Phosphoenolpyruvate Carboxylase during Maturation and Germination Sorghum Seeds: Enzyme Activity and Regulation

Sorghum (Sorghum bicolor (L.) Moench) is a species of great socio-economic and ecological importance for countries in arid and semi-arid climate. In C₄ plants like sorghum, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) plays a key role in seed development and germination. In this work, the PEPC activity shows an increase followed by a decrease at the early and later stages of maturation, respectively. In germinating seeds, the PEPC activity quickly increases after soaking. The L-malate test and the ratio of PEPC activity determined at pH 8.0 and 7.1, indicates, that PEPC is phosphorylated at the early stages of maturation then becomes dephosphorylated at the later stages and during seed germination, PEPC takes back its phosphorylated form. The determination of the affinity constant showed different K_M depending on the seed developmental stage. As there is no PEPC-C4 isoform in developing sorghum seeds, this result indicates that the different K_M observed during seed maturation could be a result of a post-translational regulation such as phosphorylation or ubiquitination of a pre-existing isoform. This regulation enhances the PEPC activity at early stages of seed development.     

Two-Stage Feature Selection of Voice Parameters for Early Alzheimer's Disease Prediction

Background

The goal of this work is to develop a non-invasive method in order to help detecting Alzheimer's disease in its early stages, by implementing voice analysis techniques based on machine learning algorithms.

Dynamic aspects of colicin N translocation through the Escherichia coli outer membrane.

Colicin N is a bacteriocin that kills sensitive Escherichia coli cells. After binding to the cell surface-exposed receptor, a short period exists when a significant number of the cell-associated colicin N molecules are sensitive to external enzymes. Two colicin N populations are discriminated by proteases: the susceptible pool bound to OmpF porin on the cell surface and another population corresponding to protease-inaccessible colicin N. During translocation, colicin N reaches the periplasmic space and proteolytic cleavage of the colicin occurs only when the outer membrane barrier is permeabilized.     

High level of genetic differentiation for allelic richness among populations of the argan tree [Argania spinosa (L.) Skeels] endemic to Morocco

Genetic diversity at nine isozyme loci was surveyed in an endangered tree species, the argan tree, endemic to south-western Morocco. The species is highly diverse (3.6 alleles/locus) with populations strongly differentiated from each other (F _ST=0.25). This example is used to illustrate a method for standardizing measures of allelic richness in samples of unequal sample sizes, which was developed for the estimation of the number of species and relies on the technique of rarefaction. In addition, it is shown that the measure of subdivision, _ST, obtained when allelic richness is used in place ofh (Nei's index of diversity), is much larger than the F _ST [e.g. _ST(40)=0.52, where (40) indicates the specified sample used to estimate the allelic richness]. This suggests that rare alleles (which strongly influence measures of allelic richness) have a more scattered distribution than more frequent ones, a result which raises special conservation issues for the argan tree.     

Production of solamargine by in vitro cultures of Solanum paludosum

Callus cultures of Solanum paludosum were established from roots, hypocotyles, cotyledons and leaf limbs of plantlets cultivated in sterile conditions on a Murashige and Skoog's modified medium. Non organogenous calluses were obtained with addition of BA or kinetin (10^-5M to 10^-6M) as the cytokinin and 2,4-d or NAA (10^-5M to 10^-6M) as the auxin. These calluses permitted the establishment of a cell suspension culture with BA (10-6M) and 2,4-d (10^-6M). Zeatin (10^-6M) with IAA (10^-6M) gave rise to organogenous calluses. These organogenous callus cultures developed multiple shoots which either proliferated if they were cultivated on a medium containing zeatin with IAA or IBA or were able to regenerate into whole plants when zeatin was used as the only hormone. The different plant material produced solamargine, the main steroidal glycoalkaloid present in the unripe fruits. The best production was obtained with the fruits of regenerated plants from organogenous callus cultures after reintroduction of these plants in their brasilian biotope. The solamargine content of the two types of plant materials was about 0.06% and 2.5% (dry weight) respectively for the callus cultures and the fruits from in vitro plants. The fruits were harvested a year after the beginning of the plantlet regeneration step.Abbreviations HPTLC high performance thin layer chromatography - HPLC high performance liquid chromatography - 2,4-d 2,4-dichlorophenoxyacetic acid - BA benzylaminopurine - IAA 3-indolebutyric acid - NAA -naphthaleneacetic acid - IBA 3-indolebutyric acid - IPA isopentenyladenine     

Ecological and genetic differentiation of Barbus callensis populations in Tunisia

