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1.
The ability of chloroplasts to synthesize aromatic amino acids from CO2 was investigated using highly purified, intact spinach ( Spinacia oleracea L. cv. Viking II) chloroplasts and 14 CO2 . Incorporation of 14 C into aromatic amino acids was very low, however, and this was assumed to be due to lack of phosphoenolpyruvate (PEP), one of the substrates for the shikimate/arogenate pathway leading to aromatic amino acids in chloroplasts. Therefore, the glycolytic enzymes phosphoglycerate mutase (EC 2.7.5.3) and enolase (EC 4.2.1.11) were added to the 14 CO2 fixation medium in order to convert labelled 3-phosphoglycerate exported from the intact chloroplasts to 2-phosphoglycerate and PEP. In this way a part of the glycolytic pathway was reconstituted outside the chloroplasts to substitute for the cytoplasm lost on isolation. The presence of both enzymes in the medium increased incorporation of 14 C into Tyr and Phe more than ten-fold and incorporation into Trp about two-fold, while total 13 CO2 fixation rates were not affected. Our results suggest that chloroplasts do not contain phosphoglycerate mutase or enolase, and that, in vivo, PEP is synthesized in the cytoplasm and imported to the chloroplast stroma for the biosynthesis of aromatic amino acids. The biosynthesis of all three aromatic amino acids was under feedback control. Using expected physiological concentrations (below 100 μ M ), each of the aromatic amino acids exerted a strict feedback inhibition of its own biosynthesis only. 相似文献
2.
The photosynthetic rate of Lemna gibba was measured as 14 CO2 uptake at the beginning of and after 1 h DCMU treatment during the separate excitation of PS I (703 nm), mainly PS II (662 nm) and the combined excitation of both photosystems (662 + 703 nm) in 2 and 21% oxygen. The results show the Warburg effect. Photosynthesis was significantly reduced by DCMU whenever PS II was excited, at 662 nm and 662 + 703 nm. Photosynthetic enhancement was greater in 21 than in 2% oxygen in both the treated and untreated plants.
Photorespiratory14 CO2 release was only affected by DCMU treatment at 662 + 703 nm. It was significantly decreased in 21% O2 and significantly increased in 2% O2 as compared to the controls without DCMU. The 14 C-glycolate remaining in the plant after photosynthesis/photorespiration measurements was reduced whenever the electron supply to PS I was low.
These data support the hypothesis that a relationship exists between glycolate metabolism and photosynthesis via the electron transport chain where electrons from the oxidation of glycolate are donated to PS I when the electron supply from water is low. 相似文献
Photorespiratory
These data support the hypothesis that a relationship exists between glycolate metabolism and photosynthesis via the electron transport chain where electrons from the oxidation of glycolate are donated to PS I when the electron supply from water is low. 相似文献
3.
4.
The photosynthetic potential of canola embryos 总被引:5,自引:0,他引:5
Ponita S. Asokanthan Robert W. Johnson Marilyn Griffith Marianna Krol 《Physiologia plantarum》1997,101(2):353-360
Canola embryos are green during development, but the role of embryo chloroplasts is not known. The objective of this study was to characterize the structure and function of embryo chloroplasts. Observations obtained by SDS-PAGE and transmission electron microscopy showed that thylakoids from embryo chloroplasts contained the same chlorophyll-protein complexes, but exhibited a greater proportion of granal stacking, compared with thylakoids from leaf chloroplasts. When assayed using an oxygen electrode, photosynthetic electron transport and respiration were enhanced in canola embryos bathed in concentrations of sucrose below 0.47 M. Photosynthesis, measured as the rate of incorporation of 14 CO2 , was much lower in embryos than leaves even though significant electron transport was detected. These results indicate that the primary role of chloroplasts in embryos is not to photoassimilate CO2 . Instead, canola embryos are photoheterotrophic and may use the light reactions to generate the ATP and NADPH required to fuel the conversion of maternally supplied sucrose to the fatty acids used in oil synthesis and storage. These results led us to propose that the current model of plastid differentiation be modified to include the development of photoheterotrophic chloroplasts in sink tissues. This pattern of plastid differentiation can then be used to explain patterns of embryo development. 相似文献
5.
