Academic literature on the topic 'Abiotic stress adaptation'

Abstract Extreme environments offer powerful opportunities to study how different organisms have adapted to similar selection pressures at the molecular level. Arctic plants have adapted to some of the coldest and driest biomes on Earth and typically possess suites of similar morphological and physiological adaptations to extremes in light and temperature. Here, we compare patterns of molecular evolution in three Brassicaceae species that have independently colonized the Arctic and present some of the first genetic evidence for plant adaptations to the Arctic environment. By testing for positive selection and identifying convergent substitutions in orthologous gene alignments for a total of 15 Brassicaceae species, we find that positive selection has been acting on different genes, but similar functional pathways in the three Arctic lineages. The positively selected gene sets identified in the three Arctic species showed convergent functional profiles associated with extreme abiotic stress characteristic of the Arctic. However, there was little evidence for independently fixed mutations at the same sites and for positive selection acting on the same genes. The three species appear to have evolved similar suites of adaptations by modifying different components in similar stress response pathways, implying that there could be many genetic trajectories for adaptation to the Arctic environment. By identifying candidate genes and functional pathways potentially involved in Arctic adaptation, our results provide a framework for future studies aimed at testing for the existence of a functional syndrome of Arctic adaptation in the Brassicaceae and perhaps flowering plants in general.

Environmental conditions are strong selective forces, which may influence adaptation and speciation. The wild tomato species Solanum chilense , native to South America, is exposed to a range of abiotic stress factors. To identify signatures of natural selection and local adaptation, we analysed 16 genes involved in the abiotic stress response and compared the results to a set of reference genes in 23 populations across the entire species range. The abiotic stress-responsive genes are characterized by elevated nonsynonymous nucleotide diversity and divergence. We detected signatures of positive selection in several abiotic stress-responsive genes on both the population and species levels. Local adaptation to abiotic stresses is particularly apparent at the boundary of the species distribution in populations from coastal low-altitude and mountainous high-altitude regions.

Abstract Plant life relies on complex arrays of environmental stress sensing and signalling mechanisms. Extremophile plants develop and grow in harsh environments with extremes of cold, heat, drought, desiccation, or salinity, which have resulted in original adaptations. In accordance with their polyphyletic origins, extremophile plants likely possess core mechanisms of plant abiotic stress signalling. However, novel properties or regulations may have emerged in the context of extremophile adaptations. Comparative omics of extremophile genetic models, such as Arabidopsis lyrata, Craterostigma plantagineum, Eutrema salsugineum, and Physcomitrella patens, reveal diverse strategies of sensing and signalling that lead to a general improvement in abiotic stress responses. Current research points to putative differences of sensing and emphasizes significant modifications of regulatory mechanisms, at the level of secondary messengers (Ca2+, phospholipids, reactive oxygen species), signal transduction (intracellular sensors, protein kinases, transcription factors, ubiquitin-mediated proteolysis) or signalling crosstalk. Involvement of hormone signalling, especially ABA signalling, cell homeostasis surveillance, and epigenetic mechanisms, also shows that large-scale gene regulation, whole-plant integration, and probably stress memory are important features of adaptation to extreme conditions. This evolutionary and functional plasticity of signalling systems in extremophile plants may have important implications for plant biotechnology, crop improvement, and ecological risk assessment under conditions of climate change.

Abiotic stresses, including drought, extreme temperatures, salinity, and waterlogging, are the major constraints in crop production. These abiotic stresses are likely to be amplified by climate change with varying temporal and spatial dimensions across the globe. The knowledge about the effects of abiotic stressors on major cereal and legume crops is essential for effective management in unfavorable agro-ecologies. These crops are critical components of cropping systems and the daily diets of millions across the globe. Major cereals like rice, wheat, and maize are highly vulnerable to abiotic stresses, while many grain legumes are grown in abiotic stress-prone areas. Despite extensive investigations, abiotic stress tolerance in crop plants is not fully understood. Current insights into the abiotic stress responses of plants have shown the potential to improve crop tolerance to abiotic stresses. Studies aimed at stress tolerance mechanisms have resulted in the elucidation of traits associated with tolerance in plants, in addition to the molecular control of stress-responsive genes. Some of these studies have paved the way for new opportunities to address the molecular basis of stress responses in plants and identify novel traits and associated genes for the genetic improvement of crop plants. The present review examines the responses of crops under abiotic stresses in terms of changes in morphology, physiology, and biochemistry, focusing on major cereals and legume crops. It also explores emerging opportunities to accelerate our efforts to identify desired traits and genes associated with stress tolerance.

