No description available.

Lettuce is a highly nutritional crop that is sensitive to multiple stresses, including salt stress. The decreasing availability of salt-free water is posing a major challenge to growing nutritious lettuce in hydroponic systems. Despite evidence that salt stress affects yield and nutrition, its impacts on economically important growth stages are overlooked. This study addressed the knowledge gaps regarding the salt stress impact on romaine lettuce. Four independent experiments were conducted in controlled environment conditions using 2-38 lettuce genotypes, to assess the effects of salt stress at rosette or head formation. An increase in sodium chloride (NaCl) levels (0 to 150 mM) linearly decreased lettuce biomass. A positive association was observed between NaCl and sodium to potassium ion ratio. Lettuce was found to be sensitive to salt above 40 mM NaCl. The phenotyping of 38 lettuce genotypes revealed significant variability in salt stress tolerance. Genotype, Green forest exhibited a higher decline in fresh and dry biomass compared to Burgundy delight, indicating its higher sensitivity to salt stress. Sodium accumulation was significantly higher in both genotypes under salt stress, while potassium decreased in Green forest but remained relatively stable in Burgundy Delight. Hydro-primed lettuce had higher photosynthetic efficiency and oxidative stress tolerance than the control. Hydro-priming seed treatment could be used as a cost-effective priming technique to boost economic efficiency under stress. In addition, the low sodium: potassium ratio and high biomass can be used as indicators for selecting salt-tolerant genotypes.

Soil salinity is an increasing problem facing agriculture in many parts of the world. Climate change and irrigation practices have led to decreased yields of large areas of farmland due to increased salt levels in the soil. Irrigation introduces salts to the soil that with time accumulate and threaten crop yield. In arid climates like Utah, the practice of irrigation is especially threatening to salt-sensitive crops including alfalfa (Medicago sativa). Plants that have tolerance to salt are needed to feed livestock and the world's population. One approach to address this problem is to introduce genes encoding salt tolerance into the genomes of salt-sensitive plants through genetic engineering, but this approach has limitations. These limitations include the misinformed public perception of genetically modified organisms (GMOs). Even if the GMO salt-tolerant plants could produce palatable foods, in regions of the world with saline soils incongruous with farming, if consumers refuse to purchase the food then the engineering and upfront costs of production are negated. Another fairly new approach involves the isolation and development of salt-tolerant (halophilic) plant-associated bacteria. Several reports are now available demonstrating how the use of halophilic inoculants enhance plant growth in salty soil. This enhanced plant growth is most likely associated with changes in plant gene expression; however, the mechanisms behind this growth stimulation are not yet clear. Halomonas elongata 1H9, a rhizobacteria native to Goshen UT, has been identified as a plant growth-promoting rhizobacteria (PGPR) when used as an inoculant added to alfalfa seedlings grown in salty soils. Plants grown in the presence of this Halomonas sp. and 1% salt demonstrated an average increase of 2.4x the biomass of alfalfa plants grown without inoculum in salty soils. This suggests that this Halomonas sp. positively influences plant salt tolerance, which raises the question as to how the bacteria stimulate plant growth under these conditions. To identify and characterize plant genes induced by Halomonas elongata, transcriptional analysis was performed using RNA-sequencing (RNA-seq). This analysis identified a variety of differentially expressed genes (DEGs) including transcription factors (e.g. MYB14, GATA transcription factor 9, Ethylene-responsive transcription factors ER017 and ER109) and plant enzymes involved in growth and development (e.g. xyloglucan endotransglucosylase and phosphodiesterase). This was followed by gene validation via real-time quantitative PCR (RT-qPCR), the gold standard for RNA-seq validation, however this process was never successfully completed. Suggestions for next steps are included in the discussion section of chapter 3.

No description available.

Thesis (PhD (Genetics))--University of Stellenbosch, 2011. / Includes bibliography. / Please refer to full text to view abstract.

