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1.
The paper submits the results of studies on the kinetics of spermatogenous epithelium cell number after exposure to fast neutrons (60-300 cGy) and gamma-radiation (200-600 cGy). It was shown that a relative decrease in the quantity of spermatocytes is determined by an exponential dose-response curve with D0 of 35 and 120 cGy for neutrons and gamma-radiation respectively. For spermatides and spermatozoa a single D0 value of 20 and 55 cGy was obtained for neutrons and gamma-radiation respectively. As the radiation dose increases the recovery process in the epithelium is substantially decelerated. The equation T1/2 = T1/2(0)e0.0009D well describes the dependence of the half-recovery period T1/2 upon the equivalent dose. 相似文献
2.
Using acid-ethanol extraction, two proteins with Mr=8 and 12 kD were extracted from rat glioma tissue induced with ethylnitrosourea. These proteins were shown to complete for the receptor with [125I]EGF (epidermal growth factor) on A431 cells. The 8 kD protein exhibited a marked mitogenic effect by stimulating DNA synthesis in resting NIH 3T3 cells. Stepwise chromatography of the acid-ethanol extract on Biogels P-60 and P-10 resulted in preparative amounts of the protein and allowed for its partial characterization. It was found that the half-maximum stimulation of DNA synthesis in NIH 3T3 cells was achieved at growth factor protein concentration of 5 micrograms/ml. The preparation obtained possessed the EGF-competing activity of 10 ng-equiv. EGF per 1 microgram of protein and stimulated protein phosphorylation of the 170 kD protein in NRK cell membranes. The data obtained suggest that this factor may be related to the family of the so-called EGF-like growth factors. 相似文献
3.
Day–night cycle is the main zeitgeber (time giver) for biological circadian rhythms. Recently, it was suggested that natural diurnal geomagnetic variation may also be utilized by organisms for the synchronization of these rhythms. In this study, life-history traits in Daphnia magna were evaluated after short-term and multigenerational exposure to 16 h day/8 h night cycle, 32 h day/16 h night cycle, diurnal geomagnetic variation of 24 h, simulated magnetic variation of 48 h, and combinations of these conditions. With short-term exposure, the lighting mode substantially influenced the brood to brood period and the lifespan in daphnids. The brood to brood period, brood size, and body length of crustaceans similarly depended on the lighting mode during the multigenerational exposure. At the same time, an interaction of lighting mode and magnetic variations affected to a lesser extent brood to brood period, brood size, and newborn's body length. The influence of simulated diurnal variation on life-history traits in daphnids appeared distinctly as effects of synchronization between periods of lighting mode and magnetic variations during the multigenerational exposure. Newborn's body length significantly depended on the lighting regime when the periods of both studied zeitgebers were unsynchronized, or on the interaction of light regime with magnetic variations when the periods were synchronized. These results confirm the hypothesis that diurnal geomagnetic variation is an additional zeitgeber for biological circadian rhythms. Possible mechanisms for these observed effects are discussed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society 相似文献
4.
Nina I. Smirnova Galina V. Chekhovskaya Natalia I. Davidova Ludmila F. Livanova Galina A. Yeroshenko 《FEMS microbiology letters》1996,136(2):175-180
Abstract The presence of a temperate phage was demonstrated in a strain of Vibrio cholerae O139 isolated from a patient. Spontaneous variants with translucent colonies had lost this phage. The loss of the phage was associated with increased hydrophobicity, indicating the loss of the capsule. These clones were sensitive to serum bactericidal activity, showed decreased expression of such presumed virulence factors as proteases, motility and mannose-sensitive pili. Furthermore, excision of the phage made the strain dependent on purines for growth. 相似文献
5.
T. N. Osipova H. Triebel H. Bär I. A. Zalenskaya M. Hartmann 《Molecular biology reports》1985,10(3):153-158
Complexes of histone H1 from sea urchin sperm (H1S) and calf thymus (H1T) with superhelical DNA I and relaxed circular DNA II have been analyzed by analytical sedimentation. Similar to H1T, the highly basic and relatively arginine-rich histone H1S preferentially interacts with DNA I compared to DNA II under competition conditions. However, H1S induces a stronger aggregation of bothforms of DNA than H1T. Below 0.05 M NaCl, the soluble complexes formed by both histones have similar properties, but aggregation proceeds in a different manner: H1S induces a stronger aggregation of DNA II as compared to DNA I, whereas H1T fails to aggregate DNA I.The results are explained on the basis of differences in amino acid sequence and structure of the two histones and related to the special chromatin condensing ability of histone H1S. 相似文献
6.
