ABA-importing transporter (AIT1) synergies enhances exogenous ABA minimize heavy metals accumulations in Arabidopsis.

Exogenous abscisic acid (ABA) presents a novel approach to mitigate heavy metal (HM) accumulation in plants, yet its efficacy against multiple HMs and potential enhancement methods remain underexplored. In this study, we demonstrated that the exogenous ABA application simultaneously decreased Zn, Cd and Ni accumulation by 22-25 %, 27-39 % and 60-62 %, respectively, in wild-type (WT) Arabidopsis. Conversely, ABA reduced Pb in shoots but increased its root concentration. ABA application also modulated the expression of HM uptake genes, inhibiting IRT1, NRAMP1, NRAMP4, and HMA3, and increasing ZIP1 and ZIP4 expressions. Further analysis revealed that overexpressing the ABA-importing transporter (AIT1) in plants intensified the reduction of Cd, Zn, and Ni, compared to WT. However, the inhibitory effect of exogenous ABA on Pb accumulation was mitigated in shoots with higher AIT1 expression. Furthermore, HMs-induced growth inhibition and the damage to photosynthesis were also alleviated with ABA treatment. Conclusively, AIT1's synergistic effect with ABA effectively reduces Cd, Zn and Ni accumulation, offering a synergistic approach to mitigate HM stress in plants.

A dose-dependent effect of UV-328 on photosynthesis: Exploring light harvesting and UV-B sensing mechanisms.

Benzotriazole ultraviolet (UV) stabilizers (BUVs) have emerged as significant environmental contaminants, frequently detected in various ecosystems. While the toxicity of BUVs to aquatic organisms is well-documented, studies on their impact on plant life are scarce. Plants are crucial as they provide the primary source of energy and organic matter in ecosystems through photosynthesis. This study investigated the effects of UV-328 (2-(2-hydroxy-4',6'-di-tert-amylphenyl) benzotriazole) on plant growth indices and photosynthesis processes, employing conventional physiological experiments, RNA sequencing (RNA-seq) analysis, and computational methods. Results demonstrated a biphasic response in plant biomass and the maximum quantum yield of PS II (Fv/Fm), showing improvement at a 50 µM UV-328 treatment but reduction under 150 µM UV-328 exposure. Additionally, disruption in thylakoid morphology was observed at the higher concentration. RNA-seq and qRT-PCR analysis identified key differentially expressed genes (light-harvesting chlorophyll-protein complex Ⅰ subunit A4, light-harvesting chlorophyll b-binding protein 3, UVR8, and curvature thylakoid 1 A) related to photosynthetic light harvesting, UV-B sensing, and chloroplast structure pathways, suggesting they may contribute to the observed alterations in photosynthesis activity induced by UV-328 exposure. Molecular docking analyses further supported the binding affinity between these proteins and UV-328. Overall, this study provided comprehensive physiological and molecular insights, contributing valuable information to the evaluation of the potential risks posed by UV-328 to critical plant physiological processes.

NRT1.2 overexpression enhances the synergistic interplay between ABA-generating bacteria and biochars in reducing heavy metal accumulation in pak choi.

The agricultural sector faces severe challenges owing to heavy metal (HM) contamination of farmlands, requiring urgent preventive measures. To address this, we investigated the impact of the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium producing abscisic acid (ABA), and biochar to minimize HM accumulation in pak choi, using three distinct expression levels of the ABA transporter NRT1.2 in pak choi and three different types of contaminated soils as experimental materials. The results revealed that pak choi with low, medium, and high NRT1.2 expression intensity, when subjected to bacterial strain-biochar treatment, exhibited an increasing trend in ABA content compared to the control. Correspondingly, the aboveground HM content decreased by 1-49 %, 22-52 %, and 15-96 %, whereas the fresh weight increased by 12-38 %, 88-126 %, and 152-340 %, respectively, showing a significant correlation with NRT1.2 expression. Pearson correlation analysis demonstrated that NRT1.2 expression intensity was inversely associated with the combined treatment's reduction in HM accumulation and positively correlated with the promotional effect. Simultaneously, soil discrepancies significantly affected the combined treatment, which was likely associated with variations in the active forms of HM in each soil. Consequently, when employing ABA-producing bacteria for mitigating crop HM accumulation, selecting plants with higher relative NRT1.2 expression intensity, combined with biochar, is recommended.

