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.

Almost 81% of nitrogen fertilizers are applied in form of urea but most of it is lost due to volatilization and leaching leading to environmental pollution. In this regard, slow-release nano fertilizers can be an effective solution. Here, we have synthesized different Fe₃O₄-urea nanocomposites with Fe₃O₄ NPs: urea ratio (1:1, 1:2, 1:3) ie. NC-1, 2, and 3 respectively, and checked their efficacy for growth and yield enhancement. Oryza sativa L. cv. Swarna seedlings were treated with different NCs for 14 days in hydroponic conditions and significant up-regulation of photosynthetic efficiency and nitrogen metabolism were observed due to increased availability of nitrogen and iron. The discriminant functional analysis confirmed that the NC3 treatment yielded the best results so further gene expression studies were performed for NC-3 treated seedlings. Significant changes in expression profiles of ammonia and nitrate transporters indicated that NC-3 treatment enhanced nitrogen utilization efficiency (NUE) due to sustained slow release of urea. From pot experiments, we found significant enhancement of growth, grain nutrient content, and NUE in NC supplemented sets. 1.45 fold increase in crop yield was achieved when 50% N was supplemented in form of NC-3 and the rest in form of ammonium nitrate. NC supplementation can also play a vital role in minimizing the use of bulk N fertilizers because, when 75% of the recommended N dose was supplied in form of NC-3, 1.18 fold yield enhancement was found. Thus our results highlight that, slow-release NC-3 can play a major role in increasing the NUE of rice.

Per- and polyfluoroalkyl substances (PFASs) have been found to be widely present in soil. Dissolved organic matter (DOM) in soil are supposed to greatly affect the bioavailability of PFASs in soil. Herein, hydroponic experiments were conducted to understand the impacts of two kinds of typical DOM, bovine serum albumin (BSA) and humic acid (HA), on the uptake and translocation of legacy PFASs and their emerging alternatives, perfluorooctane sulfonic acid (PFOS), perfluorooctane acid (PFOA), perfluorohexane sulfonic (PFHxS) and 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) in wheat (Triticum aestivum L.). The results indicated that both HA and BSA significantly inhibited the bioaccumulation and translocation of PFASs in the roots and shoots of wheat, and the impacts of BSA were greater than HA. This difference was explained by the greater binding affinities of the four PFASs with BSA than with HA, as evidenced by the equilibrium dialysis and isothermal titration calorimetry (ITC) analyses. It was noting that inhibition impacts of the BSA-HA mixture (1:1) were lower than BSA alone. The results of Fourier transform infrared (FT-IR) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy suggested that HA could bind with the fluorescent tryptophan residues in BSA greatly, competing the binding sites with PFASs and forming a cover on the surface of BSA. As a result, the binding of PFASs with BSA-HA complex was much lower than that with BSA, but close to HA. The results of this study shed light on the impacts of DOM in soil on the bioaccumulation and translocation of PFASs in plants.

Microplastics, an emerging pollutant in the environment, have attracted extensive attention in recent years for their possible negative impact on organisms. However, direct and indirect effects of polystyrene (PS) microplastics on vegetables are still not completely known. In this study, we used red lettuce (Lactuca sativa L. Red Sails) in a hydroponic system to investigate the effects of nano- and micro-sized PS and dibutyl phthalate (DBP) on the photosynthesis and red lettuce quality. The results clearly indicated that PS reduced the bioavailability of DBP while causing a decrease in the photosynthetic parameters as well as the total chorophyll content compared to DBP alone by affecting the crystalline structure of the water-soluble chlorophyll protein. Compared with DBP monotherapy, the presence of PS significantly increased hydrogen peroxide and malondialdehyde content in the lettuce treated with DBP, indicating serious oxidative damage. Furthermore, the soluble protein and sugar content in lettuce leaves decreased with higher PS concentration and smaller PS size. It may be due to PS inhibited lettuce root and ribulose-1,5-bisphosphate carboxylase/oxygenase activities. In contrast, nitrite content increased significantly with the induction of the glutathione-ascorbic acid cycle, indicating that the presence of PS reduced the quality of DBP-treated-red lettuce. Additionally, the nano-sized PS greatly inhibited lettuce growth and quality more than the micro-sized PS. This study described the interactions between microplastics and phthalates using molecular simulation and experimental validation to highlight the potential risks of microplastics on vegetable crop production.

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.

Antagonism between selenium (Se) and cadmium (Cd) has been demonstrated in plants. However, a mutual suppression threshold for Se and Cd has not been identified in previous studies using Cd or Se individually. To fill this knowledge gap, we determined the levels of Se and Cd in various tissues of rice under concentration gradients of Se and Cd with different Se application times via hydroponic experiments. The results showed that the application of exogenous Se or Cd reduced the uptake and transport of the other. When the molar ratio of Se/Cd (R (Se/Cd)) was higher than 1, the concentration and transfer factor of Cd (TF-Cd) in all parts of rice simultaneously reached the lowest values. The minimum Se absorption in rice was obtained at R (Cd/Se) greater than 20, while no inhibition threshold was found for Se transport. In addition, approximately 1:1 R (Se/Cd) was observed in roots and the addition of exogenous Cd or Se promoted the enrichment of the other element in roots. These data suggested a mutual inhibition of Se and Cd in their absorption, transportation and accumulation in rice, which might be related to the formation of insoluble Cd–Se complexes in roots. This study provided new insights into a plausible explanation of the interactions between Se and Cd and contributed to the remediation and treatment of combined Se and Cd pollution in farmland systems.

The radial translocation of cadmium (Cd) from the root to the shoot is one of the major processes affecting Cd accumulation in rice (Oryza sativa L.) grains, but few studies have focused on Cd apoplastic transport in rice. The aim of this study was to determine how apoplastic barriers affect Cd translocation via the apoplastic pathway, Cd accumulation levels in upper parts (shoot and grains) of rice cultivars, and the possible mechanism involved. Hydroponic and soil pot trials were conducted to study the development and chemical constituents of apoplastic barriers and their permeability to bypass flow, and to determine Cd localization in the roots of rice cultivars with different Cd-accumulating characteristics. The Cd accumulation in upper parts was positively correlated with bypass flow in the root and the apparent Cd concentration in the xylem, indicating that the apoplastic pathway may play an important role in Cd root-shoot translocation in rice. Apoplastic barriers were deposited closer to the root tip and were thicker in low Cd-accumulating cultivars than in high Cd-accumulating cultivars. The amounts and rates of increase in lignin and suberin were significantly higher in ZD14 (a low Cd-accumulating cultivar) than in FYXZ (a high Cd-accumulating cultivar) under Cd stress, indicating that stronger barriers were induced by Cd in ZD14. The stronger and earlier formation of barriers in the low Cd-accumulating cultivar decreased bypass flow more efficiently, so that more Cd was retained in the root during apoplastic translocation. This was confirmed by localization analyses of Cd in root transverse sections. These results suggest that apoplastic barriers reduce Cd root-to-shoot translocation via the apoplastic pathway, leading to lower Cd accumulation in the upper parts of rice plants. Bypass flow may have the potential to be used as a rapid screening indicator for low Cd-accumulating rice cultivars.