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1.
The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (rubisco) activity in Phaseolus vulgaris was studied under moderate CO 2 and high light, conditions in which photosynthesis in C 3 plants can be insensitive to changes in O 2 partial pressure. Steady state RuBP concentrations were higher, the calculated rate of RuBP use was lower and the activation state of rubisco was lower in low O 2 relative to values observed in normal O 2. It is suggested that the reduced activity of rubisco observed here is related to feedback effects which occur when the rate of net CO 2 assimilation approaches the maximum capacity for starch and sucrose synthesis (triose phosphate utilization). The activation state of rubisco was independent of O 2 partial pressure when light or CO 2 was limiting for photosynthesis. Reduced activity of rubisco was also observed at limiting light. However, in this species light dependent changes in the concentration of an inhibitor of rubisco controlled the apparent Vmax of rubisco in low light while changes in the CO 2-Mg 2+ dependent activation of rubisco controlled the apparent Vmax in high light. 相似文献
2.
The effects of aminoacetonitrile (a competitive inhibitor of glycine oxidation) on net photosynthesis, glycolate pathway intermediates, and ribulose-1,5-bisphosphate (RuBP) levels have been investigated at different O 2 and CO 2 concentrations with soybean ( Glycine max)[L] Merr. cv Pioneer 1677) leaf discs floated on 25 millimolar aminoacetonitrile (AAN) for 50 minutes prior to assay. At 2% O2 and 200 or 330 microliters per liter CO2, the inhibitor had no effect on the rate of net photosynthesis and RuBP levels when compared with the control levels. At 11% to 60% O2, AAN caused a decrease in net photosynthesis in addition to the inhibition by O2. This extra inhibition ranged from 22% to 59% depending on the O2 and CO2 concentrations. The levels of RuBP, however, were 1.3 to 2.7 times higher than in the control plants at the same O2 concentrations. At 40% O2 and 200 microliters per liter CO2, the inhibitor caused a 6-fold increase in glycine and more than 2-fold increase in glyoxylate levels, whereas those of glycolate decreased by approximately one-half. The decrease in net photosynthesis observed with AAN is not the result of the depletion of the RuBP pool due to the lack of recycling of carbon from the glycolate pathway to the Calvin cycle. The higher levels of RuBP caused by AAN in photorespiratory conditions, suggest that RuBP carboxylase was inhibited. Glyoxylate could be a possible candidate for the inhibition of the enzyme but what is known so far about its inhibitory properties in vitro may not fit the existing in vivo conditions. An alternative explanation for the inhibition is proposed. 相似文献
3.
The rate of CO 2 fixation by ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) following addition of ribulose 1,5-bisphosphate (RuBP) to fully activated enzyme, declined with first-order kinetics, resulting in 50% loss of rubisco activity after 10 to 12 minutes. This in vitro decline in rubisco activity, termed fall-over, was prevented if purified rubisco activase protein and ATP were added, allowing linear rates of CO 2 fixation for up to 20 minutes. Rubisco activase could also stimulate rubisco activity if added after fallover had occurred. Gel filtration of the RuBP-rubisco complex to remove unbound RuBP allowed full activation of the enzyme, but the inhibition of activated rubisco during fallover was only partially reversed by gel filtration. Addition of alkaline phosphatase completely restored rubisco activity following fallover. The results suggest that fallover is not caused by binding of RuBP to decarbamylated enzyme, but results from binding of a phosphorylated inhibitor to the active site of rubisco. The inhibitor may be a contaminant in preparations of RuBP or may be formed on the active site but is apparently removed from the enzyme in the presence of the rubisco activase protein. 相似文献
4.
Changes in photosynthesis and the ribulose 1,5-bisphosphate (RuBP) carboxylase level were examined in the 12th leaf blades of rice ( Oryza sativa L.) grown under different N levels. Photosynthesis was determined using an open infrared gas analysis system. The level of RuBP carboxylase was measured by rocket immunoelectrophoresis. These changes were followed with respect to changes in the activities of RuBP carboxylase, ribulose 5-phosphate kinase, NADP-glyceraldehyde 3-phosphate dehydrogenase, and 3-phosphoglyceric acid kinase. RuBP carboxylase activity was highly correlated with the net rate of photosynthesis (r = 0.968). Although high correlations between the activities of other enzymes and photosynthesis were also found, the activity per leaf of RuBP carboxylase was much lower than those of other enzymes throughout the leaf life. The specific activity of RuBP carboxylase on a milligram of the enzyme protein basis remained fairly constant (1.16 ± 0.07 micromoles of CO2 per minute per milligram at 25°C) throughout the experimental period. Kinetic parameters related to CO2 fixation were examined using the purified carboxylase. The Km(CO2) and Vmax values were 12 micromolar and 1.45 micromoles of CO2 per minute per milligram, respectively (pH 8.2 and 25°C). The in vitro specific activity calculated at the atomospheric CO2 level from the parameters was comparable to the in situ true photosynthetic rate per milligram of the carboxylase throughout the leaf life. The results indicated that the level of RuBP carboxylase protein can be a limiting factor in photosynthesis throughout the life span of the leaf. 相似文献
5.
