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1.
Hartmannella culbertsoni trophozoites are transformed into viable cysts on exposure to a non-nutrient agar medium containing 15 mM MgCl2 and 20 mM taurine. Amebae differentiating in this encystment medium incorporate more uracil-2-14C into RNA and more leucine-1-14C or valine-1-14C into proteins than controls. Encysting organisms incorporate significantly more glucose-U-14C into cellulose and glucosamine-1-14C into mucopolysaccharides. Incorporation of glucose-U-14C into cellulose and of glucosamine-1-14C into mucopolysaccharides are inhibited by actinomycin D or cycloheximide.  相似文献   

2.
Summary Analysis by gas chromatography revealed the presence of small amounts of squalene, but not lanosterol nor ergosterol in Pythium paroecandrum, P. ultimum, P. graminicola, and P. arrhenomonas. However, when acetate-14C was used as a precursor for sterols, even squalene was not found in P. graminicola. The deficiency in the sterol synthesizing mechanism may therefore be at or before the squalene forming step. Both squalene and ergosterol were present in the mycelium of Rhizoctonia solani, as shown by both gas chromatography and by the incorporation of acetate-14C into ergosterol. The absence of ergosterol in Pythium and its presence in Rhizoctonia is consistant with the resistance to the antibiotic filipin of Pythium species and the sensitivity of R. solani.  相似文献   

3.
Glucose metabolism of healthy and tobacco mosaic virus-infected leaf-discs of Nicotiana tabocum L. var. Xanthi showing local-necrotic lesions was investigated using glucose-14C. Local lesion formation following inoculation with tobacco mosaic virus resulted in enhanced glucose metabolism reflected by an increased rate of release of 14CO2 from glucose-U-14C and greater incorporation of 14C into all cell fractions. When specifically labelled glucose was fed to healthy and tobacco mosaic virus infected leaves, the C6/C1 ratio (rate of release of 14CO2 from glucose-6-14C/rate of release of 14CO2 from glucose-l-14C) was similar for healthy and virus-infected leaves. The C6/C1 ratios recorded from 0.30 to 0.50 indicate that both the glycolytic and pentose phosphate pathways participate in glucose catobolism in healthy and virus-infected leaves. Although the C6/C1 ratio was the same as that of the healthy leaf the rate of release of 14CO2 from glucose-6-14C and glucose-1-14C was greatly increased in the virus-infected leaf. The increased glucose catabolism occurs by both glycolytic and pentose phosphate pathways in the virus-infected leaf.  相似文献   

4.
Microsomal 4-methyl sterol oxidase of cholesterol biosynthesis from lanosterol has been assayed to date by coupling of the NAD(P)H-dependent oxygenase to a NAD-dependent decarboxylase in a two-step incubation procedure. A simple assay of 4-methyl sterol oxidase of rat liver microsomes has now been developed with the model substrate, 4-hydroxy[14C]methylene-5α-cholest-7-en-3-one. In the presence of oxygen and NADPH, the 30-14C-model substrate is oxidized directly to a 3-ketosteroid and14CO2, which is collected and counted. Conditions for measurement of initial rates of oxidation of the model substrate have been established. With the model substrate, the maximal velocity is four- to five-fold greater than the rate observed with 4α-methyl sterol substrates. Furthermore, when methyl sterol oxidase is measured with both the one-step and two-step assays, parallel effects are produced upon addition of either competitive or noncompetitive inhibitorsin vitro; similarly, oxidative attack on each substrate is enhanced equally when rats are treatedin vivo with a bile salt sequestrant. Thus, the direct one-step assay of oxidase activity with the model 4-hydroxy[14C]methylene sterol substrate is rapid, the observed rates are rapid, and the enzymic steps in the multienzymic, mixed function oxidase may be elucidated with this simplified procedure.  相似文献   

5.
The dinoflagellates Amphidinium carterae and Amphidinium corpulentum have been previously characterized as having Δ8(14)-nuclear unsaturated 4α-methyl-5α-cholest-8(14)-en-3β-ol (C28:1) and 4α-methyl-5α-ergosta-8(14),24(28)-dien-3β-ol (amphisterol; C29:2) as predominant sterols, where they comprise approximately 80% of the total sterol composition. These two sterols have hence been considered as possible major sterol biomarkers for the genus. Here, we have examined the sterols of four recently identified species of Amphidinium (Amphidinium fijiense, Amphidinium magnum, Amphidinium theodori, and Amphidinium tomasii) that are closely related to Amphidinium operculatum as part of what is termed the Operculatum Clade to show that each species has its sterol composition dominated by the common dinoflagellate sterol cholesterol (cholest-5-en-3β-ol; C27:1), which is found in many other dinoflagellate genera, rather than Δ8(14) sterols. While the Δ8(14) sterols 4α-methyl-5α-cholest-8(14)-en-3β-ol and 4α,23,24-trimethyl-5α-cholest-8(14),22E-dien-3β-ol (C30:2) were present as minor sterols along with another common dinoflagellate sterol, 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol; C30:1), in some of these four species, amphisterol was not conclusively observed. From a chemotaxonomic perspective, while this does reinforce the genus Amphidinium's ability to produce Δ8(14) sterols, albeit here as minor sterols, these results demonstrate that caution should be used when considering Δ8(14) sterols, especially amphisterol, as Amphidinium-specific biomarkers within these species where cholesterol is the predominant sterol.  相似文献   

