Long terminal repeats (LTRs) are non-coding repeats flanking the protein-coding genes of LTR retrotransposons. The variability of LTRs poses a challenge in studying them. Hidden Markov models (HMMs), probabilistic models widely used in pattern recognition, are useful in dealing with this variability. The aim of this work was mainly to study LTRs of retroviruses and LTR retrotransposons using HMMs. Paper I describes the methodology of HMM modelling applied to different groups of LTRs from exogenous retroviruses (XRVs) and endogenous retroviruses (ERVs). The detection capabilities of HMMs were assessed and were found to be high for homogeneous groups of LTRs. The alignments generated by the HMMs displayed conserved motifs some of which could be related to known functions of XRVs. The common features of the different groups of retroviral LTRs were investigated by combining them into a single alignment. They were the short inverted terminal repeats TG and CA and three AT-rich stretches which provide retroviruses with TATA boxes and AATAAA polyadenylation signals. In Paper II, phylogenetic trees of three groups of retroviral LTRs were constructed by using HMM-based alignments. The LTR trees were consistent with trees based on other retroviral genes suggesting co-evolution between LTRs and these genes. In Paper III, the methods in Paper I and II were extended to LTRs from other retrotransposon groups, covering much of the diversity of all known LTRs. For the first time an LTR phylogeny could be achieved. There were no major disagreement between the LTR tree and trees based on three different domains of the Pol gene. The conserved LTR structure of paper I was found to apply to all LTRs. Putative Integrase recognition motifs extended up to 12 bp beyond the short inverted repeats TG/CA. Paper IV is a review article describing the use of sequence similarity and structural markers for the taxonomy of ERVs. ERVs were originally classified into three classes according to the length of the target site duplication. While this classification is useful it does not include all ERVs. A naming convention based on previous ERV and XRV nomenclature but taking into account newer information is advocated in order to provide a practical yet coherent scheme in dealing with new unclassified ERV sequences. Paper V gives an overview of bioinformatics tools for studies of ERVs and of retroviral evolution before and after endogenization. It gives some examples of recent integrations in vertebrate genomes and discusses pathogenicity of human ERVs including their possible relation to cancers. In conclusion, HMMs were able to successfully detect and align LTRs. Progress was made in understanding their conserved structure and phylogeny. The methods developed in this thesis could be applied to different kinds of non-coding DNA sequence element.

As a part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, the decay of the superallowed 0⁺ --> 0⁺ beta emitters ³⁸Ca and ⁴⁶V has been studied in this dissertation. For ³⁸Ca, the half-life, 443.88(36) ms, and superallowed branching ratio, 0.7738(41), have been measured. In our half-life experiment, pure sources of ³⁸Ca were produced and the decay positrons detected in a high-efficiency 4[pi] proportional gas counter. Since the beta⁺ decay of ³⁸Ca feeds ³⁸K^m, which is itself a superallowed beta⁺ emitter, the data were analyzed as a linked parent-daughter decay. Our result for the half-life of ³⁸Ca, with a precision of 0.08%, is a factor of five improvement on the best previous result. The branching-ratio of ³⁸Ca depended on beta-delayed gamma-ray intensities being measured with a high-purity germanium detector calibrated for absolute efficiency to 0.2% precision. This branching-ratio result represents our first step in bringing the ft value for the superallowed ³⁸Ca transition into the desired range of 0.1%. With our half-life and superallowed branching ratio results for ³⁸Ca, we obtain the Ft to be 3072(17) s, in good agreement with the conserved vector current expectation. The half-life of ⁴⁶V has been measured to be 422.66(6) ms, a factor of two more precise than the best previous measurement. Our present result determines the corresponding Ft value to be 3074.5(26) s, which is consistent with the average $\overline{\mathcal{F}t}$ value of 3072.08(79) s established from the 13 best-known superallowed transitions. This demonstrates that previously accepted half-lives of ⁴⁶V were correct in their contribution to a precision test of the conserved vector current hypothesis.

