Lead (Pb) contamination of agricultural soils, and subsequently of crops, has been widely reported. Soybean (Glycine max (L.) Merr.) has been indicated as a plant that accumulates Pb, even in soils that do not exceed the maximum permissible levels. Considering the toxicity of this heavy metal, the aim of the present study was to assess different concentrations of Pb, from low to extremely high (0.25 mM, 1 mM, and 2.5 mM), in soybean seedlings and their tolerance by analyzing morpho-physiological parameters in hydroponic experiments. Soybean seedlings were exposed to control and Pb treatments during 8 days, coinciding with the early growth stages, and the following variables were analyzed: biomass, Pb content in roots, stems and leaves, photosynthetic efficiency, leaf area, biochemical response (antioxidant power, chlorophylls, malondialdehyde), and relative water content of leaves. Results showed that roots accumulated much more Pb than the other organs, with Pb accumulation in roots being saturated even at the lowest Pb concentration, which was reflected in root biomass. Moreover, absorption of culture solutions was lower in Pb treatments, which was also reflected in the lower leaf relative water content. Lead toxicity symptoms in leaves (chlorosis and dark spots, and a decrease of biomass and leaf area, chlorophyll content, and photosynthetic efficiency), and an increase of the oxidative defense system were associated only with the highest Pb concentration (2.5 mM). Our findings support the evidence of soybean as a species tolerant to Pb, showing the effects of toxicity at very high concentrations. | Instituto de Fisiología y Recursos Genéticos Vegetales | Fil: Blanco, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Blanco, Andrés. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Pignata, María L. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores; Argentina | Fil: Pignata, María L. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina | Fil: Lascano, Hernán Ramiro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Cátedra de Fisiología Vegetal; Argentina | Fil: Lascano, Hernán Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Unidad de Estudios Agropecuarios (UDEA); Argentina | Fil: Lascano, Hernán Ramiro. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales. Argentina | Fil: Rodriguez, Judith H. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto Multidisciplinario de Biología Vegetal (IMBIV). Área Contaminación y Bioindicadores. Argentina | Fil: Rodriguez, Judith H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina

peer reviewed | Contamination of land and aquatic ecosystems with heavy metals (HMs) is a global issue having the persistent potential to damage the quality of food and water. In the present study, Tagetes erecta L. plants were used to assess their potential to uptake HMs from wastewater. Plants were grown in soil for 20 days and then transplanted in hydroponic system containing Hoagland nutrient solution. After more than 15 days of growth, plants were then subjected to wastewater from tannery and surgical industries in different concentrations ranging from 25 to 100% in combination of citric acid (5 and 10 mM). After 6 weeks of treatment, plants were collected and segmented into roots, stem, and leaves for characterizing the morphological properties including plant height, roots length, fresh and dry mass of roots, stem, and leaves. For evaluation of the effect of wastewater on the plants, photosynthetic pigments; soluble proteins; reactive oxygen species (ROS); antioxidant enzymes SOD, POD, CAT, and APX; and metal accumulation were analyzed. Application of industrial wastewater revealed a significant effect on plant morphology under wastewater treatments. Overall growth and physiological attributes of plant decreased, and metal accumulation enhanced with increasing concentration of wastewater. Similarly, the production of ROS and antioxidant enzymes were also increased. Chlorophyll, protein content, and enzyme production enhanced with CA (5 and 10 mM) mediation; however, ROS production and EL were reduced. Metals analysis showed that the maximum accumulation of Pb was in roots, while Cr and Ni in the stem which further increased under CA mediation. Overall, the metal accumulation ability was in the order of Pb > Ni > Cr under CA.