Evolution might rescue populations from extinction in changing environments. Using experimental evolution with microalgae, we investigated if competition influences adaptation to an abiotic stressor, and vice versa, if adaptation to abiotic change influences competition. In a first set of experiments, we propagated monocultures of five species with and without increasing salt stress for approximately 180 generations. When assayed in monoculture, two of the five species showed signatures of adaptation, that is, lines with a history of salt stress had higher population growth rates at high salt than lines without prior exposure to salt. When assayed in mixtures of species, however, only one of these two species had increased population size at high salt, indicating that competition can alter how adaptation to abiotic change influences population dynamics. In a second experiment, we cultivated two species in monocultures and in pairs, with and without increasing salt. While we found no effect of competition on adaptation to salt, our experiment revealed that evolutionary responses to salt can influence competition. Specifically, one of the two species had reduced competitive ability in the no-salt environment after long-term exposure to salt stress. Collectively, our results highlight the complex interplay of adaptation to abiotic change and competitive interactions.

Modifications of the cellular proteome pool upon stress allow plants to tolerate environmental changes. Alternative splicing is the most significant mechanism responsible for the production of multiple protein isoforms from a single gene. The spliceosome, a large ribonucleoprotein complex, together with several associated proteins, controls this pre-mRNA processing, adding an additional level of regulation to gene expression. Deep sequencing of transcriptomes revealed that this co- or post-transcriptional mechanism is highly induced by abiotic stress, and concerns vast numbers of stress-related genes. Confirming the importance of splicing in plant stress adaptation, key players of stress signaling have been shown to encode alternative transcripts, whereas mutants lacking splicing factors or associated components show a modified sensitivity and defective responses to abiotic stress. Here, we examine recent literature on alternative splicing and splicing alterations in response to environmental stresses, focusing on its role in stress adaptation and analyzing the future perspectives and directions for research.

Under global warming and climate change conditions fruit orchards facing different environmental challenges which cause negative impacts on the growth and productivity of various fruit trees particularly in arid and semi-arid areas, various abiotic stress such as rising temperature, drought, heatwaves, and soil salinity represented a major challenge for growth and productivity of fruit orchards. Fruit trees used different strategies to cope with abiotic stress and minimize their adverse effects. Plants used different physiological, anatomical, and morphological mechanisms to tolerate abiotic stress, such as ion homeostasis, synthesis of more compatible solute, polyamines production, antioxidant regulation, closing stomata, in addition tol modification of root system, abscission of the leaves partially, compactness canopy, reducing leaf size, furthermore, under abiotic stress plants produce various organic solutes to cope with Reactive Oxygen solutes like Proline, in addition, using proper management practices that include providing adequate nutrients requirement particularly Potassium and Calcium, maintain soil moisture, using proper rootstocks tolerant for drought and salinity stress as well as exogenous application of plant growth substances could sustain orchards growth and productivity

Les contraintes environnementales dans un monde en changement remettent en cause la survie des plantes ; les plus drastiques sont les contraintes abiotiques, comme les stress hydriques, thermiques, ou la pollution par les métaux lourds. Les mécanismes inductibles de la tolérance des plantes sous stress ont été étudiés par une approche physiologique combinée à une analyse protéomique. Des plants de Populus tremula x P. alba genotype 717-1B4 ont été exposés à plusieurs contraintes en chambre phytotronique : 1) un sol contenant des concentrations importantes de Cd2+ ou Zn2+, 2) une sécheresse induite par arrêt d'arrosage, 3) une contrainte thermique par élévation subite ou graduelle de 22 à 42°C. Les paramètres physiologiques des plantes ont été suivis au cours des traitements ainsi que durant la période de recouvrement qui a suivi les contraintes hydriques et thermiques. La réponse de stress a été caractérisée par ces paramètres physiologiques et par les changements dans les profils protéomiques du tissu foliaire et de la zone cambiale. Les aspects communs et particuliers du stress induit par chaque contrainte ont été décrits. Les données rassemblées dans cette étude, en enrichissant les connaissances sur la gamme de réponse des essences ligneuses, contibuent à déterminer la frontière entre le stress générique et les réponses plus spécifiques ; elles apportent également des éléments de réponse à l'utilisation du peuplier en phytoremédiation des sols pollués par les métaux.

