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Plants and their associated bacteria have been suggested to play a role in air pollution mitigation, especially in urban areas. Particularly, epiphytic bacteria might be able to degrade atmospheric hydrocarbons. However, phyllospheric bacterial communities are highly variable depending on several factors, e.g. tree species, leaf age and physiology, environmental conditions. In this work, bacterial communities hosted by urban Platanus x acerifolia leaves were taxonomically characterized using high throughput sequencing of 16S rRNA gene, and their temporal and spatial variability was assessed by comparing samples collected from different locations in the city of Milan (Italy) and in different months. The diversity of alkane hydroxylase ( alk B) phylotypes harboured by phyllospheric bacteria associated to urban Platanus trees was also evaluated. Results revealed that temporal changes, which are related to seasonality, acted as a stronger driver both on Platanus phyllospheric community structure and on alk B phylotype diversity than sampling location. Biodiversity of bacterial communities decreased along the growing season, leading to a strong dominance by the genus Stenotrophomonas . On the contrary, diversity of hydrocarbon-degrading populations increased over the months, although it resulted lower than that reported for other habitats. It was therefore hypothesized that atmospheric hydrocarbons might play a key role in the selection of phyllospheric populations in urban areas. [ABSTRACT FROM AUTHOR]

Retention of particles containing potentially toxic elements (PTEs) on plants that spontaneously colonize mine tailings was studied through comparison of washed and unwashed shoot samples. Zn, Pb, Cd, Cu, Ni, Co and Mn concentrations were determined in plant samples. Particles retained on leaves were examined by Scanning Electronic Microscopy and energy dispersive X-Ray analysis. Particles containing PTEs were detected on both washed and unwashed leaves. This indicates that the thorough washing procedure did not remove all the particles containing PTEs from the leaf surface, leading to an overestimation of the concentrations of PTEs in plant tissues. Particularly trichomes and fungal mycelium were retaining particles. The quantity and composition of particles varied among plant species and place of collection. It is obvious that plants growing on toxic mine tailings form a physical barrier against particle dispersion and hence limit the spread of PTEs by wind. [ABSTRACT FROM AUTHOR]

The TCE-degrading poplar endophyte Pseudomonas putida W619-TCE was inoculated in poplar cuttings, exposed to 0, 200 and 400 mg l−1 TCE, that were grown in two different experimental setups. During a short-term experiment, plants were grown hydroponically in half strength Hoagland nutrient solution and exposed to TCE for 3 days. Inoculation with P. putida W619-TCE promoted plant growth, reduced TCE phytotoxicity and reduced the amount of TCE present in the leaves. During a mid-term experiment, plants were grown in potting soil and exposed to TCE for 3 weeks. Here, inoculation with P. putida W619-TCE had a less pronounced positive effect on plant growth and TCE phytotoxicity, but resulted in strongly reduced amounts of TCE in leaves and roots of plants exposed to 400 mg l−1 TCE, accompanied by a lowered evapotranspiration of TCE. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), which are known intermediates of TCE degradation, were not detected. [Copyright &y& Elsevier]

The aim of this work was to investigate if engineered endophytes can improve phytoremediation of co-contaminations by organic pollutants and toxic metals. As a model system, yellow lupine was inoculated with the endophyte Burkholderia cepacia VM1468 possessing (a) the pTOM-Bu61 plasmid, coding for constitutive trichloroethylene (TCE) degradation, and (b) the ncc–nre Ni resistance/sequestration system. Plants were exposed to Ni and TCE and (a) Ni and TCE phytotoxicity, (b) TCE degradation and evapotranspiration, and (c) Ni concentrations in the roots and shoots were determined. Inoculation with B. cepacia VM1468 resulted in decreased Ni and TCE phytotoxicity, as measured by 30% increased root biomass and up to 50% decreased activities of enzymes involved in anti-oxidative defence in the roots. In addition, TCE evapotranspiration showed a decreasing trend and a 5 times higher Ni uptake was observed after inoculation. [Copyright &y& Elsevier]

Soil metal pollution can trigger evolutionary adaptation in soil-borne organisms. An in vitro screening test showed cadmium adaptation in populations of Suillus luteus (L.: Fr.) Roussel, an ectomycorrhizal fungus of pine trees. Cadmium stress was subsequently investigated in Scots pine (Pinus sylvestris L.) seedlings inoculated with a Cd-tolerant S. luteus, isolated from a heavy metal contaminated site, and compared to plants inoculated with a Cd-sensitive isolate from a non-polluted area. A dose–response experiment with mycorrhizal pines showed better plant protection by a Cd-adapted fungus: more fungal biomass and a higher nutrient uptake at high Cd exposure. In addition, less Cd was transferred to aboveground plant parts. Because of the key role of the ectomycorrhizal symbiosis for tree fitness, the evolution of Cd tolerance in an ectomycorrhizal partner such as S. luteus can be of major importance for the establishment of pine forests on Cd-contaminated soils. [Copyright &y& Elsevier]

Abstract: The diversity of endophytic bacteria found in association with poplar was investigated as part of a larger study to assess the possibility and practicality of using endophytic bacteria to enhance in situ phytoremediation. Endophytic bacteria were isolated from the root, stem and leaf of two cultivars of poplar tree growing on a site contaminated with BTEX compounds. They were further characterised genotypically by comparative sequence analysis of partial 16S rRNA genes and BOX-PCR genomic DNA fingerprinting, and phenotypically by their tolerance to a range of target pollutants, heavy metals and antibiotics. One hundred and 21 stable, morphologically distinct isolates were obtained, belonging to 21 genera, although six isolates could not be identified with confidence to a genus. The endophytic bacteria exhibited marked spatial compartmentalisation within the plant, suggesting there are likely to be species-specific and non-specific associations between bacteria and plants. A number of isolates demonstrated the ability to degrade BTEX compounds or to grow in the presence of TCE. This study demonstrates that within the diverse bacterial communities found in poplar several endophytic strains are present that have the potential to enhance phytoremediation strategies. [Copyright &y& Elsevier]

