Uptake, tolerance, and detoxification mechanisms of antimonite and antimonate in Boehmeria nivea L

Crucial role of the Pht1;4 Gene in Sb(V) tolerance and uptake in Arabidopsis thaliana

There has been increasing awareness of the risks of antimony (Sb) in the environment, but the process of Sb(V) absorption by plants and its effects on plants remain unclear. This study focused on four independent T-DNA insertion mutant strains of Arabidopsis thaliana and wild-type (WT) plants to investigate their tolerance, uptake, and response to Sb(V). Compared with those of the WT, the Pht1;4 knockout mutant M-P4 presented greater tolerance to Sb(V) and lower absorption levels. The roots of the M-P4 were longer and the malondialdehyde (MDA) content in the roots of M-P4 was lower than WT (0.194 < 1.333, μM/mg FW). The amount of Sb(V) absorbed by the roots of M-P4 under Sb(V) treatment was lower than that absorbed by WT plants (by 25 %-50 %), and the levels of Sb in the stems and leaves were also lower. Moreover, the transmembrane transport ratio of Sb(V) in M-P4 was lower than that in the WT (0.748 < 0.937). The Pht1;1 knockout mutant exhibited a predominant transmembrane absorption mode for Sb(V), while gene expression data show that knocking out either Pht1;1 or Pht1;4 leads to the upregulation of the other gene. These results collectively demonstrate that the characteristics of M-P4 are due to the important role of Pht1;4 in Sb(V) transport. In summary, this study investigates the influence of several genes on plant tolerance and uptake to Sb(V) and elucidates the crucial role of the Pht1;4 gene, shedding light on the development of Sb phytoremediation strategies and Sb-resistant plants.

Reduction of antimony bioavailability with the application of stable exogenous organic matter: a comparative study between rice straw and manure compost

Considering the widespread use of organic amendments to improve soil quality and enhance soil carbon sequestration, it is crucial to understand their impact on the bioavailability of metalloids in soils. Antimony (Sb), a priority pollutant, is particularly impacted by organic matter, yet the effects of different organic amendments-varying in stability and composition-on Sb bioavailability remain unclear. This study investigates the influence of different organic amendments, rice straw and compost, on Sb bioavailability in the rice-soil system, with rice ingestion being a major Sb exposure pathway in humans. Results show that while both amendments increased dissolved organic carbon in soil solution, their effects on Sb bioavailability differed markedly. Rice straw increased CDGT-SbIII by 13.24 %-66.63 %, whereas compost decreased CDGT-SbIII by 32.47 %-43.51 %. These differences were also reflected in Sb accumulation in rice shoots, where compost application resulted in lower Sb content. This reduction may be attributed to increased microbial genera such as Ramlibacter and Sphingomonas, which are associated with SbIII oxidation. Conversely, organic matter with low stability, prone to rapid degradation, could promote reducing soil conditions, thereby increasing SbIII concentrations. Our findings suggest that stable exogenous organic matter, such as pre-decomposed compost, is preferable for managing Sb-contaminated soils.

Polystyrene influence on Pb bioavailability and rhizosphere toxicity: Challenges for ramie (Boehmeria nivea L.) in soil phytoremediation

