Conductivity and photoconductivity of NaDNA in the solid state

The d. c. conductivity of five samples of NaDNA in dry state was investigated. All specimens show similar behavior, with specific resistivity at 40°C of the order of 10¹³–10¹⁴ ohm-cm and an energy gap of E_c = 2.04–2.25 eV. Based on the Eley's model for conductivity mechanism, the possibility of conservation of an ordered structure in the dry state (temperature range 20–80°C) is discussed. This is ascribed to the interaction of electron systems of individual bases. From the activation energy values it may be estimated that 17–19 π-electrons take part in the interaction. Photoconductivity measurements indicated activation energies E_f of 0.88–0.96 eV in the visible region.     

UV sensitivity of germinating culture ofBacillus cereus

The spores ofBacillus cereus can be germinated in reasonable synchrony in rich media. The survival of germinating cells after UV irradiation is strongly affected by repair. When plating on mineral agar a linear decrease of survival is obtained between 20–60 min of germination, whereas the survival on nutrient agar shows only minor fluctuations. The difference in survival on these two media which reached 1–2 orders of magnitude is due mostly to the shape of the shoulder on the survival curve. Survival on mineral agar may be increased by postincubation in complex media or by preincubation in mineral media. It was concluded that repression and derepression of biosynthetic pathways was responsible for the different efficiency of repair.     

Mycoplasma-like bodies in plants infected with potato witches' broom disease and the response of plants to tetracycline treatment

The virus origin of a Czechoslovak isolate of potato witches' broom disease is discounted: electron micrographs of ultrathin section of phloem tissues from plants infected with potato witches' broom disease demonstratedMycoplasma-like bodies, spherical or elongated showing binary fission and fragmentation. The minute corpuscles have a diameter of about 50–60 nm, the largest bodies of 1000 nm. The width of elongated filamentous structures is about 200 nm, most oval bodies have a diameter of 250 nm. A weak tetracycline treatment of diseased plants causes a delay of symptom development; a strong dose of tetracycline (applied by means of the wick method into the stem) inhibits symptom appearance completely. Tetracycline produces a phytotoxic effect inhibiting the growth of tomato plants and causing (at higher concentrations) necrosis and death of these plants. There is a note in the paper dealing with the term “mycoplasma”. The word mycoplasma in the sense ofEriksson (1897) or ofMereschkowsky (1910) does not correspond to the genus nameMycoplasma Nowak (1929).     

Influence of exogenous DNA on Ypenyl-treated chromosomes ofVicia faba L.

This paper is a study of the effect of exogenous DNA of different genetic origins on the repair of meristematic cells of primary roots ofVicia faba, damaged by 24 hour treatment with 0·01mm solution of Ypenyl. Both kinds of DNA,i.e. isologous and heterologous, stimulated cell proliferation which was decreased by the action of the radiomimetic and influenced both dynamics of production of chromosome aberrations and the interchromosomal distribution of induced damage. While heterologous DNA increased the frequency of aberrations after all recovery periods studied, isologous DNA significantly decreased the number of chromosomal aberrations. Heterologous DNA increased at the same time the relative number of breaks in the group of small chromosomes, while by the action of isologous DNA the number of aberrations related to this group of chromosomes was relatively decreased.     

Study of the effect of volatile substances from cereal roots

We traced the liberation and biological effect of volatile substances released from the roots of cereals,i. e. barley, wheat, rye and oats, on seedlings of the same and other plant species. Experiments were carried out in a closed glass apparatus with a static or circulating atmosphere in which the CO₂ and O₂ were permanently absorbed and supplemented, respectively. In some experiments the air was bubbled through water or through solutions of boric acid, barium hydroxide and potassium permanganate. The roots of all four cereals tested released volatile substances with a biological activity which appeared to be non-specific with respect to plant species. The effect of volatile substances was partially decreased by bubbling through water, barium hydroxide and boric acid and was completely removed after passing through the solution of potassium permanganate. Volatile substances liberated from roots of barley inhibited elongation of roots and coleoptile, decreased SH-group content and caused excessive formation of root hairs as well as inhibition of both dry matter production and respiration of roots of rye seedlings. Ethylene was found in the atmosphere of experimental vessels.     