Abstract: A contaminated soil was collected in a field adjacent to a derelict As(III) smelter in Reppel (Bocholt, Belgium). A single soil treatment (% by soil weight) based on either iron grit (SS, 1%), beringite (B, 5%), or iron grit (1%) + beringite (5%) (BSS) was applied. Untreated and treated Reppel soils and a control soil were placed in lysimeters inside a greenhouse and cropped annually. The efficiency of soil treatments in decreasing As and metals in exposure sources and restoring soil functions was assessed 6 years after the treatments commenced. Decreases in extractable Cd, Mn, Zn and As occurred in the BSS soil. Only BSS treatment reduced both As and metal concentrations in leachates. BSS treatment produced best growth of lettuce and cabbage, the highest shoot and pod yields for dwarf bean, the lowest As, Cd and Zn concentrations in plant tissues, and partly restored Rhizobium nodulation on bean roots. The epigeic earthworm (Dendrobaena octaedra) could only survive in the BSS soil. Depurated living worms from the BSS soil had Cd concentration similar to those in control worms, but higher As, Ca, Fe, and Zn concentrations. Based on physiologically based extraction test (PBET), As bioaccessibility was reduced from 12% (untreated soil) to 7.4% (BSS) and 3% (SS), but only the SS treatment decreased the bioaccessibility of Cd (−30%) and Pb (−35%). The range of chemical and biological indicators suggested that BSS amendment was the most effective treatment for restoration of normal soil functions 6 years after initial treatment of the Reppel soil. [Copyright &y& Elsevier]

Abstract: In order to reduce the health risks associated with historically enriched metal smelting sites in Flanders (Belgium), the capacities of a non-beringite cyclonic ash and commercial Na-silicates to fix metals and create conditions to restore vegetation cover were evaluated and compared to lime and H3PO4. All tested amendments reduced Ca(NO3)2-extractable soil metal concentrations and reduced metal uptake in Agrostis capillaris seedlings. Sodium released by Na-silicates was possibly toxic to bean plants while an isotopic dilution technique revealed that metals were only weakly sorbed by silicates (i.e. reversible sorption). Cyclonic ash appeared more efficient than lime in both reducing oxidative stress in beans and Zn, Cu and Pb uptake in grasses. The metal fixing mechanism for both amendments appeared similar (i.e. irreversible fixation at constant pH), in contrast to H3PO4 where at least part of the immobilised Cd was irreversibly fixed across a range of pH. [Copyright &y& Elsevier]

Abstract: An international inter-laboratory research program investigated the effectiveness of in situ remediation of soils contaminated by cadmium, lead and zinc, measuring changes in soil and soil solution chemistry, plants and soil microbiota. A common soil, from mine wastes in Jasper County MO, was used. The soil was pH 5.9, had low organic matter (1.2 g kg−1 C) and total Cd, Pb, and Zn concentrations of 92, 5022, and 18 532 mg kg−1, respectively. Amendments included lime, phosphorus (P), red mud (RM), cyclonic ashes (CA), biosolids (BIO), and water treatment residuals (WTR). Both soil solution and NH4NO3 extractable metals were decreased by all treatments. Phytotoxicity of metals was reduced, with plants grown in P treatments having the highest yields and lowest metal concentration (0.5, 7.2 and 406 mg kg−1 Cd, Pb, and Zn). Response of soil micro-organisms was similar to plant responses. Phosphorus addition reduced the physiologically based extraction test Pb from 84% of total Pb extracted in the untreated soil to 34.1%. [Copyright &y& Elsevier]

A population of the metallophyte, Thlaspi caerulescens, originating from a Cd–Pb–Zn old mining and smelter site at Plombières (Belgium) was studied. T. caerulescens was cultivated hydroponically to investigate Cd uptake and tolerance. Cd was added to Hoagland’s medium at concentration range from 5 to 500 μM. The plants could tolerate 500 μM Cd in the solution showing only minor visible symptoms of toxicity but with a 32% decrease in fresh weight. After 14 days at 500 μM, Cd content in roots and shoots was 707 and 602 mg kg-1 of dry weight (d.w.), respectively. Application of Cd to hydroponically cultivated T. caerulescens induced the accumulation of PCs in plant roots and shoots. Buthionine sulfoximine (BSO) application almost completely reduced (by 98–100%) the accumulation of PCs without simultaneous increase in plants sensitivity to Cd. These results suggest a minor if any role of PCs in tolerance to Cd of the studied population of T. caerulescens in hydroponics. On the other hand, no PC accumulation was detected either in T. caerulescens plants growing in their natural environment at Plombierès or in plants growing in their native soil in a greenhouse. These results suggest that naturally selected tolerance in T. caerulescens population from Plombières is not associated with enhanced PCs synthesis. [Copyright &y& Elsevier]

Tissue and cellular compartmentation of Cd in roots and leaves of the hyperaccumulator Thlaspi caerulescens was investigated, using energy-dispersive X-ray microanalysis. In roots, Cd was determined in cortex parenchyma cells, endodermis, parenchyma cells of the central cylinder and xylem vessels. In leaves, it was found in cells lying on the way of water migration from the vascular cylinder to epidermal cells, which is in line with passive Cd transport by the transpiration stream. The mechanisms of Cd-detoxification in roots seem to be localized both in apoplast (e.g. binding to cell wall compounds) and inside cells since Cd was accumulated in these two compartments. On the other hand, in leaves Cd was found only in electron-dense deposits inside vacuoles, which suggests that vacuoles are the main compartment of its storage and detoxification in these organs. [Copyright &y& Elsevier]

Biosensors based on whole bacterial cells and on bacterial heavy metal binding protein were used to determine the mercury concentration in soil. The soil samples were collected in a vegetable garden accidentally contaminated with elemental mercury 25 years earlier. Bioavailable mercury was measured using different sensors: a protein-based biosensor, a whole bacterial cell based biosensor, and a plant sensor, i.e. morphological and biochemical responses in primary leaves and roots of bean seedlings grown in the mercury-contaminated soil. For comparison the total mercury concentration of the soil samples was determined by AAS. Whole bacterial cell and protein-based biosensors gave accurate responses proportional to the total amount of mercury in the soil samples. On the contrary, plant sensors were found to be less useful indicators of soil mercury contamination, as determined by plant biomass, mercury content of primary leaves and enzyme activities. [Copyright &y& Elsevier]