Chez les végétaux supérieurs, la régulation des mouvements stomatiques permet de contrôler les échanges de CO2 et la montée de la sève brute tout en limitant les pertes excessives d'eau par transpiration. Ce contrôle est assuré par des variations rapides de la turgescence des deux cellules de garde formant le stomate dues à l'activité de nombreux canaux et transporteurs ioniques. Nous avons identifié un nouveau membre de la famille des CLC chez A. thaliana, AtCLC-c exprimé dans la cellule de garde. L'étude de l'expression d'AtCLC-c et du phénotype de mutants invalidés ont permis de démontrer son rôle dans l'ouverture stomatique à la lumière et la fermeture en réponse à l'ABA. Les mutants clcc accumulent moins d'ions Cl- dans leurs cellules de garde par rapport aux plantes sauvages et sont hypersensibles à un stress salin. Enfin, nous avons confirmé par des études d'électrophysiologie la sélectivité d'AtCLC-c aux ions Cl-. L'ensemble de ce travail montre l'importance du transporteur vacuolaire d'ions Cl- AtCLC-c dans les mouvements stomatiques et la tolérance au stress salin. / In plants, the high turgor is assured by ion transport and involves the creation and maintenance of a large vacuolar volume. In recent years, various chloride channels and transporters have been identified to be involved in specific functions such as plant nutrition, stomatal movements or metal tolerance. We have characterized a new member of the CLC family in A. thaliana, AtCLC-c, highly expressed in guard cell and up-regulated by ABA and salt treatment in the whole plant. Knock-out mutants in AtCLC-c are impaired in light-induced stomatal opening and ABA-induced stomatal closing correlated to a large decrease in guard cell Cl- content. Furthermore, clcc mutants are hypersensitive to salt stress compared to wild-type. Finally, using electrophysiological studies, we demonstrated that AtCLC-c is selective to Cl-. Altogether, this work shows that AtCLC-c is a tonoplastic Cl- transporter involved in stomatal movements and salt tolerance.

Le stress salin est l'un des principaux facteurs environnementaux limitant la croissance des plantes et entraînant des pertes de rendement des cultures céréalières. Il est ainsi impératif de développer des variétés plus tolérantes à la salinité afin d’augmenter leurs rendements et assurer la sécurité alimentaire. La voie signalétique reliant la perception du stress salin à la réponse cellulaire, encore peu connue, a été abordée ici par l’étude des protéines RSS1-like conservées chez les plantes. La protéine RSS1 (Rice Salt Sensitive 1) du riz joue un rôle primordial dans la tolérance au stress salin en agissant à l’interface entre la perception des stress et le contrôle du développement et de la division dans les méristèmes. Lors de ce travail, l'homologue de RSS1 nommé TdRL1 (Triticum durum RSS-Like 1) a été isolé à partir de la variété tunisienne de blé dur “Oum Rabiaa“. Nous avons démontré que TdRL1 porte les motifs D et DEN-Box conservés impliqués dans la régulation post-traductionnelle de la protéine. En outre nous avons apporté la preuve que TdRL1 est l’homologue fonctionnel de RSS1 puisqu'il est capable de complémenter le mutant de perte de fonction rss1, hypersensible au stress salin. En outre, l’expression hétérologue de TdRL1 améliore la tolérance au stress salin chez la levure ainsi que chez Arabidopsis et ce par l’augmentation du pouvoir germinatif et la réduction de l’accumulation des espèces oxygénées réactives. Nos études cytologiques ont montré que la protéine TdRL1 est cytoplasmique en interphase et se localise au niveau des microtubules kinétochoriens pendant la mitose. Remarquablement, TdRL1 change de localisation cellulaire sous stress salin et montre une accumulation partielle dans le noyau, soulignant le caractère multifonctionnel de cette protéine dans la réponse au stress salin. L’ensemble des données suggère que sous contrainte saline, TdRL1 joue un rôle dans la régulation du cycle cellulaire en relation avec le réseau microtubulaire. L‘étude de la famille RSS1-like multifonctionnelle permettra ainsi d’aborder de nouvelles voies de recherche pour la création variétale de blé plus résilientes aux stress de l'environnement. / Salt stress is one of the main environmental factors limiting plant growth and yield in cereal crops. It is therefore imperative to develop varieties more tolerant to salt stress in order to increase yield and ensure food security. The signaling pathway linking salt stress perception to cellular response was addressed here by studying RSS1-like proteins in plants. RSS1 (Rice Salt Sensitive 1) protein plays an important role in salt stress tolerance. It acts at the interface of stress perception and developmental control and division in meristems. During this work, the RSS1 counterpart named TdRL1 (Triticum durum RSS-Like 1) was isolated from the durum wheat Tunisian variety "Oum Rabiaa". We have demonstrated that TdRL1 carries the conserved D and DEN-Box motifs involved in the post-translational regulation of the protein. In addition, we show that TdRL1 is the functional homologue of RSS1 since it was able to complement the loss-of-function mutant rss1, hypersensitive to salt stress. In addition, heterologous expression of TdRL1 enhances salt stress tolerance in yeast and in Arabidopsis by increasing germination and reducing the accumulation of reactive oxygen species. Our cytological studies have shown that the TdRL1 protein is cytoplasmic in interphase and is localized at the spindle during mitosis. Remarkably, TdRL1 changes its subcellular localization under salt stress treatment and shows a partial accumulation in the nucleus, highlighting the multifunctional nature of this protein during salt stress response. Our data suggest that under salt stress, TdRL1 plays a role in the regulation of the cell cycle in relation with the microtubule network. Pursuing the study of RSS1-like multifunctional proteins will open up new research areas for the creation of wheat varieties that are more resilient to environmental stresses.