6.
Acid spring effluents are often covered with mats of the eucaryotic phycocyanin-containing alga. Cyanidium caldarium. The primary bacterial component of such mats is an acidophilic strain of Bacillus coagulans, and the primary fungal component is Dactylaria gallopava. Because of the limited species diversity, C. caldarium mats appeared to be an excellent system for studying algal excretion and various microbial interactions in nature. From 2 to 6% of the NaH14CO3 taken up by natural or laboratory populations of the alga was excreted as 14C-labeled materials. The maximum excretion occurred at temperature, light, and pH values optimum for NaH14CO3 uptake. However, when excretion was expressed as a percentage of NaH14 CO3 uptake, a higher percentage of the radioactivity was excreted at nonoptimal conditions for NaH14CO3 uptake. Fungal biomass was directly proportional to algal density, but bacterial numbers varied widely and did not correlate with algal numbers. The bacterial and fungal components could be grown in mixed culture with either growing C. caldarium cultures or in an extract prepared, by healing algal cells.  相似文献   

7.
Tolbutamide partially inhibited the growth but increased the glycogen content of Tetrahymena pyriformis in logarithmically growing cultures. Tolbutamide slightly increased 14CO2 production from [1-14C] and [6-14HC] glucose and [2-14C] pyruvate, but had little effect on the oxidation of [1-14C] acetate when any of these substrates were added to the proteose-peptone medium in which the cells had been grown. Measurement of 14CO2 production from [1-14C] and [2-I4C]-glyoxylate showed that this substrate was primarily oxidized via the glyoxylate cycle, with little if any oxidation occurring via the peroxisomal glyoxylate oxidase. Addition of tolbutamide inhibited the glyoxylate cycle as indicated by a marked reduction in label appearing in CO2 and in glycogen from labeled acetate. In control cells, addition of acetate strongly inhibited the oxidation of [2-14C]-pyruvate whereas addition of pyruvate had little effect on the oxidation of [1-14C]-acetate. Acetate was more effective than pyruvate in preventing the growth inhibitory and glycogen-increasing effects of tolbutamide. The data suggest that one effect of tolbutamide may be to interfere with the transfer of isocitrate and acetyl CoA across mitochondrial membranes.  相似文献   

8.
With 14CO2, d-glucose-[U-14C] and dl-mevalonate-[4R-4-3H1] used as precursors, a study was made of the labelling dynamics of the steryl glucosides (SG) and steryl acylglucosides (ASG) in Sinapis alba seedlings. The radioactivity of the sterol and sugar moieties, as well as of the fatty acid moieties in the case of ASG, was analysed separately. The course of incorporation of 14C from 14 CO2 and glucose-[U-14C] into the sugar part of SG and ASG indicated that about 23 of the whole pool of the newly synthesized sterol glycosides of both types underwent rapid deglucosylation. Likewise, fatty acids in the ASG pool were rapidly exchanged. The present results point to a high metabolic activity of the sterol glycoside derivatives in plant cells.  相似文献   

9.
14C methods were applied to young, woody, branched and well-watered cork oak (Quercus suber L.) plants to determine carbon assimilation and its distribution among plant organs. Carbon assimilation rates by attached leaves clamped in a foliar 14CO2 assimilation chamber containing 3.7 × 104 Bq of a portable ventilated diffusion porometer were measured at different 14CO2 pulse-labeling periods (15, 30, 45, 60 and 120 s) in summer. Allocation of recently fixed C by attached leaves within plants was evaluated 7 days after a 60-min of 5.6 MBq of 14CO2 pulse-labeling in late winter. 14CO2 pulse-labeling was separately induced on leaves of a lower branch, two opposite branches at the same lower level, a middle branch and a top branch. 14C activity incorporated into the plants was measured by liquid scintillation and autoradiography. Our results show the optimum 14CO2 pulse-labeling period is between 15 and 30 s, which corresponds to 9.81 ± 0.15 and 9.16 ± 0.12 µmol m−2 s−1 C assimilation rates in summer, respectively. The investment of current assimilates ranged from 18 to 29% in leaves, 1 to 7% in lateral branches, 0 to 3% in the stem and over 65% in roots, in late winter. Roots displayed the greatest sink strength for the total 14C recovered by whole-plants. These results were expected because the trial was done in winter, when cork oak does not produce their leaves. Our results highlight the contribution of current assimilates for growth and maintenance of roots, in young woody plants under Mediterranean climate.  相似文献   

