Transcriptomic mechanisms of reduced PM2.5-Pb retention in the leaves of the low-Pb-accumulation genotype of Chinese cabbage

Combined μ-XRF and XANES Track the Behavior of Pb from PM2.5 Entering Chinese Cabbage Leaves

Atmospheric fine particulate matter (PM2.5) is the main contributor to Pb accumulation in edible Chinese cabbage leaves in North China. PM2.5-Pb primarily enters leaves via stomatal foliar uptake. However, how PM2.5-Pb is transported and stored within the leaf cells of Chinese cabbage remains unclear. Thus, this study mapped Pb, Ca, and Mg distributions in Chinese cabbage leaves following PM2.5-Pb stress using synchrotron and fast micro-X-ray fluorescence. Findings revealed that PM2.5-Pb was transported and localized in guard cells, the epidermal cell wall, and chloroplasts. X-ray absorption near-edge structure revealed that Pb(CO3)2·Pb(OH)2 in PM2.5 was converted to Pb(OH)2, glutathione-Pb (GSH-Pb), and PbC2O4 in Chinese cabbage leaves. GSH-Pb proportion in the low Pb accumulation (LPA) variety Chinese cabbage leaves was 2.13 times higher than that in the high Pb accumulation (HPA) variety. Glutamate concentration decreased by 44.53% in the LPA variety leaves under PM2.5-Pb stress, increasing GSH-Pb efflux symplasm and reducing Pb accumulation. X-ray fluorescence mapping of Ca and Mg in leaves indicated chlorophyll biosynthesis inhibition in the HPA variety leaves but not in the LPA variety leaves. Pb speciation and distribution vary drastically between the LPA and HPA variety leaves. This study provides guidance for breeding a high-quality LPA variety of Chinese cabbages.

Silicon reduces lead accumulation in Moso bamboo via immobilization and suppression of metal cation transporter genes in roots

Lead (Pb) is a hazardous element that affects the growth and development of plants, while silicon (Si) is a beneficial element for alleviating the stress caused by heavy metals, including Pb. However, the mechanisms by which Si reduces Pb accumulation in Moso bamboo (Phyllostachys edulis (Carr ·) H · de Lehaie) remain unclear. In this study, physiological assessments and transcriptome analyses were conducted to investigate the interaction between Si and Pb. Our findings showed that Si application has no significant effect on alleviating Pb-induced inhibition of root elongation and dry weight in short-term and long-term experiments, respectively. However, it did rescue leaf yellowing and reduce Pb accumulation, particularly in the shoot. Pre-treatment with Si led to a reduction in Pb uptake, translocation and accumulation, coupled with an increase in Pb fixation within the hemicellulose of the root cell wall, resulting in a lower Pb concentration in the cell sap. At the cellular level, Pb was found to be distributed in all cells of roots, and Si pretreatment did not alter Pb distribution. Additionally, Si application downregulated the expression of genes related to ABC and metal cation transporters. These findings indicate that Si reduces Pb accumulation in Moso bamboo by immobilizing Pb in the hemicellulose of root cell walls and downregulating the expression of transporter genes involved in Pb uptake and transport.

Contribution, absorption mode, and model prediction of atmospheric deposition to copper and lead accumulation in soybean

