Natural organic matter (NOM) affects the environmental behaviors of AgNPs, which may change their phytotoxicity to plants. However, more evidence can be provided to illustrate how NOM influences AgNPs-induced phytotoxicity. In this study, using rice (Oryza sativa) as a model, the effects of NOM, Suwannee River humic acid (SRHA) and fulvic acid (FA), on the dissolution and phytotoxicity of AgNPs were investigated. Silver ions decreased in both AgNPs and AgNO₃ solution in the presence of NOM, and the effect of SRHA was stronger than FA. Image-XRF (iXRF) results showed that Ag mainly remained in the root rather than the shoot of rice seedling exposed to AgNPs. NOM mitigated the negative effects of AgNPs and AgNO₃ on rice with lower germination inhibition rate, less chlorophyll reduction, more relative biomass and less O₂•⁻ content. Moreover, NOM improved root cell viability according to FDA fluorescent dye as well as maintained the normal root morphology. Interestingly, the neutral sugars content from pectin, hemicellulose 1, hemicellulose 2 and cellulose of root cell wall in AgNPs and AgNO₃ treatments differed from the control, while it was close to the regular content in AgNPs/AgNO₃+SRHA/FA groups, which implied that NOM regulated the changes. Besides, SRHA led to less germination and less relative biomass than FA due to different chemical characters. Thus, NOM needs to be considered when studying the phytotoxicity of AgNPs.

Cell wall acts as a major metal sink in plant roots, while a few studies focused on root cell wall binding in plants for the phytostabilization of multi-metal contaminated soils. A pot experiment was performed to characterize root cell wall properties of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) in response to Cd and Pb. The cell wall was found to be the major sink for Cd (41.3–54.3%) and Pb (71.4–73.8%) accumulation in roots of the ME when exposed to Cd and/or Pb. The ME showed more Cd and Pb accumulation in root cell walls when exposed to Cd and Pb simultaneously, compared with those exposed to single Cd or Pb as well as the NME, suggesting some modifications for cell walls. The uronic acid contents of pectin and hemicellulose 1 (HC1) in root cell walls of the ME increased significantly when exposed to Cd and Pb simultaneously, suggesting enhanced cell wall binding capacity, thus resulting in more Cd and Pb bound to pectin and HC1. In particular, pectin was found to be the predominant binding site for Cd and Pb. Greater pectin methylesterase activity along with a lower degree of methylesterification were observed in the cell walls of the ME when exposed to Cd and Pb simultaneously. Furthermore, the ME present more O–H, N–H, C–OH, C–O–C, C–C and/or Ar–H in root cell walls when exposed to Cd and Pb simultaneously. These changes of root cell wall properties of the ME lead to enhanced cell wall binding ability in response to the co-contamination of Cd and Pb, thus could be considered a key process for enhanced Cd and Pb accumulation in roots of the ME when exposed to Cd and Pb simultaneously.

Aluminum (Al) phytotoxicity is a major limitation in the production of crops in the soils with pH ≤ 5. Boron (B) is indispensable nutrient for the development of higher plants and B role has been reported in the alleviation Al toxicity. Trifoliate orange rootstock was grown in two B and two Al concentrations. The results of the present study showed that Al toxicity adversely inhibited root elongation and exhibited higher oxidative stress in terms of H2O2 and O2− under B-deficiency. Additionally, the X-ray diffraction (XRD) analysis confirmed the increase of the cellulose crystallinity in the cell wall (CW). Al-induced remarkable variations in the CW components were prominent in terms of alkali-soluble pectin, 2-keto-3-deoxyoctonic acid (KDO) and the degree of methyl-esterification (DME) of pectin. Interesting, B supply reduced the pectin (alkali-soluble) under Al toxicity. Moreover, the results of FTIR (Fourier transform infrared spectroscopy) and 13C-NMR (13C nuclear magnetic resonance) spectra revealed the decrease of carboxyl groups and cellulose by B application during Al exposure. Furthermore, B supply tended to decrease the Al uptake, CW thickness and callose formation. The study concluded that B could mitigate Al phytotoxicity by shielding potential Al binding sites and by reducing Al induced alterations in the CW cellulose and pectin components.

