The allotetraploid invasive weedBromus hordeaceus L. (Poaceae): Genetic diversity, origin and molecular evolution

Bromus hordeaceus (sectionBromus, Poaceae), a predominantly self-fertilizing tetraploid (2n=28), is an annual weed native to the Mediterranean Basin, which now has a world-wide distribution. High morphological variation led to the recognition of four subspecies, three of which correlated with habitat-type. We examined genetic diversity at enzyme loci in 15 populations from the Mediterranean and the Atlantic region. Although sampled over a larger range of ecological and geographical conditions, the North-African populations appeared less genetically differentiated than populations from Brittany, suggesting higher levels of gene flow among the first ones (Nm=3.756 and 1.066 respectively). No genetic differentiation was encountered among the four subspecies. The populations were homozygous at homologous loci, suggesting high rates of selfing, but they frequently exhibited fixed intergenomic heterozygosity. The meiotic chromosome behaviour and disomic inheritance encountered are in accordance with the previously proposed allopolyploid origin of the species. The diploidsB. arvensis andB. scoparius have been previously implicated in the parentage ofB. hordeaceus on the basis of morphology and serology. We comparedB. hordeaceus with related diploid species belonging to the same section (sectionBromus) using different sources of data (flow cytometry, karyotypes, RAPD and DNA sequences). Molecular phylogeny based on internal transcribed spacer sequences of nuclear ribosomal genes provided the first clear scheme of relationships among monogenomic species of the section. A new hypothesis is proposed concerning the origin ofB. hordeaceus: We found that it diverged earlier than all other species of sectionBromus excluding the diploidB. caroli-henrici which is basal in this group. The 13 autapomorphies accumulated byB. hordeaceus, and the absence of intra-individual sequence heterogeneity are also consistent with the relatively ancient origin of the species within the section.     

Coordinated transcriptional regulation of the divinyl ether biosynthetic genes in tobacco by signal molecules related to defense

In tobacco, 9-divinyl ethers (DVEs) produced by the lipoxygenase NtLOX1 and DVE synthase NtDES1 are important for full resistance to pathogens. In this work, the regulation of NtLOX1 and NtDES1 expression by signal molecules was investigated in LOX1 promoter-reporter transgenic plants and by RT-qPCR. Methyl jasmonate, ACC and elicitor were shown to coordinately trigger the DVE pathway. Induction was strongly attenuated in the presence of salicylic acid, which seems to act as a negative regulator of the 9-DVE biosynthetic enzymes. Our data suggest that, in tobacco, DVE biosynthesis is cross-regulated by jasmonates, and by other hormonal and signal molecules such as ethylene and SA.     

Two multigene families for marsupial neurohypophysial hormones? Identification of oxytocin,mesotocin, lysipressin and arginine vasopressin in the North American opossum (Didelphis virginiana)

Oxytocin, mesotocin ([Ile⁸]-oxytocin), lysipressin ([Lys⁸]-vasopressin) and arginine vasopressin have been identified in the North American opossum ($\text{Didelphis virginiana}$) by amino acid composition and high pressure liquid chromatography. The same peptides with the exception of mesotocin have previously been found in two South American opossums ($\text{Didelphis marsupialis}$ and $\text{Philander opossum}$). Although a dual heterozygocity could also explain the simultaneous presence of oxytocin/mesotocin on one hand, lysipressin/arginine vasopressin on the other, it is assumed, from the results obtained with individual glands of Australian and South American marsupials, that distinct genes encode for the four peptides.     

Precursors of mesotocin and vasotocin in birds: Identification of VLDV- and MSEL-neurophysins in chicken,goose, and ostrich

Precursors of neurohypophysial hormones are small proteins processed into nonapeptide hormones and neurophysins during axonal transport to the neurohypophysis. In mammals, oxytocin is associated with VLDV-neurophysin and vasopressin with MSEL-neurophysin. In birds, mesotocin and vasotocin are found instead of mammalian oxytocin and vasopressin. From goose, chicken and ostrich posterior pituitary glands, two types of neurophysins related to mammalian VLDV-and MSEL-neurophysins, respectively, have been identified by their N-terminal sequences. It is assumed that, as in mammals, hormonal peptide and the first 9 residues of the corresponding neurophysin are encoded by a common exon and that mesotocin and vasotocin, evolutionary predecessors of oxytocin and vasopressin, are associated in the precursors with VLDV-neurophysin and MSEL-neurophysin, respectively.     

