Interactions between plant roots and soil microorganisms in the rhizosphere are critical for plant growth. However, understanding of precisely how root exudates influence the diversity and activity of rhizosphere microorganisms is limited. The main objective of this study was to investigate the effect of radiata pine (Pinus radiata) root exudates on rhizosphere soil microbial communities, with an emphasis on the role of low molecular weight organic anions. The study involved the development and validation of new methods for investigating rhizosphere processes in a purpose-built facility. This included development of an in situ sampling technique using an anion exchange membrane strip to collect a range of organic anions exuded from radiata pine roots grown in large-scale rhizotrons. These included tartarate, quinate, formate, malate, malonate, shikimate, lactate, acetate, maleate, citrate, succinate and fumarate. Soil microbial activity and diversity were determined using dehydrogenase activity and denaturing gradient gel electrophoresis. Links between organic anions in root exudates and rhizosphere soil microbial community structures were investigated by comparing wild type and genetically modified radiata pine trees which were grown in rhizotrons for 10 months. As expected, there was considerable temporal and spatial variability in the amounts and composition of organic anions collected, and there were no consistent or significant differences determined between the two tree lines. Significant differences in rhizosphere microbial communities were detected between wild type and genetically modified pine trees; however, they were inconsistent throughout the experiment. The shifts in microbial communities could have been related to changes in exudate production and composition. Based on results from the main rhizotron experiment, a microcosm study was carried out to investigate the influence of selected pine root exudate sugars (glucose, sucrose and fructose) and organic anions (quinate, lactate and maleate) on soil microbial activity and diversity. Soil microbial activity increased up to 3-fold in all of the sugar and organic anion treatments compared to the control, except for a mixture of sugars and maleate where it decreased. The corresponding impacts on soil microbial diversity were assessed using denaturing gradient gel electrophoresis and 16S rRNA phylochips. Addition of the exudate compounds had a dramatic impact on the composition and diversity of the soil microbial community. A large number of bacterial taxa (88 to 1043) responded positively to the presence of exudate compounds, although some taxa (12 to 24) responded negatively. Organic anions had a greater impact on microbial communities than sugars, which indicated that they may have important roles in rhizosphere ecology of radiata pine. In addition, a diverse range of potentially beneficial bacterial taxa were detected in soil amended with organic anions, indicating specific regulation of rhizosphere microbial communities by root exudates. This project highlighted the considerable challenges and difficulties involved in detailed investigation of in situ rhizosphere processes. Nonetheless, the findings of this study represent a significant contribution to advancing understanding of relationships between root exudates and soil microbial diversity, which will be further enhanced by refinement and application of the specific methodologies and techniques developed.

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Submitted by Fabiana Gonçalves Pinto (benf@ndc.uff.br) on 2017-02-22T18:44:53Z No. of bitstreams: 1 Willian Alves dos Santos.pdf: 2856868 bytes, checksum: 09e364c04de604bece868531688a5915 (MD5) / Made available in DSpace on 2017-02-22T18:44:53Z (GMT). No. of bitstreams: 1 Willian Alves dos Santos.pdf: 2856868 bytes, checksum: 09e364c04de604bece868531688a5915 (MD5) Previous issue date: 2016 / Mestrado Acadêmico em Ciências do Cuidado em Saúde / A ferida neoplásica acomete cerca de 5% a 10% dos pacientes com câncer em cuidados paliativos. O foco central do cuidado dessas feridas é o controle dos sintomas, em que o odor está presente em 10,4% e o exsudato em 14,6% dos casos, sendo responsáveis pelo impacto no aspecto psicossocial do paciente. O estudo teve como objetivo de avaliar as associações entre odor, exsudato e isolamento social em pacientes com feridas neoplásicas. Trata-se de uma pesquisa quantitativa do tipo transversal prospectivo realizado com os pacientes com feridas neoplásicas no Ambulatório de cuidados paliativos do Núcleo de Atenção Oncológica do Hospital Universitário Antônio Pedro, aprovada pelo Comitê de Ética do HUAP c/nº: 183.757. A coleta de dados foi realizada durante a consulta de enfermagem pela da aplicação das escalas de odor, exsudação (Push) e escala de Likert de três dimensões para avaliação dos aspectos sociais do paciente, bem como dados contidos em prontuário para caracterização da clientela. Para a análise