Glycogen in Methanothrix

An intracellular glycogen was purified and characterized from the acetoclastic bacteria Methanothrix str. FE, its average chain length was about 13 glucose residues. Acetyl-CoA was shown to be synthesized by the action of acetate thiokinase; in addition pyruvate synthase, phosphoenolpyruvate synthetase and enzymes of gluconeogenesis were detected in cell extracts. For glycogen synthase activity, both adenosine diphosphate glucose and uridine diphosphate glucose were used as glycosyl donors, apparent K _m were, respectively, 8 M for ADPGlc and 625 M for UDPGLe, at the opposite the V _m were the same for both precursors. This was in accordance with competition experiments and strongly suggested that only one glucosyl transferase was involved and that ADPGlc was the physiological glycosyl donor in Methanothrix str. FE. In addition branching enzyme activity (1-4-glucan-6-glucosyl transferase) was detected in cell extracts.Abbreviations ADPGlc adenosine diphosphate glucose - UDPGlc uridine diphosphate glucose     

Rate of differentiation and emergence of nodal maize roots

The timing of root production is one of the parameters required for modelling the root system architecture. The objectives of this study are (1) to describe the rate of appearance of adventitious root primordia of maize and their rate of emergence out of the stem; (2) to test equations for the prediction of the rank of the phytomer on which root emergence occurs, in a wide range of field situations.Maize, cultivar Dea, was grown in controlled conditions and in the field in 1987, 1988, 1989 and 1991. Plants were regularly sampled and the following data were recorded: foliar stage, number of root primordia and number of emerged roots per phytomer. Root primordia were counted in transverse thin sections in the stem.At a single plant level, root primordia differentiation occurred sequentially on the successive phytomers, with no overlapping between two phytomers. The same was true for root emergence. Roots belonging to the same phytomer emerged at approximately the same time.At a plant population level, there was a linear relationship between the rank of the phytomer on which root primordia were differentiated and cumulated degree-days after sowing. A linear relationship was also observed between the rank of the phytomer on which roots were emerging and cumulated degree-days or foliar stage. In the range of field situations tested (several years, sowing dates and planting densities), both equations gave an accurate prediction of the timing of root emergence during the plant cycle.     

Effect of mutual shading on the emergence of nodal roots and the root/shoot ratio of maize

The effect of mutual shading on the root/shoot ratio and on the number of nodal roots of maize was studied. Plants of two varieties (Dea and LG2281) were grown in individual pots of 9 L, at three plant densities: 7.5, 11 and 15 plants m^–2. A control experiment was carried out in order to study if root growth was affected by the small size of the pots. Maize plants (cv Dea) were grown at a low plant density (7.5 plants m^–2) in pots of two different volumes (9 and 25 L respectively). In both experiments plants were watered every two hours with a nutrient solution. Some plants were sampled at five dates in the main experiment and the following data were recorded: foliar stage; root, stem and leaf dry weight; number of root primordia and number of emerged roots per phytomer. The final sampling date occurred at silking.Results of the control experiment showed that the root biomass was lower in small pots but the number of nodal roots per phytomer was not affected.Results of the main experiment showed that the total plant biomass and the root/shoot ratio were lower at high plant density. The number of emerged roots was strongly reduced on the upper phytomer (P₈). This reduction was mainly due to a lower percentage of root primordia which elongated. A proposed interpretation is that the number of roots which emerge on upper phytomers is controlled by carbohydrate availability.     

Release of arachidonic acid by NMDA-receptor activation in the rat hippocampus

In hippocampal slices arachidonic acid released after NMDA post-synaptic receptor activation is thought to act as a retrograde trans-synaptic messenger which facilitates the pre-synaptic release of L-glutamate to be involved in the expression of long-term synaptic potentiation (LTP). We measured the mass amount of arachidonic acid released from hippocampal slices incubated under conditions which maintain the electrophysiological responsiveness of the slice. Melittin released arachidonic, oleic and docosahexaenoic acids by phospholipase A₂ activation but not palmitic or stearic acids. Of greater interestl-glutamate, N-methyl-d-aspartate and incubation conditions known to induce LTP selectively and rapidly increased the release of archidonic acid in amounts over basal levels of 200–300 ng/mg protein. This is the first direct determination of the mass amount of arachidonic acid released following NMDA receptor activation in the hippocampus.Special issue dedicated to Dr. Louis Sokoloff.     

