Abstract Background Conifers like Scots pine ( Pinus sylvestris ) are a potential bioindicator species for radioactive contamination as they are among the most radiosensitive plant species. Phytohormones and amino acids are central to plant growth and stress signaling, but their roles in the pine radiation response, particularly in a tissue-specific context, have not been adequately studied. Results Here, we investigated the morphological, metabolic and transcriptional consequences of chronic gamma irradiation in pine seedlings under controlled laboratory conditions. We exposed P. sylvestris seedlings to 10 weeks of low-dose external gamma irradiation (682 µGy/h) and performed targeted metabolomic analysis of phytohormones and amino acids and RT-qPCR analysis of hormone-related gene expression in the shoot tip, root tip, young needles, and cotyledons, alongside a microscopic analysis of the shoot apical meristem. Irradiation induced a significant reduction in the height and area of the meristem. This morphological change coincided with a trend towards decreased abundance of growth-promoting hormones in the shoot tip, namely cytokinins and gibberellins. Our data also indicate the potential involvement of specific cytokinin and gibberellin signals in the young needles in the response to irradiation, and hint towards a tissue-specific role for jasmonyl-ACC conjugation in the young shoot. Concurrently, the cotyledons of irradiated seedlings displayed a massive and significant increase in free amino acid concentrations and decreased cytokinin abundance, consistent with accelerated senescence. Conclusions Taken together, these results reveal a tissue-specific pattern of metabolic and transcriptional changes in irradiated pine seedlings. The data are consistent with a scenario in which apical growth is hormonally suppressed and resources may be liberated from cotyledon tissue, which could then potentially be reallocated toward a stress response in developing organs. This study thereby provides an integrated view of the organ-level metabolic response to chronic radiation.

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative contaminants of emerging concern in aquatic ecosystems, yet their uptake dynamics and physiological effects on macrophytes remain poorly understood. This study investigated PFAS bioaccumulation and physiological responses of Lemna minor exposed to seven PFAS compounds under both acute and chronic conditions. Longer exposure durations resulted in detectable accumulation of a greater number of PFAS, particularly at lower exposure concentrations. Concentration-dependent accumulation was observed, although the direction and magnitude of these relationships varied among PFAS types. PFBS showed the highest accumulation, with concentrations up to 8736 ± 5715 ng/g dw detected after 10 days of exposure to 100,000 ng/L. When expressed as bioconcentration factors (BCFs), an inverse relationship with exposure concentration indicated higher uptake efficiency at environmentally relevant concentrations. The highest BCF (6076 ± 898 L/g) was observed for PFBS after 20 days of exposure to 1 ng/L. Differences in accumulation and BCF values were attributed to functional group and chain length, which affect solubility and hydrophobicity. Despite measurable bioaccumulation, physiological responses were generally minor, as neither growth nor photosynthetic efficiency (Fv/Fm and Y(II)) showed consistent impairment. Growth stimulation was observed in a limited number of treatments, suggesting potential hormetic effects. Overall, these findings highlight that both exposure duration and concentration range should be considered when assessing PFAS bioaccumulation in macrophytes, and that integrating time-dependent accumulation into risk assessments is essential for accurately evaluating PFAS behaviour and ecological risks.

IntroductionRestored estuarine floodplains with an artificially controlled reduced tide (CRT) are dynamic areas created for flood protection whilst also providing habitats for estuarine wildlife. However, the reintroduction of the tide poses stressors, including salinity and waterlogged soils because of periodic flooding, on established vegetation such as English oak (Quercus robur). Therefore, newly opened CRT areas give the opportunity of studying the effects of flooding, salinity, and drainage, on hydrogen peroxide (H2O2) concentrations in plants, as a proxy for stress.MethodsThis was done on English oak samples retrieved from both field and mesocosm settings using commercially available peroxide assay kits.ResultsOur results indicated that H2O2 concentrations measured in the field were affected by the time of sampling, while concentrations in the mesocosm were influenced by soil type. Flooding and salinity did not show detectable effects on H₂O₂ concentrations, either individually or in combination with soil type, within the scope of our experimental design, which had constrained statistical power to detect subtle effects. Additionally, our results did not correspond with the deterioration and mortality of English oak observed in the field and mesocosm experiments, indicating limited suitability of H₂O₂ as a standalone indicator of physiological stress under these conditions.DiscussionOverall, we recommend that future studies include a broader range of indicators to assess the tree stress responses in dynamic CRT environments.

