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1.
The role of light in soybean seed filling metabolism 总被引:2,自引:0,他引:2
Doug K. Allen John B. Ohlrogge Yair Shachar-Hill 《The Plant journal : for cell and molecular biology》2009,58(2):220-234
Soybean (Glycine max) yields high levels of both protein and oil, making it one of the most versatile and important crops in the world. Light has been implicated in the physiology of developing green seeds including soybeans but its roles are not quantitatively understood. We have determined the light levels reaching growing soybean embryos under field conditions and report detailed redox and energy balance analyses for them. Direct flux measurements and labeling patterns for multiple labeling experiments including [U‐13C6]‐glucose, [U‐13C5]‐glutamine, the combination of [U‐14C12]‐sucrose + [U‐14C6]‐glucose + [U‐14C5]‐glutamine + [U‐14C4]‐asparagine, or 14CO2 labeling were performed at different light levels to give further insight into green embryo metabolism during seed filling and to develop and validate a flux map. Labeling patterns (protein amino acids, triacylglycerol fatty acids, starch, cell wall, protein glycan monomers, organic acids), uptake fluxes (glutamine, asparagine, sucrose, glucose), fluxes to biomass (protein amino acids, oil), and respiratory fluxes (CO2, O2) were established by a combination of gas chromatography‐mass spectrometry, 13C‐ and 1H‐NMR, scintillation counting, HPLC, gas chromatography‐flame ionization detection, C:N and amino acid analyses, and infrared gas analysis, yielding over 750 measurements of metabolism. Our results show: (i) that developing soybeans receive low but significant light levels that influence growth and metabolism; (ii) a role for light in generating ATP but not net reductant during seed filling; (iii) that flux through Rubisco contributes to carbon conversion efficiency through generation of 3‐phosphoglycerate; and (iv) a larger contribution of amino acid carbon to fatty acid synthesis than in other oilseeds analyzed to date. 相似文献
2.
The effects of methionine sulfoximine and ammonium chloride on [14C] glutamate metabolism in excised leaves of Triticum aestivum were investigated. Glutamine was the principal product derived from [U14C]glutamate in the light and in the absence of inhibitor or NH4Cl. Other amino acids, organic acids, sugars, sugar phosphates, and CO2 became slightly radioactive. Ammonium chloride (10 mm) increased formation of [14C] glutamine, aspartate, citrate, and malate but decreased incorporation into 2-oxoglutarate, alanine, and 14CO2. Methionine sulfoximine (1 mm) suppressed glutamine synthesis, caused NH3 to accumulate, increased metabolism of the added radioactive glutamate, decreased tissue levels of glutamate, and decreased incorporation of radioactivity into other amino acids. Methionine sulfoximine also caused most of the 14C from [U-14C]glutamate to be incorporated into malate and succinate, whereas most of the 14C from [1-14C]glutamate was metabolized to CO2 and sugar phosphates. Thus, formation of radioactive organic acids in the presence of methionine sulfoximine does not take place indirectly through “dark” fixation of CO2 released by degradation of glutamate when ammonia assimilation is blocked. When illuminated leaves supplied with [U-14C] glutamate without inhibitor or NH4Cl were transferred to darkness, there was increased metabolism of the glutamate to glutamine, aspartate, succinate, malate, and 14CO2. Darkening had little effect on the labeling pattern in leaves treated with methionine sulfoximine. 相似文献
3.
Richard W. Joyiv Trevor A. Thorpe 《In vitro cellular & developmental biology. Plant》1990,26(6):643-646
Summary The effects of excision, light and cytokinin (N6-benzyladenine) on14C-acetate metabolism in cotyledons ofPinus radiata (D. Don) were determined.14CO2 was released and the distribution of radioactivity into lipids, sugars, organic acids and amino acids was determined. While
light and cytokinin generally caused some increase in metabolism, the effect of excision, i.e., wounding, was most pronounced.
Specific metabolites examined (citrate, malate, succinate, alanine, aspartate, glutamate and glutamine) were at least 50%
greater in14C-labeling in excised cotyledons as compared to intact seedlings. This enhancement of wound metabolism would mask possible
morphogenically-related changes occurring at that time.
