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1.
The relationship of malate synthesis to K + absorption from solutions of K 2SO 4 and KHCO 3 was compared in nonvacuolate barley ( Hordeum vulgare) root tips and whole excised roots. The comparison has permitted separation of the process which evokes organic acid synthesis from that which leads to stoichiometry between net acid equivalents formed and excess K + absorbed from K 2SO 4, on the one hand, and total K + absorbed from KHCO 3, on the other. Both in tips and in roots K + uptake from 20 mN salt solution exceeds malate synthesis in the first hour. In vacuolate roots the expected stoichiometry is achieved with time. When root tips are transferred to dilute CaSO 4, malate is rapidly metabolized, and K + is lost to the solution. By contrast, in excised whole roots the malate level remains unchanged, the salt-induced organic acid presumably being retained in the vacuole. In excised roots malonate leads to a marked drop in malate levels in untreated roots as well as in roots which have experienced salt-induced net malate synthesis. In consequence, it is contended that malonate makes available normally sequestered vacuolar malate. 相似文献
2.
Excised roots of barley ( Hordeum vulgare, var. Campana) were incubated in KCl, K 2SO 4, CaCl 2, and NaCl solutions at concentrations of 10 −5 to 10 −2 n. Changes in substrate solution pH, cell sap pH, and organic acid content of the roots were related to differences in cation and anion absorption. The pH of expressed sap of roots increased when cations were absorbed in excess of anions and decreased when anions were absorbed in excess of cations. The pH of the cell sap shifted in response to imbalances in cation and anion uptake in salt solutions as dilute as 10 −5 n. Changes in cell sap pH were detectable within 15 minutes after the roots were placed in 10 −3 n K 2SO 4. Organic acid changes in the roots were proportional to expressed sap pH changes induced by unbalanced ion uptake. Changes in organic acid content in response to differential cation and anion uptake appear to be associated with the low-salt component of ion uptake. 相似文献
3.
In the higher plant Vicia faba, anomalous labeling patterns in the organic acids and related amino acids of the tricarboxylic acid cycle which result from photosynthetic 14CO 2 fixation (in conjunction with an enzyme localization pattern unique to plant mitochondria) suggest that the tricarboxylic acid cycle functions primarily as a pathway leading to glutamic acid biosynthesis during autotrophic growth. The distribution of isotope in citrate indicates little recycling of oxaloacetate for the resynthesis of citrate. Rather, malate appears to provide both the C 2 and C 4 fragments for the synthesis of citrate, and [ 3H]formate and 14CO 2-labeling patterns implicate serine as the ultimate C 3 precursor of malate. 相似文献
4.
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
5.
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
6.
Fruits of Lycopersicon esculentum Mill cv Sonatine stored in 6% CO 2, 6% O 2, and 88% N 2 for 14 weeks at 12°C, exhibited a temporal separation of certain biochemical events associated with ripening. The specific activity of two citric acid cycle enzymes, citrate synthase and malate dehydrogenase, fell substantially during the first 2 weeks of storage when changes in organic acid concentration also occurred. During this period, lycopene, polygalacturonase, and ethylene were undetectable. When fruit were removed from store, ethylene was evolved and polygalacturonase and invertase activity were rapidly initiated as was synthesis of lycopene. To determine whether the changes in organic acid metabolism were affected by ethylene, fruit was kept at 22°C in either a normal atmosphere or a normal atmosphere supplemented with 27 microliters per liter of ethylene, and it was shown that in both atmospheres similar quantitative changes to those described above occurred in the citric acid cycle enzymes specific activities before any detectable increase in the specific activities of invertase and polygalacturonase. These latter changes, together with pigment changes, occurred between 2 and 3 days earlier in fruit exposed to ethylene, compared with those kept in a normal atmosphere. 相似文献
7.
- 14CO2 fixation into organic acids in tips and proximal sectionsof both corn and barley roots was studied as a function of thenature and concentration of the salt in the external solution.
- In comparison with the level of 14CO2 fixation by vacuolateproximal sections in KCI, incorporation was markedly enhancedin K2SO4 and diminished in CaCk. By contrast, non-vacuolateroot tips were indifferent to the type of external salt withrespect to UCO2 incorporation into organic acids.