MASAHISA NAKAMURA IKUO YASUMASU SHOICHI OKINAGA KIYOSHI ARAI 《Development, growth & differentiation》1982,24(3):265-272
Rotenone-sensitive 14 CO2 formation from [14 C]lactate and oxygen consumption by round spermatids were found to be greater at elevated temperatures than at 34°C. More than 96% of the total radioactivity of the metabolized [14 C]lactate was recovered in the released CO2 and the acid soluble fraction of the cells. There was practically no incorporation of [14 C]latctate into the lipid, nucleic acid, and protein fractions. Intracellular level of ATP in spermatids was enhanced in the presence of lactate (20 mM) at 34°C (scrotal temperature), whereas it was decrease at 37°C (body temperature). However, this was reversible when the cells were transferred from the elevated temperature to 34°C. It was also found that oxygen consumption and CO2 production were increased at 34°C by 2, 4-dinitrophenol (DNP), but decreased by oligomycin. On the other hand, oligomycin and DNP had no effect on oxygen consumption and 14 CO2 formation at the elevated temperature.
These findings provide evidence that lactate utilization by spermatids is coupled with oxidative phosphorylation at scrotal temperature, but becomes uncoupled at elevated temperature, although more lactate is consumed. 相似文献
These findings provide evidence that lactate utilization by spermatids is coupled with oxidative phosphorylation at scrotal temperature, but becomes uncoupled at elevated temperature, although more lactate is consumed. 相似文献
6.
Effects of elevated ozone on CO2 uptake and leaf structure in sugar maple under two light environments 总被引:2,自引:2,他引:0
The interactive effects of ozone and light on leaf structure, carbon dioxide uptake and short-term carbon allocation of sugar maple ( Acer saccharum Marsh.) seedlings were examined using gas exchange measurements and 14 C-macroautoradiographic techniques. Two-year-old sugar maple seedlings were fumigated from budbreak for 5 months with ambient or 3 × ambient ozone in open-top chambers, receiving either 35% (high light) or 15% (low light) of full sunlight. Ozone accelerated leaf senescence, and reduced net photosynthesis, 14 CO2 uptake and stomatal conductance, with the effects being most pronounced under low light. The proportion of intercellular space increased in leaves of seedlings grown under elevated ozone and low light, possibly enhancing the susceptibility of mesophyll cells to ozone by increasing the cumulative dose per mesophyll cell. Indeed, damage to spongy mesophyll cells in the elevated ozone × low light treatment was especially frequent. 14 C macroautoradioraphy revealed heterogeneous uptake of 14 CO2 in well defined areole regions, suggesting patchy stomatal behaviour in all treatments. However, in seedlings grown under elevated ozone and low light, the highest 14 CO2 uptake occurred along larger veins, while interveinal regions exhibited little or no uptake. Although visible symptoms of ozone injury were not apparent in these seedlings, the cellular damage, reduced photosynthetic rates and reduced whole-leaf chlorophyll levels corroborate the visual scaling of whole-plant senescence, suggesting that the ozone × low light treatment accelerated senescence or senescence-like injury in sugar maple. 相似文献
7.
Hilary J. Crompton D. G. Hill-Cottingham G. A. Hudd C. P. Lloyd-Jones 《Physiologia plantarum》1984,60(4):543-546
Whole bean plants, ev. Cockfield, grown in pots crowded or well-spaced (50 or 10 plants m2 , respectively) were treated with 14 CO2 at the pod-fill stage (25 modes) and the radioactivity in each leaf was determined after 30 min. With spaced plants the uptake was greatest in the mid-stem leaves and was proportional to leaf area. In contrast, 70% of the total assimilation took place in the upper six leaves of crowded plants and there was a steady decrease down the stem.