Sacred sites in Ysyk-Köl area of Kyrgyzstan represent areas of land and bodies of water which are spiritually and culturally meaningful for local people. The present study mapped about 130 sacred sites, which are conserved-through-use by local communities and represent traditional model of conservation. The entire territory of Ysyk-Köl region is a formal protected area as a UNESCO Biosphere Reserve. Thus, sacred sites, as traditional model of community conserved area, are embedded in the formal government-run Biosphere Reserve. The study scrutinizes how these two models of conservation (sacred sites and the Biosphere Reserve) co-exist in the same territory and interact with each other. Results indicate that these two models are parallel. However, recognition of sacred sites can improve formal conservation by: a) providing a complementary culture-based set of incentives for conservation, b) fostering a biocultural approach, and c) serving as a communication hub for YKBR managers and local communities. / February 2016

Precision measurements of superallowed Fermi β-decay allow for stringent tests of the magnitude of isospin-symmetry-breaking effects in nuclei, the validity of the conserved vector current hypothesis, and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. A high-precision measurement of the branching ratio for the superallowed β+ decay of 74Rb has been performed at the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF. The 8π spectrometer, an array of 20 HPGe detectors, was used to detect γ-rays emitted following the Gamow-Teller and non-analogue Fermi β-decays of 74Rb. PACES, an array of 5 Si(Li) detectors, was used to detect emitted conversion electrons, while half of SCEPTAR, a close-packed array of 10 plastic scintillators, was used to detect emitted β particles. In this experiment, 23 excited states were identified in 74Kr which were populated following the β-decay of 74Rb. A total of 58 γ-rays were identified following the 8.241(4)x108 detected β-particles. An observed non-superallowed branching ratio of 0.396(7)% was determined from the intensity of the identified γ-rays, while the unobserved non-superallowed intensity was calculated to be 0.05(5)%, leading to a superallowed branching ratio of 99.55(5)%. The superallowed branching ratio is now the most precise experimental quantity in the determination of the superallowed ft-value of 74Rb. Combining the half-life and Q-value with the superallowed branching ratio measured in this work leads to a superallowed ft-value of 3082.6(66) s. Finally, comparisons between the superallowed ft-value, the world average Ft-value, and the non-analogue Fermi branching ratio are made to provide future guidance in the refinement of the theoretical models required to describe the crucial isospin-symmetry-breaking term in superallowed β-decay.

All challenges associated with influenza A viruses including antigenic variation in hemagglutinin (HA) and neuraminidase (NA), the evolving drug resistance and the drawbacks of current vaccines hinder our ability to control this constant threat. Furthermore, gene reassortment as well as the direct transmission of highly pathogenic avian viruses to humans can result in an occasional emergence of novel influenza strains with devastating pandemic potential. Therefore, it is crucial to investigate alternative approaches to better control these viruses and to develop new prophylactic and treatment options. Targeting highly conserved epitopes or antigens among the different subtypes of influenza A virus could offer protection against broad range of influenza viruses, including emerging strains. In my research, I have investigated the potential of broadly neutralizing antibodies against HA and conducted mechanistic study of a prototype vaccine based on the highly conserved nucleoprotein (NP). We recently found that the 14 amino acids of the amino-terminus of the fusion peptide of influenza HA2 subunit is the only universally conserved sequence in all HA subtypes of influenza A and the two lineages of influenza B viruses. Here, I show that universal antibodies targeting this linear sequence in the viral HA (Uni-1 antibodies) can cross-neutralize multiple subtypes of influenza A virus by inhibiting the pH-dependant fusion of viral and cellular membranes. It is noted that the influenza NP is a highly conserved antigen and has the potential to induce heterosubtypic immunity against divergent subtypes of influenza A virus. However, NP-based vaccination only affords weak protective immunity compared to HA. This is mostly due to the non-sterilizing immunity induced by NP. Using CD40 ligand (CD40L), a key regulator of the immune system, as both a targeting ligand and a molecular adjuvant, I show that single immunization with recombinant adenovirus carrying a fused gene encoding the secreted NP-CD40L fusion protein provided robust and long-lasting protection against influenza in normal mice. It enhanced both B-cell and T-cell responses and augmented the role of both NP-specific antibodies and CTLs in protection. Importantly, it afforded effective protection in CD40L and CD4 deficient mice, confirming that the induced protection is CD40L-mediated and CD4+ T cell-independent. The rapid evolution of the influenza A viruses necessitates the development of new alternatives to contain this medically important pathogen. The results of these studies could significantly contribute to future vaccine development and avert the necessity of yearly vaccine updates.

