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  • 1
    ISSN: 1432-2048
    Keywords: Antisense RNA ; Carbon dioxide assimilation ; Carbonic anhydrase ; Nicotiana (transgenic plants)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract As an approach to understanding the physiological role of chloroplast carbonic anhydrase (CA), this study reports on the production and preliminary physiological characterisation of transgenic tobacco (Nicotiana tabacum L.) plants where chloroplast CA levels have been specifically suppressed with an antisense construct directed against chloroplast CA mRNA. Primary transformants with CA levels as low as 2% of wild-type levels were recovered, together with intermediate plants with CA activities of about 20–50% of wild-type levels. Plants with even the lowest CA levels were not morphologically distinct from the wild-type plants. Segregation analysis of the low-CA character in plants grown from T1 selfed seed indicated that at least one of the low-CA plants appears to have two active inserts and that at least two of the intermediate-CA plants have one active insert. Analysis of CO2 gas exchange of a group of low-CA plants with around 2% levels of CA indicated that this large reduction in chloroplastic CA did not appear to cause a measurable alteration in net CO2 fixation at 350 μbar CO2 and an irradiance of 1000 μmol quanta·m−2·s−1. In addition, no significant differences in Rubisco activity, chlorophyll content, dry weight per unit leaf area, stomatal conductance or the ratio of intercellular to ambient CO2 partial pressure could be detected. However, the carbon isotope compositions of leaf dry matter were significantly lower (0.85%o) for low-CA plants than for wildtype plants. This corresponds to a 15-μbar reduction in the CO2 partial pressure at the sites of carboxylation. The difference, which was confirmed by concurrent measurement of discrimination with gas exchange, would reduce the CO2 assimilation rate by 4.4%, a difference that could not be readily determined by gas-exchange techniques given the inherent variability found in tobacco. A 98% reduction in CA activity dramatically reduced the 18O discrimination in CO2 passing over the leaf, consistent with a marked reduction in the ratio of hydrations to carboxylations. We conclude that a reduction in chloroplastic CA activity of two orders of magnitude does not produce a major limitation on photosynthesis at atmospheric CO2 levels, but that normal activities of the enzyme appear to play a role in facilitated transfer of CO2 within the chloroplast, producing a marginal improvement in the efficiency of photosynthesis in C3 plants.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 371 (1994), S. 566-566 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Several studies have yielded disc-repant estimates for the change in carbon storage from the Last Glacial Maximum (LGM) to pre-industrial times which range widely from 0 to 4-1,350 Pg (1 Pg=1015 g) (refs 1-6). Two recent advances now permit a more rigorous evaluation of the available ...
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During terrestrial photosynthesis, heavier C18O16O molecules diffuse into leaves more slowly than do the lighter CI6O2. Fur-ther, within the chloroplasts, carbonic anhydrase catalyses the exchange of oxygen atoms between CO2 and the water there. The 18O/16O ratio of chloroplast water is enriched ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 396 (1998), S. 619-620 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Whether Amazonia is a carbon-dioxide source or sink has a significant effect on estimates of the global carbon budget. On an annual basis, El Niño, and its influence on precipitation in the region, seems to be a controlling factor. What is happening to all of the extra carbon dioxide ...
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature biotechnology 18 (2000), S. 600-601 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Current technologies for the remediation of polluted environments that rely on nonbiological, physical-chemical approaches are often cost prohibitive. Microorganisms that can convert toxic organic compounds to harmless products, often carbon dioxide and water, have been increasingly used as a ...
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 99 (1994), S. 201-215 
    ISSN: 1432-1939
    Keywords: Carbon isotope discrimination ; Global carbon cycle ; Stomata ; Photosynthesi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Estimates of the extent of the discrimination against13CO2 during photosynthesis (ΔA) on a global basis were made using gridded data sets of temperature, precipitation, elevation, humidity and vegetation type. Stomatal responses to leaf-to-air vapour mole fraction difference (D, leaf-to-air vapour pressure difference divided by atmospheric pressure) were first determined by a literature review and by assuming that stomatal behaviour results in the optimisation of plant water use in relation to carbon gain. Using monthly time steps, modelled stomatal responses toD were used to calculate the ratio of stomatal cavity to ambient CO2 mole fractions and then, in association with leaf internal conductances, to calculate ΔA. Weighted according to gross primary productivity (GPP, annual net CO2 asimilation per unit ground area), estimated ΔA for C3 biomes ranged from 12.9‰ for xerophytic woods and shrub to 19.6‰ for cool/cold deciduous forest, with an average value from C3 plants of 17.8‰. This is slightly less than the commonly used values of 18–20‰. For C4 plants the average modelled discrimination was 3.6‰, again slightly less than would be calculated from C4 plant dry matter carbon isotopic composition (yielding around 5‰). From our model we estimate that, on a global basis, 21% of GPP is by C4 plants and for the terrestrial biosphere as a whole we calculate an average isotope discrimination during photosynthesis of 14.8‰. There are large variations in ΔA across the globe, the largest of which are associated with the precence or absence of C4 plants. Due to longitudinal variations in ΔA, there are problems in using latitudinally averaged terrestrial carbon isotope discriminations to calculate the ratio of net oceanic to net terrestrial carbon fluxes.