- The effectof salt type on organic acid formation from 14CO2was most pronouncedat relatively high concentrations.
- The conclusion was reachedthat organic acid synthesis in responsetoexcess cation uptakeis the result of cation movement into thevacuole, and thattransport into the vacuole is mediated bythe low-affinity componentof the dual mechanisms involved inion absorption.
1Present address: Government Forst Experiment Station, Meguro,Tokyo. 相似文献
8.
Detached roots and nodules of the N 2-fixing species, Albus glutinosa (European black alder), actively assimilate CO 2. The maximum rates of dark CO 2 fixation observed for detached nodules and roots were 15 and 3 micromoles CO 2 fixed per gram dry weight per hour, respectively. The net incorporation of CO 2 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 CO 2 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 CO 2 fixation and N 2 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 N 2-fixing nodules and roots of alder. 相似文献
9.
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
10.
A method has been described which permits the determination of the specific activity of 14CO 2 with an accuracy limited only by the accuracy of the liquid scintillation counter. Its principal idea is the selective conversion of CO 2 to nonvolatile organic compounds, such as benzoic acid. While this method is applicable quite generally it has been applied with particular success in connection with the Schmidt degradation of samples as small as 0.2 mmole where contamination of the evolved CO 2 is serious due to the necessarily large excess of reactants. 相似文献
11.
Abscisic acid inhibited the rate of 14CO 2 fixation in leaves of Pennisetum typhoides (Burm. f.) Stapf & Hubbard seedlings, but increased the activities of phosphoenol-pyruvate-carboxylase and malic enzyme. The leaves of the seedlings grown in the presence of abscisic acid incorporated, in comparison to the control, more radioactivity in the fraction of organic acids, but less radioactivity was recorded in the amino acid fraction. On the other hand, gibberellic acid which also inhibits photosynthetic 14CO 2 assimilation and decreases the activities of photosynthetic enzymes, favours greater incorporation in alanine, and reduces that in malate. It is deduced that bio-regulants can greatly influence the flow of 14C into individual photosynthetic products. As in growth, abscisic and gibberellic acids in combination tended to antagonize each other in their effects on enzyme activity as well as in incorporation of 14CO 2 into photosynthetic products. 相似文献
12.
The effects of CO 2 concentration and illumination on net gas exchange and the pathway of 14CO 2 fixation in detached seeds from developing fruits of Lupinus albus (L.) have been studied. Increasing the CO2 concentration in the surrounding atmosphere (from 0.03 to 3.0% [v/v] in air) decreased CO2 efflux by detached seeds either exposed to the light flux equivalent to that transmitted by the pod wall (500 to 600 micro-Einsteins per square meter per second) in full sunlight or held in darkness. Above 1% CO2 detached seeds made a net gain of CO2 in the light (up to 0.4 milligrams of CO2 fixed per gram fresh weight per hour) but 14CO2 injected into the gas space of intact fruits (containing around 1.5% CO2 naturally) was fixed mainly by the pod and little by the seeds. Throughout development seeds contained ribulose-1,5-bisphosphate carboxylase activity (EC 4.1.1.39), especially in the embryo (up to 99 micromoles of CO2 fixed per gram fresh weight per hour) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) in both testa (up to 280 micromoles of CO2 fixed per gram fresh weight per hour) and embryo (up to 355 micromoles of CO2 fixed per gram fresh weight per hour). In kinetic experiments the most significant early formed product of 14CO2 fixation in both light and dark was malate but in the light phosphoglyceric acid and sugar phosphates were also rapidly labeled. 14CO2 fixation in the light was linked to the synthesis of sugars and amino acids but in the dark labeled sugars were not formed. 相似文献
13.