Nanoplastics promote the dissemination of antibiotic resistance genes and diversify their bacterial hosts in soil.

The wide application of plastics has led to the ubiquitous presence of nanoplastics and microplastics in terrestrial environments. However, few studies have focused on the mechanism underlying the effects of plastic particles on soil microbiomes and resistomes, especially the differences between nanoplastics and microplastics. This study investigated the microbiome and resistome in soil exposed to polystyrene microplastics (mPS) or nanoplastics (nPS) through 16S rRNA and shotgun metagenomic sequencing. Distinct microbial communities were observed between mPS and nPS exposure groups, and nPS exposure significantly changed the bacterial composition even at the lowest amended rate (0.01%, w/w). The abundance of antibiotic resistance genes (ARGs) in nPS exposure (1%) was 0.26 copies per cell, significantly higher than that in control (0.21 copies per cell) and mPS exposure groups (0.21 copies per cell). It was observed that nanoplastics, bacterial community, and mobile genetic elements (MGEs) directly affected the ARG abundance in nPS exposure groups, while in mPS exposure groups, only MGEs directly induced the change of ARGs. Streptomyces was the predominant host for multidrug in the control and mPS exposure, whereas the primary host was changed to Bacillus in nPS exposure. Additionally, exposure to nPS induced several bacterial hosts to exhibit possible multi-antibiotic resistance characteristics. Our results indicated that the effects of plastic particles on the soil microbial community were size-dependent, and nano-sized plastic particles exhibited more substantial impacts. Both microplastics and nanoplastics promoted ARG transfer and diversified their bacterial hosts. These findings bear implications for the regulation of plastic waste and ARGs.

A promising product: Abscisic acid-producing bacterial agents for restricting cadmium enrichment in field vegetable crops.

Soil heavy metal contamination and its enrichment in the edible parts of crops have gained global concern. In this study, a compound bacterial agent possessing the ability to produce the plant hormone, abscisic acid (ABA), was applied to contaminated farmland in Hunan province. Its application reduced the concentration of Cd in radish, cabbage, mustard, and lettuce by 15-144%. Accordingly, the Cd contents in these vegetables were found to be below the maximum limits set by GB 2762-2017. Meanwhile, bacteria agents also led to a significant increase in crops yield by 45-82%. Furthermore, the nutritional indices, including soluble sugar and soluble protein increased by 18-66%, as well as the antioxidant indices, including total phenolic, ascorbate content, and DPPH capacity, enhanced by 12-76%, 10-49% and 50-140%, respectively. In conclusion, the use of ABA-producing bacteria is anticipated to be a novel approach for the safe use of soil with moderate and low pollution.

[Effects of Exogenous Plant Hormone Spraying on the Phytoremediation by Bidens pilosa L. in Cadmium-contaminated Soil].

To explore the effect of exogenous plant hormone spraying on the absorption of heavy metals by hyperaccumulated plants, Bidens pilosa L. was selected as the tested plant owing to the large biomass, short growth cycle, and high accumulation efficiency. Here, the effect of foliar spraying 6-benzylaminopurine (6-BA), salicylic acid (SA), and 24-epi-brassinosteroid (24-EBR) on the remediation of cadmium (Cd)-contaminated soil by B. pilosa L. was examined. The results showed:① the efficiency of the remediation in Cd-contaminated soil by B. pilosa L. was effectively enhanced after the spraying of all three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote the cadmium concentration in the leaves of B. pilosa L. to increase by 4.21%, 31.79%, and 14.89%; promote the translocation factor (TF) to increase by 9.67%, 18.83%, and 17.85%; promote the phytoextraction rates (PR) to increase by 15.36%, 32.33%, and 64.38%, respectively. ② The growth of B. pilosa L. was significantly promoted after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote plant growth under cadmium stress, and the dry weight of the plant root, stem, and leaf was increased by 37.53%, 74.50%, and 104.02%, respectively. ③ The photosynthesis of B. pilosa L. was significantly enhanced after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The chlorophyll concentration of the plant was significantly increased after foliar spraying with plant hormones, and the concentration of chlorophyll a was increased by 79.31%, 92.27%, and 51.12%; the photochemical quenching coefficient (qP) was increased by 11.32%, 89.16%, and 78.43%; and the non-photochemical quenching coefficient (NPQ) was increased by 51.71%, 241.12%, and 27.85%, respectively, after foliar spraying with appropriate concentrations of 6-BA, SA, and 24-EBR. ④ The antioxidant capacity of B. pilosa L. was significantly strengthened after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The malondialdehyde (MDA) concentration of the plant was reduced by 62.41%, 68.67%, and 46.76% after the application of 6-BA, SA, and 24-EBR, respectively. Meanwhile, superoxide dismutase (SOD) was increased by 68.33%, 10.28%, and 6.17%, and catalase (CAT) was increased by 31.43%, 37.87%, and 37.31%, respectively. Generally, the spraying of exogenous 6-BA, SA, and 24-EBR with the appropriate concentration under Cd stress could significantly increase the biomass of B. pilosa L. and promote the accumulation of heavy metals in the plant, improve the photosynthetic ability of the plant, reduce the oxidative damage of the plant under heavy metal stress, enhance the antioxidant capacity, and improve the absorption and tolerance of plants to Cd. It also could promote the transfer of Cd from roots to shoots, improve the phytoextraction rates of Cd from the plant, and effectively strengthen the phytoremediation efficiency. Among them, 30 mg·L-1 SA foliar spraying had the best effect.

