Esta tese refere-se a pesquisa cujo o principal objetivo foi estudar os efeitos da sinalização elétrica sobre parâmetros fisiológicos de trocas gasosas e fluorescência da clorofila, bem como caracterizar e identificar rotas de propagação de sinais elétricos desencadeados por estímulos de queima em plantas de girassol. Os resultados obtidos a partir deste estudo demonstram que os sinais elétricos desencadeados por estímulo de queima podem ser classificados como potenciais de variação (PV). Estes sinais apresentaram maior facilidade de propagação no eixo vertical da planta atingindo folhas intactas que provavelmente possuem conexão vascular com a folha de estímulo. Apresentaram maior número de eventos de propagação na direção acrópeta da planta e foram incapazes de propagar-se lateralmente não atingindo folhas opostas à de estímulo. Nas folhas opostas onde não houve propagação de PVs foi registrada a ocorrência de hiperpolarização de membranas característica de potencial sistêmico (PS). Quanto aos efeitos fisiológicos do PV, observou-se que este promoveu redução na assimilação líquida de CO2 (A) que provavelmente está relacionada a inativação da fase não fotoquímica da fotossíntese, uma vez que, esteve acompanhada de queda da dissipação fotoquímica dos fotossistemas (qP) e da taxa de transporte de elétrons (ETR). Embora tenha sido registrada alterações na condutância estomática (gs), na concentração intercelular de CO2 (Ci), elevação da dissipação não fotoquímica (qN) e queda na eficiência quântica efetiva do fotossistema II (ΦFSII), estes não foram responsáveis pela queda de A, uma vez que, foram registrados posteriormente a sua redução. / This thesis mainly aimed to study the effects of electrical signaling on physiological parameters of gas exchange and chlorophyll fluorescence, and to characterize and identify route propagation of electrical signals triggered by burning stimuli in sunflower plants. The results from this study demonstrate that the electrical signals triggered by burning stimulus can be classified as variation potentials (VP). These signals showed greater ease of propagation in the vertical axis of the plant, reaching intact leaves that are likely to have vascular connection with the stimulus leaf. They presented greater ease of propagation in acropetal direction of the plant and are unable to spread laterally, not reaching leaves opposed to the stimulus. On opposed leaves, where there was no VPs propagation, it was recorded the occurrence of membrane hyperpolarization of systemic potential (PS). Concerning the physiological effects of PV, it was observed that this promoted a reduction in the liquid CO2 assimilation (A) which is probably related to the inactivation of non-photochemical phase of the photosynthesis, since it was accompanied by the decrease of the photochemical dissipation of the photosystems (qP) and the electron transport rate (ETR). Although changes were recorded in stomatal conductance (gs), CO2 intercellular concentration (Ci), increase of nonphotochemical dissipation (qN) and a decrease in the effective quantum efficiency of the photosystem II (Φ FSII) were not responsible for the A fall, since its reduction was subsequently reported.

Esta tese refere-se a pesquisa cujo o principal objetivo foi estudar os efeitos da sinalização elétrica sobre parâmetros fisiológicos de trocas gasosas e fluorescência da clorofila, bem como caracterizar e identificar rotas de propagação de sinais elétricos desencadeados por estímulos de queima em plantas de girassol. Os resultados obtidos a partir deste estudo demonstram que os sinais elétricos desencadeados por estímulo de queima podem ser classificados como potenciais de variação (PV). Estes sinais apresentaram maior facilidade de propagação no eixo vertical da planta atingindo folhas intactas que provavelmente possuem conexão vascular com a folha de estímulo. Apresentaram maior número de eventos de propagação na direção acrópeta da planta e foram incapazes de propagar-se lateralmente não atingindo folhas opostas à de estímulo. Nas folhas opostas onde não houve propagação de PVs foi registrada a ocorrência de hiperpolarização de membranas característica de potencial sistêmico (PS). Quanto aos efeitos fisiológicos do PV, observou-se que este promoveu redução na assimilação líquida de CO2 (A) que provavelmente está relacionada a inativação da fase não fotoquímica da fotossíntese, uma vez que, esteve acompanhada de queda da dissipação fotoquímica dos fotossistemas (qP) e da taxa de transporte de elétrons (ETR). Embora tenha sido registrada alterações na condutância estomática (gs), na concentração intercelular de CO2 (Ci), elevação da dissipação não fotoquímica (qN) e queda na eficiência quântica efetiva do fotossistema II (ΦFSII), estes não foram responsáveis pela queda de A, uma vez que, foram registrados posteriormente a sua redução. / This thesis mainly aimed to study the effects of electrical signaling on physiological parameters of gas exchange and chlorophyll fluorescence, and to characterize and identify route propagation of electrical signals triggered by burning stimuli in sunflower plants. The results from this study demonstrate that the electrical signals triggered by burning stimulus can be classified as variation potentials (VP). These signals showed greater ease of propagation in the vertical axis of the plant, reaching intact leaves that are likely to have vascular connection with the stimulus leaf. They presented greater ease of propagation in acropetal direction of the plant and are unable to spread laterally, not reaching leaves opposed to the stimulus. On opposed leaves, where there was no VPs propagation, it was recorded the occurrence of membrane hyperpolarization of systemic potential (PS). Concerning the physiological effects of PV, it was observed that this promoted a reduction in the liquid CO2 assimilation (A) which is probably related to the inactivation of non-photochemical phase of the photosynthesis, since it was accompanied by the decrease of the photochemical dissipation of the photosystems (qP) and the electron transport rate (ETR). Although changes were recorded in stomatal conductance (gs), CO2 intercellular concentration (Ci), increase of nonphotochemical dissipation (qN) and a decrease in the effective quantum efficiency of the photosystem II (Φ FSII) were not responsible for the A fall, since its reduction was subsequently reported.

