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21.
The age, growth and reproduction ofRutilus lemmingii (Steindachner, 1866), an endemic cyprinid from the Iberian Peninsula, was studied for over a period of two years in a small seasonal tributary of the Guadalquivir river basin. Approximately 65 % of the total growth in length occured in the first year of life. Males reached a maximum age of 3+ yr (Fork Length, F.L. = 114 mm) and females 4+ yr (F.L. = 144 mm). Both sexes matured during their second year of life (1 +). The overall sex ratio (334 males to 389 females) differed significantly from unity. Somatic condition decreased markedly during the reproductive period of March to May.R. lemmingii is a multiple spawner and releases two batches of eggs per female each year. Mean egg diameter of the first batch was larger than the second one. The regression between fecundity and Fork Length (mm) was: Fec = 0.014 F.L.Z.2.858 Compared with available information, thisR. lemmingii population, located at a lower latitude, is characterized by fast growth, early maturity, high level of reproductive effort, and a short life-span. These life-history characteristices are typical of species in unstable environments, where adult mortality is high, variable or unpredictable. 相似文献
22.
Toxicology of vanadium compounds in diabetic rats: The action of chelating agents on vanadium accumulation 总被引:1,自引:0,他引:1
Jose L. Domingo Mercedes Gomez Domenec J. Sanchez Juan M. Llobet Carl L. Keen 《Molecular and cellular biochemistry》1995,153(1-2):233-240
The possible use of vanadium compounds in the treatment of diabetic patients is now being evaluated. However, previously to establish the optimal maximum dose for diabetes therapy, it should be taken into account that vanadium is a highly toxic element to man and animals. The toxic effects of vanadium are here reviewed. The tissue vanadium accumulation, which would mean an additional risk of toxicity following prolonged vanadium administration is also discussed. Recently, it has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect of vanadium. However, previously to assess the effectiveness of this treatment in diabetic patients, a critical reevaluation of the antidiabetic action of vanadium and its potential toxicity is clearly needed. 相似文献
23.
In vitro pollen germination of five species and two interspecific hybrids from the genus Brassica was tested in four media. Genetically fixed differences in the demands for optimal pollen germination among species were found. The experiments were designed to define optimal content of mineral salts, sugar, and PEG for every investigated species or hybrids. The differences found among species are discussed in relation to the evolutionary trend. 相似文献
24.
Mercedes Umali-Garcia David H. Hubbell Murray H. Gaskins Frank B. Dazzo 《Applied microbiology》1980,39(1):219-226
The association between grass roots and Azospirillum brasilense Sp 7 was investigated by the Fahraeus slide technique, using nitrogen-free medium. Young inoculated roots of pearl millet and guinea grass produced more mucilaginous sheath (mucigel), root hairs, and lateral roots than did uninoculated sterile controls. The bacteria were found within the mucigel that accumulated on the root cap and along the root axes. Adherent bacteria were associated with granular material on root hairs and fibrillar material on undifferentiated epidermal cells. Significantly fewer numbers of azospirilla attached to millet root hairs when the roots were grown in culture medium supplemented with 5 mM potassium nitrate. Under these growth conditions, bacterial attachment to undifferentiated epidermal cells was unaffected. Aseptically collected root exudate from pearl millet contained substances which bound to azospirilla and promoted their adsorption to the root hairs. This activity was associated with nondialyzable and proteasesensitive substances in root exudate. Millet root hairs adsorbed azospirilla in significantly higher numbers than cells of Rhizobium, Pseudomonas, Azotobacter, Klebsiella, or Escherichia. Pectolytic activities, including pectin transeliminase and endopolygalacturonase, were detected in pure cultures of A. brasilense when this species was grown in a medium containing pectin. These studies describe colonization of grass root surfaces by A. brasilense and provide a possible explanation for the limited colonization of intercellular spaces of the outer root cortex. 相似文献
25.
Mercedes Hernandez-Asensio Francisca F. Del Campo 《Archives of biochemistry and biophysics》1980,200(1):309-318
The rate of α-methylglucoside efflux from wild-type cells of Escherichia coli K-12 is enhanced by different substrates, as long as they are readily respired. A similar enhancement takes place in strains with impaired oxidative phosphorylation (unc mutants), regardless of their being able (strains AN120, N144, and AN382) or unable (strain NR70) to energize the membrane through respiratory electron flow. The uncouplers carbonylcyanide-m-chlorophenylhydrazone and tetrachlorosalicylanilide do not diminish the efflux acceleration in wild-type strains or unc mutants. However, the stimulation of α-methylglucoside efflux does not occur in the mutant AN59 which cannot perform a normal respiratory electron transport due to a defective synthesis of ubiquinone. The failure to stimulate the efflux is observed with succinate, which is a typical substrate of respiration, as well as with substrates which can yield ATP both at respiratory and substrate levels such as gluconate or glycerol. Moreover, potassium cyanide nullifies the acceleration of α-methylglucoside efflux caused in any type of strain and by any substrate. These results show that neither ATP nor an energized state of the membrane appears to be needed for respiration to accelerate α-methylglucoside release from E. coli cells, and question the existence of any energy-requiring reaction for αMG exit, previously proposed by other authors. 相似文献
26.