Indoor plants can be used to monitor atmospheric particulates. Here, we report the label-free detection of combustion-derived particles (CDPs) on plants as a monitoring tool for indoor pollution. First, we measured the indoor CDP deposition on Atlantic ivy leaves (Hedera hibernica) using two-photon femtosecond microscopy. Subsequently, to prove its effectiveness for using it as a monitoring tool, ivy plants were placed near five different indoor sources. CDP particle area and number were used as output metrics. CDP values ranged between a median particle area of 0.45 × 102 to 1.35 × 104 μm2, and a median particle number of 0.10 × 102 to 1.42 × 10³ particles for the indoor sources: control (greenhouse) < milling machine < indoor smokers < wood stove < gas stove < laser printer. Our findings demonstrate that Atlantic ivy, combined with label-free detection, can be effectively used in indoor atmospheric monitoring studies. Image 1 • Combustion-derived particles (CDPs) are emitted in the air by many indoor sources. • Plants can scavenge atmospheric particulates to monitor indoor exposure. • Two-photon femtosecond microscopy is used to quantify CDPs deposited on the plants. • Selective measurements of indoor CDP exposure at different exposure levels from various indoor sources. Two-photon femtosecond microscopy can be used to selectively measure the deposition of combustion-derived particles on indoor plants at different exposure levels. [ABSTRACT FROM AUTHOR]

Abstract: To improve the knowledge about the use of plants for the removal of toxic metals from contaminated soils, metabolic and transcriptional responses of Brassica carinata to different forms of copper (Cu) were studied. Two-week-old hydroponically grown seedlings were exposed for 24h to 30μM CuSO4 or CuEDDS. CuSO4 appeared to be more toxic than CuEDDS as roots showed higher levels of thiobarbituric acid reactive substances (TBARS) and increased relative leakage ratios (RLR), although the superoxide dismutase (SOD, EC 1.15.1.1) activity increased following both exposures. In CuSO4-exposed seedlings the higher toxicity was underlined by increased transcription of lipoxygenases (EC 1.13.11.12) and NADPH oxidases (EC 1.6.99.6) and by the higher Cu accumulation in both tissues compared to CuEDDS exposure. The presence of EDDS increased Cu translocation, which resulted 5-times higher than when exposed to CuSO4. Decreases in catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) activities together with increases of reduced glutathione (GSH) and tocopherols and a reduction of lipoic acid (LA) were observed in roots of CuSO4-exposed seedlings. On the contrary, CuEDDS exposure induced a general increase in enzyme activities and decreases in ascorbate (AsA) and tocopherol levels. In the primary leaves, in both exposures Cu differently affected the oxidative stress responses indicating that the cellular redox balance was anyway maintained. EDDS plays a crucial role in B. carinata tolerance to oxidative stress induced by Cu and might be proposed to improve the efficiency of Cu phytoextraction. [Copyright &y& Elsevier]

The uptake and effects of stable Cs and Co on L. minor were extensively studied, together with the effects of gamma radiation using a 137Cs or 60Co source. Innovative is that we combined external irradiation (from 137Cs or 60Co sources) with the direct uptake of certain amounts of stable Cs or Co to simulate the impact of the same mass of a radioisotope compared with that of the stable element. Such approach allows to differentiate between chemo- and radiotoxicity of 137Cs or 60Co, permitting to study the 137Cs and 60Co uptake by L. minor without using high concentrations of these elements in solution. Our results indicate that radiotoxicity of both 137Cs and 60Co has a greater importance compared to their chemotoxicity. This was also supported by the independent action and concentration addition concepts. Both concepts resulted in a good prediction of the dose-response curve of the combination exposure. The maximal removal of 137Cs or 60Co per gram dry matter of L. minor was lower compared with the removal of the corresponding stable isotope. The toxicity of 60Co was higher compared to 137Cs based on EC 50 values and uptake data. With respect to the effects on photosynthetic pigments, starch and soluble sugars contents, only starch increased in a concentration- and dose-dependent manner. • Higher radiotoxicity of 137Cs and 60Co compared to chemotoxicity. • High toxicity for 60Co as a result of low EC 50 value. • Starch content shows a concentration- and dose-dependent increase. [ABSTRACT FROM AUTHOR]

Glutathione (GSH) is an important player in plant responses to cadmium (Cd) through its dual function as an antioxidant and precursor for metal-chelating phytochelatins (PCs). In addition, it was shown to be involved in cell cycle regulation in Arabidopsis thaliana roots, but its involvement in this process in leaves is largely unknown and has never been evaluated in Cd-exposed plants. This study aimed to elucidate the role of GSH in leaf growth and development, metal chelation, nutrient homeostasis and cell cycle regulation in A. thaliana plants upon prolonged Cd exposure. Responses were compared between wild-type (WT) plants and three GSH-deficient mutants. Our results indicate that PC production remains important in plants exposed to Cd for an extended duration. Furthermore, an important role for GSH in regulating nutrient homeostasis in Cd-exposed plants was revealed. Cell cycle analysis demonstrated that negative effects of Cd exposure on cell division and endoreplication were more pronounced in leaves of the GSH-deficient cadmium-sensitive 2–1 (cad2-1) mutant in comparison to the WT, indicating the involvement of GSH in cell cycle regulation. Finally, a crucial role for GSH in transcriptional activation of the Cd-induced DNA damage response (DDR) was revealed, as the Cd-induced upregulation of DDR-related genes was either less pronounced or completely abolished in leaves of the GSH-deficient mutants. • Phytochelatin biosynthesis remains important upon prolonged cadmium exposure. • Glutathione is involved in regulating nutrient homeostasis upon cadmium exposure. • Glutathione affects cell cycle regulation in control and cadmium-exposed plants. • Glutathione levels affect the cadmium-induced DNA damage response. [ABSTRACT FROM AUTHOR]

Highlights • Leaf position can be used as an alternative for leaf age in cell cycle analysis. • Concentrations of nuclei in leaf extracts are a proxy for effects on cell division. • Cadmium inhibits cell division and endoreduplication in Arabidopsis thaliana leaves. • Cadmium induces SIAMESE-RELATED gene expression in Arabidopsis thaliana leaves. Abstract Cadmium (Cd) is well known to inhibit vegetative plant growth. However, knowledge regarding its influence on the cell cycle is scarce and mainly limited to cell cultures and root tissue. Therefore, the main aim of this study was to investigate the effects of Cd exposure on cell division and endoreduplication in Arabidopsis thaliana leaves. In order to do so, we first investigated whether different leaves of the same rosette harvested at one time point ( i.e. leaf position) could be used as an alternative for leaf age when investigating the cell cycle. To this end, wild-type A. thaliana plants were grown hydroponically with or without the addition of 5 μM CdSO 4. Leaf growth and development, cell division, endoreduplication and the expression of cell cycle-related genes were investigated in separate leaves. The results show that different leaf positions constitute a developmental series that can be used to deduce the development of a single leaf over time. Furthermore, our data indicate that the concentration of nuclei in leaf extracts measured via flow cytometry can be used as a proxy to determine the effects of stress factors on the extent of cell division in A. thaliana leaves, reducing the need to perform time consuming microscopic analyses. Finally, we show that Cd exposure significantly reduces cell number, cell size and nuclear DNA content, implying an inhibition of both cell division and endoreduplication. These effects accumulate over time and contribute to the Cd-induced disturbance of leaf growth and development. At the molecular and cellular level, Cd increases hydrogen peroxide levels and induces the expression of marker genes for oxidative stress and DNA damage and genes encoding CDK inhibitors of the SIAMESE-RELATED family, suggesting that the Cd-induced inhibition of cell cycle progression is intertwined with oxidative stress and subsequent DNA damage. [ABSTRACT FROM AUTHOR]

