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1.
The rates of dark CO 2 fixation and the label distribution in malate following dark 14CO 2 fixation in a C-4 plant (maize), a C-3 plant (sunflower), and two Crassulacean acid metabolism plants ( Bryophyllum calycinum and Kalanchoë diagremontianum leaves and plantlets) are compared. Within the first 30 minutes of dark 14CO 2 fixation, leaves of maize, B. calycinum, and sunflower, and K. diagremontianum plantlets fix CO 2 at rates of 1.4, 3.4, 0.23, and 1.0 μmoles of CO 2/mg of chlorophyll· hour, respectively. Net CO 2 fixation stops within 3 hours in maize and sunflower, but Crassulaceans continue fixing CO 2 for the duration of the 23-hour experiment. A bacterial procedure using Lactobacillus plantarum ATCC No. 8014 and one using malic enzyme to remove the β-carboxyl (C4) from malate are compared. It is reported that highly purified malic enzyme and the bacterial method provide equivalent results. Less purified malic enzyme may overestimate the label in C4 as much as 15 to 20%. The contribution of carbon atom 1 of malate is between 18 and 21% of the total carboxyl label after 1 minute of dark CO2 fixation. Isotopic labeling in the two carboxyls approached unity with time. The rate of increase is greatest in sunflower leaves and Kalanchoë plantlets. In addition, Kalanchoë leaves fix 14CO2 more rapidly than Kalanchoë plantlets and the equilibration of the malate carboxyls occurs more slowly. The rates of fixation and the randomization are tissue-specific. The rate of fixation does not correlate with the rate of randomization of isotope in the malate carboxyls. 相似文献
2.
Combined gas chromatography-mass spectrometry of malic acid derivatives has been used to show unequivocally that malic acid, synthesized during active acid accumulation in the dark by Kalanchoë daigremontiana Hammet et Perrier in the presence of 13CO 2 is produced by a pathway involving a single carboxylation. The significance of the finding that crassulacean malate synthesized in the dark and in the presence of 14CO 2 often contains 66% of the total carboxyl label in carbon atom 4, which has previously been taken to indicate the operation of a double carboxylation pathway or has been dismissed as an artefact, is discussed. 相似文献
3.
A mathematical model is developed which can be used to predict in vivo carbon isotope fractionations associated with carbon fixation in plants in terms of diffusion, CO 2 hydration, and carboxylation components. This model also permits calculation of internal CO 2 concentration for comparison with results of gas-exchange experiments. The isotope fractionations associated with carbon fixation in Kalanchoë daigremontiana and Bryophyllum tubiflorum have been measured by isolation of malic acid following dark fixation and enzymic determination of the isotopic composition of carbon-4 of this material. Corrections are made for residual malic acid, fumarase activity, and respiration. Comparison of these data with calculations from the model indicates that the rate of carbon fixation is limited principally by diffusion, rather than by carboxylation. Processes subsequent to the initial carboxylation also contribute to the over-all isotopic composition of the plant. 相似文献
4.
The labeling patterns in malic acid from dark 13CO 2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12–14 h dark 13CO 2 fixation the ratio of [4- 13C] to [1- 13C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The 13C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87–89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following 13CO 2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of [ 13C] malic acid ( 13CO 2 or [1- 13C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to 13CO 2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284–291). In the shortest times, only singly-labeled [4- 13C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.Abbreviations CAM
Crassulacean acid metabolism
- GCMS
gas chromatography-mass spectrometry
- MS
mass spectrometry
- NMR
nuclear magnetic resonance spectrometry
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate 相似文献
5.
The carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoë daigremontiana and Bryophyllum tubiflorum was calculated from the isotopic composition of carbon-4 of malic acid, after appropriate corrections. In the lowest temperature treatment (17°C nights, 23°C days), the isotope fractionation for both plants is −4‰ (that is, malate is enriched in 13C relative to the atmosphere). For K. daigremontiana, the isotope fractionation decreases with increasing temperature, becoming approximately 0‰ at 27°C/33°C. Detailed analysis of temperature effects on the isotope fractionation indicates that stomatal aperture decreases with increasing temperature and carboxylation capacity increases. For B. tubiflorum, the temperature dependence of the isotope fractionation is smaller and is principally attributed to the normal temperature dependences of the rates of diffusion and carboxylation steps. The small change in the isotopic composition of remaining malic acid in both species which is observed during deacidification indicates that malate release, rather than decarboxylation, is rate limiting in the deacidification process. 相似文献
6.
