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91.
During early embryogenesis of the nematode Parascaris univalens (2n=2) the processes of chromatin diminution and segregation of the germ and somatic cell lineages take place simultaneously. In this study we analyzed the nucleolar cycle in early embryos, both in germinal and somatic blastomeres, by means of silver staining and antibodies against the nucleolar protein fibrillarin. We observed an identical nucleolar cycle in both types of blastomeres, hence, the chromatin diminution process has no effect on the nucleolar cycle of somatic blastomeres. We report the existence of outstanding differences between this cycle and those previously reported during early embryogenesis of other species. There is a true nucleolar cycle in early embryos that shows a peculiar nucleolar disorganization at prophase, and a preferential localization of prenucleolar bodies only on the euchromatic regions during nucleologenesis. Moreover, fibrillarin does not form a perichromosomal sheath in metaphase or anaphase holocentric chromosomes, probably owing to their special centromeric organization. The number and location of nucleolus organizer regions (NORs) in the chromosomal complement have been determined using silver impregnation, chromomycin A3/distamycin A staining, and fluorescent in situ hybridization using an rDNA probe. There are only two NORs, one per chromosome, and these are lost in blastomeres after chromatin diminution. Moreover, the constant presence of two nucleoli in somatic blastomeres suggests that NORs are not affected during the fragmentation of euchromatic regions when this process occurs. 相似文献
92.
Purified recombinant urate oxidase (urate oxygen oxidoreductase EC 1.7.3.3. re-Uox) has been studied by means of differential scanning calorimetry (DSC) in correlation with enzymatic activity measurements and size exclusion chromatography. Differential scanning calorimetry curves versus pH show two endothermal effects in the pH range 6-10. The first endotherm reveals a maximum stability between pH 7.25 and pH 9.5 corresponding to a temperature of transition T(m1) of 49.0 degrees C and an enthalpy of transition of 326 kJ mol(-1). This value dramatically decreases below pH 7.25. The behavior of the second endotherm is more complex but the temperature of transition T(m2) is constant between pH 9 and 7.25 and a maximum for the corresponding enthalpy is obtained near pH 8 with DeltaH(2)=272 kJ mol(-1). An optimal pH of 8.0 for the stability of the enzymatic activity at elevated temperature was also found which was in good agreement with calorimetric results. Reversibility of the first endotherm is obtained from 20 to 51.5 degrees C. The calorimetric result is correlated to enzymatic activity, purity by size exclusion chromatography (SEC) and protein concentration measurements. In contrast, for the second endotherm, after heating up to 68.9 degrees C, no reversibility was found. Interaction with structural analogues of urate has been studied by DSC. 8-Azahyooxanthine has only a small effect and caffeine has no effect at all. With 8-azaxanthine, a rapid increase of the T(m1) function of the concentration is obtained. At high concentration T(m1) reached the T(m2) value which remained unaffected. 相似文献
93.
Fernández José A. Clavero Vicente Villalobos José A. Niell F. Xavier 《Hydrobiologia》1997,344(1-3):205-214
Phosphorus fluxes in phytoplankton, between intracellular andexternal compartments have been measured, in the epilimnion ofatemperate eutrophic reservoir, by means of phosphorusdepletionexperiments performed in situ. Flow rates betweencompartments were plotted against the phosphorus concentrationofthe compartments' origin of the flows and fitted to saturationfunctions.A value of phosphorus cell subsistence quota for the wholecommunity has been computed from the X-intercept values ofeveryfunction. The obtained figures are 10–100 times higher,dependingon the reference value, than those measured running theclassicalsingle species growth response experiments in chemostats.We propose a model using five compartments and a series offlowrates between them in order to simulate the general phosphoruscycling in freshwater phytoplankton. Short term simulation ofphosphorus content in every compartment shows a fluctuatingpatternaround rates of equilibrium, in agreement with the pattern ofvariation observed in situ for the selectedcompartments. 相似文献
94.
Maira Oropeza Palmira Guevara Eva de García José Luis Ramírez 《Plant Molecular Biology Reporter》1995,13(2):182-191
Somaclonal variants resistant to sugarcane mosaic virus (SCMV) were obtained from susceptible sugarcane cv PR62258 through
somatic embryogenesis by increasing the number of subcultures of the embryogenic callus tissue in MS medium with 3 mg/L 2,4-dichlorophenoxyacetic
acid. Transfers were made at 30-day intervals for 1, 2 or 3 subcultures. Two somaclones, namely AT626 and BT627, were selected
by their resistance to SCMV. These subclones have maintained the resistance trait over seven years of testing in the field.
In this report we identified the somaclonal SCMV resistant variants from the maternal line and the nonresistant somaclones,
using the RAPD technique. 相似文献
95.
