Activité de la phosphatase alcaline bactérienne à l'interface eau-sédiment au sein du réservoir Sahela (Maroc)

Les variations temporelles des concentrations en phosphore, celles des abondances bactériennes et de l'activité de la phosphatase alcaline (APA) ont été estimées in situ en chambre benthique placée en deux points du réservoir Sahela (Maroc) durant les mois de septembre et octobre 98. En période de faible oxygénation, nous avons enregistré des élévations relativement faibles des concentrations en orthophosphates (de 0,020 à 0,035 mg. l-1 au point 1 et 0,015 à 0,025 mg. l-1 au point 2) par rapport au phosphore total (0,080 à 0,100 mg. l-1 au point 1 et de 0,035 à 0,040 mg. l-1 au point 2). À cette période, les abondances bactériennes et l'APA montrent des valeurs maximales (8. 106 bact. ml-1 et 0,323 mmol.PNP l-1.h-1 au point 1 et 6.106 bact. ml-1 et 0,438 mmol.PNP l-1.h-1 au point 2 respectivement). L'apparition des conditions anoxiques et la diminution du pH favorisaient la dissolution du phosphore particulaire et la libération du phosphore réactif soluble. Cette libération s'accompagne d'une élévation des abondances de bactéries anaérobies (de 5.106 à 9,2. 106 bact. ml-1 au point 1 et de 3,8.106 à 7,2. 106 bact. ml-1 au point 2) et une diminution progressive d'APA (de 0,200 à 0,025 mmol.PNP l-1.h-1 au point 1 et de 0,125 à 0,077 mmol.PNP l-1.h-1 au point 2). Ce relargage du phosphore à partir du sédiment est accentué par les rejets domestiques et industriels de la ville de Taounate, ce qui accélère le processus d'eutrophisation de ce réservoir.Temporal variations of phosphorus concentrations, bacterial abundance and alkaline phosphatase activity (APA) were estimated in situ in a benthic chamber. The chamber used has a surface of 0.4m2 and a volume of 90 l ; it resembles those used in oceanography, with a tube connecting the interior of the chamber to the lake surface. The water in the chamber was permanently mixed by an electric agitation system. The chamber was placed at two points in the Sahela reservoir (Morocco). Point 1 was located near Guelta El Haila, a site that receives both domestic and industrial effluent, and point 2 was located in the centre of the reservoir. During the two incubations, eight samples were taken over 24 d in September and October 1998 from point 1, and seven samples were taken from point 2 over 29 d in October. After each sampling, an equal volume of water was injected into the chamber to avoid bubble formation.Under low dissolved oxygen concentrations in the benthic chamber, we noticed a relatively small elevation in orthophosphate concentrations (from 0.020 to 0.035 mg×L-1 at point 1 and from 0.015 to 0.025 mg×L-1 at point 2) in relation to total phosphorus (from 0.080 to 0.100 mg×L-1 and from 0.035 to 0.040 mg×L-1 at points 1 and 2 respectively). The low residual oxygenation of hypolimnic layer allowed the oxidation of iron, manganese and led to their binding to phosphorus released from the interstitial water. Dissociation of calcium-phosphorus complexes as a result of a pH decrease may have contributed to phosphorus release. The orthophosphate concentrations were relatively low, a situation that favours the synthesis of alkaline phosphatase by aerobic bacteria and facultative aerobic bacteria. In this period, the bacterial abundance and APA were comparable and showed the maximal values (8. 106 bact. ml-1 and 0.323 mmol. PNP l-1.h-1 (phosphate nitrophenol) in point 1 and 6. 106 bact. ml-1and 0.438 mmol. PNP l-1.h-1 in point 2 respectively). The lack of a significant correlation between total APA and bacterial abundance at the two sampling points is probably due to the decrease of aerobic bacteria followed by a repopulation with anaerobic bacteria. However, the relative contribution of two bacterial populations that have different sizes, as at points 1 and 2, showed that the majority of total APA was produced by bacteria that are attached to organic matter. Therefore we suggest that attached bacteria contribute more than free bacteria to APA production.The beginning of anoxic conditions and the decrease in pH favored the dissolution of particulate phosphorus and the liberation of reactive phosphorus. We noted an elevation in orthophosphate concentrations (from 0.035 to 0.050 mg×L-1 at point 1 and stabilised at 0.025 mg×L-1 at point 2) and total phosphorus (from 0.100 to 0.150 mg×L-1 at point 1 and from 0.040 to 0.050 mg×L-1 at point 2). This liberation followed an increase in anaerobic bacterial abundance (from 5×106 to 9.2×106 bact×mL-1 at point 1 and from 3.8×106 to 7.2×106 bact×mL-1 at point 2) and the progressive decrease in APA (from 0.200 to 0.025 mmol PNP L-1 ×h-1 at point 1 and from 0.125 to 0.077 mmol PNP L-1 ×h-1 at point 2). The anaerobic bacteria did not activate their alkaline phosphatase and the synthesis of their enzyme was progressively inhibited by a de-repression phenomenon caused by high phosphorus concentrations.We conclude that low oxygen and a decrease in pH favoured the release of phosphorus by dissolution of chemical complexes: calcium-phosphorus, iron-phosphorus, manganese-phosphorus and aluminium-phosphorus. This release is also the result of bacterial phosphatase activity to which fixed bacteria contributed the most. The release of phosphorus from water-sediment interface is further amplified by phosphate import from domestic and industrial waste waters originating from Taounate, which accelerates the eutrophication process in this reservoir

