Root Elongation Research Articles

OROSOMUCOID PROTEIN 1 regulation of sphingolipid synthesis is required for nodulation in Aeschynomene evenia.

Legumes establish symbiotic interactions with nitrogen-fixing rhizobia that are accommodated in root-derived organs known as nodules. Rhizobial recognition triggers a plant symbiotic signaling pathway that activates 2 coordinated processes: infection and nodule organogenesis. How these processes are orchestrated in legume species utilizing intercellular infection and lateral root base nodulation remains elusive. Here, we show that Aeschynomene evenia OROSOMUCOID PROTEIN 1 (AeORM1), a key regulator of sphingolipid biosynthesis, is required for nodule formation. Using A. evenia orm1 mutants, we demonstrate that alterations in AeORM1 function trigger numerous early aborted nodules, defense-like reactions, and shorter lateral roots. Accordingly, AeORM1 is expressed during lateral root initiation and elongation, including at lateral root bases where nodule primordium form in the presence of symbiotic bradyrhizobia. Sphingolipidomics revealed that mutations in AeORM1 lead to sphingolipid overaccumulation in roots relative to the wild type, particularly for very long-chain fatty acid-containing ceramides. Taken together, our findings reveal that AeORM1-regulated sphingolipid homeostasis is essential for rhizobial infection and nodule organogenesis, as well as for lateral root development in A. evenia.

Abscisic acid biosynthesis is necessary for full auxin effects on hypocotyl elongation.

In concert with other phytohormones, auxin regulates plant growth and development. However, how auxin and other phytohormones coordinately regulate distinct processes is not fully understood. In this work, we uncover an auxin-abscisic acid (ABA) interaction module in Arabidopsis that is specific to coordinating activities of these hormones in the hypocotyl. From our forward genetics screen, we determine that ABA biosynthesis is required for the full effects of auxin on hypocotyl elongation. Our data also suggest that ABA biosynthesis is not required for the inhibitory effects of auxin treatment on root elongation. Our transcriptome analysis identified distinct auxin-responsive genes in root and shoot tissues, which is consistent with differential regulation of growth in these tissues. Further, our data suggest that many gene targets repressed upon auxin treatment require an intact ABA pathway for full repression. Our results support a model in which auxin stimulates ABA biosynthesis to fully regulate hypocotyl elongation.

Effects of biodegradable P3HB on the specific growth rate, root length and chlorophyll content of duckweed, Lemna minor

The extensive production and use of plastics have led to widespread pollution of the environment. As a result, biodegradable polymers (BDPs) are receiving a great deal of attention because they are expected to degrade entirely in the environment. Therefore, in this work, we tested the effect of two fractions (particles <63 μm and particles from 63 to 125 μm) of biodegradable poly-3-hydroxybutyrate (P3HB) at different concentrations on the specific growth rate, root length, and photosynthetic pigment content of the freshwater plant Lemna minor. Microparticles with similar properties made of polyethylene terephthalate (PET) were also tested for comparison. No adverse effects on the studied parameters were observed for either size fraction; the only effect was the root elongation with increasing P3HB concentration. PET caused statistically significant root elongation only in the highest concentration, but the effect was not as extensive as for P3HB. The development of a biofilm on P3HB particles was observed during the experiment, and the nutrient sorption experiment showed that the sorption capacity of P3HB was greater than PET's. Therefore, depleting the nutrients from the solution could force the plant to increase the root surface area by their elongation. The results suggest that biodegradable microplastics may cause secondary nutrient problems in the aquatic environment due to their biodegradability.

Protein Phosphorylation Orchestrates Acclimations of Arabidopsis Plants to Environmental pH

