Cell wall: An important medium regulating the aggregation of quantum dots in maize (Zea mays L.) seedlings

Organic matters adsorbed on goethite inhibited the heterogeneous aggregation and adsorption of CdSe quantum dots: Experiments and extended DLVO theory

The widespread use of Cd-based quantum dots (Cd-QDs) has led to their inevitable release into the environment, and the prevalent iron oxides and natural organic matter (NOM) are the key factors affecting the environmental behavior and fate of Cd-QDs. However, the impact of NOM adsorbed on iron oxides on the behavior of Cd-QDs with iron oxides and the mechanism of its interaction are not clear. In this study, two kinds of water-soluble QDs (CdSe QDs and core-shell CdSe/ZnS QDs) were selected to study the aggregation and adsorption behavior on goethite (Goe) and goethite-humic acid/fulvic acid composites (Goe-HA/FA). Aggregation kinetics and adsorption experiments between QDs and Goe(-HA/FA), characterization, and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory calculations indicated that electrostatic interaction was the dominant force for QDs adsorption on Goe(-HA/FA). HA/FA changed the surface charge of Goe and increased the electrostatic repulsion and steric hindrance between the particles, which in turn inhibited the adsorption of QDs on Goe. Besides, unsubstituted aromatic carbons, carboxy carbons, and carbonyl carbons played an important role in the adsorption process, and chemisorption occurred between QDs and Goe(-HA/FA). Our findings are important for better assessing the transport, fate, and potential environmental impacts and risks of Cd-QDs in iron-rich environments.

Comparison of Toxicity and Cellular Uptake of CdSe/ZnS and Carbon Quantum Dots for Molecular Tracking Using Saccharomyces cerevisiae as a Fungal Model

Plant resource sharing mediated by mycorrhizal fungi has been a subject of recent debate, largely owing to the limitations of previously used isotopic tracking methods. Although CdSe/ZnS quantum dots (QDs) have been successfully used for in situ tracking of essential nutrients in plant-fungal systems, the Cd-containing QDs, due to the intrinsic toxic nature of Cd, are not a viable system for larger-scale in situ studies. We synthesized amino acid-based carbon quantum dots (CQDs; average hydrodynamic size 6 ± 3 nm, zeta potential -19 ± 12 mV) and compared their toxicity and uptake with commercial CdSe/ZnS QDs that we conjugated with the amino acid cysteine (Cys) (average hydrodynamic size 308 ± 150 nm, zeta potential -65 ± 4 mV) using yeast Saccharomyces cerevisiae as a proxy for mycorrhizal fungi. We showed that the CQDs readily entered yeast cells and were non-toxic up to 100 mg/L. While the Cys-conjugated CdSe/ZnS QDs were also not toxic to yeast cells up to 100 mg/L, they were not taken up into the cells but remained on the cell surfaces. These findings suggest that CQDs may be a suitable tool for molecular tracking in fungi (incl. mychorrhizal fungi) due to their ability to enter fungal cells.

Exposure pathways, environmental processes and risks of micro (nano) plastics to crops and feasible control strategies in agricultural regions

Micro/nanoplastics (MPs/NPs) pollution may adversely impact agricultural ecosystems, threatening the sustainability and security of agricultural production. This drives an urgent need to comprehensively understand the environmental behavior and effects of MPs/NPs in soil and atmosphere in agricultural regions, and to seek relevant pollution prevention strategies. The rhizosphere and phyllosphere are the interfaces where crops are exposed to MPs/NPs. The environmental behavior of MPs/NPs in soil and atmosphere, especially in the rhizosphere and phyllosphere, determines their plant accessibility, bioavailability and ecotoxicity. This article comprehensively reviews the transformation and migration of MPs/NPs in soil, transportation and deposition in the atmosphere, environmental behavior and effects in the rhizosphere and phyllosphere, and plant uptake and transportation pathways. The article also summarizes the key factors controlling MPs/NPs environmental processes, including their properties, biotic and abiotic factors. Based on the sources, environmental processes and intake risks of MPs/NPs in agroecosystems, the article offers several feasible pollution prevention and risk management options. Finally, the review highlights the need for further research on MPs/NPs in agro-systems, including developing quantitative detection methods, exploring transformation and migration patterns in-situ soil, monitoring long-term field experiments, and establishing pollution prevention and control systems. This review can assist in improving our understanding of the biogeochemistry behavior of MPs/NPs in the soil-plant-atmosphere system and provide a roadmap for future research.

