Genome-wide identification and characterization of major latex-like protein genes responsible for crop contamination in Cucurbita pepo.

BACKGROUND: Zucchini plants (Cucurbita pepo) accumulate persistent organic pollutants (POPs) at high concentrations in their aerial parts, and major latex-like proteins (MLPs) play crucial roles in their accumulation. MLPs bind to POPs in root cells, MLP-POP complexes are then translocated into xylem vessels, and POPs are transported to the aerial parts. We previously identified three CpMLP genes (MLP-PG1, MLP-GR1, and MLP-GR3) as transporting factors for POPs; however, other studies have shown that the genomes of several plant species contain more than 10 MLP genes, thus, further MLP genes responsible for POP accumulation may have been overlooked. METHODS AND RESULTS: Here, we investigated the number of CpMLP genes by performing a hidden Markov model search against the C. pepo genome database and characterized their effects on POP accumulation by performing the expression analysis in the organs and in silico structural analysis. The C. pepo genome contained 21 CpMLP genes, and several CpMLP genes, including MLP-PG1 and MLP-GR3, were highly expressed in roots. 3D structural prediction showed that all examined CpMLPs contained a cavity with a hydrophobic region, which facilitated binding to POPs. CONCLUSIONS: The present study provides insights regarding CpMLP genes responsible for POP accumulation.

Soil lead (Pb) and urban grown lettuce: Sources, processes, and implications for gardener best management practices.

Urban community gardeners employ a range of best practices that limit crop contamination by toxicants like lead (Pb). While Pb root uptake is generally low, the relative significance of various Pb deposition processes and the effectiveness of best practices in reducing these processes have not been sufficiently characterized. This study compared leafy lettuce (Lactuca sativa) grown in high Pb (1150 mg/kg) and low Pb (90 mg/kg) soils, under three different soil cover conditions: 1) bare soil, 2) mulch cover to limit splash, and 3) mulch cover under hoophouses to limit splash and air deposition, in a New York City (NYC) community garden and a rural site in Ithaca, New York (NY). The lettuces were further compared to greenhouse (Ithaca) and supermarket (NYC) samples. Atmospheric deposition was monitored by passive trap collection through funnel samplers. Results show that in low Pb soils, splash and atmospheric deposition accounted for 84 and 78% of lettuce Pb in NYC and Ithaca, respectively. In high Pb soils, splash and atmospheric deposition accounted for 88 and 93% of Pb on lettuces, with splash being the dominant mechanism. Soil covers were shown to be effective at significantly (p < 0.05) reducing lettuce Pb contamination, and mulching is strongly recommended as a best practice.

Crop Contamination and Human Exposure to Per- and Polyfluoroalkyl Substances around a Fluorochemical Industrial Park in China.

Due to their significant environmental impact, there has been a gradual restriction of the production and utilization of legacy per- and polyfluoroalkyl substances (PFAS), leading to continuous development and adoption of novel alternatives. To effectively identify the potential environmental risks from crop consumption, the levels of 25 PFAS, including fourteen perfluoroalkyl acids (PFAAs), two precursor substances and nine novel alternatives, in agricultural soils and edible parts of various crops around a fluoride industrial park (FIP) in Changshu city, China, were measured. The concentration of ΣPFAS in the edible parts of all crops ranged from 11.64 to 299.5 ng/g, with perfluorobutanoic acid (PFBA) being the dominant compound, accounting for an average of 71% of ΣPFAS. The precursor substance, N-methylperfluoro-octanesulfonamidoacetic acid (N-MeFOSAA), was detected in all crop samples. Different types of crops showed distinguishing accumulation profiles for the PFAS. Solanaceae and leafy vegetables showed higher levels of PFAS contamination, with the highest ΣPFAS concentrations reaching 190.91 and 175.29 ng/g, respectively. The highest ΣAlternative was detected in leafy vegetables at 15.21 ng/g. The levels of human exposure to PFAS through crop consumption for various aged groups were also evaluated. The maximum exposure to PFOA for urban toddlers reached 109.8% of the standard value set by the European Food Safety Authority (EFSA). In addition, short-chained PFAAs and novel alternatives may pose potential risks to human health via crop consumption.

Major latex-like proteins show pH dependency in their binding to hydrophobic organic pollutants.