10.
The floating, stoloniferous plant, Eichhornia crassipes, has high rates of productivity and rapidly invades new sites. Because the transport of carbon among connected ramets is known to increase the growth of clonal plants, we asked whether there is intraclonal carbon transport in E. crassipes. Because net photosynthesis of E. crassipes is significantly higher at high levels of atmospheric CO2, we also asked if high CO2 can change patterns of carbon transport in ways that might modify clonal growth. We exposed individual ramets within groups of connected ramets to 14CO2 for 15–45 min and measured the distribution of 14C in the group after 4 days of growth at 350, 700, 1,400, or 2,800 μ1 1−-1 CO2. At 350 μ1 1−-1 CO2, a parent ramet exported approximately 10% of the 14C that it assimilated to its first rooted offspring ramet. The offspring exported a similar percentage of the l4C it assimilated toward the parent; two-thirds of this 14C was retained by the parent, and one-third moved into new offspring of the parent. In all ramets, imported carbon moved into leaves as well as roots. At the higher levels of CO2, the percentage of assimilated carbon exported from a parent ramet to the leaf blades of its first offspring was lower by half. High CO2 had little other effect on carbon transport. E. crassipes maintains bidirectional transport of carbon between ramets even under uniform and favorable environmental conditions and when external CO2 levels are very high.  相似文献   

11.
Enhanced soil respiration in response to elevated atmospheric CO2 has been demonstrated, and ectomycorrhizal (ECM) fungi are of particular interest since they partition host-derived photoassimilates belowground. Although a strong response of ECM fungi to elevated CO2 has been shown, little is still known about the functional diversity among species. We studied carbon (C) partitioning in mycorrhizal Scots pine seedlings in response to short-term CO2 enrichment, using seven ECM species with different ecological strategies. Mycorrhizal associations were synthesised and seedlings grown in large Petri dishes containing peat:vermiculite and nutrient solution for 10–15 weeks, after which half of the microcosms were exposed to elevated CO2 treatment (710 ppm) for 15 days and the other half were kept in ambient CO2 treatment. Partitioning of C was quantified by pulse labelling the seedlings with 14CO2 and examining the distribution of labelled assimilates in shoot, root and extraradical mycelial compartments by destructive harvest and liquid scintillation counting. Fungal biomass was determined with PLFA analysis. The respiratory loss of 14CO2 was on average greater in the elevated CO2 treatment for most species compared to the ambient CO2 treatment. More label was retrieved in the shoots in the ambient CO2 treatment compared to elevated CO2 (significant for P. involutus and P. fallax). Greater amounts of label were found in the extraradical mycelial compartment in all species (except P. involutus) in elevated CO2 compared to ambient CO2 (significant for L. bicolor, P. byssinum, P. fallax and R. roseolus). Fungal biomass production increased significantly with elevated CO2 for two species (H. velutipes and A. muscaria); three species (P. fallax, P. involutus and R. roseolus) showed a similar but non-significant trend, whereas L. bicolor and P. byssinum produced less biomass in elevated CO2 compared to ambient CO2. When 14C in the mycelial compartment and respiration was expressed per unit fungal PLFA the difference between CO2 treatments disappeared. We demonstrated that different ECM fungal isolates respond differently in C partitioning in response to CO2 enrichment. These results suggest that under certain growth conditions, when nutrients are not limiting, ECM fungi respond rapidly to increasing C-availability through changed biomass production and respiration.  相似文献   