Accumulation, translocation, and transformation of two CdSe/ZnS quantum dots in rice and pumpkin plants

As a widely applied semiconductor nanomaterial, quantum dots (QDs) have drawn considerable interest. In this study, pumpkin and rice seedlings were hydroponically exposed to two core/shell CdSe/ZnS QDs coated with cysteamine (CdSe/ZnS-CA) and polyethylene glycol-carboxy (CdSe/ZnS-PEG-COOH) for 10 days to analyze their time-varying uptake, translocation, and transformation behaviors in plants. Both QDs were mainly adsorbed/absorbed by the roots in the particulate state, and more CdSe/ZnS-CA accumulated than CdSe/ZnS-PEG-COOH. For CdSe/ZnS-CA-treated plants, the Se and Cd concentrations (CSe and CCd) associated with the roots were 561 ± 75 and 580 ± 73 μg/g (dw) for rice and 474 ± 49 and 546 ± 53 μg/g (dw) for pumpkin, respectively, on day 10. For CdSe/ZnS-PEG-COOH-treated plants, the concentrations of Se and Cd associated with roots were 392 ± 56 and 453 ± 56 μg/g (dw) for rice and 363 ± 52 and 417 ± 52 μg/g (dw) for pumpkin, respectively. The surface charges and coatings significantly affected the accumulation of QDs at the beginning of exposure; however, the impaction decreased with time. The ratios between the Cd and Se concentrations (CCd/CSe) in the stems and leaves varied from those of the QD standards, indicating the transformation of the QDs in the exposure system. Se and Cd were more likely to translocate in CdSe/ZnS-PEG-COOH-treated plants than in CdSe/ZnS-CA-treated plants. The vertical translocation of Se was greater than that of Cd. Rice showed greater abilities of accumulation and translocation of Se and Cd from both QDs than pumpkin. These findings improve our understanding of the interference of QDs with plants and their environmental fate.

Nanoplastic impacts on the foliar uptake, metabolism and phytotoxicity of phthalate esters in corn (Zea mays L.) plants

Nanoplastic pollution in terrestrial plants is of increasing concern for its negative effects on living organisms. However, the impacts of nanoplastics on chemical processes and plant physiology of phthalate esters (PAEs) remain unclear. The present work offers insight into the foliar uptake, metabolism and phytotoxicity of two typical PAEs, namely, di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), in corn (Zea mays L.) seedlings and the effects of amino-functionalized polystyrene nanoplastics (PSNPs-NH₂). The presence of PSNPs-NH₂ increased DBP and DEHP accumulation in the leaves by 1.36 and 1.32 times, respectively. PSNPs-NH₂ also promoted the leaf-to-root translocation of DBP and DEHP, with the translocation factor increasing by approximately 1.05- and 1.16-fold, respectively. Furthermore, the addition of PSNPs-NH₂ significantly enhanced the transformation of PAEs to their primary metabolites, mono-butyl phthalate and mono(2-ethylhexyl) phthalate in corn leaves and roots. The co-presence of PSNPs-NH₂ and PAEs showed stronger impairment of photosystem II efficiency via the downregulation of transporter D1 protein, thus exhibiting a greater inhibitory effect on plant growth. Our findings reveal that nanoplastics promote the foliar uptake and transformation of PAE chemicals in crops and exacerbate their toxicity to crop plants, thereby threatening agricultural safety and human health.

Quantum Dots and Their Interaction with Biological Systems

Quantum dots are nanocrystals with bright and tunable fluorescence. Due to their unique property, quantum dots are sought after for their potential in several applications in biomedical sciences as well as industrial use. However, concerns regarding QDs’ toxicity toward the environment and other biological systems have been rising rapidly in the past decade. In this mini-review, we summarize the most up-to-date details regarding quantum dots’ impacts, as well as QDs’ interaction with mammalian organisms, fungal organisms, and plants at the cellular, tissue, and organismal level. We also provide details about QDs’ cellular uptake and trafficking, and QDs’ general interactions with biological structures. In this mini-review, we aim to provide a better understanding of our current standing in the research of quantum dots, point out some knowledge gaps in the field, and provide hints for potential future research.

Understanding the phytotoxic impact of Al3+, nano-size, and bulk Al2O3 on growth and physiology of maize (Zea mays L.) in aqueous and soil media

