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1.
Altered Growth of Transgenic Tobacco Lacking Leaf Cytosolic Pyruvate Kinase   总被引:4,自引:1,他引:3  
Previously, we reported that transformation of tobacco (Nicotiana tabacum L.) with a vector containing a potato cytosolic pyruvate kinase (PKc) cDNA generated two plant lines specifically lacking leaf PKc (PKc−) as a result of co-suppression. PKc deficiency in these primary transformants did not appear to alter plant development, although root growth was not examined. Here we report a striking reduction in root growth of homozygous progeny of both PKc− lines throughout development under moderate (600 μE m−2 s−1) or low (100 μE m−2 s−1) light intensities. When both PKc− lines were cultivated under low light, shoot and flower development were also delayed and leaf indentations were apparent. Leaf PK activity in the transformants was significantly decreased at all time points examined, whereas root activities were unaffected. Polypeptides corresponding to PKc were undetectable on immunoblots of PKc− leaf extracts, except in 6-week-old low-light-grown PKc− plants, in which leaf PKc expression appeared to be greatly reduced. The metabolic implications of the kinetic characteristics of partially purified PKc from wild-type tobacco leaves are discussed. Overall, the results suggest that leaf PKc deficiency leads to a perturbation in source-sink relationships.  相似文献   

2.
Individual leaves of potato (Solanum tuberosum L. W729R), a C3 plant, were subjected to various irradiances (400-700 nm), CO2 levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm−2·sec−1 (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm−2·sec−1. These results contrast with many C3 plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.  相似文献   

3.
C4 photosynthesis allows faster photosynthetic rates and higher water and nitrogen use efficiency than C3 photosynthesis, but at the cost of lower quantum yield due to the energy requirement of its biochemical carbon concentration mechanism. It has also been suspected that its operation may be impaired in low irradiance. To investigate fluxes under moderate and low irradiance, maize (Zea mays) was grown at 550 µmol photons m−2 s−l and 13CO2 pulse-labeling was performed at growth irradiance or several hours after transfer to 160 µmol photons m−2 s−1. Analysis by liquid chromatography/tandem mass spectrometry or gas chromatography/mass spectrometry provided information about pool size and labeling kinetics for 32 metabolites and allowed estimation of flux at many steps in C4 photosynthesis. The results highlighted several sources of inefficiency in low light. These included excess flux at phosphoenolpyruvate carboxylase, restriction of decarboxylation by NADP-malic enzyme, and a shift to increased CO2 incorporation into aspartate, less effective use of metabolite pools to drive intercellular shuttles, and higher relative and absolute rates of photorespiration. The latter provides evidence for a lower bundle sheath CO2 concentration in low irradiance, implying that operation of the CO2 concentration mechanism is impaired in this condition. The analyses also revealed rapid exchange of carbon between the Calvin–Benson cycle and the CO2-concentration shuttle, which allows rapid adjustment of the balance between CO2 concentration and assimilation, and accumulation of large amounts of photorespiratory intermediates in low light that provides a major carbon reservoir to build up C4 metabolite pools when irradiance increases.

Analysis of metabolite pools, sizes, and fluxes reveals that multiple interlocking factors decrease the efficiency of photosynthesis in low irradiance in maize.  相似文献   

4.
Oxidative Damage in Pea Plants Exposed to Water Deficit or Paraquat   总被引:24,自引:0,他引:24       下载免费PDF全文
Enhanced Cl efflux during acidosis in plants is thought to play a role in cytosolic pH (pHc) homeostasis by short-circuiting the current produced by the electrogenic H+ pump, thereby facilitating enhanced H+ efflux from the cytosol. Using an intracellular perfusion technique, which enables experimental control of medium composition at the cytosolic surface of the plasma membrane of charophyte algae (Chara corallina), we show that lowered pHc activates Cl efflux via two mechanisms. The first is a direct effect of pHc on Cl efflux; the second mechanism comprises a pHc-induced increase in affinity for cytosolic free Ca2+ ([Ca2+]c), which also activates Cl efflux. Cl efflux was controlled by phosphorylation/dephosphorylation events, which override the responses to both pHc and [Ca2+]c. Whereas phosphorylation (perfusion with the catalytic subunit of protein kinase A in the presence of ATP) resulted in a complete inhibition of Cl efflux, dephosphorylation (perfusion with alkaline phosphatase) arrested Cl efflux at 60% of the maximal level in a manner that was both pHc and [Ca2+]c independent. These findings imply that plasma membrane anion channels play a central role in pHc regulation in plants, in addition to their established roles in turgor/volume regulation and signal transduction.  相似文献   