Juan Ortín Concepción Martínez Lucía del Río Mercedes Dávila Cecilio López-Galíndez Nieves Villanueva Esteban Domingo 《Gene》1983,23(2):233-239
The complete genetic information contained in the influenza virus RNA segment 7 of the A/Bangkok/ (H3N2) strain has been cloned by in vitro synthesis of the complementary dsDNA and its insertion into plasmid pBR322. The nucleotide sequence of the viral RNA segment has been determined from the cDNA insert. It is 1027 nucleotides long, and contains two open reading frames, as shown for other influenza virus strains. When compared with the previously published sequence for the A/Udorn/72 (H3N2) strain, 15 nucleotide exchanges are observed, most of them silent mutations, and only two causing amino acid changes in each of the M1 and M2 protein sequences. 相似文献
27.
Elisabet Font Mercedes Sitges Fausto G. Hegardt 《Biochemical and biophysical research communications》1982,105(2):705-710
Rat liver homogeneous 32P-labeled hydroxy methylglutaryl coenzyme A reductase, was treated independently with CNBr and trypsin and the resulting [32P]phosphopeptides were analyzed by disc gel electrophoresis. CNBr treatment produced only one 32P-fragment of Mr 18,000. The time course of trypsin hydrolysis initially showed the appearance of some phosphopeptides, which were lately converted in two phosphopeptides of low Mr. These results provide direct support for the concept that hydroxy methyl glutaryl coenzyme A reductase kinase solubilized from microsomes phosphorylates only two sites or set of sites in the reductase molecule. 相似文献
28.
Tunicamycin, an inhibitor of the asparagine-linked protein N-glycosylation, blocks the initiation of DNA synthesis in Swiss 3T3 cells stimulated by prostaglandin F2α alone or with insulin. This effect is exerted only when tunicamycin is added from 0 to 8 h after stimulation and it decreases the rate of entry into S phase. Blocking of labeled sugar incorporation to proteins occurs regardless of the time of PGF2α stimulation. In contrast tunicamicin does not inhibit protein synthesis. These results suggest that N-glycoprotein synthesis early during the prereplicative phase is an important event controlling the mitogenic action of PGF2α 相似文献
29.
Mercedes Hernandez-Asensio Juan M. Ramirez Francisca F. Del Campo 《Archives of microbiology》1975,103(1):155-162
The uptake of methyl α-d-glucopyranoside (α-MG) by Escherichia coli K12 was decreased by the addition of substrates which stimulated the rate of oxygen consumption by the cells. The inhibition, which occurred only at non-saturating concentrations of α-MG, was not the result of a stimulation of the rate of exit of intracellular α-MG, and was abolished by the presence of carbonyl cyanide m-chlorophenylhydrazone or sodium azide. Since those drugs inhibit energy conservation at the respiratory chain and did not alter significantly the rate of oxygen consumption under the conditions for the assay of α-MG uptake, it appears that the inhibition of the transport system by respirable substrates is mediated by some form of energy derived from respiration. 相似文献
30.
Alexandrium taylori Balech is a phototrophic marine dinoflagellate. It produced recurrent blooms during the summer months (July and August) of 1994 to 1997 in La Fosca beach (NW Mediterranean). In addition to a motile vegetative form, A. taylori had two benthic forms: temporary cysts and resting cysts. Temporary cysts were a temporally quiescent stage produced from the ecdysis of the vegetative cell in both natural populations and laboratory cultures. Temporary cysts may divide to form motile cells. Resting cysts had a thicker wall than the temporary cysts and had a red accumulation body. Gametes and planozygotes were also observed in laboratory cultures. Alexandrium taylori showed in situ diurnal vertical migration with an increase of vegetative cells in the water column in the morning through midday, with concentrations peaking in the afternoon followed by lower levels at night. Most vegetative cells lost their thecae and flagella, and with them their motility, turning into temporary cysts that settled in the early evening. The number of temporary cysts in the water column rose in the evening and at night. The temporary cysts gave rise to motile cells the following morning. Synthesis of DNA occurred in vegetative cells at night, and a preferential period of cell division occurred at sunrise. The estimated division rate in the field was 0.4–0.5 vegetative cells·day−1 . Temporary cysts had twice the DNA of a G1 vegetative cell. The minimum in situ division rate of the temporary cysts was 0.14 day−1 . The role of the resting and temporary cyst population in the annual recurrence and maintenance of the A. taylori bloom is discussed. 相似文献