Os modelos de Toda admitem uma representação de suas equações de movimento em termos da curvatura nula, isto é, existem potenciais que são funcionais dos campos da teoria e pertencem a uma álgebra de Kac-Moody tal que a condição de curvatura nula seja equivalente às equações de movimento. Para a construção das soluções solitônicas e cargas conservadas são necessários a gradação inteira da álgebra de Kac-Moody e a existência de soluções de vácuo, de forma que os potenciais assumam valores em uma subálgebra abeliana quando calculados nestas soluções de vácuo. A gradação da álgebra é de extrema importância pois garante que o potencial transformado tenha a mesma estrutura que o potencial de vácuo. As cargas conservadas são então construídas partindo de soluções da órbita do vácuo por meio de transformações de dressing, que consistem na aplicação da decomposição de Gauss para a produção de um potencial transformado a partir de duas transformações de Gauge. Nesta dissertação calculamos as infinitas cargas conservadas dos modelos de Toda sl(3) e também sl(N), avaliadas nas soluções pertencentes à órbita do vácuo sob transformações de dressing. As soluções de interesse físico, como sólitons e breathers pertencem a esta órbita, e as cargas conservadas para tais soluções são escritas como uma soma sobre os sólitons. Mostramos que a energia e o momento proveem de termos de superfície. / The Toda models admit a zero curvature representation of their equations of motion, i.e. there exist potentials, (A), wich are functionals of the fields of the theory and which belong to a Kac-Moody algebra G such that the zero curvature condition is equivalent to the equations of motion. For the construction of the solitons solutions and conserved charges is required an integer gradation of the Kac-Moody algebra and a ``vacuum solution\'\', such that the potentials evaluated on it belong to an abelian subalgebra. The gradation of the algebra is of extreme importance since it guarantees that the transformed potential have the same structure as the vacuum potential. The conserved charges are then constructed using the dressing method, that through the Gauss decomposition, leads to the transformed potentials by two gauge transformations. In this dissertation we calculate the infinite conserved charges of models Toda sl (3) and also sl (N) evaluated on the solutions belonging to the orbit of the vacuum under dressing transformations. The solutions of physical interest, like solitons and breathers belong to this orbit and the conserved charges for such solutions are written as a sum over the number the solitons. We show that the energy and momentum are boundary terms.

Uma generalização dos modelos de Toda bidimensionais pela inclusão de campos de Dirac é estudada através de métodos algébricos que possibilitam a construção de cargas e soluções para o modelo. Após desenvolver o formalismo matemático necessário, as cargas conservadas do modelo em questão são determinadas para soluções sóliton, a partir da órbita do vácuo. Uma comparação direta com o modelo de sine-Gordon revela que o mesmo processo de interação entre os sólitons ocorre em ambas as teorias, indicando a possibilidade deste modelo ser utilizado para analisar a equivalência entre esse modelo e os de sine-Gordon e Thirring. / A generalization of two dimensional Toda models by the inclusion of Dirac fields is studied through algebraic methods that allow the construction of charges and solutions. After developing the necessary mathematical formalism, the conserved charges of such model are determined forsoliton solutions belonging to the orbits of the vacuum. A direct comparison between Toda model coupled to matter fields and sine-Gordon model shows that the same interaction process among solitons occurs in both theories, indicating the possibility of this model to be used to analyze the equivalence between sine-Gordon and Thirring models.