When Vicia faba guard cell protoplasts were treated with fusicoccin, dark 14CO 2 fixation rates increased by as much as 8-fold. Rate increase was saturated with less than 1 micromolar fusicoccin. Even after 6 minutes of dark 14CO 2 fixation, more than 95% of the incorporated radioactivity was in stable products derived from carboxylation of phosphoenolpyruvate (about 50% and 30% in malate and aspartate, respectively). The relative distribution of 14C among products and in the C-4 position of malate (initially more than 90% of [ 14C]malate) was independent of fusicoccin concentration. After incubation in the dark, malate content was higher in protoplasts treated with fusicoccin. A positive correlation was observed between the amounts of 14CO 2 fixed and malate content. It was concluded that (a) fusicoccin causes an increase in the rate of dark 14CO2 fixation without alteration of the relative fluxes through pathways by which it is metabolized, (b) fusicoccin causes an increase in malate synthesis, and (c) dark 14CO2 fixation and malate synthesis are mediated by phosphoenolpyruvate carboxylase. 相似文献
14.
Isolated, purified mesophyll and guard-cell protoplasts of Vicia faba L. and Allium cepa L. were exposed to 14CO 2 in the light and in the dark. The guard-cell protoplasts of Vicia and Allium did not show any labeling in phosphorylated products of the Calvin cycle, thus appearing to lack the ability to reduce CO 2 photosynthetically. In Vicia, high amounts of radioactivity (35%) appeared in starch after 60-s pulses of 14CO 2 both in the light and in the dark. Presumably, the 14CO 2 is fixed into the malate via PEP carboxylase and then metabolized into starch as the final product of gluconeogenesis. This is supported by the fact that guard-cell protoplasts exposed to malic acid uniformly labeled with 14CO 2 showed high amounts of labeled starch after the incubation, whereas cells labeled with [4- 14C]malate had minimal amounts of labeled starch (1/120).In contrast, the starch-deficient Allium, guard-cell protoplasts did not show any significant 14CO 2 fixation. However, adding PEP to an homogenate stimulated 14CO 2 uptake, thus supporting the interpretation that the presence of starch as a source of PEP is necessary for incorporating CO 2 and delivering malate. With starch-containing Vicia guard-cell protoplasts, the correlation between changes in volume and the interconversion of malate and starch was demonstrated. It was shown that the rapid gluconeogenic conversion of malate into starch prevents an increase of the volume of the protoplasts, whereas the degradation of starch to malate is accompanied by a swelling of the protoplasts.Abbreviations GCPs
guard-cell protoplasts
- MCPs
mesophyll cell protoplasts
- PEP
phosphoenolpyruvate
- DTT
dithiothreitol
- 3-PGA
3-phosphoglyceric acid
- RiBP
ribulose 1,5 bisphosphate
- MDH
malate dehydrogenase
- MES
2-(N-morpholino)ethane sulfonic acid
- CAM
crassulacean acid metabolism 相似文献
15.
The influence of indoleacetic acid, 0.03% CO 2, and malate on protein metabolism of etiolated Avena sativa coleoptile sections has been investigated. All three were found to elevate both the rate of incorporation of labeled leucine into protein, and the level of soluble protein. The combination of indoleacetic acid and CO 2 stimulated these values in an additive or weakly synergistic manner, in contrast to the nonadditive influence of malate and CO 2. Evidence is presented that cyclo-heximide inhibited the stimulation of protein synthesis by CO 2, and that indoleacetic acid increased the incorporation of 14C-bicarbonate into protein. These data are discussed in the context of CO 2-stimulated growth of etiolated tissue, and proposals that CO 2-stimulated growth involves dark CO 2 fixation. 相似文献
16.
The nature and sequence of metabolic events during phase II (early morning) Crassulacean acid metabolism in Opuntia erinacea var columbiana (Griffiths) L. Benson were characterized. Gas exchange measurements under 2 and 21% O 2 revealed increased O 2 inhibition of CO 2 fixation with progression of phase II. Malate and titratable acidity patterns indicated continued synthesis of C 4 acids for at least 30 minutes into the light period. Potential activities of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme exhibited little change during phase II, while light activation of NADP-malate dehydrogenase, pyruvate, orthophosphate dikinase, and ribulose-1,5-bisphosphate carboxylase was apparent. Short-term 14CO 2 fixation experiments showed that the per cent of 14C incorporated into C 4 acids decreased while incorporation into other metabolites increased with time. PEPC exhibited increased sensitivity to 2 millimolar malate, and the Ki(malate) for PEPC decreased markedly with time. Sensitivity of PEPC to malate inhibition was considerably greater at pH 7.5 than at 8.0. The results indicate that decarboxylation and synthesis of malate occur simultaneously during the early morning period, and that phase II acid metabolism is not limited by CO 2 diffusion through stomata. With progression of phase II, CO 2 fixation by PEPC decreases while fixation by ribulose-1,5-bisphosphate carboxylase increases. 相似文献
17.