Environment pH (pHe) is a key parameter dictating a surfeit of conditions critical to plant survival and fitness. To elucidate the mechanisms that recalibrate cytoplasmic and apoplastic pH homeostasis, we conducted a comprehensive proteomic/phosphoproteomic inventory of plants subjected to transient exposure to acidic or alkaline pH, an approach that covered the majority of protein-coding genes of the reference plant Arabidopsis thaliana. Our survey revealed a large set-of so far undocumented pHe-dependent phospho-sites, indicative of extensive post-translational regulation of proteins involved in the acclimation to pHe. Changes in pHe altered both electrogenic H+ pumping via P-type ATPases and H+/anion co-transport processes, putatively leading to altered net trans-plasma membrane translocation of H+ ions. In pH 7.5 plants, the transport (but not the assimilation) of nitrogen via NRT2-type nitrate and AMT1-type ammonium transporters was induced, conceivably to increase the cytosolic H+ concentration. Exposure to both acidic and alkaline pH resulted in a marked repression of primary root elongation. No such cessation was observed in nrt2.1 mutants. Alkaline pH decreased the number of root hairs in the wild type but not in nrt2.1 plants, supporting a role of NRT2.1 in developmental signaling. Sequestration of iron into the vacuole via alterations in protein abundance of the vacuolar iron transporter VTL5 was inversely regulated in response to high and low pHe, presumptively in anticipation of associated changes in iron availability. A pH-dependent phospho-switch was also observed for the ABC transporter PDR7, suggesting changes in activity and, possibly, substrate specificity. Unexpectedly, the effect of pHe was not restricted to roots and provoked pronounced changes in the shoot proteome. In both roots and shoots, the plant-specific TPLATE complex components AtEH1 and AtEH2-essential for clathrin-mediated endocytosis-were differentially phosphorylated at multiple sites in response to pHe, indicating that the endocytic cargo protein trafficking is orchestrated by pHe.

The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L−1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L−1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.

Ethylene and ROS mediate root growth inhibition induced by the endocrine disruptor bisphenol A (BPA)

Bisphenol A (BPA) functions as a detrimental substance that disrupts the endocrine system in animals while also impeding the growth and development of plants. In our previous study, we demonstrated that BPA hinders the growth of roots in Arabidopsis by diminishing cell division and elongation, which is ascribed to the increased accumulation and redistribution of auxin. Here, we examined the mediation of ROS and ethylene in BPA-induced auxin accumulation and root growth inhibition. BPA enhanced ROS levels, and ROS increased auxin contents but reduced cell division activity and the expression of EXPA8 involved in root elongation. ROS scavenger treatment reversed BPA-triggered root growth retardation, auxin accumulation, and cell division inhibition. In addition, BPA induced ethylene, and ethylene synthesis inhibitor treatment reversed BPA-triggered root growth retardation and auxin accumulation. Taken together, ROS and ethylene are involved in BPA-inhibited cell elongation and cell division by mediating auxin accumulation and redistribution.

Remediation of the landfill leachate of Fez city (Morocco) by sono-photo-Fenton process: Cost and phytotoxicity assessment

A new Advanced Oxidation process (AOP) using the ultrasound-photo-Fenton process (US-P-FP) was used to treat stabilized landfill leachate from Fez City (Morocco). The effectiveness of the US-P-FP for landfill leachate treatment was investigated in terms of COD, UV254, and color removal. The operating factors (Fe2+ dosage, pH, H2O2 dosage, ultrasonic (US), UV-A) were optimized by the two-level factorial design. The findings reveal that the highest removal of COD, UV254, and color from the landfill leachate was 93 %, 77 %, and 98 %, respectively, at the optimum operation conditions [Fe2+] = 446 mg/L, [H2O2] = 250 mg/L and a pH = 3 in the presence of both US and UV-A irradiations.The phytotoxicity assessment of untreated and sono-photo-Fenton treated leachate samples was conducted through seed germination and root elongation tests using Medicago sativa seeds as bioindicators. The experimental results showed that the ultrasound-photo-Fenton process allowed a significant phytotoxicity reduction. Overall, the sono-photo-Fenton process proves to be a viable and efficient method for landfill leachate treatment.

Patch Track Software for Measuring Kinematic Phenotypes of Arabidopsis Roots Demonstrated on Auxin Transport Mutants.

Plant roots elongate when cells produced in the apical meristem enter a transient period of rapid expansion. To measure the dynamic process of root cell expansion in the elongation zone, we captured digital images of growing Arabidopsis roots with horizontal microscopes and analyzed them with a custom image analysis program (PatchTrack) designed to track the growth-driven displacement of many closely spaced image patches. Fitting a flexible logistics equation to patch velocities plotted versus position along the root axis produced the length of the elongation zone (mm), peak relative elemental growth rate (% h-1), the axial position of the peak (mm from the tip), and average root elongation rate (mm h-1). For a wild-type root, the average values of these kinematic traits were 0.52 mm, 23.7% h-1, 0.35 mm, and 0.1 mm h-1, respectively. We used the platform to determine the kinematic phenotypes of auxin transport mutants. The results support a model in which the PIN2 auxin transporter creates an area of expansion-suppressing, supraoptimal auxin concentration that ends 0.1 mm from the quiescent center (QC), and that ABCB4 and ABCB19 auxin transporters maintain expansion-limiting suboptimal auxin levels beginning approximately 0.5 mm from the QC. This study shows that PatchTrack can quantify dynamic root phenotypes in kinematic terms.

