How does sulphur availability modify N acquisition of white clover (Trifolium repens L.)?

The role of S in legume growth, N uptake, and N2 fixation was investigated using white clover (Trifolium repens L.) as a model species. We examined whether the effect of sulphate addition on N fixation resulted from a stimulation of host plant growth, a specific effect of S on nodulation, or a specific effect of S on nodule metabolism. Clones of white clover, inoculated with Rhizobium leguminosarum, were grown for 140 d in a hydroponic system with three levels of sulphate concentration (0 mM, 0.095 mM, and 0.380 mM). Nodule morphological and biochemical traits, such as root length, nodule biomass and volume, nodule protein contents (nitrogenase and leghaemoglobin obtained by an immunological approach), and root amino acid concentrations, were used to analyse the effect of sulphate availability on N2 fixation. The application of sulphate increased whole plant dry mass, root length, and nodule biomass, expressed on a root-length basis. N uptake proved less sensitive than N2 fixation to the effects of S-deficiency, and decreased as a consequence of the lower root length observed in S-deficient plants. N2 fixation was drastically reduced in S-deficient plants as a consequence of a low nodule development, but also due to low nitrogenase and leghaemoglobin production. This effect is likely to be due to down-regulation by a N-feedback mechanism, as, under severe S-deficiency, the high concentration of whole plant N and the accumulation of N-rich amino acids (such as asparagine) indicated that the assimilation of N exceeded the amount required for plant growth

The Hepatokine TSK does not affect brown fat thermogenic capacity, body weight gain, and glucose homeostasis

Objectives Hepatokines are proteins secreted by the liver that impact the functions of the liver and various tissues through autocrine, paracrine, and endocrine signaling. Recently, Tsukushi (TSK) was identified as a new hepatokine that is induced by obesity and cold exposure. It was proposed that TSK controls sympathetic innervation and thermogenesis in brown adipose tissue (BAT) and that loss of TSK protects against diet-induced obesity and improves glucose homeostasis. Here we report the impact of deleting and/or overexpressing TSK on BAT thermogenic capacity, body weight regulation, and glucose homeostasis. Methods We measured the expression of thermogenic genes and markers of BAT innervation and activation in TSK-null and TSK-overexpressing mice. Body weight, body temperature, and parameters of glucose homeostasis were also assessed in the context of TSK loss and overexpression. Results The loss of TSK did not affect the thermogenic activation of BAT. We found that TSK-null mice were not protected against the development of obesity and did not show improvement in glucose tolerance. The overexpression of TSK also failed to modulate thermogenesis, body weight gain, and glucose homeostasis in mice

Plasticité fonctionnelle du trèfle blanc en réponse à la disponibilité en soufre

Les programmes de diminution des principaux polluants industriels ont entraîné d importantes réductions des teneurs en S atmosphérique et par conséquent un appauvrissement des sols en S dans les prairies du Nord de l Europe. Le travail de thèse centré sur le trèfle blanc (Trifolium repens L.) en tant qu espèce clef des prairies, s est attaché à analyser sa plasticité en réponse à la disponibilité en S. La plasticité du trèfle a été évaluée par la variation de traits fonctionnels le long d'un gradient de fertilisation azoté et soufré appliquée sur un sol pauvre, ou de concentration en SO42- en système hydroponique. Un double marquage 15N/34S a été réalisé pour évaluer l absorption de l N et du S de la solution ainsi que la fixation du N2 et le dépôt foliaire du soufre atmosphérique. Les résultats ont mis en évidence une plasticité phénotypique, à la fois morphologique et physiologique, importante du trèfle. Le soufre module sa biomasse finale ainsi que ses fonctions biologiques ; aptitude potentielle à la compétition, multiplication végétative, photosynthèse et acquisition du S et de N. Il intervient notamment via la fixation de N2. La réduction de la fixation du N2 observée chez les plantes déficientes en S résulte principalement d une réduction de la nodulation, mais une moindre synthèse de protéines nodulaires, la nitrogénase et la léghémoglobine a été observée. Le S atmosphérique s est révélé être une source importante pour la croissance, à travers le dépôt foliaire. La déficience en soufre accroît l absorption foliaire par unité de surface. L apport d engrais soufrés, à l inverse d apports azotés pourrait permettre un maintien prolongé du trèfle dans les prairies.Recent control of atmospheric S pollution is leading to important soil sulphur impoverishment. As a result, a decrease in soil sulphur content has appeared in the last decades in grasslands of Northern Europe. White clover (Trifolium repens L.) is a key species in grasslands and was chosen as a model species. These phD focused on clover response to sulphur availability. Clover plasticity was assessed through the measurement of a set of functional traits along a gradient of nitrogen and sulphur fertilisation applied on a poor soil or a gradient of sulphate concentration when cultivated on a hydroponic system. A 15N / 34S double labelling was used to measure nitrate and sulphate uptake, N2 fixation an atmospheric S foliar deposition. White clover traits showed a great phenotypic plasticity, due to both morphological and physiological plasticity. Sulphur availability modify clover biomass as well as major functions such as the potential competitive ability, the vegetative reproduction, photosynthesis and sulphur and nitrogen acquisition. Sulphur effect on clover is linked to N2 fixation. N2 fixation was drastically reduced in S deficient plants mainly as a consequence of a decreased nodule development, but also as a consequence of decreased protein synthesis in nodules. Nitrogenase and leghaemoglobin were lower in S deficient nodules. S derived from the atmospheric deposition (Sdad) through foliar deposition appeared to be a significant source of S for clover growth. Sdad:leaf area ratio increased with decreasing S concentration in the nutrient solution. In contrast with N fertilisation, S fertilisation could help to maintain white clover in grassland.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Glucose Induces Slow-Wave Sleep by Exciting the Sleep-Promoting Neurons in the Ventrolateral Preoptic Nucleus: A New Link between Sleep and Metabolism