Summary The distribution of radioactivity between the products of 14CO 2 light fixation in phyllodia of Bryophyllum tubiflorum could be influenced experimentally by manipulating the malic acid content of the cells. Accelerating the deacidification of the tissue during the light period by application of higher light intensities accelerated the increase of malate labelling and the decrease of the sucrose labelling after 14CO 2 light fixation under our standard conditions (10 min preillumination, 15 min 14CO 2 light fixation, 8000 lux).In other experiments different malate contents of the tissues were induced by treating the phyllodia with different temperatures during the night period. In the morning, phyllodia with low malate content transferred most of the label into malate, and phyllodia with high malate content incorporated most of the 14C radioactivity into sugars. However, this was true only after preillumination of 1 hour. When the phyllodia fixed 14CO 2 without preillumination, no differences in the labelling patterns between acidified and non-acidified phyllodia could be observed.In experiments using leaf tissue slices of Bryophyllum daigremontianum we could again observe that malate was labelled more heavily in the deacidified tissue than in the acidified controls, with less radioactivity being transferred into phosphate esters and sugars. The rates of 14CO 2 light fixation were identical in tissue slices with high and low malate content. However, the rates of CO 2 dark fixation in the acidified samples were clearly lower than those in the deacidified ones. The low rate of CO 2 dark fixation in acidified samples could not be inhibited by an inhibitor of PEP-carboxylase as the high CO 2 dark fixation rate of the deacidified tissue could be inhibited.The results are discussed in relation to the feed back inhibition of PEP-carboxylase in vivo by malate. Compartmentation also seemed to be involved in controlling the flow of carbon during CO 2 light fixation in succulent tissue. 相似文献
7.
Malate synthesis by CO 2 fixation in wheat ( Triticum aestivum L.) and lupin ( Lupinus luteus) roots was investigated by labeling with NaH 13CO 3 as well as with NaH 14CO 3. The distribution of 14C label in the malate was examined, using enzymic degradation methods (malic enzyme, pyruvate decarboxylase) and, in the case of 13C, gas chromatography-mass spectrometry. In long-term experiments (2 to 12 hours), both methods showed that the [1-C] and [4-C] positions of malic acid are approximately equally labeled, in agreement with former findings. Short-term experiments (15, 30 seconds) showed that 14C is confined initially to the [4-C] position of malate but then is distributed quickly to the [1-C] atom. Neither labeling pattern nor rate of randomization was influenced by salt treatment. Analysis of malate from roots by gas chromatography-mass spectrometry, a procedure which was tested against in vitro-prepared [1- 13C]-, [4- 13C]-, and [1,4- 13C] malate, gave strong evidence for the existence of only singly labeled malate molecules. These data suggest that only one carboxylation step, catalyzed by phosphoenolpyruvate carboxylase and/or phosphoenolpyruvate carboxykinase, is responsible for malic acid synthesis in roots and that malate label is randomized by a fumarase-like reaction, presumably in mitochondria. 相似文献
8.
The end products of cellulose metabolism by the trichomonad flagellate Trichomitopsis termopsidis from the termite Zootermopsis sp. were investigated by growing axenic flagellates on [ 14C]cellulose. The growth of T. termopsidis resulted in the release of label into the supernatant fraction of the culture fluid, and > 75% was volatile under acid conditions. The label was analyzed for 14CO 2 and for [ 14C]volatile compounds by vacuum distillation under acid and alkaline conditions in disposable micro-distillation vessels. The distillate and undistilled culture supernatant fluid were chromatographed on cellulose thin layers to identify the labeled end product. T. termopsidis produced 14CO 2 and [ 14C]acetate which accounted for 25 to 30% and 55 to 60% of the labeled end products, respectively. The ratio of label in CO 2 to acetate suggests that they are produced in equimolar amounts. No neutral volatile compounds were produced. The remaining unidentified end product (10 to 20%) was not volatile nor extractable into ether. Hydrogen was produced by T. termopsidis, and the cells were killed by the drug metronidazole. Enzymatic activities were found which account for these end products: pyruvate:ferredoxin oxidoreductase and hydrogenase. The results indicate that acetate is the end product of T. termopsidis cellulose metabolism and is available to the termite for energy metabolism and biosynthesis. 相似文献
9.
