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1.
The aim of this work was to establish the pathways of carbohydrate oxidation used in the dark by leaves of Pisum sativum and Triticum aestivum. Segments of young and mature leaves of pea released the carbons of glucose-[ 14C] as 14CO 2 in the order 3,4 > 1 > 2 > 6 whereas in segments of young and mature leaves of wheat the order was 3,4 > 1 > 6 > 2. The detailed labelling of the constituents of mature leaves of wheat by glucose-[1- 14C], -[2- 14C], -[3,4- 14C], and -[6- 14C] was determined and showed that the high yield of CO 2 from C-6 relative to that from C-2 was due to release of C-6 during pentan synthesis. Estimates were made of the maximum catalytic activities of phosphofructokinase and glucose-6-phosphate dehydrogenase in pea and wheat leaves of three ages. The results of all the above investigations strongly indicate that both pea and wheat leaves in the dark oxidize carbohydrate via glycolysis and the pentose phosphate pathway with the latter accounting for no more than a third of the total. No evidence was obtained of any major change in the relative activities of the two pathways during the development of either type of leaf. 相似文献
2.
Many changes that occur in a cell during the cell cycle can be demonstrated in synchronous cultures and can reveal dimensions of cell metabolism not attainable by the study of balanced growth of asynchronous populations in batch cultures or the steady state in chemostat cultures. The release of 14CO 2 from specifically labeled glucose by phased (continuously synchronized) cultures follows a characteristic pattern ( profile) that depends upon the stage in the cell cycle and the period of labeling used. Successive profiles throughout a cycle showed differences that were altered under different nutrient-limiting growth conditions. Profiles obtained with glucose-1- 14C, glucose-2- 14C, glucose-3,4- 14C, and glucose-6- 14C and phased cells of Candida utilis under N-, P-, and C-limited growth demonstrated the variable character of the metabolic activity that occurred in the cells while contour changes within the profiles across the cycle indicated possible correlations with activities of the hexose monophosphate, Embden-Meyerhof-Parnas, and tricarboxylic acid cycle pathways during the cell cycle. The basis of these changes and their use as elementary parameters for study of problems of physiological changes in vivo are considered. 相似文献
3.
Glucose metabolism of healthy and tobacco mosaic virus-infected leaf-discs of Nicotiana tabocum L. var. Xanthi showing local-necrotic lesions was investigated using glucose- 14C. Local lesion formation following inoculation with tobacco mosaic virus resulted in enhanced glucose metabolism reflected by an increased rate of release of 14CO 2 from glucose-U- 14C and greater incorporation of 14C into all cell fractions. When specifically labelled glucose was fed to healthy and tobacco mosaic virus infected leaves, the C 6/C 1 ratio (rate of release of 14CO 2 from glucose-6- 14C/rate of release of 14CO 2 from glucose-l- 14C) was similar for healthy and virus-infected leaves. The C 6/C 1 ratios recorded from 0.30 to 0.50 indicate that both the glycolytic and pentose phosphate pathways participate in glucose catobolism in healthy and virus-infected leaves. Although the C 6/C 1 ratio was the same as that of the healthy leaf the rate of release of 14CO 2 from glucose-6- 14C and glucose-1- 14C was greatly increased in the virus-infected leaf. The increased glucose catabolism occurs by both glycolytic and pentose phosphate pathways in the virus-infected leaf. 相似文献
4.
Summary Goldfish acclimated to normal oxygen levels and to 20°C were made anoxic and injected i.p. with U- 14C-glucose, 6- 14C-glucose, U- 14C-lactate, 3- 14C-lactate, 1- 14C-acetate or 3,4- 14C-glutamate. Radioactivity released into the water (total 14C and 14CO 2) was monitored over a period of about 12 h. With the exception of 3,4- 14C-glutamate from which only 4% was released, the release of 14C from the other compounds was found to be over 30%. The fraction of the radioactivity released as CO 2 varied with the compound injected but was high during the first 4 h after injection. It is argued that the acid-stable 14C component is ethanol, which arises by the combined action of a modified pyruvate dehydrogenase and of alcohol dehydrogenase in muscle (Shoubridge and Hochachka 1980; Mourik et al. 1982). 14CO 2 release from 3- 14C-lactate, 6- 14C-glucose, 3,4- 14C-glutamate and 1- 14C-acetate cannot be explained by ethanol fermentation. Neither was there a stoichiometric relation between 14CO 2 and 14C-ethanol release after U- 14C-glucose and U- 14C-lactate injection. It is concluded that at least 20% of the CO 2 released is produced by Krebs cycle activity. 相似文献
5.
