Physiological and Molecular Response of <i>Arabidopsis thaliana</i> (L.) to Nanoparticle Cerium and Indium Oxide Exposure

The effects of cerium oxide (CeO₂) and indium oxide (In₂O₃) nanoparticles (NPs) exposure on <i>Arabidopsis thaliana</i> (L.) Heynh. were investigated. After inoculation in half strength MS medium amended with 0–2000 ppm CeO₂ and In₂O₃ NPs for 25 days, both physiological and molecular responses were evaluated. Exposure at 250 ppm CeO₂ NPs significantly increased plant biomass, but at 500–2000 ppm, plant growth was decreased by up to 85% in a dose-dependent fashion. At 1000 and 2000 ppm CeO₂ NPs, chlorophyll production was reduced by nearly 60% and 85%, respectively, and anthocyanin production was increased 3–5-fold. Malondialdehyde (MDA) production, a measure of lipid peroxidation, was unaffected by exposure to 250–500 ppm CeO₂ NPs, but at 1000 ppm, MDA formation was increased by 2.5-fold. Exposure to 25–2000 ppm In₂O₃ NPs had no effect on <i>A. thaliana</i> biomass and only minor effects (15%) on root elongation. Total chlorophyll and MDA production were unaffected by In₂O₃ NPs exposure. Molecular response to NP exposure as measured by qPCR showed that both types of elements altered the expression of genes central to the stress response such as the sulfur assimilation and glutathione (GSH) biosynthesis pathway, a series of genes known to be significant in the detoxification of metal toxicity in plants. Interestingly, In₂O₃ NPs exposure resulted in a 3.8–4.6-fold increase in glutathione synthase (GS) transcript production, whereas CeO₂ NPs yielded only a 2-fold increase. It seems likely that the significantly greater gene regulation response upon In₂O₃ NPs exposure was directly related to the decreased phytotoxicity relative to CeO₂ treatment. The use of NP rare earth oxide elements has increased dramatically, yet knowledge on fate and toxicity has lagged behind. To our knowledge, this is the first report evaluating both physiological and molecular plant response from exposure to these important nanoparticles

Analysis of Silver Nanoparticles in Antimicrobial Products Using Surface-Enhanced Raman Spectroscopy (SERS)

Silver nanoparticles (AgNPs) are the most commonly used nanoparticles in consumer products. Concerns over human exposure to and risk from these particles have resulted in increased interest in novel strategies to detect AgNPs. This study investigated the feasibility of surface-enhanced Raman spectroscopy (SERS) as a method for the detection and quantification of AgNPs in antimicrobial products. By using ferbam (ferric dimethyl-dithiocarbamate) as an indicator molecule that binds strongly onto the nanoparticles, AgNPs detection and discrimination were achieved based on the signature SERS response of AgNPs-ferbam complexes. SERS response with ferbam was distinct for silver ions, silver chloride, silver bulk particles, and AgNPs. Two types of AgNPs with different coatings, citrate and polyvinylpirrolidone (PVP), both showed strong interactions with ferbam and induced strong SERS signals. SERS was effectively applicable for detecting Ag particles ranging from 20 to 200 nm, with the highest signal intensity in the 60–100 nm range. A linear relationship (<i>R</i>² = 0.9804) between Raman intensity and citrate-AgNPs concentrations (60 nm; 0–20 mg/L) indicates the potential for particle quantification. We also evaluated SERS detection of AgNPs in four commercially available antimicrobial products. Combined with ICP-MS and TEM data, the results indicated that the SERS response is primarily dependent on size, but also affected by AgNPs concentration. The findings demonstrate that SERS is a promising analytical platform for studying environmentally relevant levels of AgNPs in consumer products and related matrices

Modified Biochars Reduce Leaching while Maintaining Bioavailability of Phosphate to Dragoon Lettuce (Lactuca sativa) in Potting Tests

