Behavior of Silene vulgaris (Moench.) Garcke against exposure to chromium. Evaluation of potential use in soil remediation

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Agrícola. Fecha de lectura: 17-07-201

Fungal-associated NO is involved in the regulation of oxidative stress during rehydration in lichen symbiosis

[EN] Background Reactive oxygen species (ROS) are normally produced in respiratory and photosynthetic electron chains and their production is enhanced during desiccation/rehydration. Nitric oxide (NO) is a ubiquitous and multifaceted molecule involved in cell signaling and abiotic stress. Lichens are poikilohydrous organisms that can survive continuous cycles of desiccation and rehydration. Although the production of ROS and NO was recently demonstrated during lichen rehydration, the functions of these compounds are unknown. The aim of this study was to analyze the role of NO during rehydration of the lichen Ramalina farinacea (L.) Ach., its isolated photobiont partner Trebouxia sp. and Asterochloris erici (Ahmadjian) Skaloud et Peksa (SAG 32.85 = UTEX 911). Results Rehydration of R. farinacea caused the release of ROS and NO evidenced by the fluorescent probes DCFH2-DA and DAN respectively. However, a minimum in lipid peroxidation (MDA) was observed 2 h post-rehydration. The inhibition of NO in lichen thalli with c-PTIO resulted in increases in both ROS production and lipid peroxidation, which now peaked at 3 h, together with decreases in chlorophyll autofluorescence and algal photobleaching upon confocal laser incidence. Trebouxia sp. photobionts generate peaks of NO-endproducts in suspension and show high rates of photobleaching and ROS production under NO inhibition which also caused a significant decrease in photosynthetic activity of A. erici axenic cultures, probably due to the higher levels of photo-oxidative stress. Conclusions Mycobiont derived NO has an important role in the regulation of oxidative stress and in the photo-oxidative protection of photobionts in lichen thalli. The results point to the importance of NO in the early stages of lichen rehydration.This project was funded by the Spanish Ministry of Education and Science [project numbers CGL2006 12917 C02 0 and CGL2009 13429 C02 01], project Prometeo 2008/1/4 of the Generalitat Valenciana and the project AECID PCI/A/024755/09 of the Spanish Ministry of Foreign Affaires. We are grateful to F. Gasulla, J. Gimeno-Romeu, E. Barreno, (ICBIBE, University of Valencia) and A. Guera (Plant Biology, University of Alcala) for communicating unpublished data, to Dr. R. Catala (CIB, Madrid), Dr. P. D'Ocon (UVEG, Valencia) and Dr. J. Medina (INIA, Madrid) for critical revision of the manuscript, and J. L. Rodriguez Gil for MDA protocol optimization. English revision was done by Wendy Ran.Catalá, M.; Gasulla Vidal, F.; Pradas Del Real, AE.; García-Breijo, F.; Reig Armiñana, J.; Barreno Rodriguez, E. (2010). Fungal-associated NO is involved in the regulation of oxidative stress during rehydration in lichen symbiosis. BMC Microbiology. 10. https://doi.org/10.1186/1471-2180-10-297S1

Apports des techniques spectroscopiques en biologie végétale

International audienceAlthough spectroscopic techniques based on very large research infrastructures are commonly used in disciplines such as physics or material sciences, they are less common among plant biologists. However, they give access to information that can greatly advance our understanding of biological mechanisms. Micro X-ray fluorescence micro-spectroscopy (μXRF) based on synchrotron radiation makes it possible to obtain elemental distribution maps with a lateral resolution down to submicrometer scale and high sensitivity. In compliment to μXRF, some synchrotron beamlines have the capability to perform micro-X-ray absorption spectroscopy (µXAS) analysis. This technique allows to probe the local structure of the element of interest and to determine its oxidation state and its ligands. This is for example very useful in ecotoxicology to understand the behavior and fate of a contaminant to better evaluate its bioavailability and possible impacts on the environment. Alternatively, in agronomy this information can be used to improve plant nutrition. These techniques are, however, extremely dependent on a proper sample preparation. For about ten years, much progress has been made both on the equipment of synchrotron beamlines and on the sample preparation techniques to take into account the particular nature of biological samples (highly hydrated, fragile and sensitive to radiation). These different points will be developed through the example of plants (Lactuca sativa, lettuce) exposed to a foliar iron salt supply and addition of silver nanoparticles

Distinguishing Engineered TiO2 Nanomaterials from Natural Ti Nanomaterials in Soil Using spICP-TOFMS and Machine Learning

International audienceABSTRACT: Identifying engineered nanomaterials (ENMs) made from earth-abundant elements in soils is difficult because soil also contains natural nanomaterials (NNMs) containing similar elements. Here, machine learning models using elemental fingerprints and mass distributions of three TiO2 ENMs and Ti-based NNMs recovered from three natural soils measured by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) was used to identify TiO2 ENMs in soil. Synthesized TiO2 ENMs were unassociated with other elements (>98%), while 40% of Ti-based ENM particles recovered from wastewater sludge had distinguishable elemental associations. All Ti-based NNMs extracted from soil had a similar chemical fingerprint despite the soils being from different regions, and >60% of Ti-containing NNMs had no measurable associated elements. A machine learning model best distinguished NNMs and ENMs when differences in Ti-mass distribution existed between them. A trained LR model could classify 100 nm TiO2 ENMs at concentrations of 150 mg kg−1 or greater. The presence of TiO2 ENMs in soil could be confirmed using this approach for most ENM-soil combinations, but the absence of a unique chemical fingerprint in a large fraction of both TiO2 ENMs and Ti-NNMs increases model uncertainty and hinders accurate quantification

