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  • 1
  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Scandinavian journal of immunology 11 (1980), S. 0 
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Hybrid cells have been recovered from selective culture medium after fusion of concanavalin-A-activated human lymphocytes with an AKR mouse thymoma (BW 5147). After 6 months of culture twenty-seven out of forty-nine clones still contained human chromosomes. Human chromosome 6 was present in 89% of these clones, and human X in 70%. Clones from one hybrid line contained several human chromosomes. In twelve of the clones carrying human chromosomes, the rosetting with sheep Erythrocytes (SRBC) was 3 times as high as In the BW 5147 cell line. All these clones Carried the human chromosome 6, and eight clones contained the human X chromosome as well. In some of these clones (25%) chromosome 6 was the only human one present. In the two clones In which human chromosome 6 was completely missing, the resetting with SRBC was at the level of the BW line. We therefore suggest that genes on human chromosome 6 are responsible for rosetting with SRBC.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Quantum (photon) yields for CO2 uptake on an absorbed photon fluence rate (PFR) basis (φa) were determined for a number of diploid and tetraploid species under a range of experimental conditions. Little variation in φa was found either between species or across ploidy levels, which suggests that there are no intrinsic differences in the kinetics of CO2 fixation. Variations in photosynthetic rate or quantum yield expressed on an incident PFR basis (φj) were found to be largely due to differences in leaf absorptance. On this basis these results do not support the biochemical evidence showing ploidy-related differences in the Km (CO2) of ribulose -1,5-bisphosphate carboxylase/oxygenase. However, there are obvious difficulties in relating in vitro enzyme kinetic data to in vivo studies and these problems are discussed.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Photosynthesis by aquatic plants based on the supply of CO2 from air-equilibrated solutions may be limited by the low diffusion coefficient of CO2 in water. For plants in which the transport of CO2 from the bulk medium is by diffusion, and the initial carboxylation uses RUBISCO, CO2 supply can be increased by growth in habitats with fast water flow over the surface (reducing unstirred layer thickness), or with heterotrophically-augmented CO2 levels, including the direct use of sediment CO2. Many aquatic plants using RUBISCO as their initial carboxylase counter the limitations on CO2 supply via the operation of biophysical CO2 concentrating mechanisms which are based on active transport of HCO−3, CO2 or H+ at the plasmalemma, and use bulk-phase HCO−3 or CO2 as the C source. A final group of aquatic plants use biochemical CO2 concentrating mechanisms based on auxiliary carboxylation by PEPc: C4-like and Crassulacean Acid Metabolism–like processes are involved. These various mechanisms for increasing CO2 supply to RUBISCO also help to offset the low specific reaction rate of aquatic plant RUBISCOs at low [CO2] and low [CO2]: [CO2]. In addition to overcoming restrictions on CO2 supply, the various methods of increasing inorganic C availability may also be important in alleviating shortages of nitrogen or photons.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Photon requirements for O2-evolution in red (λ=680nm) light (Фr) were measured for six C3 species, one C3-like, C3–C4 intermediate species, and three C4 species, including examples of NADP-malic enzyme and PEP-carboxykinase C4 sub-groups. Variation in Фr within the C3 species was small with a mean value of 7.96 ±0.12 mol photon mol−1 O2, whereas the mean value for the C4 species was 12.27± 1.53 mol photon mol−1 O2, with the lowest value, 9.24 ±0.13 mol photon mol−1 O2, for the PEP-carboxykinase C4 species Spartina townsendii. The C3–C4 intermediate species Panicum milioides had a value of 9.05 ±0.29 mol photon mol−1 O2, approximately 1 mol photon mol−1 O2 greater than the C3 species. The possibility that this extra cost is due to PEP-carboxylase-dependent recycling of CO2 is discussed. No correlation was found between Фr and chlorophyll content or leaf absorptance. Based on white (ФW) and red light measurements of the photon requirement, values in red light were approximately 20% higher than white-light estimates. These results are discussed with reference to accepted mechanisms of energy transduction in thylakoid membranes (Z-scheme), expected inefficiencies and losses during light-harvesting and electron transport reactions, and the influence of respiratory processes.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: An assessment of the effects of arbuscular mycorrhizal (AM) infection on photosynthesis, carbon (C) allocation, translocation and biomass production of cucumber, grown in sand culture, was made using a previously determined phosphorus (P) supply (0·13 mol m−3 P) which had a significant impact on AM infection. Separation of a direct effect of AM infection from an indirect one due to an enhanced leaf P status was achieved using a comparable non-mycorrhizal treatment (NAM + P) supplemented with extra P (0·19 mol m−3 P). Total leaf P concentration, specific leaf mass, photosynthetic capacity, and incorporation of 14C into non-structural carbohydrate pools were dependent on leaf age. Both maximum and ambient photosynthetic rates were significantly higher in the youngest fully expanded leaves from AM and NAM + P plants which also had the higher leaf P concentrations. There were no differences in the total concentrations of starch, sucrose, raffinose or stachyose in young or old leaves among AM, non-mycorrhizal (NAM) and NAM + P treatments. However, younger leaves of NAM plants showed a shift in 14C-partitioning from stachyose and raffinose synthesis to starch accumulation. Determination of ADP-glucose pyrophosphorylase (AGPase), sucrose synthase and sucrose phosphate synthase enzyme activities revealed that only AGPase activity was correlated with the increased incorporation rate of 14C into starch in young leaves of NAM plants. Although there were significant AM-specific effects on C translocation to the root system, AM plants had similar rate of photosynthesis to NAM + P plants. These results suggest that the increase in photosynthetic rate in leaves of AM-infected cucumber was due to an increased P status, rather than a consequence of a mycorrhizal ‘sink’ for assimilates.