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  • 1
    Electronic Resource
    Electronic Resource
    The drelationship between CO2-assimilation rate, Rubisco carbamylation and Rubisco activase content in activase-deficient transgenic tobacco suggests a simple model of activase action (1996)
    Springer
    Planta 198 (1996), S. 604-613 
    Details
    ISSN: 1432-2048
    Keywords: Activase (Rubisco) ; Nicotiana (transgenic) ; Photosynthesis (C3) ; Ribulose-1,5-bisphosphate carboxylase/oxygenase ; Transgenic tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transgenic tobacco (Nicotiana tabacum L. cv. W38) plants with an antisense gene directed against the mRNA of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) activase were used to examine the relationship between CO2-assimilation rate, Rubisco carbamylation and activase content. Plants used were those members of the r1 progeny of a primary transformant with two independent T-DNA inserts that could be grown without CO2 supplementation. These plants had from 〈 1% to 20% of the activase content of control plants. Severe suppression of activase to amounts below 5% of those present in the controls was required before reductions in CO2-assimilation rate and Rubisco carbamylation were observed, indicating that one activase tetramer is able to service as many as 200 Rubisco hexadecamers and maintain wild-type carbamylation levels in vivo. The reduction in CO2-assimilation rate was correlated with the reduction in Rubisco carbamylation. The anti-activase plants had similar ribulose-1,5-bisphosphate pool sizes but reduced 3-phosphoglycerate pool sizes compared to those of control plants. Stomatal conductance was not affected by reduced activase content or CO2-assimilation rate. A mathematical model of activase action is used to explain the observed hyperbolic dependence of Rubisco carbamylation on activase content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262648
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  • 2
    Electronic Resource
    Electronic Resource
    The relationship between steady-state gas exchange of bean leaves and the levels of carbon-reduction-cycle intermediates (1984)
    Springer
    Planta 160 (1984), S. 305-313 
    Details
    ISSN: 1432-2048
    Keywords: Phaseolus (gas exchange) ; Photosynthesis (intermediates) ; Ribulose-1,5-bisphosphate carboxylase-oxygenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the gas-exchange characteristics of attached leaves of Phaseolus vulgaris L. and the pool sizes of several carbon-reduction-cycle intermediates was examined. After determining the rate of CO2 assimilation at known intercellular CO2 pressure, O2 pressure and light, the leaf was rapidly killed (〈0.1 s) and the levels of ribulose-1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA), fructose-1,6-bisphosphate, fructose-6-phosphate, glucose-6-phosphate, glyceraldehyde-3-phosphate, and dihydroxyacetone phosphate were measured. In 210 mbar O2, photosynthesis appeared RuBP-saturated at low CO2 pressure and RuBP-limited at high CO2 pressure. In 21 mbar (2%) O2, the level of RuBP always appeared saturating. Very high levels of PGA and other phosphate-containing compounds were found with some conditions, especially under low oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393411
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  • 3
    Electronic Resource
    Electronic Resource
    A model of photosynthetic CO2 assimilation and carbon-isotope discrimination in leaves of certain C3−C4 intermediates (1989)
    Springer
    Planta 178 (1989), S. 463-474 
    Details
    ISSN: 1432-2048
    Keywords: C3−C4 intermediates ; Carbon isotope discrimination ; Photosynthesis (model)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A model of leaf, photosynthesis has been developed for C3−C4 intermediate species found in the generaPanicum, Moricandia, Parthenium andMollugo where no functional C4 pathway has been identified. Model assumptions are a functional C3 cycle in both mesophyll and bundle-sheath cells and that glycine formed in the mesophyll, as a consequence of the oxygenase activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39), diffuses to the bundle sheath, where most of the photorespiratory CO2 is released. The model describes the observed gas-exchange characteristics