Apports des techniques spectroscopiques en biologie végétale

International audienceAlthough spectroscopic techniques based on very large research infrastructures are commonly used in disciplines such as physics or material sciences, they are less common among plant biologists. However, they give access to information that can greatly advance our understanding of biological mechanisms. Micro X-ray fluorescence micro-spectroscopy (μXRF) based on synchrotron radiation makes it possible to obtain elemental distribution maps with a lateral resolution down to submicrometer scale and high sensitivity. In compliment to μXRF, some synchrotron beamlines have the capability to perform micro-X-ray absorption spectroscopy (µXAS) analysis. This technique allows to probe the local structure of the element of interest and to determine its oxidation state and its ligands. This is for example very useful in ecotoxicology to understand the behavior and fate of a contaminant to better evaluate its bioavailability and possible impacts on the environment. Alternatively, in agronomy this information can be used to improve plant nutrition. These techniques are, however, extremely dependent on a proper sample preparation. For about ten years, much progress has been made both on the equipment of synchrotron beamlines and on the sample preparation techniques to take into account the particular nature of biological samples (highly hydrated, fragile and sensitive to radiation). These different points will be developed through the example of plants (Lactuca sativa, lettuce) exposed to a foliar iron salt supply and addition of silver nanoparticles.Si les techniques spectroscopiques basées sur les très grandes infrastructures de recherche (TGIR) sont couramment utilisées dans des disciplines telles que la physique ou encore les sciences des matériaux, elles sont moins répandues chez les biologistes. Elles permettent pourtant d’accéder à des informations qui peuvent faire grandement avancer notre compréhension des mécanismes biologiques. La micro-spectroscopie par fluorescence X (µXRF) basée sur le rayonnement synchrotron permet de réaliser des cartographies élémentaires avec une résolution latérale pouvant descendre à quelques centaines de nanomètres et une grande sensibilité. En parallèle à la µXRF, certaines lignes de lumière au synchrotron permettent de coupler la micro-spectroscopie d’absorption des rayons X (µXAS). Grâce à cette technique, on peut sonder la structure de l’élément d’intérêt et déterminer en particulier son état d’oxydation et ses ligands. C’est par exemple très utile en écotoxicologie pour comprendre le comportement et le devenir d’un contaminant pour mieux évaluer son impact sur l’environnement ou en agronomie pour enrichir des cultures en éléments minéraux. Ces techniques sont cependant extrêmement tributaires d’une bonne préparation d’échantillons. Depuis une dizaine d’années environ, de nombreux progrès ont été fait tant sur l’équipement des lignes de lumière que sur les techniques de préparation d’échantillons pour prendre en compte la nature particulière des échantillons biologiques (hautement hydratés, fragiles et sensibles aux rayonnements). Ces différents points seront développés au travers de l’exemple de plantes (Lactuca sativa, salade) exposées à un apport foliaire en fer avec ajout de nanoparticules d’argent

The Chromium Detoxification Pathway in the Multimetal Accumulator <i>Silene vulgaris</i>

Phytomanagement could be a viable alternative in areas polluted with wastes from chromium-using industries. This study investigated the ability of <i>Silene vulgaris</i> to take up Cr­(III) and Cr­(VI) with special attention on the mechanism used by this species to tolerate high doses of Cr­(VI). Plants were grown semihydroponically with different concentrations of either Cr­(III) or Cr­(VI). A combination of synchrotron X-ray spectroscopic techniques, scanning electron and light microscopy and infrared spectroscopy were used to determine the distribution and speciation of Cr. <i>S. vulgaris</i> accumulated more Cr when grown with Cr­(VI) resulting in an overall reduction in biomass. Starch accumulation in leaves may be attributed to an impartment between carbon utilization and assimilation resulted from stunted plant growth but not the complete inhibition of photosynthesis indicating that <i>S. vulgaris</i> possess tolerance mechanisms that allows it to survive in Cr­(VI) rich environments. These primary tolerance mechanisms are (a) the total reduction of Cr­(VI) to Cr­(III) in the rhizosphere or just after uptake in the fine lateral root tips and (b) chelation of Cr­(III) to the cell wall both of which reduce metal interference with critical cell functions. These mechanisms make <i>S. vulgaris</i> suitable for in situ remediation of Cr polluted soils