Microplastics (MPs) and heavy metals often coexist in soil, however their interactions and effects on the soil-plant system remain largely unclear. In this study, ramie (Boehmeria nivea L.) was exposed to soil contaminated with lead (Pb) and polystyrene (PS) of different sizes, dosages, and surface-charged functional groups. This design aimed to simulate the effects of MPs on phytoremediation. The experimental results revealed that PS exacerbated the damaging effects of Pb on ramie. Compared to the effect of Pb alone, PS-COOH had a greater influence on root vigor, leading to a 15.6 % reduction in the active absorption ratio. Laser scanning confocal microscope showed PS entered the roots. Adsorption/desorption experiments demonstrated that PS had a weaker adsorption capacity for Pb than soil but a greater desorption rate than soil when simulating rhizosphere secretion. Moreover, PS reduced soil pH and increased the reducible state of Pb by 6-12 %. After 100 days of phytoremediation, Pb content in the soil with PS-5 μm was 150 μg g-1 less than that in the soil without PS. These results demonstrated that PS improved Pb bioavailability and enhanced the efficiency of Pb uptake by ramie. The redundancy analysis demonstrated that PS mitigated the toxicity of Pb to rhizosphere microorganisms, potentially via its effects on metal chemical fractions, dehydrogenase activity (S-DHA), cation exchange capacity (CEC), and soil organic matter (SOM). This study indicates that the presence of PS could potentially enhance the phytoremediation efficiency of ramie in Pb-contaminated land by influencing soil microenvironmental properties. This study provides insights into the complex interactions of MPs with soil-plant-microbial systems during metal remediation, thereby enhancing our understanding of their environmental impacts.

Rare earth elements applied to phytoremediation: Enhanced endocytosis promotes remediation of antimony contamination with different valence levels in Solanum nigrum L

Antimony (Sb) pollution poses a noteworthy risk to human health and ecosystem sustainability, therefore effective, eco-friendly, and widely accepted restoration methods are urgently needed. This study introduces a new approach of using La(III) foliar application on Solanum nigrum L. (S. nigrum), a cadmium hyperaccumulator, to improve its photosynthetic and root systems under Sb stress, resulting in a higher biomass. Notably, La(III) also enhances endocytosis in root cells, facilitating efficient and non-selective remediation of both Sb(III) and Sb(V) forms. The absorption of Sb by root cell endocytosis was observed visually with a confocal laser scanning microscope. The subcellular distribution of Sb in the cell wall of S. nigrum is reduced. And the antioxidant enzyme activity system is improved, resulting in an enhanced Sb tolerance in S. nigrum. Based on the existing bibliometric analysis, this paper identified optimal conditions for S. nigrum to achieve maximum translocation and bioconcentration factor values for Sb. The foliar application of La(III) on plants treated with Sb(III), Sb(V), and a combination of both resulted in translocation factor values of 0.89, 1.2, 1.13 and bioconcentration factor values of 11.3, 12.81, 14.54, respectively. Our work suggests that La(III)-enhanced endocytosis of S. nigrum root cells is a promising remediation strategy for Sb-contaminated environments.

Selenium increases antimony uptake in ramie (Boehmeria nivea L.) by enhancing the physiological, antioxidative, and ionomic mechanisms

Ramie (Boehmeria nivea L.) is a promising phytoremediation candidate due to its high tolerance and enrichment capacity for antimony (Sb). However, challenges arise as Sb accumulated mainly in roots, complicating soil extraction. Under severe Sb contamination, the growth of ramie may be inhibited. Strategies are needed to enhance Sb accumulation in ramie's aboveground parts and improve tolerance to Sb stress. Considering the beneficial effects of selenium (Se) on plant growth and enhancing resistance to abiotic stresses, this study aimed to investigate the potential use of Se in enhancing Sb uptake by ramie. We investigated the effects of Se (0.5, 1, 2, 5, or 10 μM) on ramie growth, Sb uptake and speciation, antioxidant responses, and ionomic profiling in ramie under 10 mg/L of SbIII or antimonate (SbV) stresses. Results revealed that the addition of 0.5 μM Se significantly increased shoot biomass by 75.73% under SbIII stress but showed minimal effects on shoot and root length in both SbIII and SbV treatments. Under SbIII stress, 2 μM Se significantly enhanced Sb concentrations by 48.42% in roots and 62.88% in leaves. In the case of SbV exposure, 10 μM Se increased Sb content in roots by 42.57%, and 1 μM Se led to a 91.74% increase in leaves. The speciation analysis suggested that Se promoted the oxidation of SbIII to less toxic SbV to mitigate Sb toxicity. Additionally, Se addition effectively minimized the excess reactive oxygen species produced by Sb exposure, with the lowest malondialdehyde (MDA) content at 0.5 μM Se under SbIII and 2 μM Se under SbV, by activating antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione peroxidase. Ionomic analysis revealed that Se helped in maintaining the homeostasis of certain nutrient elements, including magnesium, potassium (K), calcium (Ca), iron (Fe), and copper (Cu) in the SbIII-treated roots and K and manganese (Mg) in the SbV-treated roots. The results suggest that low concentrations of Se can be employed to enhance the phytoremediation of Sb-contaminated soils using ramie.