Protective mechanisms of neral as a plant-derived safener against fenoxaprop-p-ethyl injury in rice.

The use of herbicide safeners effectively minimises crop damage while maintaining the full efficacy of herbicides. The present study aimed to assess the potential protective effects of neral (NR) as a safener, in order to mitigate injury caused by fenoxaprop-p-ethyl (FE) on rice. The alleviating effect of NR was similar to that of the safener isoxadifen-ethyl (IE). The root elongation of rice was significantly promoted under the FE + NR and FE + IE treatments, as compared to the FE treatment. The transcriptome analysis further suggested that the effects of NR treatment on plant metabolic pathways differed from those of IE treatment. In total, 895 and 47 up-differentially expressed genes induced by NR (NR-inducible genes) and IE (IE-inducible genes) were identified. NR-inducible genes were mainly enriched in phytohormone synthesis and signalling response, including 'response to brassinosteroid', 'response to jasmonic acid', 'response to ethylene', 'brassinosteroid metabolic process', 'brassinosteroid biosynthesis' and 'plant hormone signal transduction'. In contrast, IE-inducible genes were predominantly enriched in glutathione metabolism. The activity of glutathione S-transferase was found to be increased after IE treatment, whereas no significant increase was observed following NR treatment. Moreover, several transcription factor genes, such as those encoding AP2/ERF-ERF and (basic helix-loop-helix) bHLH were found to be significantly induced by NR treatment. This is the first report of the utilisation of NR as an herbicide safener. The results of this study suggest the toxicity of FE to rice is mitigated by NR through a distinct mechanism compared to IE. © 2023 Society of Chemical Industry.

Feasibility of anaerobic co-digestion of biodegradable plastics with food waste, investigation of microbial diversity and digestate phytotoxicity

The effects of biodegradable plastics of different thicknesses (30 and 40 μm) and sizes (20 × 20, 2 × 2, and 1 × 1 mm) on anaerobic digestion of food waste and digestate phytotoxicity were investigated. Methane productions (38 days) for the groups with 20 × 20, 2 × 2, and 1 × 1 mm of 30 μm plastics were 92.46, 138.27, and 259.95 mL/gVSremoval, respectively which are nearly 58 % higher than the control group (58.86 mL/gVSremoval). Methane production in 40 μm plastics groups was lower than in 30 μm groups of equal size. All sizes of 30 µm plastics promoted substrate hydrolysis, acidification, and relative abundance of key hydrolytic bacteria and methanogens. Phytotoxicity tests results showed that seed root elongation was inhibited in groups with 40 μm plastics. In conclusion, 30 μm biodegradable plastics were more suitable for anaerobic digestion with food waste than 40 μm.

Identification and expression profile of the SMAX/SMXL family genes in chickpea and lentil provide important players of biotechnological interest involved in plant branching

Main conclusionSMAX/SMXL family genes were successfully identified and characterized in the chickpea and lentil and gene expression data revealed several genes associated with the modulation of plant branching and powerful targets for use in transgenesis and genome editing.Strigolactones (SL) play essential roles in plant growth, rooting, development, and branching, and are associated with plant resilience to abiotic and biotic stress conditions. Likewise, karrikins (KAR) are “plant smoke-derived molecules” that act in a hormonal signaling pathway similar to SL playing an important role in seed germination and hairy root elongation. The SMAX/SMXL family genes are part of these two signaling pathways, in addition to some of these members acting in a still little known SL- and KAR-independent signaling pathway. To date, the identification and functional characterization of the SMAX/SMXL family genes has not been performed in the chickpea and lentil. In this study, nine SMAX/SMXL genes were systematically identified and characterized in the chickpea and lentil, and their expression profiles were explored under different unstressless or different stress conditions. After a comprehensive in silico characterization of the genes, promoters, proteins, and protein-protein interaction network, the expression profile for each gene was determined using a meta-analysis from the RNAseq datasets and complemented with real-time PCR analysis. The expression profiles of the SMAX/SMXL family genes were very dynamic in different chickpea and lentil organs, with some genes assuming a tissue-specific expression pattern. In addition, these genes were significantly modulated by different stress conditions, indicating that SMAX/SMXL genes, although working in three distinct signaling pathways, can act to modulate plant resilience. Most CaSMAX/SMXL and partner genes such as CaTiE1 and CaLAP1, have a positive correlation with the plant branching level, while most LcSMAX/SMXL genes were less correlated with the plant branching level. The SMXL6, SMXL7, SMXL8, TiE1, LAP1, BES1, and BRC1 genes were highlighted as powerful targets for use in transgenesis and genome editing aiming to develop chickpea and lentil cultivars with improved architecture. Therefore, this study presented a detailed characterization of the SMAX/SMXL genes in the chickpea and lentil, and provided new insights for further studies focused on each SMAX/SMXL gene.

