Showing papers by "Centre national de la recherche scientifique published in 1969"

Haploid Plants from Pollen Grains

Abstract: A method is presented by which hundreds of haploid plants of various species of Nicotiana can be raised from pollen grains. Stamens should be excised when pollen grains have been individualized, but are still uninucleate and free of starch. When grown in vitro on a relatively simple medium, some pollen grains proliferate into embryo-like, structures which develop in stages similar to those of zygotic embryos. The plantlets mature and flower profusely, but do not set seed.

Fields, observables and gauge transformations I

Abstract: Starting from an algebra of fields $$\mathfrak{F}$$ and a compact gauge group of the first kind ℊ, the observable algebra $$\mathfrak{A}$$ is defined as the gauge invariant part of $$\mathfrak{F}$$ . A gauge group of the first kind is shown to be automatically compact if the scattering states are complete and the mass and spin multiplets have finite multiplicity. Under reasonable assumptions about the structure of $$\mathfrak{F}$$ it is shown that the inequivalent irreducible representations of $$\mathfrak{A}$$ (“sectors”) which occur are in one-to-one correspondence with the inequivalent irreducible representations of ℊ and that all of them are “strongly locally equivalent”. An irreducible representation of $$\mathfrak{A}$$ satisfies the duality property only if the sector corresponds to a 1-dimensional representation of ℊ. If ℊ is Abelian the sectors are connected to each other by localized automorphisms.

Radiative Recombination in Highly Excited CdS

Abstract: The processes involved in the laser effect in CdS excited by electron bombardment have been studied with the aid of an experimental technique allowing the spectral dependence of the optical gain to be obtained. It is shown that at least three different processes can lead to a laser effect in CdS. The first, which corresponds to a low gain, is due to the annihilation of a free exciton with the emission of a photon and an LO phonon. The second, yielding a medium gain, is due to an exciton-exciton interaction; and the third, which results in a high gain, involves an exciton-electron interaction. These last two processes have been studied theoretically, and the results are compared with the experimental data.

Interactions of Proteins and Lipids: Structure and Polymorphism of Protein–Lipid–Water Phases

Abstract: The phases present in a variety of protein–lipid–water systems have been identified, and their structure established by X-ray diffraction. A spectrophotometric and circular dichroism analysis has been carried out on phases of known structure, and correlations between optical properties and structure are discussed.

Immunoglobulin peptide with complement fixing activity.

Abstract: INDIVIDUAL immunoglobulin molecules often possess several biological activities in addition to reactivity with appropriate antigen. Such activities include complement fixation, skin sensitization, attachment to macrophages and the tissue fixation required for placental passage1,2. Some members of this protein group lack one or more of these capacities: human IgG γ4 myeloma molecules and human IgD are unable to fix complement, for example3,4. Hill et al.5 suggested, on the basis of their observation of repeating amino-acid sequences in immunoglobulins, that these molecules might have arisen by a series of gene duplications, and Edelman et a1.6 have recently proposed that certain repeating regions of immunoglobulin polypeptide chains might have been selected for participation in biological effector functions such as complement fixation (domain hypothesis). According to this concept it should be possible to associate a complement fixation function with a specific submolecular domain in certain immunoglobulin molecules.

Quasielastic Rayleigh Scattering in Nematic Liquid Crystals

Abstract: Using a light-beat laser spectrometer, we observe the relaxation of the thermally excited fluctuations of anisotropy in the nematic phase of $p\ensuremath{-}\mathrm{azoxyanisole}$. We identify the two low-frequency purely dissipative modes recently predicted. A first study of the angular dependence of the width of these modes allows a determination of three among the six viscosity coefficients introduced by Leslie.

Primitive Low-energy Particle Irradiation of Meteoritic Crystals

Abstract: Observations of large track densities (≃109 cm−2) produced by iron-group nuclei at the surface of certain crystals and chondrules in the dark parts of gas-rich meteorites. An early solar origin of these particles is inferred.