The traditional use of soluble phosphate fertilizers in agriculture depletes finite global supplies and accounts for a major nonpoint source of phosphorus pollution. In potting experiments, we tested whether two modified softwood biochars that strongly bind phosphate could fertilize romaine “Dragoon” lettuce while retarding P leaching. Modifications included doping with MgO (MgO-BC), or binding, postpyrolysis, of a cationic polymer, poly­(diallyldimethylammonium) chloride (pDADMAC-BC). The former sorbs phosphate via coordination with MgO nanoparticles or coatings and the latter through enhanced anion exchange. The presterilized potting soil (SS) was a mixture of fine sand and peat moss. The test sets contained modified biochars (3 or 2% g-C/g-SS) either preadsorbed with phosphate or added along with the same amount of soluble phosphate, all at the rate of 180 or 120 mg-P/pot. We also tested sets containing the P-rich mineral dolomite. Control sets included SS and SS amended with unmodified biochar, with or without soluble phosphate, and SS amended with MgO-BC but without soluble phosphate. All pots were fertilized weekly with a phosphate-free Hoagland nutrient solution. Sets amended with the modified biochars, either preadsorbed with phosphate or added along with soluble phosphate, gave dramatically higher plant yields than the control or dolomite sets. Sets amended with modified biochars preadsorbed with phosphate leached a small fraction (0.1–23%) of P relative to the controls fertilized with soluble phosphate. Plant uptake of Mg was high in sets amended with MgO-doped biochars and induced a toxic response when those biochars were incorporated uniformly in a fine powdered form. Arbuscular mycorrhizal fungi added to some sets decreased the root:shoot ratio but otherwise had little impact. The results indicate that the tested modified biochars can appreciably reduce P leaching while providing a bioavailable source of P for crop growth

Tannic acid alleviates bulk and nanoparticle Nd₂O₃ toxicity in pumpkin: a physiological and molecular response

<p>The effect of dissolved organic matter (DOM) on nanoparticle toxicity to plants is poorly understood. In this study, tannic acid (TA) was selected as a DOM surrogate to explore the mechanisms of neodymium oxide NPs (Nd₂O₃ NPs) phytotoxicity to pumpkin (<i>Cucurbita maxima</i>). The results from the tested concentrations showed that 100 mg L⁻¹ Nd₂O₃ NPs were significantly toxic to pumpkin in term of fresh biomass, and the similar results from the bulk particles and the ionic treatments were also evident. Exposure to 100 mg L⁻¹ of Nd₂O₃ NPs and BPs in 1/5 strength Hoagland’s solution not only significantly inhibited pumpkin growth, but also decreased the S, Ca, K and Mg levels in plant tissues. However, 60 mg L⁻¹ TA significantly moderated the observed phytotoxicity, decreased Nd accumulation in the roots, and notably restored S, Ca, K and Mg levels in NPs and BPs treated pumpkin. TA at 60 mg L⁻¹ increased superoxide dismutase (SOD) activity in both roots (17.5%) and leaves (42.9%), and catalase (CAT) activity (243.1%) in the roots exposed to Nd₂O₃ NPs. This finding was confirmed by the observed up-regulation of transcript levels of SOD and CAT in Nd₂O₃ NPs treated pumpkin analyzed by quantitative reverse transcription polymerase chain reaction. These results suggest that TA alleviates Nd₂O₃ BPs/NPs toxicity through alteration of the particle surface charge, thus reducing the contact and uptake of NPs by pumpkin. In addition, TA promotes antioxidant enzymatic activity by elevating the transcript levels of genes involved in ROS scavenging. Our results shed light on the mechanisms underlying the influence of DOM on the bioavailability and toxicity of NPs to terrestrial plants.</p

Impact of Ag Nanoparticle Exposure on <i>p,p′</i>-DDE Bioaccumulation by Cucurbita pepo (Zucchini) and Glycine max (Soybean)