Wastewater treatment plants (WWTPs) are increasingly implementing ozonation and granular activated carbon (GAC) filtration to remove micropollutants. Biological activated carbon (BAC) has demonstrated extended operational lifespans through biodegradation. Pre-ozonation can further enhance BAC performance by converting micropollutants into more biodegradable forms for microbial consumption, though how these microbial communities develop over time under these conditions remains understudied. This study investigated the impact of pre-ozonation on BAC biofilm development through ATP quantification and 16S rRNA sequencing over 525 days across six filters. Micropollutant removal through ozonation and BAC at two different stages of use was measured 21 times during this period, and a batch incubation experiment at 25 °C and 4 °C to disentangle biological from adsorptive removal. Pre-ozonation reduced DOC remaining in effluent relative to influent by 10–12% and significantly improved removal of four indicator micropollutants. Batch incubation experiments indicated that biodegradation is the primary removal mechanism in mature, heavily loaded, BAC systems. Bioaugmentation via placing established BAC filters in series with fresh downstream filters steered developing communities toward greater diversity, with the ozonated bioaugmented filter achieving the highest microbial diversity among ozonated filters despite compositional divergence from its source.

Apical dominance and culture heterogeneity significantly limit the efficiency of olive micropropagation, hindering the rapid production of plantlets. This study explores how manipulating the explant origin (topophysis) and density can mitigate these challenges. Explants originating from apical and middle sections were cultivated at densities of 18, 24, and 30 explants per vessel. After 12 weeks, significant differences in the growth parameters were observed based on the explant origin and density. The middle-section explants exhibited superior shoot proliferation and node production, especially at higher densities. The callus weight also increased with the density, while the internode length remained relatively stable. Hormone analysis demonstrated the density-dependent spatial distribution pattern of aromatic and isoprenoid cytokinins. Notably, at higher densities, the aromatic free bases in the apical-section leaves showed migration toward the shoot apices, while this migration was less pronounced in the middle-section leaves. Isoprenoid cytokinins displayed complex distribution patterns, with free bases and O-glucosides often increasing toward the basal nodes. These findings demonstrate that optimizing the explant origin and density can effectively reduce apical dominance and enhance culture homogeneity in olive micropropagation. This approach offers a promising strategy for improving the micropropagation protocols for olive and potentially other woody plants, leading to more efficient and cost-effective production of high-quality plantlets for commercial use.

The Flanders region (Belgium) has several per- and polyfluoroalkyl substances (PFAS) hotspots due to industrial activities, including a fluorochemical plant (FCP) near Antwerp. Previous studies in this area reported exceptionally high levels of legacy PFAS in soils, invertebrates and birds using targeted liquid chromatography-mass spectrometry (LC-MS/MS) methods. In this study, bird eggs were used as biomonitoring tools to comprehensively investigate PFAS bioaccumulation near the hotspot through suspect and non-target high-resolution mass spectrometry (HRMS) screening. A total of 40 eggs (26 Great tit Parus major, 14 Blue tit Cyanistes caeruleus) were collected from three sites near the FCP during the 2022 breeding season. Suspect screening was based on two PFAS lists covering over 10,000 compounds, and non-targeted analysis using the FluoroMatch software. In addition to target PFAS, 62 compounds spanning 16 classes were identified and assigned Confidence Levels 2 or 3. Semi-quantification revealed notably high levels of emerging PFAS, particularly homologues of ether-substituted perfluoroalkyl sulfonic acids (PFESAs) and pentafluorosulfide perfluoroalkyl sulfonic acids (SF5-PFSAs), including the first detection of SF5-PFSA C6 in biota. Quantification and semi-quantification showed the highest levels of some PFAS ever measured in bird eggs, with compounds identified by HRMS contributing up to 15% of the total PFAS burden. This is the first study to report such a broad and highly concentrated profile of emerging, largely non-oxidizable PFAS in bird eggs, underscoring the importance of suspect and non-targeted analysis. These rarely monitored PFAS should be considered for inclusion in both human and environmental monitoring programmes and risk assessments.