[ES] El pimiento es un cultivo muy importante a nivel mundial, pero es sensible a la falta de agua y a la salinidad. No obstante, se puede mejorar la tolerancia mediante la técnica del injerto. El Instituto Valenciano de Investigaciones Agrarias y la Universidad Politécnica de Valencia han realizado estudios previos para seleccionar accesiones de pimiento tolerantes a ambos estreses, utilizando después una selección de ellos como portainjertos para estudiar los mecanismos fisiológicos de tolerancia y aumentar la rentabilidad de su producción. Sin embargo, después de todos estos estudios, la información disponible es limitada. En este sentido, los objetivos que se han planteado en esta tesis doctoral fueron: i) seleccionar nuevas accesiones tolerantes de pimiento a la salinidad y escasez de agua, para aumentar la disponibilidad de genotipos tolerantes y usarlos en futuros programas de mejora, con el objetivo final de obtener nuevos portainjertos con una tolerancia mejorada; ii) identificar a corto plazo los mecanismos fisiológicos de tolerancia al estrés hídrico de una accesión tolerante (A25) usada como portainjerto; iii) identificar a corto plazo los mecanismos fisiológicos de tolerancia a la salinidad de un nuevo portainjerto híbrido tolerante (NIBER®); iv) encontrar los principales mecanismos moleculares de tolerancia a la salinidad de una accesión tolerante (A25) respecto a una sensible (A6) desde el punto de vista transcriptómico. Una vez realizados estos ensayos, en primer lugar, pudimos relacionar positivamente la capacidad fotosintética y el mantenimiento del crecimiento en plantas tolerantes a estrés hídrico y salino, tanto sin injertar como injertadas; de hecho, basándonos principalmente en esta relación, seleccionamos las accesiones A34 y A31 como tolerantes a estrés salino e hídrico, respectivamente. Además, demostramos que el papel principal de la prolina en los estreses estudiados no está ligado a la bajada de potencial osmótico; sin embargo, se identificaron funciones protectoras de este aminoácido que, junto a otras moléculas antioxidantes como los fenoles, contribuyen en el pimiento a aumentar la tolerancia. Igualmente importante es el peróxido de hidrógeno, que se relacionó con la capacidad antioxidante en pimiento, funcionando como molécula señalizadora en estrés salino. Asimismo, la bajada de ácido abscísico y la modificación de la expresión de genes relacionados han sido también relevantes en condiciones de estrés salino para mantener la apertura estomática y, por consiguiente, el crecimiento en plantas sin injertar e injertadas sobre portainjertos tolerantes. Se demostró también que la limitación del transporte de Na+ a hojas, así como el transporte y acumulación eficiente de K+ en raíces y hojas, son esenciales para alcanzar la homeostasis iónica y por tanto la tolerancia en pimientos injertados sobre portainjertos tolerantes. Para finalizar, el estudio de las rutas moleculares fue una herramienta útil para confirmar el comportamiento fisiológico y agronómico de una accesión de pimiento previamente clasificada como tolerante a la salinidad, descubriendo además nuevos mecanismos no referenciados hasta el momento. Los genes diferencialmente expresados encontrados estaban relacionados con la señalización hormonal, el crecimiento y desarrollo de las plantas, la fotoprotección, la regulación de los transportadores de iones y la detoxificación de ROS.
[CA] El pimentó és un cultiu molt important mundialment, però és sensible a la falta d'aigua i la salinitat. No obstant això, es pot millorar la tolerància mitjançant la tècnica de l'empelt. L'Institut Valencià d'Investigacions Agràries i la Universitat Politècnica de València han fet estudis previs per a seleccionar accessions de pimentó tolerants a tots dos estressos i a continuació, una selecció d'entre elles es va utilitzar per a estudiar els mecanismes fisiològics de tolerància i augmentar la rendibilitat de la seua producció. No obstant això, després de tots aquests experiments, la informació encara és limitada. En aquest sentit, els objectius que s'han plantejat en aquesta tesi doctoral van ser: i) seleccionar noves accessions tolerants de pimentó a la salinitat i la falta d'aigua, per a augmentar la disponibilitat de genotips tolerants i usar-los en futurs programes de millora, amb l'objectiu final d'obtindre nous portaempelts amb una tolerància millorada; ii) identificar a curt termini els mecanismes fisiològics de tolerància a l'estrès hídric d'una accessió tolerant (A25) usada com portaempelt; iii) identificar a curt termini els mecanismes fisiològics de tolerància a la salinitat d'un nou portaempelt híbrid tolerant (NIBER®); iv) trobar els principals mecanismes moleculars de tolerància a la salinitat d'una accessió tolerant (A25) respecte a una sensible (A6) des d'un punt de vista de la transcriptòmica. Després de realitzar aquests assajos, en primer lloc, vam poder relacionar positivament la capacitat fotosintètica i el manteniment del creixement en plantes tolerants a l'estrès hídric i salí, tant sense empeltar com empeltades; de fet, basant-nos principalment en aquesta relació, vam seleccionar les accessions A34 i A31 com tolerants a l'estrès salí i hídric, respectivament. A més a més, vam demostrar que el paper principal de la prolina en els estressos estudiats no està lligat a la baixada de potencial osmòtic; en canvi, es van identificar diferents funcions protectores d'aquest aminoàcid, que, junt a altres molècules antioxidants com els fenols, contribueixen en el pimentó a combatre'ls. Igualment important és el peròxid d'hidrogen, que es va relacionar amb la capacitat antioxidant del pimentó, funcionant com a molècula senyalitzadora a l'estrès salí. Així mateix, la baixada d'àcid abscísic i la modificació de l'expressió de gens relacionats de la seua senyalització han sigut també rellevants en condicions d'estrès salí per a mantindre l'obertura estomàtica i per tant el creixement en plantes sense empeltar i empeltades amb portaempelts tolerants. Es va demostrar també que la limitació del transport de Na+ a les fulles, així com el transport i l'acumulació eficient de K+ a les arrels i les fulles, són essencials per a aconseguir l'homeòstasi iònica i per tant la tolerància en pimentons empeltats damunt portaempelts tolerants. Per concloure, l'estudi de les rutes moleculars va ser un instrument útil per a confirmar el comportament fisiològic i agronòmic d'una accessió de pimentó prèviament classificada com a tolerant, descobrint a més nous mecanismes no trobats fins ara. Els gens diferencialment expressats trobats estaven relacionats amb la senyalització hormonal, el creixement i el desenvolupament de les plantes, la fotoprotecció, la regulació dels transportadors de ions i la detoxificació de ROS.
[EN] Pepper culture is economically very important worldwide, although it is very sensitive to suboptimal conditions of water and high salinity. However, the tolerance to these stresses can be improved by the grafting technique. Previous studies of the Valencian Institute for Agricultural Research and the Polytechnic University of Valencia have been conducted to select pepper accessions that showed tolerance to both stresses, after which a further selection of them was used as rootstocks to find physiological mechanisms of tolerance and to increase its agronomic profit. However, after all these studies, the available information in this regard is still scarce. Therefore, the objectives of this thesis were to: i) screen new tolerant pepper accessions under high salt concentrations and suboptimal water conditions, to increase the availability of tolerant genotypes to be used in future breeding programmes, with the final aim of obtaining new and improved tolerant rootstocks; ii) identify the short-term physiological mechanisms of water stress tolerance of a tolerant accession (A25) used as a rootstock; iii) identify the physiological mechanisms of short-term tolerance to salinity of a new tolerant hybrid rootstock (NIBER®); and iv) find the main molecular pathways of salinity tolerance of a tolerant accession (A25) compared to a sensitive one (A6) by a transcriptomic approach. After conducting these studies, we firstly found a positive relationship between photosynthetic capacity and growth maintenance in plants that were tolerant to water or salt stress, both grafted or ungrafted; indeed, based mainly on this relationship, we selected accessions A34 and A31 as tolerant to salt and water stress, respectively. In addition, we were able to demonstrate that the main role of proline under salinity and water scarcity is not linked herein to the drop in osmotic potential; on the contrary, we identified different protective roles that, together with other antioxidant protective molecules such as phenols, contribute to the tolerance of pepper plants to these environmental stresses. Moreover, hydrogen peroxide, a reactive oxygen species, was found to play important roles in the antioxidant capacity of pepper, working as a signalling molecule under salinity stress. Furthermore, the drop in abscisic acid concentration and its signalling deregulation were also shown to maintain stomatal aperture and thus the growth of the scion when grafted onto tolerant rootstocks and ungrafted accessions under high salt concentration conditions. It was also demonstrated that a limitation of Na+ transport to leaves, as well as a more efficient transport and accumulation of K+ in roots and leaves, are essential to reach ion homeostasis and, thus, tolerance in pepper plants grafted onto tolerant rootstocks. Finally, the study of the molecular pathways of tolerance was a useful tool to confirm the physiological and agronomical behaviour of a pepper accession previously classified as tolerant, although new mechanisms were also found. The differentially expressed genes found were linked to hormonal signalling, plant growth and development, photoprotection, regulation of ion transporters and ROS detoxification.
Quiero agradecer al Instituto Valenciano de Investigaciones Agrarias (IVIA), al Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) y al Ministerio de Ciencia, Innovación y Universidades por darme la oportunidad de disfrutar de la beca predoctoral FPI-INIA (proyectos RTA2013-00022-C02-1 y RTA2017-00030-C02-00) con la que he realizado esta tesis doctoral y he podido aprender tanto todos estos años, asistir a los congresos y realizar las estancias de investigación en el extranjero.
López Serrano, L. (2021). Unravelling the Physiological and Genetic Adaptation of Grafted Pepper under Saline and Hydric Stresses [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/162875
TESIS