When14 CO2 was fed to single leaves of similar crowded plants the resultant distribution of labelled assimilates varied with the position of the treated leaf. After 6 h, 67% of the 14 C fixed by a mid-stem leaf (node 13) was recovered from the beans, whereas 76% of that from an upper leaf (node 23) had accumulated along the stem. Due to the shading of mid-stem leaves at the higher planting densities, seed yield becomes increasingly dependent upon re-distribution of assimilates from stem to beans. 相似文献
When
8.
L-GLUTAMIC ACID DECARBOXYLASE IN NON-NEURAL TISSUES OF THE MOUSE 总被引:7,自引:5,他引:2
Abstract— Low levels of γ-aminobutyric acid (GABA) and of glutamic acid decarboxylase (GAD) activity have been detected in mouse kidney, liver, spleen and pancreas. Quantitation of both 14 CO2 and [14 C]GABA produced in radiometric assays from [U-14 CJglutamic acid has shown that measurement of 14 CO2 evolution alone is not, in all cases, a valid estimate of true GAD activity. As evidenced by increased ,14 CO2 production upon addition of NAD and CoA to assay mixtures, radiometric assay of GAD activity in crude homogenates may yield 14 CO2 via the coupled reactions of glutamic acid dehydrogenase and a-ketoglutarate dehydrogenase. The addition of 1 mM aminooxyacetic acid (AOAA) to assays of kidney homogenates inhibited [,14 C]GABA production 92 per cent while 14 CO2 production was inhibited only 53 per cent. No evidence was found to confirm the reported existence of a second form of the enzyme, GAD II. previously described by Haber el al. (H aber B., K uriyama K. & R oberts E. (1970) Biochem. Pharmac. 19, 1119-1136). Based on sensitivity-to AOAA and chloride inhibition, the GAD activity in mouse kidney is. apparently, indistinguishable from that of neural origin. 相似文献
9.
THE EFFECT OF DIABETES, INSULIN AND WALLERIAN DEGENERATION ON LEUCINE METABOLISM OF ISOLATED RAT SCIATIC NERVES 总被引:4,自引:3,他引:1
Maria G. Buse H. Franklin Herlong Dorothy A. Weigand S. S. Spicer 《Journal of neurochemistry》1976,27(6):1339-1345
Abstract– 14 CO2 production and 14 C incorporation into proteins was studied in isolated rat sciatic nerves during incubation with 0.1 mM-[1-14 C]leucine. Rats were made diabetic with streptozotocin. Nerves from diabetic rats incubated with glucose oxidized more [14 C]leucine than controls. This difference was abolished in the presence of insulin (1 mU/ml). The effects of diabetes and insulin on leucine oxidation could not be demonstrated in the absence of glucose. Insulin stimulated the incorporation of [14 C] from leucine into proteins by nerves from controls and diabetic rats.
Nerves undergoing Wallerian degeneration showed a marked increase in DNA content and stimulated incorporation of [14 C]leucine into proteins. 14 CO2 production from leucine proceeded at 75% of the rate observed in intact nerves. Neither insulin nor diabetes affected leucine metabolism in degenerating nerves.
Neither the extracellular space nor the concentration of free amino acids were significantly different in nerves obtained from control and diabetic rats, except for lower glutamine content in the latter.
In vitro leucine metabolism of nerves is affected by diabetes, insulin and the integrity of the axon. The Schwann cell is suggested as a possible site of the observed changes in leucine metabolism. 相似文献
Nerves undergoing Wallerian degeneration showed a marked increase in DNA content and stimulated incorporation of [
Neither the extracellular space nor the concentration of free amino acids were significantly different in nerves obtained from control and diabetic rats, except for lower glutamine content in the latter.