Root cell wall (RCW) modification is a widespread important defense strategy of plant to cope with trace metals. However, mechanisms underlying its remolding in cadmium (Cd) accumulation are still lacking in hyperaccumulators. In this study, changes of RCW structures and components between nonhyperaccumulating ecotype (NHE) and hyperaccumulating ecotype (HE) of Sedum alfredii were investigated simultaneously. Under 25 μM Cd treatment, RCW thickness of NHE is nearly 2 folds than that of HE and the thickened cell wall of NHE was enriched in low-methylated pectin, leading to more Cd trapped in roots tightly. In the opposite, large amounts of high-methylated pectin were assembled around RCW of HE with Cd supply, in this way, HE S. alfredii decreased its root fixation of Cd and enhanced Cd migration into xylem. TEM and AFM results further confirmed that thickened cell wall was caused by the increased amounts of cellulose and lignin while root tip lignification was resulted from variations of sinapyl (S) and guaiacyl (G) monomers. Overall, thickened cell wall and methylated pectin have synchronicity in spatial location of roots, and their coordination contributed to Cd accumulation in S. alfredii.

We investigated the roles of rootstocks in Cu accumulation and tolerance in Malus plants by grafting ‘Hanfu’ (HF) scions onto M. baccata (Mb) and M. prunifolia (Mp) rootstocks, which have different Cu tolerances. The grafts were exposed to basal or excess Cu for 20 d. Excess Cu-treated HF/Mb had less biomass, and pronounced root architecture deformation and leaf ultrastructure damage than excess Cu-challenged HF/Mp. Root Cu concentrations and bio-concentration factor (BCF) were higher in HF/Mp than HF/Mb, whereas HF/Mb had higher stem and leaf Cu concentrations than HF/Mp. Excess Cu lowered root and aerial tissue BCF and translocation factor (Tf) in all plants; however, Tf was markedly higher in HF/Mb than in HF/Mp. The subcellular distribution of Cu in the roots and leaves indicated that excess Cu treatments increased Cu fixation in the root cell walls, which decreased Cu mobility. Compared to HF/Mb, HF/Mp sequestered more Cu in its root cell walls and less Cu in leaf plastids, nuclei, and mitochondria. Moreover, HF/Mp roots and leaves had higher concentrations of water-insoluble Cu compounds than HF/Mb, which reduced Cu mobility and toxicity. Fourier transform infrared spectroscopy analysis showed that the carboxyl, hydroxyl and acylamino groups of the cellulose, hemicellulose, pectin and proteins were the main Cu binding sites in the root cell walls. Excess Cu-induced superoxide anion and malondialdehyde were 28.6% and 5.1% lower, but soluble phenolics, ascorbate and glutathione were 10.5%, 41.9% and 17.7% higher in HF/Mp than HF/Mb leaves. Compared with HF/Mb, certain genes involved in Cu transport were downregulated, while other genes involved in detoxification were upregulated in HF/Mp roots and leaves. Our results show that Mp inhibited Cu translocation and mitigated Cu toxicity in Malus scions by regulating Cu mobility, antioxidant defense mechanisms, and transcription of key genes involved in Cu translocation and detoxification.

Florfenicol is one of the most-used antimicrobial agents in global fish farming. Nevertheless, in most countries, its use is not conducted in accordance with good practices. The aim of this work was to evaluate the leaching of florfenicol from coated fish feed into the water. Analytical methods were developed and validated for the quantitation of florfenicol in medicated feed and water by UHPLC-MS/MS. Florfenicol residues in the water were quantified after 5- and 15-min exposures of the medicated feed in the water at 22 and 28 °C and at pH 4.5 and 8.0. The influence of pellet size and three coating agents (vegetable oil, carboxymethylcellulose, and low-methoxylated pectin) on the leaching of the drug was also assessed. Pellet size, coating agent, water temperature, and time of exposure significantly (p < 0.05) affected florfenicol leaching, while water pH did not interfere with the leaching. Coating with vegetable oil was the most efficient method to reduce florfenicol leaching, while coating with carboxymethylcellulose presented the highest leaching (approximately 60% after 15 min at 28 °C). Thus, the coating agent has a significant effect on the florfenicol leaching rate and, consequently, on the necessary dose of the drug to be administered. Moreover, it is worth mentioning that higher florfenicol leaching will pose a greater risk to environmental health, specifically in terms of the development of bacteria resistant to florfenicol. Additional studies are needed with other polymers and veterinary drugs used in medicated feed for fish farming.

Low-methylesterified homogalacturonans have been suggested to play a role in the binding and immobilization of Pb in CW. Using root apices of hybrid aspen, a plant with a high phytoremediation potential, as a model, we demonstrated that the in situ distribution pattern of low-methylesterified homogalacturonan, pectin epitope (JIM5-P), reflects the pattern of Pb occurrence. The region which indicated high JIM5-P level corresponded with “Pb accumulation zone”. Moreover, JIM5-P was especially abundant in cell junctions, CWs lining the intercellular spaces and the corners of intercellular spaces indicating the highest accumulation of Pb. Furthermore, JIM5-P and Pb commonly co-localized.The observations indicate that low-methylesterified homogalacturonan is the CW polymer that determines the capacity of CW for Pb sequestration. Our results suggest a promising directions for CW modification for enhancing the efficiency of plant roots in Pb accumulation, an important aspect in the phytoremediation of soils contaminated with trace metals.

