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  • 1
    Electronic Resource
    Electronic Resource
    Isoforms of glutamine synthetase in asparagus spears: the cytosolic enzyme increases after harvest (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Two distinct forms of glutamine synthetase (GS) have been identified in the spear tip tissues of harvested asparagus (Asparagus officinalis L. cv. Limbras 10). The GS activities were separated by anion exchange chromatography. They have distinct kinetic properties and contain polypeptides of different sizes, and the abundances of the GS isoforms change differently after harvest. Plastid GS has a 44 kD polypeptide, and during the post-harvest period the abundance of this polypeptide declined dramatically. After 5 d, the activity of plastid GS had declined to just 20% of that at harvest. Cytosolic GS has a 40 kD polypeptide and is the major constituent of the GS activity present at harvest (73% of total). After harvest, cytosolic GS activity declined by half and then, at 3 or 4 d after harvest, rose to 80% of the cytosolic GS activity present at harvest. The nitrogen metabolism of asparagus spears is significantly altered as the tissues deteriorate rapidly after harvest. We demonstrate that cytosolic GS activity increases during the post-harvest period and is likely to be a critical feature of the physiology of the tip of a harvested asparagus spear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb02027.x
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  • 2
    Electronic Resource
    Electronic Resource
    Dual effect of monovalent cations on the glucose-induced transient increase in the rate of DMP influx into Saccharomyces cerevisiae (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 95 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The transient increase in the rate of 2-(4-dimethyl-aminostyryl)-1-ethylpyridinium (DMP) influx in Saccharomyces cerevisiae caused by addition of glucose to a suspension of non-metabolizing cells at relatively high pH can be prevented by monovalent cations. Their concentrations for half-maximum inhibition of DMP uptake are of the same order of magnitude as the corresponding Km values for their uptake into yeast cells. It is argued that the inhibition of DMP uptake by monovalent cations caused by a fast depolarization of the cell membrane and a second further decrease in the rate of DMP uptake. The latter effect develops slowly with time and depends upon the extent of accumulation of the monovalent cations in the cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05349.x
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetics of NH4+ and K+ uptake by ectomycorrhizal fungi. Effect of NH4+ on K+ uptake (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 83 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: NH4+ and K+ uptake experiments have been conducted with 3 ectomycorrhizal fungi, originating from Douglas fir (Pseudotsuga menziesii (Mirb.] Franco) stands. At concentrations up to 250 μM, uptake of both NH4+ and K+ follow Michaelis-Menten kinetics. Laccaria bicolor (Maire) P. D. Orton, Lactarius rufus (Scop.) Fr. and Lactarius hepaticus Plowr. ap. Boud. exhibit Km values for NH4+ uptake of 6, 35, and 55 μM, respectively, and Km values for K+ uptake of 24, 18, and 96 μM, respectively. Addition of 100 μM NH4+ raises the Km of K+ uptake by L. bicolor to 35 μM, while the Vmax remains unchanged. It is argued that the increase of Km is possibly caused by depolarization of the plasma membrane. It is not due to a competitive inhibition of K+ by NH4+ since the apparent inhibitor constant is much higher than the Km, for NH4+ uptake. The possibility that NH4+ and K+ are taken up by the same carrier can be excluded. The Km, values for K+ uptake in the two other fungi are not significantly affected by 100 μM NH4+. Except for a direct effect of NH4+ on influx of K+ into the cells, there may also be an indirect effect after prolonged incubation of the cells in the presence of 100 μM NH4+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb00116.x
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  • 4
    Electronic Resource
    Electronic Resource
    Physiological changes in asparagus spear tips after harvest (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To extend our understanding of the physiology of asparagus after harvest, changes in respiration rate, protein and amino acid complement, and ultrastructure of tip sections (0–30 mm) of asparagus spears (Asparagus officinalis L. cv. Limbras 10) were investigated. Spears had been stored for up to 4 days in the dark at 20°C. Respiration rate (carbon dioxide efflux) declined rapidly after harvest before stabilizing at 12 h at ca 50% of the rate at harvest. Protein, amino acid, and ammonium content of tip sections of 180 mm spears (intact tip sections) during storage, and comparable sections; excised from spears at harvest and subsequently stored (excised tip sections), were compared. Total protein content of intact and excised tip sections increased ca 10% 6–12 h after harvest, and then declined to ca 85% of harvest levels at 48 h. Gel electrophoresis in the presence of sodium dodecyl sulphate revealed the net loss of specific proteins at 48 h. Free amino acid content of excised tip sections declined to ca 75% of harvest levels 12 h after harvest, and then increased to 150% of harvest levels by 48 h. Glutamine levels declined rapidly after harvest, and asparagine content increased ca 200% at 24 h. Similar trends in free amino acid content were found in sections of intact tips. Ammonia (ammonium ions) accumulated to ca 0.3% dry weight at 48 h in both intact and excised tip sections. Ultrastructural studies revealed that tonoplast breakdown commenced 48–96 h after harvest. Results are discussed in relation to the sequence of physiological events following harvest and the timing of mechanisms responsible for their initiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb00058.x
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