Integrated transcriptomic and metabolomic analysis reveals the potential mechanisms underlying indium-induced inhibition of root elongation in wheat plants

Soil contamination by indium, an emerging contaminant from electronics, has a negative impact on crop growth. Inhibition of root growth serves as a valuable biomarker for predicting indium phytotoxicity. Therefore, elucidating the molecular mechanisms underlying indium-induced root damage is essential for developing strategies to mitigate its harmful effects. Our transcriptomic findings revealed that indium affects the expression of numerous genes related to cell wall composition and metabolism in wheat roots. Morphological and compositional analysis revealed that indium induced a 2.9-fold thickening and a 17.5 % increase in the content of cell walls in wheat roots. Untargeted metabolomics indicated a substantial upregulation of the phenylpropanoid biosynthesis pathway. As the major end product of phenylpropanoid metabolism, lignin significantly accumulated in root cell walls after indium exposure. Together with increased lignin precursors, enhanced activity of lignin biosynthesis-related enzymes was observed. Moreover, analysis of the monomeric content and composition of lignin revealed a significant enrichment of p-hydroxyphenyl (H) and syringyl (S) units in root cell walls under indium stress. The present study contributes to the existing knowledge of indium toxicity. It provides valuable insights for developing sustainable solutions to address the challenges posed by electronic waste and indium contamination on agroecosystems.

Assessment of Aqueous Leaf Extracts of Parthenium Hysterophorus L. On Seedlings Growth of Wheat

An investigation was conducted to assess the effect of Parthenium hysterophorus L. leaf extracts on seedling growth of three wheat (Triticum aestivum L.) varieties viz. Sourav, BARI Gom 22 and BARI Gom 33. It was observed that the growth of wheat seedlings was significantly influenced by the Parthenium extract treatments. BARI Gom 22 showed more tolerance to Parthenium treatments than BARI Gom 33 and Sourav. Generally, wheat seedlings growth was inhibited by Parthenium extract treatments at all periods. The percent inhibition of shoot and root elongation were more visible at 5% treatment concentration at all periods than other extract treatments. On the other hand the number of root of wheat seedlings was not found to be affected by Parthenium at 7 and 10-day periods. It was also noted that the effect of Parthenium extracts on wheat seedling growth is concentrations dependent manner. J. Bio-Sci. 31(1): 61-70, 2023

Genotypic differences in systemic root responses to mechanical obstacles.

As roots grow through the soil to forage for water and nutrients, they encounter mechanical obstacles such as patches of dense soil and stones that locally impede root growth. Here, we investigated hitherto poorly understood systemic responses of roots to localised root impedance. Seedlings of two wheat genotypes were grown in hydroponics and exposed to impenetrable obstacles constraining the vertical growth of the primary or a single seminal root. We deployed high-resolution in vivo imaging to quantify temporal dynamics of root elongation rate, helical root movement, and root growth direction. The two genotypes exhibited distinctly different patterns of systemic responses to localised root impedance, suggesting different strategies to cope with obstacles, namely stress avoidance and stress tolerance. Shallower growth of unconstrained seminal roots and more pronounced helical movement of unconstrained primary and seminal roots upon localised root impedance characterised the avoidance strategy shown by one genotype. Stress tolerance to localised root impedance, as exhibited by the other genotype, was indicated by relatively fast elongation of primary roots and steeper seminal root growth. These different strategies highlight that the effects of mechanical obstacles on spatiotemporal root growth patterns can differ within species, which may have major implications for resource acquisition and whole-plant growth.