On-Line Optical and Morphological Studies of Silver Nanoparticles Growth Formed by Nanosecond Laser Irradiation of Silver-Exchanged Silicate Glass

Silver-exchanged silicate glass has been irradiated by 532-nm pulsed Nd:YAG laser in order to locally form metallic nanoparticles. The particular interest of this process is to locally control the silver nanoparticles (NPs) growth. Silver ions are exchanged with sodium ions near the glass surface after dumping of a silicate glass few minutes in silver and sodium nitrates molten salt. A low-energy density laser exposure (0.239 J/cm²) chosen at the ablation threshold allows to observe the kinetics of the silver NPs growth according to the increasing shots number. An on-line optical measurement is carried out after each shot to identify the most important steps during the irradiation process. According to this measurement, we have determined four steps highlighted by UV/Visible spectrophotometry and we have identified the influence of located surface plasmon resonance. Three combined material analysis methods were used to understand the glass/laser interaction mechanism: we outlined the material volume variations by profilometric method, the element distribution by scanning electron microscopy and finally the structural distribution of the irradiated region by a local infrared investigation. The trend for NPs formation revealed by the UV/Visible spectrophotometry is thus explained by the formation of a ring expelled from a central hole. We highlight that the on-line extinction measurement can be used to data process the NPs evolution.     

Cell-Type-Specific Gene Expression Profiling in Adult Mouse Brain Reveals Normal and Disease-State Signatures

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Matching habitat choice promotes species persistence under climate change

Species may survive under contemporary climate change by either shifting their range or adapting locally to the warmer conditions. Theoretical and empirical studies recently underlined that dispersal, the central mechanism behind these responses, may depend on the match between an individuals’ phenotype and local environment. Such matching habitat choice is expected to induce an adaptive gene flow, but it now remains to be studied whether this local process could promote species’ responses to climate change. Here, we investigate this by developing an individual‐based model including either random dispersal or temperature‐dependent matching habitat choice. We monitored population composition and distribution through space and time under climate change. Relative to random dispersal, matching habitat choice induced an adaptive gene flow that lessened spatial range loss during climate warming by improving populations’ viability within the range (i.e. limiting range fragmentation) and by facilitating colonization of new habitats at the cold margin. The model even predicted range contraction under random dispersal but range expansion under optimal matching habitat choice. These benefits of matching habitat choice for population persistence mostly resulted from adaptive immigration decision and were greater for populations with larger dispersal distance and higher emigration probability. We also found that environmental stochasticity resulted in suboptimal matching habitat choice, decreasing the benefits of this dispersal mode under climate change. However population persistence was still better under suboptimal matching habitat choice than under random dispersal. Our results highlight the urgent need to implement more realistic mechanisms of dispersal such as matching habitat choice into models predicting the impacts of ongoing climate change on biodiversity.     

Roles of ATP and cytoskeleton in the regulation of Na+/H+ exchanger along the nephron luminal membrane

Although in LLC-PK cells ATP depletion has been shown to result in alterations of cytoskeleton actin and an inhibition of Na+/H+ exchanger activity, there is little information concerning the regulation of this exchanger in the distal luminal membrane by ATP and actin filaments. The present study examined the direct effect of ATP and cytochalasin B on the Na+/H+ exchanger activity in the proximal and distal tubule luminal membranes. The presence of 100 microM ATP in the luminal membrane vesicles from rabbit proximal tubules did not influence the Ethyl Isopropyl Amiloride sensitive Na+ uptake by these membranes. In contrast, the same treatment of luminal membranes from distal tubules significantly enhanced the exchanger activity from 0.22 +/- 0.04 to 0.39 +/- 0.08 pM/microg/10 sec (P < 0.02). When ATP was replaced by its nonhydrolysable form, ATPgammas, the effect on the distal luminal membrane was strongly diminished suggesting that the action of the nucleotide implicates a phosphorylation step. Confirming this hypothesis, addition of 300-microM-Rp cAMP, a protein kinase A inhibitor, completely abolished the effect of ATP. In view of the fact that a tight relationship has been described between ATP, the cytoskeleton complex and the exchanger activity, we studied the effect of cytochalasin B on this activity. The presence of 20 microM cytochalasin B in the distal luminal membrane vesicles induced, as observed with ATP, a significant increase in the Na+ uptake. However, the actions of ATP and cytochalasin B were not additive. These results suggest that firstly, ATP and short actin filaments of the cytoskeleton regulate the distal luminal isoform through an intramembranous mechanism and secondly, a phosphorylation mechanism is, at least partially, implicated in the action of ATP. In contrast, the proximal tubule exchanger is regulated through different mechanisms.     

Switch from an aquaporin to a glycerol channel by two amino acids substitution

The MIP (major intrinsic protein) proteins constitute a channel family of currently 150 members that have been identified in cell membranes of organisms ranging from bacteria to man. Among these proteins, two functionally distinct subgroups are characterized: aquaporins that allow specific water transfer and glycerol channels that are involved in glycerol and small neutral solutes transport. Since the flow of small molecules across cell membranes is vital for every living organism, the study of such proteins is of particular interest. For instance, aquaporins located in kidney cell membranes are responsible for reabsorption of 150 liters of water/day in adult human. To understand the molecular mechanisms of solute transport specificity, we analyzed mutant aquaporins in which highly conserved residues have been substituted by amino acids located at the same positions in glycerol channels. Here, we show that substitution of a tyrosine and a tryptophan by a proline and a leucine, respectively, in the sixth transmembrane helix of an aquaporin leads to a switch in the selectivity of the channel, from water to glycerol.