Dissertations / Theses on the topic 'Antiporno'

This thesis examines the embodiment of the sexed body and the struggle of fitting into the narrow frames of what a woman is supposed to behave and look like in Japanese cinema. Using the medium of film, I, therefore, seek to produce knowledge regarding the internalized gaze of the oppressor, and self-objectification, caused by the capitalist heteropatriarchy. Thus, I am drawing from cyborg feminism, and the second wave of sexual difference theory’s concept of becoming, expanded upon by the Italian-Australian philosopher Rosi Braidotti. I further use the French sociologist Pierre Bourdieu’s notion of masculine domination and the American philosopher Gayle Rubin’s charmed circle, in creating a theoretical framework, and using the methods of cultural and feminist film analysis to contextualize the films and locate the subjectification of the women. The movies that I will be analyzing are the Japanese director and poet Sion Sono’s Antiporno (アンチポルノ, 2016) and the Japanese director and photographer Mika Ninagawa’s Helter Skelter (ヘルタースケルター, 2012), which both center around two women and their struggle in becoming-cyborg, in relation to power, trauma, sexuality, technology, and beauty ideals in ‘modernized’ Japan. In that sense, I will study the phenomenon of operating outside the lines of social norms of femininity and desire.

Os tripanosomatídeos são protozoários flagelados pertencentes à ordem Kinetoplastida (HONIBERG et al., 1964). São caracterizados por possuírem uma única mitocôndria que percorre toda extensão da célula, na qual se localiza o cinetoplasto, composto por uma rede de fibras circulares de DNA, unidas entre si (HOARE & WALLACE, 1966; CAMARGO, 1979). Encontram-se comumente parasitando animais invertebrados, vertebrados e plantas (VICKERMAN, 1976). Dentre os membros da família Trypanosomatidae, os gêneros Trypanosoma e Leishmania são constituídos de protozoários digenéticos de vertebrados e insetos (CAMARGO, 1979) e são os que mais despertam interesse em medicina humana e veterinária (CANÇADO, 1968). Os graves problemas implicados nas doenças causadas por algumas espécies destes gêneros, tem atraído o interesse de um grande número de pesquisadores para o estudo da biologia dos membros da família Trypanosomatidae. Entre estes incluem-se não só os que se dedicam aos problemas de ordem prática relativos ao controle das tripanosomíases, mas também os voltados para os problemas biológicos de interesse mais geral, que vão desde os estudos filogenéticos até os relacionados com a ultraestrutura e biologia molecular

Vibrio cholerae, l'agent du cholera est une bacterie halotolerante capable de survivre dans les environnements sales. Chez escherichia coli, l'expulsion du sodium est liee a un flux de h + via un antiport na +/h + qui permet de maintenir un gradient de na + sur une large gamme de concentration de na + extracellulaire. L'extrusion du na + jouerait egalement un role dans la regulation du ph intracytoplasmique. Le but de ce travail etait d'etudier le role des antiports na + /h + dans la survie et la virulence de v. Cholerae. En effet, de tels mecanismes doivent permettre a la bacterie de maintenir son homeostasie intracellulaire (na + et ph) en fonction des variations de son environnement. Nous avons etudie 3 antiports de v. Cholerae : nhaa, nhab et nhad. Nous avons montre que ces trois proteines ont une fonction antiport na +(li +)/h + en restaurant la croissance d'un mutant nhaab, chaa de e. Coli en milieu sale (0,2m nacl, ph 7,5, et 0,01m licl, ph 7,5). Les genes nhaa, nhab et nhad ont ete inactives et l'etude de la croissance des mutants a ete realisee en presence de na + et de li +. Un mutant nhaa ne pousse plus en licl 120 mm a ph 8,5. Il en est de meme pour les mutants nhaab, nhaad et nhaabd. En revanche, a la difference des mutants nhaa ou nhaab de e. Coli, les mutants nhaa, nhab, nhad, nhaab, nhaad, nhabd et nhaabd de v. Cholerae continuent de croitre a differentes concentrations de nacl. L'inactivation des antiports n'entraine pas de difference de virulence chez le souriceau. L'absence de phenotype de ces mutants suggere qu'il existerait d'autres antiports na +/h +. L'analyse recente de la sequence complete du genome de la bacterie a permis de mettre en evidence la presence de 3 autres antiports putatifs : yqki, nhap, nhac-1. Notre travail constitue la premiere etude des antiports de v. Cholerae. Une etude plus complete du cycle du na + permettrait de mieux comprendre les facteurs qui contribuent a sa survie dans l'environnement et au cours du processus infectieux chez l'hote.