L'Eucalyptus, feuillu le plus planté dans le monde, est fortement exposé au froid en raison de l'absence de dormance. Les gènes DREB sont connus comme étant les principaux régulateurs de la réponse aux stress abiotiques. Un nombre élevé de gènes DREB1/CBF (C-Repeat Factor) a été identifié chez Eucalyptus grandis. Le but de l'étude est de mieux comprendre le rôle de la voie DREB chez Eucalyptus pour le contrôle de la tolérance au stress, du développement et de la formation du bois. La présente étude a permis une annotation des gènes CBF et DREB2 dans le cadre d'un projet de sequençage partiel du génome d'E. gunnii. Une analyse complète de l'expression des genes par qRT-PCR a été réalisée sur les différents organes des deux espèces d'Eucalyptus après les traitements au stress. L'existence d'une copie de CBF supplémentaire dans le génome E. gunnii par rapport à E. grandis suggère que ce groupe est encore en évolution contrairement au groupe DREB2. Un nombre élevé de transcrits CBF chez E. gunnii, tolérant au froid, et forte une vitesse d'induction ce ces facteurs chez E. grandis, à croissance rapide, suggère que les facteurs CBF sont impliqués à la fois dans la protection au stress et la limitation de croissance. Des facteurs de transcription des familles MYB, NAC, KNOX et AP2/ERF impliqués dans le contrôle de la croissance et de la formation de la paroi cellulaire ont été identifiés comme étant des gènes putatifs cibles de CBF. Ces résultats sont en accord avec le phénotype modifié de surexpresseurs CBF. Les deux approches suggèrent un rôle central de la voie de DREB dans le compromis entre la croissance et la résistance au stress chez cette espèce ligneuse
Eucalyptus, the most widely planted hardwood in the world, is highly exposed to the cold due to the lack of dormancy. DREB (Drought Responsive Element Binding) genes are known as master regulators of abiotic stress response. A high number of the DREB1/CBF (C-Repeat Factor) genes has been annotated in Eucalyptus grandis. The aim of the study was to better understand the role of DREB pathway in Eucalyptus for the control of stress tolerance, development and wood formation. The present study provides an annotation of the CBF and DREB2 genes from a partial draft of the E. gunnii genome sequence. A comprehensive transcriptional analysis through high-throughput qRT-PCR was carried out on different organs from the two Eucalyptus species after stress treatments. An additional CBF copy in the E. gunnii genome compared to E. grandis suggests that this group is still evolving unlike the DREB2 group. The higher CBF transcript amounts in the cold tolerant E. gunnii together with higher induction rates in the fast growing E. grandis suggest that CBF factors promote both stress protection and growth limitation. In addition, transcription factors from MYB, NAC, KNOX and AP2/ERF families involved in the control of growth and cell wall formation have been identified as putative CBF target genes. These results are in agreement with the modified phenotype of CBF overexpressors. Both approaches suggest a central role of DREB pathway in the trade-off between growth and stress resistance in this woody species