• Non-optimal temperatures result in stress-related decreased growth rates. • Stress-related conditions result in increased starch and soluble sugars. • Lower temperatures are more stressful to L. minor compared to higher temperatures. • Lower phosphorous availability has no observable effect on starch/soluble sugars. • Light induced effects increased growth rates and also starch formation. [ABSTRACT FROM AUTHOR]

The natural accession Columbia (Col-0) is considered as the reference genome of the model plant Arabidopsis thaliana . Nonetheless, Col-0 plants are more sensitive to excess copper (Cu) and cadmium (Cd) than other widely used accessions such as Wassilewskija (Ws) plants. In the current study, this accession-specific metal sensitivity is further explored by comparing the responses in leaves of Col-0 and Ws plants exposed to excess Cu and Cd. Our results suggest that different life strategies favored by both accessions under physiological conditions affect their response to metal exposure. While Col-0 plants mainly invest in metal detoxification, Ws plants center on nutrient homeostasis. In particular, the higher expression of genes related to Cu homeostasis genes in non-exposed conditions indicates that Ws plants possess a constitutively efficient metal homeostasis. On the other hand, oxidative stress-related MAPK signaling appears to be boosted in leaves of Col-0 plants exposed to excess Cu. Furthermore, the upregulation of the glutathione (GSH) biosynthesis GSH2 gene and the increased GSH concentration after Cd exposure suggest the activation of detoxification mechanisms, such as phytochelatin production, to counteract the more severe Cd-induced oxidative stress in leaves of Col-0 plants. Exposure to Cd also led to a more pronounced ethylene signaling response in leaves of Col-0 as compared to Ws plants, which could be related to Cd-induced GSH metabolism. In conclusion, accession-specific life strategies clearly affect the way in which leaves of A. thaliana plants cope with excess Cu and Cd. [ABSTRACT FROM AUTHOR]

The resistance of crops to herbicides can be due to target site based resistance or non-target site based resistance mechanisms or a combination of both. In non-target site resistance, the detoxification efficiency plays a major role by involvement of enzymes such as P450s, GTs, GSTs and ABC transporters. The resistance of the first commercial Clearfield sunflower hybrids ( Imisun trait) to herbicides of imidazolinone group is based on a combination of both types of resistance. The target site resistance consists of a mutation in Ahasl1 gene, encoding the synthesis of the AHAS enzyme. The non-target site resistance is supposed to be due to intensified herbicide disposal and is not fully understood. The objective of this study was to detect the fast response of the glutathione-mediated detoxification system in IMI-R and IMI-S sunflower hybrids to the herbicide imazamox and to study the possible participation of GSTs in the enhancement of the hybrids' tolerance. The obtained results allow to presume that GSTs are involved in imazamox detoxification in the sunflower Imisun trait and thus contributing to its non-target site resistance. [ABSTRACT FROM AUTHOR]

Gentle remediation options (GRO), i.e. in situ stabilisation, (aided) phytoextraction and (aided) phytostabilisation, were implemented at ten European sites contaminated with trace elements (TE) from various anthropogenic sources: mining, atmospheric fallout, landfill leachates, wood preservatives, dredged-sediments, and dumped wastes. To assess the performance of the GRO options, topsoil was collected from each field trial, potted, and cultivated with lettuce ( Lactuca sativa L.) for 48 days. Shoot dry weight (DW) yield, photosynthesis efficiency and major element and TE concentrations in the soil pore water and lettuce shoots were measured. GRO implementation had a limited effect on TE concentrations in the soil pore water, although use of multivariate Co-inertia Analysis revealed a clear amelioration effect in phytomanaged soils. Phytomanagement increased shoot DW yield at all industrial and mine sites, whereas in agricultural soils improvements were produced in one out of five sites. Photosynthesis efficiency was less sensitive than changes in shoot biomass and did not discriminate changes in soil conditions. Based on lettuce shoot DW yield, compost amendment followed by phytoextraction yielded better results than phytostabilisation; moreover shoot ionome data proved that, depending on initial soil conditions, recurrent compost application may be required to maintain crop production with common shoot nutrient concentrations. [ABSTRACT FROM AUTHOR]

Plant growth promoting (PGP) bacterial strains possess different mechanisms to improve plant development under common environmental stresses, and are therefore often used as inoculants in soil phytoremediation processes. The aims of the present work were to study the effects of a collection of plant growth promoting bacterial strains on plant development, antioxidant enzyme activities and nutritional status of Cytisus striatus and/or Lupinus luteus plants a) growing in perlite under non-stress conditions and b) growing in diesel-contaminated soil. For this, two greenhouse experiments were designed. Firstly, C. striatus and L. luteus plants were grown from seeds in perlite, and periodically inoculated with 6 PGP strains, either individually or in pairs. Secondly, L. luteus seedlings were grown in soil samples of the A and B horizons of a Cambisol contaminated with 1.25% (w/w) of diesel and inoculated with best PGP inoculant selected from the first experiment. The results indicated that the PGP strains tested in perlite significantly improved plant growth. Combination treatments provoked better growth of L. luteus than the respective individual strains, while individual inoculation treatments were more effective for C. striatus . L. luteus growth in diesel-contaminated soil was significantly improved in the presence of PGP strains, presenting a 2-fold or higher increase in plant biomass. Inoculants did not provoke significant changes in plant nutritional status, with the exception of a subset of siderophore-producing and P-solubilising bacterial strains that resulted in significantly modification of Fe or P concentrations in leaf tissues. Inoculants did not cause significant changes in enzyme activities in perlite experiments, however they significantly reduced oxidative stress in contaminated soils suggesting an improvement in plant tolerance to diesel. Some strains were applied to non-host plants, indicating a non-specific performance of their plant growth promotion. The use of PGP strains in phytoremediation may help plants to overcome contaminant and other soil stresses, increasing phytoremediation efficiency. [ABSTRACT FROM AUTHOR]