ABA-metabolizing bacteria and rhamnolipids as valuable allies for enhancing phytoremediation efficiency in heavy metal-contaminated soils.

Microbial-assisted phytoremediation has great potential to improve the efficiency of phytoremediation in heavy metal (HM)-contaminated soils. In this study, the synergistic effects of rhamnolipids and the abscisic acid (ABA)-metabolizing bacterium Rhodococcus qingshengii on the phytoremediation efficiency of Indian mustard (Brassica juncea) in HM-contaminated soils were investigated. The Cd, Zn, and Pb contents in plants treated with a combination of rhamnolipids and R. qingshengii were 48.4-77.1 %, 14.6-40.4 %, and 16.1-20.0 % higher, respectively, than in those treated with R. qingshengii alone, and 42.8-59.2 %, 13.1-48.2 %, and 7.3-67.5 % higher, respectively, than in those treated with rhamnolipids alone. In addition, the bioconcentration factors of each metal were improved, and the biomass further increased by 36.6-65.7 % compared to that of single treatments. Pearson's correlation analysis showed that rhamnolipids and R. qingshengii enhanced the accumulation of HMs in B. juncea by activating the available forms of HMs in the soil and regulating the ABA and indole-3-acetic acid in plants, respectively. The structural equation model indicated that R. qingshengii had a larger path coefficient than rhamnolipids in terms of HM content and plant biomass, suggesting that R. qingshengii may have a greater contribution to promoting the extraction of HMs from the soil under synergistic conditions. In conclusion, the combination of rhamnolipids and R. qingshengii has great potential to enhance the phytoremediation efficiency of hyperaccumulating plants in HM-contaminated soils.

Nitrate-induced AHb1 expression aggravates Cd toxicity in plants.

Cadmium (Cd) causes severe toxicity in plants. However, the molecular mechanisms underlying plant resistance to Cd in relation to nitrogen (N) supply remain unclear. The non-symbiotic hemoglobin gene Hb1 plays an important role in scavenging nitric oxide (NO) in plants. In this study, there was no differential effect of Cd on the biomass of wild-type (WT) and AHb1-overexpressing (H7) plants when NH4+-N was used as a nitrogen source. However, under NO3--N conditions, Cd exerted less biomass stress on AHb1-silenced (L3) plants and more stress on H7 plants than on WT plants. The Cd tolerance index followed the order: L3 > WT > H7. However, there was no difference in Cd concentrations in the roots or shoots of the WT, L3, and H7 plants, indicating that differences in AHb1 expression were unrelated to Cd uptake. Further investigation showed that Cd exposure enhanced H2O2 accumulation and aggravated oxidative damage in H7 plants. The application of an NO donor effectively reversed growth inhibition, H2O2 burst, and oxidative stress induced by Cd in H7 plants. Thus, we suggest that NO3--induced AHb1 expression suppresses Cd-induced NO production in plants, increasing the ROS burst and exacerbating Cd toxicity.

Ketoprofen exposure perturbs nitrogen assimilation and ATP synthesis in rice roots: An integrated metabolome and microbiome analysis.