The release and accumulation of metal-oxide nanoparticles in soils have threatened terrestrial plants. However, limited knowledge is available on the accumulation of nano-Al₂O₃ (22 nm), bulk-Al₂O₃ (167 nm), and Al³⁺ by maize plants and the subsequent impact on its physiology and growth in agar (0.7% w/v), hydroponic (1X), and soil. Maize plants were cultivated with 0.05-2 mg g^-1 or ml^-1 of three Al types and their biological attributes, oxidative status, Al bioaccumulation, and translocation were measured. The ICP-MS results revealed a dose-dependent increase (P ≤ 0.05 or ≤0.01) in Al content in maize tissues following nano-Al₂O₃ and Al³⁺ exposure, however, plants exposed to bulk-Al₂O₃ showed no significant uptake of Al. Atomic mapping by EDX during SEM analysis and TEM revealed varied distributions of nano-Al₂O₃ from roots to aerial parts and intracellular transportation. Al deposition in tissues followed the order: Al³⁺ > nano-Al₂O₃ > bulk-Al₂O₃ and therefore, a similar trend of toxicity was observed for seed germination, the emergence of plant organs, length, biomass accumulation, total chlorophyll, phosphorus content, and total soluble protein. Oxidative stress was profoundly induced dose-dependently and was highest at 2 mg ml^-1 or g^-1 of Al³⁺ and nano-Al₂O₃ when superoxide radical formation, proline induction, activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (GPX), and glutathione reductase (GR) and membrane lipid peroxidation were measured. Aluminum toxicity was found higher in hydroponically grown maize compared to soil-grown maize. Forty days exposure in soil showed greater inhibition of maize growth compared to 20 days exposure. This study is significant in understanding the maize response to different Al types in soil and soil-free media.

Altering natural photosynthesis through quantum dots: effect of quantum dots on viability, light harvesting capacity and growth of photosynthetic organisms

Quantum dots are versatile fluorescent semiconductor nanocrystals with unique photophysical properties. They have been used in various research fields of biotechnology effectively for almost three decades including cell imaging, protein tracking, energy transfer, etc. With their great potential as energy donors or acceptors, quantum dots have also been used in many studies about altering growth rate and photosynthetic activity of photosynthetic organisms by manipulating their light harvesting capacity. In this review, effect of quantum dots on growth rate of photosynthetic organisms and light harvesting capacity of photosynthetic organisms were discussed in details together with toxic effects of cadmium-based and carbon-based quantum dots on photosynthetic organisms. In short, as one of the promising materials of nanotechnology, quantum dots have become one of the essential research topics in photosynthesis research area and will help researchers to manipulate natural photosynthesis in future.

Surface charge affects foliar uptake, transport and physiological effects of functionalized graphene quantum dots in plants

The present study focused on evaluating the effects of surface charge on foliar uptake, translocation and physiological response of graphene quantum dots (GQDs) in maize (Zea mays L.) plants. Here, maize seedlings were foliar exposed to 10 mg/L GQDs modified with positively charged amino functional groups (NH₂-GQDs) and negatively charged hydroxyl functional groups (OH-GQDs) for 8 days, respectively. Positively charged NH₂-GQDs adhered on the cuticle layer were approximately 2.1 times more than the negatively charged OH-GQDs due to the electrostatic attraction to plant cell wall with negative charge. Within the initial 5 days, most of the GQDs internalized into the leaves via stomatal opening were efficiently translocated to the vasculature and moved down to the roots. Thereafter, the enlargement of aggregation made the particle sizes approach and even exceed the pipe diameter of vascular bundle, thus limiting the leaf-to-root translocation of GQDs, especially for NH₂-GQDs. Compared with positively charged NH₂-GQDs, negatively charged OH-GQDs induced stronger inhibitory effect on photosynthesis, higher accumulation of malondialdehyde and stimulation to enzyme activities of superoxide dismutase, catalase, and peroxidase. Overall, our findings provide direct evidence for the influence of surface charge on foliar uptake, translocation, and physiological effects of GQDs in crop plants, and imply that foliar exposure of GQDs negatively impact plant photosynthesis and growth health.

Foliar uptake and leaf-to-root translocation of nanoplastics with different coating charge in maize plants

Foliar uptake of nanoplastics could represent a pathway responsible for pollutant loads in crop plants, thereby posing risks to human health. To evaluate the foliar uptake, leaf-to-root translocation of nanoplastics, as well as the influences of surface charge on the above processes and physiological effects to plants, maize (Zea mays L.) seedlings were foliar exposed to carboxyl-modified polystyrene nanoplastics (PS-COOH) and amino-modified polystyrene nanoplastics (PS-NH₂), respectively. Both PS nanoplastics could effectively accumulate on the maize leaves, accompanied by observable particle aggregation. Due to electrostatic attraction to the negatively charged cell wall, positively charged PS-NH₂ association with the leaf surfaces was significantly more than negatively charged PS-COOH. The fraction of PS nanoplastics entry into the leaves could efficiently transfer to the vasculature mainly through stomatal opening and move down to the roots through vascular bundle. Meanwhile, the occurrence of aggregation limited the nanoplastic translocation to the roots, especially for PS-NH₂ with larger aggregate sizes relative to PS-COOH. Compared with negatively charged PS-COOH, positively charged PS-NH₂ treatment had a higher inhibitory effect on photosynthesis and a stronger stimulation to the activity of antioxidant systems. Overall, our findings give a scientific basis for the risk assessment of nanoplastic exposure in air-plant systems.