The growing demand for sustainable agriculture necessitates innovative strategies to enhance crop productivity while minimizing environmental impact. This study explores the biopriming potential of Cucumis sativus L. seeds using extracts derived from a consortium of nitrofixing cyanobacteria Nostoc commune, Calothrix sp., and Aphanothece minutissima subjected to static magnetic field (SMF) treatments. The cyanobacterial consortia were exposed to SMF at varying magnetic inductions (40-50 mT and 100-200 mT), followed by extract preparation and application as biopriming agents. Results demonstrated significant improvements in key seedling growth parameters, including root and stem length, vigor index I, and fresh biomass. The consortium treated with 40-50 mT SMF showed the most pronounced growth-stimulating activity, suggesting enhanced bioactive compound production under this treatment that might be related to auxin biosynthesis. Biopriming with cyanobacterial extracts maintained a balanced nutritional uptake and plant health, as indicated by stable fresh weight dry weight ratios. These findings highlight the potential of SMF-enhanced cyanobacterial consortia as biopriming agents for horticultural crops. Future research should elucidate the underlying modes of action and optimize conditions for broader crop applications.

This article comments on: Hladík P, Brunoni F, Žukauskaitė A, Zatloukal M, Bělíček J, Kopečný D, Briozzo P, Ferchaud N, Novák O, Pěnčík A. 2025. Phenylacetic acid metabolism in land plants: novel pathways and metabolites. Journal of Experimental Botany 76, https://doi.org/10.1093/jxb/eraf092

Climate change is leading to more persistent precipitation regimes (PRs) featuring prolonged dry and wet periods in Northern Europe. Plants and plant communities can acclimatize, reducing the impact of repeated exposures to extreme PRs. We addressed the hypothesis that PR adaptations by the soil microbiome contribute to the acclimatization of plants. We used soils from grassland mesocosms exposed to a 1-d (1SPR) or a 30-d (30SPR) wet/dry cycle to investigate how soil legacy affects the response of four grassland plant species to subsequent PR events. During the 40-d experiment, 5-d PR (5PR) treatments reduced growth compared with 1-d (1PR) samples, independent of soil legacy. The 30SPR treatment altered soil fungal communities, influencing plant responses, with Plantago and Phleum showing significant stress adaptations when compared with 1SPR. Integrating genome-wide transcriptional, physiological, and biochemical analyses enabled us to propose a mechanistic model showing how soil 30SPR influences four grassland plant species by activating common mechanisms, including redox signaling pathways and stress hormones (jasmonic acid, ethylene, and abscisic acid) under 5PR. These responses lead to cell wall reinforcement through increased lignin and callose, enhancing resilience. Overall, these findings underscore the role of soil legacy in helping grassland plants adapt to potential future PR variations.

Cadmium (Cd) pollution in soils and uptake by plant roots is a widespread problem, illustrating the requirement to enhance our knowledge of stress responses underlying its phytotoxicity. Acute Cd exposure induces an oxidative challenge in roots through the use of glutathione (GSH) for Cd-chelating phytochelatin (PC) production. To further uncover the acute Cd stress response of varying intensities, especially related to endoplasmic reticulum (ER) stress, autophagy, and the ethylene response, wild-type (WT) Arabidopsis thaliana were exposed to 2 and 5 µM Cd for 24 h. The dependence of these responses on stress intensity was explored by comparing Cd-sensitive cad2–1 and cad1–3 mutants with disturbed biosynthesis of GSH and PCs, respectively, to the WT. Indicative of ER stress, inositol requiring 1 (IRE1)-dependent basic region/leucine zipper 60 (bZIP60) splicing and target genes were induced with increasing Cd stress in roots. In leaves, this response was already initiated at a lower stress intensity, but also reached its limit more quickly upon increasing stress. On the other hand, more severe Cd stress decreased transcript levels of two autophagy-inhibiting targets of IRE1-dependent decay of mRNAs (RIDD). Lower levels of these transcripts correlated with autophagy induction, suggesting a connection between ER stress and autophagy upon increasing Cd stress. Furthermore, while higher stress intensity stimulated the ethylene response, it also steered the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) towards conjugation, forming malonyl-ACC. Lastly, this study demonstrates that the increased Cd sensitivity of the cad2–1 mutant is mostly related to lower PC production rather than depleted GSH levels.