5.
A normal appearing plant with a low rate of photorespiration (ratio of 14CO2 released light/dark = 1.6) was found in an unselected tobacco (Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO2 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of 14CO2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO2 dm−2 hr−1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations.  相似文献   

6.
The ability of 21 C3 and C4 monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO2 levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state 14CO2-labeling procedure. At ambient CO2 photosynthesis and export rates for C3 species were 5 to 15 and 1 to 10 μmol C m−2 s−1, respectively, and 20 to 30 and 15 to 22 μmol C m−2 s−1, respectively, for C4 species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C3 dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C4 species. At high CO2 photosynthetic and export rates were only slightly altered in C4 species, and photosynthesis increased but export rates did not in all C3 species. The C3 species that had high efflux rates relative to photosynthesis at ambient CO2 exported at rates comparable to those of C4 species on both an absolute basis and as a percentage of photosynthesis. At ambient CO2 there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO2 the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated.  相似文献   

7.
Most models of carbon gain as a function of photosynthetic irradiance assume an instantaneous response to increases and decreases in irradiance. High- and low-light-grown plants differ, however, in the time required to adjust to increases and decreases in irradiance. In this study the response to a series of increases and decreases in irradiance was observed in Chrysanthemum × morifolium Ramat. “Fiesta” and compared with calculated values assuming an instantaneous response. There were significant differences between high- and low-light-grown plants in their photosynthetic response to four sequential photosynthetic photon flux density (PPFD) cycles consisting of 5-minute exposures to 200 and 400 micromoles per square meter per second (μmol m−2s−1). The CO2 assimilation rate of high-light-grown plants at the cycle peak increased throughout the PPFD sequence, but the rate of increase was similar to the increase in CO2 assimilation rate observed under continuous high-light conditions. Low-light leaves showed more variability in their response to light cycles with no significant increase in CO2 assimilation rate at the cycle peak during sequential cycles. Carbon gain and deviations from actual values (percentage carbon gain over- or underestimation) based on assumptions of instantaneous response were compared under continuous and cyclic light conditions. The percentage carbon gain overestimation depended on the PPFD step size and growth light level of the leaf. When leaves were exposed to a large PPFD increase, the carbon gain was overestimated by 16 to 26%. The photosynthetic response to 100 μmol m−2 s−1 PPFD increases and decreases was rapid, and the small overestimation of the predicted carbon gain, observed during photosynthetic induction, was almost entirely negated by the carbon gain underestimation observed after a decrease. If the PPFD cycle was 200 or 400 μmol m−2 s−1, high- and low-light leaves showed a carbon gain overestimation of 25% that was not negated by the underestimation observed after a light decrease. When leaves were exposed to sequential PPFD cycles (200-400 μmol m−2 s−1), carbon gain did not differ from leaves exposed to a single PPFD cycle of identical irradiance integral that had the same step size (200-400-200 μmol m−2 s−1) or mean irradiance (200-300-200 μmol m−2 s−1).  相似文献   

8.
In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO2 assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO2 loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO2 assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36°C and 50 millibars bar−1, respectively). Studies on the relationship between CO2 assimilation rate and intercellular CO2 partial pressure at various temperatures and humidities showed that this decrease in CO2 assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO2 diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher 13C content of Welwitschia compared to the majority of C3 species.  相似文献   

9.
The product of pxcA (formerly known as cotA) is involved in light-induced Na+-dependent proton extrusion. In the presence of 2,5-dimethyl-p-benzoquinone, net proton extrusion by Synechocystis sp. strain PCC6803 ceased after 1 min of illumination and a postillumination influx of protons was observed, suggesting that the PxcA-dependent, light-dependent proton extrusion equilibrates with a light-independent influx of protons. A photosystem I (PS I) deletion mutant extruded a large number of protons in the light. Thus, PS II-dependent electron transfer and proton translocation are major factors in light-driven proton extrusion, presumably mediated by ATP synthesis. Inhibition of CO2 fixation by glyceraldehyde in a cytochrome c oxidase (COX) deletion mutant strongly inhibited the proton extrusion. Leakage of PS II-generated electrons to oxygen via COX appears to be required for proton extrusion when CO2 fixation is inhibited. At pH 8.0, NO3 uptake activity was very low in the pxcA mutant at low [Na+] (~100 μM). At pH 6.5, the pxcA strain did not take up CO2 or NO3 at low [Na+] and showed very low CO2 uptake activity even at 15 mM Na+. A possible role of PxcA-dependent proton exchange in charge and pH homeostasis during uptake of CO2, HCO3, and NO3 is discussed.  相似文献   