DETECTINON OF THE STATIC MAGNETIC FIELD PRODUCED BY THE ORIENTED NUCLEI OF OPTICALLY PUMPED $sup 3$He GAS.

Abstract: A new type of very sensitive low-field magnetometer is used to detect the static magnetic field produced by optically pumped $^{3}\mathrm{He}$ nuclei in a vapor. Various signals (pumping and relaxation transients) are obtained in this way. This magnetostatic detection allows a direct study of $^{3}\mathrm{He}$ nuclear polarization without perturbing the spins.

Genetic and regulatory aspects of methionine biosynthesis in Saccharomyces cerevisiae.

Abstract: Methionine biosynthesis and regulation of four enzymatic steps involved in this pathway were studied in Saccharomyces cerevisiae , in relation to genes concerned with resistance to ethionine ( eth 1 and eth 2 ). Data presented in this paper and others favor a scheme which excludes cystathionine as an obligatory intermediate. Kinetic data are presented for homocysteine synthetase [K m ( O -acetyl-l-homoserine) = 7 × 10 −3 m; K i (l-methionine) = 1.9 × 10 −3 m]. Enzymes catalyzing steps 3, 4, 5, and 9 were repressible by methionine. Enzyme 4 (homoserine- O -transacetylase) and enzyme 9 (homocysteine synthetase) were simultaneously derepressed in strains carrying the mutant allele eth 2 r . Studies on diploid strains confirmed the dominance of the eth 2 s allele over eth 2 r . Regulation of enzyme 3 (homoserine dehydrogenase) and enzyme 5 (adenosine triphosphate sulfurylase) is not modified by the allele eth 2 r . The other gene eth 1 did not appear to participate in regulation of these four steps. Gene enzyme relationship was determined for three of the four steps studied (steps 3, 4, and 9). The structural genes concerned with the steps which are under the control of eth 2 ( met 8 : enzyme 9 and met a : enzyme 4) segregate independently, and are unlinked to eth 2 . These results are compatible with the idea that the gene eth 2 is responsible for the synthesis of a pleiotropic methionine repressor and suggest the existence of at least two different methionine repressors in S. cerevisiae . Implications of these findings in general regulatory mechanisms have been discussed. Images

Regulation of the biosynthesis of amino acids of the aspartate family in Coliform bacteria and Pseudomonads.

Abstract: The control of aspartokinase and homoserine dehydrogenase activities was compared in aerobic and fermentative pseudomonads (genera Pseudomonas and Aeromonas), and in coliform bacteria representative of the principal genera of the Enterobacteriaceae. Isofunctional aspartokinases subject to independent end-product control occur in the Enterobacteriaceae and in Aeromonas. In Pseudomonas, there appears to be a single aspartokinase, subject to concerted feedback inhibition by lysine and threonine. Within this genus, the sensitivity of aspartokinase to the single allosteric inhibitors varies considerably: the aspartokinase of the acidovorans group is little affected by the single inhibitors, whereas that of the fluorescent group is severely inhibited by either amino acid at high concentration. In all bacteria examined, homoserine dehydrogenase activity is inhibited by threonine; inhibition is more severe in aerobic pseudomonads than in the other groups. In most of the bacteria examined, either nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate can serve as a cofactor for this enzyme, though the relative activity with the two pyridine nucleotides varies widely. Aerobic pseudomonads of the acidovorans group contain a homoserine dehydrogenase that is absolutely specific for NAD. The taxonomic implications of these findings are discussed.

Allergenic Component of a Liverwort: A Sesquiterpene Lactone

Abstract: Frullania spp. (Hepaticae, Jungermanniales) are agents of allergies. Extraction and fractionation of Frullania tamarisci has given, as the only allergenic component isolated, a levorotatory crystalline sutbstance, the structure of which is demonstrated. It is a sesquiterpene lactone. The racemic (±) form is isolated from a mixed sample of Frullania tamarisci and Frullania dilatata ; the dextrorotatory form, from Frullania dilatata . The observed allergenic properties are shared by some other-sesquiterpene lactones.