When terrestrial environments get contaminated with long-lived gamma emitting radionuclides, plants that grow in these contaminated areas are exposed to gamma radiation during consecutive generations. Therefore it is important to evaluate the gamma induced stress response in plants in and between generations. The objective of this research is to reveal differences at the level of the antioxidative stress response between generations with a different radiation history. An experiment was conducted in which 7-days old Arabidopsis thaliana plants were exposed for 14 days to four different gamma dose rates: 22 mGy/h, 38 mGy/h, 86 mGy/h and 457 mGy/h. Two different plant groups were used: plants that were not exposed to gamma radiation before (P0) and plants that received the aforementioned gamma treatment during their previous generation (S1). Growth, the concentration of the antioxidants ascorbate and glutathione, a number of antioxidative enzyme activities and their gene transcript levels were analysed. A dose-rate dependent induction was seen for catalase (CAT) and guaiacol peroxidase (GPX) in the roots and for syringaldazine peroxidase (SPX) in the shoots. Differences between the two generations were observed for CAT and GPX in the roots, where a significantly higher activity of these reactive oxygen species (ROS) detoxifying enzymes was observed in the S1 generation. For SPX in the shoots, a dose dependent upregulation was observed in the P0 generation. However, high SPX activities were present for all doses in the S1 generation. These differences in enzyme activity between generations for SPX and GPX and the involvement of these enzymes in cell wall biosynthesis, suggest an important role for cell wall strengthening in the response to gamma irradiation. [ABSTRACT FROM AUTHOR]

The mitochondrial alternative oxidase (AOX) is suggested to modulate metabolic homeostasis and is activated at transcript and protein level in cadmium (Cd)-exposed Arabidopsis thaliana plants. In this study, the importance of AOX in the metabolic response to Cd stress was investigated. Primary metabolites were determined in roots and leaves of wild-type plants and aox1a knockout mutants exposed to sublethal Cd concentrations for 24 and 72 h. Additional parameters (gene expression, enzyme capacity) were included to support the results at the metabolic level. Whereas sugar and organic acid levels initially dropped in roots, the opposite was observed in leaves of both genotypes exposed to Cd. Regarding genotype-related differences in the leaves, our results strengthen the previously proposed link between AOX1a and ethylene. Furthermore, respiratory flux dependent on amino acid degradation could be related to AOX1a function in leaves of Cd-exposed plants. In roots, a relation between AOX1a and antioxidative defence – in particular glutathione (GSH) – is demonstrated during Cd exposure. In conclusion, A. thaliana plants show a tissue-specific response to sublethal Cd exposure, with a differential role for AOX1a in roots and leaves. [ABSTRACT FROM AUTHOR]

Anthropogenic activities have led to a widespread uranium (U) contamination in many countries. The toxic effects of U at the cellular level have mainly been investigated at a pH around 5.5, the optimal pH for hydroponically grown plants. However, since the speciation of U, and hence its toxicity, is strongly dependent on environmental factors such as the pH, it is important to investigate the effects of U at different environmentally relevant pH levels. Although U is poorly translocated from the roots to the shoots, resulting in a low U concentration in the leaves, it has been demonstrated that toxic effects in the leaves were already visible after 1 day exposure at pH 5.5, although only when exposed to relatively high U concentrations (100 μM). Therefore, the present study aimed to analyse the effects of different U concentrations (ranging from 0 to 100 μM) at pH 4.5 in leaves of Arabidopsis thaliana plants. Results indicate that U induces early senescence in A. thaliana leaves as was suggested by a decreased expression of CAT2 accompanied by an induction of CAT3 expression, a decreased CAT capacity and an increased lipid peroxidation. In addition, miRNA398b/c is involved in the regulation of the SOD response in the leaves. As such, an increased MIR398b/c expression was observed leading to a decreased transcript level of CSD1 / 2 . Finally, the biosynthesis of ascorbate was induced after U exposure. This can point towards an important role for this metabolite in the scavenging of reactive oxygen species under U stress. [ABSTRACT FROM AUTHOR]

Silver nanoparticles hold great promise as effective anti-microbial compounds in a myriad of applications but may also pose a threat to non-target bacteria and fungi in the environment. Because microorganisms are involved in extensive interactions with many other organisms, these partner species are also prone to indirect negative effects from silver nanoparticles. Here, we focus on the effects of nanosilver exposure in the rhizosphere. Specifically, we evaluate the effect of 100 mg kg −1 silver nanoparticles on maize plants, as well as on the bacteria and fungi in the plant's rhizosphere and the surrounding bulk soil. Maize biomass measurements, microbial community fingerprints, an indicator of microbial enzymatic activity, and carbon use diversity profiles are used. Hereby, it is shown that 100 mg kg −1 silver nanoparticles in soil increases maize biomass, and that this effect coincides with significant alterations of the bacterial communities in the rhizosphere. The bacterial community in nanosilver exposed rhizosphere shows less enzymatic activity and significantly altered carbon use and community composition profiles. Fungal communities are less affected by silver nanoparticles, as their composition is only slightly modified by nanosilver exposure. In addition, the microbial changes noted in the rhizosphere were significantly different from those noted in the bulk soil, indicated by different nanosilver-induced alterations of carbon use and community composition profiles in bulk and rhizosphere soil. Overall, microorganisms in the rhizosphere seem to play an important role when evaluating the fate and effects of silver nanoparticle exposure in soil, and not only is the nanosilver response different for bacteria and fungi, but also for bulk and rhizosphere soil. Consequently, assessment of microbial populations should be considered an essential parameter when investigating the impacts of nanoparticle exposure. [ABSTRACT FROM AUTHOR]