We did this work to discover the pathway of CO 2 fixation into sugars in the dark during gluconeogenesis by the cotyledons of 5-day-old seedlings of Cucurbita pepo L. We paid particular attention to the possibility of a contribution from ribulosebisphosphate carboxylase. The detailed distribution of 14C after exposure of excised cotyledons to 14CO 2 in the dark was determined in a series of pulse and chase experiments. After 4s in 14CO 2, 89% of the 14C fixed was in malate and aspartate. In longer exposures, and in chases in 12CO 2, label appeared in alanine, phosphoenolpyruvate, 3-phosphoglycerate and sugar phosphates, and accumulated in sugars. The transfer of label from C-4 acids to sugars was restricted by inhibition of phosphoenolpyruvate carboxykinase in vivo by 3-mercaptopicolinic acid. We conclude as follows. Initial fixation of CO 2 in the dark is almost entirely into phosphoenolpyruvate, probably via phosphoenolpyruvate carboxylase (EC 4.1.1.31) which we showed to be present in appreciable amounts. Incorporation into sugars occurs chiefly, if not completely, as a result of randomization of the carboxyl groups of the C-4 acids and subsequent conversion of the oxaloacetate to sugars via the accepted sequence for gluconeogenesis. Ribulosebisphosphate carboxylase appears to make very little contribution to sugar synthesis from fat. 相似文献
10.
The metabolism of fixed 14CO 2 and the utilization of the C-4 carboxyl of malate and aspartate were examined during photosynthetic induction in Flaveria trinervia, a C 4 dicot of the NADP-malic enzyme subgroup. Pulse/chase experiments indicated that both malate and aspartate appeared to function directly in the C 4 cycle at all times during the induction period (examined after 30 seconds, 5 minutes and 20 minutes illumination). However, the rate of loss of 14C-label from the C-4 position of malate plus aspartate was relatively slow after 30 seconds of illumination, compared to treatments after 5 or 20 minutes of illumination. Similarly, the appearance of label in other photosynthetic products (e.g. 3-phosphoglycerate, sugar phosphates, alanine) during the chase periods was generally slower after only 30 seconds of leaf illumination, compared to that after 5 of 20 minutes illumination. This may be due to the lower rate of photosynthesis after 30 seconds illumination. The appearance of label in carbons 1→3 of each C 4 acid during the chase periods was relatively slow after either 30 seconds or 5 minutes illumination, while there was a relatively rapid accumulation of label in carbons 1→3 of both C 4 acids after 20 minutes illumination. Thus, while the turnover rate of the 14C-4 label in both C 4 acids increased only during the first 5 minutes of the induction period, only later during induction is there an increased rate of appearance of label in other carbon atoms of the C 4 acids. The implied source of 14C for labeling of the 1→3 positions of the C 4 acids is an apparent carbon flux from 3-phosphoglycerate of the reductive pentose phosphate pathway to phosphoenolpyruvate of the C 4 cycle. 相似文献
11.
