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961.
962.
Photosynthesis and inorganic carbon acquisition in the cyanobacterium Chlorogloeopsis sp. ATCC 27193 总被引:1,自引:0,他引:1
The ability of the morphologically complex cyanobacterium Chlorogloeopsis sp. ATCC 27193 to actively transport and accumulate inorganic carbon (C1= CO2+ HCO3?+ CO32?) for photosynthetic CO2 fixation was investigated. Mass-spectrometric assays revealed that Chlorogloeopsis cells grown under C1 limitation rapidly took up CO2 from the medium in a light-dependent reaction which was independent of CO2 fixation. Ethoxyzolamide, a carbonic anhydrase (CA) inhibitor, inhibited CO2 transport. Since electrometric and mass-spectrometric assays did not detect the presence of a periplasmic CA, it is suggested that CO2 transport was mediated by a CA-like activity which converted CO2 to HCO3? during passage across the membrane. Radiochemical assays, using H14CO3 as substrate, showed that C3-limited cells also had a high affinity (K0.5 HCO3?= 37 μM), Na+-independent HCO3? uptake mechanism. HCO3?uptake was light dependent and occurred against its electrochemical potential indicating a carrier-mediated, active transport process. The rate of Na+-independent HCO3? transport was sufficient to account for the steady state rate of CO2 fixation. Although not absolutely required. Na+ did specifically enhance the rate of HCO3? transport by up to 2-fold, but had no effect on the apparent affinity of the transport system for HCO3? Combined CO2 and HCO3? transport resulted in C1 accumulation as high as 25 mM and in excess of 300 times the external concentration. The C1 pool was the source of CO2 for photo-synthetic fixation and was generated, presumably, by the dehydration of HCO3? catalyzed by an intracellular CA. The collective evidence indicates that Chlorogloeopsis has a physiologically functional CO2-concentrating mechanism which is essential for photosynthesis. 相似文献
963.
Pascal Espié Anne Devin Bernard Guérin Michel Rigoulet 《Journal of bioenergetics and biomembranes》1997,29(6):591-601
This study was designed to investigate the energetics of isolated rat hepatocyte swelling due to sodium-cotransported amino acid accumulation in a medium containing either glucose or octanoate as basal substrate. We show that the size of the increase in cytosolic volume is directly correlated with the total amino acid accumulation, which depends on the difference of electrical potential across the plasma membrane. Such a change in cell volume, with either glucose or octanoate, does not modify the mitochondrial volume. Addition of sodium-cotransported amino acids for which the metabolism was avoided showed that the rise in cell volume, per se, did not change the respiratory rate, p, or phosphate potential in either mitochondrial or cytosolic compartments. Conversely, the large increase in oxidative phosphorylation flux was due to the metabolism of amino acids as a consequence of a rise in electron supply for the respiratory chain rather than an increase in cellular ATP demand, as indicated by the increase in cytosolic phosphate potential. Moreover, although we confirm that octanoate addition largely increases the respiratory rate by a process different from uncoupling, we observed that the same overall thermodynamic driving force through the respiratory chain and the same mitochondrial or cytosolic phosphate potential were maintained for much higher oxygen consumption when octanoate was present. We propose that these octanoate effects are due to a decrease in the actual protons/2 electrons stoichiometry as a consequence of a shift in electron supply toward a two-coupling site instead of a three-coupling site. The change in the FADH2/NADH formation flux ratio in either fatty acid or carbohydrate oxidation explains such results. 相似文献
964.