A highly osmotolerant rhizobial strain confers a better tolerance of nitrogen fixation and enhances protective activities to nodules of Phaseolus vulgaris under drought stress

The effect of water deficiency on nodules of common bean (Phaseolus vulgaris) inoculated with three rhizobial strains differing in their osmotolerance, was investigated in two different experiments on sterile sand. In the first experiment, the control plants were maintained at 90% field capacity (FC) and water-deficient plants were grown at 35% FC. The nitrogen fixation and growth parameters drastically decreased under water deficiency, however the three rhizobial strains, Rhizobium etli A32 (sensitive), Rhizobium tropici CIAT899 (tolerant), and Ensifer meliloti 4H41 (highly tolerant), showed different symbiotic performances. E. meliloti 4H41 allowed the best acetylene reduction activity (ARA) and biomass production and the highest number of large-sized nodules, while no significant effect was observed on lipid peroxidation, protein and legheamoglobin contents. The effect on antioxidant activities was the lowest. In the second experiment, plants were maintained at 90% FC during 45 days and then watering was stopped. The results showed that, the response to water deficit was quite similar for the three analyzed symbioses until 35% FC, but below this value of FC, symbiosis involving strain E. meliloti 4H41 was the most tolerant. This tolerance was accompanied, by in both experiments, by a stability of metabolic indices and protective antioxidant activities. These results suggest that, the relative tolerance of the nodules induced by strain 4H41 could be due to a constructive adaptation involving specific cortex structure and stress-adapted metabolic activities acquired during nodule formation and growth, rather than to a timely inducible response due to the stimulation of antioxidant enzymes. This suggestion should be confirmed through microscopic structure analysis and supplemental key enzymes in nodule metabolism such as sucrose synthase and malate dehydrogenase.Key words: Antioxidant activities, in pots experiment, leghemoglobin content, nodule, rhizobia, osmotolerance, symbiotic efficiency, water deficiency

Physical Activity and Insulin Sensitivity: The RISC Study

OBJECTIVE— Physical activity is a modifiable risk factor for type 2 diabetes, partly through its action on insulin sensitivity. We report the relation between insulin sensitivity and physical activity measured by accelerometry

High-Energy Molecular-Frame Photoelectron Angular Distributions: A Molecular Bond-Length Ruler

We present an experimental and theoretical study of core-level ionization of small hetero- and homo-nuclear molecules employing circularly polarized light and address molecular-frame photoelectron angular distributions in the light's polarization plane (CP-MFPADs). We find that the main forward-scattering peaks of CP-MFPADs are slightly tilted with respect to the molecular axis. We show that this tilt angle can be directly connected to the molecular bond length by a simple, universal formula. The extraction of the bond length becomes more accurate as the photoelectron energy is increased. We apply the derived formula to several examples of CP-MFPADs of C 1s and O 1s photoelectrons of CO, which have been measured experimentally or obtained by means of ab initio modeling. The photoelectron kinetic energies range from 70 to 1000~eV and the extracted bond lengths agree well with the known bond length of the CO molecule in its ground state. In addition, we discuss the influence of the back-scattering contribution that is superimposed over the analyzed forward-scattering peak in case of homo-nuclear diatomic molecules as N$_2$

