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  • 1
    Electronic Resource
    Electronic Resource
    Fructose 2,6-Bisphosphate as a Regulatory Metabolite in Plants (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Plant Physiology 37 (1986), S. 233-246 
    Details
    ISSN: 0066-4294
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pp.37.060186.001313
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrate reductase in higher plants: A case study for transduction of environmental stimuli into control of catalytic activity (1999)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 105 (1999), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In higher plants, cytosolic NAD(P)H-nitrate reductase (NR) is rapidly modulated by environmental conditions such as light, CO2, or oxygen availability. In leaves, NR is activated by photosynthesis, reaching an activation state of 60–80%. In the dark, or after stomatal closure, leaf NR is inactivated down to 20 or 40% of its maximum activity. In roots, hypoxia or anoxia activate NR, whereas high oxygen supply inactivates NR. Spinach leaf NR is inactivated by phosphorylation of serine 543 and subsequent Mg2+-dependent binding of 14-3-3 proteins at, or close to, this phosphorylation site. At least three different protein kinases (NR-PK) have been identified in spinach leaves that are able to phosphorylate NR on serine 543. Two of them show up as calmodulin-like domain protein kinases (CDPKs), and one as a SNF1-like protein kinase. Dephosphorylation of serine 543 is catalyzed by a Mg2+-dependent protein phosphatase and by a type 2A protein phosphatase (NR-PP), which is regulated by a trimer/dimer interconversion. The NR-PKs, NR-PPs, and 14-3-3s are present even in NR-depleted plant tissues. Artificial activation of NR in vivo is achieved by cellular acidification, by respiratory inhibitors, or by mannose feeding. As for anoxia, these treatments seem to act, at least in part, via cytosolic acidification, mediated by low cytosolic ATP levels. Activation is also achieved by ionophore-induced release of divalent cations from the cytosol. In addition, cytosolic AMP and phosphate esters seem to regulate NR-PK and NR-PP activities, thereby adapting NR activity within minutes to the changing environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1999.105225.x
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  • 3
    Electronic Resource
    Electronic Resource
    Isolation and characterization of multiple forms of maize leaf sucrose-phosphate synthase (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 70 (1987), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sucrose-phosphate synthase SPS; (EC 2.4.1.14) from maize (Zea mays L. cv. Pioneer 3184) leaves was partially purified and kinetically characterized. Maize SPS was activated by glucose-6-phosphate (G-6-P) due to an increase in Vmax and a decrease in the Km for UDP-glucose. The UDP-glucose saturation profile was biphasic; thus two Km values for UDP-glucose were calculated. Inhibition by inorganic phosphate was observed only in the presence of G-6-P. Chromatography of partially purified maize leaf extracts on hydroxyapatite resolved two forms of SPS activity, which differed in their affinity for UDP-glucose and in the degree of activation by G-6-P. SPS was partially purified from maize leaves that were harvested in the light and in the dark. The light enzyme had a higher specific activity than the enzyme isolated from dark harvested leaves, and this difference persisted during enzyme purification. The apparent molecular weight (Stokes radius) of the light enzyme was 547 kDa, which was greater than that of the dark enzyme (457 kDa). Light and dark SPS differed in their affinities for UDP-glucose in the absence G-6-P. Both the light and the dark SPS were activated by G-6-P; the Km for UDP-glucose of the light enzyme was lowered by G-6-P, while the Km for UDP-glucose for the dark enzyme remained unchanged. These results suggest that light activation involves a conformational change that results in differences in maximum velocity, substrate affinities and regulation by metabolites. Chromatography of either the light or dark SPS on hydroxyapatite yielded two peaks of enzyme activity, suggesting that the occurrence of the two activity peaks was not due to an interconversion of the light and dark forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1987.tb04320.x
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  • 4
    Electronic Resource
    Electronic Resource