Une étude de l'impact de la polyploïdie sur des indicateurs physiologiques précoces de la tolérance au sel chez les agrumes a été réalisée. De même, une étude de la diversité du gène cNHXI potentiellement impliqué dans la compartimentation vacuolaire du sodium a été initiée. L'évaluation in vitro de l'aptitude des porte-greffe à compartimenter les ions sodium et chlorures a apporté des résultats contradictoires par rapport aux comportements physiologiques observés sur jeunes plants et sur des plants âgés de 3 ans franc de pied ou greffés. Les porte-greffe sensibles (Poncirus et Citranges) favorisent le transport des chlorures vers les feuilles et limitent celui du sodium tandis que les porte-greffe du genre Citrus réputés tolérants présentent un comportement inverse. De même, la tétraploïdie favorise la tolérance en condition de stress salin. La croissance des autotétraploïdes dans ces conditions est meilleure que celle des parents diploïdes, et les symptômes foliaires (brûlures et défoliations) sont moins marqués. Enfin l'hybride somatique allotétrapoïde FLHORAGI présente lui une limitation du transport des ions sodium et chlorures vers les feuilles. La diversité du gène cNHXl hétérologue de l'antiport Na+nr, a permis de monter que ce gène n'est présent qu'en une seule copie chez les agrumes. Il apparaît que pour l'ensemble des espèces du genre Citrus les séquences génomiques sont très proches, alors que le Poncirus, considéré comme un excluant du sodium, présente une délétion de 54 paires de bases en 5' et une insertion de 70 bases en 3'. L'ensemble de ces résultats souligne l'intérêt des porte-greffe tétraploïdes vis-à-vis de la tolérance au stress salin et la nécessité de les étudier au niveau physiologique et moléculaire
The impact of ploidy on early physiological indicators of salt tolerance in citrus has been studied. We also examined the genetic diversity of the cNHXl gene that is involved in the accumulation of sodium in vacuolar compartment. Ln vitro tests on the ability of a rootstock to translocate chloride and sodium ions was not in agreement with the results we obtained on 1 year and 3 years old plants grafted or not. Sensitive rootstocks (Poncirus and Citrange) promoted the transport of chloride ions to leaves and limited the ones of sodium. On the other hand, tolerant rootstocks from the genus Citrus presented an opposite pattern. As weIl, our results shown that tetraploid had a better growth when compared to parental diploid plants. Moreover, symptoms of chlorosis and bum were observed. The somatic allotetraploid, hybrid FLHORAG 1 presented a limitation in sodium and chloride transport in the leaves. Genetic diversity of the Na+/H+ exchanger gene shown that this gene was present only in one single copy in the citrus genome. Moreover, it seems that for all species of the genus Citrus, the genomic sequences were very similar. However, for Poncirus that is believed to exclude sodium, has a deletion of 54 pair bases in the 5' region and an insertion of 70 pair bases in the 3' region. These results underline the interest of tetraploid rootstocks for their tolerance to salt stress. It is then necessary to study such rootstocks at the physiological and molecular level