Interaction of plant growth regulators and reactive oxygen species to regulate petal senescence in wallflowers (Erysimum linifolium)

Background In many species floral senescence is coordinated by ethylene. Endogenous levels rise, and exogenous application accelerates senescence. Furthermore, floral senescence is often associated with increased reactive oxygen species, and is delayed by exogenously applied cytokinin. However, how these processes are linked remains largely unresolved. Erysimum linifolium (wallflower) provides an excellent model for understanding these interactions due to its easily staged flowers and close taxonomic relationship to Arabidopsis. This has facilitated microarray analysis of gene expression during petal senescence and provided gene markers for following the effects of treatments on different regulatory pathways. Results In detached Erysimum linifolium (wallflower) flowers ethylene production peaks in open flowers. Furthermore senescence is delayed by treatments with the ethylene signalling inhibitor silver thiosulphate, and accelerated with ethylene released by 2-chloroethylphosphonic acid. Both treatments with exogenous cytokinin, or 6-methyl purine (which is an inhibitor of cytokinin oxidase), delay petal senescence. However, treatment with cytokinin also increases ethylene biosynthesis. Despite the similar effects on senescence, transcript abundance of gene markers is affected differentially by the treatments. A significant rise in transcript abundance of WLS73 (a putative aminocyclopropanecarboxylate oxidase) was abolished by cytokinin or 6-methyl purine treatments. In contrast, WFSAG12 transcript (a senescence marker) continued to accumulate significantly, albeit at a reduced rate. Silver thiosulphate suppressed the increase in transcript abundance both of WFSAG12 and WLS73. Activity of reactive oxygen species scavenging enzymes changed during senescence. Treatments that increased cytokinin levels, or inhibited ethylene action, reduced accumulation of hydrogen peroxide. Furthermore, although auxin levels rose with senescence, treatments that delayed early senescence did not affect transcript abundance of WPS46, an auxin-induced gene. Conclusions A model for the interaction between cytokinins, ethylene, reactive oxygen species and auxin in the regulation of floral senescence in wallflowers is proposed. The combined increase in ethylene and reduction in cytokinin triggers the initiation of senescence and these two plant growth regulators directly or indirectly result in increased reactive oxygen species levels. A fall in conjugated auxin and/or the total auxin pool eventually triggers abscission

Drought Impact Is Alleviated in Sugar Beets (Beta vulgaris L.) by Foliar Application of Fullerenol Nanoparticles

Over the past few years, significant efforts have been made to decrease the effects of drought stress on plant productivity and quality. We propose that fullerenol nanoparticles (FNPs, molecular formula C-60(OH)(24)) may help alleviate drought stress by serving as an additional intercellular water supply. Specifically, FNPs are able to penetrate plant leaf and root tissues, where they bind water in various cell compartments. This hydroscopic activity suggests that FNPs could be beneficial in plants. The aim of the present study was to analyse the influence of FNPs on sugar beet plants exposed to drought stress. Our results indicate that intracellular water metabolism can be modified by foliar application of FNPs in drought exposed plants. Drought stress induced a significant increase in the compatible osmolyte proline in both the leaves and roots of control plants, but not in FNP treated plants. These results indicate that FNPs could act as intracellular binders of water, creating an additional water reserve, and enabling adaptation to drought stress. Moreover, analysis of plant antioxidant enzyme activities (CAT, APx and GPx), MDA and GSH content indicate that fullerenol foliar application could have some beneficial effect on alleviating oxidative effects of drought stress, depending on the concentration of nanoparticles applied. Although further studies are necessary to elucidate the biochemical impact of FNPs on plants; the present results could directly impact agricultural practice, where available water supplies are often a limiting factor in plant bioproductivity