Ectocarpus dépend de bactéries associées pour croitre en eau douce, ce qui souligne l'importance de l'holobionte lors de stress abiotique. Le but de ma thèse est d'élucider les mécanismes moléculaires qui sous-tendent ce phénomène. Les expériences de co-culture ciblées nécessitent des organismes cultivables. Par conséquent, j'ai caractérisé 388 bactéries associées à Ectocarpus, réparties en 33 genres. Aucune des bactéries cultivées testées n'a eu d'effet bénéfique sur la croissance des algues dans l'eau douce. J'ai continué à travailler avec des holobionts, traités aux antibiotiques doux, qui différaient dans leur réponse à l'eau douce. Le métatranscriptome/métabolome de ces holobionts ont été analysés pendant l'acclimatation. L'analyse approfondie est en cours, mais les premières indications indiquent un changement dans le microbiome en ce qui concerne l'assimilation de l'azote et la virulence. Concomitamment et complémentaire à ce qui précède, les interactions algues/bactéries potentiellement bénéfiques ont été prédites in silico à l'aide d'une analyse de réseau métabolique et les prédictions ont été vérifiées expérimentalement à l'aide de co-cultures. Ensemble, ces résultats contribuent à mieux comprendre comment l'holobiont d'Ectocarpus réagit au stress abiotique et surtout comment les bactéries sont impliquées dans ce processus
Ectocarpus subulatus depends on its associated bacteria for growth in fresh water, which stresses the significance of the “holobiont” during abiotic stress. The aim of my thesis is to elucidate the molecular mechanisms that underlie this phenomenon. Targeted co-culture experiments require cultivable organisms. Therefore, I have cultivated and characterized 388 Ectocarpus-associated bacteria, which belong to 33 different genera. None of the cultivated bacteria tested had a beneficial effect on algal growth in fresh water. For functional studies, I continued to work with mild antibiotic-treated holobionts that differed in their response to fresh water. The metatranscriptome and metabolome of these holobionts were analyzed during acclimation. In-depth analysis is ongoing, but first indications point towards a change in the microbiome regarding nitrogen assimilation and virulence. In parallel and complementary to the above, potentially beneficial algal-bacterial cross-talk was predicted in silico using metabolic network analysis on a subset of cultivated bacteria, and the predictions were experimentally verified using co-culture experiments. Together, these results contribute to a better understanding of how the Ectocarpus holobiont responds during abiotic stress and especially how bacteria are involved in this process