L'antiport na/h est un mecanisme de transport membranaire, echangeant un ion na pour un proton. L'activation de cet echange par la cck et la gastrine conduit a une augmentation du ph intracellulaire. L'effet de la cck est medie par le recepteur cck et semble impliquer la stimulation de la kinase c. L'activation de l'antiport par la gastrine ne passe pas par le recepteur cck a. L'antiport na/h est egalement present au niveau de la lignee cellulaire ar4-2j, derivee d'un cancer pancreatique de rat et presente les memes caracteristiques pharmacologiques: dependance vis-a-vis des concentrations externes en na, inhibition par l'amiloride. L'activation de l'echange na/h et la stimulation de la proliferation cellulaire par le serum de veau ftal sont correlees. L'amiloride et ses analogues inhibent echange na/h et proliferation cellulaire aux memes concentrations, temoignant du role de l'antiport dans le controle de la proliferation de cette lignee cellulaire. D'autres agents sont capables de stimuler l'echange na/h sans etre des facteurs de croissances, indiquant que d'autres processus metaboliques sont controles par l'activation de l'antiport na/h, notamment des phenomenes d'hypertrophie cellulaire

En s'inspirant des processus transmembranaires de transport d'ions à l'œuvre dans les cellules vivantes, la conception d'une pile biomimétique peut être envisagée. Le principe de cette pile est d'utiliser les gradients de concentration en ions ou en protons induits par la protéine NhaA, un antiport transmembranaire Na+/2H+, pour générer de l'énergie électrique. Cette thèse contribue à l'élaboration de cette pile à travers des modifications d'électrodes permettant de détecter l'activité de transporteurs ioniques à l'interface électrode / membrane biomimétique. Une revue bibliographique des aspects fondamentaux des membranes cellulaires et du principe de la pile est présentée. Des électrodes modifiées par électrodéposition de dérivés d'acides salicyliques ont permis l'obtention de films redox-actifs sensibles aux variations de pH ou à la concentration en ions monovalents et monoatomiques. La stabilité du dépôt lipidique sur électrode a été significativement augmentée par l'électro-greffage de la 4-decylaniline. Ce dépôt lipidique stable dans le temps permet d'obtenir des membranes biomimétiques et l'insertion de transporteurs ioniques. L'activité des transporteurs ioniques insérés dans les membranes biomimétiques est suivi à travers les variations de potentiel dépendant du pH ou de la concentration en ions sodium ou potassium à l'interface électrode/membrane
Based on the transmembrane ion transport processes of living cells, the design of a biomimetic fuel cell can be considered. Its principle relies on ion or proton concentration gradients induced by the protein NhaA, a transmembrane Na+/2H+ antiport, to generate electrical energy. This thesis contributes to the development of this device through electrode modifications to detect the activity of ionic transporters at the electrode/biomimetic membrane interface.A bibliographic review of the fundamental aspects of cell membranes and of the biomimetic fuel cell principle is presented. Electrodes modified by electrodeposition of salicylic acid derivatives have yielded redox-active films sensitive to pH changes or monovalent and monoatomic ions concentration. The stability of the lipid deposit onto the electrodes was significantly increased by the electrografting of 4-decylaniline. This anchored and stable lipid deposit makes it possible to obtain biomimetic membranes allowing the insertion of ionic transporters. The activity of the ion carriers inserted into the biomimetic membranes has been monitored through the redox-active films' potential that is dependent on pH or on sodium or potassium ions concentrations at the electrode/membrane interface