10.
Zelitch I 《Plant physiology》1989,90(4):1457-1464
Plants were obtained with novel O2-resistant photosynthetic characteristics. At low CO2 (250-350 μL CO2 L−1) and 30°C when O2 was increased from 1% to 21% to 42%, the ratio of net CO2 uptake in O2-resistant whole plants or leaf discs compared to wild type increased progressively, and this was not related to stomatal opening. Dihaploid plantlets regenerated from anther culture were initially screened and selected for O2-resistant growth in 42% O2/160 μL CO2 L−1 and 0.18% of the plantlets showed O2-resistant photosynthesis. About 30% of the progeny (6 of 19 plants) of the first selfing of a fertile plant derived from a resistant dihaploid plant had O2-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O2 and low CO2, net photosynthesis of the resistant plants was about 15% greater on a leaf area basis than wild type. Net photosynthesis was compared in leaf discs at 30 and 38°C in 21% O2, and at the higher temperature O2-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O2-resistant photosynthesis described here is associated with a decreased stoichiometry of CO2 release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O2-resistant plants averaged 40% greater catalase activity than wild type.  相似文献   

11.
Excised green leaves of mung bean (Phaseolus aureus L. var. Mungo) were used to determine the effect of light on the rate of endogenous respiration via the tricarboxylic acid cycle. Illumination with white light at an intensity of 0.043 gram calories cm−2min−1 (approximately 8600 lux) of visible radiation (400-700 nm) gave a rate of apparent photosynthesis, measured as net CO2 uptake, of 21 mg CO2 dm−2hr−1 which was about 11-fold greater than the rate of dark respiration. The feeding of 14CO2 or 14C-labeled acids of the tricarboxylic acid cycle in the dark for 2 hours was established as a suitable method for labeling mitochondrial pools of cycle intermediates.  相似文献   

12.
It has been hypothesized that under NO3 nutrition a high apoplastic pH in leaves depresses Fe3+ reductase activity and thus the subsequent Fe2+ transport across the plasmalemma, inducing Fe chlorosis. The apoplastic pH in young green leaves of sunflower (Helianthus annuus L.) was measured by fluorescence ratio after xylem sap infiltration. It was shown that NO3 nutrition significantly increased apoplastic pH at distinct interveinal sites (pH ≥ 6.3) and was confined to about 10% of the whole interveinal leaf apoplast. These apoplastic pH increases presumably derive from NO3/proton cotransport and are supposed to be related to growing cells of a young leaf; they were not found in the case of sole NH4+ or NH4NO3 nutrition. Complementary to pH measurements, the formation of Fe2+-ferrozine from Fe3+-citrate was monitored in the xylem apoplast of intact leaves in the presence of buffers at different xylem apoplastic pH by means of image analysis. This analysis revealed that Fe3+ reduction increased with decreasing apoplastic pH, with the highest rates at around pH 5.0. In analogy to the monitoring of Fe3+ reduction in the leaf xylem, we suggest that under alkaline nutritional conditions at interveinal microsites of increased apoplastic pH, Fe3+ reduction is depressed, inducing leaf chlorosis. The apoplastic pH in the xylem vessels remained low in the still-green veins of leaves with intercostal chlorosis.  相似文献   

13.
Boyer JS 《Plant physiology》1971,48(5):532-536
The inhibition of photosynthesis at low leaf water potentials was studied in soil-grown sunflower to determine the degree to which photosynthesis under high light was affected by stomatal and nonstomatal factors. Below leaf water potentials of −11 to −12 bars, rates of photosynthesis at high light intensities were insensitive to external concentrations of CO2 between 200 and 400 microliters per liter. Photosynthesis also was largely insensitive to leaf temperature between 10 and 30 C. Changes in CO2 concentration and temperature had negligible effect on leaf diffusive resistance. The lack of CO2 and temperature response for both photosynthesis and leaf diffuse resistance indicates that rates of photosynthesis were not limited by either CO2 diffusion or a photosynthetic enzyme. It was concluded that photosynthesis under high light was probably limited by reduced photochemical activity of the leaves at water potentials below −11 to −12 bars.  相似文献   