Genome wide association analysis reveals multiple QTLs controlling root development in maize

Maize root system plays a crucial role in the development of the aboveground plant and determines the yield via the uptake of water and nutrients in the field. However, the genetic architecture of the maize root system is largely unknown mainly due to the complexity of maize root system and the interaction between genotype and environment. Using a high-throughput semi-automatic hydroponic platform with stable conditions, we comprehensively characterized the root system in a core population of 518 diverse inbred lines of maize. Population structure analysis revealed that the panel has a stratification and linkage disequilibrium decay distance was less than 50 Kb. Based on the genotyping with the high density of 600 K SNPs, we conducted a genome wide association analysis (GWAS) and identified nine SNPs and seven candidate genes significantly associated with 24 traits. A candidate gene GRMZM2G400533 located at the upstream 5 Kb region from the leading SNP (AX-91771718) was significantly associated with primary root length and preferentially expressed in primary root and crown root. The expression of GRMZM2G400533 increased as the primary root developed but negatively correlated with primary root elongation. We also identified three functional variants and eight allelic haplotypes based on candidate gene analysis of GRMZM2G400533. The present study will broaden our understanding of maize root development and provide a theoretical basis for maize improvement through optimizing root system.

A unique mutation in PIN-FORMED1 and a genetic pathway for reduced sensitivity of Arabidopsis roots to N-1-naphthylphthalamic acid.

The small chemical N-1-naphthylphthalamic acid (NPA) has long been used as a polar auxin transport inhibitor. Recent biochemical and structural investigations have revealed that this molecule competes with the auxin IAA (indole-3-acetic acid) inside the PIN-FORMED auxin efflux carriers. However, the existence of any mutations in PIN family proteins capable of uncoupling the docking of IAA from NPA remains unclear. We report that Arabidopsis thaliana seedlings overexpressing SMALL AUXIN UP RNA 41 were hypersensitive to NPA-induced root elongation inhibition. We mutagenized this line to improve the genetic screening efficiency for NPA hyposensitivity mutants. Using bulked segregation analysis and mapping-by-sequencing assessment of these mutants, we identified a core genetic pathway for NPA-induced root elongation inhibition, including genes required for auxin biosynthesis, transportation, and signaling. To evaluate specific changes of auxin signaling activity in mutant roots before and after NPA treatment, the DR5::GFP/DR5::YFP markers were introduced and observed. Most importantly, we discovered a unique mutation in the PIN1 protein, substituting a proline residue with leucine at position 584, leading to a loss of NPA sensitivity while keeping the auxin efflux capacity. Transforming the null mutant pin1-201 with the PIN1::PIN1P584L -GFP fusion construct rescued the PIN1 function and provided NPA hyposensitivity. The proline residue is predicted to be adjacent to a hinge in the middle region of the ninth transmembrane helix of PIN1 and is conserved from moss to higher plants. Our work may bring new insights into the engineering of NPA-resistant PINs for auxin biology studies.

RsPDR8, a member of ABCG subfamily, plays a positive role in regulating cadmium efflux and tolerance in radish (Raphanus sativus L.)

Radish (Raphanus sativus L.) is one of the most vital root vegetable crops worldwide. Cadmium (Cd), a non-essential and toxic heavy metal, can dramatically restrict radish taproot quality and safety. Although the Peiotrpic Drug Resistance (PDR) genes play crucial roles in heavy metal accumulation and transport in plants, the systematic identification and functional characterization of RsPDRs remain largely unexplored in radish. Herein, a total of 19 RsPDR genes were identified from the radish genome. A few RsPDRs, including RsPDR1, RsPDR8 and RsPDR12, showed significant differential expression under Cd and lead (Pb) stress in the ‘NAU-YH’ genotype. Interestingly, the plasma membrane-localized RsPDR8 exhibited significantly up-regulated expression and enhanced promoter activity under Cd exposure. Ectopic expression of RsPDR8 conferred Cd tolerance via reducing Cd accumulation in yeast cells. Moreover, the transient transformation of RsPDR8 revealed that it positively regulated Cd tolerance by promoting ROS scavenging and enhancing membrane permeability in radish. In addition, overexpression of RsPDR8 increased root elongation but deceased Cd accumulation compared with the WT plants in Arabidopsis, demonstrating that it could play a positive role in mediating Cd efflux and tolerance in plants. Together, these results would facilitate deciphering the molecular mechanism underlying RsPDR8-mediated Cd tolerance and detoxification in radish.

