Modèle géométrique de l'œuf de Ver à soie

Résumé L'uf de ver à soie qui se prête à de nombreuses recherches génétiques et physiologiques a été assimilé à un volume géométrique simple afin qu'on puisse calculer aisément l'aire de sa surface totale et son volume. On a d'abord cherché à justifier le modèle géométrique proposé grâce à une étude expérimentale et statistique. On a ensuite établi les formules mathématiques utiles. Enfin on a discuté de l'approximation donnée par ces formules et de leur signification biologique.

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Summary The egg of the silkworm which permits a lot of genetical and physiological researches has been assimilated to a simple geometric volume, so that the area of its total surface and its volume might be easily calculated. First we have tried to justify the geometrical model which is proposed by means of an experimental and statistical study. We have then demonstrated the useful mathematical formulas. Finally we have discussed the approximation given by these formulas and their biological significance.

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Zusammenfassung Das Seidenraupenei, das viele genetische und physiologische Forschungen ermöglicht, hat man mit einem einfachen geometrischen Modell verglichen, um seine ganze Fläche und sein Volumen leicht rechnen zu können. Zuerst hat man versucht, das vorgeschlagene geometrische Modell dank einer experimentalen und statistischen Arbeit zu rechtfertigen. Dann sind die nötigen mathematischen Formeln festgesetzt worden. Zuletzt hat man die durch diese Formeln gegebenen Annäherungen und ihre biologischen Bedeutung erörtert.

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Avec la collaboration technique de Mme.Donas     

Action de l'hydrate de chloral sur les mitoses de segmentation de l'œuf de pleurodèle

In eggs of Pleurodeles treated with chloralhydrate (0.1 M) spindle and astral fibers are progressively destroyed after 4 hours, leading to apolar nuclei, apolar mitoses and “monopolar” mitoses, the so-called star metaphases. After 1 hour the spindle is shortened, but not narrowed and separated from the poles and asters. Its microtubules, grown before metaphase, are first inhibited at their ends near the centrospheres. After 4 hours, defibrillated achromatic material, stained by methyl blue, surrounds a clearer zone originating from the nucleoplasm, in which chromosomes are embedded. At the EM level the treatment induces the formation of unusual tubular bodies connected with the centrospheres and of similar bodies related to kinetochores and chromosomes. These bodies are formed of tubular residues, parallel or in concentric systems, the latter embedded in a matrix containing tightly packed filaments of 170 Å diameter. The star metaphase is characterized by homogeneous centrospheres formed only of filaments and completely independent from kinetochores and chromosomes. Chromosomes are radially distributed around a central common mass, which keeps the chromosomes together; it is formed of a finely fibrous matrix containing disordered microtubular residues; kinetochores are embedded in the common mass. Fuzziness and alteration of chromosomes proceed as a direct action of the chloralhydrate. The star metaphase is not a real “monopolar” mitosis.     

Modifications pigmentaires et ultrastructurales chez la diatomée Detonula sp. cultivée en lumière rouge

Résumé La diatomée Detonula sp. lorsqu'elle est cultivée en lumière rouge (650 nm), est enrichie en holochrome chlorophyllien Ca 705 (pour la nomenclature des holochromes voir French et al., 1971). La composition pigmentaire est alors modifiée par rapport à celle de l'algue cultivée en lumière blanche. Si les mêmes composants, Chlorophylle a, Chlorophylle c, Carotène, Diadinoxanthine, Diatoxanthine, Fucoxanthine, Violaxanthine, sont tous présents, on note un abaissement du taux de Chlorophylle c (le rapport Chl c/Chl a passe de 30% à 5%) et un abaissement du taux de Fucoxanthine (le rapport Fucoxanthine/Chlorophylle a passe de 85% à 60%). Cette modification pigmentaire s'accompagne d'une modification ultrastructurale des plastes. Au lieu d'une vingtaine de thylakoïdes disposés par groupe de 4 au milieu d'un stroma abondant, on observe une disparition du stroma accompagnée d'une augmentation très importante du nombre de thylakoïdes, tous juxtaposés en un seul ensemble.La diminution importante du taux de Chlorophylle c et de la Fucoxanthine, pigments du photosystème II, liée à l'enrichissement en Chlorophylle a 705, indique une modification de l'équilibre entre les deux photosystèmes au profit du photosystème I. Cet enrichissement en photosystème I s'accompagne d'une modification ultrastructurale qui est rapprochée des modifications observées dans d'autres organismes lorsque l'équilibre des deux photosystèmes est perturbé.

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Pigments and ultrastructure modifications in diatom Detonula sp. cultivated in red light

Summary Cultivation of the diatom Detonula sp. with red light, which causes an enrichment of the chlorophyll holochrome Ca 705 (for nomenclature of chlorophyll holochromes see French et al., 1971), also modifies the gross pigment composition of the cells. Relative to chlorophyll a, the cellular contents of chlorophyll c and fucoxanthin are considerably lower than in cells grown with white light; and this is accompanied by a change in plastid ultrastructure. The plastids of cells grown in white light contain about 20 thylakoids disposed in groups of 4, within an abundant stroma; those of cells grown in red light contain a much greater number of thylakoids (about 40), evenly distributed throughout the plastid.The diminution of chlorophyll c and fucoxanthin, pigments associated with photosystem II, coupled with the enrichment in chlorophyll a 705, points to a shift in the ratio between photosystems I and II in favor of the former. The accompanying ultrastructural modification of the plastid resembles that observed in other organisms as a result of changes in the relative amounts of the two photosystems.

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Cet article recouvre en partie le travail d'une thèse de Doctorat d'Etat ès Sciences Naturelles qui sera soutenue à la Faculté des Sciences de Paris. VI.     

Sur l'évolution de la fonction respiratoire chez les œufs d'Amphibiens

Sans résumé     

Préparation d'un tétramère dihéminique dérivé de l'hémoglobine

The preparation and partial characterization of an unusual hemoglobin derivative, containing only 2 hemes per 4 chains, are described. The compound has been isolated in small yield from a solution of methemoglobin having undergone a partial loss of heme through transfer to apomyoglobin.The reaction mixture consists intially of methemoglobin and apomyoglobin, 6 mg/ml of each, at pH 7. After about half the total heme has been transferred to apomyoglobin, the reaction products are separated by fractional precipitation with ammonium sulfate. At 62% saturation, large amounts of apohemoglobin precipitate, together with small but significant amounts of a hemoprotein having solubility characteristics different from those of methemoglobin.The hemoprotein has been purified successively by gel filtration, CM-Sephadex chromatography and electrophoresis until it satisfied reasonably good criteria of purity.Sedimentation coefficients and molecular weight determinations accord well in demonstrating that the hemoprotein is a tetramer. Simultaneous analysis of iron and amino acids reveals a two-fold excess of amino acids over iron as compared with normal hemoglobin. The visible spectrum resembles that of methemoglobin in the relevant ionization state; the absorbance in the ultraviolet region (280 mμ) is, however, about twice as great as for methemoglobin for equal Soret band absorbance. The hemoprotein binds an amount of heme equivalent to that already present.We have called this di-heme derivative of hemoglobin semi-hemoglobin.