    Control of galactosyl-sugar metabolism in relation to rate of germination (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 59 (1983), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The storage sugars stachyose and raffinose (galactosyl derivatives of sucrose) are metabolized early during germination of soybean [Glycine max (L.) Merr.] seeds. The activities of four enzymes involved in the catabolism of these sugars were monitored in soybean cotyledons and embryonic axes during a 7-day germination period. An increase in enzyme activities correlated with a decline in galactosyl sugars. In embryonic axes, uridine diphosphate glucose (UDPglc)-hexose-l-P uridyltransferase (EC 2.7.7.12), an enzyme characteristic of the Leloir pathway, predominated over galactose-1-phosphate uridyltransferase (EC 2.7.7.10), an enzyme characteristic of the pyrophosphorylase pathway; whereas in cotyledons, the situation was reversed. There were differences between two cultivars. Ransom and Amsoy, in the levels of UDPglc-4-epimerase (EC 5.1.3.2); but not in glucose-1-phosphate uridyltransferase (EC 2 7.7.9). An accelerated aging treatment had a significant effect on the development of embryonic axes, as measured by dry weight. In vitro aging of seeds reduced the rate of growth and resulted in higher levels of galactose-containing sugars and significantly lower levels of UDPglc-hexose-l-P uridyltransferase. Thus, reduced development may be related to inability to mobilize or utilize stored carbon reserves. However, it has not been proved that the reduced enzyme activity is responsible for the effects of accelerated aging on growth and sugar metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1983.tb04219.x
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  • 5
    Electronic Resource
    Electronic Resource
    Diurnal changes in sucrose phosphate synthase activity in leaves (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 64 (1985), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Studies were conducted to identify and compare diurnal changes in sucrose phosphate synthase (EC 2.4.1.14) activity in leaves of different species, and the effect of nitrogen nutrition on the rhythm in soybean [Glycine max (L). Merr] leaves. In recently expanded corn (Zea mays L.) leaves, a single peak of enzyme activity was observed at the beginning of the photoperiod. A similar pattern was observed in older corn leaves, but activities (leaf fresh weight basis) were lower. In recently expanded pea (Pisum sativum L.) and soybean leaves, two peaks of sucrose phosphate synthase activity were observed over a 24-h light:dark period, one at the beginning and one at the end of the photoperiod. A similar pattern was observed in older soybean leaves, but activities were generally lower and the amplitude of the changes was reduced. In a separate experiment, soybean plants were grown in the greenhouse with either 2 or 10 mM nitrate. The high-N plants had higher rates of photosynthesis and translocation, and greater activities of sucrose phosphate synthase in leaf extracts, compared to low-N plants. Over both experiments with soybeans, changes in sucrose phosphate synthase activity during the photoperiod were closely aligned with changes in translocation rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1985.tb01216.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of CO2 enrichment on photosynthesis and photosynthate partitioning in soybean (Glycine max) leaves (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 62 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The short-term and long-term effects of CO, enrichment on certain aspects of photosynthesis and leaf carbohydrate metabolism were studied with soybean [Glycine max (L.) Merr.] plants. In general, both long-term and short-term CO2 enrichment (300 ppm CO2 above ambient) of soybean plants resulted in increased rates of photosynthesis (per unit leaf area) and starch accumulation. Leaf sucrose concentrations were increased slightly, but the rate of assimilate export and activity of sucrose phosphate synthase (EC 2.4.1.14) were usually not increased. Plant N-status affected the response of vegetative soybean ‘Ransom’ plants to short-term CO, enrichment. When plants were N-stressed (2 mM NO3- supplied), CO2 enrichment resulted in increased rates of both starch accumulation and export. As N-supply was increased, partitioning of carbon into starch in CO2-enriched atmospheres increased at the expense of assimilate export. When plants were grown with high-N (20 mM NO3), the rate of assimilate export from CO2-enriched leaves was reduced below the rate observed with plants maintained at ambient CO2. The reduction in export rate was associated with decreased activities of sucrose phosphate synthase in leaf extracts. The activity of sucrose phosphate synthase in leaf extracts was closely associated with partitioning of carbon between starch and sucrose in leaves, and with the rate of assimilate export.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb05929.x
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  • 7
    Electronic Resource
    Electronic Resource