Pascal Jouquet Virginie Tavernier Luc Abbadie Michel Lepage 《African Journal of Ecology》2005,43(3):191-196
Savannah are ecosystems in which mineral nitrogen is considered as a limiting factor for plant productivity. They are heterogeneous and spatially structured in patches, or islands, where mineral nitrogen content is concentrated. Among the soil macrofauna, termites of the Macrotermitinae subfamily are major determinants of soil heterogeneity through the biogenic underground nest structures (fungus‐comb chambers) they produce. To study the role of the heterogeneity created by termites on Pennisetum pedicellatum, an herbaceous grass species was grown in greenhouse. This was carried out using an homogeneous soil poor in mineral nitrogen, and an heterogeneous soil with patch, made of (i) Ancistrotermes cavithorax fungus‐comb chamber wall and (ii) soil with the same mineral nitrogen content as the termite handled soil. Plants exhibited a better growth on patch of termite‐modified soil whereas no significant differences were shown with the supply of mineral nitrogen. The presence of fungus‐comb chamber wall material resulted in an increase of fine root biomass and root/shoot ratio. We conclude that termites, through their building activities, may create nutrient patches available to grasses. Concurrently, our data illustrate that the higher mineral nitrogen content in termite‐built structures is not the only factor responsible for plant growth. 相似文献
965.
966.
Véronique Alary Samir Messad Ibrahim Daoud Adel Aboul-Naga Mona Abdelzaher Osman Pascal Bonnet Jean-François Tourrand 《Human ecology: an interdisciplinary journal》2016,44(1):81-90
In the last 60 years, the livelihoods of agro-pastoral and pastoral families in the arid and semi-arid zones in North Africa and the Middle East have undergone major changes caused by significant incentives to adopt a sedentary lifestyle and the increasing intensity of drought events. Such changes have also been influenced by land reclamation projects accompanied by the construction of reservoirs and dikes in the dry lands as well as the extension of irrigation canals in the desert in the Coastal Zone of the Western Desert, Egypt. To understand the changes in the traditional social organization of this desert society, and how these social changes have affected families’ ability to adapt to external shocks such as the recent 15-year drought, we developed a typological approach to investigate the link between family livelihoods and social capital in Bedouin society. We showed a clear link between physical assets (mainly land and animals), the nature and intensity of social links within the traditional society, and level of education. The analysis revealed also some new wealth accumulation processes in link with the socio-political influence of urban zones and the increasing level of education in the zone. 相似文献
967.
968.
Alexandra Müller Jakob Eller Frank Albrecht Pascal Prochnow Katja Kuhlmann Julia Elisabeth Bandow Alan John Slusarenko Lars Ingo Ole Leichert 《The Journal of biological chemistry》2016,291(22):11477-11490
Allicin (diallyl thiosulfinate) from garlic is a highly potent natural antimicrobial substance. It inhibits growth of a variety of microorganisms, among them antibiotic-resistant strains. However, the precise mode of action of allicin is unknown. Here, we show that growth inhibition of Escherichia coli during allicin exposure coincides with a depletion of the glutathione pool and S-allylmercapto modification of proteins, resulting in overall decreased total sulfhydryl levels. This is accompanied by the induction of the oxidative and heat stress response. We identified and quantified the allicin-induced modification S-allylmercaptocysteine for a set of cytoplasmic proteins by using a combination of label-free mass spectrometry and differential isotope-coded affinity tag labeling of reduced and oxidized thiol residues. Activity of isocitrate lyase AceA, an S-allylmercapto-modified candidate protein, is largely inhibited by allicin treatment in vivo. Allicin-induced protein modifications trigger protein aggregation, which largely stabilizes RpoH and thereby induces the heat stress response. At sublethal concentrations, the heat stress response is crucial to overcome allicin stress. Our results indicate that the mode of action of allicin is a combination of a decrease of glutathione levels, unfolding stress, and inactivation of crucial metabolic enzymes through S-allylmercapto modification of cysteines. 相似文献
969.
Facultative nitrogen fixation by legumes in the central Congo basin is downregulated during late successional stages 下载免费PDF全文
The contribution of the legume community to the nitrogen cycle during natural forest regeneration remains poorly understood. We systematically assessed the changes in abundance and nodulation status of all legumes, across taxa and plant types, in a forest succession gradient in the Equateur Province of the Democratic Republic of the Congo. Our results clearly show that symbiotic N2 fixation is downregulated during late successional stages. 相似文献