The uptake, transportation, and chemical speciation of Sb(III) and Sb(V) by wetland plants Arundinoideae (Phragmites australis) and Potamogetonaceae (Potamogeton crispus)

Antimony (Sb) is increasingly released and poses a risk to the environment and human health. Antimonite (Sb(III)) oxidation can decrease Sb toxicity, but the current knowledge regarding the effects of Sb(III) and antimonate (Sb(V)) exposure is limited to wetland plants, especially the Sb speciation in plants. In this study, Phragmites australis and Potamogeton crispus were exposed to 10 and 30 mg/L Sb(III) or Sb(V) for 20 days. The total concentration, subcellular distribution, and concentration in the iron plaque of Sb were determined. The Sb speciation in plants was analyzed by HPLC-ICP-MS. It illustrated that Sb(III) exposure led to more Sb accumulation in plants than Sb(V) treatments, with the highest Sb concentration of 405.35 and 3218 mg/kg in Phragmites australis and Potamogeton crispus, respectively. In the subcellular distribution of Sb, accumulation of Sb mainly occurred in cell walls and cell cytosol. In Phragmites australis, the transport factor in the Sb(V) treatments was about 3 times higher than the Sb(III) treatments, however, it was lower in the Sb(V) treatments than Sb(III) treatments for Potamogeton crispus. Sb(V) was detected in the plants of Sb(III) treatments with different Sb(V)-total Sb vitro (Phragmites australis: 34 % and, Potamogeton crispus: 15 %), moreover, Sb(V) was also detected in the nutrient solution of Sb(III) treatments. Antimony exposure caused a reduction of the iron plaque formation, at the same time, the root aerenchyma formation was disrupted, and this phenomenon is more pronounced in the Sb(III) treatments. Moreover, the iron plaque has a higher sorption potential to Sb under Sb(III) exposure than that under Sb(V) exposure. The results can fill the gap for antinomy speciation in wetland plants and expand the current knowledge regarding the Sb translocation in wetland systems.

Effect of endophytic bacteria on the phytoremediation potential of halophyte Tamarix smyrnensis for Sb-contaminated soils

Phytoremediation, including bacteria-assisted phytoremediation, presents a promising technology for treating shooting range soils contaminated with toxic metalloids. In this study, a pot experiment was performed using the halophyte Tamarix smyrnensis and soil collected from a shooting range and artificially spiked at two different antimonite (Sb(III)) concentrations (50 mg/kg and 250 mg/kg) with the aim to explore the Sb phytoremediation of the halophyte. The effect of salt (0.3%) and Mn addition (300 ppm) on its remediation capacity was also investigated. Moreover, the root endophytic community of the halophyte was found able to remove Sb(III) and was periodically inoculated to the plants. The consortium application increased the Sb bioavailable fraction in the soil and enhanced the Sb accumulation in root and aerial parts (up to 50% and 55% respectively at high Sb(III) concentration) compared to the uninoculated plants. Moreover, the presence of Mn increased the translocation factor (21% increase for inoculated and 46% increase for uninoculated plants) while lower TF was observed at high Sb concentrations (0,2 and 0,07 was the lowest value at low and high Sb treatments respectively). The addition of salt, Mn and root endophytic bacteria aided the halophyte to cope with elevated Sb concentrations. The total chlorophyll concentration was higher in inoculated plants compared to the uninoculated ones in all treatments, implying the positive effects of endophytic inoculation. The halophyte T. smyrnensis with the aid of endophytic community presents a promising alternative for remediating shooting range soils especially in areas impacted by salinity.