De nombreux processus physiologiques tels que les mouvements stomatiques, l’absorption des nutriments, l’élongation cellulaire et la signalisation cellulaire impliquent des flux d’anions entre les membranes plasmique et vacuolaire des cellules végétales. Ces flux ioniques sont régulés par des canaux et transporteurs membranaires. Les canaux ioniques transportent passivement les ions au travers des membranes selon le gradient électrochimique. Les transporteurs actifs permettent le transport contre le gradient électrochimique de l’ion transporté induisant son accumulation dans un compartiment cellulaire. Dans les cellules végétales, le gradient de H+ entre différents compartiments constitue la principale source d’énergie couplée par les symports et les antiports au transport de NO₃⁻ et Cl⁻. Au cours de ma thèse, j’ai analysé ces flux ioniques avec deux approches. Une première approche a consisté en l’étude fonctionnelle par électrophysiologie de deux protéines membranaires, AtCLCc et AtCLCg impliquées dans le transport d’anions. Dans une deuxième approche, un biosenseur, clopHensor a été exprimé chez A. thaliana et a permis de mesurer simultanément la [NO₃⁻] et le pH cytosoliques in vivo. Les cellules de garde ont été choisies comme modèle cellulaire pour l’étude de la dynamique in vivo de la [NO₃⁻]cyt et du pH. Nous avons mis en évidence que la [NO₃⁻]cyt est influencée par les conditions extracellulaires dans ces cellules. Enfin l’expression de clopHensor en plantes KO pour un antiport NO₃⁻/H⁺ vacuolaire, AtCLCa, et d’un canal anionique de la membrane plasmique, SLAC1, nous a permis d’étudier la contribution de deux membranes dans la régulation de [NO₃⁻] et du pH cytosolique. Les travaux menés ont permis de visualiser l’activité de canaux et de transporteurs d’anions et H⁺ in vivo et de quantifier leur impact sur l’homéostasie du cytosol
Many physiological processes like stomata aperture, nutrient up-take, cellular elongation and cell signalling involve anion fluxes at the two main membranes, the plasma and vacuolar membranes of plant cells. Specialized membrane proteins form active and passive anion transport systems mediating and regulating anion fluxes. Ion channels are passive transport systems mediating ion fluxes across membranes along the electrochemical gradient. Whereas active transporters work against the electrochemical gradient of the transported ion allowing its accumulation into a cellular compartment. In plant cells, the H⁺ gradient is the main energy source of antiporters and symporters that couple the transport of anions like NO₃⁻ and Cl⁻ to the transport of H⁺. In the presents work, we aimed at analysing anion and H⁺ fluxes at two levels. First, we used an electrophysiological approach to study the functional properties of two anion transport systems acting at the vacuolar membrane, AtCLCc and AtCLCg. We also expressed a biosensor, clopHensor in A. thaliana to dynamically measure in vivo the [NO₃⁻] and pH of the cytosol. We chose stomata guard cells as a cellular model to study these fluxes. Our results illustrate the in vivo dynamics of cytosolic [NO₃⁻] and pH variations in the cytosol of guard cells. Our data show that in guard cells the cytosolic [NO₃⁻] is highly influenced by the extracellular [NO₃⁻]. At last, clopHensor’s expression in plants KO for the vacuolar NO₃⁻/H⁺ antiporter AtCLCa and for the plasma membrane anion channel SLAC1 allowed us to dissect the role of the two membranes in controlling the variation of cytosolic [NO₃⁻] and pH. This work enabled to visualize the activity of an anion channel (SLAC1) and of a NO₃⁻/H⁺ antiporter (AtCLCa) in vivo and to quantify the impact of anion and proton fluxes on cytosolic homeostasis of guard cells