Atmospheric deposition plays a significant role in the introduction of trace metals into agricultural ecosystems; however, accurately determining its impact on the accumulation of metals in crops remains a challenge. Here, the contribution, absorption mode, and model prediction of atmospheric deposition to trace metal accumulation in soybean were investigated by a three-year full factorial atmospheric and soil exposure experiment near a large copper (Cu) smelter. The results showed that newly deposited (one-year atmospheric deposition) metals only accounted for 0.2 %-14 % of total soil pools, while they contributed 8 %-77 % of Cu and 14 %-84 % of lead (Pb) in soybean plants. Meanwhile, the extension of soil exposure time to atmospheric deposition (two- and three-year atmospheric deposition) did not lead to significant increase in the bioavailable fraction of Cu and Pb in soil plough horizon and the bioaccumulation in soybean tissues. This suggested that the newly atmospheric deposition during the growth period was the key source of Cu and Pb in soybean plants. Furthermore, foliar absorption was an important pathway for metal accumulation in aboveground tissues as evidenced by its relative high contributions in metal bioaccumulation, i.e., 17 %-62 %, 26 %-70 %, 19 %-75 %, and 20 %-46 % of Cu and Pb in stem, leaf, hull, and seed, respectively. Besides, two models were developed to predict the Cu and Pb concentrations in soybean seeds using multiple regression analysis with atmospherically deposited metals and soil metals as variables. Compared with models based on a single variable, these models significantly improved the prediction accuracy of Cu and Pb concentrations in soybean seeds (adjusted R2 = 0.936 and 0.995). The model prediction results suggested that the threshold value of atmospherically deposited Pb to ensure the safe production of soybean was 17.7 mg/m2/year. This study offers new insights into the effective management of metal pollution in soybeans, focusing on atmospheric deposition and foliar absorption.

Bioaccumulation of Atmospherically Deposited Cadmium in Soybean: Three-Year Field Experiment Combined with Cadmium Isotopes

Atmospheric deposition plays a significant role in introducing cadmium (Cd) into agroecological systems; however, accurately determining its accumulation in crops through foliar and root uptake presents challenges. This study investigated the bioaccumulation of atmospherically deposited Cd in soybean using a three-year fully factorial atmospheric exposure experiment incorporating Cd isotope analysis. Results shown that atmospheric deposition accounted for 1-13% of soil Cd pools, yet contributed 11-72% of Cd to soybean tissues during the growing seasons. Over the course of soil exposure to atmospheric deposition ranging from 1 to 3 years, no notable variations were observed in Cd concentrations in soil solutions and soybean tissues, nor in isotope ratios. Newly deposited Cd was a major source in soybean plants, and the bioavailability of deposited Cd rapidly aged in soils. Atmospheric Cd enriched in lighter isotopes induced negative isotope shifts in soybean plants. By employing an optimized isotope mixing model in conjunction with a mass balance approach, foliar Cd uptake contributed 13-51%, 16-45%, and 21-56% to stem, leaf, and seed, respectively. This study highlights substantial contribution of foliar uptake of atmospheric deposition to Cd levels in soybean and controlling foliar uptake as a potential strategy in agroecological systems experiencing high atmospheric Cd deposition.

Transcriptomics Combined with Physiology and Metabolomics Reveals the Mechanism of Tolerance to Lead Toxicity in Maize Seedling

Lead (Pb) exposure can induce molecular changes in plants, disrupt metabolites, and impact plant growth. Therefore, it is essential to comprehend the molecular mechanisms involved in Pb tolerance in plants to evaluate the long-term environmental consequences of Pb exposure. This research focused on maize as the test subject to study variations in biomass, root traits, genes, and metabolites under hydroponic conditions under Pb conditions. The findings indicate that high Pb stress significantly disrupts plant growth and development, leading to a reduction in catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activities by 17.12, 5.78, and 19.38%, respectively. Conversely, Pb stress led to increase malondialdehyde (MDA) contents, ultimately impacting the growth of maize. The non-targeted metabolomics analysis identified 393 metabolites categorized into 12 groups, primarily consisting of organic acids and derivatives, organ heterocyclic compounds, lipids and lipid-like molecules and benzenoids. Further analysis indicated that Pb stress induced an accumulation of 174 metabolites mainly enriched in seven metabolic pathways, for example phenylpropanoid biosynthesis and flavonoid biosynthesis. Transcriptome analysis revealed 1933 shared differentially expressed genes (DEGs), with 1356 upregulated and 577 downregulated genes across all Pb treatments. Additionally, an integrated analysis identified several DEGs and differentially accumulated metabolites (DAMs), including peroxidase, alpha-trehalose, and D-glucose 6-phosphate, which were linked to cell wall biosynthesis. These findings imply the significance of this pathway in Pb detoxification. This comprehensive investigation, employing multiple methodologies, provides a detailed molecular-level insight into maize's response to Pb stress.