Total and polysome-bound ribosomes and the uptake and incorporation of3H-uridine and14C-leucine were examined in dividing microspores and in pollen grains isolated from anthers of 6 different developmental stages. Direct evidence was obtained that the formation of cytoplasm of the vegetative cell following microspore division is related to a rapid activation of RNA and protein synthesis and of ribosomes in differentiating pollen. Total ribosomes associated with gametophytic programme rose about 10times and the process of differentiation was accompanied by a rapid increase in uptake capacity of pollen grains for both uridine and leucine. Pollen development after cytoplasm synthesis and starch deposition continued by pollen maturation, which was characterized by a decline in RNA synthesis, dissociation of polysomes and by a further rise of transport activity of pollen grain wall for exogenous substrates, indicating probable pollen adaptation for utilization of metabolites from the degenerating tapetal cytoplasm. 相似文献
7.
Ludmila Šilhánková 《Folia microbiologica》1966,11(1):29-38
Visible region of an absorption spectrum was followed in cells of original strains and of rough mutants ofSaccharomyces cerevisiae andS. cerevisiae var.ellipsoideus. It was found that there are no substantial differences in relative content of cytochromesb andc in aerobically grown rough and smooth yeast forms, in spite of the fact that both forms differ substantially in the metabolic
oxygen quotient. If the cytochromes present were not reduced in washed cells by dithionite or by substrate addition, the rough
forms exhibited a lower cytochrome b:c ratio than the smooth forms. Under anaerobic conditions of cultivation, the rough forms retained a typical aerobic spectrum,
lacking, however, the cytochromea and a3 band; the ratio of cytochromesb andc was changed in favour of cytochromeb (from the original 1.7: 1 up to 3.4: 1). The inability of the rough mutants to produce anaerobic cytochrome spectrum represented
by cytochrome b1 was connected with their inability to reproduce under anaerobic conditions. 相似文献
8.
The method of velocity sedimentation have been used to investigate ionic-strength-induced compaction of sea urchin sperm chromatin characterized by extremely long linker DNA (100 b.p.). The dependence of sedimentation coefficients of oligonucleosomes on the number of nucleosomes in the chain have been studied in the range of ionic strength from 0.005 to 0.085. Analysis of these data indicates that such structural parameters of sea urchin sperm chromatin fibre as the diameter of the chain and the length of the chain per nucleosome are quite similar to those of chromatin with shorter linker DNA, but the DNA packing ratio is higher. The structure of sea urchin sperm oligonucleosomes agrees well with the model of three-dimensional zig-zag-shaped chain with linker DNA forming a loop. The possible role of alpha-helical regions of the C-terminal domain of sea urchin sperm histone H1 in the long linker DNA folding is discussed. 相似文献
9.
Anthers of diploid genotypes of Solanum tuberosum capable of androgenesis were cultured on different media to examine the effect on induction of pollen embryogenesis of 2,4-d and lactose. Anthers cultured in callogenic medium with 2,4-d and sucrose produced pollen derived embryoids only exceptionally. When sucrose was replaced by lactose the frequency of embryogenesis was as high or higher than in embryogenic auxin-free medium. Substitution of lactose for sucrose in the embryogenic medium had no effect. Supplementing the embryogenic medium with 2,4-d strongly reduced the frequency of pollen embryoids in the presence of sucrose but not with lactose.Abbreviations 2,4-d
2,4-dichlorophenoxyacetic acid 相似文献
10.
Brenda S. Speer Ludmila Chistoserdova Mary E. Lidstrom 《FEMS microbiology letters》1994,121(3):349-355
Abstract A fragment of Methylobacter marinus A45 DNA has been cloned and sequenced, and an open reading frame has been identified that could code for a 46-kDa polypeptide. Comparison of the deduced amino acid sequence of the polypeptide against the protein data bank has revealed strong similarity with a number of alcohol dehydrogenases, with highest similarity towards class III alcohol dehydrogenases, which recently have been shown to be identical to glutathione-dependent formaldehyde dehydrogenases. We were unable to measure appreciable levels of NAD(P)-dependent formaldehyde dehydrogenases or alcohol dehydrogenase activities using aldehydes or primary or secondary alcohols in cell-free extracts from batch cultures of M. marinus A45. However, formaldehyde dehydrogenases activity was detected on zymograms. Our data suggest that, although NAD(P)-linked formaldehyde dehydrogenase or alcohol dehydrogenase activities are undetectable in cell-free extracts of most methylotrophs employing the ribulose monophosphate pathway for formaldehyde assimilation and dissimilation, the gene encoding formaldehyde dehydrogenase is present in M. marinus A45 and may be present in more of these organisms as well. 相似文献