Biosynthesized Selenium Nanoparticles as an Effective Tool to Combat Soil Metal Stresses in Rice (Oryza sativa L.).

Nanotechnology has demonstrated significant potential to improve agricultural production and increase crop tolerance to abiotic stress including exposure to heavy metals. The present study investigated the mechanisms by which aloe vera extract gel-biosynthesized (AVGE) selenium nanoparticles (Se NPs) alleviated cadmium (Cd)-induced toxicity to rice (Oryza sativa L.). AVGE Se NPs, chemically synthesized bare Se NPs, and NaSeO3 as an ionic control were applied to Cd-stressed rice seedlings via root exposure in both hydroponic and soil systems. Upon exposure to AVGE Se NPs at 15 mg Se/L, the fresh root biomass was significantly increased by 100.7% and 19.5% as compared to Cd control and conventional bare Se NPs. Transcriptional analyses highlighted that AVGE Se NPs activated stress signaling and defense related pathways, including glutathione metabolism, phenylpropanoid biosynthesis and plant hormone signal transduction. Specifically, exposure to AVGE Se NPs upregulated the expression of genes associated with the gibberellic acid (GA) biosynthesis by and 4.79- and 3.29-fold as compared to the Cd-alone treatment and the untreated control, respectively. Importantly, AVGE Se NPs restored the composition of the endophyte community and recruit of beneficial species under Cd exposure; the relative abundance of Azospirillum was significantly increased in roots, shoots, and the rhizosphere soil by 0.73-, 4.58- and 0.37-fold, respectively, relative to the Cd-alone treatment. Collectively, these findings highlight the significant potential of AVGE Se NPs to enhance plant growth and to minimize the Cd-induced toxicity in rice and provide a promising nanoenabled strategy to enhance food safety upon crop cultivation in contaminated agricultural soils.

Size Effects of Copper Oxide Nanoparticles on Boosting Soybean Growth via Differentially Modulating Nitrogen Assimilation.

Nanoscale agrochemicals have been widely used in sustainable agriculture and may potentially affect the nitrogen fixation process in legume crops. The present study investigated the size-effects of copper oxide nanoparticles (CuO NPs) on nitrogen assimilation in soybean (G. max (L.) Merrill) plants, which were treated with different sizes (20 and 50 nm) of CuO NPs at low use doses (1 and 10 mg/kg) for 21 days under greenhouse conditions. The results showed that 50 nm CuO NPs significantly increased the fresh biomass more than 20 nm CuO NPs achieved at 10 mg/kg. The activities of N assimilation-associated enzymes and the contents of nitrogenous compounds, including nitrates, proteins, and amino acids, in soybean tissues were greatly increased across all the CuO NP treatments. The use doses of two sizes of CuO NPs had no impact on the Cu contents in shoots and roots but indeed increased the Cu contents in soils in a dose-dependent fashion. Overall, our findings demonstrated that both 20 and 50 nm CuO NPs could positively alter soybean growth and boost N assimilation, furthering our understanding that the application of nanoscale micro-nutrient-related agrochemicals at an optimal size and dose will greatly contribute to increasing the yield and quality of crops.

Nanoscale ZnO Improves the Amino Acids and Lipids in Tomato Fruits and the Subsequent Assimilation in a Simulated Human Gastrointestinal Tract Model.

With the widespread use of nanoenabled agrochemicals, it is essential to evaluate the food safety of nanomaterials (NMs)-treated vegetable crops in full life cycle studies as well as their potential impacts on human health. Tomato seedlings were foliarly sprayed with 50 mg/L ZnO NMs, including ZnO quantum dots (QDs) and ZnO nanoparticles once per week over 11 weeks. The foliar sprayed ZnO QDs increased fruit dry weight and yield per plant by 39.1% and 24.9, respectively. It also significantly increased the lycopene, amino acids, Zn, B, and Fe in tomato fruits by 40.5%, 15.1%, 44.5%, 76.2%, and 12.8%, respectively. The tomato fruit metabolome of tomatoes showed that ZnO NMs upregulated the biosynthesis of unsaturated fatty acids and sphingolipid metabolism and elevated the levels of linoleic and arachidonic acids. The ZnO NMs-treated tomato fruits were then digested in a human gastrointestinal tract model. The results of essential mineral release suggested that the ZnO QDs treatment increased the bioaccessibility of K, Zn, and Cu by 14.8-35.1% relative to the control. Additionally, both types of ZnO NMs had no negative impact on the α-amylase, pepsin, and trypsin activities. The digested fruit metabolome in the intestinal fluid demonstrated that ZnO NMs did not interfere with the normal process of human digestion. Importantly, ZnO NMs treatments increased the glycerophospholipids, carbohydrates, amino acids, and peptides in the intestinal fluids of tomato fruits. This study suggests that nanoscale Zn can be potentially used to increase the nutritional value of vegetable crops and can be an important tool to sustainably increase food quality and security.

