The Méry-sur-Oise (France) storage reservoir is an artificial basin of 9 m average depth, fed by water from the river Oise with a mean residence time of about 4 days. Sediments are accumulating at a rate of about 0.7 cm/month. In the sediments, two fractions of organic nitrogen with different rates of bacterial degradation could be distinguished, one associated with fresh phytoplankton, the other made of detrital and more refractory compounds. The fluxes of oxygen, nitrate and ammonium across the sediment-water interface were measured with a bell-jar system at different seasons during a 3 year period following flooding of the basin. The measurements show clear seasonal variations in relation with the variations of temperature and input of fresh phytoplanktonic material to the sediment. In addition, a long term trend of increasing ammonium was observed. Measurements were also carried out after dredging of all accumulated sediments of the basin. They showed a considerable reduction of the flux of nitrate to the sediments and a significant reduction of the flux of ammonium to the water column.These results are interpreted in the light of a non stationary model of N diagenesis in accumulating sediments. This model is able to predict at least the general trends of benthic N cycling of basins during the early stage of their ecological succession. 相似文献
Bacterial reaction centers use light energy to couple the uptake of protons to the successive semi-reduction of two quinones, namely QA and QB. These molecules are situated symmetrically in regard to a non-heme iron atom. Four histidines and one glutamic acid, M234Glu, constitute the five ligands of this atom. By flash-induced absorption spectroscopy and delayed fluorescence we have studied in the M234EH and M234EL variants the role played by this acidic residue on the energetic balance between the two quinones as well as in proton uptake. Delayed fluorescence from the P+QA? state (P is the primary electron donor) and temperature dependence of the rate of P+QA? charge recombination that are in good agreement show that in the two RC variants, both QA? and QB? are destabilized by about the same free energy amount: respectively ~ 100 ± 5 meV and 90 ± 5 meV for the M234EH and M234EL variants, as compared to the WT. Importantly, in the M234EH and M234EL variants we observe a collapse of the high pH band (present in the wild-type reaction center) of the proton uptake amplitudes associated with formation of QA? and QB?. This band has recently been shown to be a signature of a collective behaviour of an extended, multi-entry, proton uptake network. M234Glu seems to play a central role in the proton sponge-like system formed by the RC protein. 相似文献
Generation and characterization of knockout clones is a widely used approach to evaluate the specific function of a gene product in Dictyostelium discoideum. The mutant clones are generally obtained by double homologous recombination in the target gene. A frequent limitation to obtaining mutants is the low frequency of homologous recombination. Here we present an easy method to identify rare mutants, based on PCR analysis of pools of clones. This method also allows the isolation of functional knockout mutants created by a single homologous recombination event, which can be more frequent than a double recombination event. 相似文献
The folding and assembly of Rubisco large and small subunits into L8S8 holoenzyme in chloroplasts involves many auxiliary factors, including the chaperone BSD2. Here we identify apparent intermediary Rubisco‐BSD2 assembly complexes in the model C3 plant tobacco. We show BSD2 and Rubisco content decrease in tandem with leaf age with approximately half of the BSD2 in young leaves (~70 nmol BSD2 protomer.m2) stably integrated in putative intermediary Rubisco complexes that account for <0.2% of the L8S8 pool. RNAi‐silencing BSD2 production in transplastomic tobacco producing bacterial L2 Rubisco had no effect on leaf photosynthesis, cell ultrastructure, or plant growth. Genetic crossing the same RNAi‐bsd2 alleles into wild‐type tobacco however impaired L8S8 Rubisco production and plant growth, indicating the only critical function of BSD2 is in Rubisco biogenesis. Agrobacterium mediated transient expression of tobacco, Arabidopsis, or maize BSD2 reinstated Rubisco biogenesis in BSD2‐silenced tobacco. Overexpressing BSD2 in tobacco chloroplasts however did not alter Rubisco content, activation status, leaf photosynthesis rate, or plant growth in the field or in the glasshouse at 20°C or 35°C. Our findings indicate BSD2 functions exclusively in Rubisco biogenesis, can efficiently facilitate heterologous plant Rubisco assembly, and is produced in amounts nonlimiting to tobacco growth. 相似文献
1. 1. Cycles of oxidation followed by reduction at pH 7.2 have been induced in uncoupled anaerobic mung bean mitochondria treated with succinate and malonate by addition of oxygen-saturated medium. Under the conditions used, cytochromes b557, b553, c549 (corresponding to c1 in mammalian mitochondria) and ubiquinone are completely oxidized in the aerobic state, but become completely reduced in anaerobiosis.