SummarySummarySummarySummary Cytokinins (CKs) are important group of plant hormones involved in a wide range of physiological and developmental processes. Endogenous levels of CKs as well as proportions of individual CK forms and derivatives are not constant and differ among plant species. The amounts of biological active CK forms (free bases and ribosides) are regulated through tangled machinery of metabolic conversions including biosynthesis, conjugation and degradation pathways. The main object of this thesis was to characterize the metabolic pathways involved in the regulation of bioactive CK levels in plants especially via CK biosynthesis with aspect to the environmental stimuli and via N- glucosylation pathway. It was shown, that light signal is an important input for modulating some CK-related genes and CK levels in Arabidopsis plants. The complex diurnal expression profiles of CK-biosynthetic genes (AtIPT1 - AtIPT9) in Arabidopsis plants indicated a strong dependence of AtIPT1 and AtIPT5 on light/dark phase in leaf rossetes. In contrast, no diurnal oscillation of AtIPT transcript levels was recorded in roots. Although the content of endogenous CKs was not constant in plants and varied during a day, no statistically significant correlation between light/dark cycle and oscillation in CK levels was...

Submitted by (ana.araujo@ufrpe.br) on 2017-02-20T17:04:51Z No. of bitstreams: 1 Manuela Maria Cavalcante Granja.pdf: 696391 bytes, checksum: 1cfe62663cfe614a373e837e03fde09b (MD5) / Made available in DSpace on 2017-02-20T17:04:51Z (GMT). No. of bitstreams: 1 Manuela Maria Cavalcante Granja.pdf: 696391 bytes, checksum: 1cfe62663cfe614a373e837e03fde09b (MD5) Previous issue date: 2010-02-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Sugarcane (Saccharum officinarum) is a grass considered moderately sensitive to salinity. Although traditionally cultivated in the soil of the Atlantic Coast and the Northeast, the cultivation of sugarcane is expanding to semi-arid regions. The poor quality of irrigation water, high rates of evaporation and low rainfall, combined with other factors contribute to the process of soil salinization in semi-arid. For the development and selection of tolerant genotypes, it is necessary to understand the physiological mechanisms with which plants face the salt stress. Techniques for in vitro plant tissue for studies of physiology and biochemistry of plants under stress are important tools to allow control and uniformity of culture conditions. In this study, two genotypes of sugarcane (RB931011 and RB872552) developed within the Program of Genetic Improvement of Sugarcane of rides, for the Northeast region (RIDESA) were evaluated for sudden and gradual action of salt stress-induced by adding NaCl to the culture medium during in vitro development of plants. The varieties of sugarcane were subjected to three concentrations of NaCl (0 mM, 50 mM and 100 mM) in a gradual and sudden. At 35 days of experiment, enzyme activities (CAT, POX, APX, PPO), levels of sodium (Na+), potassium (K+), soluble protein content and free proline were recorded. It was possible to observe differences in responses of varieties depending on the condition of induced salt stress, shock or gradual, rather than depending on the concentration of NaCl in the culture medium. The stress response is therefore not only conditioned by salt concentration, but by way of exposure to salt. / A cana-de-açúcar (Saccharum officinarum) é uma gramínea considerada moderadamente sensível à salinidade. Embora tradicionalmente cultivada nas zonas de Mata úmida e Litoral da região Nordeste, o cultivo da cana-de-açúcar vem se expandindo também para regiões semi-áridas. A má qualidade da água de irrigação, altas taxas de evaporação e baixa precipitação pluviométrica, aliada a outros fatores contribuem para o processo de salinização dos solos do semi–árido. Para o desenvolvimento e seleção de genótipos tolerantes, é necessário conhecer os mecanismos fisiológicos com os quais as plantas enfrentam o estresse salino. Técnicas