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  • 1
    Electronic Resource
    Electronic Resource
    Resource Limitation in Plants-An Economic Analogy (1985)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 16 (1985), S. 363-392 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.16.110185.002051
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  • 2
    Electronic Resource
    Electronic Resource
    Oxygen consumption during leaf nitrate assimilation in a C3 and C4 plant: the role of mitochondrial respiration (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Measurements of net fluxes of CO2 and O2 from leaves and chlorophyll a fluorescence were used to determine the role of mitochondrial respiration during nitrate (NO3–) assimilation in both a C3 (wheat) and a C4 (maize) plant. Changes in the assimilatory quotient (net CO2 consumed over net O2 evolved) when the nitrogen source was shifted from NO3– to NH4+ (ΔAQ) provided a measure of shoot NO3– assimilation. According to this measure, elevated CO2 inhibited NO3– assimilation in wheat but not maize. Net O2 exchange under ambient CO2 concentrations increased in wheat plants receiving NO3– instead of NH4+, but gross O2 evolution from the photosynthetic apparatus (JO2) was insensitive to nitrogen source. Therefore, O2 consumption within wheat photosynthetic tissue (ΔΟ2), the difference between JO2 and net O2 exchange, decreased during NO3– assimilation. In maize, NO3– assimilation was insensitive to changes in intercellular CO2 concentration (Ci); nonetheless, ΔΟ2 at low Ci values was significantly higher in NO3–-fed than in NH4+-fed plants. Changes in O2 consumption during NO3– assimilation may involve one or more of the following processes: (a) Mehler ascorbate peroxidase (MAP) reactions; (b) photorespiration; or (c) mitochondrial respiration. The data presented here indicates that in wheat, the last process, mitochondrial respiration, is decreased during NO3– assimilation. In maize, NO3– assimilation appears to stimulate mitochondrial respiration when photosynthetic rates are limiting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01257.x
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  • 3
    Electronic Resource
    Electronic Resource
    The chilling sensitivity of root ammonium influx in a cultivated and wild tomato (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A chilling episode of a few hours damaged root ammonium absorption in a cultivated tomato (Lycopersicon esculentum cv. T-5), but not in a wild congener from high altitudes (Lycopersicon hirsutum LA1778). In the cultivar, ammonium influx was strongly temperature dependent and showed the residual effects of chilling, whereas ammonium efflux was nearly temperature invariant and showed no persistent effects. A 2 h exposure to 5 °C significantly depressed subsequent ammonium absorption at 20 °C, and about 12 h at 20 °C was required for recovery. For both the cultivated and wild species, rerooted cuttings were slightly less sensitive to chilling than seedlings. The relative inhibition (mean ± SE) of ammonium absorption before and after chilling was 58·4 ± 2·5% for the cultivated species and 29·0 ± 9·1% for the wild species. The F1 hybrid between the species showed a relative inhibition of 52·4 ± 3·6%, suggesting that chilling sensitivity may be dominant. In a backcross of the hybrid to L. esculentum, the phenotypic distribution of the relative inhibition of ammonium absorption indicated that this trait is segregating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00254.x
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  • 4
    Electronic Resource
    Electronic Resource
    Ammonium, nitrate, and proton fluxes along the maize root (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Ion-selective microelectrodes were used to measure NH4+, NO3– and H+ fluxes along the primary root of maize seedlings. Plants were exposed to nutrient solutions containing NH4+, NO3– or both ions. Nitrogen fluxes along the root varied substantially among the different treatments. Net NH4+ and NO3– uptake and H+ extrusion were low at the very apex of the root and generally increased in the more basal regions. In the absence of nitrogen or in the presence of NO3– alone, net H+ uptake (and root surface alkalinization) occurred at the root tip (0–1 mm), whereas net H+ extrusion occurred in all other regions. In the presence of NH4+ alone, a dramatic increase in net H+ extrusion was detected in all regions except for the region 6–11 mm from the apex. In contrast, when NO3– alone was supplied, net H+ extrusion was depressed at all locations except for the tip (0–1 mm). When both NH4+ and NO3– were supplied, NO3– uptake was suppressed at all locations while net H+ extrusion was increased relative to NO3– alone. The capacities to absorb NH4+ and NO3– at the tip were similar, as indicated by flux rates when NH4+ or NO3– were supplied as sole sources, but when supplied together, net NO3– uptake was half that of net NH4+ uptake, indicating that NH4+ may satisfy the nitrogen requirements of the poorly vascularized apical tissue in the most energy-efficient way. The high spatial resolution of the measurements enabled us to establish that acidification in the root expansion zone is maintained regardless of nitrogen source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00357.x