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 12 (1989), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Marked increases in growth and nitrogen content were found with Gunnera tinctoria Molina (Mirbel) plants infected (+Nostoc) with the cyanobacterium Nostoc punctiforme L., in comparison to uninfected (—Nostoc) plants and this was attributed to N2-fixation by the phycobiont. Whilst host and symbiont can be grown separately, preliminary data indicates that the host plant is reliant on the cyanobacterium to meet its nitrogen requirements because it has little capacity to assimilate nitrate. Although the maximum light-saturated rate of photosynthesis was higher in the +Nostoc plants, there was no reduction in photosynthetic efficiency under lightlimiting conditions, despite marked differences in plant nitrogen status. Differences in photosynthetic rate were implicated as the major reason for the differences in plant productivity. Stomatal conductance was insensitive to changes in plant nitrogen status and did not parallel the variation in photosynthetic rates. The ecological significance of the largely invariant stomatal response and the consequences of differences in water and nitrogen-use efficiencies between + and —Nostoc plants is discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 10 (1987), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Photon requirements for growth (φg−1) of the diatom Phaeodactylum tricornutum were determined under nutrient-sufficient conditions at two photon flux densities corresponding to light limited and near-saturating conditions for growth. The value of φg−1 based on assimilated carbon was light-dependent and varied from 8.8 to 14.0 mol photon mol C−1 with the minimum value at the lowest photon flux density. These results are lower than might be predicted for microalgal growth based on the Z scheme of photosynthesis. Conversion of these values for carbon fixation to estimates based on oxygen evolution is problematical due to uncertainty over the appropriate assimilatory quotient (Qa= mol O2 mol C−1). Minimum values based on oxygen evolution rates ranged from 6.2 to 7.6 mol photon mol O2−1 using a Qa of 1.41 mol O2 mol C−1 obtained by Myers (1980). These estimates are similar to our previous measurements for photosynthesis and indicate a high efficiency for light energy transforming reactions during growth. The values of (φg−1 obtained in this work indicate a number of inadequacies in our understanding of the energetics of microalgal growth and are inconsistent with our present knowledge of photosynthetic energy coupling in plant cells.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 9 (1986), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Nitrate limited growth of the diatom Phaeodactylum tricornutum in chemostat cultures produced marked changes in biochemical composition and a six-fold reduction in the specific growth rate. This was associated with a reduction in the carbon and chlorophyll a specific light saturated rates, with little effect on light limited photosynthesis. Variations in specific growth rate were quantitatively related to carbon specific net photosynthesis and maximum chlorophyll a specific light saturated rates were positively correlated with cell nitrogen contents. The correlation between nitrogen content and photosynthesis for P. tricornutum and the differential effect of nitrogen supply on the light response curve of photosynthesis is qualitatively and quantitatively similar to published results for terrestrial vascular plants. There was little change in the photon (quantum) yield of photosynthesis which was not significantly different from 0.125mol O2 mol photon-1 the theoretical upper limit based on the Z scheme, even under severe nitrate deficiency. The capacity to maintain a high photon yield under nitrate limitation is discussed in relation to the nitrogen requirements of the stromal and membrane components of the photosynthetic apparatus.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 100 (1989), S. 151-159 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The magnitude of the package effect in five small phytoplankters [Thalassiosira sp., Clone 2601 (an unidentified eucaryote), Nannochloris atomus, Synechococcus ‘Syn’ and Synechococcus WH 7803] was assessed by comparison of the absorption spectra of intact and disrupted cells. The package effect was considerably reduced with reductions in cell size and this was broadly in agreement with theoretical predictions based on Mie theory. However, the quantitative assessment of the package effect is confounded by an inability to assign attenuation (apparent absorption) measurements at λ=750 nm to either scattering or absorption. The magnitude of the apparent absorption at λ=750 nm was greatest with the smallest picoplankton species examined, and was reduced, but not eliminated, after cell disruption. Whilst the apparent absorption at λ=750 nm is commonly thought to be due to residual scattering losses, the available evidence does not exclude the possibility that this may be due in part to absorption by cells or cell constituents and this requires further examination. Although these difficulties are particularly evident with the small picoplankton species, there is no reason to expect that they will not complicate the assessment of the package effect in larger phytoplankton cells.
    Type of Medium: Electronic Resource
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