The effect of nanoparticle (NP), bulk, or ionic Ag exposure on dichlorodiphenyldichloroethylene (<i>p,p′</i>-DDE; DDT metabolite) accumulation by Glycine max L. (soybean) and Cucurbita pepo L. (zucchini) was investigated. The plants were grown in 125-mL jars of vermiculite amended with 500 or 2000 mg/L of bulk or NP Ag; ion controls at 5 and 20 mg/L were established. During 19 d of growth, plants were amended with solution containing 100 ng/mL of <i>p,p′</i>-DDE. Total shoot <i>p,p′</i>-DDE levels in non-Ag exposed G. max and C. pepo were 500 and 970 ng, respectively; total root DDE content was 13 700 and 20 300 ng, respectively. Ag decreased the <i>p,p′</i>-DDE content of G. max tissues by up to 40%, with NP exposure resulting in less contaminant uptake than bulk Ag. Total Ag content of exposed G. max ranged from 50.5 to 373 μg; NP-exposed plants had 1.9–2.2 times greater overall Ag than corresponding bulk particle treatments and also significantly greater relative Ag transport to shoot tissues. Bulk and NP Ag at 500 mg/L suppressed DDE uptake by C. pepo by 21–29%, although Ag exposure at 2000 mg/L had no impact on contaminant uptake. Similar to G. max, C. pepo whole plant Ag content ranged from 50.5 to 182 μg, with tissue element content generally being greater for NP exposed plants. These findings show that the Ag may significantly alter the accumulation and translocation of cocontaminants in agricultural systems. Notably, the cocontaminant interactions vary both with Ag particle size (NP vs bulk) and plant species. Future investigations will be needed to clarify the mechanisms responsible for the cocontaminant interactions and assess the impact on overall exposure and risk

Reduced Silver Nanoparticle Phytotoxicity in Crambe abyssinica with Enhanced Glutathione Production by Overexpressing Bacterial γ‑Glutamylcysteine Synthase

Silver nanoparticles (Ag NPs) are widely used in consumer products, and their release has raised serious concerns about the risk of their exposure to the environment and to human health. However, biochemical mechanisms by which plants counteract NP toxicity are largely unknown. We have previously engineered Crambe abyssinica plants expressing the bacterial γ-glutamylecysteine synthase (γ-ECS) for enhancing glutathione (GSH) levels. In this study, we investigated if enhanced levels of GSH and its derivatives can protect plants from Ag NPs and AgNO₃ (Ag⁺ ions). Our results showed that transgenic lines, when exposed to Ag NPs and Ag⁺ ions, were significantly more tolerant, attaining a 28%–46% higher biomass and 34–49% more chlorophyll content, as well as maintaining 35–46% higher transpiration rates as compared to those of wild type (WT) plants. Transgenic γ-ECS lines showed 2–6-fold Ag accumulation in shoot tissue and slightly lower or no difference in root tissue relative to levels in WT plants. The levels of malondialdehyde (MDA) in γ-ECS lines were also 27.3–32.5% lower than those in WT Crambe. These results indicate that GSH and related peptides protect plants from Ag nanotoxicity. To our knowledge, this is the first direct report of Ag NP detoxification by GSH in transgenic plants, and these results will be highly useful in developing strategies to counteract the phytotoxicty of metal-based nanoparticles in crop plants

Nanoscale Sulfur Improves Plant Growth and Reduces Arsenic Toxicity and Accumulation in Rice (Oryza sativa L.)

Rice is known to accumulate arsenic (As) in its grains, posing serious health concerns for billions of people globally. We studied the effect of nanoscale sulfur (NS) on rice seedlings and mature plants under As stress. NS application caused a 40% increase in seedling biomass and a 26% increase in seed yield of mature plants compared to untreated control plants. AsIII exposure caused severe toxicity to rice; however, coexposure of plants to AsIII and NS alleviated As toxicity, and growth was significantly improved. Rice seedlings treated with AsIII + NS produced 159 and 248% more shoot and root biomass, respectively, compared to plants exposed to AsIII alone. Further, AsIII + NS-treated seedlings accumulated 32 and 11% less As in root and shoot tissues, respectively, than the AsIII-alone treatment. Mature plants treated with AsIII + NS produced 76, 110, and 108% more dry shoot biomass, seed number, and seed yield, respectively, and accumulated 69, 38, 18, and 54% less total As in the root, shoot, flag leaves, and grains, respectively, compared to AsIII-alone-treated plants. A similar trend was observed in seedlings treated with AsV and NS. The ability of sulfur (S) to alleviate As toxicity and accumulation is clearly size dependent as NS could effectively reduce bioavailability and accumulation of As in rice via modulating the gene expression activity of As transport, S assimilatory, and glutathione synthesis pathways to facilitate AsIII detoxification. These results have significant environmental implications as NS application in agriculture has the potential to decrease As in the food chain and simultaneously enable crops to grow and produce higher yields on marginal and contaminated lands