de cultivo in vitro para estudos da fisiologia e bioquímica de plantas, em condições de estresse, são importantes ferramentas por permitirem o controle e homogeneidade das condições de cultivo. No presente trabalho, dois genótipos de cana-de-açúcar (RB931011 e RB872552) desenvolvidos pelo Programa de Melhoramento Genético da Cana-de-Açúcar da RIDESA, para a região Nordeste, foram submetidos ao estresse salino in vitro mediante o acréscimo de NaCl ao meio de cultura sob uma ação gradativa e súbita para avaliar o comportamento fisiológico e bioquímico dessas plantas. As variedades de cana-de-açúcar foram submetidas a duas concentrações de NaCl (56mM, 112mM e o controle) de forma gradativa e repentina. Aos 35 dias de experimento, atividades enzimáticas da Catalase (CAT), Peroxidase (POX), Ascorbato peroxidase (APX), Polifenoloxidase (PPO), teores de sódio (Na+), potássio (K+), concentração de proteínas solúveis e prolina livre foram determinadas. Foi possível observar diferenças nas respostas das variedades em função da condição de indução do estresse salino, gradativo ou por choque, mais do que em função das concentrações de NaCl no meio de cultura. A resposta ao estresse é, portanto, condicionada não só pela concentração dos sais, mas pela forma que a planta é exposta ao meio salino.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A presente tese propÃs testar a hipÃtese de que a reduÃÃo no comprimento de raÃzes de feijÃo-caupi, tratadas com NaCl, pode està relacionada com mudanÃas na atividade de enzimas antioxidantes intracelulares e apoplÃsticas. Isto seria relacionado ao aumento e/ou controle da concentraÃÃo de espÃcies reativas oxigÃnio por mecanismos enzimÃticos que controlam o crescimento. O trabalho foi subdividido em 5 capÃtulos independentes e interligados. O primeiro capÃtulo trata de uma revisÃo teÃrica do tema abordado na tese justificando-a e colocando em evidÃncia a relevÃncia cientÃfica do trabalho. Esta revisÃo trata de todos os aspectos abordados na tese, alÃm de temas conexos como a descriÃÃo das vias sinalizaÃÃo ativadas sobre estresse salino e algumas molÃculas sinalizadoras. No capÃtulo 2, avaliou-se o efeito do NaCl no comprimento da raiz, conteÃdo relativo de Ãgua (CRA), teor de massa seca, concentraÃÃo de Na+ e relaÃÃo K+/Na+ alÃm da atividade de dismutase de superÃxido (SOD), peroxidase de ascorbato (APX), peroxidase de fenÃis (POX) e catalase (CAT) nas cultivares PÃrola (sensÃvel) e PitiÃba (resistente) de feijÃo-caupi, contrastantes quanto à resistÃncia ao estresse salino e oxidativo no estÃdio de germinaÃÃo. Este trabalho possibilitou concluir que embora as cultivares apresentem grau de sensibilidade diferenciado ao NaCl e estresse oxidativo, no estÃdio de germinaÃÃo, essas caracterÃsticas nÃo sÃo mantidas no estÃdio fisiolÃgico de plantula. AlÃm disso, os parÃmetros avaliados nÃo foram capazes de determinar diferenÃas contrastantes entre as duas cultivares que pudessem classificÃ-las como resistente e/ou susceptÃvel ao sal. No intuito de compreender melhor os mecanismos antioxidantes das cultivares estudadas e avaliar se a concentraÃÃo de NaCl interfere na reposta das mesmas, no capÃtulo 3 determinou-se comprimento radicular, CRA e concentraÃÃo de Na+, alÃm das atividades de SOD, APX, CAT e POX em raÃzes de plÃntulas tratadas com 0; 25; 50; 75 e 100 mM de NaCl durante dois dias. Este capÃtulo possibilitou concluir que a resposta no crescimento e na atividade de enzimas antioxidantes à dependente da dose e da cultivar. Ademais, verificou-se que um sistema envolvendo a atividade de POX poderia estar associado tanto à manutenÃÃo dos nÃveis de H2O2 quanto à reduÃÃo no comprimento radicular. Para determinar se os mecanismos antioxidantes sÃo dependentes do tempo de exposiÃÃo ao NaCl, no capÃtulo 4, raÃzes de feijÃo-caupi da cultivar PitiÃba foram tratadas com 0; 50 e 100 mM de NaCl durante 0; 24; 48; 72 e 96 horas. Neste capÃtulo, demonstrou-se que a reduÃÃo no comprimento radicular, depende da dose e do tempo de exposiÃÃo ao NaCl e que os efeitos sÃo