Le but de notre travail a été de mettre au point un modèle animal permettant d'étudier la sidération myocardique différent des modèles habituels d'occlusion-reperfusion. Pour ce faire, nous nous sommes imposé trois obligations : (a) utiliser un modèle animal éveillé, chroniquement implanté afin d'éviter les interférences pharmacologiques, (b) envisager un modèle expérimental proche de la physiopathologie humaine et (c) concevoir un modèle adapté aux études pharmacologiques. A ce titre, l'exercice musculaire réalisé en présence d'une sténose coronaire représente une situation physiopathologique particulièrement intéressante. L'utilisation d'une sténose contrôlée de l'artère circonflexe avant, pendant et après l'exercice a permis de créer un stimulus ischémique pur, sévère et reproductible. Notre modèle permet l'étude de l'ischémie myocardique en s'affranchissant des phénomènes de reperfusion et de l'intervention des radicaux libres. Ainsi pouvons-nous étudier les effets, d'une ischémie profonde sans reperfusion et sans les effets métaboliques de l'arrêt circulatoire ceci grace au "lavage" permanent des catabolites du métabolisme ischémique. Il apparaît au terme de ce travail que la comparaison de notre modèle d'exercice ischémique et de ceux basés sur l'occlusion-reperfusion est riche d'enseignements, comme par exemple, l'absence d'efficacité dans ce modèle du préconditionement et d'un inhibiteur de l'échangeur Na+/H+, le cariporide à l'opposé d'un antagoniste des canaux T et L calcique, le mibéfradil qui ici s'est révélé particulièrement efficace sur les mécanismes initiés par l'ischémie proprement dite. Notre approche méthodologique, soulignant la dichotomie physiologique entre occlusion/reperfusion et ischémie myocardique nous semble très importante pour la définition de nouvelles cibles pharmacologiques pour la cardioprotection. Enfin, notre travail démontre une nouvelle fois la difficulté de disposer d'un modèle prédictif et transposable à l'homme.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
A busca por estratÃgias de cultivo que possam contribuir para a aclimataÃÃo de plantas à salinidade à de fundamental importÃncia, pois, alÃm de possibilitar a identificaÃÃo de genes potenciais para guiar ensaios de modificaÃÃo genÃtica, permite selecionar cultivares com maior capacidade de crescer em solos com excesso de sais. A fim de testar a hipÃtese que a nutriÃÃo nitrogenada com NH4+ aumenta a tolerÃncia de plantas de Sorghum bicolor à salinidade, atravÃs da ativaÃÃo de mecanismos voltados ao controle da homeostase iÃnica, estabeleceram-se trÃs etapas experimentais. Na primeira delas, que objetivou definir a relaÃÃo entre as fontes de nitrogÃnio (N), NO3- e NH4+, que proporcionasse melhor crescimento das plantas sob salinidade, observou-se claramente que a nutriÃÃo somente com NH4+ (proporÃÃo NO3-/NH4+ de 0:100) foi mais vantajosa para o crescimento de S. bicolor sob salinidade que a nutriÃÃo apenas com NO3- ou com o regime misto desses dois Ãons, dado os maiores Ãndices de Ãrea foliar e massa seca da parte aÃrea. Verificou-se tambÃm que, sob estresse, as plantas nutridas somente com NH4+ acumularam menos Na+ nas folhas e nas raÃzes, influenciando positivamente a relaÃÃo K+/Na+, e apresentaram maiores teores de aminoÃcidos solÃveis, principalmente aqueles ricos em N (glutamina e asparagina), que contribuÃram para evitar a toxicidade do NH4+ e provavelmente para o ajustamento osmÃtico. AlÃm disso, enquanto plantas nutridas com proporÃÃes NO3-/NH4+ de 100:0, 75:25, 50:50 e 25:75 apresentaram taxas de assimilaÃÃo lÃquida de CO2 inalteradas ou reduzidas pela salinidade, plantas cultivadas somente com NH4+ (proporÃÃo 0:100) apresentaram incrementos nessa variÃvel, em reposta ao estresse. A segunda etapa teve como objetivo principal investigar se a tolerÃncia à salinidade mediada pelo NH4+ era resultante da regulaÃÃo efetiva dos processos relacionados à fotossÃntese. Nessa ocasiÃo, esse argumento foi refutado, pois a melhor eficiÃncia do fotossistema II sob estresse salino foi observada nas plantas cultivadas com a mesma proporÃÃo de NO3- e NH4+ (proporÃÃo 50:50). Nesse grupo de plantas, a reduÃÃo no quenching nÃo fotoquÃmico (NPQ) confirmou a maior eficiÃncia fotoquÃmica, dado o aumento na eficiÃncia quÃntica potencial (Fv/Fm) e efetiva (ΦPSII) do fotossistema II e a elevada taxa de transporte de elÃtrons (ETR). Esse fenÃmeno foi diretamente relacionado com os incrementos nos teores de clorofila b e de antocianinas. Por fim, na terceira etapa, objetivou-se elucidar os mecanismos envolvidos no controle do acÃmulo de Na+, sob salinidade, na cÃlula e na planta inteira, bem como identificar o papel da nutriÃÃo com NH4+ nesses processos. Em estudos com vesÃculas de membrana de raÃzes, verificou-se que plantas estressadas cultivadas somente com NH4+ apresentaram maior ativaÃÃo dos transportadores do tipo antiporte Na+/H+ (SOS1) de membrana plasmÃtica e, em menor proporÃÃo, do antiporte Na+/H+ (NHX) de tonoplasto, ao passo que o oposto foi observado nas plantas nutridas com NO3-. Esses dados sugerem que o cultivo somente com NO3- induziu o mecanismo de compartimentaÃÃo de Na+ no vacÃolo, como evidenciado pela anÃlise dos transcritos da famÃlia NHX, em que a expressÃo do gene SbNHX2 (principal isoforma expressa) nas raÃzes das plantas foi aumentada em quase todos os tempos analisados (24, 48, 120 e 240 horas apÃs exposiÃÃo ao NaCl). Mesmo assim, essa resposta nÃo foi suficiente para o controle do Na+, jà que a entrada contÃnua desse Ãon no xilema radicular afetou o influxo de K+ na seiva e limitou o acÃmulo de K+ nas folhas. Por outro lado, a nutriÃÃo somente com NH4+ ativou potencialmente mecanismos de controle do acÃmulo de Na+, uma vez que houve acionamento efetivo do efluxo de Na+ para o apoplasto via SOS1, que restringiu o carregamento desse Ãon no xilema e, consequentemente, limitou a acumulaÃÃo dele nos tecidos aÃreos. A formaÃÃo do gradiente de potencial eletroquÃmico, essencial para a atividade dos transportadores Na+/H+, foi modulada diferencialmente pela fonte de N. A atividade de bombeamento de prÃtons da H+-ATPase de membrana plasmÃtica (P-ATPase) foi estimulada em maior proporÃÃo pela presenÃa de NH4+, sem haver, contudo, aumento na atividade de hidrÃlise de ATP. Jà o aumento da translocaÃÃo de H+ pela P-ATPase em plantas estressadas cultivadas com NO3- foi diretamente relacionado ao incremento na hidrÃlise de ATP. Esses resultados sugerem que a disponibilidade de NH4+ aumentou a afinidade da P-ATPase por H+, pois houve melhor eficiÃncia de acoplamento H+/ATP, e isso tornou a enzima mais efetiva para transportar H+ com menos gasto de energia. AlÃm disso, esse aumento no bombeamento de prÃtons resultou em um maior potencial eletroquÃmico, e favoreceu diretamente a atividade do antiporte SOS1 de membrana plasmÃtica. Os nÃveis de transcritos dos genes SbPHA3 e SbPHA5 (principais isoformas expressas da famÃlia) foram aumentados nas plantas cultivadas somente com NO3-, nos tempos iniciais de exposiÃÃo ao estresse salino (12 e 24 h), enquanto que, nos cultivos somente com NH4+, essa resposta sà foi detectada apÃs 24 h. No vacÃolo, a principal bomba responsÃvel pela formaÃÃo do gradiente de H+ durante a exposiÃÃo ao estresse salino foi a H+-ATPase (V-ATPase), em comparaÃÃo à H+-PPiase. Nas plantas cultivadas somente com NO3-, observou-se uma melhor regulaÃÃo da V-ATPase, em associaÃÃo à atividade aumentada do antiporte NHX, enquanto que no cultivo com NH4+, a ativaÃÃo do transporte de H+ sob salinidade foi diretamente relacionada a incrementos na atividade de hidrÃlise de ATP da V-ATPase, bem como ao aumento da expressÃo dos transcritos do gene SbVHA2, ao longo de todo o perÃodo experimental. Essas observaÃÃes revelam que o NH4+, como fonte Ãnica de N, ativa mecanismos que envolvem uma regulaÃÃo coordenada, nas raÃzes, da atividade e da expressÃo gÃnica de bombas de H+ e transportadores Na+/H+ de membrana plasmÃtica e de tonoplasto, que culminam no controle do acÃmulo de Na+ na planta inteira e aumentam a tolerÃncia de S. bicolor ao estresse salino.