Effects of Transporter Inhibitors and Chemical Analogs on the Uptake of Antimonite and Antimonate by Boehmeria nivea L

Antimony (Sb) is a non-essential metalloid that can be taken up by plants from contaminated soils and thus enter the food chain and threaten human health. Boehmeria nivea L. (ramie) is a promising phytoremediation plant for Sb-polluted soils. However, the mechanisms of antimonite (SbIII) and antimonate (SbV) uptake by ramie remain unclear. In this study, a hydroponic system was established to investigate how different substances affect the uptake of SbIII or SbV by ramie, including an energy inhibitor (malonic acid), an aquaglyceroporin inhibitor (silver nitrate), an SbV analog (phosphate-PV), and SbIII analogs (arsenite-AsIII, glycerol, silicic acid-Si, and glucose). The results indicated that ramie primarily transported Sb by increasing the Sb concentration in the bleeding sap, rather than increasing the weight of the bleeding sap. After 16 h of Sb exposure, the absolute amount of transported Sb from the roots to the aboveground parts was 1.90 times higher under SbIII than under SbV. The addition of malonic acid significantly inhibited the uptake of SbV but had limited effects on SbIII, indicating that SbV uptake was energy dependent. PV addition significantly reduced SbV uptake, while the addition of AsIII, glycerol, and Si obviously inhibited SbIII uptake. This suggested that the uptake of SbV might be via low-affinity P transporters and SbIII might use aquaglyceroporins. These findings deepen the understanding of Sb uptake pathways in ramie, contribute to a better comprehension of Sb toxicity mechanisms in ramie, and establish a foundation for identifying the most effective Sb uptake pathways, which could further improve the efficiency of phytoremediation of Sb-polluted soils.

Transcriptomic analysis reveals the molecular mechanisms of Boehmeria nivea L. in response to antimonite and antimonate stresses

Soil antimony (Sb) pollution is a global concern that threatens food security and human health. Boehmeria nivea L. (ramie) is a promising phytoremediation plant exhibiting high tolerance and enrichment capacity for Sb. To reveal the molecular mechanisms and thus enhance the ramie uptake, transport, and detoxification of Sb with practical strategies, a hydroponic experiment was conducted to compare the physiological and transcriptomic responses of ramie towards antimonite (Sb(Ⅲ)) and antimonate (Sb(Ⅴ)). Phenotypic results showed that Sb(Ⅲ) had a stronger inhibitory effect on the growth of ramie. Root Sb content under Sb(Ⅲ) was 2.43 times higher than that in Sb(Ⅴ) treatment. Based on the ribonucleic acid sequencing (RNA-Seq) technique, 3915 and 999 significant differentially expressed genes (DEGs) were identified under Sb(Ⅲ) and Sb(Ⅴ), respectively. Transcriptomic analysis revealed that ramie showed different adaptation strategies to Sb(Ⅲ) and Sb(V). Key DEGs and their involved pathways such as catalytic activity, carbohydrate metabolisms, phenylpropanoid biosynthesis, and cell wall modification were identified to perform crucial roles in Sb tolerance and detoxification. Two heavy metal-associated domain-type genes, six heavy metal-associated isoprenylated plant proteins, and nine ABC transporters showed possible roles in the transport and detoxification of Sb. The significant upregulation of NRAMP5 and three NIPs suggested their roles in the transport of Sb(V). This study is the basis for future research to identify the exact genes and biological processes that can effectively enhance Sb accumulation or improve plant tolerance to Sb, thereby promoting the phytoremediation of Sb-polluted soils.