Speciation, bioaccumulation, and toxicity of the newly deposited atmospheric heavy metals in soil-earthworm (Eisenia fetida) system near a large copper smelter

The speciation, bioaccumulation, and toxicity of the newly deposited atmospheric heavy metals in the soil-earthworm (Eisenia fetida) system were investigated by a fully factorial atmospheric exposure experiment using soils exposed to 0.8-year and 1.8-year atmospheric depositions. The results shown that the newly deposited metals (Cu, Cd, and Pb) primarily accumulated in the topsoil (0-6 cm) and were present as the highly bioavailable speciation. They can migrate further to increase the concentrations of Cu, Cd, and Pb in soil solution of the deeper layer (at 10 cm) by 12 %-436 %. Earthworms tended to preferentially accumulate the newly deposited metals, which contributed 10 %-61 % of Cu, Cd, and Pb in earthworms. Further, for the unpolluted and moderately polluted soils, the newly deposited metals induced the significant oxidative stress in earthworms, resulting in significant increases in antioxidant enzyme activities (SOD, CAT, and GSH-Px). No significant differences were observed in the levels of heavy metals in soil solutions, bioaccumulation, and enzyme activities in earthworms exposed to 0.8-year and 1.8-year depositions, indicating the bioavailability of atmospheric metals deposited into soils was rapidly decreased with time. This study highlights the high bioaccumulation and toxicity of heavy metals to earthworm from the new atmospheric deposition during the earthworm growing period.

Metabolomics reveals the phytotoxicity mechanisms of foliar spinach exposed to bulk and nano sizes of PbCO3

PbCO3 is an ancient raw material for Pb minerals and continues to pose potential risks to the environment and human health through mining and industrial processes. However, the specific effects of unintentional PbCO3 discharge on edible plants remain poorly understood. This study unravels how foliar application of PbCO3 induces phytotoxicity by potentially influencing leaf morphology, photosynthetic pigments, oxidative stress, and metabolic pathways related to energy regulation, cell damage, and antioxidant defense in Spinacia oleracea L. Additionally, it quantifies the resultant human health risks. Plants were foliarly exposed to PbCO3 nanoparticles (NPs) and bulk products (BPs), as well as Pb2+ at 0, 5, 10, 25, 50, and 100 mg·L-1 concentrations once a day for three weeks. The presence and localization of PbCO3 NPs inside the plant cells were confirmed by TEM-EDS analysis. The maximum accumulation of total Pb was recorded in the root (2947.77 mg·kg-1 DW for ion exposure), followed by the shoot (942.50 mg·kg-1 DW for NPs exposure). The results revealed that PbCO3 and Pb2+ exposure had size- and dose-dependent inhibitory effects on spinach length, biomass, and photosynthesis attributes, inducing impacts on the antioxidase activity of CAT, membrane permeability, and nutrient elements absorption and translocation. Pb2+ exhibited pronounced toxicity in morphology and chlorophyll; PbCO3 BP exposure accumulated the most lipid peroxidation products of MDA and H2O2; and PbCO3 NPs triggered the largest cell membrane damage. Furthermore, PbCO3 NPs at 10 and 100 mg·L-1 induced dose-dependent metabolic reprogramming in spinach leaves, disturbing the metabolic mechanisms related to amino acids, antioxidant defense, oxidative phosphorylation, fatty acid cycle, and the respiratory chain. The spinach showed a non-carcinogenic health risk hierarchy: Pb2+ > PbCO3 NPs > PbCO3 BPs, with children more vulnerable than adults. These findings enhance our understanding of PbCO3 particle effects on food security, emphasizing the need for further research to minimize their impact on human dietary health.