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  • 1
    ISSN: 1617-4623
    Keywords: Key wordsUstilago maydis ; Zea mays ; Corn smut ; Meiosis ; Cell cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The heterobasidiomycetes responsible for plant smuts obligatorily require their hosts for the completion of the sexual cycle. Accordingly, the sexual cycle of these fungi could so far be studied only by infecting host plants. We have now induced Ustilago maydis, the causative agent of corn smut, to traverse the whole life cycle by growing mixtures of mating-compatible strains of the fungus on a porous membrane placed on top of embryogenic cell cultures of its host Zea mays. Under these conditions, mating, karyogamy and meiosis take place, and the fungus induces differentiation of the plant cells. These results suggest that embryogenic maize cells produce diffusible compounds needed for completion of the sexual cycle of U. maydis, as the plant does for the pathogen during infection.
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To investigate the possible induction of Crassulacean acid metabolism (CAM) by drought in Talinum paniculatum ([Jacq.] Gaertn.), a deciduous herb with succulent leaves and lignified stems, nocturnal acid accumulation and CO2-exchange were studied in watered and droughted greenhouse-grown plants. Watered plants had a typical C3 pattern of CO2-exchange. When plants were subjected to drought, nocturnal acid accumulation increased significantly from 0.9 to 13.4 μmol H+ cm−2 after 21 days. Water deficit provoked a rapid reduction of daytime CO2 assimilation of as much as 92% and a slower increase in night-time fixation. A maximum of 24% of the diel carbon gain was contributed by dark fixation in droughted plants. After 34 days of drought, only CO2 compensation and a small accumulation of acid (idling) was detected during the night. Relative recycling of respiratory CO2 was approximately 100% for most of the water deficit treatment, the amount of CO2 recycled showing a high positive correlation with nocturnal acid accumulation. A low rate of nocturnal loss of CO2 in watered plants did not explain the amount recycled nightly in droughted plants, implying that respiration increased with drought. Leaf lamina area was reduced by 49% during drought due to rolling. Leaf biomass remained unchanged during the water-deficit treatment. Neither apparent quantum yield nor light-saturated photosynthetic rate differed significantly between control and 14-day water-stressed plants rewatered for 20 h. Chlorophyll content did not change with drought. These results confirm that CAM is induced by drought in T. paniculatum; the carbon acquired through this pathway only contributes to maintain, but not to increase, leaf biomass; also, CAM is responsible for a high recycling of respiratory CO2 during the night. Recycling through CAM, plus the reduction of exposed leaf area during drought, may help explain the maintenance of chlorophyll, quantum yield and saturated photosynthetic rates in water-stressed plants of T. paniculatum.
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  • 3
    ISSN: 1432-0983
    Keywords: Key wordsCandida albicans ; Ornithine decarboxylase ; Dimorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gene (CaODC) coding for ornithine decarboxylase, a key enzyme in polyamine biosynthesis, was cloned from Candida albicans by PCR and characterized. The deduced protein contains 470 amino acids together with the substrate- and co-factor-binding sequences which define the ornithine decarboxylases of eukaryotic species. It shows a high homology with other ODCs, mainly those from Saccharomyces cerevisiae and Neurospora crassa. A putative PEST sequence, which correlates quite well with those described for other fungal ODCs, could be identified in the protein. The mRNA of the gene is 2.4 kb in size and by primer extension a long leader sequence was found at –558 bases upstream of the predicted start of translation. An identical single ODC gene was identified in three different C. albicans strains. During the dimorphic switch, a transient initial increase in ODC activity was observed. This increase was not accompanied by a rise in the levels of the transcript, suggesting that ODC activity levels may be regulated post-transcriptionally during differentiation.
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  • 4
    ISSN: 1432-072X
    Keywords: Key words Transglutaminase ; Cell wall ; Candida ; albicans ; Wall epitopes ; Covalent bonds ; Protein ; interactions ; Protoplasts ; Dimorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Activity of the enzyme glutaminyl-peptide-—glutamylyl-transferase (EC 2.3.2.13; transglutaminase), which forms the interpeptidic cross-link Nε-(γ-glutamic)-lysine, was demonstrated in cell-free extracts obtained from both the yeast like and mycelial forms of Candida albicans. Higher levels of enzymatic activity were observed in the cell wall fraction, whereas the cytosol contained only trace amounts of activity. Cystamine, a highly specific inhibitor of the enzyme, was used to analyze a possible role of transglutaminase in the organization of the cell wall structure of the fungus. Cystamine delayed protoplast regeneration and inhibited the yeast-to-mycelium transition and the incorporation of proteins into the cell wall. The incorporation of covalently bound high-molecular-weight proteins into the wall was sensitive to cystamine. Proteic epitopes recognized by two monoclonal antibodies, one of which is specific for the mycelial walls of the fungus, were also sensitive to cystamine. These data suggest that transglutaminase may be involved in the formation of covalent bonds between different cell wall proteins during the final assembly of the mature cell wall.