The Cucurbitaceae family accumulates hydrophobic organic pollutants in its aerial parts at high concentrations. Major latex-like proteins (MLPs) were identified in zucchini (Cucurbita pepo) as a transporting factor for hydrophobic organic pollutants. MLPs bind to hydrophobic organic pollutants in the roots, are secreted to xylem vessels as complexes, and are transported to the aerial parts. However, the suitable conditions for binding MLPs to hydrophobic organic pollutants remain elusive. In the present study, we show that MLPs bind to the hydrophobic organic pollutant pyrene with higher affinity under acidic conditions. Our results demonstrated that pH regulates the binding of MLPs to hydrophobic organic pollutants.

Air Mapping of Polycyclic Aromatic Hydrocarbons and Their Uptake by Crops in the Urban Area of Nice, France.

Urban gardening is becoming increasingly popular. Air pollution, which is a major concern in cities might, however, threaten food safety and thus must be assessed. Health risks arise particularly from toxic persistent organic pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) which are formed by incomplete combustion. A first assessment of crop contamination in two different atmospheric environments in the urban area of Nice reveals a predominance of light PAHs. These pollutants present in the gaseous phase, seem to bioaccumulate while heavy PAHs are absent in vegetation. By understanding the PAH sources and their behavior in the atmosphere but also by analyzing the spatial and temporal data since the European directive in 2004, a link between concentrations found in vegetables grown in experimental gardens and PAH cadastral emission data is presented. The first results could be used as a possible guidance for urban agriculture.

A lognormal model for evaluating maximum residue levels of pesticides in crops.

To evaluate pesticide regulatory standards in agricultural crops, we introduced a regulatory modeling framework that can flexibly evaluate a population's aggregate exposure risk via maximum residue levels (MRLs) under good agricultural practice (GAP). Based on the structure of the aggregate exposure model and the nature of variable distributions, we optimized the framework to achieve a simplified mathematical expression based on lognormal variables including the lognormal sum approximation and lognormal product theorem. The proposed model was validated using Monte Carlo simulation, which demonstrates a good match for both head and tail ends of the distribution (e.g., the maximum error = 2.01% at the 99th percentile). In comparison with the point estimate approach (i.e., theoretical maximum daily intake, TMDI), the proposed model produced higher simulated daily intake (SDI) values based on empirical and precautionary assumptions. For example, the values at the 75th percentile of the SDI distributions simulated from the European Union (EU) MRLs of 13 common pesticides in 12 common crops were equal to the estimated TMDI values, and the SDI values at the 99th percentile were over 1.6-times the corresponding TMDI values. Furthermore, the model was refined by incorporating the lognormal distributions of biometric variables (i.e., food intake rate, processing factor, and body weight) and varying the unit-to-unit variability factor (VF) of the pesticide residues in crops. This ensures that our proposed model is flexible across a broad spectrum of pesticide residues. Overall, our results show that the SDI is significantly reduced, which may better reflect reality. In addition, using a point estimate or lognormal PF distribution is effective as risk assessments typically focus on the upper end of the distribution.

Effects of brewery sludge on soil chemical properties, trace metal availability in soil and uptake by wheat crop, and bioaccumulation factor.

Brewery sludge is the solid residue obtained from agro-industrial processing. It is possible to utilize the waste products in an environment friendly and economical way to replace mineral fertilizer due to its sufficient macronutrients and organic carbon content. However, its use is limited due to heavy metal concentration that may contaminate crops and then the food chain. The objective of this study was to assess the suitability of brewery sludge for using to grow bread wheat (Triticum aestivum L.) by determining the effect of brewery sludge (7 levels: 0, 3, 6, 9, 12 and 15 t ha-1, and 1 recommended rate of NPS only) on soil chemical properties, bioaccumulation factor, and heavy metal absorption in the soil and in the bread wheat grain using a Randomized Blocks Design field experiment conducted at two sites during the 2018 cropping season. Amendment of brewery sludge at a rate of 15 t ha-1 led to substantial variations in soil chemical properties except for Mg2+ content at both study sites. Concentrations of the studied heavy metals (except Zn in the soil) increased with increasing brewery sludge application rate in the soil and in the wheat grain. However, heavy metal uptake by wheat grain and heavy metal concentration in the soil were below the allowed limits. The bioaccumulation factor in the wheat grain was <1.0 for the studied heavy metals. The findings of the study suggest that brewery sludge at a rate of 15 t ha-1 could be recommended due to its high nourishing effect for soil and for promoting nutritional quality of wheat crop and is safe for human consumption. However, since sludge application may lead to increase in the amount of trace metals in the soil-plant system, a long-term study is recommended.

