The energy cost of primary metabolism vacuole expansion: central to shape toamto leaf development under ammonium nutrition

231 p.Ammonium (NH4+) is a nitrogen source of great interest in the context of sustainable agriculture. Its application in the field together with nitrification inhibitors has been extensively proven efficient to limit detrimental N losses compared to the use of nitrate (N03). NH4+ is a common intermediate involved in numerous metabolic routes. However, high NH4 concentrations may lead to a stress situation provoking a set of symptoms collectively known as "ammonium syndrome" mainly characterized by growth retardation. Those symptoms are caused by a combination of, among others, a profound metabolic reprogramming, disruption of photosynthesis, pH deregulation and ion imbalance. Numerous studies have described the way plant copes to ammonium nutrition. However, the organ developmental stage has been generally neglected.To fill in this gap, in the first chapter we first aimed studying how the metabolism is adapted in function of the leaf position in the vertical axis of the tomato plants (Solanum lycopersicum) grown with NH4+, N03- or NH4N03 supply. To do so, we dissected leaf biomass composition and metabolism through a complete analysis of metabolites, ions and enzyme activities. The results showed that C and N metabolic adjustment in function of the nitrogen source was more intense in older leaves compared to younger ones. Importantly, we propose a trade-off between NH4+ accumulation and assimilation to preserve young leaves from ammonium stress. Besides, NH4+-fed plants exhibited a rearrangement of carbon skeletons with a higher energy cost respect to plants supplied with N03-. We explain such reallocation by the action of the biochemical pH-stat, to compensate the differential proton production that depends on the nitrogen form provided.Ammonium nutrition may limit cell expansion, suggesting that the cellular processes involved would be altered. Among others, cell growth is largely dependent of the internal pressure exerted on the cell wall by the vacuole. However, the role of the vacuole in ammonium stress has been rarely addressed. In the second chapter, we evaluated the effect of ammonium stress on leaf development with a special focus on vacuole expansion and metabolism. To carry out this aim, we monitored the leaf development from its appearance until its complete expansion in plants grown under NH4+ or NO/ as unique nitrogen source. Cytological analysis evidenced that the reduced cell expansion under ammonium nutrition was associated with smaller vacuole size. Besides, we reported an acidification of the vacuole of NH4+-fed plants compared to nitrate nutrition. Moreover, a model was built to predict the thermodynamic equilibrium of different soluble species across the tonoplast. The model was set up through an extensive reviewing of vacuolar transporters and integrated subcellular volumes, vacuolar electrochemical gradients and the formation of ionic complex in the vacuole to fit the subcellular concentration of ions, organic acids and sugars measured in the leaf. Further, predictions obtained with the model were cross validated with data from non-aqueous fractionation. Firstly, the entrance of solutes was higher in vacuoles of N03--fed leaves but was not associated with higher vacuolar osmolarity likely because of the adjustment of the vacuolar volume. In this sense, we proposed that the lack of malate in cells of ammonium-fed leaves was central in the limitation of vacuolar expansion. Secondly, we conclude that the energy cost of solute transport into the vacuole is higher under NH4+ based nutrition because of the higher electrochemical gradient generated by the proton pumps across tonoplast.This work highlights the importance of considering leaf phenological state when studying nitrogen metabolism. In addition, our integrated approach place cytosolic pH control and vacuole expansion in the center of tomato leaf adaptation to ammonium stress and pave the way for future studies in the field of ammonium nutrition

Space and time-related firing in a model of hippocampo-cortical interactions

International audienceIn a previous model [3], a spectral timing neural network [4] was used to account for the role of the Hs in the acquisition of classical conditioning. The ability to estimate the timing between separate events was then used to learn and predict transitions between places in the environment. We propose a neural architecture based on this work and explaining the out-of-field activities in the Hs along with their temporal prediction capabilities. The model uses the hippocampo-cortical pathway as a means to spread reward signals to entorhinal neurons. Secondary predictions of the reward signal are then learned, based on transition learning, by pyramidal neurons of the CA region

Impaired cell growth under ammonium stress explained by modeling the energy cost of vacuole expansion in tomato leaves

Ammonium (NH4+)-based fertilization efficiently mitigates the adverse effects of nitrogen fertilization on the environment. However, high concentrations of soil NH4+ provoke growth inhibition, partly caused by the reduction of cell enlargement and associated with modifications of cell composition, such as an increase of sugars and a decrease in organic acids. Cell expansion depends largely on the osmotic-driven enlargement of the vacuole. However, the involvement of subcellular compartmentation in the adaptation of plants to ammonium nutrition has received little attention, until now. To investigate this, tomato (Solanum lycopersicum) plants were cultivated under nitrate and ammonium nutrition and the fourth leaf was harvested at seven developmental stages. The vacuolar expansion was monitored and metabolites and inorganic ion contents, together with intracellular pH, were determined. A data-constrained model was constructed to estimate subcellular concentrations of major metabolites and ions. It was first validated at the three latter developmental stages by comparison with subcellular concentrations obtained experimentally using non-aqueous fractionation. Then, the model was used to estimate the subcellular concentrations at the seven developmental stages and the net vacuolar uptake of solutes along the developmental series. Our results showed ammonium nutrition provokes an acidification of the vacuole and a reduction in the flux of solutes into the vacuoles. Overall, analysis of the subcellular compartmentation reveals a mechanism behind leaf growth inhibition under ammonium stress linked to the higher energy cost of vacuole expansion, as a result of alterations in pH, the inhibition of glycolysis routes and the depletion of organic acids.TP benefited from a cotutelle PhD (University of Bordeaux and University of the Basque Country) and thanks the University of the Basque Country (UPV/EHU, Spain) for his PhD grant during the execution of this work. This research was financially supported by the Basque Government (IT-932-16) and the Spanish Government (BIO2017-84035-R co-funded by Fondo Europeo para el Desarrollo Regional [FEDER]). Analytics were supported by MetaboHUB (ANR-11-INBS-0010) and PHENOME (ANR-11-INBS-0012) projects. Technical support was provided by Cedric Cassan, Ana Renovales and Mandy Bordas. The authors also thank SGIker (UPV/EHU, FEDER, EU) for the technical and human support provided