Human activity has led to an increasing amount of radionuclides in the environment and subsequently to an increased risk of exposure of the biosphere to ionising radiation. Due to their high linear energy transfer, α-emitters form a threat to biota when absorbed or integrated in living tissue. Among these, 241 Am is of major concern due to high affinity for organic matter and high specific activity. This study examines the dose-dependent biological effects of α-radiation delivered by 241 Am at the morphological, physiological and molecular level in 14-day old seedlings of Arabidopsis thaliana after hydroponic exposure for 4 or 7 days. Our results show that 241 Am has high transfer to the roots but low translocation to the shoots. In the roots, we observed a transcriptional response of reactive oxygen species scavenging and DNA repair pathways. At the physiological and morphological level this resulted in a response which evolved from redox balance control and stable biomass at low dose rates to growth reduction, reduced transfer and redox balance decline at higher dose rates. This situation was also reflected in the shoots where, despite the absence of a transcriptional response, the control of photosynthesis performance and redox balance declined with increasing dose rate. The data further suggest that the effects in both organs were initiated in the roots, where the highest dose rates occurred, ultimately affecting photosynthesis performance and carbon assimilation. Though further detailed study of nutrient balance and 241 Am localisation is necessary, it is clear that radionuclide uptake and distribution is a major parameter in the global exposure effects on plant performance and health. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) induces the generation of reactive oxygen species (ROS) and stimulates ethylene biosynthesis. The phytohormone ethylene is a regulator of many developmental and physiological plant processes as well as stress responses. Previous research indicated various links between ethylene signalling and oxidative stress. Our results support a correlation between the Cd-induced oxidative challenge and ethylene signalling in Arabidopsis thaliana leaves. The effects of 24 or 72 h exposure to 5 μM Cd on plant growth and several oxidative stress-related parameters were compared between wild-type (WT) and ethylene insensitive mutants ( etr1-1 , ein2-1 , ein3-1 ). Cadmium-induced responses observed in WT plants were mainly affected in etr1-1 and ein2-1 mutants, of which the growth was less inhibited by Cd exposure as compared to WT and ein3-1 mutants. Both etr1-1 and ein2-1 showed a delayed response in the glutathione (GSH) metabolism, including GSH levels and transcript levels of GSH synthesising and recycling enzymes. Furthermore, the expression of different oxidative stress marker genes was significantly lower in Cd-exposed ein2-1 mutants, evidencing that ethylene signalling is involved in early responses to Cd stress. A model for the cross-talk between ethylene signalling and oxidative stress is proposed. [ABSTRACT FROM AUTHOR]

The stress hormone ethylene is known to be crucial for the survival of adverse environmental stimuli. Cadmium (Cd), a toxic metal, increases ethylene biosynthesis through an upregulated expression of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) isozymes, ACS2 and ACS6. In this study, wild-type (WT) and acs2-1acs6-1 double KO-mutant Arabidopsis thaliana plants were exposed to moderate (5 μM) and more severe (10 μM) Cd stress. The short-term influence of the Cd-induced ethylene production on growth and different oxidative stress parameters, and the consequent long-term influence on plant acclimation were investigated. Short-term moderate Cd stress conditions elicited enhanced stress-related responses in WT plants compared to the acs2-1acs6-1 mutants. The fresh weight of acs2-1acs6-1 mutant leaves was higher compared to the WT after 72 h exposure to moderate Cd stress. The transcript levels of pro-oxidative and oxidative stress marker genes as well as the expression of GSH1 and GSH2 , the enzymes synthesising the antioxidative metabolite glutathione (GSH) were lower in the acs2-1acs6-1 mutant plants compared to the WT. This also resulted in a lower GSH content in the leaves of the acs2-1acs6-1 mutant plants. Severe stress apparently overwhelmed the stress signal sensing system of both genotypes, overruling most of these different responses. Long-term exposure to moderate and severe Cd stress inhibited root and leaf development as well as the reproductive capacity of WT and acs2-1acs6-1 mutant plants without inducing differences between both genotypes, suggesting ethylene independence. We can conclude that ethylene plays an important role in the early oxidative challenge induced by moderate Cd stress in A. thaliana . [ABSTRACT FROM AUTHOR]

The impact of soil metal pollution on plant communities has been studied extensively in the past. However, very little is known about the fungal species that co-occur with these plant communities on metal polluted soils. We characterized the belowground fungal community in a heavy metal polluted and a non-polluted soil using 454 pyrosequencing. The fungal communities at both study sites were shown to consist mainly of the same ectomycorrhizal species, but a consistent shift in the relative abundances of these species was observed, whereas no differences in fungal diversity were found. In metal polluted soil, root tips of young pines were initially largely colonized by stress-tolerant dark Ascomycota that were mostly replaced by metal-tolerant Basidiomycota within 2 years. Compared to older forests, a low belowground fungal diversity was observed in the two pioneer stands. [ABSTRACT FROM AUTHOR]

The biosphere is constantly exposed to ionising radiation, due to cosmic radiation and the presence of natural and anthropogenic radionuclides in the environment. The biological effects of the resulting radiation exposure are currently poorly understood in plants, due to a large influence of parameters such as species, cultivar, experimental setup and plant age on the response. In this study, 7-, 10- and 14-day - old Arabidopsis thaliana seedlings were exposed to 96 h and 168 h of 100 mGy h −1 chronic γ-radiation in a hydroponic setup. The response of growth, photosynthesis and the transcription of genes involved in DNA repair, cell cycle and signalling were measured. The results show that there is a difference in growth response between plants of different ages and decreasing radiosensitivity with increasing seedling age. This is linked to differences in regulation of DNA repair and cell cycle control at the transcriptional level. [ABSTRACT FROM AUTHOR]

During the past decades a number of field trials with gentle remediation options (GRO) have been established on trace element (TE) contaminated sites throughout Europe. Each research group selects different methods to assess the remediation success making it difficult to compare efficacy between various sites and treatments. This study aimed at selecting a minimum risk assessment battery combining chemical and ecotoxicological assays for assessing and comparing the effectiveness of GRO implemented in seven European case studies. Two test batteries were pre-selected; a chemical one for quantifying TE exposure in untreated soils and GRO-managed soils and a biological one for characterizing soil functionality and ecotoxicity. Soil samples from field studies representing one of the main GROs (phytoextraction in Belgium, Sweden, Germany and Switzerland, aided phytoextraction in France, and aided phytostabilization or in situ stabilization/phytoexclusion in Poland, France and Austria) were collected and assessed using the selected test batteries. The best correlations were obtained between NH 4 NO 3 -extractable, followed by NaNO 3 -extractable TE and the ecotoxicological responses. Biometrical parameters and biomarkers of dwarf beans were the most responsive indicators for the soil treatments and changes in soil TE exposures. Plant growth was inhibited at the higher extractable TE concentrations, while plant stress enzyme activities increased with the higher TE extractability. Based on these results, a minimum risk assessment battery to compare/biomonitor the sites phytomanaged by GROs might consist of the NH 4 NO 3 extraction and the bean Plantox test including the stress enzyme activities. [ABSTRACT FROM AUTHOR]