Increasing rates of commercialization and industrialization have led to the comprehensive evaluation of toxic effects of microplastics on crop plants. However, research on the impact of functionalized polystyrene nanoplastics on the toxicity of heavy metals remains limited. This study investigated the effects of polystyrene, carboxy-modified polystyrene, and amino-modified polystyrene on lead (Pb) toxicity in dandelion seedlings. The results showed that carboxy -modified polystyrene with a negative charge absorbed more Pb²⁺ than polystyrene and amino-modified polystyrene, and their maximum adsorption amounts were 5.328, 0.247, and 0.153 μg g⁻¹, respectively. The hydroponic experiment demonstrated that single amino-modified polystyrene was more toxic to dandelion seedlings than polystyrene and carboxy-modified polystyrene. The presence of Pb²⁺ was found to increase antioxidant enzymes (superoxide dismutase and catalase) and non-antioxidant enzymes (glutathione and ascorbic acid) activities in response to excessive reactive oxygen species in dandelion leaves and roots treated with polystyrene and carboxy-modified polystyrene, while it did not change much when amino-modified polystyrene was added. Interestingly, compared with single Pb²⁺, the addition of amino-modified polystyrene with positive charges induced an obvious decrease in the above parameters; however, they declined slightly in the treatments with polystyrene and carboxy-modified polystyrene despite a stronger adsorption capacity for Pb²⁺. Similarly, the bioactive compounds, including flavonoids, polyphenols, and polysaccharides in dandelion, showed a scavenging effect on O₂⁻ and H₂O₂, thereby inhibiting the accumulation and reducing medicinal properties. This study found that the effects of microplastics on the uptake, distribution, and toxicity of heavy metals depended on the nanoparticle surface charge.

Antimony (Sb) and arsenic (As) are chemical analogs, but their behaviors in plants are different. To investigate the Sb uptake, translocation and speciation in As-hyperaccumulator P. cretica, a hydroponic experiment was conducted. In this study, P. cretica was exposed to 0.2-strength Hoagland nutrient solution, which contained 0.5 or 5 mg/L antimonite (SbIII) or antimonate (SbV). After 14 d exposure, P. cretica took up 1.4–2.8 times more SbIII than SbV. Since P. cretica was unable to translocate Sb, its roots accumulated >97% Sb with the highest at 7965 mg/kg. In both SbIII and SbV treatments, SbIII was the predominant species in P. cretica, with 90–100% and 46–100% SbIII in the roots. As the first barrier against Sb to enter plant cells, more Sb was accumulated in cell wall than cytosol or organelles. The results suggest that P. cretica may detoxify Sb by reducing SbV to SbIII and immobilizing it in root cell walls. Besides, the presence of SbIII significantly reduced the concentrations of dissolved organic C including organic acids in P. cretica root exudates. Further, increasing Sb levels promoted P accumulation in the plant, especially in the fronds, which may help P. cretica growth. The information from this study shed light on metabolic transformation of Sb in As-hyperaccumulators P. cretica, which helps to better understand Sb uptake and detoxification by plants.

Since the urbanization and industrialization are wildly spread in recent decades, the concentration of Zn in soil has increased in various regions. Although the interactions between P and Zn has long been recognized, the effect of high level of Zn on P uptake, translocation and distribution in rice and its molecular mechanism are not fully understood. In this study, we conducted both hydroponic culture and field trial with different combined applications of P and Zn to analyze the rice growth and yield, the uptake, translocation and distribution of P and Zn, as well as the P- and Zn-related gene expression levels. Our results showed that high level of Zn decreased the rice biomass and yield production, and inhibited the root-to-shoot translocation and distribution of P into new leaves by down-regulating P transporter genes OsPT2 and OsPT8 in shoot, which was controlled by OsPHR2-OsmiR399-OsPHO2 module. High Zn supply triggered P starvation signal in root, thereafter increased the activities of both root-endogenous and -secreted acid phosphatase to release more Pi, and induced the expression OsPT2 and OsPT8 to uptake more P for plant growth. On the other hand, high level of P significantly decreased the Zn concentrations in both root and shoot, and the root uptake ability of Zn through altering the expression levels of OsZIPs, which were further confirmed by the P high-accumulated mutant osnla1-2 and OsPHR2-OE transgenic plant. Taken together, we revealed the physiological and molecular mechanisms of P–Zn interactions, and proposed a working model of the cross-talk between P and Zn in rice plants. Our results also indicated that appropriate application of P fertilizer is an effective strategy to reduce rice uptake of excessive Zn when grown in Zn-contaminated soil.