estatística aplicou-se o teste de normalidade Shapiro wilk, verificando que a amostra não é paramétrica (p valor ≤ 0,05) para as variáveis: tamanho da lesão, ferida total, odor total e exsudato total (escala likert) e paramétrica (p valor > 0,05) para a variável idade. Os dados foram apresentados em forma de mediana e intervalo interquartil (x ̃± Q3-Q1) para análises das variáveis não paramétricas; média e desvio padrão (x̅ ±D.P) para variável paramétrica. Realizou-se o teste de Kruskal Wallis para verificação de associação multivariada entre os dados clínicos e da escala e o teste de Spearman para verificar se o grau do odor, quantidade de exsudato, tamanho e localização da lesão apresentam correlação com a interferência da socialização do paciente. A confiabilidade da ISPOE foi medida pelo coeficiente Alfa de Cronbach. Constatou-se, então a correlação entre o grau de odor e as perguntas 1 e 5 da escala da dimensão odor. Assim, o odor interfere no constrangimento (p; 0,0053) e frequentar locais públicos (p; 0,0495). A quantidade de exsudato apresentou correlação com a primeira questão da escala da dimensão exsudato, interferindo no constrangimento (p; 0,0453). A variável tipo de ferida apresentou correlação com as questões 3 e 5, logo, interferindo na relação com a família e em frequentar locais públicos, fatores esses que favorecem o isolamento social em pacientes com feridas neoplásicas As variáveis: tamanho da lesão e local da lesão não apresentaram correlação significativa com as questões da escala na dimensão ferida. As três dimensões da escala apresentaram consistência interna satisfatória com alfa: 0,82 (dimensão ferida); 0,94 (dimensão exsudato) e 0,88 (dimensão odor). Com isso, o odor e o exsudato interferem negativamente fatores sociais e psicológicos que podem favorecer, diretamente, o isolamento social. Além do conhecimento sobre as particularidades dessas lesões e dos produtos adequados ao cuidados, é fulcral que o profissional de enfermagem conheça os principais queixas relacionadas à lesão e o impacto que causam ao cotidiano do paciente. Conhecer esse conflito social e psicológico fará toda a diferença no cuidado de enfermagem, pois, dessa forma, poderá atuar de maneira assertiva e holística no cuidado no cotidiano do paciente, enxergando-o para além dos sintomas: seus anseios psicológicos e sociais. A constatação da associação entre as variáveis poderá auxiliar a avaliação dos aspectos que podem interferir na qualidade de vida e no cuidado prestado aos pacientes com feridas neoplásicas. / Neoplastic wound affects about 5% to 10% of cancer patients in palliative care. The central focus of the care of these wounds is to control the symptoms, where the odor is present in 10.4% and exudate in 14.6% of cases, being responsible for the impact on the psychosocial aspect of the patient. The study aimed to evaluate the association between odor, exudate and social isolation in patients with neoplastic wounds. This is a quantitative study of the kind prospective cross-sectional with patients with neoplastic wounds in outpatient palliative care in Oncology Attention Core of University Hospital Antonio Pedro, approved by HUAP Ethics Committee c / No: 183757. Data collection was performed during the nursing consultation by the application of odor scales, exudation (Push) and Likert scale of three dimensions to assess the social aspects of the patient, as well as data contained in records for population. The statistical analysis was applied to the normality test Shapiro Wilk, verifying that the sample is not parametric (p value ≤ 0.05) for the variables: size of the lesion, the total wound, the total odor and overall exudate (Likert scale) and parametric (p value> 0.05) for the age variable. Data were presented as median and interquartile range ((x) ± Q3-Q1) for analysis of nonparametric variables; mean and standard deviation (x ̅ ± S.P) for parametric variable. He held the Kruskal Wallis test for multivariate association check between clinical data and scale and the Spearman test to see if the odor degree, amount of exudate, size and location of the lesion correlate with the interference of socialization patient. The reliability of ISPOE was measured by Cronbach alpha coefficient. It was found, then the correlation between the degree of odor and the questions 1 to 5 scale of the odor scale. Thus, the odor interferes with the constraint (p, 0.0053) and attend public places (p; 0.0495). The amount of exudate correlated with the first issue of exudate size scale, interfering with embarrassment (p; 0.0453). The variable type of injury correlated with the issues 3:05, so interfering with the relationship with the family and attend public places, factors that favor social isolation in patients with neoplastic Variables wounds: lesion size and location of injury no significant correlation with the range of issues in the wound size. The three dimensions of the scale showed satisfactory internal consistency with alpha: 