Made available in DSpace on 2017-07-10T17:48:06Z (GMT). No. of bitstreams: 1 Rafael_Frank.pdf: 1053662 bytes, checksum: eb7ec01d3ec53c5bff8738bcd9ca4984 (MD5) Previous issue date: 2014-12-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The objective of this study was to determine the aerobic stability, centesimal composition and energy values and the amino acids digestibility of high moisture corn grain silage (HMCS), and evaluate the effect of HMCS inclusion in different levels in diets on performance and gut parameters of Label Rouge broilers. In Experiment 1, to determine the applicability of inoculants usage the growth of main microorganisms involved in fermentation of high moisture corn grain silage was evaluated among time periods, as well as aerobic stability when silages were made with or without the addition of inoculum Lactobacillus plantarum + Propionibacterium acidipropionici. Significant changes were observed for temperature and pH as a function of storage time and use of inoculum. For the population of fungi and entero-bacteria a significant decrease in function of the storage time was observed more expressive for silages in which the inoculum was applied. Changes in all populations of microorganisms studied as a function of storage time were observed. For the chemical composition differences were obtained for dry matter, neutral detergent fiber and acid detergent fiber, when we used silage additive and changes in the concentration of acid detergent fiber in function of the different storage times. Aerobic stability was of 156 hours for silage ensiled by 28 days, without significant difference for inoculation. When ensiled for 56 days, the silage inoculated presented greater stability (60 hours) when compared to no inoculant (32 hours). The high moisture grain corn silage with microbial inoculum based on Lactobacillus plantarum and Propionibacterium acidipropionici was able to reduce the population of fungi and enterobacteria. In Experiment 2, to determine the energy values of high moisture corn silage (HMCS), male broilers from 21 to 31 days old were used, averaging 765 ± 1.70 g. The experimental period lasted ten days, five of adaptation and five for collection. The HMCS replaced in 10, 20, 30 and 40% the reference ration (RR). The method of analysis was the total excreta collection for subsequent analysis of apparent metabolizable energy (AME) and AME corrected for nitrogen balance (AMEn) of HMCS. To determine the amino acid values, the technique of forced feeding was applied in 12 cecectomized Leghorn roosters, with average weight of 1912.10 ± 133.73 g. Six animals received HMCS and the other six were fasted. At the end of the excreta collection period, the essential amino acid profile was determined, as the true digestibility coefficients and the true digestible content of amino acids in HMCS. This food presented average values of 2283 kcal/kg of EMA and 2272 kcal/kg of AMEn, and these energy values were negatively influenced by the inclusion levels of HMCS. Cystine presented the lower digestibility coefficients while leucine and glutamine had the highest digestibility and digestible amino acids values. In Experiment 3, one thousand and two hundred Label Rouge chicks with an average initial weight of 41 ±0.55g were distributed in a completely randomized design, in a factorial 2x5 (with and without the addition of acidifying X 0, 25, 50, 75 and 100% of high-moisture corn grain silage - HMCS). The weight gain (WG), feed intake (FI) and feed conversion (F:G) were determined, beyond the intestinal morphometric analysis and microbiota, carcass yield and cuts. From 1-28 and 1-63 days there was a quadratic effect (P<0.05) of HMCS on FI and F:G. There was interaction (P<0.05) between the levels of HMCS and the addition of acidifying for carcass yield and cuts (wing and chest) and liver of females. Males presented interaction (P<0.05) between levels of HMCS and acidifying for carcass, drumstick, chest and fat. There was an interaction (P<0.05) between HMCS and the inclusion of acidifying in the counting of Lactobacillus and Clostridium at 28 days old and for Lactobacillus at 63 days old. At 28 days there was an interaction (P<0.05) between HMCS and the inclusion of acidifying for villi height. At 63 days there was and quadratic effect of HMCS and the acidifying for crypts, which presented higher diameter for treatments without acidifying. The results suggest that jerk chickens fed up to 50% of HMCS with acidifying had good carcass yield and cuts and had no damage on intestinal development / O objetivo deste trabalho foi determinar a estabilidade aeróbica, a composição bromatológica e energética e a digestibilidade de aminoácidos da silagem de grãos úmidos de milho (SGUM), além de avaliar o desempenho e parâmetros intestinais de frangos Label Rouge recebendo diferentes níveis de SGUM na alimentação. No Experimento 1, para determinar a aplicabilidade da utilização de inóculos, foi avaliado o crescimento dos principais