This research was supported by the Natural Sciences and Engineering Research Council of Canada Grant A-6467 to T.A. Thorpe. 相似文献
4.
Summary The distribution of radioactivity in ethanol-water-soluble compounds after short periods of photosynthetic incorporation of 14CO2 is consistent with the operation of the photosynthetic carbon reduction (PCR) cycle in the fresh water diatom Navicula pelliculosa. Incorporation of 14CO2 for extended time periods established the presence of the intermediates of the PCR and tricarboxylic acid (TCA) cycles, amino acids, and organic acids; free sugars were not observed. The main labelled soluble carbohydrate was a glucan. Hydrolysis of the radioactive insoluble material indicated the presence of carbohydrates containing several distinct sugars, and proteins with the usual amino-acid composition. During silicon starvation of exponentially growing cultures, rates of incorporation of both 32P
i
and 14CO2 decreased. Incorporation into the lipid increased, with a corresponding decrease into protein and carbohydrate. Reintroduction of Si to staryed cells led to an increased rate of incorporation of both isotopes, and transient changes in the radioactivity in most metabolic intermediates investigated. After 30 min the radioactivity in all PCR cycle intermediates, except phosphoglyceric acid, had increased by about 300%. The radioactivity of citrate and -keto-glutarate increased, whereas that of other TCA-cycle intermediates decreased. An initial decrease in the levels of glutamate, aspartate and glutamine was apparently reversed by cleavage of glutamate-aspartate peptides, as radioactivity of other amino acids increased. Incorporation into the soluble glucan and into protein increased markedly although the rate of incorporation into insoluble carbohydrates remained constant. 相似文献
5.
6.
Photosynthetic Activity in the Flower Buds of ;Valencia' Orange (Citrus sinensis [L.] Osbeck) 总被引:5,自引:2,他引:3
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Flower buds of `Valencia' orange (Citrus sinensis [L.] Osbeck) were able to fix 14CO2 into a number of compounds in their own tissues under both light and dark conditions. The total incorporation, however, was about 4-fold higher in the light than in the dark. In the light, 50% of the total 14C label was found in the neutral fraction (sugars), 22% in the basic fraction (amino acids), and 26% in the acid-1 fraction (organic acids). In the dark, about 95% of the 14C label was incorporated into the basic and acid-1 fractions. Activities of ribulose bisphosphate carboxylase and phosphoenolpyruvate carboxylase (expressed in micromoles CO2 per milligram protein per hour) averaged 1.95 and 8.87 for the flower buds, and 28.5 and 3.6 for the leaves, respectively. The ability of orange flower buds to fix ambient CO2 into different compounds suggests that this CO2 assimilation may have some regulatory role during the early reproductive stages in determining citrus fruit initiation and setting. 相似文献
7.
Carbon Dioxide Fixation in Roots and Nodules of Alnus glutinosa: I. Role of Phosphoenolpyruvate Carboxylase and Carbamyl Phosphate Synthetase in Dark CO(2) Fixation, Citrulline Synthesis, and N(2) Fixation 总被引:4,自引:4,他引:0
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Detached roots and nodules of the N2-fixing species, Albus glutinosa (European black alder), actively assimilate CO2. The maximum rates of dark CO2 fixation observed for detached nodules and roots were 15 and 3 micromoles CO2 fixed per gram dry weight per hour, respectively. The net incorporation of CO2 in these tissues was catalyzed by phosphoenolpyruvate carboxylase which produces organic acids, some of which are used in the synthesis of the amino acids, aspartate, glutamate, and citrulline and by carbamyl phosphate synthetase. The latter accounts for approximately 30 to 40% of the CO2 fixed and provides carbamyl phosphate for the synthesis of citrulline. Results of labeling studies suggest that there are multiple pools of malate present in nodules. The major pool is apparently metabolically inactive and of unknown function while the smaller pool is rapidly utilized in the synthesis of amino acids. Dark CO2 fixation and N2 fixation in nodules decreased after treatment of nodulated plants with nitrate while the percentage of the total 14C incorporated into organic acids increased. Phosphoenolpyruvate carboxylase and carbamyl phosphate synthetase play key roles in the synthesis of amino acids including citrulline and in the metabolism of N2-fixing nodules and roots of alder. 相似文献
8.