Spectres de vibration de quelques halogénures de pyridinium

Abstract: Les spectres infrarouges et RAMAN des halogenures de pyridinium C6 H5 NH+ Cl- , C5 HS ND+Cl- , C5 D5 NH+Cl- , C5 D5 ND+Cl- , C5 H6 NH+ Br- , C5 H5 ND+ Br- et C5 H5 NH+ 1- a l’etat solide ont ete etudies dans la region de 3 300 a 300 cm-1 . Nous proposons une attribution de vingt-huit vibrations fondamentales pour chacune des quatre especes isotopiques de l’ion pyridinium ; l’influence de la protonation et de la liaison hydrogene NH+ . . . X- sur les frequences pyridiniques est discutee.

Kinetics of the biosynthesis of phospholipids in neurons and glial cells isolated from rat brain cortex

Abstract: —32P incorporation into different rat-brain cortex neuronal and glial phospholipids was investigated. The half life of each compound was measured. Neuronal phospholipids had a faster turnover than glial phospholipids. Phosphatidyl-inositol and choline plasmalogen had the fastest, diphosphatidylglycerol the lowest turnover in both cell-types. Phosphatidylcholine, ethanolamine phospholipids and serine phospholipids had turnover intermediate with that of the previously described compounds. Turnover of neuronal sphingomyelin was similar to that of phosphatidylcholine, whereas in glial cells it was much lower.

Malignancy of somatic cell hybrids.

Abstract: HARRIS et al.1 have observed the suppression of the malignancy of three types of malignant cell as a result of their fusion with cells of line A9, which they considered non-malignant. Here we supplement their data with information neglected by or unavailable to them. As will be seen, this information supplies answers to at least some of the questions raised by Harris et al.1.

Analyse électrophysiologique du plateau des réponses myocardiques, mise en évidence d'un courant lent entrant en absence d'ions bivalents

Abstract: In isolated perfused rat heart, electrophysiological analysis of myocard membrane properties in the absence of divalent ions during the plateau of the action potential, shows that:

The Aspartokinases and Homoserine Dehydrogenases of Escherichia coli

Abstract: Publisher Summary This chapter discusses the aspartokinases and homoserine dehydrogenases of Escherichia coli . The repression of the synthesis of an early enzyme of the biosynthetic pathway—such as aspartokinase—or its efficient feedback inhibition by any one of the essential metabolites should create insuperable difficulties for the bacterial cell, because it would limit the supply of the synthesis of the common intermediates necessary for the synthesis of the other essential metabolites of the pathway. When E. coli K12 is grown under one or the other repressive conditions, only one type of aspartokinase is found, which can then be totally inhibited by its specific feedback inhibitor. The synthesis of homoserine dehydrogenase, as in the case of the threonine-sensitive aspartokinase, is repressed when threonine and isoleucine are present in excess and are derepressed under the limitation of either of the two amino acids.

Single presynaptic neurone mediates a two component postsynaptic inhibition.

Abstract: A TWO component postsynaptic inhibition recorded from a group of identifiable neurones of the pleural ganglia of Aplysia has been recently described. It is composed of a rapidly decaying, chloride dependent component, and a more slowly decaying, potassium dependent component1,2. An ionophoretic injection of acetylcholine (ACh) onto cells showing this two component inhibition produces a response which also has two components. As with the synaptic potential, the initial, more rapid phase is chloride dependent and the delayed, more slowly decaying phase is potassium dependent1. That ACh is the transmitter responsible for both phases of the synaptic inhibition was further indicated by the fact that the chloride dependent component of both the synaptic and ACh potentials was completely blocked by d-tubocurarine or strychnine1,2, whereas the potassium dependent component—unaffected by these drugs—was selectively suppressed by the addition of tetra-ethyl-ammonium chloride (TEA-Cl) to the external medium2. These data suggest that the two component inhibition is caused by a single transmitter (ACh) acting on two pharmacologically distinct receptors and triggering two different permeability changes in the postsynaptic cells.