14.
Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO2 assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O2) and at low (1%) O2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 μL L−1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 μmol m−2 s−1) a progressive decrease in the ratio of variable (Fv) to maximal (Fm) fluorescence was observed with decreasing temperature. At 6oC the high-light-induced decrease in the Fv/Fm ratio was partially prevented by low O2 but values were comparable in all lines. Methyl viologen caused decreased Fv/Fm ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.  相似文献   

15.
In many species translocation of sucrose from the mesophyll to the phloem is carrier mediated. A sucrose/H+-symporter cDNA, NtSUT1, was isolated from tobacco (Nicotiana tabacum) and shown to be highly expressed in mature leaves and at low levels in other tissues, including floral organs. To study the in vivo function of NtSUT1, tobacco plants were transformed with a SUT1 antisense construct under control of the cauliflower mosaic virus 35S promoter. Upon maturation, leaves of transformants expressing reduced amounts of SUT1 mRNA curled downward, and strongly affected plants developed chloroses and necroses that led to death. The leaves exhibited impaired ability to export recently fixed 14CO2 and were unable to export transient starch during extended periods of darkness. As a consequence, soluble carbohydrates accumulated and photosynthesis was reduced. Autoradiographs of leaves show a heterogenous pattern of CO2 fixation even after a 24-h chase. The 14C pattern does not change with time, suggesting that movement of photosynthate between mesophyll cells may also be impaired. The affected lines show a reduction in the development of the root system and delayed or impaired flowering. Taken together, the effects observed in a seed plant (tobacco) demonstrate the importance of SUT1 for sucrose loading into the phloem via an apoplastic route and possibly for intermesophyll transport as well.  相似文献   

16.
Needles from phosphorus deficient seedlings of Pinus radiata D. Don grown for 8 weeks at either 330 or 660 microliters CO2 per liter displayed chlorophyll a fluorescence induction kinetics characteristic of structural changes within the thylakoid chloroplast membrane, i.e. constant yield fluorescence (FO) was increased and induced fluorescence ([FP-FI]/FO) was reduced. The effect was greatest in the undroughted plants grown at 660 μl CO2 L−1. By week 22 at 330 μl CO2 L−1 acclimation to P deficiency had occurred as shown by the similarity in the fluorescence characteristics and maximum rates of photosynthesis of the needles from the two P treatments. However, acclimation did not occur in the plants grown at 660 μl CO2 L−1. The light saturated rate of photosynthesis of needles with adequate P was higher at 660 μl CO2 L−1 than at 330 μl CO2 L−1, whereas photosynthesis of P deficient plants showed no increase when grown at the higher CO2 concentration. The average growth increase due to CO2 enrichment was 14% in P deficient plants and 32% when P was adequate. In drought stressed plants grown at 330 μl CO2 L−1, there was a reduction in the maximal rate of quenching of fluorescence (RQ) after the major peak. Constant yield fluorescence was unaffected but induced fluorescence was lower. These results indicate that electron flow subsequent to photosystem II was affected by drought stress. At 660 μl CO2 L−1 this response was eliminated showing that CO2 enrichment improved the ability of the seedlings to acclimate to drought stress. The average growth increase with CO2 enrichment was 37% in drought stressed plants and 19% in unstressed plants.  相似文献   

17.
Using 14CO2 gas exchange and metabolite analyses, stomatal as well as total internal CO2 uptake and evolution were estimated. Pulse modulated fluorescence was measured during induction and steady state of photosynthesis. Leaf water potential of Digitalis lanata EHRH. plants decreased to −2.5 megapascals after withholding irrigation. By osmotic adjustment, leaves remained turgid and fully exposed to irradiance even at severe water stress. Due to the stress-induced reduction of stomatal conductance, the stomatal CO2 exchange was drastically reduced, whereas the total CO2 uptake and evolution were less affected. Stomatal closure induced an increase in the reassimilation of internally evolved CO2. This `CO2 recycling' consumes a significant amount of light energy in the form of ATP and reducing equivalents. As a consequence, the metabolic demand for light energy is only reduced by about 40%, whereas net photosynthesis is diminished by about 70% under severe stress conditions. By CO2 recycling, carbon flux, enzymatic substrate turnover and consumption of light energy were maintained at high levels, which enabled the plant to recover rapidly after rewatering. In stressed D. lanata plants a variable fluorescence quenching mechanism, termed `coefficient of actinic light quenching,' was observed. Besides water conservation, light energy dissipation is essential and involves regulated metabolic variations.  相似文献   