This study aims to uncover the spatiotemporal involvement of glutathione (GSH) in two major mechanisms of cadmium (Cd)-induced detoxification (i.e. chelation and antioxidative defence). A kinetic study was conducted on hydroponically grown Arabidopsis thaliana (L. Heyhn) to gain insight into the early events after exposure to Cd. Cadmium detoxification was investigated at different levels, including gene transcripts, enzyme activities and metabolite content. Data indicate a time-dependent response both within roots and between plant organs. Early on in roots, GSH was preferentially allocated to phytochelatin (PC) synthesis destined for Cd chelation. This led to decreased GSH levels, without alternative pathways activated to complement GSH's antioxidative functions. After one day however, multiple antioxidative pathways increased including superoxide dismutase (SOD), ascorbate (AsA) and catalase (CAT) to ensure efficient neutralization of Cd-induced reactive oxygen species (ROS). As a consequence of Cd retention and detoxification in roots, a delayed response occurred in leaves. Together with high leaf thiol contents and possibly signalling responses from the roots, the leaves were protected, allowing them sufficient time to activate their defence mechanisms. [ABSTRACT FROM AUTHOR]

To study the impact of environmental uranium (U) contamination, effects should be analysed at different environmentally relevant pH levels as the speciation of U, and hence its toxicity, is strongly dependent on the pH. As photosynthesis is a major energy producing process in plants intimately connected to plant growth and known to be susceptible to metal stress, the effects of different U concentrations on photosynthesis in 18-day-old Arabidopsis thaliana (Columbia ecotype) are investigated at two contrasting pH levels, pH 4.5 and pH 7.5. At pH 4.5, U is highly taken up by the roots but is poorly translocated to the shoots, while at pH 7.5, less U is taken up but the translocation is higher. The lower U concentrations in the shoots at pH 4.5 are accompanied by a more reduced leaf growth as compared to pH 7.5. In addition, U does not influence the photosynthetic machinery at pH 7.5, while an optimization of the photosynthesis takes place after U exposure at pH 4.5. As such, more of the absorbed quanta are effectively used for photosynthesis accompanied by a decreased non-photochemical quenching and an increased electron transport rate. Since the enhanced photosynthesis at pH 4.5 is accompanied by a decreased growth, we suggest that the energy produced during photosynthesis is used for defence reactions against U-induced oxidative stress rather than for growth. As such, a high discrepancy was observed between the two pH levels, with an optimized photosynthetic apparatus at pH 4.5 and almost no effects at pH 7.5. [ABSTRACT FROM AUTHOR]

Abstract: Treatment and/or disposal of metal contaminated biomass are still an unsolved problem. Knowledge of the metal distribution is of prime importance concerning the application of pyrolysis product streams. Sorghum bicolor (L.) Moench was cultivated in a semi-hydroponic system to assess its potential use in phytoremediation and biomass production. Plants were grown in a greenhouse using perlite as substrate, half-strength Hoagland's solution as control (CTR) and the same solution supplemented with a mixture of Ni and Zn (CTM; 10 g m−3 each). Shoot and root biomass were determined and analyzed for their metals content. Flash and slow pyrolysis were performed on S. bicolor shoots at 450 °C. Biomass and pyrolysis products were analyzed focusing on metal distribution. Mass and energy balances were determined. S. bicolor delivered good shoot biomass with relatively moderate concentrations of Ni and Zn. Metal concentrations in the pyrolysis oils were below detection limits and almost all metals accumulated in the char. In fact, 99% of Ni and 98% of Zn were recovered in the char when a slow pyrolysis process was applied, while in flash pyrolysis conditions both metals were found back in the char and in the heating transfer medium. Furthermore, the percentages of char and oil were higher in slow pyrolysis compared to flash pyrolysis. Energy recovery in the char from slow pyrolysis was higher than flash pyrolysis. Flash and slow pyrolysis can likely offer a valuable processing method for metal contaminated biomass, thus limiting the waste disposal problem associated with phytoremediation of metals. [Copyright &y& Elsevier]

Abstract: Plant growth and development can be highly restricted by environmental stressors such as cadmium (Cd) pollution. The mitochondrial non-phosphorylating alternative respiratory pathway, mediated by alternative oxidase (AOX), alternative NAD(P)H dehydrogenases (NDs) and uncoupling protein (UCP), was suggested to be crucial in the acclimation of plants to fluctuating environmental conditions. Therefore, we examined the effects of environmentally realistic Cd exposure (5 and 10μM) on the alternative respiratory chain in Arabidopsis thaliana using a kinetic exposure setup. We demonstrated that during exposure to Cd, Arabidopsis seedlings show a mitochondrial oxidative challenge to which they acutely respond by increasing the transcript level of several AOX, ND and UCP isoforms in both roots and leaves. In addition, AOX protein levels increased during acute Cd exposure (2 and 24h). Based on our data, we suggest the formation of a condensed non-phosphorylating electron transport chain (ETC) functioning through cytosolic NDs and AOX, with co-regulation of ND and AOX expression during Cd stress. Therefore, both enzymes might cooperate in the potential acclimation of Arabidopsis seedlings to environmentally realistic Cd exposure by modulating the extent of mitochondrial ROS production. [Copyright &y& Elsevier]

Abstract: Phytoextraction makes use of trace element-accumulating plants that concentrate the pollutants in their tissues. Pollutants can be then removed by harvesting plants. The success of phytoextraction depends on trace element availability to the roots and the ability of the plant to intercept, take up, and accumulate trace elements in shoots. Current phytoextraction practises either employ hyperaccumulators or fast-growing high biomass plants; the phytoextraction process may be enhanced by soil amendments that increase trace element availability in the soil. This review will focus on the role of plant-associated bacteria to enhance trace element availability in the rhizosphere. We report on the kind of bacteria typically found in association with trace element – tolerating or – accumulating plants and discuss how they can contribute to improve trace element uptake by plants and thus the efficiency and rate of phytoextraction. This enhanced trace element uptake can be attributed to a microbial modification of the absorptive properties of the roots such as increasing the root length and surface area and numbers of root hairs, or by increasing the plant availability of trace elements in the rhizosphere and the subsequent translocation to shoots via beneficial effects on plant growth, trace element complexation and alleviation of phytotoxicity. An analysis of data from literature shows that effects of bacterial inoculation on phytoextraction efficiency are currently inconsistent. Some key processes in plant–bacteria interactions and colonization by inoculated strains still need to be unravelled more in detail to allow full-scale application of bacteria assisted phytoremediation of trace element contaminated soils. [Copyright &y& Elsevier]