Haemoglobin I Toulouse: β66 (E 10) Lys --> Glu: a New Abnormal Haemoglobin with a Mutation localized on the E 10 Porphyrin Surrounding Zone

Abstract: THE haemoglobin defined in the title was isolated in the Blood Bank of Toulouse. The propositus was 39 years old, born in the south of France of Caucasian parents. He was in good health and a blood donor until a mild anaemia was discovered after an acute attack of gout. Haematological data were as follows: RBC 3.3 × 106 mm3, reticulocytosis 1.4 per cent, MCV 120 microns3, MCD 8 microns, haemoglobin 15.7 g/100 ml. Electrophoresis had shown a fast moving abnormal haemoglobin, and we undertook its study.

Anomalous Dispersion of Birefringence of Sapphire and Magnesium Fluoride in the Vacuum Ultraviolet

Abstract: Previous measurements of the birefringence of sapphire and magnesium fluoride have been extended to their respective limits of transparency, revealing anomalous dispersion effects at short wavelengths, which are qualitatively discussed. Possible practical applications to Lyot filters and quarter-wave plates for Lyman-alpha are indicated.

Etude Cytologique, Systématique et Pathologique d'Ichtyobodo necator (Henneguy, 1883) Pinto, 1928 (Zooflagelle)

Abstract: SYNOPSIS. The free form of Ichtyobodo necator is typically quadrangular, with rounded corners, and flattened dorso-ventrally. Its dorsal surface is strongly convex and its ventral surface somewhat concave. A longitudinal groove traverses the posterior 2/3 of the ventral surface near its right margin. The part of the organism anterior to the groove is rather thick; that containing the depression thins out progressively toward the posterior end. Most of the organelles are in the major part of the cytoplasm to the left of the groove. Anteriorly this depression continues into a rather short canal. Two (4 in predivision stages) flagella originate near the anterior end of the canal, from which they run posteriorly. The cytostome is also near the anterior part of the canal. The cytostome, canal, and cell membrane are reinforced by microtubules. The chondriome, undoubtedly represented by a single very elongated mitochondrion, contains numerous dilated areas rich in deoxyribonucleic acid. The fixed form of the flagellate is highly modified. Its anterior part becomes attached to the host cell by forming a plate. A type of sucking organelle that contains the cytostome forms from the plate and penetrates the host cell. I. necator belongs in the family Bodonidae. RESUME La forme libre d'Ichtyobodo necator est quadrangulaire avec des angles arrondis, et presente un aplatissement dorsoventral. Sa surface dorsale est fortement convexe et sa surface ventrale legerement concave. Une gouttiere longitudinale traverse les 2/3 posterieurs de la face ventrale sur le bord droit. La region cellulaire anterieure a, la gouttiere est plus epaisse que celle qui contient la depression et s'amincit progressivement vers la partie terminale. La plupart des organites cellulaires occupent la partie gauche de la cellule. Dans la region anterieure la gouttiere se prolonge par un canal assez court. Deux (quatre dans les stades de predivision) flagelles partent de ce canal et se dirigent vers la region posterieure. Le cytostome est egalement localise pres de la region anterieure du canal. Le cytostome, le canal et la membrane cellulaire sont jouxtes de microtubules. Le chondriome, sans doute represente par une seule mitochondrie tres allongee, presente de nombreuses dilatations riches en acide desoxyribonucleique. La forme fixee du flagelle est tres modifiee. Sa partie anterieure adhere a la cellule hǒte par l'intermediaire d'un plateau. Une sorte de sucoir, qui contient le cytostome, se forme a partir de ce plateau et penetre dans la cellule hǒte. Ichtyobodo necator appartient a la famille des Bodonidae.