Cadmium (Cd) is a potentially hazardous element with substantial biological toxicity, adversely affecting plant growth and physiological metabolism. Therefore, it is necessary to explore practical and environment-friendly approaches to reduce toxicity. Jasmonic acid (JA) is an endogenous growth regulator which helps plants defend against biological and abiotic stresses. To determine how JA help relieve Cd toxicity in rice, both laboratory and field experiments were implemented. In the seedling stage, the role of JA in mediating rice Cd tolerance was investigated via a fluorescent probe in vivo localization, Fourier Transform Infrared Spectroscopy (FTIR), and colorimetry. At the mature growth stage of rice, field experiments were implemented to research the effects of JA on the Cd uptake and translocation in rice. In the seedling stage of rice, we found that JA application increased the cell wall compartmentalization of Cd by promoting the Cd combination on chelated-soluble pectin of rice roots and inhibited Cd movement into protoplasts, thereby reducing the Cd content in the roots by 30.5% and in the shoots by 53.3%, respectively. Application of JA reduced H₂O₂ content and helped relieve Cd-induced peroxidation damage of membrane lipid by increasing the level of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), but had no significant effect on the superoxide dismutase (SOD) activity. Additionally, field experiments showed that foliar spraying of JA inhibited rice Cd transport from the stalk and root to the grain and reduced Cd concentration in grain by 29.7% in the high-Cd fields and 28.0% in the low-Cd fields. These results improve our understanding of how JA contributes to resistance against Cd toxicity in rice plants and reduces the accumulation of Cd in rice kernels.

To explore whether lead (Pb)-induced defense responses are responsible for the low root-to-shoot Pb translocation, we exposed saplings of the two contrasting poplar species, Populus × canescens with relatively high root-to-shoot Pb translocation and P. nigra with low Pb translocation, to 0 or 8 mM PbCl₂. Pb translocation from the roots to aboveground tissues was lower by 57% in P. nigra than that in P. × canescens. Lower Pb concentrations in the roots and aerial tissues, greater root biomass, and lower ROS overproduction in the roots were found in P. nigra than those in P. × canescens treated with Pb. P. nigra roots had higher proportions of cell walls (CWs)-bound Pb and water insoluble Pb compounds, and higher transcript levels of some pivotal genes related to Pb vacuolar sequestration, such as phytochelatin synthetase 1.1 (PCS1.1), ATP-binding cassette transporter C1.1 (ABCC1.1) and ABCC3.1 than P. × canescens roots. Pb exposure induced defense responses including increases in the contents of pectin and hemicellulose, and elevated oxalic acid accumulation, and the transcriptional upregulation of PCS1.1, ABCC1.1 and ABCC3.1 in the roots of P. nigra and P. × canescens. These results suggest that the stronger defense barriers in P. nigra roots are probably associated with the lower Pb translocation from the roots to aerial tissues, and that Pb exposure-induced defense responses can enhance the barriers against Pb translocation in poplar roots.

This study aimed to investigate the difference of osmoregulation between two edible amaranth cultivars, Liuye (high Cd accumulator) and Quanhong (low Cd accumulator), under salinity stress and determine the effects of such difference on Cd accumulation. A pot experiment was conducted to expose the plants to sewage-irrigated garden soil (mean 2.28 mg kg⁻¹ Cd) pretreated at three salinity levels. Under salinity stress, the concentrations of Cd in the two cultivars were significantly elevated compared with those in the controls, and the Cd concentration in Liuye was statistically higher than that in Quanhong (p < 0.05). Salinity-induced osmoregulation triggered different biogeochemical processes involved in Cd mobilization in the rhizosphere soil, Cd absorption, and translocation by the two cultivars. Rhizosphere acidification induced by an imbalance of cation over anion uptake was more serious in Liuye than in Quanhong, which obviously increased soil Cd bioavailability. Salinity-induced injuries in the cell wall pectin and membrane structure were worse in Liuye than in Quanhong, increasing the risk of Cd entering the protoplasts. The chelation of more cytoplasmic Cd²⁺ with Cl⁻ ions in the roots of Liuye promoted Cd translocation into the shoots. Furthermore, the less organic solutes in the root sap of Liuye than in that of Quanhong also favored Cd translocation into the shoots. Hence, osmoregulation processes can be regarded as important factors in reducing Cd accumulation in crop cultivars grown on saline soils.