Ketoprofen, a commonly used non-steroidal anti-inflammatory drug (NSAID), can enter farmland environments via sewage irrigation and manure application and is toxic to plants. However, there have been relatively few studies on the association of ketoprofen with nitrogen (N) assimilation and metabolic responses in plants. Accordingly, the goal of this study was to investigate the effects of ketoprofen on ATP synthesis and N assimilation in rice roots. The results showed that with increasing ketoprofen concentration, root vitality, respiration rate, ATP content, and H+-ATPase activity decreased and plasma membrane permeability increased. The expressions of OSA9, a family III H+-ATPase gene, and OSA6 and OSA10, family IV genes, were upregulated, indicating a response of the roots to ketoprofen. Nitrate, ammonium, and free amino acids content decreased with increased ketoprofen. The levels of enzymes involved in N metabolism, namely nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase, also decreased under ketoprofen treatment. Principal component analysis revealed that ketoprofen treatment can significantly affect energy synthesis and nitrogen assimilation in rice roots, while these effects can be alleviated by the antioxidant response. Most of the metabolite contents increased, including amino acids, carbohydrates, and secondary metabolites. Key metabolic pathways, namely substance synthesis and energy metabolism, were found to be disrupted. Microbiome analysis showed that community diversity and richness of rice root microorganisms in solution increased with increasing levels of ketoprofen treatment, and the microbial community structure and metabolic pathways significantly changed. The results of this study provides new insights into the response of rice roots to ketoprofen.

Ultraefficient OG-Mediated Photodynamic Inactivation Mechanism for Ablation of Bacteria and Biofilms in Water Augmented by Potassium Iodide under Blue Light Irradiation.

While photodynamic inactivation (PDI) has emerged as a novel sterilization strategy for drinking water treatment that recently attracted tremendous attention, its efficiency needs to be further improved. In this study, we aimed to clarify the ultraefficient mechanism by which potassium iodide (KI) potentiates octyl gallate (OG)-mediated PDI against bacteria and biofilms in water. When OG (0.15 mM) and bacteria were exposed to blue light (BL, 420 nm, 210 mW/cm2), complete sterilization (>7.5 Log cfu/mL of killing) was achieved by the addition of KI (250 mM) within only 5 min (63.9 J/cm2). In addition, at lower doses of OG (0.1 mM) with KI (100 mM), the biofilm was completely eradicated within 10 min (127.8 J/cm2). The KI-potentiated mechanism involves in situ rapid photogeneration of a multitude of reactive oxygen species, especially hydroxyl radicals (•OH), reactive iodine species, and new photocytocidal substances (quinone) by multiple photochemical pathways, which led to the destruction of cell membranes and membrane proteins, the cleavage of genomic DNA and extracellular DNA within biofilms, and the degradation of QS signaling molecules. This multitarget synergistic strategy provided new insights into the development of an environmentally friendly, safe, and ultraefficient photodynamic drinking water sterilization technology.

Enrichment of cadmium and selenium in soil-crop system and associated probabilistic health risks in black shale areas.

Selenium (Se) is the essential component of selenoenzymes and contributes to antioxidant defenses. The capability of Se to antagonize the toxicity of heavy metals makes it an essential trace element for human and plant health. Soils derived from black shales are naturally enriched with Se; however, these soils often contain high geological cadmium (Cd), due to the weathering of black shales rich in Cd and Se. Cadmium, as a known Group I carcinogen, could induce damage to various organs. This therefore poses a major challenge for safe cultivation of Se-rich land resources. In this study, a total of 247 paired soil-crop samples were collected from a typical farmland derived from black shales. The concentrations of Cd and Se in the samples were analyzed by inductively coupled plasma mass spectroscopy and atomic fluorescence spectrometry. Monte Carlo simulation was applied to evaluate potential health risks associated with Cd exposure. Cadmium was the critical pollutant in the study area, with the average value of 1.53 mg/kg. Moreover, both children and adults living in the area had a significant non-carcinogenic health risk. Additional health risk assessments revealed that diet was the main contributor for both children and adults among the four pathways (diet > soil ingestion > soil dermal adsorption > soil inhalation). Furthermore, our results revealed that leguminous vegetables and maize were ideal for this site due to their high Se and low Cd accumulation abilities. These findings provide support for adjusting planting structure by variety screening to mitigate the health risk induced by Cd.

Plant growth-promoting rhizobacteria: A good companion for heavy metal phytoremediation.