Early physiological effects of developing Mn toxicity in young leaves of burley tobacco ( Nicotiana tabacum L. cv KY 14) were examined in glass-house/water cultured plants grown at high (summer) and low (winter) photon flux. Following transfer of plants to solutions containing 1 millimolar Mn 2+, sequential samplings were made at various times for the following 9 days, during which Mn accumulation by leaves increased rapidly from ~70 on day 0 to ~1700 and ~5000 microgram per gram dry matter after 1 and 9 days, respectively. In plants grown at high photon flux, net photosynthesis declined by ~20 and ~60% after 1 and 9 days, respectively, and the onset of this decline preceded appearance (after 3 to 4 days) of visible foliar symptoms of Mn toxicity. Intercellular CO 2 concentrations and rates of transpiration were not significantly affected; moreover, the activity of the Hill and photosystem I and II partial reactions of chloroplasts remained constant despite ultimate development of severe necrosis. Though the activity of latent or activated polyphenol oxidase increased in parallel with Mn accumulation, neither leaf respiration nor the activity of catalase [EC 1.11.1.6] and peroxidase [EC 1.10.1.7] were greatly affected. These effects from Mn toxicity could not be explained by any changes in protein or chlorophyll abundance. Additionally, they were not a consequence of Mn induced Fe deficiency. Therefore, inhibition of net photosynthesis and enhancement of polyphenol oxidase activity are early indicators of excess Mn accumulation in tobacco leaves. These changes, as well as leaf visual symptoms of Mn toxicity, were less severe in plants cultured and treated at low photon flux even though the rates of leaf Mn accumulation at high and low photon flux were essentially equivalent. 相似文献
6.
The enzyme-catalyzed activation of ribulosebisphosphate carboxylase/oxygenase (rubisco) was investigated in an illuminated reconstituted system containing thylakoid membranes, rubisco, ribulosebisphosphate (RuBP), MgCl 2, carbonic anhydrase, catalase, the artificial electron acceptor pyocyanine, and partially purified rubisco activase. Optimal conditions for light-induced rubisco activation were found to include 100 micrograms per milliliter rubisco, 300 micrograms per milliliter rubisco activase, 3 millimolar RuBP, and 6 millimolar free Mg 2+ at pH 8.2. The half-time for rubisco activation was 2 minutes, and was 4 minutes for rubisco deactivation. The rate of rubisco deactivation was identical in the presence and absence of activase. The Kact(CO 2) of rubisco activation in the reconstituted system was 4 micromolar CO 2, compared to a Kact(CO 2) of 25 to 30 micromolar CO 2 for the previously reported spontaneous CO 2/Mg 2+ activation mechanism. The activation process characterized here explains the high degree of rubisco activation at the physiological concentrations of 10 micromolar CO 2 and 2 to 4 millimolar RuBP found in intact leaves, conditions which lead to almost complete deactivation of rubisco in vitro. 相似文献
7.