Radioactive contamination represents a significant environmental stressor and can result in long-term exposure of terrestrial ecosystems to harmful levels of ionizing radiation. While Scots pine (Pinus sylvestris) has become a cornerstone reference species for environmental radiation protection studies due to its pronounced radiosensitivity, the underlying physiological mechanisms governing its responses to chronic low-dose radiation exposure remain poorly characterized. We therefore investigated the effect of chronic gamma irradiation on the growth and the oxidative stress response of young pine seedlings. The plants were exposed to 682 μGy·h⁻¹ for 10 weeks, with phenotypical measurements and analysis of molecular and biochemical markers of oxidative stress measured at two-week intervals. Chronic exposure induced significant inhibition of shoot development and a transient reduction of axillar bud formation, correlating with a dynamic oxidative stress response. An initial stress phase involved a significant disruption of the antioxidant system, evidenced by elevated glutathione oxidation and suppressed antioxidative enzyme activities. Despite this disruption, seedlings demonstrated the capacity for swift stress acclimation, first re-establishing glutathione homeostasis through an increase in its reduced form and then transitioning to an enhanced defensive state characterized by elevated superoxide dismutase activity and increased expression of ascorbate peroxidase. Understanding the dynamic radiation stress response during seedling establishment of this keystone forest species may prove beneficial for predicting ecosystem resilience and informing environmental radiation protection strategies in radioactively contaminated environments.

Due to the limited number of field studies investigating associations between environmentally relevant per- and polyfluoroalkyl substances (PFAS) mixtures and reproductive impairment, there is uncertainty as to whether birds are affected by PFAS pollution, whether species differ in sensitivity to PFAS, and whether the observed reproductive impairment is caused by PFAS or rather due to other potential confounding variables. Therefore, we investigated PFAS concentrations in eggs and blood plasma of great tit (Parus major) and blue tit (Cyanistes caeruleus) nestlings near a PFAS hotspot in Belgium, reproductive impairment, and associations between the accumulated levels and nestling body condition. In total, 29 eggs and 22 blood plasma samples of great tit clutches, and 10 egg and 10 blood plasma samples of blue tit clutches, were collected. Despite more types of PFAS being detected in eggs compared to plasma, only minor differences in profiles were observed between species. On the other hand, tissue-specific differences were more pronounced and likely reflect a combination of maternal transfer and dietary exposure post-hatching. Despite the high concentrations detected in both species, limited reproductive impairment was observed. Our results support previous findings that great tits and blue tits may not be very susceptible to PFAS pollution and provide evidence that other factors, including ecological stoichiometry, may be more important in explaining inter-species variation in PFAS accumulation and reproductive impairment.

Topolin cytokinins have emerged as valuable tools in micropropagation. This study investigates the metabolism of meta-topolin riboside (mTR) in three distinct tree species: Handroanthus guayacan and Tabebuia rosea (Bignoniaceae), and Tectona grandis (Lamiaceae). Employing labeled N15 mTR, we unraveled the complex mechanisms underlying cytokinin homeostasis, identifying N9-glucosylation as the principal deactivation pathway. Our findings demonstrate a capacity in T. rosea and H. guayacan to reposition the hydroxyl group on the cytokinin molecule, a previously unexplored metabolic pathway. Notably, this study reveals remarkable interfamilial and interspecies differences in mTR metabolism, challenging established perspectives on the role of callus tissue in cytokinin storage. These insights not only illuminate the metabolic intricacies of mTR, a cytokinin with interesting applications in plant tissue culture, but also enhances our understanding of cytokinin dynamics in plant systems, thereby enriching the scientific discourse on plant physiology and cytokinin biology.

