Natural organic matter–induced alleviation of the phytotoxicity to rice (Oryza sativa L.) caused by copper oxide nanoparticles

Abstract

Natural organic matter (NOM) can interact with engineered nanoparticles (NPs) in the environment and modify their behavior and toxicity to organisms. In the present study, the phytotoxicity of copper oxide (CuO) NPs to rice seedlings in the presence of humic acid as a model NOM was investigated. The results showed that CuO NPs induced the inhibition of root elongation, aberrations in root morphology and ultrastructure, and losses of cell viability and membrane integrity. The adverse effects partly resulted from the generation of reactive oxygen species caused by CuO NPs, which led to lipid peroxidation, mitochondrial dysfunction, and programmed cell death in rice seedlings. However, all the phytotoxicity was alleviated with the addition of humic acid because humic acid coatings on nanoparticle surfaces enhanced electrostatic and steric repulsion between the CuO NPs and the plant cell wall/membrane, reducing contact between NPs and plant and CuO NP-induced oxidative damage to plant cells. The present study's results shed light on the mechanism underlying NP phytotoxicity and highlight the influence of NOM on the bioavailability and toxicity of NPs.

Rhizosphere interactions between copper oxide nanoparticles and wheat root exudates in a sand matrix: Influences on copper bioavailability and uptake

“…The roots assayed had been rinsed only with deionized water, to avoid tissue damage and leakage occurring with more rigorous cleaning methods. Despite not distinguishing between Cu physically associated with the roots, such as agglomerates on root hairs (Adams et al 2017) and within root cells, the concentration of Cu associated with the roots was orders of magnitude higher than in the shoots, implying control of translocation of Cu within the plant, as reported by Gao et al (2018) for wheat and in rice (Peng et al 2015(Peng et al , 2017. In the present study, only the control showed greater accumulation of Cu in the shoots than roots, with a shoot to root ratio >1; all doses of CuONPs resulted in partial exclusion of Cu partitioned into shoots (shoot/root >1; Figure 1E).…”

“…Copper is sequestered in vacuoles of the root cells (Clemens et al ) as an exclusion strategy (Baker ). The observed binding of Cu to root cell walls also would limit Cu flux to the shoots (Kopittke et al , ; Peng et al ; Meychik et al ). The translocation of intact CuONPs with subsequent dissolution of CuONPs in planta also, however, is a potential mechanism for increased uptake into the shoot (Wang et al ).…”

“…Modeling CuONP toxicity is still in its infancy; no model of NP uptake or direct toxicity yet exists, despite several studies showing that plant uptake of CuONPs occurs in hydroponics and soil for rice (Peng et al 2015(Peng et al , 2017 and maize . Taken together, this may mean that Cu toxicity from CuONPs in these systems is derived from all forms, including the NPs (Mudunkotuwa et al 2012), and certain bioavailable Cu complexes but with minor effects of free Cu 2þ ions.…”

“…Metallochaperones move Cu internally, with sequestration as a nonharmful form (Clemens et al 2002). Specific efflux pumps remove Cu from the cells (Clemens et al 2002), and Cu binding to plant cell walls is seen in roots (Kopittke et al 2011(Kopittke et al , 2014Peng et al 2015;Meychik et al 2016). Phytotoxicity occurs when these systems are overwhelmed.…”

Foliar Application of Copper Nanoparticles Increases the Fruit Quality and the Content of Bioactive Compounds in Tomatoes

“…The currently available technology affords several approaches to increasing crop production and crop nutraceutical quality. One of these is the application of nanotechnology to improve productivity [4,5]. In recent years, nanotechnology has been used by means of the application of nanomaterials such as nanofertilizers, nanoparticles, or nanopesticides for nutrient management, genetic improvement, plant disease treatment, and plant growth promotion [4].…”