Phytoremediation is an environment-friendly approach regarded as a potential candidate for remediating heavy metal (HM)-contaminated soils. However, the low efficacy of phytoremediation is a major limitation that hampers its large-scale application. Therefore, developing strategies to enhance phytoremediation efficacy for contaminated soils is crucial. Plant growth-promoting rhizobacteria (PGPR) considerably contribute to phytoremediation intensification. To improve the efficiency of plant-microbe symbiosis for remediation, the mechanisms underlying PGPR-stimulated HM accumulation and tolerance in plants should be comprehensively understood. This review focuses on hyperaccumulators, PGPR, and the mechanisms by which PGPR enhance phytoremediation from four aspects: providing nutrients to plants, secreting plant hormones and specific enzymes, inducing systemic resistance, and altering the bioavailability of HMs in soils. It also provides a theoretical and technical basis for future research on PGPR synergism in promoting the phytoextraction efficiency in HM-contaminated soils.

Synergistic interplay between ABA-generating bacteria and biochar in the reduction of heavy metal accumulation in radish, pakchoi, and tomato.

Heavy metal (HM) contamination is an environmental concern that threatens the agricultural product safety and human health. To address this concern, we developed a novel strategy involving the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium which produces abscisic acid (ABA), and biochar to minimize HM accumulation in the edible parts of vegetable crops. Compared to A. brasilense or biochar alone, the concentrations of Cd, Ni, Pb, and Zn in radish (Raphanus sativus L.), pakchoi (Brassica chinensis L.), and tomato (Lycopersicon esculentum L.) decreased by 18-63% and 14-56%, respectively. Additionally, the synergistic treatment led to a 14-63% decrease in the bioconcentration factor. The biomass of the edible parts of the three crops increased by 65-278% after synergistic treatment, surpassing the effects of single treatments. Furthermore, the synergistic application enhanced the SPAD values by 1-45% compared to single treatments. The MDA concentrations in stressed plants decreased by 16-39% with the bacteria-biochar co-treatment compared to single treatments. Co-treatment also resulted in increased soluble protein and sugar concentrations by 8-174%, and improvements in flavonoids, total phenols, ascorbic acid, and DPPH levels by 2-50%. Pearson correlation analysis and structural equation modeling revealed that the synergistic effect was attributed to the enhanced growth of A. brasilense facilitated by biochar and the improved availability of HMs in soils. Notably, although ABA concentrations were not as high as those achieved with A. brasilense alone, they were maintained at relatively high levels. Overall, the synergistic application of A. brasilense-biochar might have remarkable potential for reducing the accumulation of HMs while promoting growth and improving nutritional and antioxidant qualities in tuberous, leafy, and fruit crops.

N fertilizers promote abscisic acid-catabolizing bacteria to enhance heavy metal phytoremediation from metalliferous soils.

Bacterial-assisted phytoextraction is an attractive strategy to enhance the phytoremediation efficiency of heavy metal (HM)-contaminated soils. In the present study, we investigated the synergistic effects of N fertilizers and abscisic acid (ABA)-catabolizing bacteria on the HM (Cd, Zn, and Pb) phytoremediation efficiency of Brassica juncea L. (B. juncea). Compared with Rhodococcus qingshengii (R. qingshengii) alone, urea, ammonium­nitrogen (NH4+-N), and nitrate­nitrogen (NO3--N) fertilizers combined with R. qingshengii increased HM concentrations in B. juncea by 13.8 %-48.2 %, 44.2 %-54.4 %, and 59.4 %-113.6 %, respectively, and enhanced the biomass of B. juncea by 7.7 %-38.8 %, 10.9 %-29.5 %, and 19.9 %-46.8 %, respectively. Consequently, the bioconcentration factor increased by 3.4 %-30.9 % and the phytoextraction rate increased by 18.5 %-98.7 %. Treatment with NO3--N showed the most significant effect. In structural equation modeling, R. qingshengii inoculation showed greater path coefficients with soil pH and ABA and indoleacetic acid concentrations of B. juncea than N fertilization, indicating that R. qingshengii contributed more to HM extraction efficiency than N fertilizers. Additionally, differences in the extraction rates of Cd, Zn, and Pb from B. juncea were reduced following N fertilization. In summary, synergistic R. qingshengii inoculation and N fertilization have substantial potential to enhance phytoremediation efficiency. Combined application of R. qingshengii and NO3--N fertilizers is recommended.

[Role and Mechanism of Low Molecular-Weight-Organic Acids in Enhanced Phytoremediation of Heavy Metal Contaminated Soil].