Silver nanoparticles and wheat roots: a complex interplay

International audienceAgricultural soils are major sinks of silver nanoparticles in the environment, and crops are directly exposed to these emerging contaminants. A clear picture of their chemical transformations, uptake and transport mechanisms, and phytotoxic impacts is still lacking. In this work, wheat plants were exposed to pristine metallic (Ag-NPs) and sulfidized (Ag$_2$S-NPs) silver nanoparticles and ionic Ag. Data on Ag distribution and speciation, phytotoxicity markers and gene expression were studied. A multi-technique and multi-scale approach was applied combining innovating tools at both laboratory and synchrotron. Various chemical transformations were observed on the epidermis and inside roots, even for Ag$_2$S-NPs, leading to an exposure to multiple Ag forms, which likely evolve over time. Genes involved in various functions including oxidative stress, defense against pathogens and metal homeostasis were impacted in different ways depending on the Ag source. This study illustrates the complexity of the toxicity pattern for plants exposed to Ag-NPs, the necessity of monitoring several markers to accurately evaluate the toxicity, and the interest of interpreting the toxicity pattern in light of the distribution and speciation of Ag

Assessing implications of nanoplastics exposure to plants with advanced nanometrology techniques

International audienceDespite the increasing attention given to the impacts of nanoplastics in terrestrial environments, there is limited data about the effects on plants, and the quantitative information on uptake. In the present study, wheat plants grown in hydroponics were exposed to Pd-doped nanoplastics. This allowed us to quantify nanoplastics uptake and translocation to the shoots. Visualization of nanoplastics in roots was performed with synchrotron micro X-ray fluorescence (µXRF). Nanoplastics accumulated on the root epidermis, especially at the root tip and in root maturation zones. A close relationship between plant roots, rhizodeposits and nanoplastics behaviour was shown. Reinforcement of the cell wall in roots was evidenced using Fourier transform infrared spectroscopy (FTIR) and synchrotron-computed microtomography (µCT). Synchrotron-computed nanotomography (nanoCT) evidenced the presence of globular structures but they could not be identified as nanoplastics since they were observed both in the control and treated roots. By utilizing the inorganic tracer in the doped-nanoplastics, this study paves the road for elucidating interactions in more complex systems by using an integrative approach combining classical phytotoxicity markers with advanced nanometrology techniques

Impact of a Model Soil Microorganism and of Its Secretome on the Fate of Silver Nanoparticles

International audienceSulfidation is a key process for silver nano-particles released from consumer products in the environment. This study focuses on the impact of a model soil microorganism , Bacillus subtilis, on the fate of pristine and already sulfidized Ag-NPs. The nanoparticles were incubated with the initial growth medium, isolated secretome, and living bacteria, and characterized for their size and morphology, agglomeration state, structure, and Ag speciation. No Ag internalization or sorption on the cell wall was detected. A partial sulfidation, leading to an Ag−Ag 2 S core−shell structure, was observed in the presence of the secretome, and the rate limiting step of the reaction was the oxidation of Ag 0 , and it was favored near the crystal dislocations. The sulfidation was complete in the presence of the living bacteria and followed an indirect pathway. Both crystalline Ag 2 S and amorphous Ag 2 S and/or Ag-thiol were identified. At the opposite, the bacteria had no impact on Ag 2 S. These results suggest that microorganisms participate in the sulfidation of Ag-NPs in aerobic systems such as unsaturated soils, and thus affect the bioavailability of Ag. It is important to take these transformations into account during exposure experiments, since they drastically change the exposure conditions. Finally, the secretome of B. subtilis might be used for the green synthesis of Ag−Ag 2 S core−shell nanoparticles

Searching for relevant criteria to distinguish natural vs. anthropogenic TiO 2 nanoparticles in soils

International audienceis one of the most produced nanomaterials. Agricultural soils are a major compartment of accumulation of TiO 2-NPs after release from consumer products into the sewer system, due to the use of sewage sludge as a soil amendment. TiO 2 is naturally present in soils, and distinguishing between anthropo-genic and natural TiO 2 in soils is thus important to assess the risks associated with the increased use of nano-TiO 2. Methods to distinguish these materials in complex matrices such as soils are currently lacking. The purpose of this study was, therefore, to search for characteristic physical and chemical properties of natural and engineered nano-TiO 2 , based on a combination of bulk, micro and nanofocused X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, X-ray diffraction and chemical analyses. Digested sewage sludge, agricultural soil and sludge-amended soil were studied by these techniques. The particle size distribution was not a relevant criterion since the sludge and the sludge-amended soil contained a variety of nanometer-and micrometer sized Ti-containing particles. Both the sludge and the soil contained a mixture of rutile and anatase, with a minor proportion of amorphous TiO 2. In the sludge, there was no trend relating particle size and Ti mineralogy. The morphology of the TiO 2 particles proved to be different in the two matrices, with smooth faceted particles in the sludge and rough irregular ones in the soil. In addition, natural TiO 2 particles were included in micro and macroaggregates of the soil and formed intricate assemblages with minerals and organic compounds. In the sludge, TiO 2 formed homo and heteroaggregates of simpler structure, richer in organic matter. Thus, the study of the morphology of TiO 2 particles and their status in unperturbed mineral-organic assemblages may provide some insights into their origin. The observed differences may attenuate over time, due to the incorporation of the sludge material within the soil structure