Aloe Vera Extract Gel-Biosynthesized Selenium Nanoparticles Enhance Disease Resistance in Lettuce by Modulating the Metabolite Profile and Bacterial Endophytes Composition.

The use of nanotechnology to suppress crop diseases has attracted significant attention in agriculture. The present study investigated the antifungal mechanism by which aloe vera extract gel-biosynthesized (AVGE) selenium nanoparticles (Se NPs) suppressed Fusarium-induced wilt disease in lettuce (Lactuca sativa). AVGE Se NPs were synthesized by utilizing sodium selenite as a Se source and AVGE as a biocompatible capping and reducing agent. Over 21 d, 2.75% of total AVGE Se NPs was dissolved into Se ions, which was more than 8-fold greater than that of bare Se NPs (0.34%). Upon exposure to soil applied AVGE Se NPs at 50 mg/kg, fresh shoot biomass was significantly increased by 61.6 and 27.8% over the infected control and bare Se NPs, respectively. As compared to the infected control, the shoot levels of citrate, isocitrate, succinate, malate, and 2-oxo-glutarate were significantly upregulated by 0.5-3-fold as affected by both Se NPs. In addition, AVGE Se NPs significantly increased the shoot level of khelmarin D, a type of coumarin, by 4.40- and 0.71-fold over infected controls and bare Se NPs, respectively. Additionally, AVGE Se NPs showed greater upregulation of jasmonic acid and downregulation of abscisic acid content relative to bare Se NPs in diseased shoots. Moreover, the diversity of bacterial endophytes was significantly increased by AVGE Se NPs, with the values of Shannon index 40.2 and 9.16% greater over the infected control and bare Se NPs. Collectively, these findings highlight the significant potential of AVGE Se NPs as an effective and biocompatible strategy for nanoenabled sustainable crop protection.

ZnO quantum dots outperform nanoscale and bulk particles for enhancing tomato (Solanum lycopersicum) growth and nutritional values.

Tomato (Solanum lycopersicum) seedlings were exposed by foliar or root applications to Zn in different nanoscale and non-nanoscale forms (40 mg Zn/L) under hydroponic conditions for 15 days. Under foliar exposure, ZnO QDs significantly promoted tomato growth, while ZnO NPs and BPs had lower impacts. ZnO QDs increased fresh weight and plant height by 42.02 % and 21.10 % relative to the untreated controls, respectively. The ionic control (ZnSO4·7H2O, 176.6 mg/L) decreased fresh weight by 39.31 %. ZnO QDs also significantly increased the Chla/Chlb ratio, as well as carotenoids and protein content by 7.70 %, 8.90 % and 26.33 %, respectively, over the untreated controls, suggesting improvement in seedling photosynthetic performance. Antioxidant enzyme (POD, PPO and PAL) activities in ZnO QDs treated shoots were significantly decreased by 31.1 %, 17.8 % and 48.3 %, respectively, indicating no overt oxidative damage from exposure. Importantly, the translocation factor of Zn (TFZn) in the foliar exposure of the ZnO QDs treatment was 73.2 %, 97.1 % and 276.9 % greater than the NPs, BPs, and ionic controls, respectively. Overall, these findings clearly demonstrate that foliar spray of nanoscale nutrients at the appropriate concentration and size can significantly increase crop growth and be a sustainable approach to nano-enabled agriculture.

Copper Oxide Nanoparticle-Embedded Hydrogels Enhance Nutrient Supply and Growth of Lettuce (Lactuca sativa) Infected with Fusarium oxysporum f. sp. lactucae.

The use of nanotechnology to suppress crop diseases has attracted increasing attention in agriculture. The present work investigated the antifungal efficacy of copper oxide nanoparticle (CuO NP)-embedded hydrogels, which were synthesized by loading CuO nanoparticles (NPs) in hydrogels formed from cross-linked interaction between chitosan and acrylic acid, against Fusarium wilt of lettuce (Lactuca sativa) caused by Fusarium oxysporum f. sp. lactucae. In comparison with CuO NPs, 7-day Cu dissolution from CuO NP-embedded hydrogels was 34.2-94.8% slower regardless of media type, including water, potato dextrose broth, or a soil extract. In a greenhouse study, upon exposure to CuO NP-embedded hydrogels, CuO NPs, or Kocide 3000 with equivalent amounts of Cu (31 mg/kg), the fresh shoot biomass was significantly increased by 40.5, 26.1 and 27.2%, respectively, as compared to that of the infected control. Notably, CuO NP-embedded hydrogels enhanced uptake of P, Mn, Zn, and Mg and increased the levels of organic acids as compared to the diseased control. Increased salicylic acid (SA) and decreased jasmonic acid (JA) and abscisic acid (ABA) levels with the addition of different forms of Cu may have enhanced disease resistance. Taken together, our findings provide useful information and approach for improving the delivery efficiency of agrichemicals via nanoenabled strategies and an advanced understanding of plant defense mechanisms triggered by Cu-based NPs.

