ions had inhibitory effects on root growth and development. Overall, soybean responses to the smallest size of CuONPs–25 nm—were greater for all parameters tested compared to the two larger-sized CuONPs (50 nm, 250 nm) or Cu2+ ions. Results suggest that minor changes in soil-root physicochemical attributes may not be a major driver for Cu uptake in soybean. Cu bioaccumulation followed the order: root > leaf > stem > seed. Despite reduction in root architecture and seed yield, the smallest size CuONPs–25 nm led to increased total seed Cu uptake compared to the larger-sized CuONPs or Cu2+ ions. Our findings also suggest that soil amendment with CuONPs, and more so with the smallest size of CuONPs–25 nm—could significantly improve seed nutritional Cu value in soybean as reflected by the % Daily Values (DV) and are rated “Good” to “Very Good” according to the “World’s Healthiest Foods” rating. However, until the potential toxicity and risk from CuONP-fortified soybean seed ingestion is characterized in humans, we caution recommending such seeds for daily human consumption when addressing food Cu-deficiency and associated diseases, globally.

Perspective of Melatonin-Mediated Stress Resilience and Cu Remediation Efficiency of Brassica juncea in Cu-Contaminated Soils

“…In this study, Cu inhibited the activity of NR and N assimilation in the stressed plants, and maximum reduction was observed in the plants raised with Cu (60 mg kg –1 ). The deduction may be due to reduced uptake of N by the roots, dysfunction of the enzyme under excess Cu conditions, alterations in membrane fluidity and composition ( Llorens et al, 2000 ) and root architecture ( Yusefi-Tanha et al, 2020 ), and metabolic dysfunction of the protein enzyme involved in nitrogen assimilation ( Hippler et al, 2018 ). However, the application of MEL mitigated the adverse effect induced by Cu and improved the activity of NR and N content ( Table 7 ).…”

Effects of Iron Oxide Nanoparticles (Fe3O4) on Growth, Photosynthesis, Antioxidant Activity and Distribution of Mineral Elements in Wheat (Triticum aestivum) Plants

“…In this context, different effects on plants’ operations can be caused by NPs of the same type but different sizes or shapes. For example, small-sized CuO NP (25 nm) led to increased Cu uptake in seeds and significantly improved Cu content in soybean seeds, despite reduction in root size [ 15 ]; these effects were not reported for larger-sized CuO NPs (50 nm and 250 nm) nor Cu 2+ ions. The same group of authors also reported differences in efficiency of different shaped ZnO NPs (spherical vs. floral-like vs. rod-like) on antioxidant defense systems and seed yield in soybeans [ 16 ].…”

Effects and Mechanisms of Copper Oxide Nanoparticles with Regard to Arsenic Availability in Soil–Rice Systems: Adsorption Behavior and Microbial Response

“…The application of nanomaterials in agriculture has garnered widespread interest. Previous study showed that about 63–91% of the nanomaterials ended up in landfills, 8–28% in soils, and nanomaterials in the atmosphere get deposited on the surfaces of land and water. , Nearly 9% of nanoproducts are used in agricultural nanomaterials and nanocides; copper oxide nanoparticles (CuO NPs) are widely used in agricultural fungicides due to their bacteriostatic properties. − CuO NPs have been demonstrated to be considerably effective in controlling plant diseases as they cause mechanical damage to cell biofilm development, which is toxic to bacteria. − In addition, CuO NPs are considered to be one of the most essential engineered NPs; the growing use and demand for recycled waste water for irrigation has opened up the possibility of releasing CuO NPs into paddy soil via waste water. , CuO NPs are also used as plant growth promoters to enhance the uptake of iron (Fe), calcium, magnesium, and phosphorus in agriculture. , Although CuO NPs are generally recognized as safe salts (GRAS, the FDA’s safety index for food additives), a high dose of CuO NPs (50–1000 mg kg –1 ) significantly increased excessive oxidative stress, inhibited root growth, and decreased the crop yield. − Therefore, the extensive or large-scale use of CuO NPs in paddy soil requires further studies.…”