The light and CO 2 response of (a) photosynthesis, (b) the activation state and total catalytic efficiency ( kcat) of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) the pool sizes of ribulose 1,5-bisphosphate, (RuBP), ATP, and ADP were studied in the C 3 annuals Chenopodium album and Phaseolus vulgaris at 25°C. The initial slope of the photosynthetic CO 2 response curve was dependent on light intensity at reduced light levels only (less than 450 micromoles per square meter per second in C. album and below 200 micromoles per square meter per second in P. vulgaris). Modeled simulations indicated that the initial slope of the CO 2 response of photosynthesis exhibited light dependency when the rate of RuBP regeneration limited photosynthesis, but not when rubisco capacity limited photosynthesis. Measured observations closely matched modeled simulations. The activation state of rubisco was measured at three light intensities in C. album (1750, 550, and 150 micromoles per square meter per second) and at intercellular CO 2 partial pressures ( C1) between the CO 2 compensation point and 500 microbars. Above a C1 of 120 microbars, the activation state of rubisco was light dependent. At light intensities of 550 and 1750 micromoles per square meter per second, it was also dependent on C1, decreasing as the C1 was elevated above 120 microbars at 550 micromoles per square meter per second and above 300 microbars at 1750 micromoles per square meter per second. The pool size of RuBP was independent of C1 only under conditions when the activation state of rubisco was dependent on C1. Otherwise, RuBP pool sizes increased as C1 was reduced. ATP pools in C. album tended to increase as C1 was reduced. In P. vulgaris, decreasing C1 at a subsaturating light intensity of 190 micromoles per square meter per second increased the activation state of rubisco but had little effect on the kcat. These results support modelled simulations of the rubisco response to light and CO 2, where rubisco is assumed to be down-regulated when photosynthesis is limited by the rate of RuBP regeneration. 相似文献
8.
A model of the regulation of the activity of ribulose-1,5-bisphosphate carboxylase, electron transport, and the rate of orthophosphate regeneration by starch and sucrose synthesis in response to changes in light intensity and partial pressures of CO 2 and O 2 is presented. The key assumption behind the model is that nonlimiting processes of photosynthesis are regulated to balance the capacity of limiting processes. Thus, at CO 2 partial pressures below ambient, when a limitation on photosynthesis by the capacity of rubisco is postulated, the activities of electron transport and phosphate regeneration are down-regulated in order that the rate of RuBP regeneration matches the rate of RuBP consumption by rubisco. Similarly, at subsaturating light intensity or elevated CO 2, when electron transport or Pi regeneration may limit photosynthesis, the activity of rubisco is downregulated to balance the limitation in the rate of RuBP regeneration. Comparisons with published data demonstrate a general consistency between modelled predictions and measured results. 相似文献
9.
As part of an extensive analysis of the factors regulating photosynthesis in Agropyron smithii Rydb., a C 3 grass, we have examined the response of leaf gas exchange and ribulose-1,5-bisphosphate (RuBP) carboxylase activity to temperature. Emphasis was placed on elucidating the specific processes which regulate the temperature response pattern. The inhibitory effects of above-optimal temperatures on net CO 2 uptake were fully reversible up to 40°C. Below 40°C, temperature inhibition was primarily due to O 2 inhibition of photosynthesis, which reached a maximum of 65% at 45°C. The response of stomatal conductance to temperature did not appear to have a significant role in determining the overall temperature response of photosynthesis. The intracellular conductance to CO 2 increased over the entire experimental temperature range, having a Q 10 of 1.2 to 1.4. Increases in the apparent Michaelis constant ( Kc) for RuBP carboxylase were observed in both in vitro and in vivo assays. The Q 10 values for the maximum velocity ( Vmax) of CO 2 fixation by RuBP carboxylase in vivo was lower (1.3-1.6) than those calculated from in vitro assays (1.8-2.2). The results suggest that temperature-dependent changes in enzyme capacity may have a role in above-optimum temperature limitations below 40°C. At leaf temperatures above 40°C, decreases in photosynthetic capacity were partially dependent on temperature-induced irreversible reductions in the quantum yield for CO 2 uptake. 相似文献
10.
The mechanisms regulating transient photosynthesis by soybean ( Glycine max) leaves were examined by comparing photosynthetic rates and carbon reduction cycle enzyme activities under flashing (saturating 1 s lightflecks separated by low photon flux density (PFD) periods of different durations) and continuous PFD. At the same mean PFD, the mean photosynthetic rates were reduced under flashing as compared to continuous light. However, as the duration of the low PFD period lengthened, the CO 2 assimilation attributable to a lightfleck increased. This enhanced lightfleck CO 2 assimilation was accounted for by a greater postillumination CO 2 fixation occurring after the lightfleck. The induction state of photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), fructose 1,6-bisphosphatase (FBPase) and ribulose 5-phosphate kinase (Ru5P kinase) activities all responded similarly and were all lower under flashing as compared to constant PFD of the same integrated mean value. However, the fast phase of induction and FBPase and Ru5P kinase activities were reduced more than were the slow phase of induction and rubisco activity. This was consistent with the role of the former enzymes in the fast induction component that limited RuBP regeneration. Competition for reducing power between carbon metabolism and thioredoxin-mediated enzyme activation may have resulted in lower enzyme activation states and hence lower induction states under flashing than continuous PFD, especially at low lightfleck frequencies (low mean PFD).Abbreviations FBPase
fructose 1,6-bisphosphatase (EC 3.1.3.11)
- LUE
lightfleck use efficiency
- P-glycerate
3-phosphoglycerate
- PICF
post-illumination CO 2 fixation
- Ru5P kinase
ribulose 5-phosphate kinase (EC 2.7.1.19)
- RuBP
ribulose 1,5-bisphosphate
- rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39)
- SBpase
sedoheptulose 1,7-bisphosphatase (EC 3.1.3.37) 相似文献
11.