of these C3−C4 intermediates, such as low CO2-compensation points (Γ) at an O2 pressure of 200 mbar, a curvilinear response of Γ to changing O2 pressures, and typical responses of CO2-assimilation rate to intercellular CO2 pressure. The model predicts that bundle-sheath CO2 concentration is highest at low mesophyll CO2 pressures and decreases as mesophyll CO2 pressure increases. A partitioning of 5–15% of the total leaf Rubisco into the bundle-sheath cells and a bundlesheath conductance similar to that proposed for C4 species best mimics the gas-exchange results. The model predicts C3-like carbon-isotope discrimination for photosynthesis at atmospheric levels of CO2, but at low CO2 pressures it predicts a higher discrimination than is typically found during C3 photosynthesis at lower CO2 pressures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00963816
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  • 4
    Electronic Resource
    Electronic Resource
    Short-term carbon-isotope discrimination in C3−C4 intermediate species (1989)
    Springer
    Planta 178 (1989), S. 475-481 
    Details
    ISSN: 1432-2048
    Keywords: C3−C4 intermediates ; Carbon isotope discrimination ; Flaveria ; Panicum ; Photosynthesis (C3−C4)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Short-term discrimination in assimilation of stable isotopes of carbon was measured for leaves of the C3 speciesPhaseolus vulgaris L. cv. Hawkesbury Wonder andFlaveria pringlei Gandoger, the C4 speciesAmaranthus edulis Speg., and the C3−C4 intermediate speciesPanicum milioides Nees ex. Trin,Flaveria floridana Johnson, andFlaveria anomala B.L. Robinson. Discriminations in the C3 and C4 species were similar to those expected from theoretical considerations. When ambient CO2 pressure was 330 μbar the mean discriminations in the C3 species andPanicum milioides were similar, whereas the mean discriminations inF. floridana andF. anomala were less than discrimination in C3 species andPanicum milioides. When ambient CO2 pressure was 100 μbar the mean discriminations inPanicum milioides andF. anomala were greater, and that inF. floridana was less, than that inPhaseolus vulgaris. We conclude that the pattern of discrimination inPanicum milioides is consistent with the presence of a glycine shuttle; inF. floridana andF. anomala, discrimination is consistent with the presence of a C4 pathway coupled with the operation of a glycine shuttle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00963817
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  • 5
    Electronic Resource
    Electronic Resource
    The kinetics of ribulose-1,5-bisphosphate carboxylase/oxygenase in vivo inferred from measurements of photosynthesis in leaves of transgenic tobacco (1994)
    Springer
    Planta 195 (1994), S. 88-97 
    Details
    ISSN: 1432-2048
    Keywords: Gas exchange ; Nicotiana ; Photosynthesis (C3) ; Ribulose-1,5-bisphosphate carboxylase/oxygenase kinetics ; Transgenic tobacco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transgenic tobacco (Nicotiana tabacum L. cv. W38) with an antisense gene directed against the mRNA of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit was used to determine the kinetic properties of Rubisco in vivo. The leaves of these plants contained only 34% as much Rubisco as those of the wild type, but other photosynthetic components were not significantly affected. Consequently, the rate of CO2 assimilation by the antisense plants was limited by Rubisco activity over a wide range of CO2 partial pressures. Unlike in the wild-type leaves, where the rate of regeneration of ribulose bisphosphate limited CO2 assimilation at intercellular partial pressures above 400 ubar, photosynthesis in the leaves of the antisense plants responded hyperbolically to CO2, allowing the kinetic parameters of Rubisco in vivo to be inferred. We calculated a maximal catalytic turnover rate, kcat, of 3.5+0.2 mol CO2·(mol sites)−1·s−1 at 25° C in vivo. By comparison, we measured a value of 2.9 mol CO2·(mol sites)−1·−1 in vitro with leaf extracts. To estimate the Michaelis-Menten constants for CO2 and O2, the rate of CO2 assimilation was measured at 25° C at different intercellular partial pressures of CO2 and O2. These measurements were combined with carbon-isotope analysis (13C/12C) of CO2 in the air passing over the