Douglas-Fir ( Pseudotsuga menziesii (Mirb.) Franco) Transcriptome Profile Changes Induced by Diesel Emissions Generated with CeO2 Nanoparticle Fuel Borne Catalyst

CeO2 nanoparticle dose and exposure modulate soybean development and plant-mediated responses in root-associated bacterial communities

Agricultural soils are increasingly undergoing inadvertent and purposeful exposures to engineered CeO2 nanoparticles (NPs), which can impact crops and root-associated microbial communities. However, interactions between NP concentration and exposure duration on plant-mediated responses of root-associated bacterial communities are not well understood. Soybeans seedlings were grown in soil with uncoated NPs added at concentrations of 0, 1 or 100 mg kg-1. Total soil exposure durations were either 190 days, starting 106 days before planting or 84 days with NP amendments coinciding with planting. We assessed plant development, bacterial diversity, differential abundance and inferred functional changes across rhizosphere, rhizoplane, and root tissue compartments. Plant non-monotonic dose responses were mirrored in bacterial communities. Most notably, effects were magnified in the rhizoplane under low-dose, short-exposures. Enriched metabolic pathways were primarily related to biosynthesis and degradation/utilization/assimilation, rather than responses to metals or oxidative stress. Our results indicate that plant-mediated bacterial responses were greater than direct NP impacts. Also, we identify needs for modeling non-monotonic legume stress responses that account for coinfection with mutualistic and parasitic bacteroids. Our findings provide new insights regarding effects of applications of soil amendments such as biosolids containing NPs or nano-enabled formulations used in cultivation of legumes and other crops.

Focused Microbiome Shifts in Reconstructed Wetlands Correlated with Elevated Copper Concentrations Originating from Micronized Copper Azole-Treated Wood

Micronized copper (Cu) azole (MCA) wood preservative formulations include Cu in nano form, and relatively little is known about longer term effects of Cu leached from MCA into wetland ecosystems. We tested the hypothesis that changes in soil microbiomes within reconstructed freshwater wetlands will be associated with exposure to elevated Cu concentrations originating from immersed MCA-treated wood stakes. Eight replicate communities were assembled with Willamette Valley (OR, USA) flood plain soil and clonally propagated wetland plants within mesocosms. Inundated communities were equilibrated for 5 months before installation of MCA or control southern yellow pine stakes (n = 4 communities/experimental group). Soil samples were collected for 16S and internal transcribed spacer amplicon sequencing to quantify responses in prokaryotes and eukaryotes, respectively, at 15 time points, spanning two simulated seasonal dry downs, for up to 678 days. Physiochemical properties of water and soil were monitored at 20 and 12 time points respectively, over the same period. For both taxonomic groups of organisms, phylogenetic diversity increased and was positively correlated with elapsed days. Furthermore, there was significant divergence among eukaryotes during the second year based on experimental group. Although the composition of taxa underwent succession over time, there was significantly reduced relative abundance of sequence variants from Gomphonema diatoms and Scutellinia fungi in communities where MCA wood stakes were present compared with the controls. These focused microbiome shifts were positively correlated with surface water Cu and soil Cu concentrations, which were significantly elevated in treated communities. The reconstructed communities were effective systems for assessing potential impacts to wetland microbiomes after exposure to released copper. The results further inform postcommercialization risk assessments on MCA-treated wood. Environ Toxicol Chem 2021;40:3351-3368. Published 2021. This article is a U.S. Government work and is in the public domain in the USA.

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.