Phytoremediation is an environmentally friendly technology to remove heavy metals from polluted soil by using the physical and chemical roles of plants. This can effectively reduce the production of secondary pollutants and is economically feasible. Low molecular-weight-organic acids (LMWOAs) are biodegradable and environmentally friendly and have strong application potential in the phytoremediation of heavy metal-contaminated soils. The role and mechanism of LMWOAs in phytoremediation was elaborated on in this study with the aim to:① regulate the development of roots, stems, and leaves; increase plant biomass; and enhance plant enrichment of heavy metals; ② improve photosynthesis, enhance plant resistance, and promote tolerance to heavy metals; ③ change the properties of rhizosphere soil, improve rhizosphere microbial activity, and promote the absorption of heavy metals; and ④ change the form of heavy metals, reduce the toxicity of heavy metals, and improve transport efficiency. Moreover, the advantages, disadvantages, and application of LMWOAs in enhanced phytoremediation of heavy metal-contaminated soil were explored in this study. Finally, the research direction of LMWOAs in the phytoremediation of heavy metal-contaminated soils was proposed, which will have practical scientific significance for the research and application of LMWOAs in future phytoremediation.

Graphene oxide decreases the abundance of nitrogen cycling microbes and slows nitrogen transformation in soils.

Graphene oxide (GO) has been widely used in many applications due to its excellent properties. Given the extensive production and use of this nanomaterial, its release into the environment is inevitable. However, little is known about the effects of GO on microbial nitrogen transformation and the related processes after GO enters the soil environment. The present study showed that GO significantly reduced soil microbial biomass and caused a decline in microbial diversity after the soils were subjected to various GO concentrations (10, 100, and 1000 mg kg-1) for 4 months. Among them, the abundances of nitrogen transformation related bacteria such as Firmicutes, Nitrospirota, Proteobacteria, Planctomycetota, and Cyanobacteria were significantly decreased with GO incubation. Among the enzymes that are related to nitrogen transformation, nitrate reductase was the most sensitive even at low concentrations of GO, followed by ammonia monooxygenase and urease, which were reduced by 13-31%, 5-26%, and 9-19% respectively, than those of the control. We found that high concentrations of GO significantly increased the retention of soil urea by 32-59%, and the contents of ammonium and nitrate were 22-28% and 55-69% lower compared to those of the control, respectively. Moreover, the response of most of the indicators in the above process to multilayer GO was more significant than that to single layer GO. Overall, this study provides new insights into the comprehensive understanding of GO's impacts on the soil nitrogen cycle.

Different pathways for exogenous ABA-mediated down-regulation of cadmium accumulation in plants under different iron supplies.

Exogenous abscisic acid (ABA) could inhibit cadmium (Cd) accumulation in plants; however, its performance in an uneven iron (Fe) background remains unknown. Here, we found that the inhibitory effects of ABA on Cd accumulation in plants were optimal under nonlimiting Fe availability (25 and 50 µM), causing a reduction of 25-50 %, whereas only a 0-29 % decrease was observed in a Fe-free or -deficient (5 µM) medium. Although ABA significantly inhibited the expression of IRT1 under different Fe supplies, the inhibitory effects of ABA on Cd accumulation were lower (or absent) in irt1-mutants than in wild-type plants growing under nonlimiting Fe availability, whereas no significant difference was found under Fe deficiency. The mechanisms by which ABA reduces Cd accumulation under different Fe environments may differ. Furthermore, under Fe sufficiency, ABA increased Fe levels of root apoplasts by 91 % without changing the activity level of root ferric reductase (FCR). In contrast, ABA resulted in a 17 % decrease in Fe concentration in apoplasts and a 37 % decrease in FCR activity under Fe-deficient conditions. Thus, under Fe sufficiency, plants may show a reduced accumulation of Cd by accumulating more Fe in the apoplasts, which in turn inhibits the expression of IRT1. However, plants are more prone to redirect apoplastic Fe to prevent Cd accumulation under Fe deficiency. The different mechanisms of inhibition of Cd accumulation by ABA under different Fe supplies revealed in this study may provide guidelines for the precise regulation of Cd accumulation in crops via ABA-based strategies.

Understanding the effect of GO on nitrogen assimilation in wheat through transcriptomics and metabolic process analysis.