leaf to estimate the conductance for transfer of CO2 from the substomatal cavities to the sites of carboxylation (0.3 mol·m−2·s−1·bar−1) and thus the partial pressure of CO2 at the sites of carboxylation. The calculated Michaelis-Menten constants for CO2 and O2 were 259 ±57 μbar (8.6±1.9μM) and 179 mbar (226 μM), respectively, and the effective Michaelis-Menten constant for CO2 in 200 mbar O2 was 549 μbar (18.3 μM). From measurements of the photocompensation point (Γ* = 38.6 ubar) we estimated Rubisco's relative specificity for CO2, as opposed to O2 to be 97.5 in vivo. These values were dependent on the size of the estimated CO2-transfer conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206296
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  • 6
    Electronic Resource
    Electronic Resource
    The relationship between contents of photosynthetic metabolites and the rate of photosynthetic carbon assimilation in leaves of Amaranthus edulis L. (1988)
    Springer
    Planta 174 (1988), S. 253-262 
    Details
    ISSN: 1432-2048
    Keywords: Amaranthus (gas exchange) ; C4 plants ; Photosynthesis (metabolites) ; Zea (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the gas-exchange characteristics of attached leaves of Amaranthus edulis L. and the contents of photosynthetic intermediates was examined in response to changing irradiance and intercellular partial pressure of CO2. After determination of the rate of CO2 assimilation at known intercellular CO2 pressure and irradiance, the leaf was freeze-clamped and the contents of ribulose-1,5-bisphosphate, glycerate-3-phosphate, fructose-1,6-bisphosphate, glucose-6-phosphate, fructose-6-phosphate, triose phosphates, phosphoenolpyruvate, pyruvate, oxaloacetate, aspartate, alanine, malate and glutamate were measured. A comparison between the sizes of metabolite pools and theoretical calculations of metabolite gradients required for transport between the mesophyll and the bundle-sheath cells showed that aspartate, alanine, glycerate-3-phosphate and triose phosphates were present in sufficient quantities to support transport by diffusion, whereas pyruvate and oxaloacetate were not likely to contribute appreciably to the flux of carbon between the two cell types. The amounts of ribulose-1,5-bisphosphate were high at low intercellular partial pressures of CO2, and fell rapidly as the CO2-assimilation rate increased with increasing intercellular partial pressures of CO2, indicating that bundle-sheath CO2 concentrations fell at low intercellular partial pressures of CO2. In contrast, the amount of phosphoenolpyruvate and of C4-cycle intermediates declined at low intercellular partial pressures of CO2. This behaviour is discussed in relation to the co-ordination of carbon assimilation between the Calvin and C4 cycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00394779
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  • 7
    Electronic Resource
    Electronic Resource
    Regulation of photosynthetic carbon assimilation in leaves of C3–C4 intermediate species of Moricandia and Flaveria (1994)
    Springer
    Planta 192 (1994), S. 232-238 
    Details
    ISSN: 1432-2048
    Keywords: C3–C4 intermediate plants ; Flaveria (gas exchange) ; Moricandia (gas exchange) ; Photosynthesis (metabolites)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the gas-exchange characteristics, the contents of photosynthetic intermediates and the quantum yield of photosystem II was examined at different intercellular partial pressures of CO2 (p i) in attached leaves of Moricandia arvensis L. (D.C.) and Flaveria floridana J.R. Johnson (both C3–C4 intermediate plants) and, for comparison, in F. pringlei Gandoger (a C3 plant) and in F. bidentis (a C4 plant). Both C3–C4 intermediate species had pools of phosphoenolpyruvate, pyruvate, alanine and aspartate intermediate to those of the C3 and C4 species examined. Moricandia arvensis had large pools of glycine at low p i, consistent with the operation of a glycine shuttle from mesophyll to bundle-sheath cells. It also had a high pool of triose-phosphate at ambient partial pressures of CO2, indicating that a glycerate-3-phosphate/triose-phosphate shuttle could operate in this species. This was not the case in F. floridana. A decline in the ribulose-1,5-bisphosphate and triose-phosphate pool in M. arvensis, and a rise in the pools of glycerate-3-phosphate and pyruvate in F. floridana, at low p i, show different patterns of metabolic regulation in M. arvensis and F. floridana at low p i in comparison to C3 and C4 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194457
