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The present study investigates the phytotoxic potential of azelaic acid (AZA) on Arabidopsis thaliana roots. Effects on root morphology, anatomy, auxin content and transport, gravitropic response and molecular docking were analysed. AZA inhibited root growth, stimulated lateral and adventitious roots, and altered the root apical meristem by reducing meristem cell number, length and width. The treatment also slowed down the roots' gravitropic response, likely due to a reduction in statoliths, starch-rich organelles involved in gravity perception. In addition, auxin content, transport and distribution, together with PIN proteins' expression and localisation were altered after AZA treatment, inducing a reduction in auxin transport and its distribution into the meristematic zone. Computational simulations showed that AZA has a high affinity for the auxin receptor TIR1, competing with auxin for the binding site. The AZA binding with TIR1 could interfere with the normal functioning of the TIR1/AFB complex, disrupting the ubiquitin E3 ligase complex and leading to alterations in the response of the plant, which could perceive AZA as an exogenous auxin. Our results suggest that AZA mode of action could involve the modulation of auxin-related processes in Arabidopsis roots. Understanding such mechanisms could lead to find environmentally friendly alternatives to synthetic herbicides., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Coumarin is a phytotoxic natural compound able to affect plant growth and development. Previous studies have demonstrated that this molecule at low concentrations (100 µM) can reduce primary root growth and stimulate lateral root formation, suggesting an auxin-like activity. In the present study, we evaluated coumarin's effects (used at lateral root-stimulating concentrations) on the root apical meristem and polar auxin transport to identify its potential mode of action through a confocal microscopy approach. To achieve this goal, we used several Arabidopsis thaliana GFP transgenic lines (for polar auxin transport evaluation), immunolabeling techniques (for imaging cortical microtubules), and GC-MS analysis (for auxin quantification). The results highlighted that coumarin induced cyclin B accumulation, which altered the microtubule cortical array organization and, consequently, the root apical meristem architecture. Such alterations reduced the basipetal transport of auxin to the apical root apical meristem, inducing its accumulation in the maturation zone and stimulating lateral root formation.

DNA methylation carried out by different methyltransferase classes is a relevant epigenetic modification of DNA which plays a relevant role in the development of eukaryotic organisms. Accordingly, in Arabidopsis thaliana loss of DNA methylation due to combined mutations in genes encoding for DNA methyltransferases causes several developmental abnormalities. The present study describes novel growth disorders in the drm1 drm2 cmt3 triple mutant of Arabidopsis thaliana, defective both in maintenance and de novo DNA methylation, and highlights the correlation between DNA methylation and the auxin hormone pathway. By using an auxin responsive reporter gene, we discovered that auxin accumulation and distribution were affected in the mutant compared to the wild type, from embryo to adult plant stage. In addition, we demonstrated that the defective methylation status also affected the expression of genes that regulate auxin hormone pathways from synthesis to transport and signalling and a direct relationship between differentially expressed auxin-related genes and altered auxin accumulation and distribution in embryo, leaf and root was observed. Finally, we provided evidence of the direct and organ-specific modulation of auxin-related genes through the DNA methylation process., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Farnesene is a sesquiterpene with semiochemical activity involved in interspecies communication. This molecule, known for its phytotoxic potential and its effects on root morphology and anatomy, caused anisotropic growth, bold roots and a "left-handedness" phenotype. These clues suggested an alteration of auxin distribution, and for this reason, the aim of the present study was to evaluate its effects on: i) PIN-FORMED proteins (PIN) distribution, involved in polar auxin transport; ii) PIN genes expression iii) apical meristem anatomy of primary root, in 7 days old Arabidopsis thaliana seedlings treated with farnesene 250 μM. The following GFP constructs: pSCR::SCR-GFP, pDR5::GFP,pPIN1::PIN1-GFP, pPIN2::PIN2-GFP, pPIN3::PIN3-GFP, pPIN4::PIN4-GFP and pPIN7::PIN7-GFP were used to evaluate auxin distribution. Farnesene caused a reduction in meristematic zone size, an advancement in transition zone, suggesting a premature exit of cells from the meristematic zone, a reduction in cell division and an impairment between epidermal and cortex cells. The auxin-responsive reporter pDR5::GFP highlighted that auxin distribution was impaired in farnesene-treated roots, where auxin distribution appeared maximum in the quiescent center and columella initial cells, without extending to mature columella cells. This finding was further confirmed by the analysis on PIN transport proteins distribution, assessed on individual constructs, which showed an extreme alteration mainly dependent on the PIN 3, 4 and 7, involved in pattern specification during root development and auxin redistribution. Finally, farnesene treatment caused a down-regulation of all the auxin transport genes studied. We propose that farnesene affected auxin transport and distribution causing the alteration of root meristem, and consequently the left-handedness phenotype., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

Citral is a linear monoterpene which is present, as a volatile component, in the essential oil of several different aromatic plants. Previous studies have demonstrated the ability of citral to alter the mitotic microtubules of plant cells, especially at low concentrations. The changes to the microtubules may be due to the compound acting directly on the treated root and coleoptile cells or to indirect action through certain phytohormones. This study, performed in Arabidopsis thaliana, analysed the short-term effects of citral on the auxin content and mitotic cells, and the long-term effects of these alterations on root development and ethylene levels. The results of this study show that citral alters auxin content and cell division and has a strong long-term disorganising effect on cell ultra-structure in A. thaliana seedlings. Its effects on cell division, the thickening of the cell wall, the reduction in intercellular communication, and the absence of root hairs confirm that citral is a strong phytotoxic compound, which has persistent effects on root development.