0.82 (wound size); 0.94 (exudate dimension) and 0.88 (size odor). Thus, the odor and exudate negatively affect social and psychological factors that may contribute, directly, social isolation. In addition to the knowledge about the characteristics of these injuries and products suitable for care, it is crucial that nursing professionals know the main complaints related to the injury and the impact they cause to the daily life of the patient. Knowing that social and psychological conflict will make all the difference in nursing care, because thus may act assertively and holistic care in the patient's daily life, seeing it beyond the symptoms: their psychological and social aspirations. The finding of association between variables may assist the evaluation of aspects that can interfere with quality of life and care provided to patients with neoplastic wounds.

Loss or partial loss of eye sight can have major effect on quality of person's life. One of the most common diseases, which causes loss or partial loss of eye sight are diabetic retinopathy and age releated macular degeneration. Both of these diseases can be prevented or mediated by early detection and proper treatment. The fundus camera, which is used to capture eye retina, has had major effect on increasing quality and speed of early detection. Images captured by fundus camera can be automatically analyzed in order to detect any possible signs of retina damage. This thesis proposes one possible way of automating this process. First part of this thesis describes eye, its diseases and capturing technology. Second part then proposes way of automating detection process and its implementation. Lastly, the results are evaluated.

En los ultimos años el número de casos de ceguera se ha reducido significativamente. A pesar de este hecho, la Organización Mundial de la Salud estima que un 80% de los casos de pérdida de visión (285 millones en 2010) pueden ser evitados si se diagnostican en sus estadios más tempranos y son tratados de forma efectiva. Para cumplir esta propuesta se pretende que los servicios de atención primaria incluyan un seguimiento oftalmológico de sus pacientes así como fomentar campañas de cribado en centros proclives a reunir personas de alto riesgo. Sin embargo, estas soluciones exigen una alta carga de trabajo de personal experto entrenado en el análisis de los patrones anómalos propios de cada enfermedad. Por lo tanto, el desarrollo de algoritmos para la creación de sistemas de cribado automáticos juga un papel vital en este campo. La presente tesis persigue la identificacion automática del daño retiniano provocado por dos de las patologías más comunes en la sociedad actual: la retinopatía diabética (RD) y la degenaración macular asociada a la edad (DMAE). Concretamente, el objetivo final de este trabajo es el desarrollo de métodos novedosos basados en la extracción de características de la imagen de fondo de ojo y clasificación para discernir entre tejido sano y patológico. Además, en este documento se proponen algoritmos de pre-procesado con el objetivo de normalizar la alta variabilidad existente en las bases de datos publicas de imagen de fondo de ojo y eliminar la contribución de ciertas estructuras retinianas que afectan negativamente en la detección del daño retiniano. A diferencia de la mayoría de los trabajos existentes en el estado del arte sobre detección de patologías en imagen de fondo de ojo, los métodos propuestos a lo largo de este manuscrito evitan la necesidad de segmentación de las lesiones o la generación de un mapa de candidatos antes de la fase de clasificación. En este trabajo, Local binary patterns, perfiles granulométricos y la dimensión fractal se aplican de manera local para extraer información de textura, morfología y tortuosidad de la imagen de fondo de ojo. Posteriormente, esta información se combina de diversos modos formando vectores de características con los que se entrenan avanzados métodos de clasificación formulados para discriminar de manera óptima entre exudados, microaneurismas, hemorragias y tejido sano. Mediante diversos experimentos, se valida la habilidad del sistema propuesto para identificar los signos más comunes de la RD y DMAE. Para ello se emplean bases de datos públicas con un alto grado de variabilidad sin exlcuir ninguna imagen. Además, la presente tesis también cubre aspectos básicos del paradigma de deep learning. Concretamente, se presenta un novedoso método basado en redes neuronales convolucionales (CNNs). La técnica de transferencia de conocimiento se aplica mediante el fine-tuning de las arquitecturas de CNNs más importantes en el estado del arte. La detección y localización de exudados mediante redes neuronales se lleva a cabo en los dos últimos experimentos de esta tesis doctoral. Cabe destacar que los resultados obtenidos mediante la extracción de características "manual" y posterior clasificación se comparan de forma objetiva con las predicciones obtenidas por el mejor modelo basado