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  • 8
    Electronic Resource
    Electronic Resource
    Some relationships between contents of photosynthetic intermediates and the rate of photosynthetic carbon assimilation in leaves of Zea mays L. (1989)
    Springer
    Planta 178 (1989), S. 258-266 
    Details
    ISSN: 1432-2048
    Keywords: C4 plant ; Photosynthesis (metabolites) ; Zea (gas exchange)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the gas-exchange characteristics of attached leaves of Zea mays L. and the contents of photosynthetic intermediates was examined at different intercellular partial pressure of CO2 and at different irradiances at a constant intercellular partial pressure of CO2. (i) The behaviour of the pools of the C4-cycle intermediates, phosphoenolpyruvate and pyruvate, provides evidence for light regulation of their consumption. However, light regulation of phosphoenolpyruvate carboxylase does not influence the assimilation rate at limiting intercellular partial pressures of CO2. (ii) A close correlation between the pools of phosphoenolpyruvate and glycerate-3-phosphate exists under many different flux conditions, consistent with the notion that the pools of C4 and C3 cycles are connected via the interconversion of glycerate-3-phosphate and phosphoenolpyruvate. (iii) The ratio of triose-phosphate to glycerate-3-phosphate is used as an indicator of the availability of ATP and NADPH. Changes of this ratio with CO2 and with irradiance are compared with results obtained in C3 leaves and indicate that the mechanism of regulation of carbon assimilation by light in leaves of C4 plants may differ from that in C3 plants. (iv) The behaviour of the ribulose-1,5-bisphosphate pool with CO2 and irradiance is contrasted with the behaviour of these pools measured in leaves of C3 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393202
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  • 9
    Electronic Resource
    Electronic Resource
    Regulation of photosynthetic carbon assimilation in leaves of C3–C4 intermediate species ofMoricandia andFlaveria (1994)
    Springer
    Planta 192 (1994), S. 232-238 
    Details
    ISSN: 1432-2048
    Keywords: C3–C4 intermediate plants ; Flaveria (gas exchange) ; Moricandia (gas exchange) ; Photosynthesis (metabolites)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between the gas-exchange characteristics, the contents of photosynthetic intermediates and the quantum yield of photosystem II was examined at different intercellular partial pressures of CO2 (p i) in attached leaves ofMoricandia arvensis L. (D.C.) andFlaveria floridana J.R. Johnson (both C3–C4 intermediate plants) and, for comparison, inF. pringlei Gandoger (a C3 plant) and inF. bidentis (a C4 plant). Both C3–C4 intermediate species had pools of phosphoenolpyruvate, pyruvate, alanine and aspartate intermediate to those of the C3 and C4 species examined.Moricandia arvensis had large pools of glycine at lowp i, consistent with the operation of a glycine shuttle from mesophyll to bundle-sheath cells. It also had a high pool of triose-phosphate at ambient partial pressures of CO2, indicating that a glycerate-3-phosphate/triose-phosphate shuttle could operate in this species. This was not the case inF. floridana. A decline in the ribulose-1,5-bisphosphate and triose-phosphate pool inM. arvensis, and a rise in the pools of glycerate-3-phosphate and pyruvate inF. floridana, at lowp i, show different patterns of metabolic regulation inM. arvensis andF. floridana at lowp i in comparison to C3 and C4 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01089039
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  • 10
    Electronic Resource
    Electronic Resource
    Specific reduction of chloroplast carbonic anhydrase activity by antisense RNA in transgenic tobacco plants has a minor effect on photosynthetic CO2 assimilation (1994)
    Springer
    Planta 193 (1994), S. 331-340 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201810
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