Over the last decades, several researchers have focused the development of cultivation strategies in order to improve the plantâs ability to withstand salinity. Understanding the plant salt tolerance is one of important trait to enhance productivity of crops in saline soils because it provides molecular basis for plant breeding, as well as allows identify plant species with a greater ability to grown in salinized areas. In order to test the hypothesis that nitrogen nutrition with NH4+ improves the salt tolerance in Sorghum bicolor plants, through the restrict control of ionic homeostasis, three experimental steps were established. In the first one, we investigated what would nitrogen regime, as NO3-:NH4+ ratio, contribute to the better growth of plants under salinity. Our data clearly showed that the nutrition with only NH4+ (NO3-/NH4+ at 0:100) was more advantageous for the growth of S. bicolor under salinity than the supply with solely NO3- or the mixed regimes, as evidenced by the higher leaf area and shoot dry mass. Under salinity, Na+ accumulation was severely limited in presence of NH4+ (0:100), which positively influenced on K+/Na+ homeostasis. In parallel, NH4+-fed plants displayed a substantial accumulation of N-rich amino acids (mainly glutamine and asparagine) in both tissues, which seems to be fundamental in alleviating the NH4+ toxicity. Furthermore, whereas plants treated with NO3-:NH4+ ratio of 100:0, 75:25, 50:50 and 25:75 ratios had their photosynthetic rates (A) unaltered or reduced by salinity, plants supplied with only NH4+ showed an increased CO2 assimilation in response to stress. During the second step, we evaluated if the better salt tolerance in NH4+ cultivated plants was due to an effective regulation of photosynthesis-related processes. This idea was rejected because of the most striking effects of nitrogen regime were observed in plants supplied with equal amounts of NO3-: NH4+ (50:50). Under salt stress, plants from 50:50 NO3-:NH4+ treatments displayed a lower non-photochemical quenching (NPQ) and an improved photosystem II maximum efficiency (Fv/Fm). Their superior performance was also indicated by a higher effective quantum yield of PSII (ΦPSII) and electron transport rate (ETR), as well as increased chlorophyll b and anthocyanins. Finally, at the third step, we supply S. bicolor plants with NO3- or NH4+ to investigate changes in pathways for control of Na+ accumulation, at cell and whole plant level, in response to 75 mM NaCl-stress. By using root membrane-enriched vesicles, it was found that a more pronounced plasma membrane Na+/H+ antiporter (SOS1) activity and low loading of Na+ in the xylem in the NH4+ treated plants, whereas a largest vacuolar Na+/H+ exchanger (NHX) activity was noticed by NO3- grown plants. These data suggest that the NO3- availability induced the compartmentalization of Na+ into the vacuole, as supported by the upregulation of SbNHX2 gene expression over time of NaCl exposure (12, 24, 48, 120 and 240 h). Nonetheless, it composed an inefficient pathway of Na+ control, since the incessant entrance of Na+ in the xylem sap impaired the K+ loading and limited the K+ accumulation in the shoot. On the other hand, the NH4+ supply potentially activated the mechanisms for control of Na+ accumulation, driving an effective efflux of Na+ out of the cell, via SOS1, restricting its loading in the xylem and thus limiting Na+ reach and accumulation in the aerial tissues. Surprisingly, we found that the generation of electrochemical potential gradient for Na+/H+ exchange activity is differentially modulated by the nitrogen source. The H+-pumping activity driven by plasma membrane H+-ATPase (P-ATPase) was greatly stimulated by the presence of NH4+ in growth medium, however, without an increase in ATP hydrolysis activity. Conversely, the improvement of P-ATPase-generated H+-pumping of NO3- fed stressed plants was directly related to the increase of ATP hydrolysis. These data show that the NH4+ availability enhances the H+/ATP coupling efficiency of P-ATPase, i. e. the enzyme displayed a high capacity of transport H+ across plasma membrane with low ATP consumption. Moreover, the bigger H+ translocation resulted in a greater electrochemical potential which in turn favored the SOS1 activity. The expression of SbPHA3 and SbPHA5 genes was upregulated in NO3- grown stressed plants at the beginning of salt exposure (12 and 24 h), whereas it was enhanced in NH4+ supplied stressed plants only after 24 h. At vacuole level, the H+-ATPase (V-ATPase) was the main proton pump responsive to salinity, as compared do H+-Pyrophosphatase (PPase). A better regulation between V-ATPase and NHX antiporter activities was noticed by plants from NO3- treatments. Under NH4+ supply, the increase of H+ pumping was directly associated to the improvement of ATP hydrolysis by V-ATPase, coupled to upregulation of SbVHA2 gene expression over time of salinity exposure. Taken together, our data reveal that the NH4+, as the only nitrogen source, activates an intricate regulation of Na+ control pathways, involving the existence of a robust regulation and systematic mechanism firstly on root cell and subsequently on whole plant in sorghum upon salinity. In conclusion, the NH4+ stimulated salt tolerance is resulted from a more active SOS1 protein and high efficiency of P- and V-ATPase in the roots, which help to efficient Na+ exclusion and counteract net Na+ accumulation in the cytosol, thus preventing the loading of Na+ in the xylem sap and its reach in the photosynthetic tissues.