microrganismos envolvidos na fermentação da SGUM ao longo do tempo, assim como a estabilidade aeróbia quando silagens foram confeccionadas com ou sem adição de inóculo Lactobacillus plantarum + Propionibacterium acidipropionici. Foram observadas alterações significativas para temperatura e pH em função de tempo de estocagem e utilização de inóculo. Para a população de fungos e enterobactérias foi observada redução significativa em função do tempo de armazenamento de forma mais expressiva para as silagens em que foi aplicado o inóculo. Observou-se alteração em todas as populações de microrganismos estudados em função do tempo de armazenamento. Para a composição química, foram obtidas diferenças para matéria seca, fibra em detergente neutro e fibra em detergente ácido, quando foi utilizado inoculante, e alterações na concentração de fibra em detergente ácido em função dos diferentes tempos de armazenagem. A estabilidade aeróbica foi de 156 horas para silagens ensiladas por 28 dias, sem diferença significativa para inoculação. Quando ensilada por 56 dias, a silagem inoculada apresentou maior estabilidade (60 horas) quando comparada à sem inoculante (32 horas). A ensilagem de grão úmido de milho com inóculo microbiano à base de Lactobacillus plantarum e Propionibacterium acidipropionici foi capaz de reduzir a população de fungos e enterobactérias. No Experimento 2, para a determinação dos valores energéticos da SGUM, foram utilizados frangos de corte machos, dos 21 aos 31dias de idade, com peso médio de 765 ± 1,70 g. O período experimental teve duração de dez dias, sendo cinco de adaptação e cinco de coleta. A SGUM substituiu em 10, 20, 30 e 40% uma ração referência (RR). O método de análise foi o de coleta total de excretas, para posterior análises de energia metabolizável aparente (EMA) e EMA corrigida pelo balanço de nitrogênio (EMAn) da SGUM. Para a determinação dos valores de aminoácidos, foi usada a técnica de alimentação forçada em 12 galos Leghorn cecectomizados, com peso médio de 1912,10 ±133,73g. Seis animais receberam a SGUM e os outros seis permaneceram em jejum. Ao final do período de coleta de excretas, foi determinado o perfil de aminoácidos essenciais, coeficientes de digestibilidade verdadeira e o conteúdo digestível verdadeiro dos aminoácidos no alimento. A SGUM apresentou valores médios de 2283 kcal/kg de EMA e 2272 kcal/kg de EMAn, sendo que os valores energéticos foram negativamente influenciados pelos níveis de inclusão da SGUM. A cistina apresentou o menor coeficiente de digestibilidade, enquanto que a leucina e a glutamina apresentaram os maiores coeficientes de digestibilidade e os valores de aminoácidos digestíveis. No Experimento 3, foram utilizados 1200 pintos da linhagem Label Rouge, com peso médio inicial de 41 ±0,55g, distribuídos em um delineamento inteiramente casualizado, em esquema fatorial 2x5, (com e sem acidificante X 0, 25, 50, 75 e 100% de silagem de grãos úmidos de milho - SGUM). Foram determinados o ganho de peso (GP), consumo de ração (CR), conversão alimentar (CA), além da análise morfométrica e de microbiota intestinal, rendimento de carcaça e de cortes. De 1 a 28 e de 1 a 63 dias, houve efeito quadrático (P<0,05) da SGUM sobre o CR e CA. Houve interação (P<0,05) entre os níveis de SGUM e a adição de acidificante para o rendimento de carcaça e de cortes (asa, peito) e fígado das fêmeas. Os machos apresentaram interação (P<0,05) entre os níveis de SGUM e o acidificante para carcaça, sobrecoxa, peito e gordura. Houve interação (P<0,05) da inclusão de SGUM e a adição ou não de acidificante para a contagem de Lactobacillus e Clostridium aos 28 dias de idade e Lactobacillus aos 63 dias de idade. Aos 28 dias, houve interação (P<0,05) entre os níveis de SGUM e a adição de acidificante para a altura dos vilos. Aos 63 dias, foi observado efeito quadrático da SGUM para o tratamento com acidificante e as criptas apresentaram maior diâmetro para o tratamento sem acidificante. Os resultados sugerem que frangos caipiras alimentados com até 50% de SGUM com acidificante apresentam boas características de carcaça e de cortes e não sofrem danos sobre os parâmetros intestinais

All challenges associated with influenza A viruses including antigenic variation in hemagglutinin (HA) and neuraminidase (NA), the evolving drug resistance and the drawbacks of current vaccines hinder our ability to control this constant threat. Furthermore, gene reassortment as well as the direct transmission of highly pathogenic avian viruses to humans can result in an occasional emergence of novel influenza strains with devastating pandemic potential. Therefore, it is crucial to investigate alternative approaches to better control these viruses and to develop new prophylactic and treatment options. Targeting highly conserved epitopes or antigens among the different subtypes of influenza A virus could offer protection against broad range of influenza viruses, including emerging strains. In my research, I have investigated the potential