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1.
A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species   总被引:39,自引:0,他引:39  
Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.Abbreviations RuP2 ribulose bisphosphate - PGA 3-phosphoglycerate - C=p(CO2) partial pressure of CO2 - O=p(O2) partial pressure of O2 - PCR photosynthetic carbon reduction - PCO photorespiratory carbon oxidation  相似文献   

2.
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.Abbreviations and symbols C1 intercellular CO2 pressure - PGA 3-phosphoglyceric acid - RuBP ribulose-1,5-bisphosphate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase  相似文献   

3.
Susanne von Caemmerer 《Planta》1989,178(4):463-474
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 () at an O2 pressure of 200 mbar, a curvilinear response of 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.Abbreviations and symbols PEP phosphoenolpyruvate - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) - RuBP ribulose-1,5-bisphosphate - p(CO2) partial pressure of CO2 - p(O2) partial pressure of O2. See also p. 471  相似文献   

4.
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.Abbreviations PEP phosphoenolpyruvate - PGA glycerate-3-phosphate - p i intercellular CO2 pressure - RuBP ribulose-1,5-bisphosphate - triose-P triose phosphates  相似文献   

5.
Phosphorus-deficient spinach plants were grown by transferring them to nutrient solutions without PO4. Photosynthetic rates were measured at a range of intercellular CO2 partial pressures from 50–500 bar and then the leaves were freeze-clamped in situ to measure ribulose bisphosphate carboxylase (Rubisco) activity and metabolite concentrations. Compared with control leaves, deficient leaves had significantly lower photosynthetic rates, percentage activation of Rubisco, and amounts of ribulose bisphosphate and 3-phosphoglycerate at all CO2 partial pressures. After feeding 10 mM PO4 to the petioles of detached deficient leaves, all these measurements increased within 2 hours. At atmospheric CO2 partial pressure the photosynthetic rate was stimulated in 19 mbar O2 compared with 200 mbar. At higher CO2 partial pressures this stimulation was less but the percentage stimulation in deficient leaves was no different from controls in either CO2 partial pressure. It was concluded that phosphorus deficiency affects both Rubisco activity and the capacity for ribulose bisphosphate regeneration, and possible causes are discussed.Abbreviations A CO2 assimilation rate - Ci intercellular CO2 partial pressure - PGA 3-phosphoglycerate - RuP2 ribulose 1,5-bisphosphate - Rubisco RuP2 carboxylase/oxygenase  相似文献   

6.
Evans JR 《Plant physiology》1983,72(2):297-302
Wheat (Triticum aestivum L. cv Yecora 70) plants were grown with various concentrations of nitrate nitrogen available to the roots. Sampling of flag leaves began after they had reached full expansion and continued throughout senescence. Rates of gas exchange, ribulose-1,5-bisphosphate (RuP2) carboxylase activity, and the amounts of chlorophyll, soluble protein, nitrogen, and phosphorus were determined for each flag leaf. Rate of CO2 assimilation was uniquely related to total leaf nitrogen irrespective of nutrient treatment, season, and leaf age. Assimilation rate increased with leaf nitrogen, but the slope of the relationship declined markedly when leaf nitrogen exceeded 125 millimoles nitrogen per square meter. Chlorophyll content and RuP2 carboxylase activity were approximately proportional to leaf nitrogen content. As leaves aged, RuP2 carboxylase activity and calculated Hill activity declined in parallel. With normal ambient partial pressure of CO2, the intercellular partial pressure of CO2 was always such that rate of assimilation appeared colimited by RuP2 carboxylation and RuP2 regeneration capacity.

The initial slope of rate of CO2 assimilation against intercellular partial pressure of CO2 varied nonlinearly with carboxylase activity. It is suggested that this was due to a finite conductance to CO2 diffusion in the wall and liquid phase which causes a drop in CO2 partial pressure between the intercellular spaces and the site of carboxylation. A double reciprocal plot was used to obtain an estimate of the transfer conductance.