The triple response phenotype is characteristic for seedlings treated with the phytohormone ethylene or its direct precursor 1-aminocyclopropane-carboxylic acid, and is often employed to find novel chemical tools to probe ethylene responses. We identified a benzoxazole-urea derivative (B2) partially mimicking ethylene effects in a triple response bioassay. A phenotypic analysis demonstrated that B2 and its closest analogue arinole (ARI) induced phenotypic responses reminiscent of seedlings with elevated levels of auxin, including impaired hook development and inhibition of seedling growth. Specifically, ARI reduced longitudinal cell elongation in roots, while promoting cell division. In contrast to other natural or synthetic auxins, ARI mostly acts as an inducer of adventitious root development, with only limited effects on lateral root development. Quantification of free auxins and auxin biosynthetic precursors as well as auxin-related gene expression demonstrated that ARI boosts global auxin levels. In addition, analyses of auxin reporter lines and mutants, together with pharmacological assays with auxin-related inhibitors, confirmed that ARI effects are facilitated by TRYPTOPHAN AMINOTRANSFERASE1 (TAA1)-mediated auxin synthesis. ARI treatment in an array of species, including Arabidopsis, pea, tomato, poplar, and lavender, resulted in adventitious root formation, which is a desirable trait in both agriculture and horticulture. Arinole elevates auxin through induction of biosynthesis, primarily via TRYPTOPHAN AMINOTRANSFERASE1. It can be employed to probe auxin responses and is an interesting tool to induce adventitious roots in various species.

The plant hormone ethylene is of vital importance in the regulation of plant development and stress responses. Recent studies revealed that 1-aminocyclopropane-1-carboxylic acid (ACC) plays a role beyond its function as an ethylene precursor. However, the absence of reliable methods to quantify ACC and its conjugates malonyl-ACC (MACC), glutamyl-ACC (GACC), and jasmonyl-ACC (JA-ACC) hinders related research. Combining synthetic and analytical chemistry, we present the first, validated methodology to rapidly extract and quantify ACC and its conjugates using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). Its relevance was confirmed by application to Arabidopsis mutants with altered ACC metabolism and wild-type plants under stress. Pharmacological and genetic suppression of ACC synthesis resulted in decreased ACC and MACC content, whereas induction led to elevated levels. Salt, wounding, and submergence stress enhanced ACC and MACC production. GACC and JA-ACC were undetectable in vivo; however, GACC was identified in vitro, underscoring the broad applicability of the method. This method provides an efficient tool to study individual functions of ACC and its conjugates, paving the road toward exploration of novel avenues in ACC and ethylene metabolism, and revisiting ethylene literature in view of the recent discovery of an ethylene-independent role of ACC.

The replacement of long-chained per- and polyfluoroalkyl substances (PFAS) with their short-chained homologues may have an impact on the accumulation in plants. The extent to which PFAS are absorbed by plants may differ among species and may depend on environmental factors, including temperature. The effect of an increased temperature on root uptake and translocation of PFAS in plants has been poorly studied. In addition, very few studies have examined toxicity of environmentally realistic PFAS concentrations to plants. Here, we investigated the bioaccumulation and tissue-distribution of fifteen PFAS in Arabidopsis thaliana L. grown in vitro at two different temperatures. Additionally, we examined the combined effects of temperature and PFAS accumulation on plant growth. Short-chained PFAS mainly accumulated in the leaves. The perfluorocarboxylic acid (PFCA) concentrations in roots and leaves, and the relative contribution of PFCAs to the ΣPFAS concentrations increased with carbon chain length regardless of temperature, with the exception of perfluorobutanoic acid (PFBA). An increased uptake of PFAS in leaves and roots at higher temperatures was observed for PFAS containing either eight or nine carbon atoms and could hence potentially result in higher risks for human intake. Leaf:root ratios of PFCAs followed a U-shaped pattern with carbon chain length, which is attributed to both hydrophobicity and anion exchange. Overall, no combined effects of realistic PFAS concentrations and temperature on the growth of A. thaliana were observed. PFAS exposure positively affected early root growth rates and root hair lengths, indicating a potential effect on factors involved in root hair morphogenesis. However, this effect on root growth rate became negligible later on in the exposure, and solely a temperature effect was observed after 6 days. Temperature also affected the leaf surface area. The underlying mechanisms on how PFAS stimulates root hair growth require further examination.