Role of Pyruvate Carboxylase in Facilitation of Synthesis of Glutamate and Glutamine in Cultured Astrocytes 总被引:5,自引:4,他引:1
William C. Gamberino Deborah A. Berkich Christopher J. Lynch Baiyang Xu Kathryn F. LaNoue 《Journal of neurochemistry》1997,69(6):2312-2325
Abstract: CO2 fixation was measured in cultured astrocytes isolated from neonatal rat brain to test the hypothesis that the activity of pyruvate carboxylase influences the rate of de novo glutamate and glutamine synthesis in astrocytes. Astrocytes were incubated with 14CO2 and the incorporation of 14C into medium or cell extract products was determined. After chromatographic separation of 14C-labelled products, the fractions of 14C cycled back to pyruvate, incorporated into citric acid cycle intermediates, and converted to the amino acids glutamate and glutamine were determined as a function of increasing pyruvate carboxylase flux. The consequences of increasing pyruvate, bicarbonate, and ammonia were investigated. Increasing extracellular pyruvate from 0 to 5 mM increased pyruvate carboxylase flux as observed by increases in the 14C incorporated into pyruvate and citric acid cycle intermediates, but incorporation into glutamate and glutamine, although relatively high at low pyruvate levels, did not increase as pyruvate carboxylase flux increased. Increasing added bicarbonate from 15 to 25 mM almost doubled CO2 fixation. When 25 mM bicarbonate plus 0.5 mM pyruvate increased pyruvate carboxylase flux to approximately the same extent as 15 mM bicarbonate plus 5 mM pyruvate, the rate of appearance of [14C]glutamate and glutamine was higher with the lower level of pyruvate. The conclusion was drawn that, in addition to stimulating pyruvate carboxylase, added pyruvate (but not added bicarbonate) increases alanine aminotransferase flux in the direction of glutamate utilization, thereby decreasing glutamate as pyruvate + glutamate →α-ketoglutarate + alanine. In contrast to previous in vivo studies, the addition of ammonia (0.1 and 5 mM) had no effect on net 14CO2 fixation, but did alter the distribution of 14C-labelled products by decreasing glutamate and increasing glutamine. Rather unexpectedly, ammonia did not increase the sum of glutamate plus glutamine (mass amounts or 14C incorporation). Low rates of conversion of α-[14C]ketoglutarate to [14C]glutamate, even in the presence of excess added ammonia, suggested that reductive amination of α-ketoglutarate is inactive under conditions studied in these cultured astrocytes. We conclude that pyruvate carboxylase is required for de novo synthesis of glutamate plus glutamine, but that conversion of α-ketoglutarate to glutamate may frequently be the rate-limiting step in this process of glutamate synthesis. 相似文献
9.
Rates and products of photosynthetic 14CO2 fixation by division synchronized cultures of Euglena gracilis strain Z were determined over the cycle. Rate of 14CO2 fixation doubled in a continuous manner throughout the light phase followed by a slight reduction of photosynthetic capacity in the dark phase. Greater 14C incorporation into the nucleic acid-polysaccharide fraction occurred with mature cells. Products of 14CO2 fixation varied markedly over the cycle: although with mature cells 14C-labeled sucrose was not detected, with dividing cells this was the main sugar labeled; in young cells 14C maltose was formed. Cells removed at end of dark phase accumulated 14C in glycolate, whereas at other stages over the cycle less 14C was present in glycolate, and this was accompanied by a rapid incorporation of 14C into glycine and serine. Glycerate was an early and major product of photosynthesis with cells at the mature stage of the cycle. 相似文献
10.