acompanhados por um acÃmulo de Na+ nos tecidos, embora isto nÃo leve a uma peroxidaÃÃo de lipÃdeos. Este capÃtulo tambÃm levantou dÃvidas com relaÃÃo ao envolvimento das enzimas SOD, APX, CAT e POX durante o crescimento. Para contribuir com a elucidaÃÃo desses mecanismos o capÃtulo 5 envolveu pelo menos 3 experimentos onde as plÃntulas de feijÃo-caupi foram expostas a perÃodos de estresse de curta e longa duraÃÃo. Nestes experimentos foram relacionados o metabolismo das espÃcies reativas de oxigÃnio de apoplasto com a atividade de oxidase de NADPH (NOX), SOD apoplÃstica e POX de parede celular. Uma explicaÃÃo plausÃvel para uma relaÃÃo entre o estresse oxidativo e o estresse salino à que a resposta antioxidante pode simular parcialmente uma resposta hipersensitiva. As enzimas NOX, SOD apoplÃstica e POX de parede apresentaram um aumento de atividade precedido de uma explosÃo oxidativa. Adicionalmente o H2O2 pode funcionar como sinalizador celular de estresse e ser coadjuvante na lignificaÃÃo da parede. / In the present thesis, the hypothesis that the salt-induced impairment of root growth is due to changes in the symplastic and apoplastic antioxidant enzyme activity was investigated. Root growth impairment may be related to the enhancement and/or the control of the reactive oxygen species by enzymatic systems involved in growth regulation. This work was divided into five interconnected chapters. The first is a theoretical review of the approached subject and includes the scientific relevance of this study. This review details the oxidative mechanisms involved in root growth regulation under salinity, besides the signaling pathways activated under salt stress and related signaling molecules. In the chapter 2, the PÃrola (sensitive) and PitiÃba (resistant) cultivars showing contrasting responses to salt stress at germination were evaluated during the seedling stage. Four-day-old seedlings were exposed to 100 mM NaCl for two days and it was determined the root length, dry weight, relative water content (RWC), Na+ content, K+/Na+ ratio and the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), phenol peroxidase (POX) and catalase (CAT). The obtained results were insufficient to categorize the tested cultivars as sensitive or resistant to salt stress at the seedling stage. The effect of the external NaCl concentration on the antioxidant responses in the studied cultivars was investigated in the chapter 3. It was assessed the root lenght, RWC, Na+ content and the activity of SOD, APX, CAT, and POX in seedlings treated with 0; 25; 50; 75 and 100 mM NaCl during two days. The root growth impairment was more pronounced in the PitiÃba cultivar under 100 mM NaCl. Additionally, it was verified that a metabolic network involving the POX activity could be associated with the maintenance of H2O2 levels and the root growth restriction. In the chapter 4, a time-course of the antioxidant responses were assessed in the PitiÃba cultivar. Then, the seedlings were exposed to 0, 50 and 100 mM NaCl during 0; 24; 48; 72; and 96 h and the same variables determined in the previous experiment were evaluated again. It was demonstrated that the root length reduction depends on the NaCl concentration and the time of exposure. Although the root Na+ content could suggest Na+ toxicity, no lipid peroxidation was detected. The involvement of SOD, APX, CAT, and POX activity in root growth regulation was minutely investigated in the chapter 5. Thus, the seedlings were exposed to salt stress in short- and long-term experiments. The reactive oxygen species metabolism in the apoplastic fraction was associated with the activity of NADPH oxidase (NOX), apoplastic SOD and cell wall POX. It is possible that oxidative stress and salt stress are interconnected as the antioxidant response could mimic the hypersensitive reaction. NOX, apoplastic SOD and cell wall POX showed enhanced activity preceding an oxidative burst. Additionally, H2O2 could act as an extracellular signal triggered by stress and play a role in cell wall strengthening.