The extensive use of graphene oxide (GO) has resulted in its inevitable entry into the environment. It has been established that GO is detrimental to nitrogen accumulation in plants, as nitrogen is one of the most important nutrient for plant growth. However, its influence on nitrogen assimilation has not yet been investigated comprehensively. Based on the analysis of transcriptomics and nitrogen metabolites, this study showed that 400 mg L-1 GO exposure downregulated most of the genes encoding nitrogen-assimilating enzymes, including nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH). The activities of the above enzymes in wheat roots were also reduced with GO addition, and the activities of NR and GS, the rate-limiting enzymes of nitrate and ammonium assimilation, were approximately 75% and 76% lower with 400 mg L-1 GO supply, respectively, compared to those upon control treatment. Correspondingly, GO appears to exert a negative effect on multiple nitrogen assimilation products, including nitrous nitrogen, ammonium nitrogen, glutamine, glutamate, and soluble protein. In summary, this study showed that GO has adverse effects on the nitrogen assimilation of plants, and NR and GS are the most affected sites. Our findings would provide deeper insights into the physiological and molecular mechanisms underlying GO phytotoxicity.

Abscisic acid-catabolizing bacteria: A useful tool for enhancing phytoremediation.

Bacteria-facilitated phytoextraction has been gaining recognition for the phytoremediation of heavy metal (HM)-contaminated soils. Nevertheless, it remains unclear whether catabolizing abscisic acid (ABA) in hyperaccumulating plants via rhizobacteria could facilitate HM phytoextraction. In this study, inoculation with the ABA-catabolizing bacterium, Rhodococcus qingshengii, increased HM (Cd, Zn, Pb, and Cu) concentrations in the shoots of hyperaccumulators Vetiveria zizanioides, Brassica juncea, Lolium perenne L., Solanum nigrum L., and Sedum alfredii Hance grown in mildly and severely contaminated soils by 28.8%-331.3%, 8.5%-393.4%, 21.2%-222.5%, 14.7%-115.5%, and 28.3%-174.2%, respectively, compared with non-inoculated plants. The fresh biomass of these hyperaccumulators was elevated by 16.5%-94.4%, compared to that of the bacteria-free control. Phytoremediation potential indices, including bioconcentration and translocation factors, also revealed that the bacteria markedly boosted the phytoextraction efficacy from soil. Furthermore, principal component analysis (PCA) suggested that the effects of bacteria on the concentrations of Cd and Zn in hyperaccumulators were significantly correlated with ABA metabolism, but not with Pb and Cu. Combined with the synergistic effects on plant biomass, the bacteria also improved the phytoextraction of Pb and Cu in hyperaccumulators. Overall, the application of microorganism-assisted remediation based on ABA-catabolizing bacteria might be an alternative strategy for enhancing phytoremediation efficiency in HM-contaminated soils.

Rhodococcus qingshengii facilitates the phytoextraction of Zn, Cd, Ni, and Pb from soils by Sedum alfredii Hance.

The enhanced heavy metal (HM) phytoextraction efficiency of hyperaccumulating plants via plant-growth-promoting microbes has been proposed as an effective strategy to remove HMs from contaminated soil. Nevertheless, it remains unclear whether catabolizing the abscisic acid (ABA) in hyperaccumulating plants via rhizobacteria can facilitate HM phytoextraction. In the present study, a hyperaccumulator, Sedum alfredii Hance, inoculated with an ABA-catabolizing bacterium Rhodococcus qingshengii, showed higher concentrations of Zn, Cd, Ni, and Pb in the contaminated paddy-grown plant shoots by 35%, 63%, 49%, and 49%, and in plants grown in mine soils by 112%, 105%, 46%, and 49%, respectively, than in the controlbacteria-free plants. However, no significant changes were observed in Cu content between these plants. Furthermore, parameters indicating phytoremediation potential, including the translocation factor (TF) and bioconcentration factor (BCF), revealed that bacterial inoculation could markedly increase the efficacy of Zn, Cd, Ni, and Pb phytoextraction from the soil. Notably, the bioavailabilities of HMs in soils were not influenced by R. qingshengii; however, the expression of transporters related to the uptake of these HMs, including SaIRT1, SaZIP1, SaZIP2, SaZIP3, SaNramp1, SaNramp3, SaNramp6, SaHMA2, and SaHMA3, was upregulated. These findings indicate that R. qingshengii inoculation could increase the HM-uptake ability of plants by catabolizing ABA and may provide a promising strategy for enhancing the phytoremediation efficacy in HM-contaminated soils.