Photoautotrophic growth of soybean cells in suspension culture IV. Free amino acid pools and the effect of nitrogen on chlorophyll levels 总被引:1,自引:0,他引:1
A photoautotrophic soybean suspension culture was used to study free amino acid pools during a subculture cycle. Free amino acid analysis showed that the intracellular concentrations of asparagine, serine, glutamine, and alanine reached peaks of 200, 10, 9 and 7 mM, respectively, at specific times in the 14-day subculture cycle. Asparagine and serine levels peaked at day 14 but glutamine level rose quickly after subculture, peaking at day three and then declined gradually. Roughly similar patterns were found in the conditioned culture medium although the levels were 1000-fold lower than those found in cells. Photoautotrophic (SB-P) and photomixotrophic (SB-M) cultures were quantitatively similar with regard to free asparagine and serine but not glutamine or free ammonia. Heterotrophic (SB-H) cells had 81–85% less free asparagine on day seven than did SB-M or SB-P cells. Hence, similar to the phloem sap of a soybean plant, asparagine, glutamine, alanine and serine were the predominant amino acids in photoautotrophic soybean cell cultures. Varying the amount of total nitrogen in culture medium for two subcultures at 10, 25, 50, and 100% Of normal levels showed that growth was inhibited only at the 10 and 25% levels but that growth on medium containing 50% of the normal nitrogen was as good as that on 100% nitrogen. Moreover, cellular chlorophyll content correlated exceptionally well with initial nitrogen content of the medium. Thus, the photosynthesis of SB-P cells was not limited by chlorophyll content. SB-P cells grown for two subcultures on 10% nitrogen contained very low free amino acid levels and only 1% of the free ammonia levels found in cells growing on a full nitrogen complement.Abbreviations SB-P
photoautotrophic soybean cells (no sucrose, high CO2, high light)
- SB-M
photomixotrophic soybean cells (1% w/v sucrose, high light)
- SB-H
heterotrophic soybean cells (3% sucrose, dark) 相似文献
11.
Summary Activated phytochrome lowers the free amino acid pools of all plants investigated by about 15%. The action of red light is preferentially directed to Asp, Glu and Phe. Exogenously supplied Leu-U-14C is incorporated more quickly into protein of red-light-treated samples compared with dark controls. In contrast, red light decreases the amount of Asp-U-14C incorporated into protein, but increases the amount of 14CO2 respired after feeding with Asp-U-14C. Red light has no effect on the amount of 14CO2 respired after feeding with Leu-U-14C. Red-light-mediated stimulation of incorporation of Leu-U-14C into protein occurred within 15 min, well before the red-light-mediated increase in 14CO2 production following feeding with Asp-U-14C could be detected.Abbreviations R
red light
- FR
far-red light
- R+FR
red immediately followed by far-red light
- D
dark control
- TCA
tricarboxylic acid cycle
For amino acids as stated in Biochem. J. 126, 773–780 (1972). 相似文献
12.
Grard Febvay Isabelle Liadouze Josette Guillaud Guy Bonnot 《Archives of insect biochemistry and physiology》1995,29(1):45-69
Aphids are highly specialized insects that feed on the phloem-sap of plants, the amino acid composition of which is very unbalanced. Amino acid metabolism is thus crucial in aphids, and we describe a novel investigation method based on the use of 14C-labeled amino acids added in an artificial diet. A metabolism cage for aphids was constructed, allowing for the collection and analysis of the radioactivity incorporated into the aphid body, expired as CO2, and rejected in the honeydew and exuviae. This method was applied to the study of the metabolism of eight energetic amino acids (aspartate, glutamate, glutamine, glycine, serine, alanine, proline, and threonine) in the pea aphid, Acyrthosiphon pisum. All these amino acids except threonine were subject to substantial catabolism as measured by high 14CO2 production. The highest turnover was displayed by aspartate, with 60% of its carbons expired as CO2. For the first time in an aphid, we directly demonstrated the synthesis of three essential amino acids (threonine, isoleucine, and lysine) from carbons of common amino acids. The synthesis of these three compounds was only observed from amino acids that were previously converted into glutamate. This conversion was important for aspartate, and lower for alanine and proline. To explain the quantitative results of interconversion between amino acids, we propose a compartmentation model with the intervention of bacterial endosymbiotes for the synthesis of essential amino acids and with glutamate as the only amino acid supplied by the insect to the symbiotes. Moreover, proline exhibited partial conversion into arginine, and it is suggested that proline is probably indirectly involved in excretory nitrogen metabolism. © 1995 Wiley-Liss, Inc. 相似文献
13.