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen isotope composition of tomato (Lycopersicon esculentum Mill. cv. T-5) grown under ammonium or nitrate nutrition (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Studies that quantify plant δ15N often assume that fractionation during nitrogen uptake and intra-plant variation in δ15N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetum Mill. cv. T-5) at NH4+ or NO−3 concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole-plant δ15N was not significantly different from source δ15 N for plants grown on either nitrogen form. No intra-plant variation in δ15N was observed for plants grown with NH+4. In contrast. δ15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO−3. The contrasting patterns of intra-plant variation are probably caused by different assimilation patterns. NH+4 is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO−3 assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ15N of NO−3 to become enriched relative to organic nitrogen; the δ15N of NO−3 was 11.1 and 12.9% greater than the δ15N of organic nitrogen in leaves and roots, respectively. Leaf δ15N may therefore be greater than that of roots because the NO−3 available for assimilation in leaves originates from a NO−3 pool that was previously exposed to nitrate assimilation in the root.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00010.x
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  • 6
    Electronic Resource
    Electronic Resource
    Root growth as a function of ammonium and nitrate in the root zone (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We examined the effect of soil NH4+ and NO3− content upon the root systems of field-grown tomatoes, and the influence of constant, low concentrations of NH4+ or NO3− upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH4+ or NO3−; they increased to a maximum in zones having 2μg-N NO3− g−1 soil and 6 μg-N NO3= g−1 soil, but decreased in zones having higher NH4+ or NO3− levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH4+ or NO3−, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO3−. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH4+ and NO3−.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00861.x
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of elevated CO2 and nitrogen nutrition on photosynthesis and nitrate photo-assimilation in maize (Zea mays L.) (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Measurements of CO2 and O2 gas exchange and chlorophyll a fluorescence were used to test the hypothesis that elevated atmospheric CO2 inhibits nitrate (NO3–) photo-assimilation in the C4 plant, maize (Zea mays L.). The assimilatory quotient (AQ), the ratio of net CO2 assimilation to net O2 evolution, decreases as NO3– photo-assimilation increases so that the difference in AQ between the ammonium- and nitrate-fed plants (ΔAQ) provided an in planta estimate of NO3– photo-assimilation. In fully expanded maize leaves, NO3– photo-assimilation was detectable only under high light and was not affected by CO2 treatments. Furthermore, CO2 assimilation and O2 evolution were higher under NO3– than ammonia (NH4+) regardless of CO2 levels. In conclusion, NO3– photo-assimilation in maize primarily occurred at high light when reducing equivalents were presumably not limiting. Nitrate photo-assimilation enhanced C4 photosynthesis, and in contrast to C3 plants, elevated CO2 did not inhibit foliar NO3– photo-assimilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01075.x
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  • 8
    Electronic Resource
    Electronic Resource