    An Evaluation of Some Parameters Required for the Enzymatic Isolation of Cells and Protoplasts with CO2 Fixation Capacity from C3 and C4 Grasses (1975)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 35 (1975), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Variable factors affecting the enzymatic isolation of mesophyll protoplasts from Triticum aestivum (wheat), a C3 gras, and mesophyll protoplasts and bundle sheath strands from Digitaria sanguinalis (crabgrass), a C4 grass, have been examined with respect to yields and also photosynthetic capacity after isolation. Preparations with high yields and high photosynthetic capacity were obtained when small transverse leaf segments were incubated in enzyme medium in the light at 30°C, without mechanical shaking and without prior vacuum infiltration. Best results were obtained with an enzyme medium that included 0.5 M sorbitol, 1 mM MgCl2, 1 mM KH2PO4, 2% cellulase and 0.1% pectinase at pH 5.5. In gerneral, leaf age and leaf segment size were important factors, with highest yields and photosynthetic capacities obtained from young leaves cut into segments less than 0.8 mm. To facilitate the cutting of such small segments, a mechanical leaf cutter is described that uniformly (± 0.05 mm) cuts leaf tissue into transverse segments of variable size (0.4–2 mm). Isolations that required more than roughly 4 h gave poor yields with reduced photosynthetic capacity; however, using the optimum conditions described, functional preparations could be roughly 2 h. High rates of light dependent CO2 fixation by the C4 mesophyll protoplasts required the addition of pyruvate and low levels of oxalacetate, while isolated bundle sheath strands and C3 mesophyll protoplasts supported CO2 fixation without added substrates. Rates of CO2 fixation by isolated wheat protoplasts generally exceeded the reported rates of whole leaf photosynthesis. Wheat mesophyll protoplasts and crabgrass bundle sheath strands were stable when stored at 4°C while C4 mesophyll protoplasts were stable when stored at 25°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1975.tb03894.x
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  • 8
    Electronic Resource
    Electronic Resource
    Decarboxylation of malate by isolated bundle-sheath cells of certain plants having the C4-dicarboxylic acid cycle of photosynthesis (1973)
    Springer
    Planta 113 (1973), S. 53-66 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Bundle-sheath cells isolated by the grinding and filtration procedure of Edwards and Black (1971b) from species of plants having the C4-dicarboxylic acid pathway of photosynthesis were tested for the decarboxylation of malate from the C4-carboxyl position. The bundle-sheath cells, which showed high malic enzyme activity in extracts, decarboxylated 4[14C]malate at rates sufficient to be involved in photosynthesis. The malate decarboxylation is dependent on the addition of magnesium or manganese and NADP+. The activity was increased by raising the temperature from 30 to 50°. The evidence supports the idea that malate may be a carboxyl donor to the reductive pentose-phosphate cycle in bundle-sheath cells in certain C4-dicarboxylic acid pathway plants such as Zea mays L., Sorghum bicolor L., and Digitaria sanguinalis (L.) Scop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385189
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  • 9
    Electronic Resource
    Electronic Resource
    Glycerol permeability of rye leaf protoplasts as affected by temperature and electroporation (1997)
    Springer
    Plant cell, tissue and organ culture 50 (1997), S. 215-219 
    Details
    ISSN: 1573-5044
    Keywords: activation energy ; electroporation ; glycerol ; permeability ; Secale cereale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The permeability of rye leaf protoplasts to glycerol was determined using 1,3-14C glycerol and liquid scintillation spectrometry. Estimates were 1.0×10−8 m s−1 at 0°C and 4.1×10−8 m s−1 at 22 and 31°C. The activation energy for glycerol permeability was 32.8 kJ/mol. The effect of electroporation on glycerol uptake was also explored. Treatments were performed with a field strength of 100 V/cm and an exponential decay constant of 5.8 ms. At 22 °C, electroporation affected the rate and extent of glycerol permeation, causing an increase in the intercept of the glycerol uptake curve and a decrease in the slope. Electroporation had no significant effect on glycerol uptake when performed at 0°C, when the cells were electroporated at 0°C then warmed to 31 °C, or when the cells were electroporated at 22 °C then cooled to 0°C. The results at 22°C were consistent with an influx of glycerol during electroporation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005972908734
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