In order to investigate some aspects of Orobanche hederae physiology in relation to its parasitism, the pigment composition and the 14CO2 incorporation, both in light and in dark, were studied. By means of various chromatographic techniques, it was shown that chlorophyll is probably quite absent and that the carotenoids are very largely distrihuted and consist almost exclusively of xanthophylls. Flavochrome, flavoxanthin, and a pigment resembling neoxanthin were found to be the major components; lutein-5,6-epoxide, taraxanthin, and traces of β-carotene and α-carotene-5,6-epoxide were also present. CO2 incorporation is completely of heterotrophic type, being in no way stimulated by the light; the major radioactivity was detected in the fractions containing amino acids and organic acids. 相似文献
14.
Inorganic carbon fixation and metabolism in maize roots as affected by nitrate and ammonium nutrition 总被引:5,自引:0,他引:5
The effects of NO?3 and NH+4 nutrition on the rates of dark incorporation of inorganic carbon by roots of hydroponically grown Zea mays L. cv. 712 and on the metabolic products of this incorporation, were determined in plants supplied with NaH14CO3 in the nutrient solution. The shoots and roots of the plants supplied with NaH14CO3 in the root medium for 30 min were extracted with 80%; (v/v) ethanol and fractionated into soluble and insoluble fractions. The soluble fraction was further separated into the neutral, organic acid, amino acid and non-polar fractions. The amino acid fraction was then analyzed to determine quantities and the 14C content of its individual components. The rates of dark incorporation of inorganic carbon calculated from H14CO?3 fixation and attributable to the activity of phosphoenolpyuvate carboxylase (EC 4.1.1.31), were 5-fold higher in ammonium-fed plants than in nitrate-fed plants after a 30-min pulse of 14C. This activity forms a small, but significant component of the carbon budget of the root. The proportion of 14C located in the shoots was also significantly higher in ammonium-fed plants than in nitrate-fed plants, indicating more rapid translocation of the products of dark fixation to the shoots in plants receiving NH+/sp4 nutrition. Ammonium-fed plants favoured incorporation of 14C into amino acids, while nitrate-fed plants allocated relatively more 14C into organic acids. The amino acid composition was also dependent on the type of nitrogen supplied, and asparagine was found to accumulate in ammonium-fed plants. The 14C labelling of the amino acids was consistent with the diversion of 14C-oxaloacetate derived from carboxlyation of phosphoenolpyruvate into the formation of both asparatate and glutamate. The results support the conclusion that inorganic carbon fixation in the roots of maize plants provides an important anaplerotic source of carbon for NH+4 assimilation. 相似文献
15.
The intensity and fate of 14CO2-fixation in the dark are studied on Fucus serratus apices previously maintained under low illumination conditions using white, blue, red or yellow isoquantic lights.In the case of a 180 s pulse, light quality affected dark carbon-fixation, with a higher level of incorporation into ethanol-soluble organic matter in the case of yellow light cultivated apices. After a 30 s pulse 14C was mainly fixed into glycerate and aspartate-malate pools whatever the pre-treatment light conditions, with a higher level into glycerate when apices were pre-illuminated with blue or yellow light. After a 180 s pulse, 14C was mainly transferred into amino acids (glutamate and alanine) at the expense of aspartate and malate in red and yellow pre-illumination conditions, as found in the white light reference experiment, and only at the expense of glycerate in blue light pre-illumination conditions.The metabolic pathway of glycerate formation, principally enhanced by blue light preillumination, remains unexplained under these non-photosynthetic conditions. Results are discussed with reference to CO2-fixation via phosphoenolpyruvate carboxykinase and light quality effects on its in vitro activity. 相似文献
16.