International audienceSleep-active neurons located in the ventrolateral preoptic nucleus (VLPO) play a crucial role in the induction and maintenance of slow-wave sleep (SWS). However, the cellular and molecular mechanisms responsible for their activation at sleep onset remain poorly understood. Here, we test the hypothesis that a rise in extracellular glucose concentration in the VLPO can promote sleep by increasing the activity of sleep-promoting VLPO neurons. We find that infusion of a glucose concentration into the VLPO of mice promotes SWS and increases the density of c-Fos-labeled neurons selectively in the VLPO. Moreover, we show in patch-clamp recordings from brain slices that VLPO neurons exhibiting properties of sleep-promoting neurons are selectively excited by glucose within physiological range. This glucose-induced excitation implies the catabolism of glucose, leading to a closure of ATP-sensitive potassium (KATP) channels. The extracellular glucose concentration monitors the gating of KATP channels of sleep-promoting neurons, highlighting that these neurons can adapt their excitability according to the extracellular energy status. Together, these results provide evidence that glucose may participate in the mechanisms of SWS promotion and/or consolidation.SIGNIFICANCE STATEMENT:Although the brain circuitry underlying vigilance states is well described, the molecular mechanisms responsible for sleep onset remain largely unknown. Combining in vitro and in vivo experiments, we demonstrate that glucose likely contributes to sleep onset facilitation by increasing the excitability of sleep-promoting neurons in the ventrolateral preoptic nucleus (VLPO). We find here that these neurons integrate energetic signals such as ambient glucose directly to regulate vigilance states accordingly. Glucose-induced excitation of sleep-promoting VLPO neurons should therefore be involved in the drowsiness that one feels after a high-sugar meal. This novel mechanism regulating the activity of VLPO neurons reinforces the fundamental and intimate link between sleep and metabolism

Influence of rhizobacterial volatile compounds on growth and root system architecture of Brachypodium distachyon (L.) Beauv.

Many rhizobacterial strains are classified as plant growth-promoting rhizobacteria (PGPR) and are potentially useful to enhance plant fitness and productivity. Among the mechanisms by which PGPR improve plant growth, the emission of volatile organic compounds (VOCs) and their biological impacts on plants remain little documented. The aim of this work is to evaluate the growth promotion ability of 19 bacterial strains on the model grass Brachypodium distachyon Bd21 (Bd21), with a focus on this peculiar mode of interaction. A collection of 19 strains was selected for their known growth promotion potential. The impact of the rhizobacteria on the model grass was studied using an in vitro cocultivation system allowing interactions through VOCs without physical contact between plants and bacteria. The results show that the VOCs of several strains promote total biomass production, modulate biomass partitioning and affect shoot and root architecture of Bd21. The effects of the PGPR strains emitting different volatile blends were investigated via principal component analysis coupled to clustering and univariate analysis to unravel their biological effects. On the basis of volatile emissions and of their effects on plant growth, two strains have been selected in order to evaluate such interactions using an ex vitro system. The set-up of this system is in progress

Efficient paradoxical (REM) sleep homeostatic regulation in mice: reports on sleep architecture and neuronal activation

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Modulation of hypothalamic MCH-expressing neurons by pharmacogenetic tools strongly alters the sleep-waking cycle in mice

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