12.
Abstract When tomato plants of the high-altitude species Lycopersicon hirsutum and of the cultivated Lycopersicon esculentum were grown at 24/18°C (day/night), the effects of temperature, photon flux density, and intercellular CO2 concentration up to about 600 μl l?1 on net CO2 uptake were similar in the two species. Acclimation of these plants at 12/6°C (day/night) resulted, after 4 d or longer, in a similar downward shift of about 5°C in the optimum temperature for CO2 uptake. However, in comparison with the cultivated species, the high-altitude plants achieved a higher rate of CO2 uptake at saturating concentrations of intercellular CO2, maintained a higher level of saturating-light CO2 uptake rate at 10°C after exposure to chilling stress (10°C and photon flux density of 400 μmol m?2s?1 d and 5°C night) for 7–18 d, and displayed a better capacity for rapid recovery after prolonged stress. The greater capacity for CO2 uptake observed in the high-altitude species during and after exposure to chilling stress was also reflected in its higher growth rate under those conditions compared with plants of L. esculentum. These advantages of the high-altitude species may partly explain its ability to survive and complete its life cycle under the environmental conditions prevailing in its natural habitat.  相似文献   

13.
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   

14.
The quantity of free and esterified sterols in the whole body, intestine, hemolymph, fat body, and frass of 6th-instar larvae of H. zea, fed cholesterol or cholestanol, was measured in order to determine if there was a difference in the utilization of these two molecules. The principal sterol in the tissues of the larvae was cholestanol or cholesterol, when they were fed diet containing these two molecules, respectively; there was little, if any, metabolism of dietary cholestanol to cholesterol. There was little or no difference in the amount of total sterol in the whole body, tissues, or frass of larvae fed the two different diets, indicating that the absence of a Δ5-bond in cholestanol does not prevent the uptake or distribution of this sterol to various tissues. However, the relative percentage of steryl ester was significantly higher in prepupae reared on a diet containing cholestanol instead of cholesterol (6–7-, 4-, 13-, 4-, and 2-fold increase, for the whole body, intestine, hemolymph, fat body, and frass, respectively). The average percentage of total sterol that was esterified in the tissues was greater in the fat body (10.8 ± 15.4 and 44.2 ± 12.3%, respectively, for larvae fed cholesterol and cholestanol) than in the hemolymph (0.5 ± 0.1 and 6.3 ± 0.8%) and intestine (1.2 ± 0.1 and 4.7 ± 1.1%). The percentage of sterol that was esterified in the frass of larvae was large (26.9 ± 3.7 and 48.2 ± 0.5%, respectively, for larvae fed cholesterol and cholestanol). Therefore, the fact that larvae of H. zea fed cholestanol, instead of cholesterol, contain this saturated molecule as their principal tissue sterol and preferentially esterify it may explain, at least in part, why their rate of growth on cholestanol is slower than on cholesterol.  相似文献   

15.
1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster‐growing elodeids. In these C‐limited systems, this may be related to rising aquatic CO2 levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four different CO2 levels, ranging from 20 to 230 μmol L−1. In addition, we tested the effect of the nutrient status of the sediment on the growth of C. hamulata at the different CO2 levels. 3. Shoot and root growth increased with rising CO2 availability. Irrespective of sediment type, growth was minimal to negative at the lowest CO2 treatment level, while becoming positive at CO2 levels around 40–50 μmol L−1. Substantial growth was only obtained when the macrophytes were growing on mesotrophic sediments. The plants reached close to maximal growth at CO2 levels of c. 100 μmol L−1. 4. Within this experiment, the growth of C. hamulata at CO2 levels above 90 μmol L−1 may have been limited by N and P availability in both sediment types. The growth rate of M. alterniflorum did not seem to be limited by N and P availability, most likely due to its much higher relative root production. 5. The experimental results show that neither M. alterniflorum nor C. hamulata is able to invade isoetid‐dominated softwater lakes at very low aquatic CO2 concentrations. However, if the sediments contain enough nutrients, a rise in aquatic CO2 could allow the invasion of elodeid species leading to the subsequent disappearance of slow‐growing isoetids.  相似文献   

16.
Desulfovibrio baarsii is a sulfate reducing bacterium, which can grown on formate plus sulfate as sole energy source and formate and CO2 as sole carbon sources. It is shown by 14C labelling studies that more than 60% of the cell carbon is derived from CO2 and the rest from formate. The cells thus grow autotrophically. Labelling studies with [14C]acetate, 14CO and [14C]formate indicate that CO2 fixation does not proceed via the Calvin cycle. The labelling patterns of alanine, aspartate, glutamate, and glucosamine indicate that acetate (or activated acetic acid) is an early intermediate in formate and CO2 assimilation; the methyl group of acetate is derived from formate, and the carboxyl group from CO2 via CO; pyruvate is formed from acetyl-CoA by reductive carboxylation. The capacity to synthesize an acetate unit from two C1-compounds obviously distinguishes D. baarsii from those Desulfovibrio species, which require acetate as a carbon source in addition to CO2.  相似文献   