Fe-based nanoparticles (Fe-based NPs) have great potential as a substitute for traditional Fe-fertilizer; however, their environmental risk and impact on plant growth are not fully understood. In this study, we compared the physiological impacts of three different Fe-based NP formulations: zero-valent iron (ZVI), Fe₃O₄ and Fe₂O₃ NPs, on hydroponic rice after root exposure for 2 weeks. Fe-normal (Fe(+)) and Fe-deficiency (Fe(−)) conditions were compared. Results showed that low dose (50 mg L⁻¹) of ZVI and Fe₃O₄ NPs improved the rice growth under Fe(−) condition, while Fe₂O₃ NPs did not improve plant growth and caused phytotoxicity at high concentration (500 mg L⁻¹). Under Fe(+) conditions, none of the Fe-based NPs exhibited positive effects on the rice plants with plant growth actually being inhibited at 500 mg L⁻¹ evidenced by reduced root volume and leaf biomass and enhanced oxidative stress in plant. Under Fe(−) condition, low dose (50 mg L⁻¹) of ZVI NPs and Fe₃O₄ NPs increased the chlorophyll content by 30.7% and 26.9%, respectively. They also alleviated plant stress demonstrated by the reduced oxidative stress and decreased concentrations of stress related phytohormones such as gibberellin and indole-3-acetic acid. Low dose of ZVI and Fe₃O₄ NPs treatments resulted in higher Fe accumulation in plants compared to Fe₂O₃ NPs treatment, by down-regulating the expression of IRT1 and YSL15. This study provides significant insights into the physiological impacts of Fe-based NPs in rice plants and their potential application in agriculture. ZVI and Fe₃O₄ NPs can be used as Fe-fertilizers to improve rice growth under Fe-deficient condition, which exist in many rice-growing regions of the world. However, dose should be carefully chosen as high dose (500 mg L⁻¹ in this study) of the Fe-based NPs can impair rice growth.

Metal-resistant bacteria can reduce Cd accumulation in plants, but mechanisms underlying this effect are poorly understood. In this study, a highly effective Cd-resistant WRS8 strain was obtained from the rhizoshere soil of Triticum aestivum L. Yangmai-13 and identified as Pseudomonas taiwanensis based on 16S rRNA gene sequence analysis. Strain WRS8 was investigated for its effects on Cd availability and wheat tissue Cd contents and the related mechanisms using a hydroponic culture experiment. In strain WRS8-inoculated solution, the Cd concentration reduced and the pH and cell-adsorbed Cd increased with time. Strain WRS8 increased the wheat root and above-ground tissue dry weights by 11–36% compared to the controls. In strain WRS8-inoculated wheat plants, the Cd contents of the roots and above-ground tissues decreased by 78–85% and 88–94% and the Cd bioconcentration and translocation factors decreased by 78–85% and 46–58% at days 3 and 10, respectively, compared with the controls. The root surface-adsorbed Cd contents increased by 99–121% in the WRS8 strain-inoculated wheat plants at days 3 and 10 compared to the controls. Furthermore, strain WRS8 colonized the wheat root surfaces and interiors and reduced the expression levels of the LCT1 and HMA2 genes involved in Cd accumulation and transport in wheat roots by 46% and 30%, respectively, compared to the controls. In the Cd-contaminated soils, strain WRS8 significantly reduced the available Cd content by 20–24% and increased the pH compared to the controls. These findings showed the important role of strain WRS8 in reducing solution and soil Cd availability and suggested that strain WRS8 reduced the wheat tissue Cd accumulation by increasing root surface Cd adsorption and decreasing wheat root Cd uptake and transport-related gene expression and may provide a new and effective wheat rhizobacteria-enhanced approach for reducing wheat Cd uptake in Cd-polluted environments.

Though the interaction between humic acid (HA) and heavy metals has been widely reported, the effects of HA on the toxicity of heavy metals to plants are still in debate. In this study, the regulation mechanisms of HA on Pb stress in tea plant (Camellia sinensis L.) was investigated through hydroponic experiments, and the experimental results were explained by using transmission electron microscope (TEM), scanning transmission X-ray microscopes (STXM) and isobaric tags for relative and absolute quantitation (iTRAQ) differential proteomics. Significant alleviation of Pb stress was found with HA coexistence. TEM results showed that HA greatly mitigated the damage of cells caused by Pb stress. Compared with sole Pb treatment, the addition of HA increased the contents of pectin and pectic acid in the cell wall by 10.5% and 30.5%, while arabinose (Ara) and galactose (Gal) decreased by 20.5% and 15.9%, respectively, which were beneficial for increasing Pb adsorption capacity of the cell wall and promoting cell elongation. Moreover, iTRAQ differential proteomics analysis proved that HA strengthened the antioxidant system, promoted the synthesis of cell wall, and stabilized protein and sulfur-containing substance metabolism in molecular level. Notably, the concentration of calcium (Ca) in the cell wall of HA coexistence treatment was 47.4% higher than Pb treatment. STXM results also indicated that the distribution of Ca in the cell wall was restored with the presence of HA. This might promote the formation of the egg-box model, thus alleviating Pb stress in cells. Our results reveal the regulation mechanisms of HA on Pb detoxification in plants and provide useful information for improving the safety of agricultural products.