Role of Nanoscale Hydroxyapatite in Disease Suppression of Fusarium-Infected Tomato.

The present study investigated the mechanisms by which large- and small-sized nanoscale hydroxyapatite (nHA) suppressed Fusarium-induced wilt disease in tomato. Both nHA sizes at 9.3 mg/L (low) and 46.5 mg/L (high dose) phosphorus (P) were foliar-sprayed on Fusarium-infected tomato leaf surfaces three times. Diseased shoot mass was increased by 40% upon exposure to the low dose of large-sized nHA compared to disease controls. Exposure to both nHA sizes significantly elevated phenylalanine ammonialyase activity and total phenolic content in Fusarium-infected shoots by 30-80% and 40-68%, respectively. Shoot salicylic acid content was also increased by 10-45%, suggesting the potential relationship between antioxidant and phytohormone pathways in nHA-promoted defense against fungal infection. Exposure to the high dose of both nHA sizes increased the root P content by 27-46%. A constrained analysis of principal coordinates suggests that high dose of both nHA sizes significantly altered the fatty acid profile in diseased tomato. Particularly, the diseased root C18:3 content was increased by 28-31% in the large-sized nHA treatments, indicating that nHA remodeled the cell membrane as part of defense against Fusarium infection. Taken together, our findings demonstrate the important role of nHA in promoting disease suppression for the sustainable use of nHA in nanoenabled agriculture.

In situ and real time investigation of foliarly applied silver nanoparticles on and in spinach leaves by surface enhanced Raman spectroscopic mapping.

Understanding the behavior and biological fate of silver nanoparticles (AgNPs) applied on plant surfaces is significant for their risk assessment. Our study's objective is to investigate the interactions between AgNPs and plant biomolecules as well as to monitor and quantify the penetration of AgNPs in spinach by an in situ and real-time surface enhanced Raman spectroscopic (SERS) mapping technique. AgNPs (2 µg per leaf) of different surface coatings (citrate, CIT, and polyvinylpyrrolidone, PVP) and sizes (40 and 100 nm) were foliarly applied onto spinach leaves with different exposure times (1-48 h). Cysteine is the major biomolecule that interacts with AgNPs in spinach based on the in situ and in vitro SERS pattern recognition. The interaction between CIT-AgNPs and cysteine happened in as early as 1 h after AgNP foliar deposition, which is faster than the interaction between PVP-AgNPs and cysteine. Also, the SERS depth mapping shows that particle size rather than surface coating determines the penetration capability of AgNPs in spinach, in which 40 nm AgNPs show a deeper penetration than the 100 nm ones. Last but not least, based on the results of SERS mapping, we detected significantly higher amounts of 40 nm CIT-/PVP-AgNPs than 100 nm CIT-AgNPs internalized in the leaf tissues after 1 h exposure. The estimated percentage of internalized AgNPs (0.2-0.8%) was significantly smaller than that of the total residual Ag (9-12%), indicating the potential transformation of the AgNPs into other Ag species inside the plant tissues. This study facilitates a better understanding of the behavior and biological fate of AgNPs in plant tissues.

Food-Grade Titanium Dioxide Particles Decreased the Bioaccessibility of Vitamin D3 in the Simulated Human Gastrointestinal Tract.

Food-grade titanium dioxide (E171) particles, as a "whiteness" additive, are often co-ingested with lipid-rich foods. Therefore, we explored the impact of E171 on lipid digestion and vitamin D3 (VD3) bioaccessibility encapsulated within oil-in-water emulsions in a simulated human gastrointestinal tract (GIT) model. VD3 bioaccessibility significantly decreased from 80 to 74% when raising E171 from 0 to 0.5 wt %. The extent of lipid digestion was reduced by E171 addition in a dose-dependent manner. VD3 bioaccessibility was positively correlated with the final amount of free fatty acids (FFAs) produced by lipid digestion (R2 = 0.95), suggesting that the reduction in VD3 bioaccessibility was due to the inhibition of lipid digestion by E171. Further experiments showed that E171 interacted with lipase and calcium ions, thereby interfering with lipid digestion. The findings of this study enhance our understanding toward the potential impact of E171 on the nutritional attributes of foods for human digestion health.

Maize (Zea mays L.) root exudates modify the surface chemistry of CuO nanoparticles: Altered aggregation, dissolution and toxicity.