Exogenous IAA enhances low potassium tolerance of sweetpotato by regulating root response strategy

ABSTRACT Plant roots are sensitive to potassium (K+) deficiency signals. Therefore, regulating root growth by exogenous methods is a vital strategy to improve low K+ tolerance of sweetpotato. We studied the effects of exogenous indole-3-acetic acid (IAA) on growth, K+ absorption, and root characteristics in sweetpotato exposed to low K+ treatment (LK). LK significantly inhibited dry mass, K+ concentration and accumulation, as well as the root elongation (length) and branching (forks and crossings) in sweetpotato seedlings. However, exogenous IAA increased the length, ratio, and density of lateral roots and promoted absorption and accumulation of K+, which effectively alleviated the inhibitory effect of low K+. Exogenous IAA also increased the expression levels of auxin synthesis (IbYUC6 and IbTAR2) and transport (IbPIN1, IbPIN3, and IbPIN8) genes in leaves and roots, which promoted the increase of endogenous IAA content. Furthermore, exogenous IAA was more effective on low-K-tolerant variety (XS32) than low-K-sensitive variety (NZ1) under LK stress, depending on their different IAA synthesis and transport strategies. These results indicated that exogenous IAA enhanced root responsiveness of sweetpotato to low K+ stress by modulating auxin biosynthesis and transport, thereby improving the tolerance of sweetpotato to low K+ stress.

Dormancy-Associated Gene 1 (OsDRM1) as an axillary bud dormancy marker: Retarding Plant Development, and Modulating Auxin Response in Rice (Oryza sativa L.)

Dormancy-Associated Genes 1/Auxin-Repressed Proteins (DRM1/ARP) are associated with bud dormancy, repression of plant growth, and responsiveness to hormones. To further explore the function of DRM1 proteins in rice, we isolated a dormancy-associated gene1 (OsDRM1) through microarray analysis. In situ hybridization analyses revealed that OsDRM1 is predominantly expressed in dormant axillary buds, while it is weakly expressed in growing buds, indicating that OsDRM1 gene can be used as a molecular marker for bud dormancy in rice. Overexpression of OsDRM1 in transgenic plants delayed axillary bud outgrowth by suppressing cell division within the buds. Further studies in OsDRM1-overexpressing transgenic plants showed a reduction in plant height, inhibition of root and hypocotyl elongation, and delayed heading time. Under auxin treatment, overexpression of OsDRM1 in transgenic lines partially rescued the shortened length of the primary and crown root. Taken together, these results indicated that OsDRM1 delayed bud growth by arresting the cell cycle and act as a growth repressor affect rice development by modulated auxin signaling.

Alteration of Hordeum vulgare and Sinapis alba germination and early growth in response to airborne low-metallic automotive brake wear debris

Road transportation significantly contributes to environmental pollution, both in terms of exhaust and non-exhaust (brake wear) emissions. As was proven, brake wear debris is released in a wide variety of sizes, shapes, and compositions. Although studies confirming the possible adverse health and environmental impact of brake wear debris were published, there is no standardized methodology for their toxicity testing, and most studies focus only on one type of brake pad and/or one test. The lack of methodology is also related to the very small amount of material released during the laboratory testing. For these reasons, this study deals with the mixture of airborne brake wear debris from several commonly used low-metallic brake pads collected following the dynamometer testing. The mixture was chosen for better simulation of the actual state in the environment and to collect a sufficient amount of particles for thorough characterization (SEM, XRPD, XRF, chromatography, and particle size distribution) and phytotoxicity testing. The particle size distribution measurement revealed a wide range of particle sizes from nanometers to hundreds of nanometers, elemental and phase analysis determined the standard elements and compounds used in the brake pad formulation. The Hordeum vulgare and Sinapis alba were chosen as representatives of monocotyledonous and dicotyledonous plants. The germination was not significantly affected by the suspension of brake wear debris; however, the root elongation was negatively influenced in both cases. Sinapis alba (IC50 = 23.13 g L−1) was more affected than Hordeum vulgare (IC50 was not found in the studied concentration range) the growth of which was even slightly stimulated in the lowest concentrations of brake wear debris. The plant biomass was also negatively affected in the case of Sinapis alba, where the IC50 values of wet and dry roots were determined to be 44.83 g L−1 and 86.86 g L−1, respectively.