en CNNs. Los prometedores resultados obtenidos en esta tesis y el bajo coste y portabilidad de las cámaras de adquisión de imagen de retina podrían facilitar la incorporación de los algoritmos desarrollados en este trabajo en un sistema de cribado automático que ayude a los especialistas en la detección de patrones anomálos característicos de las dos enfermedades bajo estudio: RD y DMAE. / In last years, the number of blindness cases has been significantly reduced. Despite this promising news, the World Health Organisation estimates that 80% of visual impairment (285 million cases in 2010) could be avoided if diagnosed and treated early. To accomplish this purpose, eye care services need to be established in primary health and screening campaigns should be a common task in centres with people at risk. However, these solutions entail a high workload for trained experts in the analysis of the anomalous patterns of each eye disease. Therefore, the development of algorithms for automatic screening system plays a vital role in this field. This thesis focuses on the automatic identification of the retinal damage provoked by two of the most common pathologies in the current society: diabetic retinopathy (DR) and age-related macular degeneration (AMD). Specifically, the final goal of this work is to develop novel methods, based on fundus image description and classification, to characterise the healthy and abnormal tissue in the retina background. In addition, pre-processing algorithms are proposed with the aim of normalising the high variability of fundus images and removing the contribution of some retinal structures that could hinder in the retinal damage detection. In contrast to the most of the state-of-the-art works in damage detection using fundus images, the methods proposed throughout this manuscript avoid the necessity of lesion segmentation or the candidate map generation before the classification stage. Local binary patterns, granulometric profiles and fractal dimension are locally computed to extract texture, morphological and roughness information from retinal images. Different combinations of this information feed advanced classification algorithms formulated to optimally discriminate exudates, microaneurysms, haemorrhages and healthy tissues. Through several experiments, the ability of the proposed system to identify DR and AMD signs is validated using different public databases with a large degree of variability and without image exclusion. Moreover, this thesis covers the basics of the deep learning paradigm. In particular, a novel approach based on convolutional neural networks is explored. The transfer learning technique is applied to fine-tune the most important state-of-the-art CNN architectures. Exudate detection and localisation tasks using neural networks are carried out in the last two experiments of this thesis. An objective comparison between the hand-crafted feature extraction and classification process and the prediction models based on CNNs is established. The promising results of this PhD thesis and the affordable cost and portability of retinal cameras could facilitate the further incorporation of the developed algorithms in a computer-aided diagnosis (CAD) system to help specialists in the accurate detection of anomalous patterns characteristic of the two diseases under study: DR and AMD. / En els últims anys el nombre de casos de ceguera s'ha reduït significativament. A pesar d'este fet, l'Organització Mundial de la Salut estima que un 80% dels casos de pèrdua de visió (285 milions en 2010) poden ser evitats si es diagnostiquen en els seus estadis més primerencs i són tractats de forma efectiva. Per a complir esta proposta es pretén que els servicis d'atenció primària incloguen un seguiment oftalmològic dels seus pacients així com fomentar campanyes de garbellament en centres regentats per persones d'alt risc. No obstant això, estes solucions exigixen una alta càrrega de treball de personal expert entrenat en l'anàlisi dels patrons anòmals propis de cada malaltia. Per tant, el desenrotllament d'algoritmes per a la creació de sistemes de garbellament automàtics juga un paper vital en este camp. La present tesi perseguix la identificació automàtica del dany retiniano provocat per dos de les patologies més comunes en la societat actual: la retinopatia diabètica (RD) i la degenaración macular associada a l'edat (DMAE) . Concretament, l'objectiu final d'este treball és el desenrotllament de mètodes novedodos basats en l'extracció de característiques de la imatge de fons d'ull i classificació per a discernir entre teixit sa i patològic. A més, en este document es proposen algoritmes de pre- processat amb l'objectiu de normalitzar l'alta variabilitat existent en les bases de dades publiques d'imatge de fons d'ull i eliminar la contribució de certes estructures retinianas que afecten negativament en la detecció del dany retiniano. A diferència de la majoria dels treballs existents en l'estat