Five mutant lines of barley (Hordeum vulgare L.), which are only able to grow at elevated levels of CO2, contain less than 5% of the wild-type activity of ferredoxin-dependent glutamate synthase (EC 1.4.7.1). Two of these lines (RPr 82/1 and RPr 82/9) have been studied in detail. Leaves and roots of both lines contain normal activities of NADH-dependent glutamate synthase (EC 1.4.1.14) and the other enzymes of ammonia assimilation. Under conditions that minimise photorespiration, both mutants fix CO2 at normal rates; on transfer to air, the rates drop rapidly to 15% of the wild-type. Incorporation of 14CO2 into sugar phosphates and glycollate is increased under such conditions, whilst incorporation of radioactivity into serine, glycine, glycerate and sucrose is decreased; continuous exposure to air leads to an accumulation of 14C in malate. The concentrations of malate, glutamine, asparagine and ammonia are all high in air, whilst aspartate, alanine, glutamate, glycine and serine are low, by comparison with the wild-type parent line (cv. Maris Mink), under the same conditions. The metabolism of [14C]glutamate and [14C]glutamine by leaves of the mutants indicates a very much reduced ability to convert glutamine to glutamate. Genetic analysis has shown that the mutation in RPr 82/9 segregates as a single recessive nuclear gene.Abbreviations GDH
glutamate dehydrogenase (EC 1.4.1.2)
- GS
glutamine synthetase (EC 6.3.1.2)
- RuBP
ribulose 1,5-bisphosphate 相似文献
17.
H. Ronald Zielke Roger M. Collins Jr. Peter J. Baab Yinyin Huang Carol L. Zielke J. Tyson Tildon 《Journal of neurochemistry》1998,71(3):1315-1320
Abstract: Metabolic compartmentation of amino acid metabolism in brain is exemplified by the differential synthesis of glutamate and glutamine from the identical precursor and by the localization of the enzyme glutamine synthetase in glial cells. In the current study, we determined if the oxidative metabolism of glutamate and glutamine was also compartmentalized. The relative oxidation rates of glutamate and glutamine in the hippocampus of free-moving rats was determined by using microdialysis both to infuse the radioactive substrate and to collect 14CO2 generated during their oxidation. At the end of the oxidation experiment, the radioactive substrate was replaced by artificial CSF, 2 min-fractions were collected, and the specific activities of glutamate and glutamine were determined. Extrapolation of the specific activity back to the time that artificial CSF replaced 14C-amino acids in the microdialysis probe yielded an approximation of the interstitial specific activity during the oxidation. The extrapolated interstitial specific activities for [14C]glutamate and [14C]glutamine were 59 ± 18 and 2.1 ± 0.5 dpm/pmol, respectively. The initial infused specific activities for [U-14C]glutamate and [U-14C]glutamine were 408 ± 8 and 387 ± 1 dpm/pmol, respectively. The dilution of glutamine was greater than that of glutamate, consistent with the difference in concentrations of these amino acids in the interstitial space. Based on the extrapolated interstitial specific activities, the rate of glutamine oxidation exceeds that of glutamate oxidation by a factor of 5.3. These data indicate compartmentation of either uptake and/or oxidative metabolism of these two amino acids. The presence of [14C]glutamine in the interstitial space when [14C]glutamate was perfused into the brain provided further evidence for the glutamate/glutamine cycle in brain. 相似文献
18.