Copper oxide nanoparticles (CuO NPs), as an antimicrobial nanomaterial, have found many applications in agriculture. Ubiquitous and complex root exudates (RE) in the plant root zone motivates the determination of how specific components of RE interact with CuO NPs. This work aims to reveal the role of maize (Zea mays L.)-derived RE and their components on the aggregation and dissolution of CuO NPs in the rhizosphere. We observed that RE significantly inhibited the aggregation of CuO NPs regardless of ionic strength and electrolyte type. In the presence of RE, the CCC of CuO NPs in NaCl shifted from 30 to 125 mM and the value in CaCl2 shifted from 4 to 20 mM. Furthermore, this inhibition was correlated with molecular weight (MW) of RE fractions. Higher MW fraction (>10 kDa) reduced the aggregation most. We also discovered that RE significantly promoted the dissolution of CuO NPs and lower MW fraction (<3 kDa) RE mainly contributed to this process. Additionally, phytotoxicity of CuO NPs in the presence of RE and different fractions of RE was evaluated. The addition of 20 mg/L RE reduced the seedlings growth rate to 1.89% after 7 days exposure to 25 mg/L CuO NPs, which were significantly lower than the control group (4.82%). Notably, Cu accumulation in plant root tissues was significantly enhanced by 20 mg/L RE. This study provides useful insights into the interactions between RE and CuO NPs, which is of significance for the safe use of CuO NPs-based antimicrobial products in agricultural production.

[Effects of Continuous Application of Sewage Sludge Compost on Heavy Metals Accumulation and Mobility Characteristics in Soil Profile and on Heavy Metals Uptake of Wheat].

The use of sewage sludge compost(SSC)as fertilizer may cause increased leaching due to its high content of heavy metals and thus pose a threat to groundwater quality. The effect of SSC application on heavy metals leaching in calcareous soils has been studied in field trials, which provides basis for determining heavy metals environmental capacity and preventing metal pollution in farmland soil scientifically. The results indicated that the contents of Cu, Zn elevated obviously with the increase of the age and the dosage of SSC utilization in the topsoil(0-15 cm) under 4-year continuous application of SSC. Under higher levels of the compost treatment, the heavy metals Cu and Zn were found to migrate into the 15-30 cm soil and 60-90 cm soil under the experimental condition. Nevertheless, the majority of Cu and Zn from SSC accumulated in topsoil and the highest accumulation rates could reach 75.3% for Cu and 85.9% for Zn. The contents of Cd, Pb increased significantly in topsoil after 4-year continuous application of SSC, and their increases could reach 57.2%-165.2% for Cd and 13%-34% for Pb compared with CK. At 60-90 cm soil, the contents of Cr, As and Pb were also significantly higher than those in CK treatment. Application of SSC not only caused accumulation of some heavy metals in topsoil but also leached heavy metals located in the subsurface soil down in this experiment. Continuous utilization of SSC increased Zn concentration of wheat grain, and the increase could reach 13.3%-47.9%. For the concentrations of Cr and Pb in wheat grain, the values exceeded the national food and healthy standards value (GB 2762-2012) in part of compost treatments. The cumulative ratio of heavy metals carried out by wheat were all below 10% after 4-year experiment, wheat grain carried much more Cu, Zn out than wheat straw, but it was opposite for Cr, As, Cd, Pb. The cumulative ratio of heavy metals carried by wheat decreased with the increasing level of SSC utilization. The amounts of heavy metals migrated to deeper soil should be considered when determining the environmental capacity of heavy metals in farmland soil.

[Form tendency and bio-availability dynamics of Cu and Zn in different farm soils after application of organic fertilizer of livestock and poultry manures].

Soil incubation experiments were conducted with different sources of manures containing heavy metals to evaluate the bioavailability of heavy metals (Cu and Zn) and their form transformation in different soils. This study may assist in developing strategies to ascertain the loads of heavy metals which entered into soils together with manures, and promote policies to evaluate the ecological risk in agriculture soils. The results showed that, during the six months of soil incubation, the pH value of acidic soil increased and the pH value of calcareous soil reduced. After adding chicken manures, the contents of available Cu in both calcareous and acid soils were significant lower than those in the equivalent inorganic salt treatments, but there was no significant difference between the treatments in the contents of available Zn in both calcareous and acid soils. Furthermore, there were also no significant differences between pig matures and the equivalent inorganic salt treatments in the contents of available Cu and Zn in both calcareous and acid soils. The results of form tendency showed that the main forms of Cu and Zn in both calcareous and acid soils, which entered into soils together with manures, were exchangeable, carbonate, Fe-Mn oxides, and organic. And the proportions of different heavy metals species in calcareous and acid soils were different with different manures sources. After six months of incubation, the contents of exchangeable and Fe-Mn oxides Cu, Zn were lower than those in the equivalent inorganic salt treatments, the contents of organics Cu and Zn were higher than those in the equivalent inorganic salt treatments, and other Cu and Zn forms in soils showed no difference with inorganic salt treatments.