de l'art sobre detecció de patologies en imatge de fons d'ull, els mètodes proposats al llarg d'este manuscrit eviten la necessitat de segmentació de les lesions o la generació d'un mapa de candidats abans de la fase de classificació. En este treball, Local binary patterns, perfils granulometrics i la dimensió fractal s'apliquen de manera local per a extraure informació de textura, morfologia i tortuositat de la imatge de fons d'ull. Posteriorment, esta informació es combina de diversos modes formant vectors de característiques amb els que s'entrenen avançats mètodes de classificació formulats per a discriminar de manera òptima entre exsudats, microaneurismes, hemorràgies i teixit sa. Per mitjà de diversos experiments, es valida l'habilitat del sistema proposat per a identificar els signes més comuns de la RD i DMAE. Per a això s'empren bases de dades públiques amb un alt grau de variabilitat sense exlcuir cap imatge. A més, la present tesi també cobrix aspectes bàsics del paradigma de deep learning. Concretament, es presenta un nou mètode basat en xarxes neuronals convolucionales (CNNs) . La tècnica de transferencia de coneixement s'aplica per mitjà del fine-tuning de les arquitectures de CNNs més importants en l'estat de l'art. La detecció i localització d'exudats per mitjà de xarxes neuronals es du a terme en els dos últims experiments d'esta tesi doctoral. Cal destacar que els resultats obtinguts per mitjà de l'extracció de característiques "manual" i posterior classificació es comparen de forma objectiva amb les prediccions obtingudes pel millor model basat en CNNs. Els prometedors resultats obtinguts en esta tesi i el baix cost i portabilitat de les cambres d'adquisión d'imatge de retina podrien facilitar la incorporació dels algoritmes desenrotllats en este treball en un sistema de garbellament automàtic que ajude als especialistes en la detecció de patrons anomálos característics de les dos malalties baix estudi: RD i DMAE. / Colomer Granero, A. (2018). Fundus image analysis for automatic screening of ophthalmic pathologies [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/99745 / TESIS

La coiffe racinaire est cruciale à la croissance et survie du méristème subapical de racine. Elle libère des cellules frontières (CFs) qui assurent la protection de l’apex racinaire. Les CFs associées à leur mucilage forment le piège extracellaire de racine (RET). La caractérisation du RET et des exsudats racinaires de trois essences ligneuses sahéliennes à partir de plantules cultivées in vitro a été réalisée. B. aegyptiaca et A. raddiana prospèrent dans les zones semi-arides, à l’opposé de T. indica. La morphologie des CFs et l’organisation du RET ont été déterminées par microscopie. La compostion en glycopolymères et la détection des arabinogalactanes proteines (AGPs) dans le RET et les exsudats racinaires ont été déterminées par des analyses biochimiques. L’effet des exsudats racinaires sur la croissance d’Azospirillum brasilense, une bactérie bénéfique pour la plante a été évalué. B. aegyptiaca produit des CFs de type border cells (BCs) alors que les autres Fabaceae produisent des BCs et des border-like cells. Les BCs sont entourées d’un dense mucilage riche en polymères de paroi. Le RET et les exsudats racinaires issus de B. aegyptiaca et A. raddiana sont plus riches en AGPs que ceux provenant T. indica. Les AGPs pourraient contribuer à la survie des plantules dans un contexte semiaride. Ce travail ouvre de nouvelles perspectives de recherche concernant l'implication du RET dans la survie des plantes à l'aridité. / The root cap is primordial for seedling growth and supports root apical meristem integrity. The root cap releases root border cells (RBCs) that surround the root tip and ensure seedling protection against numerous stresses. RBCs and their associated mucilage form the root extracellular trap (RET). Here, RET and root exudate characterization of three Sahelian woody seedlings are performed. In contrast to B. aegyptiaca and A. raddiana which thrive in semi-arid areas, T. indica is more sensitive to drought. B. aegyptiaca, A. raddiana and T. indica seedlings were sub-cultured in vitro. RBC morphologies and RET organization were determined using microscopic approaches. The polysaccharide composition and arabinogalactan protein (AGP) content were determined by biochemical approaches in the RET and the root exudates. Moreover, the effect of root exudates on the growth of Azospirillum brasilense a plant benefical bacteria has been performed. While B. aegyptiaca produces only border cell (BC) type, the two Fabaceae seedlings release both BCs and border-like cells (BLCs). BCs are enclosed in a dense mucilage enriched in cell wall polymers. Compared to T. indica, RET and root exudates of B. aegyptiaca and A. raddiana include more abundant AGPs. In this context, AGPs could contribute to woody seedling survival. This work opens new research perspectives regarding involvement of RET in plant survival to aridity.