Abstract: Hypoxia impairs brain function by incompletely defined mechanisms. Mild hypoxia, which impairs memory and judgment, decreases acetylcholine (ACh) synthesis, but not the levels of ATP or the adenylate energy charge. However, the effects of mild hypoxia on the synthesis of the glucosederived amino acids [alanine, aspartate, γ-amino butyric acid (GABA), glutamate, glutamine, and serine] have not been characterized. Thus, we examined the incorporation of [U-14C]glucose into these amino acids and ACh during anemic hypoxia (injection of NaNO2), hypoxic hypoxia (15 or 10% O2), and hypoxic hypoxia plus hypercarbia (15 or 10% O2 with 5% CO2). In general, the synthesis of the amino acids and of ACh declined in parallel with each type of hypoxia we studied. For example, anemic hypoxia (75 mg/kg of NaNO2) decreased the incorporation of [U-14C]glucose into the amino acids and into ACh similarly. [Percent inhibition: ACh (57.4), alanine (34.4), aspartate (49.2), GABA (61.9). glutamine (59.2), glutamate (51.0), and serine (36.7)]. A comparison of several levels (37.5, 75, 150, 225 mg/kg of NaNO2) of anemic hypoxia showed a parallel decrease in the flux of glucose into ACh and into the amino acids whose synthesis depends on mitochondrial oxidation: GABA (r= 0.98), glutamate (r= 0.99), aspartate (r= 0.96), and glutamine (r= 0.97). The synthesis of the amino acids not dependent on mitochondrial oxidation did not correlate as well with changes in ACh metabolism: serine (r= 0.68) and alanine (r= 0.76). The decreases in glucose incorporation into ACh and into the amino acids with hypoxic hypoxia (15% or 10% O2) or hypoxic hypoxia with 5% CO2 were very similar to those with the two lowest levels of anemic hypoxia. Thus, any explanation of the brain's sensitivity to a decrease in oxygen availability must include the alterations in the metabolism of the amino acid neurotransmitters as well as ACh. 相似文献
19.
Effect of Oxygen Concentration on C-Photoassimilate Transport from Leaves of Salvia splendens L
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Partitioning and transport of recently fixed photosynthate was examined following 14CO2 pulse-labeling of intact, attached leaves of Salvia splendens L. maintained in an atmosphere of 300 microliters per liter CO2 and 20, 210, or 500 milliliters per liter O2. Under conditions of increasing O2 (210, 500 milliliters per liter), a smaller percentage of the recently fixed 14C in the leaf was allocated to starch, whereas a greater percentage of the fixed 14C appeared in amino acids, particularly serine. The increase in 14C in amino acids was reflected in material exported from source leaves. A higher percentage of 14C in serine, glycine, and glutamate was recovered in petiole extracts when source leaves were maintained under elevated O2 levels. Although pool sizes of these amino acids were increased in both the leaves and petioles with increasing photorespiratory activity, no significant changes in either 14C distribution or concentration of transport sugars (i.e. stachyose, sucrose, verbascose) were observed. The data indicate that, in addition to being recycled intracellularly into Calvin cycle intermediates, amino acids produced during photorespiration may also serve as transport metabolites, allowing the mobilization of both carbon and nitrogen from the leaf under conditions of limited photosynthesis. 相似文献
20.
The metabolism of [14C]succinate and acetate was examined in leaf slices of winter wheat (Triticum aestivum L. cv Frederick) in the dark and in the light (1000 micromoles per second per square meter photosynthetically active radiation). In the dark [1,4-14C]succinate was rapidly taken up and metabolized into other organic acids, amino acids, and CO2. An accumulation of radioactivity in the tricarboxylic acid cycle intermediates after 14CO2 production became constant indicates that organic acid pools outside of the mitochondria were involved in the buildup of radioactivity. The continuous production of 14CO2 over 2 hours indicates that, in the dark, the tricarboxylic acid cycle was the major route for succinate metabolism with CO2 as the chief end product. In the light, under conditions that supported photorespiration, succinate uptake was 80% of the dark rate and large amounts of the label entered the organic and amino acids. While carbon dioxide contained much less radioactivity than in the dark, other products such as sugars, starch, glycerate, glycine, and serine were much more heavily labeled than in darkness. The fact that the same tricarboxylic acid cycle intermediates became labeled in the light in addition to other products which can acquire label by carboxylation reactions indicates that the tricarboxylic acid cycle operated in the light and that CO2 was being released from the mitochondria and efficiently refixed. The amount of radioactivity accumulating in carboxylation products in the light was about 80% of the 14CO2 release in the dark. This indicates that under these conditions, the tricarboxylic acid cycle in wheat leaf slices operates in the light at 80% of the rate occurring in the dark. 相似文献