of broadly neutralizing antibodies against HA and conducted mechanistic study of a prototype vaccine based on the highly conserved nucleoprotein (NP). We recently found that the 14 amino acids of the amino-terminus of the fusion peptide of influenza HA2 subunit is the only universally conserved sequence in all HA subtypes of influenza A and the two lineages of influenza B viruses. Here, I show that universal antibodies targeting this linear sequence in the viral HA (Uni-1 antibodies) can cross-neutralize multiple subtypes of influenza A virus by inhibiting the pH-dependant fusion of viral and cellular membranes. It is noted that the influenza NP is a highly conserved antigen and has the potential to induce heterosubtypic immunity against divergent subtypes of influenza A virus. However, NP-based vaccination only affords weak protective immunity compared to HA. This is mostly due to the non-sterilizing immunity induced by NP. Using CD40 ligand (CD40L), a key regulator of the immune system, as both a targeting ligand and a molecular adjuvant, I show that single immunization with recombinant adenovirus carrying a fused gene encoding the secreted NP-CD40L fusion protein provided robust and long-lasting protection against influenza in normal mice. It enhanced both B-cell and T-cell responses and augmented the role of both NP-specific antibodies and CTLs in protection. Importantly, it afforded effective protection in CD40L and CD4 deficient mice, confirming that the induced protection is CD40L-mediated and CD4+ T cell-independent. The rapid evolution of the influenza A viruses necessitates the development of new alternatives to contain this medically important pathogen. The results of these studies could significantly contribute to future vaccine development and avert the necessity of yearly vaccine updates.

Chez les plantes, le nitrate est un élément essentiel mais sa disponibilité dans le sol est fluctuante. Il est donc stocké dans la vacuole grâce à un échangeur nitrate/proton appelé AtClCa. La famille de protéines ClCs comporte à la fois des échangeurs mais aussi des canaux suggérés comme issus de l’évolution des échangeurs par une conversion mécanistique. Chez Arabidopsis thaliana, seuls des ClCs échangeurs assurent la gestion du nitrate. Deux glutamates très conservés, E203 et E270 dans AtClCa, sont essentiels pour le transport des protons chez les ClCs échangeurs. La mutation du résidu E203 en une alanine, un acide aminé non protonable (E203A) a permis de produire artificiellement une telle conversion mécanistique. Afin de mieux comprendre l’importance physiologique du mécanisme d’échange, une analyse a été conduite sur des plantes exprimant la forme mutée d’AtClCa pour ce glutamate. Chez ces plantes, le stockage vacuolaire est fortement réduit au profit d’une importante assimilation accroissant la teneur en protéines. En dépit de cela, elles présentent un défaut de production de biomasse résultant en grande partie d’une perturbation de l’homéostasie hydrique. Elles sont également plus sensibles aux stress hydrique et probablement azoté. La conservation d’un échangeur est donc requise pour croitre en dépit des fluctuations environnementales. En parallèle, la mutation E270A a été introduite en plante afin d’étudier son importance sur la physiologie d’Arabidopsis. Une analyse préliminaire de la biomasse et des contenus en nitrate et eau de plantes exprimant la forme mutée de ce glutamate est donc présentée dans la seconde partie de cette thèse. / Nitrate is a major element for plant but its availability is very fluctuant in soils. Then, it is stored in vacuoles thanks to a nitrate/proton exchanger named AtClCa. In ClCs, exchangers but also channels were identified, the latest were suggested to be evolved from exchanger in which a mechanistic switch happened. In Arabidopsis thaliana, only exchangers are involved in nitrate management. Two conserved glutamate, E203 and E270 in AtClCa, are essential for protons transport in ClCs exchangers. The mutation of E203 into an alanine, a non-protonable amino acid (E203A) artificially produces such a mechanistic switch. To better understand the physiological importance of this exchange mechanism, a study was conducted in plants expressing the mutated form of AtClCa for this glutamate. In those plants, the vacuolar storage is highly restricted whereas the assimilation is favoured and the protein content increased. Despite that, the biomass production is decreased mostly because of a hydric homeostasis disruption. Those plants are also more sensitive to hydric and probably nitrogenous stress. The exchanger conservation is then required for plant growth whatever the environmental fluctuations. In parallel, the mutation E270A was introduced in planta to study its physiological importance. A preliminary analysis of plant biomass and nitrate and water contents was then performed in plants expressing the E270A mutated form of AtClCa and the results are presented in the second part of the manuscript.