Diversité des systèmes de polyculture élevage et des modes d’exploitation des prairies : quelles conséquences sur la diversité végétale ?

  Mention d'édition : Institut de l'Elevage-INRAIn a mixed crop-livestock system region, the grassland surfaces in a landscape are an asset for biodiversity management. Biodiversity is mainly characterised for permanent grasslands, rarely in temporary grasslands. But they cover most of the grassland surfaces in western France and are the base element of dairy production systems. Does knowledge of the production system or grassland management enable the estimation of plot biodiversity? Are the production system and grassland management linked? Are these managements homogenous on a farm? Is some of the grassland management specific of a production system? The analysis was based on 21 dairy farms located in 3 different geographical zones, 420 grasslands and some phytosociological surveys were realised on 94 plots. Three multifactorial analyses were realised to obtain 7 “livestock system”, 7 “grassland management” and the identification of the practices that structure the plant communities. The specific richness of the surveys were low (2 to 22) compared to some other French regions. None of the grassland management was related to higher specific richness except the young hay field. The duration of the grasslands and the mowing intensity were the main factors to explain the presence of annual weeds. These species were the main contributors of the higher specific richness. Managing biodiversity does not seem to be specific to one livestock farming system but this work suggests looking for methods to improve the duration of the grasslands.En région de polyculture élevage les surfaces en prairies sont un atout dans les paysages pour la gestion de la biodiversité. La diversité végétale est essentiellement étudiée en prairies permanentes, rarement dans les prairies temporaires. Or elles couvrent la majorité des surfaces en herbe du Grand Ouest de la France et sont la base des systèmes d’élevage laitiers. Connaître un système d’élevage ou un mode de conduite des prairies permettrait-il de prédire la biodiversité des parcelles ? Le système d’élevage renseigne-t-il sur les modes de conduite des prairies ? Certaines conduites de prairies sont-elles spécifiques de certains systèmes ? L’analyse se base sur 21 élevages laitiers de 3 secteurs géographiques différents, la conduite de 420 prairies et des relevés phyto-sociologiques de végétation dans 94 parcelles. Trois analyses multi-variées réalisées en parallèle aboutissent à 7 « orientations d’exploitation » (OE), 7 « modes d’exploitations parcellaires » (MEP) et l’identification des pratiques structurant les communautés d’espèces végétales. La relation entre les OE et les MEP est complexe : les orientations d’exploitation ne déterminent pas la conduite des prairies. La richesse spécifique (nombre d’espèces total) des relevés est faible (2 à 22 ; 9.2 en moyenne) comparée à d’autres régions de France. Aucun MEP n’est associé à des richesses spécifiques plus fortes, à part les jeunes prairies de fauches. La durée des prairies et l’intensité de la fauche sont les facteurs déterminants de la présence d’espèces annuelles dites "adventices". Ce sont ces espèces qui contribuent aux richesses spécifiques les plus élevées. Gérer la biodiversité n’est pas réservé à des systèmes particuliers : ce travail suggère plutôt de rechercher les moyens d’allonger la durée des prairies dans les rotations

TOM20-mediated transfer of Bcl2 from ER to MAM and mitochondria upon induction of apoptosis

International audienceIn this work, we have explored the subcellular localization of Bcl2, a major antiapoptotic protein. In U251 glioma cells, we found that Bcl2 is localized mainly in the ER and is translocated to MAM and mitochondria upon induction of apoptosis; this mitochondrial transfer was not restricted to the demonstrator cell line, even if cell-specific modulations exist. We found that the Bcl2/mitochondria interaction is controlled by TOM20, a protein that belongs to the protein import machinery of the mitochondrial outer membrane. The expression of a small domain of interaction of TOM20 with Bcl2 potentiates its anti-apoptotic properties, which suggests that the Bcl2-TOM20 interaction is proapoptotic. The role of MAM and TOM20 in Bcl2 apoptotic mitochondrial localization and function has been confirmed in a yeast model in which the ER-mitochondria encounter structure (ERMES) complex (required for MAM stability in yeast) has been disrupted. Bcl2-TOM20 interaction is thus an additional player in the control of apoptosis

Sphingolipids distribution at mitochondria-associated membranes (MAM) upon induction of apoptosis.

International audienceThe levels and composition of sphingolipids and related metabolites are altered in aging and common disorders such as diabetes and cancers, as well as in neurodegenerative, cardiovascular, and respiratory diseases. Changes in sphingolipids have been implicated as being an essential step in mitochondria-driven cell death. However, little is known about the precise sphingolipid composition and modulation in mitochondria or related organelles. Here, we used LC-MS/MS to analyze the presence of key components of the ceramide metabolic pathway in vivo and in vitro in purified endoplasmic reticulum (ER), mitochondria-associated membranes (MAM), and mitochondria. Specifically, we analyzed the sphingolipids in the three pathways that generate ceramide: sphinganine in the de novo ceramide pathway, sphingomyelin in the breakdown pathway, and sphingosine in the salvage pathway. We observed sphingolipid profiles in mouse liver, mouse brain, and a human glioma cell line (U251). We analyzed the quantitative and qualitative changes of these sphingolipids during staurosporine (STS)-induced apoptosis in U251 cells. Ceramide, especially C16-ceramide, levels increased during early apoptosis possibly through a conversion from mitochondrial sphinganine and sphingomyelin, but sphingosine and lactosyl- and glucosyl-ceramide levels were unaffected. We also found that ceramide generation is enhanced in mitochondria when sphingomyelin levels are decreased in the MAM. This decrease was associated with an increase in acid sphingomyelinase (ASM) activity in MAM. We conclude that meaningful sphingolipid modifications occur in MAM, the mitochondria, and ER during the early phases of apoptosis