Factors regulating the differential uptake of persistent organic pollutants in cucurbits and non-cucurbits.

Contamination with persistent organic pollutants (POPs) has become a worldwide concern owing to their the toxicity to humans and wildlife. Pumpkin, cucumber, and squash (Cucurbitaceae) accumulate POPs in their shoots in concentrations higher than those in non-cucurbits; to elucidate the underlying molecular mechanisms of this accumulation, POP transporters were analyzed in the xylem sap of cucurbits and non-cucurbits. The 17-kDa xylem sap proteins detected in all cucurbits but not in non-cucurbits readily bound polychlorinated biphenyl (PCB) in all tested cucurbits, except in cucumber and loofah, and to dieldrin in all tested cucurbits. Ten genes encoding major latex-like proteins (MLPs) responsible for the accumulation of PCBs in zucchini plants were cloned from cucurbits. Phylogenetic analysis using MLP sequences identified two separate clades, one containing Cucurbitaceae MLPs and the other containing those of non-cucurbit members. Recombinant MLPs bound PCB and dieldrin. Western blotting with anti-MLP antibodies identified translocatable and non-translocatable MLPs between root and stem xylem vessels. Translocation of MLPs from the root to stem xylem vessels and POP-binding ability of MLPs are important for selective accumulation of MLPs in cucurbits. This study provides basic knowledge about phytoremediation through overexpression of MLP genes and for breeding cucurbits that accumulate less contaminants.

Integrated Health Risk Assessment of Heavy Metals in Suxian County, South China.

The purpose of this study was to assess soil heavy metal contamination and the potential risk for local residents in Suxian county of Hunan Province, southern China. Soil, rice and vegetable samples from the areas near the mining industrial districts were sampled and analyzed. The results indicate that the anthropogenic mining activities have caused local agricultural soil contamination with As, Pb, Cu and Cd in the ranges of 8.47-341.33 mg/kg, 19.91-837.52 mg/kg, 8.41-148.73 mg/kg and 0.35-6.47 mg/kg, respectively. GIS-based mapping shows that soil heavy metal concentrations abruptly diminish with increasing distance from the polluting source. The concentrations of As, Pb, Cu and Cd found in rice were in the ranges of 0.02-1.48 mg/kg, 0.66-5.78 mg/kg, 0.09-6.75 mg/kg, and up to 1.39 mg/kg, respectively. Most of these concentrations exceed their maximum permissible levels for contaminants in foods in China. Heavy metals accumulate to significantly different levels between leafy vegetables and non-leafy vegetables. Food consumption and soil ingestion exposure are the two routes that contribute to the average daily intake dose of heavy metals for local adults. Moreover, the total hazard indices of As, Pb and Cd are greater than or close to the safety threshold of 1. Long-term As, Pb and Cd exposure through the regular consumption of the soil, rice and vegetables in the investigated area poses potential health problems to residents in the vicinity of the mining industry.

Perchlorate content of plant foliage reflects a wide range of species-dependent accumulation but not ozone-induced biosynthesis.

Perchlorate (ClO4(-)) interferes with uptake of iodide in humans. Emission inventories do not explain observed distributions. Ozone (O3) is implicated in the natural origin of ClO4(-), and has increased since pre-industrial times. O3 produces ClO4(-)in vitro from Cl(-), and plant tissues contain Cl(-) and redox reactions. We hypothesize that O3 exposure may induce plant synthesis of ClO4(-). We exposed contrasting crop species to environmentally relevant O3 concentrations. In the absence of O3 exposure, species exhibited a large range of ClO4(-) accumulation but there was no relationship between leaf ClO4(-) and O3, whether expressed as exposure or cumulative flux (dose). Older, senescing leaves accumulated more ClO4(-) than younger leaves. O3 exposed vegetation is not a source of environmental ClO4(-). There was evidence of enhanced ClO4(-) content in the soil surface at the highest O3 exposure, which could be a significant contributor to environmental ClO4(-).