In this study, we grew radish (Raphanus raphanistrum subsp. sativus L.) and broad beans (Vicia faba L.) in a greenhouse on soils spiked with a mixture of 15 per- and polyfluoroalkyl substances (PFASs) and investigated the association between accumulated ∑PFAS concentrations, growth, and hormone levels. Short-chained PFASs dominated aboveground tissues, whereas long-chained PFASs were most abundant in the plant roots. Our results showed that the presence or absence of exodermal Casparian strips, as well as the hydrophobicity and anion exchange capacities of PFASs, could explain the translocation of PFASs within plants. Significant associations found between accumulated PFAS concentrations and levels of gibberellins (GA1 and GA15), methionine, and indole-3-acetic acid (IAA) imply potential effects of PFASs on plant development and growth. This study provides the first evidence of associations between PFAS accumulation in plants and growth hormone levels, possibly leading to growth reduction of the apical dome and effects on the cell cycle in pericycle cells and methionine metabolism in plants.

An important factor affecting the uniformity of in vitro cultures is the topophysical position of the original explant. We investigated this phenomenon in Handroanthus guayacan, a tropical woody tree species. Shoots from a stock culture were separated into upper, middle and basal sections and transferred to a modified MS medium containing meta-topolin-riboside and indole-butyric acid. After 8 weeks, the middle section produced the most shoots, the longest shoots and the highest number of nodes per plant. Shoots derived from the upper section were elongated, but had the shortest internodes, while those from the basal section formed the largest callus. None of the three types of explants rooted during the proliferation phase. The topophysically dependent spatial distribution of endogenous cytokinins and auxins was determined. The topophysical effect observed could not be explained solely by analyzing the endogenous isoprenoid and auxin. However, the metabolism and distribution of the aromatic cytokinin could provide an explanation. The concentration of the meta hydroxy-substituted topolins was highest in shoots derived from the middle section. Aromatic N- and O-glucosides were much more concentrated in the leaves than in the stems. In conclusion, it is recommended to consider the explant’s topophysis when developing a multiplication protocol to avoid heterogeneity in an in vitro culture.

In vitro culturing can generate plants with a distorted morphology. Some distortions affect the plant’s survival after transfer to an ex vitro environment, while others can affect the aesthetic value. Therefore, exogenous hormones are often applied in in vitro cultures to modulate plant architecture. In this study, it was hypothesised that regulatory effects of UV-B radiation on plant morphology can be exploited under in vitro conditions, and that UV exposure will result in sturdier, less elongated plants with more branches and smaller leaves, mediated by changes in plant hormones. Plants were grown in tissue-culture containers and exposed to ~0.22 W m−2 UV-B for 8 days. Subsequently, plants were transferred to soil and monitored for a further 7 days. Results show that UV induced a marked change in architecture with a significant increase in axillary branches, and reductions in leaf area, plant height and root weight. These changes were associated with significant alterations in concentrations of hormones, including IAA, GA7, GA3 and iP–9–G. Changes in hormone concentrations suggest a regulatory, rather than a stress response to UV-B. Therefore, it is proposed that the application of UV in in vitro culture can be an innovative approach to manipulate plant architecture.

Many food contact materials (FCMs) and reusable plastics in the food industry contain poly- and perfluoroalkyl substances (PFAS), a group of synthetic pollutants that are known to be potentially harmful for wildlife, humans, and the environment. PFAS may migrate from FCMs to food consumed by humans. As a replacement for plastics, often paper and other plant-based materials are used in commercial settings. This also applies to drinking straws, where plant-based and other presumably eco-friendly straws are increasingly used to reduce plastic pollution. In order to make these materials water-repellent, PFAS are added during manufacturing but can also already be present early in the supply chain due to the use of contaminated raw materials. In the present study, we examined the PFAS concentrations in 39 different brands of straws, made from five materials (i.e. paper, bamboo, glass, stainless steel, and plastic) commercially available on the Belgian market. We combined both targeted and suspect-screening approaches to evaluate a wide range of PFAS. PFAS were found to be present in almost all types of straws, except for those made of stainless steel. PFAS were more frequently detected in plant-based materials, such as paper and bamboo. We did not observe many differences between the types of materials, or the continents of origin. The presence of PFAS in plant-based straws shows that they are not necessarily biodegradable and that the use of such straws potentially contributes to human and environmental exposure of PFAS.