Although the importance of cation/proton antiporters in cellular physiology is well recognized and widely studied, many antiport systems remain underinvestigated. In this work, I report the phenotypic and biochemical effects of deletion of the cytoplasmic C-terminal tail of the NhaP2 antiporter from Vibrio cholerae (Vc-NhaP2). Namely, deletion of the C-terminal tail results in diminished K+/H+ and Na+/H+ antiport activity, as well as a 5-fold decrease in affinity for its major substrate, K+ (measured as the apparent Km at pH 7.5). Furthermore, reconstitution of antiport activity in the truncation mutant upon addition of exogenous C-terminal tail is demonstrated. Currently, the only known mechanism of antiport is for NhaA, which lacks a cytoplasmic tail. Therefore, these results suggest that NhaP2 may employ a novel mechanism of antiport in which the cytoplasmic tail is directly or indirectly involved.

Heteropolymeric O antigen (O-Ag)-capped lipopolysaccharide is the principal constituent of the Gram-negative bacterial cell surface. It is assembled via the integral inner membrane (IM) Wzx/Wzy-dependent pathway. In Pseudomonas aeruginosa, Wzx translocates lipid-linked anionic O-Ag subunits from the cytoplasmic to the periplasmic leaflets of the IM, where Wzy polymerizes the subunits to lengths regulated by Wzz1/2. The Wzx and Wzy IM topologies were mapped using random C-terminal-truncation fusions to PhoALacZα, which displays PhoA/LacZ activity dependent upon its subcellular localization. Twelve transmembrane segments (TMS) containing charged residues were identified for Wzx. Fourteen TMS, two sizeable cytoplasmic loops (CL), and two large periplasmic loops (PL3 and PL5 of comparable size) were characterized for Wzy. Despite Wzy PL3–PL5 sequence homology, these loops were distinguished by respective cationic and anionic charge properties. Site-directed mutagenesis identified functionally-essential Arg residues in both loops. These results led to the proposition of a “catch-and-release” mechanism for Wzy function. The abovementioned Arg residues and intra-Wzy PL3–PL5 sequence homology were conserved among phylogenetically diverse Wzy homologues, indicating widespread potential for the proposed mechanism. Unexpectedly, Wzy CL6 mutations disrupted Wzz1-mediated regulation of shorter O-Ag chains, providing the first evidence for direct Wzy–Wzz interaction. Mutagenesis studies identified functionally-important charged and aromatic TMS residues localized to either the interior vestibule or TMS bundles in a 3D homology model constructed for Wzx. Substrate-binding or energy-coupling roles were proposed for these residues, respectively. The Wzx interior was found to be cationic, consistent with translocation of anionic O-Ag subunits. To test these hypotheses, Wzx was overexpressed, purified, and reconstituted in proteoliposomes loaded with I−. Common transport coupling ions were introduced to “open” the protein and allow detection of I− flux via reconstituted Wzx. Extraliposomal changes in H+ induced I− flux, while Na+ addition had no effect, suggesting H+-dependent Wzx gating. Putative energy-coupling residue mutants demonstrated defective H+-dependent halide flux. Wzx also mediated H+ uptake as detected through fluorescence shifts from proteoliposomes loaded with pH-sensitive dye. Consequently, Wzx was proposed to function via H+-coupled antiport. In summary, this research has contributed structural and functional knowledge leading to novel mechanistic understandings for O-Ag biosynthesis in bacteria.
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1.) Canadian Institutes of Health Research (CIHR) Frederick Banting and Charles Best Canada Graduate Scholarship doctoral award, 2.) CIHR Michael Smith Foreign Study Award, 3.) Cystic Fibrosis Canada (CFC) doctoral studentship, 4.) University of Guelph Dean's Tri-Council Scholarship, 5.) Ontario Graduate Scholarship in Science and Technology, 6.) Operating grants to Dr. Joseph S. Lam from CIHR (MOP-14687) and CFC