Experiments were designed to determine the significance of dark CO 2 fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate- 14C was used to determine the pathway and amounts of CO 2 fixation, while leucine- 14C was used to estimate protein synthesis in tissues aerated with various levels of CO 2. Organic acids were labeled from bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the 14C label in the ethanol-water insoluble residue. Studies with leucine-14C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-14C into protein than those aerated with CO2-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO2-free air. These studies are consistent with the suggestion that dark fixation of CO2 is involved in the growth of plant tissues. 相似文献
18.
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 [U 14C]glutamate in the light and in the absence of inhibitor or NH 4Cl. Other amino acids, organic acids, sugars, sugar phosphates, and CO 2 became slightly radioactive. Ammonium chloride (10 m m) increased formation of [ 14C] glutamine, aspartate, citrate, and malate but decreased incorporation into 2-oxoglutarate, alanine, and 14CO 2. Methionine sulfoximine (1 m m) suppressed glutamine synthesis, caused NH 3 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 CO 2 and sugar phosphates. Thus, formation of radioactive organic acids in the presence of methionine sulfoximine does not take place indirectly through “dark” fixation of CO 2 released by degradation of glutamate when ammonia assimilation is blocked. When illuminated leaves supplied with [U- 14C] glutamate without inhibitor or NH 4Cl were transferred to darkness, there was increased metabolism of the glutamate to glutamine, aspartate, succinate, malate, and 14CO 2. Darkening had little effect on the labeling pattern in leaves treated with methionine sulfoximine. 相似文献
19.
Summary Detached phyllodia of Bryophyllum tubiflorum were fed under illumination with 14CO 2 at different times during the light/dark period (12:12 hours). After photosynthesis in presence of 14CO 2 during the intrinsic dark period the greatest part of soluble radioactivity was found in malate. When the same experiment was repeated during the light period, radioactivity was incorporated mainly into sucrose in the first hours while malate was labelled rather weakly. In the late afternoon (last third of the light period), malate became most heavily labelled again during photosynthesis with 14CO 2.Our results indicate that the synthesis of malate by PEP-carboxylase/malate dehydrogenase is inhibited at certain times during the night/day period by end product inhibition of PEP-carboxylase, as was demonstrated by Queiroz (1967, 1968) and Ting (1968) in vitro.During inhibition of the PEP-carboxylase there is no competition between the synthesis of malate and CO 2-fixation by the Calvin cycle. Thus radioactivity can flow into sucrose via the Calvin cycle during this time. When the malate content of the phyllodia is low, CO 2-fixation by PEP-carboxylase is not inhibited. Now this pathway dominates over photosynthesis via the Calvin cycle, for PEP-carboxylase has a higher affinity for CO 2 than carboxydismutase. Therefore malate now becomes more labelled than sucrose. 相似文献
20.
Barley, Panicum milioides and Panicum maximum were exposed to 14CO 2 near their photosynthetic CO 2 compensation points and their respective 14C-products were determined. In short exposure times Panicum maximum had 100% of its 14C in malate and aspartate whereas Panicum milioides and barley had 16 and 3% of their respective 14C in C 4 organic acids. Near the respective CO 2 compensation points a linear relationship occurs in plotting the ratio of glycine, serine, and glycerate to C 4 organic acids. The ratio of ribulose 1,5-bisphosphate oxygenase to phosphoenolpyruvate carboxylase is linear with their CO 2 compensation points. The photosynthetic CO 2 compensation point apparently is controlled by the activity of enzymes producing photorespiration metabolites and the activity of phospheonolpyruvate carboxylase. 相似文献
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