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  • 7
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: 〈list xml:id="l1" style="custom"〉1 Eddy covariance measurements of CO2 flux, based on four and six week campaigns in Rondôdnia, Brazil, have been used in conjunction with a model to scale up data to a whole year, and thus estimate the carbon balance of the tropical forest ecosystem, and the changes in carbon balance expected from small interannual variations in climatological conditions.2 One possible source of error in this estimation arises from the difficulty in measuring fluxes under stably stratified meteorological conditions, such as occur frequently at night. Flux may be ‘lost’ because of low velocity advection, caused by nocturnal radiative cooling at sites on raised ground. Such effects may be detected by plotting the net ecosystem flux of CO2, Feco is a function of wind speed. If flux is ‘lost’ then Feco is expected to decline with wind speed. In the present data set, this did not occur, and Feco was similar to the nocturnal flux estimated independently from chamber measurements.3 The model suggests that in 1992/3, the Gross Primary Productivity (GPP) was 203.3 mol C m−2 y−1 and ecosystem respiration was 194.8 mol C m−2 y−1, giving an ecosystem carbon balance of 8.5 mol C m−2 y−1, equivalent to a sink of 1.0 ton C ha−1 y−1. However, the sign and magnitude of this figure is very sensitive to temperature, because of the strong influence of temperature on respiration.4 The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO2.
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  • 8
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: 〈list xml:id="l1" style="custom"〉1 Carbon dioxide and water vapour fluxes were measured for 55 days by eddy covariance over an undisturbed tropical rain forest in Rondonia, Brazil. Profiles of CO2 inside the canopy were also measured.2 During the night, CO2 concentration frequently built up to 500 ppm throughout the canopy as a result of low rates of exchange with the atmosphere. In the early morning hours, ventilation of the canopy occurred.3 Ecosystem gas exchange was calculated from a knowledge of fluxes above the canopy and changes of CO2 stored inside the canopy. Typically, uptake by the canopy was 15 μmol m−2 s−1 in bright sunlight and dark respiration was 6-7 μmol m−2 s−1 The quantum requirement at low irradiance was: 40 mol photons per mol of CO2.4 Bulk stomatal conductance of the ecosystem was maximal in the early morning (0.4-1.0 mol m−2 s−1) and declined over the course of the day as leaf-to-air vapour pressure difference increased.
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  • 9
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: To investigate the consequences of land use on carbon and energy exchanges between the ecosystem and atmosphere, we measured CO2 and water vapour fluxes over an introduced Brachiara brizantha pasture located in the Cerrado region of Central Brazil. Measurements using eddy covariance technique were carried out in field campaigns during the wet and dry seasons. Midday CO2 net ecosystem exchange rates during the wet season were −40 μmol m−2 s−1, which is more than twice the rate found in the dry season (−15 μmol m−2 s−1). This was observed despite similar magnitudes of irradiance, air and soil temperatures. During the wet season, inferred rates of canopy photosynthesis did not show any tendency to saturate at high solar radiation levels, with rates of around 50 μmol m−2 s−1 being observed at the maximum incoming photon flux densities of 2200 μmol m−2 s−1. This contrasted strongly to the dry period when light saturation occurred with 1500 μmol m−2 s−1 and with maximum canopy photosynthetic rates of only 20 μmol m−2 s−1. Both canopy photosynthetic rates and night-time ecosystem CO2 efflux rates were much greater than has been observed for cerrado native vegetation in both the wet and dry seasons. Indeed, observed CO2 exchange rates were also much greater than has previously been reported for C4 pastures in the tropics. The high rates in the wet season may have been attributable, at least in part, to the pasture not being grazed. Higher than expected net rates of carbon acquisition during the dry season may also have been attributable to some early rain events. Nevertheless, the present study demonstrates that well-managed, productive tropical pastures can attain ecosystem gas exchange rates equivalent to fertilized C4 crops growing in the temperate zone.
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  • 10
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaf gas exchange, water relations and ion content were measured on two-year-old Valencia orange (Citrus sinensis [L.] Osbeck), Washington Navel orange (C. sinensis) and Marsh grapefruit (C. parodisi Macfad) scions budded to either Trifoliata (Poncirus infoliata [L] Raf) or Cleopatra mandarin (C. reticuLua Blanco) rootstoeks. Trees were watered with dülute nutrient solution containing either 0 or 50 mM NaCl for 77 days. Leaf chloride concentrations (cell sap basis) were higher in all scions budded on “Trifoliata but sodium levels were lower than in equivalent foliage budded on Cleopatra mandarin rootstock. Foliar salt levels also varied according to scion. Leaves of Marsh grapefruit had higher levels of both sodium and chloride than leaves of either Valencia orange or Washington Navel orange on both rootstocks. Accumulation of sodium and chloride in salinised leaves caused a reduction in leaf osmotic potential of 0.2–1.4 MPa. and leaf water potential declined by as much as 0.5 MPa. Turgor pressure in salinised leaves was thus maintained at or above the control level. Osmotic potentials determined by psychrometry compared with pressure-volume curves were taken to imply that some accumulation of sodium or chloride in the apoplast of salinised leaves may have occurred.Despite turgor maintenance both co2 assimilation and stomatal conductance were reduced by salinity. Following onset of leaf response to salinisation, gas exchange was impaired to a greater extent in scions budded to Cleopatra mandarin compared to those on Trifoliata. Amongst those scions. leaves of salt-treated Marsh grapefruit showed greater reductions in gas exchange than Valencia orange or Washington Navel orange budded on either rootstock. Increased sensitivity of 1Marsh grapefruit was correlated with a higher foliar sodium and chloride content in this scion. Scion differences in sensitivity of leaf gas exchange to solute concentration were independent of rootstock and appeared unrelated to leaf prolinebetaine concentrations. This implies an inherent difference between scion species with respect to salt tolerance, rather than variation in their capacity to acquire that type of compatible solute.In terms of rootstock effects, all scions proved more sensitive to salinity when budded to Cleopatra mandarin compared with Trifoliata. That response was attributed to a disproportionately higher concentration of leaf sodium in scions on Cleopatra mandarin.
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