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  • 1
    Electronic Resource
    Electronic Resource
    A comparison between the utilization of storage protein and exogenous nitrate during seedling establishment in Zea mays L. (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 10 (1987), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract During the first 5 d of germination in the presence of exogenous l5NO−3 and the inhibitor of nitrification N-SERVE, the nitrogen reserves of the caryopses of Zea mays L. were found to account for 75% of the total nitrogen content of the developing seedlings. During this period, an increasing pool of 14NO−3 was detected in both the grain and the seedling. The accumulation of nitrate in the grain and the extent of hydrolysis of seed reserves were enhanced when nitrate was removed from the growing medium. The significance of a possible oxidative pathway from reduced nitrogen to nitrate is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1987.tb01613.x
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  • 2
    Electronic Resource
    Electronic Resource
    Hard X-ray images of the galactic centre (1987)
    [s.l.] : Nature Publishing Group
    Nature 330 (1987), S. 544-547 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The only detailed X-ray image of the galactic centre region until now was obtained by Watson et a/.1 in 1979 with the Einstein Observatory, using X-rays with energy 〈4.5 keV (ref. 1, referred to below as WWGH). Twelve point sources were seen in the ~1° field, together with diffuse emission ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/330544a0
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  • 3
    Electronic Resource
    Electronic Resource
    The distribution of iron in the Perseus cluster (1990)
    [s.l.] : Nature Publishing Group
    Nature 347 (1990), S. 450-452 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The coarse component of the dual X-ray telescope on Spacelab 2 (ref. 1) used coded-mask imaging2 to achieve angular resolution of 12' over a 6° field together with proportional-counter energy resolution covering the 2-32 keVband, recording ~7 x 105 photons from the Perseus cluster during an ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/347450a0
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  • 4
    Electronic Resource
    Electronic Resource
    Control of nitrate and nitrite assimilation by carbohydrate reserves, adenosine nucleotides and pyridine nucleotides in leaves of Zea mays L. under dark conditions (1987)
    Springer
    Planta 172 (1987), S. 548-554 
    Details
    ISSN: 1432-2048
    Keywords: Adenylate pool ; Glucose ; NADH ; Nitrogen metabolism (dark-O2, dark-N2) ; Zea (nitrogen metabolism, leaf)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The rate of in-vivo nitrate reduction by leaf segments of Zea mays L. was found to decline during the second hour of dark anaerobic treatment. On transfer to oxygen the capacity to reduce nitrate under dark conditions was restored. These observations led to the proposal that nitrate reductase is a regulatory enzyme with ADP acting as a negative effector. The effect of ADP on the invitro activity of nitrate reductase and the changes in the in-vivo adenylate pool under dark-N2 and dark-O2 were investigated. It was found that ADP inhibited the activity of partially purified nitrate reductase. Similarly, the in-vivo anaerobic inhibition of nitrate reduction was associated with a build-up of ADP in the leaf tissue. Under anaerobic conditions nitrite accumulated and on transfer to oxygen the accumulated nitrite was reduced. To explain this phenomenon the following hypothesis was proposed and tested. Under anaerobic conditions the supply of reducing equivalents for nitrite reduction in the plastid becomes restricted and nitrite accumulates as a consequence. On transfer to oxygen this restriction is removed and nitrite disappears. This capacity to reduce accumulated nitrite was found to be dependent on the carbohydrate status of the leaf tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393873
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of oxygen on nitrate and nitrite assimilation in leaves of Zea mays L. under dark conditions (1986)
    Springer
    Planta 169 (1986), S. 339-344 
    Details
    ISSN: 1432-2048
    Keywords: Nitrate/nitrite assimilation ; Nitrogen metabolism (dark O2, dark N2) ; Zea (nitrogen metabolism, leaf)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The assimilation of nitrate under dark-N2 and dark-O2 conditions in Zea mays leaf tissue was investigated using colourimetric and 15N techniques for the determination of organic and inorganic nitrogen. Studies using 15N indicated that nitrate was assimilated under dark conditions. However, the rate of nitrate assimilation in the dark was only 28% of the rate under non-saturating light conditions. No nitrite accumulated under dark aerobiosis, even though nitrate reduction occurred under these conditions. The pattern of nitrite accumulation in leaf tissue in response to dark-N2 conditions consisted of three phases: an initial lag phase, followed by a period of rapid nitrite accumulation and finally a phase during which the rate of nitrite accumulation declined. After a 1-h period of dark-anaerobiosis, both nitrate reduction and nitrite accumulation declined considerably. However, when O2 was supplied, nitrate reduction was stimulated and the accumulated nitrite was rapidly reduced. Anaerobic conditions stimulated nitrate reduction in leaf tissue after a period of dark-aerobic pretreatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392129