2. 2. The time course of the transition from fully oxidized to fully reduced in anaerobiosis was measured for cytochromes c549, b557, and b553. The intramitochondrial redox potential (IMPh) was calculated as a function of time for each of the three cytochromes from the time course of the oxidized-to-reduced transition and the known midpoint potentials of the cytochromes at pH 7.2. The three curves so obtained are superimposable, showing that the three cytochromes are in redox equilibrium under these conditions during the oxidized-to-reduced transition.
3. 3. This result shows that the slow reduction of cytochrome b557 under these conditions, heretofore considered anomalous, is merely a consequence of its more negative midpoint potential of +42 mV at pH 7.2, compared to +75 mV for cytochrome b553 and +235 mV for cytochrome c549. Cytochrome b557 is placed on the low potential side of coupling site II and transfers electrons to cytochrome c549via the coupling site.
4. 4. The time course of the transition from fully oxidized to fully reduced was also measured for ubiquinone. Using the change in intramitochondrial potential IMPh with time obtained from the three cytochromes, the change in redox state of ubiquinone with IMPh was calculated. When replotted as IMPhversus the logarithm of the ratio (fraction oxidized)/(fraction reduced), two redox components with n = 2 were found. The major component is ubiquinone with a midpoint potential Em7.2 = + 70 mV. The minor component has a midpoint potential Em7.2 = − 12 mV; its nature is unknown.
Abbreviations: IMPh, intramitochondrial potential, referred to the normal hydrogen electrode; Em7.2, midpoint potential at pH 7.2 相似文献
Organisms inhabiting the intertidal zone have been used to study natural ecophysiological responses and adaptations to thermal stress because these organisms are routinely exposed to high‐temperature conditions for hours at a time. While intertidal organisms may be inherently better at withstanding temperature stress due to regular exposure and acclimation, they could be more vulnerable to temperature stress, already living near the edge of their thermal limits. Strong gradients in thermal stress across the intertidal zone present an opportunity to test whether thermal tolerance is a plastic or canalized trait in intertidal organisms. Here, we studied the intertidal pool‐dwelling calcified alga, Ellisolandia elongata, under near‐future temperature regimes, and the dependence of its thermal acclimatization response on environmental history. Two timescales of environmental history were tested during this experiment. The intertidal pool of origin was representative of long‐term environmental history over the alga's life (including settlement and development), while the pool it was transplanted into accounted for recent environmental history (acclimation over many months). Unexpectedly, neither long‐term nor short‐term environmental history, nor ambient conditions, affected photosynthetic rates in E. elongata. Individuals were plastic in their photosynthetic response to laboratory temperature treatments (mean 13.2°C, 15.7°C, and 17.7°C). Further, replicate ramets from the same individual were not always consistent in their photosynthetic performance from one experimental time point to another or between treatments and exhibited no clear trend in variability over experimental time. High variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level over time. 相似文献
The pinewood nematode, Bursaphelenchus xylophilus, native to North America, is the causative agent of pine wilt disease and among the most important invasive forest pests in the East-Asian countries, such as Japan and China. Since 1999, it has been found in Europe in the Iberian Peninsula, where it also causes significant damage. In a previous study, 94 pairs of microsatellite primers have been identified in silico in the pinewood nematode genome. In the present study, specific PCR amplifications and polymorphism tests to validate these loci were performed and 17 microsatellite loci that were suitable for routine analysis of B. xylophilus genetic diversity were selected. The polymorphism of these markers was evaluated on nematodes from four field origins and one laboratory collection strain, all originate from the native area. The number of alleles and the expected heterozygosity varied between 2 and 11 and between 0.039 and 0.777, respectively. First insights into the population genetic structure of B. xylophilus were obtained using clustering and multivariate methods on the genotypes obtained from the field samples. The results showed that the pinewood nematode genetic diversity is spatially structured at the scale of the pine tree and probably at larger scales. The role of dispersal by the insect vector versus human activities in shaping this structure is discussed. 相似文献
In order to identify proteins interacting with the cardiac voltage-gated sodium channel Na(v)1.5, we used the last 66 amino acids of the C-terminus of the channel as bait to screen a human cardiac cDNA library. We identified the protein tyrosine phosphatase PTPH1 as an interacting protein. Pull-down experiments confirmed the interaction, and indicated that it depends on the PDZ-domain binding motif of Na(v)1.5. Co-expression experiments in HEK293 cells showed that PTPH1 shifts the Na(v)1.5 availability relationship toward hyperpolarized potentials, whereas an inactive PTPH1 or the tyrosine kinase Fyn does the opposite. The results of this study suggest that tyrosine phosphorylation destabilizes the inactivated state of Na(v)1.5. 相似文献