The energy cost of primary metabolism vacuole expansion: central to shape toamto leaf development under ammonium nutrition

231 p.Ammonium (NH4+) is a nitrogen source of great interest in the context of sustainable agriculture. Its application in the field together with nitrification inhibitors has been extensively proven efficient to limit detrimental N losses compared to the use of nitrate (N03). NH4+ is a common intermediate involved in numerous metabolic routes. However, high NH4 concentrations may lead to a stress situation provoking a set of symptoms collectively known as "ammonium syndrome" mainly characterized by growth retardation. Those symptoms are caused by a combination of, among others, a profound metabolic reprogramming, disruption of photosynthesis, pH deregulation and ion imbalance. Numerous studies have described the way plant copes to ammonium nutrition. However, the organ developmental stage has been generally neglected.To fill in this gap, in the first chapter we first aimed studying how the metabolism is adapted in function of the leaf position in the vertical axis of the tomato plants (Solanum lycopersicum) grown with NH4+, N03- or NH4N03 supply. To do so, we dissected leaf biomass composition and metabolism through a complete analysis of metabolites, ions and enzyme activities. The results showed that C and N metabolic adjustment in function of the nitrogen source was more intense in older leaves compared to younger ones. Importantly, we propose a trade-off between NH4+ accumulation and assimilation to preserve young leaves from ammonium stress. Besides, NH4+-fed plants exhibited a rearrangement of carbon skeletons with a higher energy cost respect to plants supplied with N03-. We explain such reallocation by the action of the biochemical pH-stat, to compensate the differential proton production that depends on the nitrogen form provided.Ammonium nutrition may limit cell expansion, suggesting that the cellular processes involved would be altered. Among others, cell growth is largely dependent of the internal pressure exerted on the cell wall by the vacuole. However, the role of the vacuole in ammonium stress has been rarely addressed. In the second chapter, we evaluated the effect of ammonium stress on leaf development with a special focus on vacuole expansion and metabolism. To carry out this aim, we monitored the leaf development from its appearance until its complete expansion in plants grown under NH4+ or NO/ as unique nitrogen source. Cytological analysis evidenced that the reduced cell expansion under ammonium nutrition was associated with smaller vacuole size. Besides, we reported an acidification of the vacuole of NH4+-fed plants compared to nitrate nutrition. Moreover, a model was built to predict the thermodynamic equilibrium of different soluble species across the tonoplast. The model was set up through an extensive reviewing of vacuolar transporters and integrated subcellular volumes, vacuolar electrochemical gradients and the formation of ionic complex in the vacuole to fit the subcellular concentration of ions, organic acids and sugars measured in the leaf. Further, predictions obtained with the model were cross validated with data from non-aqueous fractionation. Firstly, the entrance of solutes was higher in vacuoles of N03--fed leaves but was not associated with higher vacuolar osmolarity likely because of the adjustment of the vacuolar volume. In this sense, we proposed that the lack of malate in cells of ammonium-fed leaves was central in the limitation of vacuolar expansion. Secondly, we conclude that the energy cost of solute transport into the vacuole is higher under NH4+ based nutrition because of the higher electrochemical gradient generated by the proton pumps across tonoplast.This work highlights the importance of considering leaf phenological state when studying nitrogen metabolism. In addition, our integrated approach place cytosolic pH control and vacuole expansion in the center of tomato leaf adaptation to ammonium stress and pave the way for future studies in the field of ammonium nutrition

1re question Un historien entre deux mondes. Lecture des «Antiquités romaines » de Denys d'Halicarnasse par Anouk Delcourt. Rapports des Commissaires

Poucet Jacques, Bingen Jean, Lambrechts Roger. 1re question Un historien entre deux mondes. Lecture des «Antiquités romaines » de Denys d'Halicarnasse par Anouk Delcourt. Rapports des Commissaires . In: Bulletin de la Classe des lettres et des sciences morales et politiques, tome 15, n°1-6, 2004. pp. 161-171

1re question Un historien entre deux mondes. Lecture des «Antiquités romaines » de Denys d'Halicarnasse par Anouk Delcourt. Rapports des Commissaires

Poucet Jacques, Bingen Jean, Lambrechts Roger. 1re question Un historien entre deux mondes. Lecture des «Antiquités romaines » de Denys d'Halicarnasse par Anouk Delcourt. Rapports des Commissaires . In: Bulletin de la Classe des lettres et des sciences morales et politiques, tome 15, n°1-6, 2004. pp. 161-171

Méthodologie et vocabulaire utilisés par le Groupe d'étude des tourbières de Sénart dans les études conduites en 2010

Ce document présente les grandes lignes de la méthodologie développée par le Groupe d'étude des tourbières de Sénart. Ce texte synthétise et actualise des éléments dispersés auparavant dans divers documents. Cette méthodologie a été utilisée dans la session d'étude stratigraphique tourbières que ce groupe d'étude a organisée du 18 au 22 octobre 2010 [11] ainsi que dans la session organisée par la Société Batrachologique de France du 28 au 30 septembre 2010 [10]