The behavioural effects of systemically administered kainic acid: A pharmacological analysis

Systemic injection of kainic acid (KA), a powerful neuroexcitant and structural analogue of glutamate, induced a complex behaviour in the rat characterized by early “wet-dog-shakes” (WDS and delayed convulsions. 1) The WDS syndrome was antagonized by serotonin blockers (mianserin and cyproheptadine) and by GABAmimetic agents, which decrease serotonergic transmission; in contrast, WDS were potentiated by compounds which enhance serotonin-mediated events (fluoxetine, fenfluramine, imipramine and tranylcypromine) as well as by blockade of GABA receptors (bicuculline). In addition, WDS were antagonized by haloperidol (which possesses some anti-serotonin properties) whereas KA potentiated haloperidol-induced catalepsy, an effect which was blocked by cyproheptadine. This suggests that KA induces WDS and potentiates catalepsy via an increase in serotoninergic function. 2) KA induced convulsions were antagonized by GABAmimetic agents, in agreement with their broad anticonvulsant spectrum; in contrast, mianserine and cyproheptadine did not affect or even potentiated seizures. Thus KA seizures respond differently to pharmacological treatment than do WDS, and may me related to the nwuro-excitatory action of KA.     

Enameloid in the teleost fish Lophius

Summary The ultrastructural and chemical differences between mature enameloid and dentine in the teleost fish Lophius were demonstrated using transmission (TEM) and scanning (SEM) electron microscopy, X-ray diffraction analysis, electron diffraction analysis and electron microprobe analysis. An enameloid cap (about 50 m thick) and a thin layer (1 m thick) of collar enameloid were revealed in the scanning (SEM) and transmission (TEM) electron microscopes. Collar enameloid, structurally different from dentine both in SEM and TEM, proved to be less mineralized than the cap as revealed by electron microprobe analysis. The enameloid cap was seen to differ from dentine by (i) its electron density in TEM; (ii) the structural arrangement perpendicular to the underlying dentine, observed in SEM and TEM and corroborated by electron diffraction data, which showed a preferred orientation of enameloid crystallites; (iii) its higher F content decreasing gradually from the apex of the tooth to the junction with dentine and falling suddenly below this junction; and (iv) its lower Mg content. Establishment of a classification of enameloids is proposed, similar to that for dentines, in which selachian enameloid would be a reference standard.

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Résumé La microscopie électronique à transmission, la microscopie électronique à balayage, la diffraction X, la diffraction électronique et l'analyse par microsonde ont prouvé l'existence d'un émailoïde, ultrastructuralement et chimiquement différent de la dentine, chez la baudroie. La microscopie électronique à balayage et la microscopie électronique à transmission ont mis en évidence un chapeau d'émailoïde, d'environ 50 m d'épaisseur, et une couche fine (1 m) d'émailoïde du collet. L'émailoïde du collet, dont l'ultrastructure différente de celle de la dentine a été mise en évidence en microscopie électronique à transmission et en microscopie électronique à balayage, apparaît, après analyse par microsonde, moins minéralisé que le chapeau. Le chapeau d'émailoïde diffère de la dentine par (i) sa densité aux électrons en microscopie électronique à transmission; (ii) sa structure perpendiculaire à celle de la dentine sous-jacente, visible en microscopie électronique à transmission et en microscopie électronique à balayage et confirmée par la diffraction électronique, qui montre une orientation préférentielle des cristaux; (iii) son contenu en fluor plus élevé, qui diminue progressivement de l'apex à la jonction avec la dentine et chute brutalement au-dessous de cette jonction; (iv) sa teneur plus basse en magnésium. Les auteurs proposent que soit établie une classification des émailoïdes analogue à celle des dentines et dans laquelle l'émailoïde de Sélaciens constituerait un standard de référence.