In vitro leucine metabolism of nerves is affected by diabetes, insulin and the integrity of the axon. The Schwann cell is suggested as a possible site of the observed changes in leucine metabolism. 相似文献
10.
Günter Döhler Robert C. Worrest Irene Biermann Joachim Zink 《Physiologia plantarum》1987,70(3):511-515
Uptake of [15 N]-ammonia was more sensitive to UV-B exposure than the total 14 CO2 fixation rate of Lithodesmium variabile Takano. Short-term UV-B radiation (15 min) had practically no effect on the kinetics of [15 N]-ammonia, whereas there was an effect on [14 C]-bicarbonate uptake rate. A significant reduction was found after 30 and 60 min UV-B stress. The time course of photosynthetic uptake of 15 NH4 Cl at several wavelengths was markedly depressed at shorter wavelengths (irradiation with WG 280). A short-term (11 min) exposure to ultraviolet radiation had no influence on the [14 C]-labeled photosynthetic products. However, the [15 N]-label of several amino acids and the ratio of [15 N]-glutamine to [15 N]-glutamic acid varied after irradiation with different ultraviolet wavebands. The results are discussed with reference to UV damage to the key enzymes of nitrogen metabolism. 相似文献
11.
Altered resource allocation during seed development in Arabidopsis caused by the abi3 mutation 总被引:1,自引:0,他引:1
The regulation of whole-plant resource allocation during seed development in Arabidopsis thaliana was investigated by examining growth rate and partitioning of 14 CO2 in wild-type plants and those carrying the abi3 mutation. Plants carrying the abi3 mutation partitioned more resources into seed development than the wild type. The extra resources were available as a result of delayed senescence of the cauline leaves in the mutant. After supply of 14 CO2 at later stages of reproductive development differences in patterns of 14 C distribution between mutant and wild type were consistent with long-term changes in growth and allocation. The role of long-distance signals in the regulation of seed yield in Arabidopsis is discussed. 相似文献
12.
Abstract: Production of [14 C]acetylcholine and 14 CO2 was examined by using tissue prisms from neocortex, hippocampus, and striatum from rats aged approximately 5 months, 13 months, and 27 months. [14 C]Acetylcholine synthesis in the striatum showed highly significant decreases with age for measurements in the presence of both 5 m m - and 31 m m -K+ , contrasting with the lack of significant change in 14 CO2 production in this region. The neocortex and hippocampus showed only small changes, especially when comparison was made between 13-month and senescent animals. Measurements of the release of [14 C]acetylcholine and influence of atropine on this release confirmed the relative stability with age of the cholinergic system in the neocortex. 相似文献
13.
Hilary J. Crompton C. P. Lloyd-Jones D. G. Hill-Cottingham 《Physiologia plantarum》1981,51(2):189-194
When whole plants were exposed to 14 CO2 , almost the same amount of radioactivity was taken up initially by each leaf regardless of its position on the stem and of the presence of beans at that node. Thus, although developing beans are a powerful sink for assimilated carbon, they do not increase the CO2 uptake by adjoining leaves.
The distribution of labelled assimilates 6 hours after feeding14 CO2 to a single leaf for 1 hour varied with both the position of the treated leaf and the stage of development of the plant. Before any flowers were set most of the radioactivity from all expanded leaves moved downwards to the roots and the stem below the treated leaf (lower stem). Later, during pod-fill, the upper leaves maintained this supply to the roots and lower stem, whilst most of the carbon translocated from the lower and mid-stem leaves went to the beans. However, we found no exclusive relationship between a leaf and the supply to beans developing on the same node.
The amount of radioactivity moving out of a source leaf at a fruiting node increased over successive samplings up to 48 h; the pattern of distribution of the14 CO2 however remained virtually unchanged. 相似文献
The distribution of labelled assimilates 6 hours after feeding
The amount of radioactivity moving out of a source leaf at a fruiting node increased over successive samplings up to 48 h; the pattern of distribution of the
14.