Enzyme electrophoresis on horizontal starch gel was carried out on 356 barbel individuals. The sampling comprised 278 individuals of the species Barbus callensis from 10 rivers in Tunisia. The other individuals belonged to reference species (outgroups) from France and Morocco. An ecological study was also carried out on Tunisian rivers. The results show a clear differentiation of the two samples from northwestern Tunisia, which was only partly correlated with ecological characteristics of the rivers they inhabit. There is no genetic cline, but rather a discontinuity between populations in the northwestern-most watershed and all the other Tunisian populations. This differentiation probably has a paleohistoric origin not only related to adaptation to ecological conditions but also to difficulties in colonizing the watersheds. The results do not indicate clearly a colonization direction for the genus Barbus in North Africa. Analysis of the Algerian populations would appear to be indispensable. Lastly, in contrast with the usual taxonomy, Morocco and Tunisia are populated by two closely related species, but B. callensis should remain the name of the Tunisian species, which was the first to be described in the small El Kebir basin, a river that flows from Tunisia to Algeria.     

Rearrangements in the staphylococcal β-lactamase-encoding plasmid, plP1066, including a DNA inversion that generates two alternative transposons

The plasmid plP1066, harboured by a methicillin-resistant Staphylococcus aureus strain isolated in France, carries genes specifying β-lactamase. This plasmid undergoes numerous rearrangements. One of these was an insertion, between the genes binR and sin encoding resolvases, of a 16 kb element which displayed the characteristic features of a transposon. This putative transposon, named Tn 5404 , carried genes encoding proteins involved in its transposition, as well as a resolution system, which were indistinguishable from those of the S. aureus transposon Tn 552 . These were: p480 encoding a probable transposase, p271 encoding a putative ATP-binding protein, binL encoding a resolvase, and a resolution site, resL . In addition, Tn 5404 carried aminoglycoside-resistance genes ( aphA, str ) and the insertion sequence IS 1181 . Tn 5404 contained at its termini 116 bp imperfect inverted repeats, similar to those of Tn 552 , and was flanked by 6 bp direct repeats. Insertion of Tn 5404 close to resR and to the structural and regulatory β-lactamase genes ( blaZ, blal, blaR1 ) of plP1066, generated a 3.5 kb invertible segment flanked by inversely repeated resolution sites ( resR, resL ). This invertible segment, which carried p480 , p271 and binL , generated Tn 552 or Tn 5404 , depending on its orientation. Thus, these two transposons share their transposition and resolution systems.     

Tolerance to osmotic shocks in rat kidney cortex and medulla

Kidney medulla cells of mammals have to cope with large changes in environmental osmolarity, a challenge most other mammalian cells never have to experience. In these last cells, application of osmotic shocks induces dramatic modifications in chromatin organization. The present paper reports on the changes of medulla cell chromatin in situ, in rat kidney slices submitted to osmotic challenges and in vitro, on preparations of extracted chromatin submitted to changes in environmental ion concentrations. Our results show that the chromatin of kidney medulla cells: (1) does not behave differently from the other mammalian chromatins when submitted in situ or in vitro to osmotic challenges; (2) presents in vitro physico-chemical characteristics similar to those of the other mammalian chromatins; and (3) is protected in vitro, as the other mammalian chromatins, from the disrupting effects of increases in inorganic ion concentrations by different compensatory organic solutes. The ability of kidney medulla cells to adapt to large increases in osmolarity could thus be related to a rapid control of the level of such compounds rather than to some rather specific, intrinsic molecular adaptations of macromolecules.     

Evolution of PS IIα and PS IIβ centers during the greening of Euglena gracilis Z: Correlations with changes in lipid content

The building up of the two types of reaction centers, PS II and PS II, was investigated during the greening of Euglena gracilis Z cells in resting medium. The maximal values in the proportion of PS II centers (55%) and in the oxygen evolved per chlorophyll were reached at the outbreak of greening, when accumulation of galactolipids (MGDG and DGDG) rich in unsaturated fatty acids occurred, and when anionic lipids (SQDG and PG) emerged. As the greening progressed, the chlorophyll accumulation corresponded to a secondary enrichment in PS II centers, which built up more rapidly than PS II centers; correlatively, a general saturation of the fatty acids constitutive of all lipid classes took place.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DGDG digalactosyldiacylglycerol - FAME Tatty acid methyl esters - HEPES acide (N-[2-hydroxyethyl]piperazine-N-[2-ethane sulfonic] - MGDG monogalactosyldiacylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - PQ plastoquinone - PS I Photosystem I - PS II Photosystem II - Q_A primary quinone electron acceptor of PS II - Q_B secondary quinone electron acceptor of PS II - SQDG sulfoquinovosyldiacylglycerol