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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
O crescimento populacional mundial tem contribuído para uma maior demanda de arroz, enquanto que alterações ambientais, causadas pelo homem, contribuem com o aumento da frequência de precipitações. Estas condições formam um ambiente de hipoxia, e restringem a produção do arroz. Frente a isso as plantas respondem com adaptações morfológicas e alterações em nível molecular. Portanto, este trabalho teve como objetivo avaliar os efeitos morfológicos e anatômicos em cultivares de arroz Oryza sativa L. submetidas a hipoxia e verificar o perfil de expressão dos genes de regulação complexa e simples de fatores de transcrição WRKY envolvidos na resposta ao estresse por hipoxia. Os resultados obtidos demonstraram que ocorre alterações morfológicas e anatômicas nas cultivares de arroz irrigado quando submetidas ao estresse por hipoxia, principalmente no sistema radicular. Ainda, o aerênquima é mais desenvolvido nas cultivares Epagri 108 e Nipponbare quando submetidas ao estresse por hipoxia. No estudo de expressão gênica através da técnica de qRT-PCR, foi possível observar que os genes WRKY responderam ao estresse por hipoxia, mas não foi possível, para este estresse, verificar uma diferença entre a resposta do perfil de expressão dos genes de regulação simples e complexa em plântulas de arroz sob estresse por hipoxia.
The growth of the world’s population has contributed for a greater demand of rice while environmental alterations caused by men contribute to an increase of rainfall. This conditions create a hypoxia environment and restrict the production of rice. Under these conditions, plants with morphological adaptations and alterations in molecular level. Thus, this work had as its objective to evaluate the morphological and anatomical effects in rice cultivars Oryza sativa L. submitted to hypoxia and to verify the expression profile of genes of complex and simple regulation of WRKY transcription factors involved in the response of stress by hypoxia. The results obtained demonstrated that morphological and anatomical alterations occur in cultivars of irrigated rice when submitted to stress by hypoxia, manly in their root system. Furthermore, the aerenchyma is more developed in the cultivars Epagri 108 and Nipponbare when submitted to stress by hypoxia. In the study of genic expression through the qRT-PCR technique, it was possible to observe that the WRKY genes responded to stress by hypoxia but it not possible, for this stress, to verify a difference between the response of the expression profile of genes of simple and complex regulation in seedlings of rice under stress by hypoxia.