After a 5-second exposure of illuminated bermudagrass ( Cynodon dactylon L. var. `Coastal') leaves to 14CO 2, 84% of the incorporated 14C was recovered as aspartate and malate. After transfer from 14CO 2-air to 12CO 2-air under continuous illumination, total radioactivity decreased in aspartate, increased in 3-phosphoglyceric acid and alanine, and remained relatively constant in malate. Carbon atom 1 of alanine was labeled predominantly, which was interpreted to indicate that alanine was derived from 3-phosphoglyceric acid. The activity of phosphoenolpyruvate carboxylase, alkaline pyrophosphatase, adenylate kinase, pyruvate-phosphate dikinase, and malic enzyme in bermudagrass leaf extracts was distinctly higher than those in fescue ( Festuca arundinacea Schreb.), a reductive pentose phosphate cycle plant. Assays of malic enzyme activity indicated that the decarboxylation of malate was favored. Both malic enzyme and NADP +-specific malic dehydrogenase activity were low in bermudagrass compared to sugarcane ( Saccharum officinarum L.). The activities of NAD +-specific malic dehydrogenase and acidic pyrophosphatase in leaf extracts were similar among the plant species examined, irrespective of the predominant cycle of photosynthesis. Ribulose-1, 5-diphosphate carboxylase in C 4-dicarboxylic acid cycle plant leaf extracts was about 60%, on a chlorophyll basis, of that in reductive pentose phosphate cycle plants. 相似文献
12.
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 CO 2. An accumulation of radioactivity in the tricarboxylic acid cycle intermediates after 14CO 2 production became constant indicates that organic acid pools outside of the mitochondria were involved in the buildup of radioactivity. The continuous production of 14CO 2 over 2 hours indicates that, in the dark, the tricarboxylic acid cycle was the major route for succinate metabolism with CO 2 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 CO 2 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 14CO 2 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
13.
Summary Starch consumption during the dark period in detached phyllodia of Bryophyllum tubiflorum is inhibited, when the phyllodia are held in an atmosphere free from carbon dioxide during the night. This is true also in other succulent plants with Crassulacean acid metabolism=CAM (examined were Bryophyllum calycinum and Sedum morganianum). This effect seems to indicate that the role of starch in CAM is production of CO 2 acceptors rather than production of carbon dioxide by respiration. If the CO 2 acceptors are not used, starch consumption comes to an end.This hypothesis could also explain results of experiments in which phyllodia were held at different temperatures during the dark period, and net CO 2 fixation, starch loss and malate gain were determined. At 10° CO 2 uptake was at a maximum (the necessary supply of CO 2 acceptors must have therefore been at a maximum, too). Under these conditions there was the greatest amount of starch consumption. At 23° C, CO 2 uptake was clearly lowered, and this was also true for starch consumption. At 35° C net CO 2 uptake was balanced by net CO 2, output (no CO 2 acceptors were needed in CO 2 dark fixation). At this temperature no starch loss could be measured. 相似文献
14.
The metabolism of m-cresol by methanogenic cultures enriched from domestic sewage sludge was investigated. In the initial studies, bromoethanesulfonic acid was used to inhibit methane production. This led to the accumulation of 4.0 ± 0.8 mol of acetate per mol of m-cresol metabolized. These results suggested that CO 2 incorporation occurred because each molecule of m-cresol contained seven carbon atoms, whereas four molecules of acetate product contained a total of eight carbon atoms. To verify this, [ 14C]bicarbonate was added to bromoethanesulfonic acid-inhibited cultures, and those cultures yielded [ 14C]acetate. Of the label recovered as acetate, 89% was found in the carboxyl position. Similar cultures fed [ methyl- 14C] m-cresol yielded methyl-labeled acetate. A 14C-labeled transient intermediate was detected in cultures given either m-cresol and [ 14C]bicarbonate or bicarbonate and [ methyl- 14C] m-cresol. The intermediate was identified as 4-hydroxy-2-methylbenzoic acid. In addition, another metabolite was detected and identified as 2-methylbenzoic acid. This compound appeared to be produced only sporadically, and it accumulated in the medium, suggesting that the dehydroxylation of 4-hydroxy-2-methylbenzoic acid led to an apparent dead-end product. 相似文献
15.