El objetivo de esta Tesis Doctoral es estudiar diferentes herramientas para el manejo de plagas y enfermedades del cultivo de la platanera. Entre las herramientas que vamos a desarrollar, se van a analizar los compuestos orgánicos volátiles (COVs) fúngicos derivados de hongos entomopatógenos (HE) y nematófagos, como fuente de metabolitos con actividad antagónica contra el picudo negro (PN) de la platanera, Cosmopolites sordidus, para su control y manejo en el campo. Así mismo, vamos a estudiar las respuestas de cultivares de plataneras a quitosano, un polisacárido biodegradable, para evaluar su posible uso en el campo como estimulante y protector de las plantas frente a plagas y patógenos, como Fusarium oxysporum f. sp. cubense. El conjunto de capítulos de esta tesis pretende sentar las bases de una estrategia de manejo sostenible de plagas y enfermedades del cultivo de la platanera, basada en el uso de COVs derivados de hongos presentes de forma natural en los cultivos, en combinación con la suplementación de quitosano en el riego, para un efecto de protección y activación de las defensas de las plataneras antes de cualquier infección de plagas y/o enfermedades. El objetivo principal de esta Tesis Doctoral es encontrar nuevas fórmulas para la gestión integrada de plagas como Cosmopolites sordidus y enfermedades de la platanera en condiciones de campo. En esta Tesis Doctoral hemos ideado enfoques sostenibles para la gestión de las plagas y enfermedades de las plataneras. Nuestros objetivos son: a) Cosmopolites sordidus (picudo negro de la platanera, PN), la principal plaga de los cultivos de plátano y, b) el hongo del marchitamiento Fusarium oxysporum f. sp. cubense Raza Tropical 4 (FocTR4), agente causante de una nueva variante extremadamente virulenta de la enfermedad del “Mal de Panamá”, que se está extendiendo rápidamente por todo el mundo. Nuestras herramientas de gestión sostenible son: a) los hongos entomopatógenos (HE, conocidos por su uso como agentes de control biológico, ACBs) aislados de campos comerciales de plátanos, b) sus compuestos orgánicos volátiles (COVs) y, c) el quitosano, un compuesto biodegradable y elicitor de la inmunidad de las plantas con actividad antimicrobiana. Damos evidencia de que los COVs de los hongos agentes de control biológico son repelentes del PN. Pueden utilizarse en los cultivos de platanera mediante estrategias de push and pull para gestionar la plaga de forma sostenible. El quitosano puede utilizarse en el riego para prevenir las defensas de la platanera local y sistémicamente. Por lo tanto, este polímero, con probada actividad antimicrobiana frente a otros patógenos de marchitamiento de Fusarium spp., podría utilizarse contra la actual pandemia en las plataneras causada por FocTR4. La capacidad de inducir reguladores del crecimiento de las plantas sostiene también el papel fertilizante del quitosano. La inducción de compuestos relacionados con la respuesta sistémica adquirida (RSA) hace que el riego con quitosano sea una herramienta para manejar también las plagas de las plataneras sobre el suelo (PN) y las enfermedades (Sigatoka). De esta manera, los COVs y el quitosano podrían ayudar a reducir el uso de agroquímicos tóxicos en los cultivos de platanera en todo el mundo.