José Luis López-Ribot Deborah A. Cortlandt David C. Straus K. John Morrow W. LaJean Chaffin 《Mycopathologia》1995,132(2):87-93
We have previously described a monoclonal antibody, MAb DC3:H10, which recognized an epitope preferentially expressed on the surface ofCandida albicans germ tubes. In the present study we examined the MAb-reactive material further. Immunoblot analysis of the material purified partially by Sephadex G-200 and DEAE-Sephacel chromatography reacted with antibodies to theC. albicans C3d receptor (CR2). In an ELISA, MAb DC3:H10 captured antigen that was recognized by both anti-CR2 and anti-mp58 fibrinogen binding mannoprotein polyclonal antibodies. The MAb DC3:H10 failed to compete with either of these antisera in an ELISA. Indirect immunofluo-rescence (IIF) analysis showed differences in surface distribution for the MAb DC3:H10, the CR2, and the mp 58 epitopes. Dual labeling IIF experiments showed MAb DC3:H10 binding to be unaffected by binding of fibrinogen or anti-mp58 antibody. However, the binding patterns of MAb DC3:H10 were modified in the presence of anti-CR2 antibody, suggesting a complex interaction between these cell wall components. 相似文献
96.
Dinucleotide repeat polymorphism at the D4S2458 locus close to the PKD2 locus on human chromosome 4q
Miguel Viribay Dolores Tellería Eladio Velasco Felipe Moreno José L. San Millán 《Human genetics》1995,95(5):601-602
A new polymorphic CA repeat sequence was identified within the candidate region fot the autosomal dominant polycystic kidney disease type 2 (PKD2) locus. It should be a useful marker in the localization of this gene. 相似文献
97.
José Moreno Herminia Rodríguez M. Angeles Vargas Joaquín Rivas Miguel G. Guerrero 《Journal of applied phycology》1995,7(1):17-23
Ten strains of filamentous, heterocystous nitrogen-fixing blue-green algae (cyanobacteria) were screened for growth performance
and tolerance to temperature, pH, irradiance and salinity, together with their potential as producers of phycobiliprotein
pigments. Phycobiliproteins typically accounted for about 50% total cell protein, the prevalent type being C-phycocyanin,
followed by alloppycocyanin, with levels of 17 and 11% d.wt, respectively, in some strains of Anabaena and Nostoc. C-phycoerythrin was the major pigment in several Nostoc strains, reaching 10% d.wt. Some strains represent, therefore, excellent sources of one or more phycobiliproteins. All strains
tolerated an irradiance of ca 2000 μmol photon m-2 s-1. Anabaena sp. ATCC 33047 and Nostoc sp. (Albufera) exhibited the widest optimum range of both temperature (30–45 and 25–40 °C) and pH (6.5–9.5 and 6.0–9.0) for
growth, the former also showing significant salt tolerance. In an outdoor open system, productivity of cultures of two phycoerythrin-rich
strains of Nostoc was over 20 g (d.wt) m-2 d-1 during summer. The growth performance of the allophycocyanin-rich Anabaena sp. ATCC 33047 in outdoor semi-continuous culture has been assessed throughout the year. Productivity values under optimized
conditions ranged from 9 (winter) to 24 (summer) g (d.wt) m-2 d-1. 相似文献
98.
99.
Distribution and properties of pea (Pisum sativum L.) cells, competent forAgrobacterium-mediated transformation were analysed byin situ histochemical detection of GUS (-glucuronidase) activity, 4 d after inoculation with engineeredAgrobacterium tumefaciens. The vector system consisted of the hypervirulent disarmed strain EHA101 and the binary plasmid pIBGUS, carrying an intron-containing, 35S-promotor drivengusA (oruidA) gene and two selectable marker genes. Cells competent for transformation were mainly restricted to the dedifferentiating cells neighbouring the vascular system of cotyledon and epicotyl explants. A standardized assay was developed, allowing determination and quantification of factors influencing number and distribution of competent cells. In etiolated seedlings, competence for transformation decreased with the distance of the epicotyl explant from the shoot apex and was specifically induced by the exogenous application of auxins. Transient expression ofgusA afterAgrobacterium-mediated DNA transfer was dramatically reduced upon application of cell-cycle and DNA replication inhibitors aphidicolin, colchicine and nalidixic acid. GUS expression after direct DNA transfer of double-stranded plasmid DNA (via PEG into protoplasts or via particle bombardment of epicotyl segments) was independent of cell-division/DNA replication.A GUS-positive mutant of EHA101 was constructed to allowin situ analysis of attaching bacteria within the plant tissue. Attachment and invasion was inhibited by well-developed cuticula but was restored after chloroform treatment of the tissue surface. Moreover, no correlation was found between distribution of attaching bacteria and the pattern of transformation-competent cells. 相似文献
100.
André W. Schram Marianne Dreissen Johan Bastiaannet Wilma E. Donker-Koopman Elisabeth M. Brouwer-Kelder Gabriele Weitz John A. Barranger Konrad Sandhoff Joseph M. Tager 《Bioscience reports》1984,4(12):1051-1057
The immunoblotting technique was used to identify sphingomyeJinase protein in samples of tissue and urine after subjection to poIyacrylamide-gel etectrophoresis in the presence of sodium dodecyl sulphate. In a sphingomyelinase preparation purified from control urine a prominent band was seen with an Mr of 28 000 Da. Glycoprotein fractions from urine and placenta, a membrane extract from spleen, and a partially purified sphingomyelinase preparation from placenta contained the 28 000-Da band plus additional, higher-Mr bands. The 28 000-Da band was detectable in urine from a patient with Niemann-Pick disease type C, but not in urine from patients with Niemann-Pick disease types A and B. It is concluded t h a t sphingomyeJinase is composed of at least one polypeptide with an Mr of 28 000 Da and that this polypeptide is deficient in the urine of patients with Niemann-Pick disease types A and B. 相似文献