18.
Wheat (Triticum aestivum L.) was grown under CO2 partial pressures of 36 and 70 Pa with two N-application regimes. Responses of photosynthesis to varying CO2 partial pressure were fitted to estimate the maximal carboxylation rate and the nonphotorespiratory respiration rate in flag and preceding leaves. The maximal carboxylation rate was proportional to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content, and the light-saturated photosynthetic rate at 70 Pa CO2 was proportional to the thylakoid ATP-synthase content. Potential photosynthetic rates at 70 Pa CO2 were calculated and compared with the observed values to estimate excess investment in Rubisco. The excess was greater in leaves grown with high N application than in those grown with low N application and declined as the leaves senesced. The fraction of Rubisco that was estimated to be in excess was strongly dependent on leaf N content, increasing from approximately 5% in leaves with 1 g N m−2 to approximately 40% in leaves with 2 g N m−2. Growth at elevated CO2 usually decreased the excess somewhat but only as a consequence of a general reduction in leaf N, since relationships between the amount of components and N content were unaffected by CO2. We conclude that there is scope for improving the N-use efficiency of C3 crop species under elevated CO2 conditions.  相似文献   

19.
We grew velvetleaf (Abutilon theophrasti Medic.) and cotton (Gossypium hirsutum L. var. Stoneville 213) at three irradiances and determined the photosynthetic responses of single leaves to a range of six irradiances from 90 to 2000 μeinsteins m−2sec−1. In air containing 21% O2, velvetleaf and cotton grown at 750 μeinsteins m−2sec−1 had maximum photosynthetic rates of 18.4 and 21.9 mg of CO2 dm−2hr−1, respectively. Maximum rates for leaves grown at 320 and 90 μeinsteins m−2sec−1 were 15.3 and 10.3 mg of CO2 dm−2hr−1 in velvetleaf and 12 and 6.7 mg of CO2 dm−2hr−1 in cotton, respectively. In 1 O2, maximum photosynthetic rates were 1.5 to 2.3 times the rates in air containing 21% O2, and plants grown at medium and high irradiance did not differ in rate. In both species, stomatal conductance was not significantly affected by growth irradiance. The differences in maximum photosynthetic rates were associated with differences in mesophyll conductance. Mesophyll conductance increased with growth irradiance and correlated positively with mesophyll thickness or volume per unit leaf area, chlorophyll content per unit area, and photosynthetic unit density per unit area. Thus, quantitative changes in the photosynthetic apparatus help account for photosynthetic adaptation to irradiance in both species. Net assimilation rates calculated for whole plants by mathematical growth analysis were closely correlated with single-leaf photosynthetic rates.  相似文献   

20.
Wild-type Arabidopsis plants, the starch-deficient mutant TL46, and the near-starchless mutant TL25 were evaluated by noninvasive in situ methods for their capacity for net CO2 assimilation, true rates of photosynthetic O2 evolution (determined from chlorophyll fluorescence measurements of photosystem II), partitioning of photosynthate into sucrose and starch, and plant growth. Compared with wild-type plants, the starch mutants showed reduced photosynthetic capacity, with the largest reduction occurring in mutant TL25 subjected to high light and increased CO2 partial pressure. The extent of stimulation of CO2 assimilation by increasing CO2 or by reducing O2 partial pressure was significantly less for the starch mutants than for wild-type plants. Under high light and moderate to high levels of CO2, the rates of CO2 assimilation and O2 evolution and the percentage inhibition of photosynthesis by low O2 were higher for the wild type than for the mutants. The relative rates of 14CO2 incorporation into starch under high light and high CO2 followed the patterns of photosynthetic capacity, with TL46 showing 31% to 40% of the starch-labeling rates of the wild type and TL25 showing less than 14% incorporation. Overall, there were significant correlations between the rates of starch synthesis and CO2 assimilation and between the rates of starch synthesis and cumulative leaf area. These results indicate that leaf starch plays an important role as a transient reserve, the synthesis of which can ameliorate any potential reduction in photosynthesis caused by feedback regulation.  相似文献   

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