Les sols représentent une ressource non renouvelable qui soutient 95% de la production alimentaire mondiale. Cependant, les sols sont de plus en plus impactés par la pollution chimique anthropique, menaçant la santé humaine et l’environnement. Parmi les polluants les plus répandus dans les sols, l'arsenic est aussi l’un des plus dommageables pour la santé humaine, touchant près de 200 millions de personnes dans le monde. Pour limiter la contamination des sols, les approches conventionnelles de remédiation reposent principalement sur l'excavation et l'enfouissement des sols contaminés, mais sont incompatibles avec les grandes surfaces concernées par la contamination chimique, pouvant s’étendre sur des millions d’hectares. Une solution novatrice utilise les plantes et les microorganismes associés pour extraire, dégrader ou stabiliser les contaminants in situ dans une approche dite de phytoremédiation. L'exsudation d'une grande diversité de métabolites des racines dans le sol environnant serait un mécanisme essentiel qui permet aux plantes de tolérer et de détoxifier les contaminants du sol. Cependant, l’environnement chimique de la rhizosphère et les interactions complexes entre les exsudats racinaires et les contaminants restent largement inconnus. L'objectif de cette thèse est de faire progresser la compréhension de l'exsudation racinaire en réponse à la contamination et de son impact sur le devenir de l'arsenic dans la rhizosphère. Le Chapitre 1 rapporte un nouveau système de croissance à petite échelle, hautement reproductible, développé pour capturer et caractériser les exsudats racinaires. En utilisant une analyse métabolomique non ciblée basée sur la chromatographie liquide couplée à la spectrométrie de masse, l’espèce légumineuse Lupinus albus a été examinée pour identifier les différences significatives dans l’exsudation d’un large spectre de composés dans la rhizosphère. Cette approche a révélé les classes prédominantes de composés exsudés et leurs variations en réponse à la contamination, notamment les coumarines, connues pour être impliquées dans les stratégies d'acquisition de nutriments chez les plantes, ainsi que l'exsudation inattendue de phytochélatines, connues pour participer à la complexation et à la détoxification intracellulaire de l'arsenic. Pour confirmer l'exsudation des phytochélatines, une expérience supplémentaire a été menée et a permis de valider l'exsudation des phytochélatines comme mécanisme potentiel de tolérance à l'arsenic dans la rhizosphère. Le Chapitre 2 examine plus en détail les mécanismes d'exsudation des phytochélatines et leurs interactions avec l'arsenic chez Lupinus albus. Grâce à l'inhibition chimique des principales voies de synthèse et d'exsudation des phytochélatines, ce chapitre fournit les premières observations de l’exsudation active de complexes arsenic-phytochélatine chez les plantes, pouvant jouer un rôle critique dans la détoxification de l'arsenic. À partir de ces observations, le chapitre 2 propose une révision du modèle actuel d'efflux d'arsénite des racines et met en évidence l'exsudation de complexes arsenic-phytochélatine comme mécanisme jusque-là inconnu de détoxification chez les plantes. Dans le Chapitre 3, les différentes stratégies employées en réponse à la contamination à l'arsenic chez Lupinus albus et Salix miyabeana sont explorées en profondeur par différents essais en pots et à plus grande échelle, directement sur le terrain. Ces deux espèces, illustrant différents traits fonctionnels importants pour la phytoremédiation, révèlent des adaptations distinctes ainsi que des stratégies d’exsudation conservées en réponse à l'arsenic. Les résultats présentés dans ce chapitre révèlent en particulier le rôle central de l'exsudation de phytochélatines dans la rhizosphère de ces deux espèces, pourtant éloignées phylogénétiquement. Notamment, la découverte de complexes phytochélatine-arsenic dans la rhizosphère des deux espèces souligne l'importance des mécanismes extracellulaires dans la détoxification de l'arsenic chez les plantes. De plus, les mesures sur le terrain soutiennent les implications de l'exsudation des phytochélatines en tant qu’adaptation à l'exposition à l'arsenic en conditions réelles. En résumé, ce chapitre fournit de nouvelles perspectives sur l'interaction complexe entre les plantes et les sols lors de la phytoremédiation de l'arsenic. Dans l'ensemble, cette thèse présente de nouvelles stratégies d'exsudation chez deux espèces phytoremédiatrices majeures et apporte de nouvelles connaissances sur la façon