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  • 5
    ISSN: 1432-072X
    Keywords: Key wordsParacoccidioides brasiliensis ; Fungal ; dimorphism ; Ornithine decarboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ornithine decarboxylase in Paracoccidioides brasiliensis, a dimorphic human pathogenic fungus, was more active at 37° C in the yeast phase and at 30° C in the mycelial phase. In contrast to other fungal systems, yeast growth and mycelium-to-yeast transition in P. brasiliensis were accompanied by a high activity of ornithine decarboxylase at the onset of the budding process, the activity of which was inhibited by 1,4-diamino-2-butanone. The activity of ornithine decarboxylase remained at a basal level during vegetative growth of both the mycelial phase and the late stage of yeast phase, and also through the yeast-to-mycelium transition.
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  • 6
    ISSN: 1432-072X
    Keywords: Key words Archaea ; Haloalkaliphiles ; Natronococcus ; occultus ; Proteolytic activity ; Gelatin zymography ; Betaine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extracellular proteolytic activity was detected in the haloalkaliphilic archaeon Natronococcus occultus as the culture reached the stationary growth phase. Proteolytic activity was precipitated with ethanol and subjected to a preliminary characterization. Optimal conditions for activity were attained at 60° C and 1–2 M NaCl or KCl. Gelatin zymography in the presence of 4 M betaine revealed a complex pattern of active species with apparent molecular masses ranging from 50 to 120 kDa. Experiments performed with inhibitors of the various groups of proteases indicated that the extracellular proteolytic enzymes of N. occultus are of the serine type. Individual protein species showed some differences in salt and thermal stability.
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  • 7
    ISSN: 1432-072X
    Keywords: Paracoccidioides brasiliensis ; Fungal dimorphism ; Polyamines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Putrescine and spermidine were the only polyamines found inParacoccidioides brasiliensis, a dimorphic fungus pathogenic for humans. Free polyamines (putrescine〉spermidine) increased during the first 24 h of yeast growth, with a second peak at 42 h, and also during the first 12 h of mycelium-to-yeast transition (spermidine〉putrescine). Conjugated and bound polyamines were also quantified. 1,4-Diamino-2-butanone decreased free putrescine and spermidine accumulation by inhibiting the activity of ornithine decarboxylase. The increase in free polyamines corresponds to bud emergence in yeast growth and to the mycelium-to-yeast transition ofP. brasiliensis.
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  • 8
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
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  • 9
    ISSN: 1432-1106
    Keywords: Perinatal asphyxia ; Dopamine utilization ; Tyrosine hydroxylase activity ; Substantia nigra ; Neostriatum ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study was undertaken in order to study the effects of perinatal asphyxia on tyrosine hydroxylase (TH) activity, dopamine levels and turnover, and dopamine metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, homovanillic acid, HVA, and 3-methoxytyramine, 3-MT, analyzed by high-performance liquid chromatography, HPLC) measured in the basal ganglia of the 20- to 40-min-old newborn and 4-week-old male rat. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from pregnant rats at full term, in a 37°C water bath for 15–16 min or 19–20 min. Following asphyxia, the uterus horns were opened, and the pups were removed and stimulated to breathe. A 100% and 50–80% pup survival was obtained following 15–16 min and 19–20 min of asphyxia, respectively. Acute changes were studied in brains from newborn pups 20–40 min after delivery, and long-term changes were studied in brains from 4-week-old rats. No changes in TH-activity could be observed in the substantia nigra/ventral tegmental area (SN/VTA), the striatum, or the accumbens nucleus/olfactory tubercle (ACC/TUB), in the newborn or the 4-week-old rat. In the newborn rat, 19–20 min of asphyxia increased (as compared to controls) dopamine levels in the SN/VTA to 136±14% and in the ACC/TUB to 160±10%, indicating an increased synthesis and/or release of dopamine. DOPAC levels were increased in the SN/VTA to 150±14% and in the ACC/TUB to 151±10%, and HVA levels were increased to 152±16% in the striatum and to 117±4% in the ACC/TUB. Following 15–16 min of asphyxia, dopamine levels were increased to 130±12% in the ACC/TUB, and DOPAC levels were increased to 135±6% and 130±12% in the SN/VTA and the ACC/TUB, respectively. This suggests that the increased dopamine levels may preferably reflect an increased release of dopamine following perinatal asphyxia. In the 4-week-old rat, dopamine levels were decreased in the SN/VTA to 71±4%, in the striatum to 52±8%, and in the ACC/TUB to 53±7%, following 19–20 min of perinatal asphyxia as compared to controls. No changes were observed in DOPAC, HVA, or 3-MT levels, indicating that the reduced dopamine levels reflect a reduced dopamine synthesis following perinatal asphyxia. A decrease in dopamine utilization was observed in the striatum to 15±8% and in the ACC/TUB to 9±13% following 19–20 min of perinatal asphyxia as compared to controls. This indicates that perinatal asphyxia produced long-lasting reductions in activity in the mesostriatal/mesolimbic dopamine systems in the 4-week-old rat.
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  • 10
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Four distinct types of isolated growth hormone deficiency (IGHD) have been described to date. Of these IGHD type II has been defined as having a dominant mode of inheritance. We performed a molecular genetic analysis of two patients clinically characterized as IGHD type II. One of the patients and her father shared a heterozygous G–A transition in the first 5′ donor splice site of intron III. The second father and daughter studied also showed a heterozygous G–A transition in the fifth base from the 5′ donor splice site in the same intron. Both mutations altered the correct splicing of the growth hormone pre-mRNA when the corresponding genes were expressed in COS-7 cells. We propose that both inherited mutations are responsible for IGHD type II in these patients.
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