Reliable signal transmission among cells is important for long-range coordination. While higher organisms have designated structures for signal transmission, such as axons, it remains unclear how simpler communities of cells are organized to relay signals. Furthermore, many biological systems exhibit spatial heterogeneity, which can interrupt signal propagation. In this thesis, we investigate this problem by modeling the spatial organization and dynamics of electrochemical signaling, and we compare our results to experiments from our collaborators on Bacillus subtilis bacterial biofilms. The experiments show that only a fraction of cells participates in signal propagation and that these cells are spatially clustered with a size distribution that follows a power-law decay. These observations suggest that the fraction of participating cells is just at the tipping point between a disconnected and a fully connected conduit for signal transmission. We utilize percolation theory and a minimal FitzHugh-Nagumo-type excitable dynamics model to test this hypothesis, and genetically modified biofilms with altered structure and dynamics to validate our modeling. Our results suggest that the biofilm is organized near the critical percolation point in order to negotiate the benefit and cost of long-range signal transmission. Then, more detailed experiments show that the participation probability is correlated from cell to cell and varies in space. We use these observations to develop an enhanced percolation model, and show using simulations and a renormalization argument that the main conclusions are unaffected by these features. Finally, we use our dynamic model to investigate the effects of heterogeneity beyond the radial wave regime and into the spiral wave regime. We find that spatial correlations in the heterogeneity promote or suppress spiraling depending on the parameters, a surprising feature that we explain by demonstrating that these spirals form by distinct mechanisms. We characterize the dependence of the spiral period on the heterogeneity using techniques from percolation theory. Taken together, our results reveal that the spatial structure of cell-to-cell heterogeneity can have important consequences for signal propagation in cellular communities.<br>

La symbiose légumineuse-rhizobium a une importance majeure pour les écosystèmes terrestres puisqu'elle permet à la plante hôte de fixer l'azote atmosphérique. L'interaction initiale entre le poil absorbant de la plante hôte et son partenaire bactérien repose sur un dialogue moléculaire complexe. L'évènement de signalisation le plus précoce, détecté immédiatement après la perception des facteurs Nod bactériens, est un influx de Ca2+, accompagné d'une inhibition de la pompe à proton et d'un efflux de Cl- conduisant à une dépolarisation de la membrane plasmique. Cette dépolarisation provoque un efflux de K+ permettant le repolarisation de la membrane. L'objectif de ce travail a été d'identifier des acteurs moléculaires de cette signalisation électrique en utilisant Medicago truncatula comme légumineuse modèle. Dans un premier temps, nous avons identifié un répertoire de gènes candidats à partir de l'analyse du transcriptome du poil absorbant obtenu par RNA-Seq. Nous avons alors exprimé différents candidats (2 canaux anioniques, 1 canal cationique potentiel de la famille CNGC et 1 canal potassique) dans des ovocytes de xénope pour tester leur fonctionnalité (dans ce système) et préciser leurs propriétés de transport. Nous nous sommes alors focalisés sur l'analyse de la fonction in planta du gène codant le canal potassique (démontré comme étant de type rectifiant sortant) en précisant son patron d'expression par transgenèse et sa fonction par génétique inverse. L'absence d'expression fonctionnelle de ce gène se traduit par la disparition complète du courant potassique voltage-dépendant sortant des cellules de M. truncatula. Les premières analyses indiquent que cette perte de fonction n'inhibe pas la capacité de nodulation de la plante mais l'affecte significativement. Elle impacte également la régulation de l'ouverture stomatique de la plante mais n'a pas d'effet sur la translocation de K+ dans la sève xylémienne racinaire vers les parties aériennes. / The legume-rhizobium symbiosis is of crucial importance in terrestrial ecosystems because it allows the plant to assimilate atmospheric nitrogen. The establishment of the interaction between plant root hairs and their symbiotic bacterial partners relies on complex signaling mechanisms. The earliest detected event, immediately triggered by root hair perception of Nod-factors, is a Ca2+ influx, proton pump inhibition and efflux of Cl- resulting in depolarization of the cell membrane. This depolarization is followed by K+ efflux, allowing repolarization of the cell membrane. The general objective of this work is to identify the molecular mechanisms underlying this electrical signaling by using the legume model Medicago truncatula. In a first step, we identified candidate ion channels and transporters by analyzing the root hair transcriptome obtained by RNA-Seq. Then, several candidate genes (1 member from the CNGC channel family, 1 from the Shaker K+ channel family and 2 from the SLAC anion channel family) were expressed in Xenopus oocytes to check their activity in this heterologous system and determine their functional properties. Then, we focused on the gene encoding the Shaker channel, shown to mediate outwardly-rectifying voltage-gated K+ selective currents. We analyzed its expression pattern using a GUS construct and its function in planta by phenotyping a loss-of-function mutant pant. A first set of experiments has shown that the loss-of-function mutation does not suppress the plant nodulation capacity but significantly depresses it. It also affects the control of stomatal aperture upon water stress but let unchanged K+ secretion into the xylem sap in roots and translocation towards the shoots.