Background and Aims Plants growing under elevated atmospheric CO 2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO 2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase.Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4–5 years to either ambient (AC; 385 µmol mol −1) or elevated (EC; 700 µmol mol −1) CO 2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques.Key Results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO 2 assimilation ( Amax) and a decline in photorespiration ( RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima ( Topt) of Amax, Rubisco carboxylation rates ( VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO 2 concentrations. Higher values of Topt at elevated CO 2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry.Conclusions Elevated CO 2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO 2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO 2 is unlikely. The hypothesis that long-term cultivation at elevated CO 2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary. 相似文献
12.
Growth at an elevated CO 2 concentration resulted in an enhanced capacity for soybean ( Glycine max L. Merr. cv Bragg) leaflet photosynthesis. Plants were grown from seed in outdoor controlled-environment chambers under natural solar irradiance. Photosynthetic rates, measured during the seed filling stage, were up to 150% greater with leaflets grown at 660 compared to 330 microliters of CO 2 per liter when measured across a range of intercellular CO 2 concentrations and irradiance. Soybean plants grown at elevated CO 2 concentrations had heavier pod weights per plant, 44% heavier with 660 compared to 330 microliters of CO 2 per liter grown plants, and also greater specific leaf weights. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) activity showed no response (mean activity of 96 micromoles of CO 2 per square meter per second expressed on a leaflet area basis) to short-term (~1 hour) exposures to a range of CO 2 concentrations (110-880 microliters per liter), nor was a response of activity (mean activity of 1.01 micromoles of CO 2 per minute per milligram of protein) to growth CO 2 concentration (160-990 microliters per liter) observed. The amount of rubisco protein was constant, as growth CO 2 concentration was varied, and averaged 55% of the total leaflet soluble protein. Although CO 2 is required for activation of rubisco, results indicated that within the range of CO 2 concentrations used (110-990 microliters per liter), rubisco activity in soybean leaflets, in the light, was not regulated by CO 2. 相似文献
13.
Abstract. The global uptake of CO 2 in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco), which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO 2 and O 2 are substrates; CO 2 also activates the enzyme. In C 3 plants, rubisco has a low catalytic activity, operates below its K m (CO 2), and is inhibited by O 2. Consequently, increases in the CO 2/O 2 ratio stimulate C 3 photosynthesis and inhibit photorespiration. CO 2 enrichment usually enhances the productivity of C 3 plants, but the effect is marginal in C 4 species. It also causes acclimation in various ways: anatomically, morphologically, physiologically or biochemically. So, CO 2 exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO 2 enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/P i-regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/P i regeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/P iregeneration capacities, or chloroplast disruption. As exemplified by field-grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO 2 enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C 4 and CAM plants have genetically adapted to a decline in the external CO 2/O 2 ratio, by the development of mechanisms to concentrate CO 2 internally; thus circumventing O 2 inhibition of rubisco. Here rubisco affinity for CO 2 is less, but its catalytic activity is greater, a situation compatible with a high-CO 2 internal environment. In aquatic autotrophs, the CO 2 concentrating mechanisms acclimate to the external CO 2, being suppressed at high-CO 2. It is unclear, whether a doubling in atmospheric CO 2 will be sufficient to cause a de-adaptive trend in the rubisco kinetics of future C 3 plants, producing higher catalytic activities. 相似文献
14.