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of aflatoxin B1 on in vitro cultures ofNicotiana tabacum var. Samsun (1994)
    Springer
    Mycopathologia 125 (1994), S. 107-117 
    Details
    ISSN: 1573-0832
    Keywords: Aflatoxin B1 ; Immunocytochemistry ; Regeneration ; Tissue culture ; Tobacco plantlets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The effects of aflatoxin B1, (0.5–25 µg ml−1) on in vitro root and shoot development in young tobacco explants were investigated. Despite an initial apparent stimulatory effect on most measured parameters at 0.5 µg ml−1 AFB1, the number of leaves, root and leaf mass per plantlet were progressively inhibited with increasing AFB1 concentration. The number of explants developing roots was reduced to 34% at the highest (25 µg ml−1) AFB1 concentration, following 3 weeks exposure to the toxin. Leaf chlorophyll content at this toxin concentration was significantly lower than that measured for control plantlets. Thin layer chromatography confirmed the absorption of AFB1 by the plantlets. Using immunocytochemical techniques, AFB1 was immunolocated predominantly in the vacuoles, the nucleus and the cytoplasm (possibly intravesicularly). The results are discussed in terms of this immunolocation within the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01371099
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  • 7
    Electronic Resource
    Electronic Resource
    The effects of aflatoxin B1 on immature germinating maize (Zea mays) embryos (1992)
    Springer
    Mycopathologia 119 (1992), S. 181-190 
    Details
    ISSN: 1573-0832
    Keywords: aflatoxin B1 ; electron microscopy ; in vitro ; immature maize embryo ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Immature maize (Zea mays L.) embryos were treated with aflatoxin B1 concentrations, ranging from 0.1 μg ml−1 to 25 μg ml−1. Below 5 μg ml−1 aflatoxin B1, root and shoot elongation was not significantly inhibited. Ultrastructurally, root tip cells showed little deterioration, except a possible diffused clearing in mitochondria and plastids. As the toxin concentration was increased above 5 μgml−1, shoot, and particularly root elongation, was progressively inhibited. Associated with this, there was an apparent decrease in the ribosome population. Furthermore, membranes, particularly the vacuolar membrane, became abnormal and vacuolar distension occurred. At 20 and 25 μg ml−1, these effects were exacerbated, and mitochondria and plastid structure was disrupted. At these concentrations, there was evidence of a disruption in lipid metabolism. The results are discussed in the context of known aflatoxin effects on cellular control mechanisms and ultrastructure in animal systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00448817
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of aflatoxin B1 on in vitro cultures ofNicotiana tabacum var. Samsun (1994)
    Springer
    Mycopathologia 125 (1994), S. 93-105 
    Details
    ISSN: 1573-0832
    Keywords: Aflatoxin B1 ; Callus ; Differentiation ; Electron microscopy ; Organogenesis ; Tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Calli ofNicotiana tabacum (tobacco) were treated with two dose ranges of aflatoxin B1 (0.1–2.0 µg ml−1 - low does; 5–25 µg ml−1 aflatoxin B1). The ability of calli to recover following 3 weeks of toxin exposure was also investigated. The I50 (50% inhibition) value for fresh mass accumulation was approximately 2 µg ml−1 AFB1. Fresh mass accumulation was significantly lower than the control value from 0.5 µg ml−1 AFB1. Following 3 weeks growth without a toxin source, the growth of calli up to and including 10 µg ml−1 AFB1, was significantly greater than control calli, indicating reversibility of the toxic effects. With increasing toxin concentration, chlorophyll content of callus was inhibited from 0.5 µg ml−1. Transfer to a toxin-free medium resulted in a degree of recovery (up to 0.5 µg ml−1). In the dose range 5–25 µg ml−1, the levels of chlorophyll were drastically reduced, with no recovery following AFB1 removal. Electron microscopy revealed a disruption of chloroplast structure as an early deteriorative event in AFB1 exposure of callus cells. Protein levels were less sensitive, with inhibition manifested only in the high dose range. Shoot development occurred at all concentrations, but was significantly inhibited from 5 µg ml−1 AFB1. Recovery following toxin removal was minimal at these higher AFB1 concentrations. The number of necrotic calli increased progressively from 5 µg ml−1 as toxin levels increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01371098
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  • 9
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    The effect of oxygen on nitrate and nitrite assimilation in leaves of Zea mays L. under dark conditions (1986)
    Springer
    Details
    Publication Date: 1986-11-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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  • 10
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    Control of nitrate and nitrite assimilation by carbohydrate reserves, adenosine nucleotides and pyridine nucleotides in leaves of Zea mays L. under dark conditions (1987)
    Springer
    Details
    Publication Date: 1987-12-01
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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