Physiological, Metabolic, and Transcriptomic Analyses Reveal the Responses of Arabidopsis Seedlings to Carbon Nanohorns

Carbon-based nanomaterials have potential applications in nanoenabled agriculture. However, the physiological and molecular mechanisms underlying single-walled carbon nanohorn (SWCNH)-mediated plant growth remain unclear. Here, we investigated the effects of SWCNHs on Arabidopsis grown in ¹/₄-strength Murashige and Skoog medium via physiological, genetic, and molecular analyses. Treatment with 0.1 mg/L SWCNHs promoted primary root (PR) growth and lateral root (LR) formation; 50 and 100 mg/L SWCNHs inhibited PR growth. Treatment with 0.1 mg/L SWCNHs increased the lengths of the meristematic and elongation zones, and transcriptomic and genetic analyses confirmed the positive effects of SWCNHs on root tip stem cell niche activity and meristematic cell division potential. Increased expression of YUC3 and YUC5 and increased PIN2 abundance improved PR growth and LR development in 0.1 mg/L SWCNH-treated seedlings. Metabolomic analyses revealed that SWCNHs altered the levels of sugars, amino acids, and organic acids, suggesting that SWCNHs reprogrammed carbon/nitrogen metabolism in plants. SWCNHs also regulate plant growth and development by increasing the levels of several secondary metabolites; transcriptomic analyses further supported these results. The present results are valuable for continued use of SWCNHs in agri-nanotechnology, and these molecular approaches could serve as examples for studies on the effects of nanomaterials in plants.

Wheat exposure to cerium oxide nanoparticles over three generations reveals transmissible changes in nutrition, biochemical pools, and response to soil N

This study investigated the effects of third generation exposure to cerium oxide nanoparticles (CeO₂-NPs) on biomass, elemental and ¹⁵N uptake, and fatty acid contents of wheat (Triticum aestivum). At low or high nitrogen treatment (48 or 112 mg N), seeds exposed for two generations to 0 or 500 mg CeO₂-NPs per kg soil treatment were cultivated for third year in soil amended with 0 or 500 mg CeO₂-NPs per kg soil. The results showed that parental and current exposures to CeO₂-NPs increased the root biomass in daughter plants with greater magnitude of increase at low N than high N. When wheat received CeO₂-NPs in year 3, root elemental contents increased primarily at low N, suggesting an important role of soil N availability in altering root nutrient acquisition. The δ¹⁵N ratios, previously shown to be altered by CeO₂-NPs, were only affected by current and not parental exposure, indicating effects on N uptake and/or metabolism are not transferred from one generation to the next. Seed fatty acid composition was also influenced both by prior and current exposure to CeO₂-NPs. The results suggest that risk assessments of NP exposure may need to include longer-term, transgenerational effects on growth and grain quality of agronomic crops.

Metabolomics Reveals the "Invisible" Responses of Spinach Plants Exposed to CeO2 Nanoparticles

Engineered nanoparticles (NPs) with activities that mimic antioxidant enzymes have good prospects in agriculture because they can increase photosynthesis and improve stress tolerance. Here, the interaction between cerium oxide NPs with spinach plants ( Spinacia oleracea) was investigated by integrating phenotypic and metabolomic analyses. Soil-grown, four-week-old spinach plants were foliar exposed for 3 weeks to CeO₂ NPs at 0, 0.3, and 3 mg per plant. Phenotypic parameters (chlorophyll fluorescence, photosynthetic pigment contents, plant biomass, lipid peroxidation, and membrane permeability) were not affected. However, metabolomics analysis revealed that both doses of CeO₂ NPs induced metabolic reprogramming in leaves and roots in a non-dose-dependent manner. The low dose of CeO₂ NPs (0.3 mg per plant) induced stronger metabolic reprogramming in spinach leaves than high dose of CeO₂ NPs. However, the high dose of CeO₂ NPs triggered more metabolic changes in roots, compared to the low dose. Foliar spray of CeO₂ NPs at 3 mg/plant induced marked down-regulation of a number of amino acids (threonine, tryptophan, l-cysteine, methionine, cycloleucine, aspartic acid, asparagine, tyrosine, and glutamic acid). In addition, Zn decreased by 44% and 54% in leaves and Ca decreased by 38% and 32% in roots under exposure to CeO₂ NPs at 0.3 and 3 mg/plant, respectively. These results provide better understanding of the intrinsic phenotypic and metabolic changes imposed by CeO₂ NPs in spinach plants.