Abstract: Lipoxygenases (LOXes, EC 1.13.11.12) are involved in growth, development and responses to stress. Earlier results suggested a role in stress generation, signalling and/or responses when Arabidopsis thaliana is exposed to cadmium (Cd), and expression of the cytosolic LOX1 was highly upregulated in the roots after Cd exposure. To investigate the involvement of LOX1 in early metal stress responses, three-week-old wild-type and lox1-1 mutant A. thaliana plants were acutely (24 h) exposed to realistic Cd concentrations (5 and 10 μM) and several oxidative stress and signalling related parameters were studied at transcriptional and biochemical levels. Transcription of several genes encoding ROS producing and scavenging enzymes failed to be induced up to wild-type levels after Cd exposure. Expression of 9-LOX enzymes was inhibited in lox1-1 mutant roots due to lack of functional LOX1 and downregulated LOX5 expression, and the lox1-1 mutation also interfered with the expression of genes involved in jasmonate biosynthesis. LOX1 and RBOHD may be involved in stress signalling from roots to shoots, as the induction of APX2 expression, which is dependent on RBOHD activity, was disrupted in lox1-1 while RBOHD failed to be upregulated. A different pattern of H2O2 production and ascorbate and glutathione levels in lox1-1 mutants after Cd exposure may have indirectly influenced gene expression patterns. Although indirect effects of the lox1-1 mutation on gene expression complicate the determination of exact sensing – signalling – response pathways, the results presented here outline a more refined LOX1 functioning in Cd-induced stress responses that could be used in studies determining the exact involvement of LOX1 in these pathways. [Copyright &y& Elsevier]

Abstract: Zinc (Zn) is an essential micronutrient for plants, but accumulation of excess Zn causes oxidative stress, even though the element is not redox-active. An oxidative stress signature, consisting of multiple oxidative stress related parameters, is indicative of disturbance of redox homeostasis and signaling, but has not been determined after exposure to excess Zn. To reveal general and Zn-specific effects, changes in oxidative stress related gene expression, enzyme activities and metabolites were determined after 24h exposure of Arabidopsis thaliana plants to a concentration range of 0, 100, 250 or 500μM excess ZnSO4, and the oxidative stress signature compared to the ones reported previously for cadmium or copper exposure in the same experimental system. Zn accumulated in both roots and leaves, which led to a disturbed redox homeostasis as evident from increased H2O2 levels and altered glutathione redox state. In roots, magnesium uptake was affected and glutathione levels decreased due to reduced glutathione reductase activity and increased phytochelatin production. In leaves, mRNA levels of all chloroplast-localized superoxide dismutases (SOD) were downregulated, indicating that the converse regulation by Cu availability of FeSOD (FSD) and Cu/ZnSOD genes (CSDs) was disturbed. Furthermore, an opposite stress-dependent transcriptional regulation of the different loci of a miRNA species was observed: excess Zn repressed primary transcripts of the MIR398a gene, but increased MIR398b and MIR398c transcription. Also, accumulation of mRNA was inhibited for CSD2, but stimulated for CSD1. MiR398 has been reported to downregulate CSD1 and CSD2 mRNA. Here, the opposite effect on CSD1 and CSD2 mRNA accumulation under Zn stress in the leaves could be explained if CSD1 in the leaves would be regulated exclusively by miR398a, and not by miR398b/c under these conditions. The results support the existence of Zn-specific signal transduction pathways influencing anti-oxidative responses and are useful as a starting point for genetic screens identifying upstream metal-specific sensing and signaling mechanisms. [Copyright &y& Elsevier]

Abstract: Metals, like cadmium (Cd) and copper (Cu), have the ability to induce the production of reactive oxygen species (ROS) at the cellular level. It is widely known that these ROS can cause irreversible damage to cellular components, like DNA, proteins and lipids. On the other hand, ROS can also act as signaling molecules and in this way they play an essential role in many normal physiological processes, but also in defense responses against stress. ROS signaling in plants uses mitogen-activated protein kinase (MAPK) pathways leading to the transcriptional control of target genes involved in the scavenging or production of ROS. Here, oxidative signaling induced by exposure to excess Cd or Cu was investigated in relation to anti-oxidative defense responses to these metals. Three-week-old Arabidopsis thaliana plants were exposed to environmentally realistic concentrations of Cu and Cd and immediate responses were measured at the level of hydrogen peroxide (H2O2) content, lipid peroxidation and transcript levels of genes involved in ROS homeostasis and signaling. Our findings show immediate (after 2h exposure) effects in the roots following Cu exposure, whereas effects in the leaves were generally more delayed. Effects of Cd exposure in leaves and roots were observed only after 24h exposure. On one hand, exposure of roots to Cu leads via activation of NADPH oxidases and Fenton reactions to H2O2 production that can induce MAPK and oxylipin signaling to control the cellular redox status. On the other hand, conversion of H2O2 to the more damaging hydroxyl radical by Fenton and Haber–Weiss reactions can initiate lipid peroxidation leading to membrane damage. In roots exposed to elevated Cd concentrations only oxidative signaling was initiated, possibly via NADPH oxidase-mediated ROS production. In leaves, time-dependent activation of MAPK and oxylipin signaling was seen after exposure to both metals, Cu or Cd, independent of changes in H2O2 content. [Copyright &y& Elsevier]

Abstract: Plants exposed to cadmium (Cd) show morphological and physiological disorders. To increase our knowledge regarding Cd-induced signalling, most often the effects of acute exposure are investigated. However, this does not allow in-depth analysis of morphological effects. Therefore, we chronically exposed Arabidopsis thaliana plants to environmentally realistic Cd concentrations (5 or 10 μM) and, using a described phenotypic framework methodology, we determined the impact of Cd on the plant’s ability to complete its life cycle and produce germinative seeds. Visible Cd-induced morphological changes were observed within a short exposure period, with chlorotic and anthocyanous leaf colouring occurring dose-dependently. Although rosette growth was severely reduced in Cd-exposed plants, all plants were able to emerge inflorescences and produce siliques containing germinative seeds, thus confirming the non-lethality of the used Cd concentrations. Although the growth inhibition of Cd-exposed plants was dependent on the dose, both concentrations had similar effects on inflorescence height and silique counts. In conclusion, vegetative growth of plants chronically exposed to Cd is inhibited in a concentration-dependent manner. However, the effect on plant regeneration is clearly stress-determined but independent on the Cd concentration applied. In Arabidopsis thaliana, vegetative and reproductive growth are differentially influenced by Cd. [Copyright &y& Elsevier]