17.
The morphology, the general physiological characteristics, and the energy-yielding metabolism of an obligately anaerobic spirochete isolated from the colon of a swine were studied. Electron microscopy showed that the helical spirochetal cells possessed an outer sheath, a protoplasmic cylinder, and 4 periplasmic fibrils in a 2-4-2 arrangement. The spirochete grew in an atmosphere of N2 in prereduced media containing a carbohydrate, NaHCO3, rumen fluid, yeast extract, peptone, l-cysteine, and inorganic salts. The spirochete fermented carbohydrates and required substrate amounts of CO2 (HCO 3 - ) for growth. Amino acids were not fermented. Major fermentation products of cells growing with glucose as the substrate and in the presence of CO2 were acetate, formate, succinate, and lactate. Small amounts of 2,3-butanediol, pyruvate, and acetoin were also formed. Determinations of enzymatic activities in cell extracts, and of radioactivity in products formed by growing cells from [1-14C]glucose, indicated that this sugar was dissimilated to pyruvate via the Embden-Meyerhof pathway. The spirochetes used a coliform-type clastic reaction to metabolize pyruvate. Determinations of radioactivity in products formed from [14C]NaHCO3 indicated that CO2 was assimilated and used in succinate production. The guanine+cytosine content of the DNA was 36 mol%. This study indicates that this intestinal spirochete represents a new species of Treponema. It is proposed that the new species be named Treponema succinifaciens.Abbreviations cpm counts per minute - DTT dithiothreitol - EM Embden-Meyerhof - GC guanine plus cytosine - IgG immunoglobulin G - PC protoplasmic cylinder - PF periplasmic fibrils (axial fibrils) - OS outer sheath  相似文献   

18.
Two mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m?3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO2 concentration (340 and 700 cm3 m?3). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt-tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients.  相似文献   

19.
We investigated fungal species-specific responses of ectomycorrhizal (ECM) Scots pine (Pinus sylvestris) seedlings on growth and nutrient acquisition together with mycelial development under ambient and elevated CO2. Each seedling was associated with one of the following ECM species: Hebeloma cylindrosporum, Laccaria bicolor, Suillus bovinus, S. luteus, Piloderma croceum, Paxillus involutus, Boletus badius, or non-mycorrhizal, under ambient, and elevated CO2 (350 or 700 μl l−1 CO2); each treatment contained six replicates. The trial lasted 156 days. During the final 28 days, the seedlings were labeled with 14CO2. We measured hyphal length, plant biomass, 14C allocation, and plant nitrogen and phosphorus concentration. Almost all parameters were significantly affected by fungal species and/or CO2. There were very few significant interactions. Elevated CO2 decreased shoot-to-root ratio, most strongly so in species with the largest extraradical mycelium. Under elevated CO2, ECM root growth increased significantly more than hyphal growth. Extraradical hyphal length was significantly negatively correlated with shoot biomass, shoot N content, and total plant N uptake. Root dry weight was significantly negatively correlated with root N and P concentration. Fungal sink strength for N strongly affected plant growth through N immobilization. Mycorrhizal fungal-induced progressive nitrogen limitation (PNL) has the potential to generate negative feedback with plant growth under elevated CO2. Responsible Editor: Herbert Johannes Kronzucker  相似文献   

20.
Tracer kinetic experiments were performed using [ureido-14C] citrulline, [1-14C]ornithine, and isotope trapping techniques to determine if arginine is synthesized via the urea cycle in developing cotyledons of Glycine max (L.) Merrill. Excised cotyledons were injected with the 14C-solution and incubated in sealed vials containing a CO2 trap. The free and protein amino acids were analyzed using high performance liquid chromatography and arginine-specific enzyme-linked assays. In the 14C-citrulline feeding experiment argininosuccinate was the most highly labeled compound after 5 minutes and it was the first compound to lose 14C later in the time course. Carbon-14 was also recovered in free arginine, protein arginine, and CO2 up to 4 hours after introduction of label. All of the 14C in free and protein arginine could be accounted for in the C-6 position. Metabolism of 14C-ornithine resulted in 14C-incorporation into citrulline and free and protein arginine and the evolution of 14CO2. Citrulline was the most highly labeled compound after 15 minutes and was the first compound to reach a steady state level of 14C. With the addition of 800 nanomoles unlabeled citrulline to the 14C-ornithine feeding solution citrulline was the only compound labeled after 5 minutes and the steady state level of 14C-citrulline increased 12-fold. The appearance of 14C in free arginine and protein arginine was also delayed. In both 14C-ornithine feedings all of the 14C in free and protein arginine could be accounted for in the C-1 position. Together, the data support the reaction sequence: ornithine → citrulline → argininosuccinate → arginine → protein arginine.  相似文献   

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