Chromium (Cr) is a toxic element among which hexavalent chromium [Cr(VI)] is more toxic than trivalent chromium [Cr(III)]. Chromium can be reduced or oxidized in soil because soil is a complex medium and various soil components affect redox reaction of Cr in soil. Therefore, Cr speciation in hydroponics and soil was compared and Cr uptake and speciation by lettuce grown in the media were evaluated. Higher phytotoxicity was found in Cr(III) spiked soil than in Cr(VI) spiked soil, while Cr toxicity was higher in Cr(VI) treated hydroponics than Cr(III) treated hydroponics. Chromium was mainly accumulated in lettuce roots as Cr(III), and more Cr was translocated from roots to shoots grown in Cr(VI) treated hydroponics than Cr(III) treated hydroponics. Accumulation of Cr in roots grown in Cr(III) treated nutrient solution reduced Fe, K, Ca, Mg, and P uptake in lettuce. Chromium valence state was Cr(III) in lettuce leaves and roots grown in both Cr(III) and Cr(VI) treated hydroponics and soil. Chromium speciation in hydroponically grown lettuce roots was Cr(III) coordinated with 6 oxygens in the first shell and 2 or 4 carbons in the second shell as analyzed by X-ray absorption spectroscopy (XAS), which was similar to chromium acetate. The valence state of Cr in Cr(III) and Cr(VI) treated nutrient solution was not changed, while Cr(VI) was reduced to Cr(III) in Cr(VI) spiked soil by soil organic matter. Spiking of Cr(III) induced reduction of Mn in soil, which resulted in an increase of bioavailable Mn concentration in the Cr(III) spiked soil. Therefore, the increased phytotoxic effect for lettuce in Cr(III) spiked soil can be attributed to the reduction of Mn and subsequent release of Mn(II). For Cr(III) contaminated soil, Mn speciation should be considered, and bioavailable Mn concentration should be monitored although Cr existed as Cr(III) in soil.

Benzene kresoxim-methyl (BKM) is an important methoxyacrylate-based strobilurin fungicide widely used against various phytopathogenic fungi in crops. Uptake, translocation and accumulation of BKM in vegetables remain unknown. This study was designed to investigate uptake, translocation, and accumulation of ¹⁴C-BKM and/or its potential metabolites in Chinese flowering cabbage and water spinach. ¹⁴C-BKM can be gradually taken up to reach a maximum of 44.4% of the applied amount by Chinese flowering cabbage and 34.6% by water spinach at 32 d after application. The ¹⁴CO₂ fractions released from the hydroponic plant system reached 37.8% for cabbage and 45.8% for water spinach, respectively. Concentrations of ¹⁴C in leaves, stems and roots all gradually increased as vegetables growing, with relative 44.9% (cabbage) and 26.8% (water spinach) of translocated from roots to edible leaves. In addition, ¹⁴C in leaves was mainly accumulated in the bottom leaves, which was visualized by quantitative radioautographic imaging. The bioconcentration factor of ¹⁴C ranged from 7.1 to 38.2 mL g⁻¹ for the cabbage and from 8.6 to 24.6 mL g⁻¹ for the water spinach. The translocation factor of BKM ranged from 0.10 to 2.04 for the cabbage and 0.10–0.46 for the water spinach throughout the whole cultivation period, indicating that the cabbage is easier to translocate BKM from roots to leaves and stems than water spinach. In addition, the daily human exposure values of BKM in both vegetables were much lower than the limited dose of 0.15 mg day⁻¹. The results help assess potential accumulation of BMK in vegetables and potential risk.