     

Kinetic analysis of effector modulation of butyrylcholinesterase-catalysed hydrolysis of acetanilides and homologous esters

The effects of tyramine, serotonin and benzalkonium on the esterase and aryl acylamidase activities of wild-type human butyrylcholinesterase and its peripheral anionic site mutant, D70G, were investigated. The kinetic study was carried out under steady-state conditions with neutral and positively charged aryl acylamides [o-nitrophenylacetanilide, o-nitrotrifluorophenylacetanilide and m-(acetamido) N,N,N-trimethylanilinium] and homologous esters (o-nitrophenyl acetate and acetylthiocholine). Tyramine was an activator of hydrolysis for neutral substrates and an inhibitor of hydrolysis for positively charged substrates. The affinity of D70G for tyramine was lower than that of the wild-type enzyme. Tyramine activation of hydrolysis for neutral substrates by D70G was linear. Tyramine was found to be a pure competitive inhibitor of hydrolysis for positively charged substrates with both wild-type butyrylcholinesterase and D70G. Serotonin inhibited both esterase and aryl acylamidase activities for both positively charged and neutral substrates. Inhibition of wild-type butyrylcholinesterase was hyperbolic (i.e. partial) with neutral substrates and linear with positively charged substrates. Inhibition of D70G was linear with all substrates. A comparison of the effects of tyramine and serotonin on D70G versus the wild-type enzyme indicated that: (a) the peripheral anionic site is involved in the nonlinear activation and inhibition of the wild-type enzyme; and (b) in the presence of charged substrates, the ligand does not bind to the peripheral anionic site, so that ligand effects are linear, reflecting their sole interaction with the active site binding locus. Benzalkonium acted as an activator at low concentrations with neutral substrates. High concentrations of benzalkonium caused parabolic inhibition of the activity with neutral substrates for both wild-type butyrylcholinesterase and D70G, suggesting multiple binding sites. Benzalkonium caused linear, noncompetitive inhibition of the positively charged aryl acetanilide m-(acetamido) N,N,N-trimethylanilinium for D70G, and an unusual mixed-type inhibition/activation (alpha > beta > 1) for wild-type butyrylcholinesterase with this substrate. No fundamental difference was observed between the effects of ligands on the butyrylcholinesterase-catalysed hydrolysis of esters and amides. Thus, butyrylcholinesterase uses the same machinery, i.e. the catalytic triad S198/H448/E325, for the hydrolysis of both types of substrate. The differences in response to ligand binding depend on whether the substrates are neutral or positively charged, i.e. the differences depend on the function of the peripheral site in wild-type butyrylcholinesterase, or the absence of its function in the D70G mutant. The complex inhibition/activation effects of effectors, depending on the integrity of the peripheral anionic site, reflect the allosteric 'cross-talk' between the peripheral anionic site and the catalytic centre.     

A new iron-oxidizing/O2-reducing supercomplex spanning both inner and outer membranes, isolated from the extreme acidophile Acidithiobacillus ferrooxidans

The iron respiratory chain of the acidophilic bacterium Acidithiobacillus ferrooxidans involves various metalloenzymes. Here we demonstrate that the oxygen reduction pathway from ferrous iron (named downhill pathway) is organized as a supercomplex constituted of proteins located in the outer and inner membranes as well as in the periplasm. For the first time, the outer membrane-bound cytochrome c Cyc2 was purified, and we showed that it is responsible for iron oxidation and determined that its redox potential is the highest measured to date for a cytochrome c. The organization of metalloproteins inside the supramolecular structure was specified by protein-protein interaction experiments. The isolated complex spanning the two membranes had iron oxidase as well as oxygen reductase activities, indicating functional electron transfer between the first iron electron acceptor, Cyc2, and the Cu(A) center of cytochrome c oxidase aa(3). This is the first characterization of a respirasome from an acidophilic bacterium. In Acidithiobacillus ferrooxidans,O(2) reduction from ferrous iron must be coupled to the energy-consuming reduction of NAD(+)(P) from ferrous iron (uphill pathway) required for CO(2) fixation and other anabolic processes. Besides the proteins involved in the O(2) reduction, there were additional proteins in the supercomplex, involved in uphill pathway (bc complex and cytochrome Cyc(42)), suggesting a possible physical link between these two pathways.