Temps mythique et temp shistorique. Les origines et les premiers sicles de Roma

Sin resume

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

Les commissions de l’enseignement privé sous contrat depuis 1959

Afin de bien comprendre les particularités des commissions de l’enseignement privé, un rappel de l’organisation interne des établissements est nécessaire, notamment l’inexistence d’une organisation par corps comme dans l’enseignement public. Avant la loi Debré, des représentants des établissements privés siégeaient, de façon très minoritaire, dans certaines instances de concertation de l’enseignement public. Le vote de la loi Debré change profondément la donne. Des commissions mixtes (avec des représentants de l’enseignement public et de l’enseignement privé) sont créées, qui disposent d’un rôle consultatif (et non d’un pouvoir décisionnaire). Elles classent les maîtres, proposent des promotions ou au contraire la résiliation du contrat. Progressivement, elles participent aussi à l’établissement des listes d’aptitude et à la nomination des enseignants. C’est en 2013 que les commissions mixtes deviennent paritaires et qu’est créé, au niveau national, un comité consultatif ministériel des maîtres. On soulignera que depuis 1959, s’est produite une fragmentation des organisations syndicales siégeant dans ces commissions. Toutefois, les trois organisations dominantes sont demeurées les mêmes.In order to fully understand the peculiarities of private education commissions, we need an overview of the internal organisation of schools, in particular the non-existence of any organisation in the form of internal bodies, as is the case in public education. Before the Debré law, representatives of private schools served, albeit very much in the minority, on certain public education consultative committees. The passing of the Debré law profoundly changed the situation. Mixed commissions (with representatives from public and private education) were set up and had an advisory role (but no decision-making power). They classified teachers, proposed them for promotion or, conversely, cancelled their contracts. They also gradually began to participate in the drawing up of aptitude lists and the appointment of teachers. In 2013, these mixed commissions became joint commissions and a ministerial advisory committee of teachers was set up at national level. It should be emphasised that, since 1959, there has been a fragmentation of the trade union organisations on these committees. However, the three dominant organisations have remained the same

Different CA1 and CA3 Representations of Novel Routes in a Shortcut Situation

International audiencePlace cells are hippocampal neurons whose discharge is strongly related to a rat's location in its environment. The existence of place cells has led to the proposal that they are part of an integrated neural system dedicated to spatial navigation. To further understand the relationships between place cell firing and spatial problem solving, we examined the discharge of CA1 and CA3 place cells as rats were exposed to a shortcut in a runway maze. On specific sessions, a wall section of the maze was removed so as to open a shorter novel route within the otherwise familiar maze. We found that the discharge of both CA1 and CA3 cells was strongly affected in the vicinity of the shortcut region but was much less affected farther away. In addition, CA3 fields away from the shortcut were more altered than CA1 fields. Thus, place cell firing appears to reflect more than just the animal's spatial location and may provide additional information about possible motions, or routes, within the environment. This kinematic representation appears to be spatially more extended in CA3 than in CA1, suggesting interesting computational differences between the two subregions

De la rédaction à la dissertation

La dissertation est un exercice nouveau dans l’enseignement secondaire au xixe siècle – André Chervel l’a montré de façon convaincante. Certes, elle n’est pas totalement absente de quelques pratiques scolaires au xviiie siècle, mais, en tout état de cause, elle n’est pas l’exercice essentiel : discours français, analyse et rédaction du cours constituent l’héritage scolaire par rapport auquel les professeurs du xixe siècle inventent progressivement de nouveaux exercices. La dissertation en lat..

KANT (Emmanuel), Sur la différence des sexes et autres essais

Ce petit ouvrage rendra bien des services tant aux professeurs de philosophie qu’aux historiens de l’éducation. Les premiers retrouveront les travaux préparatoires à un livre publié vingt-cinq ans plus tard, en 1798 et en 1800, l’un des derniers parus du vivant de Kant, Anthropologie du point de vue pragmatique, composé, aux dires de l’auteur, à partir des notes prises par ses auditeurs en sept séries. Les spécialistes de la philosophie kantienne ouvrent ainsi la porte du laboratoire du maîtr..

Une exception française : vers un nouveau paradigme de l’enseignement de la philosophie en Terminale ?

L’enseignement scolaire français de la philosophie s’est progressivement organisé en un paradigme pédagogique qui comprend un certain nombre de dispositifs et de pratiques. Héritage de l’ancien régime, comprenant le cours dicté et la rédaction du cours, un examen sous forme de questions orales, un professeur non spécialiste, ce paradigme a été remis en cause pour atteindre un nouvel équilibre au cours du début du XXe siècle : professeur spécifique, pratique pédagogique particulière, exercice original à base de dissertation, manuels, attente de la société civile, tout concourt à cet équilibre qui sera défait lorsque l’évolution de la société et la massification de l’enseignement provoqueront des interrogations fortes sur l’existence du paradigme. C’est à la recherche d’un nouvel équilibre que professeurs et institutions tentent non sans mal d’apporter des réponses.The French teaching of philosophy has been organized with a special pattern. This pattern is coming before the great revolution. He has been upset along the XIXe siècle and a new one with typical exercises and practices (for example dissertation), a special teacher, is coming on about 1920. This new way of teaching philosophy at school will be leave by a new generation of teachers and because of the transformation of the society. Presently, the French teaching of philosophy is looking for a new pattern

Mémoires de rat...

Après un cheminement difficile, l’idée que l’animal puisse construire des représentations ou des mémoires de son environnement est maintenant largement ancrée dans les esprits. Cette hypothèse a débouché sur des résultats remarquables en neurobiologie des processus cognitifs.Un retour historique par Bruno Poucet. The notion that an animal may build a representation, or a memory, of the environment is now well accepted, though the path taken to reach this agreement was no so straightforward. Bruno Poucet describes a multidisciplinary approach to the problem