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  • 1980-1984  (4)
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  • 1
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Copper toxicity has been studied in three nickel-resistant strains ofNeurospora crassa (NiR1, NiR2, and NiR3). NiR1 and NiR2, but not NiR3, were two-to threefold more sensitive than the parent wild strain (N. crassa EM 5297a) to Cu2+ on a normal N medium. On a nitrate N medium, Cu2+ was 16-fold more toxic to NiR3 because of reduced synthesis of nitrite reductase; NiR1 and NiR2 were only fivefold more sensitive to Cu2+, and nitrite reductase synthesis was unaffected. Mn2+ reversed Cu2+ toxicity on normal N medium only, in all strains. Fe3+ counteracted Cu2+ toxicity on nitrate N medium also. It was shown that Cu2+ affected Fe3+ utilization for nitrite reductase synthesis in NiR3 only and that in these Ni2+-resistant strains, Fe3+ antagonized effects of Cu2+, but not of other toxic metal ions.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Transport of Ni2+ has been studied in three Ni2+-resistant strains ofNeurospora crassa (NiR1, NiR3) and NiR3) and in the parent wild strainN. crassa Em 5297a. Several strainspecific differences have been found. Rates of Ni2+ uptake were NiR2〉NiR1〉Em〉〉NiR3. While Km for Ni2+ uptake was similar, Vmax values were sharply different, with NiR3 having the lowest value. Observed uptake was entirely due to transport into the intracellular phase. Transport was strongly pH dependent only in Em, NiR1, and NiR2, which had a pH optimum at 4; optimum was at pH 5 for NiR3. Mg2+ was powerfully inhibitory to Ni2+ uptake in NiR1 and NiR2, but was less efficient in NiR3; in contrast, Mn2+ was most inhibitory in NiR3. It has been suggested that Ni2+ resistance in NiR3 is specifically due to lowered levels of the Ni2+ transport system herein.
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  • 3
    ISSN: 1432-0991
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Uptake of Co2+ by three nickel-resistant strains (NiR1, NiR2, and NiR3) ofNeurospora crassa that differed in resistance to Co2+ has been studied. Uptake was linear with Co2+ concentration (up to 1 mM), with time (up to 6 h), and with pH between 3 and 6. Uptake rates were in the order NiR2〉NiR1〉NiR3. In all strains, there was gradual increase in Co2+ uptake between 10° and 28°C, with a much sharper increase between 28° and 40°C. Metabolic inhibitors decreased Co2+ uptake partially in all strains, except for KF in NiR3. About 50–80 μg Co2+/100 mg dry weight was surface bound. Ni2+, Zn2+, and Mn2+ competed with Co2+, the effects being strain specific. Mg2+ inhibited Co2+ uptake in all strains with preformed mycelia. In NiR1 and NiR2 only with young mycelia (40 h old) was Mg2+ inhibitory to Co2+ uptake,during growth in the presence of Co2+. The results suggested the presence of two transport systems for Co2+ in NiR1 and NiR2, only one of which was sensitive to Mg2+; in contrast, NiR3 had a single system, which was sensitive to Mg2+.
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  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The replication of DNA in the giant chromosomes in different cells of Drosophila larval salivary glands is asynchronous. A method of in vivo synchronization of the nuclei has been successfully devised by a 5′-fluorodeoxyuridine (FdU) block-release-thymidine chase technique, and the patterns of replication sequences have been examined by 3H-thymidine autoradiography. When the larvae of Drosophila melanogaster are fed on FdU for 48 h, and the block is released thereafter, most cells are found in mid-replication phase (termed 3C). When the larvae are subjected to a chase in normal Drosophila medium (or sucrose), a series of cells arrive at 3C phase about every 8 h. When they are chased in sucrose containing thymidine, the number of cells in 3C phase rises to 70%, and then drops rapidly to 1–2% of all labelled cells. The terminal phases (3D, 2D and 1D) reach a peak between 4–8 h. At 12–14 h of chase the 3D-1D peaks decline and a third peak consisting mostly of the initial phases (DD-1C) is found at 14–16 h. The replication of DNA in polytene chromosomes of Drosophila thus seems to proceed in a regular sequence of DD-3C-1D.
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