En Amazonie orientale, l’agriculture familiale contribue significativement à la transformation des écosystèmes forestiers en pâturages. La mise en valeur pastorale se fait généralement de manière monospécifique avec une Poacée pérenne d’origine africaine (Brachiaria brizantha cv. Marandu) qui constitue la principale offre fourragère. Mais les pratiques pastorales mises en oeuvre sur une exploitation conduisent souvent à une dégradation des pâturages, qui se manifeste par une prolifération des plantes adventices. Le pâturage a été modifié par l’introduction de deux Fabacées pérennes fourragères originaires d’Amérique Latine, l’une herbacée (Arachis pintoï cv. Amarelo) et l’autre ligneuse (Leucaena leucocephala). Pendant la saison sèche, nous avons étudié les interactions entre B. brizantha et des Fabacées fourragères implantées. Cette étude est la première approche intégrée (écophysiologie) qui étudie les caractéristiques adaptatives et les effets des Fabacées sur la capacité de résistance à la contrainte hydrique des pâturages à partir des évolutions des échanges gazeux foliaires, du potentiel hydrique et de l’état hydrique du sol. Le dispositif expérimental était composé de cinq parcelles de 100 m2 isolées du bétail correspondant à cinq traitements différents. Les trois espèces étudiées ont été cultivées seules et en association. Trois répétitions ont été réalisées pour chaque traitement afin de valider statistiquement les résultats et prendre en compte la variabilité spatiale du sol. En monoculture, les valeurs de conductances stomatiques de B. brizantha sont relativement élevées au regard des conditions climatiques par rapport à des valeurs habituelles de plantes C4 au champ alors que les valeurs d’assimilations nettes sont celles mesurées couramment. A. pintoï et L. leucocephala possèdent des valeurs de conductances stomatiques et d’assimilations mesurées habituellement sur les plantes C3 au champ. En situation de sécheresse, les trois espèces étudiées en monoculture adoptent un mouvement de fermeture stomatique 30 jours après l’arrêt des pluies et ajustent ainsi leur conductance sur l’épuisement de la réserve utile du sol. Cette stratégie permet le maintien de l’activité photosynthétique indispensable à la survie cellulaire et de maintenir une transpiration suffisante pour réguler leur température. Les trois espèces survivent par évitement de la sécheresse, en réduisant leur surface foliaire active et en fermant leurs stomates dès l’abaissement du potentiel hydrique. B. brizantha a le même comportement lorsqu’il est cultivé seul ou associé à A. pintoï que ce soit au niveau de la conductance stomatique, de l’assimilation de CO2 ou de l’efficience instantanée de l’eau. Cependant, son potentiel hydrique est affecté plus précocement au cours d’un stress hydrique lorsqu’il est en concurrence avec A. pintoï. Dans le cas de cette association, notre étude montre que la présence de B. brizantha a un effet négatif sur les activités photosynthétiques et donc sur la production de biomasse d’A. pintoï, espèce considérée pourtant comme sciaphile. Enfin, les fonctions métaboliques de B. brizantha sont réduites lorsqu’il est associé à L. leucocephala du fait de l’ombrage. L. leucocephala évite la sécheresse en réduisant sa surface foliaire. L’augmentation d’insolation en fin de saison sèche affaiblit cependant les plantes associées aux strates inférieures et réduit la quantité de fourrage disponible sur pied. Nous proposons aux agriculteurs de mettre en place une gestion durable de leurs pâturages par la création d’associations végétales fourragères adaptées aux contraintes biotiques et abiotiques
In the Eastern Amazon region (Pará, Brazil), smallholder farming significantly contributes to the transformation of the Amazonian rain forest ecosystem into pasture land that typically includes a single species, generally a perennial fodder grass (Poaceae) originating from Africa (Brachiaria brizantha cv. Marandu). Such pastures rapidly lose their sustainability and get invaded by weeds. To prevent these effects, two imported perennial fodder species of the Fabaceae family (Arachis pintoï cv. Amarelo and Leucaena leucocephala Lam.) have been mixed with the African grass Brachiaria and the interrelations between B. brizantha and the Fabaceae species have been studied. In this unique ecophysiological study, plant parameters, such as gas exchange and plant water potential have been correlated with soil parameters, such as soil water content. The final goal was to assess the impact of the Fabaceae plants on pasture tolerance to water deficit. The experimental setting included five treatments applied to 100 m2 fenced plots to keep cattle away. Treatments corresponded to various combinations between the grass and the two Fabaceae species. Three biological repeats were set up for each treatment for statistical significance and in order to account for soil structure variability. In monospecific plots, B. brizantha exhibited stomatal conductance values higher than those expected from typical C4 species whereas net CO2 assimilation rates were normal. A. pintoï and L. leucocephala had usual stomatal conductance values for field-cultivated C3 plants. In response to drought, a general adjustment in stomatal conductance was observed 30 days into the dry season (i.e. without rain), suggesting that the plants limited transpiration rates according to the progressive decrease in soil water content. This strategy allowed them to maintain photosynthetic activities and to supply photosynthates to their tissues while limiting rises in temperatures. Upon exhaustion of soil water cotent, decreases in leaf water potentials were observed and plants escaped drought by reducing their leaf area and by abruptly closing their stomata. Brachiaria’s responses to drought were similar in mixed and monospecific plots regarding stomatal conductance, net CO2 assimilation rate or real-time water efficiency. However, when grown in mixed plots with A. pintoï, Brachiaria’s leaf water potential decreased rapidly after the onset of drought, due to the competition for water. In a A. pintoï ! Brachiaria plot, Brachiaria had a negative impact on A. pintoï photosynthetic activities and biomass production, even though the latter was considered as a shade plant species. On the other hand, Brachiaria metabolic activities were reduced in L. leucocephala ! Brachiaria combinations, due to the interception of light supply by L. leucocephala. L. leucocephala avoided water deficit by reducing leaf area. The resulting increase in light intensity reaching the lower strata, toward the end of the dry season weakened the shortest plants and limited fodder production. In conclusion, we propose that farmers implement pasture sustainability by developing crop mixing, using fodder species adapted to abiotic stresses. Furthermore, our results show that several crop combinations represent viable solutions to the perpetuation of new pastures. Each fodder species presents specific drought adaptation features. Combining them could be beneficial if pastoral pressure was allowed to develop according to the plants tolerance level. Improvements in fodder production and diversity could extend the life-span of smallholder settlements and as a result slow down deforestation