dont l'investissement de ressources dans la rhizosphère peut aider les plantes à tolérer, voire à surmonter, l'effet de la pollution anthropique sur l'environnement. Comprendre ces interactions naturelles est essentiel pour aider à concevoir des stratégies de gestion durables des terres, visant à réduire l'impact à long terme des activités humaines sur les sols. / Soils represent a non-renewable resource supporting 95% of global food production. However, soils face increasing threats from anthropogenic chemical pollution, creating an environmental burden impacting human and environmental health worldwide. Arsenic is one of the most widespread soil contaminants, thought to affect over 200 million people globally and posing substantial threats to public health. To limit contamination of soils, conventional remediation approaches rely on soil excavation and burial, but are incompatible with the extensive problem of soil contamination, often impacting millions of hectares. An innovative solution is to use phytoremediation to harness plants' natural abilities to extract or degrade soil contaminants. The exudation of a wide diversity of metabolites from roots into the surrounding soil is thought to be an essential mechanism used by plants to modify challenging soil environments. However, the extent and variation of root exudation remains largely uncharacterised for many important crops. The objective of this thesis is to advance the understanding of root exudation in response to contamination and how it impacts the fate of arsenic in the rhizosphere. Chapter 1 reports a novel small-scale but highly reproducible growth system developed to capture and characterise root exudates. Using untargeted liquid chromatography-tandem mass spectrometry-based metabolomic analysis, the leguminous crop white lupin (Lupinus albus) was scrutinised to identify significant differences in exuded compounds within the rhizosphere. This approach revealed the predominant classes of exuded compounds in response to contamination, including coumarins, known to be involved in plant nutrient acquisition strategies, as well as unexpected phytochelatin exudation, known to participate in intracellular arsenic complexation and detoxification. A validatory experiment was conducted and confirmed the exudation of phytochelatins as a potential arsenic tolerance mechanism for rhizosphere detoxification. Chapter 2 further investigates the mechanisms of phytochelatin exudation and their interactions with arsenic in Lupinus albus. Through chemical inhibition of key root exudates synthesis and exudation mechanisms, this chapter provides the first evidence that plants actively exude arsenic-phytochelatin complexes, which may function as a critical step for arsenic detoxification and tolerance. From this evidence, Chapter 2 provides a tentative revision of the current model of arsenite efflux from roots and demonstrates that arsenic-phytochelatin exudation may be an active mechanism conferring arsenic tolerance. In Chapter 3, the different strategies employed in response to arsenic contamination in Lupinus albus and Salix miyabeana were extensively scrutinised in larger-scale pot and field trials, to capture the diversity of rhizosphere metabolites within constructed and real-world soils. These species, illustrating different important functional traits for phytoremediation, revealed distinct as well as more conserved root exudate adaptations to arsenic. Most importantly, the findings presented in this chapter reveal a conserved and pivotal role for extracellular phytochelatin exudation in the rhizosphere of these distantly related phytoremediating species. The discovery of phytochelatin-arsenic complexes in the rhizosphere of both species underscores the importance of extracellular mechanisms in plant arsenic detoxification. Furthermore, field assessments supported the real-world implications of phytochelatin exudation as an adaptive response to arsenic exposure. In summary, this chapter provides novel insights into the complex interplay between plants and soils in arsenic phytoremediation. Overall, this thesis presents novel exudation strategies in two major phytoremediation species and brings new knowledge on how investment of resources in the rhizosphere can help plants tolerate, or even overcome, the effect of anthropogenic pollution upon the natural environment. Understanding these mechanisms is vital to devise sustainable land management strategies to reduce the long-term impact of human activity on soils around the world.