Aims: To determine if the phytotherapeutic agent, Bryophyllum pinnatum, could serve as an alternative drug for the overactive bladder syndrome, and to characterise the fraction responsible for the inhibition of detrusor contractility. Methods: Fractions were prepared from the MeOH extract of B. pinnatum and further analysed by HPLC-PDA-MS. Detrusor muscle strips were prepared from porcine bladders and the electrically induced muscle contractility measured by organ bath. The effect of B. pinnatum leaf press juice (2.5–10%), a flavonoid fraction (0.1–1 mg/ml), and a bufadienolide fraction (0.1–40 μg/ml) on detrusor contractility was assessed and compared with controls (polar fraction (0.5–5 mg/ml) and oxybutynin (10 −8–10 −6 M)). Results: The press juice, at a concentration of 10% led to a reduction of detrusor contractility. Bladder strips treated with the flavonoid fraction showed a significant reduction of the contractility to 21.3 ± 5.2% (1 mg/ml) while the bufadienolide fraction had no inhibitory effect in the investigated concentrations. The polar fraction showed a reduction of the contractility in a pH-dependent fashion. At 10 −6 M concentration oxybutynin reduced the detrusor contractility to 21.9 ± 4.7%. Conclusions: The flavonoid fraction of Bryophyllum pinnatum reduces the porcine detrusor contractility in a dose- and time-dependent manner. Fractions from B. pinnatum may be a new pharmacological approach for the treatment of OAB. 相似文献
16.
3,4-Dichloropropionanilide- 14C (propanil) labeled in either the C-1 or C-3 carbon atoms of the propionic acid moiety was applied to the roots of pea ( Pisum sativum L.) and rice ( Oryza sativa L.) plants in nutrient solution (0.1 m m-0.28 m m). Radioactivity was detected throughout the treated plants, but the greatest labeling was found in the roots. None of the products that contained aniline were radioactive, suggesting that the plants split the propionic acid moiety from propanil. The fate of the propionate moiety of propanil was determined by recovery of 14CO 2 from plants exposed to propanil- 14C. The time-course of the 14CO 2 production demonstrated that the intact propionic acid was cleaved from the propanil and subsequently catabolized by the β-oxidation catabolic sequence. The appearance of radioactivity in the shoots was attributed to the incorporation of products of propionate metabolism. Both the susceptible pea plants and the tolerant rice plants converted a high percentage of the administered propanil- 14C to 14CO 2. 相似文献
17.
The studies described in the paper were conducted with tissue slices of Crassulacean acid metabolism (CAM) plants floating in isotonic buffer. In a first series of experiments, temperature effects on the efflux of [ 14C]malate and 14CO 2 were studied. An increase of temperature increased the efflux from the tissue in a non-linear manner. The efflux was markedly influenced also by the temperatures applied during the pretreatment. The rates of label export in response to the temperature and the relative contributions of 14CO 2 and [ 14C]malate to the label export were different in the two studied CAM plants ( Kalanchoë daigremontiana, Sempervivum montanum). In further experiments, temperature response of the labelling patterns produced by 14CO 2 fixation and light and darkness were studied. In tissue which had accumulated malate (acidified state) an increase of temperature decreased the rates of dark CO 2 fixation whilst the rates of CO 2 fixation in light remained largely unaffected. An increase of temperature shifted the labelling patterns from a C 4-type (malate being the mainly labelled compound) into a C 3-type (label in carbohydrates). No such shift in the labelling patterns could be observed in the tissue which had depleted the previously stored malate (deacidified state). The results indicate that in the acidified tissue the increase of temperature increases the efflux of malate from the vacuole by changing the properties of the tonoplast. It is assumed that the increased export of malic acid lowers the in-vivo activity of phosphoenol pyruvate carboxylase by feedback inhibition.Abbreviations CAM
Crassulacean acid metabolism
- FW
fresh weight
- PEPCase
phosphoenolpyruvate carboxylase
Dedicated to Professor O.L. Lange, Würzburg, on the occasion of his 60th birthday 相似文献
18.