Organismal tolerance to abiotic environmental stresses contributes significantly to setting the distribution limits of organisms, as demonstrated by vertical zonation patterns in the marine intertidal zone. In this thesis, the ultimate (evolutionary) and proximate (mechanistic) causes of tolerance to temperature and emersion stresses associated with the intertidal zone were examined using porcelain crabs, genus Petrolisthes. Species of Petrolisthes from intertidal and subtidal microhabitats of four biogeographic regions of the Eastern Pacific were used in phylogenetically-based comparative analyses of morphological, physiological, and biochemical adaptation to environmental stress. A phylogenetic tree based on the sequence of the 16sRNA gene was developed to facilitate these analyses. Organismal thermal tolerance limits are adapted to match maximal microhabitat temperatures. Acclimation of thermal tolerance limits suggests that temperate intertidal zone species are living close to their thermal maximum in nature. Respiratory responses to emersion vary among species from different vertical zones. Experimental examination of oxygen consumption rates and lactate accumulation during emersion suggests that intertidal species are able to respire in air using thin membranous regions on the ventral meral segments of their legs (leg membranes). Leg membrane size is positively correlated with body size across species, but not within a single species. Evolutionary analyses indicate that leg membranes may not have evolved for purposes of aerial respiration, but their presence may have allowed intertidal and subtidal species to achieve larger body sizes and higher metabolic rates. The thermal stabilities of an enzyme, lactate dehydrogenase (LDH), from 22 species of Petrolisthes varied widely, but were not correlated with maximal habitat temperatures. Comparative analyses did not indicate any evolutionary relationship between LDH thermal stability and microhabitat conditions. Experimental evidence suggests that interspecific differences in LDH stability are genetically based, and are due both to intrinsic properties of the LDH molecules and extrinsic protein stabilizers. Elucidation of the mechanism(s) of LDH stabilization in Petrolisthes may provide novel insight to the field of protein stabilization. These results studies suggest that individual traits may be subjected to differing levels of selection, and thus the analysis of environmental adaptation requires careful consideration of the biological significance of the traits being examined.
Graduation date: 1999

Laboratory and field experiments evidence that silicon fertilizers contribute to plant tolerance to unfavorable growth conditions: drought, frost, salinity, heavy metal contamination, and others. Silicon-induced underlying mechanisms include thickening of the epidermal layer, enhanced root system development, chemical stability of the DNA, RNA, and chlorophyll molecules, improved transport and redistribution of elements, as well as activation of defense system in plants against oxidative damage. Application of Si fertilizers and biostimulators promoted reducing crop losses and increasing yield of rice, wheat, barley, soya, potatoes and others under drought and frost conditions.

The application of Si fertilizer is example of “green” low emission technology. The using of biochemical active forms of Si allow to reduce the greenhouse gases emission from cultivated soils, increase the carbon content in soil matrix, increase cultivated plants resistance to abiotic stresses and increase the quality and quantity of crop. Our investigations have sowed the presence of monosilicic acid in soil provide the reduction of N2O emission in 1.6-2 times because the denitrification process in such soil are complete with final formation of N2. The application of Si fertilizer increased the rice crop on 5-55% with carbon sequestration up to 15 t/ha of CO2 during one season.

Major threats to agricultural sustainability in the 21st century are drought, increasing temperatures, soil salinity and soilborne pathogens, all of which are being exacerbated by climate change and pesticide abolition and are burning issues related to agriculture in the Middle East. We have found that Class 2 fungal endophytes adapt native plants to environmental stresses (drought, heat and salt) in a habitat-specific manner, and that these endophytes can confer stress tolerance to genetically distant monocot and eudicot hosts. In the past, we generated a uv non-pathogenic endophytic mutant of Colletotrichum magna (path-1) that colonized cucurbits, induced drought tolerance and enhanced growth, and protected 85% - 100% against disease caused by certain pathogenic fungi. We propose: 1) utilizing path-1 and additional endophtyic microorganisms to be isolated from stress-tolerant local, wild cucurbit watermelon, Citrulluscolocynthis, growing in the Dead Sea and Arava desert areas, 2) generate abiotic and biotic tolerant melon crop plants, colonized by the isolated endophytes, to increase crop yields under extreme environmental conditions such as salinity, heat and drought stress, 3) manage soilborne fungal pathogens affecting curubit crop species growing in the desert areas. This is a unique and novel "systems" approach that has the potential to utilize natural plant adaptation for agricultural development. We envisage that endophyte-colonized melons will eventually be used to overcome damages caused by soilborne diseases and also for cultivation of this crop, under stress conditions, utilizing treated waste water, thus dealing with the limited resource of fresh water.