    Nitrate photo-assimilation in tomato leaves under short-term exposure to elevated carbon dioxide and low oxygen (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The role of photorespiration in the foliar assimilation of nitrate (NO3–) and carbon dioxide (CO2) was investigated by measuring net CO2 assimilation, net oxygen (O2) evolution, and chlorophyll fluorescence in tomato leaves (Lycopersicon esculentum). The plants were grown under ambient CO2 with ammonium nitrate (NH4NO3) as the nitrogen source, and then exposed to a CO2 concentration of either 360 or 700 µmol mol−1, an O2 concentration of 21 or 2%, and either NO3– or NH4+ as the sole nitrogen source. The elevated CO2 concentration stimulated net CO2 assimilation under 21% O2 for both nitrogen treatments, but not under 2% O2. Under ambient CO2 and O2 conditions (i.e. 360 µmol mol−1 CO2, 21% O2), plants that received NO3– had 11–13% higher rates of net O2 evolution and electron transport rate (estimated from chlorophyll fluorescence) than plants that received NH4+. Differences in net O2 evolution and electron transport rate due to the nitrogen source were not observed at the elevated CO2 concentration for the 21% O2 treatment or at either CO2 level for the 2% O2 treatment. The assimilatory quotient (AQ) from gas exchange, the ratio of net CO2 assimilation to net O2 evolution, indicated more NO3– assimilation under ambient CO2 and O2 conditions than under the other treatments. When the AQ was derived from gross O2 evolution rates estimated from chlorophyll fluorescence, no differences could be detected between the nitrogen treatments. The results suggest that short-term exposure to elevated atmospheric CO2 decreases NO3– assimilation in tomato, and that photorespiration may help to support NO3– assimilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01047.x
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  • 9
    Electronic Resource
    Electronic Resource
    Nitrogen balance for wheat canopies (Triticum aestivum cv. Veery 10) grown under elevated and ambient CO2 concentrations (1998)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We examined the hypothesis that elevated CO2 concentration would increase NO3– absorption and assimilation using intact wheat canopies (Triticum aestivum cv. Veery 10). Nitrate consumption, the sum of plant absorption and nitrogen loss, was continuously monitored for 23 d following germination under two CO2 concentrations (360 and 1000 μmol mol–1 CO2) and two root zone NO3– concentrations (100 and 1000 mmol m3 NO3–). The plants were grown at high density (1780 m–2) in a 28 m3 controlled environment chamber using solution culture techniques. Wheat responded to 1000 μmol mol–1 CO2 by increasing carbon allocation to root biomass production. Elevated CO2 also increased root zone NO3– consumption, but most of this increase did not result in higher biomass nitrogen. Rather, nitrogen loss accounted for the greatest part of the difference in NO3– consumption between the elevated and ambient [CO2] treatments. The total amount of NO3–-N absorbed by roots or the amount of NO3–-N assimilated per unit area did not significantly differ between elevated and ambient [CO2] treatments. Instead, specific leaf organic nitrogen content declined, and NO3– accumulated in canopies growing under 1000 μmol mol–1 CO2. Our results indicated that 1000 μmol mol–1 CO2 diminished NO3– assimilation. If NO3– assimilation were impaired by high [CO2], then this offers an explanation for why organic nitrogen contents are often observed to decline in elevated [CO2] environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00315.x
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  • 10
    Electronic Resource
    Electronic Resource
    Water relations under root chilling in a sensitive and tolerant tomato species (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The shoots of cultivated tomato (Lycopersicon esculentum cv. T5) wilt if their roots are exposed to chilling temperatures of around 5 °C. Under the same treatment, a chilling-tolerant congener (Lycopersicon hirsutum LA 1778) maintains shoot turgor. To determine the physiological basis of this differential response, the effect of chilling on both excised roots and roots of intact plants in pressure chambers were investigated. In excised roots and intact plants, root hydraulic conductance declined with temperature to nearly twice the extent expected from the temperature dependence of the viscosity of water, but the response was similar in both species. The species differed markedly, however, in stomatal behaviour: in L. hirsutum, stomatal conductance declined as root temperatures were lowered, whereas the stomata of L. esculentum remained open until the roots reached 5 °C, and the plants became flaccid and suffered damage. Grafted plants with the shoots of one genotype and roots of another indicated that the differential stomatal behaviour during root chilling has distinct shoot and root components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01200.x
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