Products of the nodule cytosol in vivo dark [ 14C]CO 2 fixation were detected in the plant cytosol as well as in the bacteroids of pea ( Pisum sativum L. cv “Bodil”) nodules. The distribution of the metabolites of the dark CO 2 fixation products was compared in effective (fix +) nodules infected by a wild-type Rhizobium leguminosarum (MNF 300), and ineffective (fix −) nodules of the R. leguminosarum mutant MNF 3080. The latter has a defect in the dicarboxylic acid transport system of the bacterial membrane. The 14C incorporation from [ 14C]CO 2 was about threefold greater in the wild-type nodules than in the mutant nodules. Similarly, in wild-type nodules the in vitro phospho enolpyruvate carboxylase activity was substantially greater than that of the mutant. Almost 90% of the 14C label in the cytosol was found in organic acids in both symbioses. Malate comprised about half of the total cytosol organic acid content on a molar basis, and more than 70% of the cytosol radioactivity in the organic acid fraction was detected in malate in both symbioses. Most of the remaining 14C was contained in the amino acid fraction of the cytosol in both symbioses. More than 70% of the 14C label found in the amino acids of the cytosol was incorporated in aspartate, which on a molar basis comprised only about 1% of the total amino acid pool in the cytosol. The extensive 14C labeling of malate and aspartate from nodule dark [ 14C]CO 2 fixation is consistent with the role of phospho enolpyruvate carboxlase in nodule dark CO 2 fixation. Bacteroids from the effective wild-type symbiosis accumulated sevenfold more 14C than did the dicarboxylic acid transport defective bacteroids. The bacteroids of the effective MNF 300 symbiosis contained the largest proportion of the incorporated 14C in the organic acids, whereas ineffective MNF 3080 bacteroids mainly contained 14C in the amino acid fraction. In both symbioses a larger proportion of the bacteroid 14C label was detected in malate and aspartate than their corresponding proportions of the organic acids and amino acids on a molar basis. The proportion of 14C label in succinate, 2-oxogultarate, citrate, and fumarate in the bacteroids of the wild type greatly exceeded that of the dicarboxylate uptake mutant. The results indicate a central role for nodule cytosol dark CO 2 fixation in the supply of the bacteroids with dicarboxylic acids. 相似文献
19.
Applied acetaldehyde is known to lead to sugar accumulation in fruit including tomatoes ( Lycopersicon esculentum) (O Paz, HW Janes, BA Prevost, C Frenkel [1982] J Food Sci 47: 270-274) presumably due to stimulation of gluconeogenesis. This conjecture was examined using tomato fruit pericarp discs as a test system and applied i-[U- 14C]malic acid as the source for gluconeogenic carbon mobilization. The label from malate was recovered in respiratory CO 2, in other organic acids, in ethanol insoluble material, and an appreciable amount in the ethanol soluble sugar fraction. In Rutgers tomatoes, the label recovery in the sugar fraction and an attendant label reduction in the organic acids fraction intensified with fruit ripening. In both Rutgers and in the nonripening tomato rin, these processes were markedly stimulated by 4000 ppm acetaldehyde. The onset of label apportioning from malic acids to sugars coincided with decreased levels of fructose-2,6-biphosphate, the gluconeogenesis inhibitor. In acetaldehyde-treated tissues, with enhanced label mobilization, this decline reached one-half to one third of the initial fructose-2,6-biphosphate levels. Application of 30 micromolar fructose-2,6-biphosphate or 2,5-anhydro-d-mannitol in turn led to a precipitous reduction in the label flow to sugars presumably due to inhibition of fructose-1,6-biphosphatase by the compounds. We conclude that malic and perhaps other organic acids are carbon sources for gluconeogenesis occurring normally in ripening tomatoes. The process is stimulated by acetaldehyde apparently by attenuating the fructose-2,6-biphosphate levels. The mode of the acetaldehyde regulation of fructose-2,6-biphosphate metabolism awaits clarification. 相似文献
20.
The dry weight yield of plants of Bryophyllum tubiflorum Harvey, a species with Crassulacean acid metabolism characteristics, increased significantly ( P < 1%) in response to added sodium (0.1 milliequivalents per liter NaCl was supplied to the culture solution initially containing less than 0.08 microequivalents per liter of Na) when grown under short day (8 hours) conditions but not when grown under long day conditions (16 hours). 相似文献
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