A strain of Holmes' ribgrass virus occurring in Yugoslavia

A virus having 300 nm long rod-shaped particles was isolated fromPlantago media L. in Yugoslavia. The virus was transmitted to 15 species of host plants the symptoms of which are described in detail. The symptoms corresponded to those that appeared after infection by the original Holmes' ribgrass virus (HRV). The investigated virus was compared both with the common strain of tobacco mosaic and the original Holmes' ribgrass viruses by means of serological tests. The agar double-diffusion tests showed that it is closely related to HRV and remotely related to the common strain of TMV. On the basis of these results we concluded that this virus represented a strain of the HRV. The investigations of the cell inclusions showed that our virus produced rounded plates instead of hexagonal prisms. Electron micrographs of ultrathin sectioned material demonstrated that these plates were formed by virus particles lying perpendicularly to the layers of the plates. The presence of plates also points to the fact that the investigated virus belongs to the HRV.     

Occurrence of lysosomes and the differentiation of rat liver cells

Summary The occurrence of lysosomes has been investigated electron microscopically and cytochemically in cells of rat liver in the course of ontogenesis.It has been found that primary lysosomes occur during the whole period under investigation and that they originate from the Golgi complex. Some of them assume the appearance of multivesicular bodies. Acid phosphatase activity is lower at the prenatal stage than after the birth. The occurrence of secondary lysosomes proceeds in two stages. Secondary lysosomes appear in a high number at the beginning of differentiation of the liver diverticulum (10–12 day of embryonic life). On the subsequent days they are, with few exceptions, no more present. At the end of the embryonic period (starting with the 20th day) and especially after the birth, they progressively grow in number and move from the region of central cytoplasm peripherally towards the bile capillary.Differences in occurrence of secondary lysosomes are in connexion with reconstruction of the liver primordium at the beginning of liver development and with the change in metabolism of the liver cell after the birth.     

A propos des ≪chloride cells≫ dans l'épithélium des lamelles branchiales du poisson rouge

Résumé L'ultrastructure des lamelles branchiales et spécialement celle des chloride cells du poisson rouge (Carassius aureus) a été étudiée. Nous avons constaté que du matériel amorphe floconneux, faiblement adiélectronique était attaché aux endroits des creux apicaux. Afin de préciser la nature de ce matériel, nous avons étudié ces structures au microscope électronique avec les techniques suivantes: acide periodique méthènamine d'argent, colorations au fer colloïdal et au bleu d'alcian. Après la réaction à l'acide periodique méthènamine d'argent, de fines précipitations aux endroits des creux apicaux, correspondant au matériel floconneux visible après la fixation au glutaraldéhyde tétroxyde d'osmium, étaient visibles. La coloration au bleu d'alcian révélait des particules fortement colorées formant un film plus ou moins continu à la surface libre des lamelles, sauf aux endroits oò les chloride cells sont en contact avec la surface. Là et notamment dans les 2reux apicaux, du matériel légèrement granuleux, de faible densité, faisait une couche assez épaisse attachée à la membrane cellulaire. Tenant compte des résultats d'autres auteurs et de nos propres observations, nous considérons que la plus grande partie du matériel se trouvant à la surface des chloride cells, et particulièrement dans les creux apicaux, est de type glycoprotéique.

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The ultrastructure of the chloride cells in the gill epithelium of the goldfish

Summary The ultrastructure of the secondary lamellae of the gills and especially that of the chloride cells of Carassius aureus was studied. We found an amorphous, flakey, slightly adielectronic material in the areas of the apical pits. In order to determine the nature of this material, we studied these structures electronmicroscopically applying the periodic acid silver methenamine, colloidal iron and alcian blue methods. The periodic acid silver methenamine reaction, resulted in finely dispersed precipitations which were deposited in the areas of the apical pits and which correspond to the flakey material seen in the ordinary electron micrographs. The alcian blue method reveales strongly stained particles which form a more or less continuous film on the free surface of the lamellae, interrupted only at the level of the chloride cells. In these areas, notably within the apical pits, a rather thick layer of finely granular low-density material is attached to the plasma membrane. In taking into account other studies performed on this subject, as well as our own observations, we consider the material found on the surface of the chloride cells and particularly within their apical pits to be predominantly of glycoproteinous nature.

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Dédié à Monsieur le Professeur Dr Ernst Horstmann, Hambourg, à l'occasion de son soixantième anniversaire.