The metabolism of 14 C-putrescine and the changes in the endogenous concentrations of putrescine, spermidine and spermine were studied when cotyledons of Pinus radiata D. Don were cultured under shoot-forming (SF, + N6 -benzyladenine) and non-shoot-forming (NSF, - N6 -benzyladenine) conditions. Differences in the total uptake of 14 C-putrescine during a 2 h pulse feeding were not significant between the SF and NSF cotyledons except on day 3. The maximum uptake of label was on day 3 in the SF cotyledons, which released the highest amount of 14 CO2 as well. 14 C from the labeled putrescine was incorporated mainly into γ-aminobutyric acid, aspartate and glutamate. High performance liquid chromatography of the endogenous polyamines indicated that spermidine was the most predominant polyamine in the cultured cotyledons of radiata pine. Spermine increased by about 60% in the SF and 25% in the NSF cotyledons between days 0 and 3 of culture. 相似文献
15.
Ivanov B 《Free radical research》2000,33(3):217-227
In spinach thylakoids prepared from intact chloroplasts by shocking in the presence of ascorbate to preserve the operation of ascorbate peroxidase, the rate of oxygen uptake with methyl viologen as acceptor decreased in response to the addition of H2O2. Such a decrease was not observed in the presence of KCN or when the thylakoids lost ascorbate peroxidase activity. Illumination of intact chloroplasts in the presence of H2O2 and methyl viologen showed an initial rate of oxygen exchange, which is intermediate between the initial rate of oxygen evolution in the presence of H2O2 alone and steady-state oxygen uptake in the presence of methyl viologen. The data showed that monodehydroascorbate radical generated in ascorbate peroxidase reaction could compete with methyl viologen for electrons supplied by the electron transport chain in both thylakoids and intact chloroplasts. During the illumination of intact chloroplasts the rate of oxygen uptake increased. The presence of nigericin swiftly led to steady-state oxygen uptake, and to a clear-cut 1:1 relationship between the electron transport rate estimated from fluorescence assay and the electron transport rate determined from oxygen uptake, taking the stoichiometry 1O2:4e. The increase in oxygen uptake was attributed to the cessation of monodehydroascorbate radical generation brought about by consumption of intrachloroplast ascorbate in the peroxidase reactions, and the effects of nigericin were explained by acceleration of such consumption. The competition between methyl viologen and monodehydroascorbate radical in the intact chloroplasts was estimated under various conditions. 相似文献
16.
J. JOSEPH BLUM 《The Journal of eukaryotic microbiology》1991,38(3):229-233
Leishmania major promastigotes were washed and resuspended in an iso-osmotic buffer. The rate of oxidation of 14 C-labeled substrates was then measured as a function of osmolality. An acute decrease in osmolality (achieved by adding H2 O to the cell suspension) caused an increase in the rates of 14 CO2 production from [6-14 C]glucose and, to a lesser extent, from [1, (3)-14 C]glycerol. An acute increase in osmolality (achieved by adding NaCl, KCl, or mannitol) strongly inhibited the rates of 14 CO2 production from [1-: 14 C]alanine, [1-14 C]glutamate, and [1, (3)-14 C]glycerol. The rates of 14 CO2 formation from [1-14 C]laurate, [1-14 C]acetate, and [2-14 C]glucose (all of which form [1-14 C]acetyl CoA prior to oxidation) were also inhibited, but less strongly, by increasing osmolality. These data suggest that with increasing osmolality there is an inhibition of mitochondrial oxidative capacity, which could facilitate the increase in alanine pool size that occurs in response to hyper-osmotic stress. Similarly, an increase in oxidative capacity would help prevent a rebuild up of the alanine pool after its rapid loss to the medium in response to hypo-osmotic stress. 相似文献
17.