Trees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO 2, we grew Pinus taeda L. seedlings for three growing seasons in open-top chambers continuously maintained at either ambient or ambient + 30 Pa CO 2. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO 2 partial pressure ( A-Ci) curves. Maximum Rubisco activity (Vc max) and ribulose 1,5-bisphosphate regeneration capacity mediated by electron transport (J max) and phosphate regeneration (PiRC) were calculated from A-Ci curves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment. Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g ?1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO 2 seedlings, elevated CO 2 increased light-saturated net photosynthetic rates 60–110% during the summer, but < 30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO 2 suggests a strong effect of leaf temperature. During the third growing season, elevated CO 2 reduced Rubisco activity 30% relative to ambient CO 2 seedlings, nearly completely balancing Rubisco and RuBP-regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO 2. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO 2 are likely to occur in natural systems. 相似文献
15.
Since activation of ribulose bisphosphate carboxylase (rubisco) by rubisco activase is sensitive to ATP and ADP in vitro, we aimed to test the correlation between ATP level and rubisco activation state in intact leaves of Spinacia oleracea L. in response to changes in irradiance and after feeding the electron acceptor methyl viologen. Leaves were exposed to various irradiances for 45 minutes at atmospheric partial pressures of CO 2 and O 2. After measuring the rate of CO 2 assimilation, leaves were freeze-clamped in situ and the punched discs assayed for rubisco activity, and amounts of ribulose bisphosphate (RuBP), ATP, and ADP. The photosynthetic rate and the activation state of rubisco increased with increasing irradiance but the levels of RuBP, ATP, and ADP were not greatly affected. Methyl viologen fed leaves under low irradiance had rubisco activation states of 93% compared to 51% in control leaves. The ATP content of the leaves was also significantly higher and the ratio of ATP to ADP was 4.1 in methyl viologen fed leaves compared to 2.2 in control leaves. From these results and other published results we conclude that a correlation between ATP level and rubisco activation can be observed in intact leaves, but that during changes in irradiance some additional factors are involved in regulating rubisco activation. 相似文献
16.
The requirements for activation of ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) were investigated in leaves of Arabidopsis wild-type and a mutant incapable of light activating rubisco in vivo. Upon illumination with saturating light intensities, the activation state of rubisco increased 2-fold in the wild-type and decreased in the mutant. Activation of fructose 1,6-bisphosphate phosphatase was unaffected by the mutation. Under low light, rubisco deactivated in both the wild-type and the mutant. Deactivation of rubisco in the mutant under high and low light led to the accumulation of high concentrations of ribulose 1,5-bisphosphate. Inhibiting photosynthesis with methyl viologen prevented ribulose 1,5-bisphosphate accumulation but was ineffective in restoring rubisco activation to the mutant. Net photosynthesis and the rubisco activation level were closely correlated and saturated at a lower light intensity in the mutant than in wild-type. At CO 2 concentrations between 100 and 2000 microliters per liter, the activation state was a function of the CO 2 concentration in the dark but was independent of CO 2 concentration in the light. High CO 2 concentration (1%) suppressed activation in the wild-type and deactivation in the mutant. These results support the concept that rubisco activation in vivo is not a spontaneous process but is catalyzed by a specific protein. The absence of this protein, rubisco activase, is responsible for the altered characteristics of rubisco activation in the mutant. 相似文献
17.
The rates of CO 2 exchange and 14CO 2 incorporation in the light and dark and the activities of several photosynthetic, photorespiratory, and respiratory enzymes of soybean ( Glycine max [L.] Merr. cv. Wye) reproductive structures were determined at weekly intervals from anthesis to pod maturity. At all stages of pod development soybean reproductive structures were found to be incapable of net photosynthesis under the experimental conditions employed, but capable of gross photosynthesis and light-induced 14CO 2 uptake. Consistent with the lack of net photosynthesis throughout the development of the reproductive structure, the maximum in vitro activity of ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) in pod tissue was only 3% of that in leaf extracts when expressed on a fresh weight basis. We concluded that the major role of the reproductive structure of the soybean with respect to photosynthetic carbon metabolism is the reassimilation of its respiratory CO 2. 相似文献
18.