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7.
The aim of this work was to examine the effect of abrupt changes in temperature in the range 5 to 30°C upon the rate of photosynthetic carbon assimilation in leaves of barley (Hordeum vulgare L.). Measurement of the CO2-assimilation rate in relation to the intercellular partial pressure of CO2 at different temperatures and O2 concentrations and at saturating irradiance showed that as the temperature was decreased photosynthesis was saturated at progressively lower CO2 partial pressures and that the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rate became more abrupt. Feeding of orthophosphate to leaves resulted in an increased rate of CO2 assimilation at lower temperatures at around ambient or higher CO2 partial pressures both in 20% O2 and in 2% O2 and it removed the abruptness in the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rates. Phosphate feeding tended to inhibit carbon assimilation at higher temperatures. The response of carbon assimilation to temperature was altered by feeding orthophosphate, by changing the concentrations of CO2 or of O2 or by leaving plants in the dark at 4°C for several hours. Similarly, the response of carbon assimilation to phosphate feeding or to changes in 2% O2 was altered by leaving the plants in the dark at 4°C. The mechanism of limitation of photosynthesis by an abrupt lowering of temperature is discussed in the light of the results.Abbreviations A rate of CO2 assimilation - P i intercellular partial pressure of CO2 - RuBP ribulose-1,5-bisphosphate  相似文献   

8.
Measurement of the changes in CO2 uptake by single leaves following the abrupt onset of darkness were made on sugarbeets (Beta vulgaris L.) and (Phaseolus vulgaris L.) The shape of the CO2 dark response curve was analyzed with respect to the reaction kinetics of CO2, RuP2 and RuP2 carboxylase. It was concluded that the net uptake of CO2 in the dark from a 1% O2 atmosphere can be approximately related to the pool size of the RuP2 substrate in the chloroplasts of C3 plants. This information was combined with CO2 levels and decay rates of the response curves to infer changes in carboxylase activity. Preliminary data are presented showing the relative concentration changes in RuP2 as light intensity decreases and as water stress increases. The method may prove useful in studies of plant response to environmental stresses.  相似文献   

9.
The effect of increased salinity on photosynthesis was studied in leaves of Plantago maritima L. that developed while plants were at low and high NaCl levels. In leaves that developed while plants were grown at 50 mol·m-3, exposure to 200 and 350 mol·m-3 NaCl resulted in reductions in net CO2 assimilation and stomatal conductance. The decline in CO2 assimilation in plants at 200 and 350 mol·m-3 NaCl occurred almost exclusively at high intercellular CO2 concentrations. The initial slope of the CO2 assimilation-intercellular CO2 (A-C i) curve, determined after salinity was increased, was identical or very similar to that measured initially. In contrast to the reductions observed in CO2 assimilation, there were no significant differences in O2 evolution rates measured at 5% CO2 among leaves from plants exposed to higher salinity and plants remaining at low salinity.Leaves that developed while plants were at increased salinity levels also had significantly lower net CO2 assimilation rates than plants remaining at 50 mol·m-3 NaCl. The lower CO2 assimilation rates in plants grown at 200 and 350 mol·m-3 NaCl were a result of reduced stomatal conductance and low intercellular CO2 concentration. There were no significant differences among treatments for O2 evolution rates measured at high CO2 levels. The increased stomatal limitation of photosynthesis was confirmed by measurements of the 13C/12C composition of leaf tissue. Water-use efficiency was increased in the plants grown at high salinity.Abbreviations and symbols A net CO2 assimilation rate - C a ambient CO2 concentration - C i intercellular CO2 concentration - 13C isotopic ratio (13C/12C) expressed relative to a standard - RuBP ribulose-1,5-bisphosphate  相似文献   

10.
A few species of Cymbopogon and Vetiveria are potentially important tropical grasses producing essential oils. In the present study, we report on the leaf anatomy and photosynthetic carbon assimilation in five species of Cymbopogon and Vetiveria zizanioides. Kranz-type leaf anatomy with a centrifugal distribution of chloroplasts and exclusive localization of starch in the bundle sheath cells were common among the test plants. Besides the Kranz leaf anatomy, these grasses displayed other typical C4 characteristics including a low (0–5 µl/l) CO2 compensation point, lack of light saturation of CO2 uptake at high photon flux densities, high temperature (35°C) optimum of net photosynthesis, high rates of net photosynthesis (55–67 mg CO2 dm-2 leaf area h-1), little or no response of net photosynthesis to atmospheric levels of O2 and high leaf 13C/12C ratios. The biochemical studies with 14CO2 indicated that the leaves of the above plant species synthesize predominantly malate during short term (5 s) photosynthesis. In pulse-chase experiments it was shown that the synthesis of 3-phosphoglycerate proceeds at the expense of malate, the major first formed product of photosynthesis in these plant species.  相似文献   

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