Abstract. An apparatus is described to carry out pulse and pulse-chase experiments with 14 CO2 on intact, attached leaves with known, steady-state rates of photosynthesis under defined conditions of temperature, vapour pressure deficit and photon flux density. Data are presented which show that the pattern of distribution of 14 C between compounds in extracts of such leaves is a true reflection of the pathways of photosynthetic carbon metabolism in the leaf during steady-state photosynthesis. 相似文献
18.
MASAHISA NAKAMURA AKIKO FUJIWARA IKUO YASUMASU SHOICHI OKINAGA KIYOSHI ARAI 《Development, growth & differentiation》1983,25(3):281-287
The rate of 14 CO2 , liberation from [14 C-1]glucose was identical to that from [14 C-6]glucose in spermatids, but more than the latter in spermatogonia. Rotenone (1 μM) completely inhibited 14 CO2 release from [14 C-1]glucose in spermatids, but decreased it only 30% in spermatogonia. The activity of glucose-6-phosphate dehydrogenase, but not 6-phosphogluconate dehydrogenase, was markedly lower in spermatocytes and spermatids than in spermatogonia. The activities of the glycolytic enzymes, glucosephosphate isomerase, fructose diphosphatase, glyceraldehyde-3-phosphate dehydrogenase and enolase, differed only slightly in spermatids and spermatogonia. It is concluded that the low glucose-6-phosphate dehydrogenase activity may contribute to the low activity of the pentose cycle in spermatocytes and spermatids. 相似文献
19.
Abstract: We studied the effects of denervation and reinnervation of the rat extensor digitorum longus muscle (EDL) on the oxidation of [6-14 C]glucose to 14 CO2 . The rate of 14 CO2 production decreased dramatically following denervation, and the decrease became significant 20 days after nerve section. Prior to day 20, changes apparently reflected the decline of muscle mass. Decreased 14 CO2 production was due to reduced capacity of the enzymatic system (apparent Vmax ); there was no change in apparent affinity for glucose (apparent K m ). Mixing experiments revealed that the loss of oxidative capacity following denervation is not caused by production of soluble inhibitors by degenerating muscle. Oxidative metabolism, as measured by 14 CO2 evolution, recovered during reinnervation. Surprisingly, the specific activity in reinnervated muscles displayed an "overshoot" of approximately 50%, which returned to control by day 60, possibly reflecting increased energy demand by the growing muscle. The time-course of the denervation-mediated change indicates that altered oxidative capacity is secondary to events that initiate denervation changes in muscle. Nevertheless, diminished oxidative capacity may be of considerable metabolic significance in denervated muscle. 相似文献
20.
David Weiss Adiva Shomer-Ilan Alexander Vainstein Abraham H. Halevy 《Physiologia plantarum》1990,78(3):345-350
Corollas of Petunia hybrida (cv. Hit Parade Rosa) flowers fixed 14 CO2 under both light and dark conditions. Rates of light fixation were much higher in mature pink corollas than in young, green corollas [57 and 9 nmol (ngchl)1 min-1 ], paralleling the development of chloroplasts in these tissues. Stomatal conductance in corollas was only 12% of that in green leaves, mainly due to the presence of few, and non-functioning stomata in the corolla. The activity and concentration of ribulose bisphosphate carboxylase (EC 4.1.1.39) in corolla extracts were only about 30% (per unit Chi) of those in extracts from green leaves. These results, together with previous results, might indicate a coordinated reduction in activity of systems participating in photosynthesis in corollas. The fixation products following a 6 s pulse with 14 CO2 , were typical of C, plants in both corollas and green leaves, but a higher level of β-carboxylation products was found in the corollas. The activity of phosphoenol-pyruvate carboxylase (EC 4.1.1.31) (per unit protein) was similar in both tissues. Although the total carbon fixed by the corolla constituted only a small part of the metabolites required for flower development, certain photosynthetic metabolites might have a regulatory role in flower development. 相似文献