Earlier work (SE Taylor, N Terry [1984] Plant Physiol 75: 82-86) has shown that the rate of photosynthesis may be colimited by photosynthetic electron transport capacity, even at low intercellular CO 2 concentrations. Here we monitored leaf metabolites diurnally and the activities of key Calvin cycle enzymes in the leaves of three treatment groups of sugar beet ( Beta vulgaris L.) plants representing three different in vivo photochemical capacities, i.e. Fe-sufficient (control) plants, moderately Fe-deficient, and severely Fe-deficient plants. The results show that the decrease in photosynthesis with Fe deficiency mediated reduction in photochemical capacity was through a reduction in ribulose 1,5-bisphosphate (RuBP) regeneration and not through a decrease in ribulose 1,5-bisphosphate carboxylase/oxygenase activity. Based on measurements of ATP and NADPH and triose phosphate/3-phosphoglycerate ratios in leaves, there was little evidence that photosynthesis and RuBP regeneration in Fe-deficient leaves were limited directly by the supply of ATP and NADPH. It appeared more likely that photochemical capacity influenced RuBP regeneration through modulation of enzymes in the photosynthetic carbon reduction cycle between fructose-6-phosphate and RuBP; in particular, the initial activity of ribulose-5-phosphate kinase was strongly diminished by Fe deficiency. Starch and sucrose levels changed independently of one another to some extent during the diurnal period (both increasing in the day and decreasing at night) but the average rates of starch or sucrose accumulation over the light period were each proportional to photochemical capacity and photosynthetic rate. 相似文献
19.
The effect of long-term (weeks to months) CO 2 enhancement on (a) the gas-exchange characteristics, (b) the content and activation state of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) leaf nitrogen, chlorophyll, and dry weight per area were studied in five C 3 species ( Chenopodium album, Phaseolus vulgaris, Solanum tuberosum, Solanum melongena, and Brassica oleracea) grown at CO 2 partial pressures of 300 or 900 to 1000 microbars. Long-term exposure to elevated CO 2 affected the CO 2 response of photosynthesis in one of three ways: (a) the initial slope of the CO 2 response was unaffected, but the photosynthetic rate at high CO 2 increased ( S. tuberosum); (b) the initial slope decreased but the CO 2-saturated rate of photosynthesis was little affected ( C. album, P. vulgaris); (c) both the initial slope and the CO 2-saturated rate of photosynthesis decreased ( B. oleracea, S. melongena). In all five species, growth at high CO 2 increased the extent to which photosynthesis was stimulated following a decrease in the partial pressure of O 2 or an increase in measurement CO 2 above 600 microbars. This stimulation indicates that a limitation on photosynthesis by the capacity to regenerate orthophosphate was reduced or absent after acclimation to high CO 2. Leaf nitrogen per area either increased ( S. tuberosum, S. melongena) or was little changed by CO 2 enhancement. The content of rubisco was lower in only two of the five species, yet its activation state was 19% to 48% lower in all five species following long-term exposure to high CO 2. These results indicate that during growth in CO 2-enriched air, leaf rubisco content remains in excess of that required to support the observed photosynthetic rates. 相似文献
20.
Ribulose-1,5-bisphosphate (RuBP) pool size was determined at regular intervals during the growing season to understand the effects of tropospheric ozone concentrations, elevated atmospheric carbon dioxide concentrations and their interactions on the photosynthetic limitation by RuBP regeneration. Soybean ( Glycine max [L.] Merr. cv. Essex) was grown from seed to maturity in open-top field chambers in charcoal-filtered air (CF) either without (22 nmol O 3 mol ?1) or with added O 3 (83 nmol mol ?1) at ambient (AA, 369 μmol CO 2 mol ?1) or elevated CO 2 (710 μmol mol ?1). The RuBP pool size generally declined with plant age in all treatments when expressed on a unit leaf area and in all treatments but CF-AA when expressed per unit ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) binding site. Although O 3 in ambient CO 2 generally reduced the RuBP pool per unit leaf area, it did not change the RuBP pool per unit Rubisco binding site. Elevated CO 2, in CF or O 3-fumigated air, generally had no significant effect on RuBP pool size, thus mitigating the negative O 3 effect. The RuBP pools were below 2 mol mol ?1 binding site in all treatments for most of the season, indicating limiting RuBP regeneration capacity. These low RuBP pools resulted in increased RuBP regeneration via faster RuBP turnover, but only in CF air and during vegetative and flowering stages at elevated CO 2. Also, the low RuBP pool sizes did not always reflect RuBP consumption rates or the RuBP regeneration limitation relative to potential carboxylation (%RuBP). Rather, %RuBP increased linearly with decrease in the RuBP pool turnover time. These data suggest that amelioration of damage from O 3 by elevated atmospheric CO 2 to the RuBP regeneration may be in response to changes in the Rubisco carboxylation. 相似文献
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