Uredospores of Puccinia graminis (Pers.) tritici (Eriks. and Henn.) were uniformly labeled with 14C by permitting the host ( Triticum aestivum L.) to carry out photosynthesis in 14CO 2 during the process of spore production by the obligate parasite. The use of 14C labeled spores provided advantages in a study of the utilization of endogenous substrates at frequent intervals with small amounts of spores under conditions conducive to germination. Because of previous uncertainties about the nature of the substrates of importance to germination, a detailed study of carbohydrate and lipid components, both in the spores and in the germination medium, was made during the first 7 hours after placing the spores on aqueous media. Diethyl ether and 80% ethanol soluble metabolites each constituted approximately 20% of the total spore carbon. During the first hour nearly 60% of the 80% alcohol solubles disappeared from the spores while the total ether soluble material did not change appreciably. A significant part of the 80% ethanol soluble materials appeared in the germination medium. During germination and germ tube extension, there was rapid utilization of trehalose, arabitol and mannitol even though appreciable amounts of these materials were present as exogenous pools in the germination medium. Although the total amounts of ether soluble components did not change as drastically as the carbohydrate fraction, there was extensive utilization of palmitic, oleic, linolenic and 9,10-epoxyoctadecanoic acids. The results indicate that the germination process in spores of obligate parasites is not based solely on the utilization of lipids and some possible roles of the changes in internal and external pools of soluble carbohydrates are discussed. 相似文献
6.
Isolated axons of show high ratios of 14CO 2 production from glucose-1- 14C to 14CO 2 production from glucose-6- 14C (ratio C 1/C 6). During osmotic stresses, there is a modification in 14CO production from glucose-6- 14C as well as in the ratio C 1/C 6 while 14CO 2 production from glucose-1- 14C does not change significantly. These results are interpreted in terms of activity of oxidative and non-oxidative pathways of glucose metabolism. 相似文献
7.
CO 2 in required continuously during germination of Streptomyces viridochromogenes spores. Spores incubated in a defined germination medium in the absence of CO 2 remain phase bright and do not release spore carbon. In the presence of CO 2, the spores initiate germination accompanied by loss of refractility and spore carbon. The CO 2 requirement is replaced by oxaloacetate or a mixture of tricarboxylic acid cycle (TCA) intermediates. Labeled CO 2 is taken up by germinating spores, and is incorporated into protein and RNA. TCA cycle intermediates and related amino acids contain most of the acid-soluble label following short term exposures of germinating spores to 14CO 2. TCA cycle inhibitors repress germination and 14CO 2 uptake whereas folic acid antagonists do not. The results indicate that CO 2 is incorporated into oxaloacetate which is converted to biosynthetic intermediates required for germination. Operation of the TCA cycle appears to be essential for spore germination. The conclusion is reached that CO 2 is required during germination in order to maintain the cycle by an anaplerotic reaction.Abbreviations SN
sucrose-nitrate medium
- TX buffer
Trisbuffer pH 7.3 containing-Triton X-100
- DGM
defined germination medium
- TX salts
TX buffer plus Mg and Ca ions
- TA
trichloroacctic acid
- TCA
tricarboxylic acid 相似文献
8.
Purified pea root plastids were supplied with glutamine, 2-oxoglutarate and phosphorylated sugars. Formation of glutamate was linear for 75 min and dependent upon the intactness of the organelle. Glucose-6-phosphate and ribose-5-phosphate were the most effective substrates in supporting glutamate synthesis. Flux through the oxidative pentose phosphate pathway during glutamate synthesis in purified plastids was followed by monitoring the release of 14CO 2 from [1- 14C]glucose-6-phosphate. 14CO 2 evolution from C-1 was dependent upon the presence of both glutamine and 2-oxoglutarate and could be inhibited by the application of azaserine. The data are discussed in view of the role of the oxidative pentose phosphate pathway in non-photosynthetic plastids. 相似文献
9.
Summary We did this work to see if there is a correlation between lignin synthesis and the activity of the pentose phosphate pathway. Excision of the third internode of the stem of Coleus blumei Benth. followed by incubation on sucrose and indoleacetic acid led to extensive formation of tracheids. During this lignification we determined the activities of glucose-6-phosphate dehydrogenase and fructose-1,6-diphosphate aldolase, and the extent to which [1- 14C]-,[3,4- 14C]-, and [6- 14C]glucose labelled CO 2 and the major cellular components. The results indicate that the pentose phosphate pathway was active during lignification, and that the activity of this pathway relative to glycolysis increased at the onset of lignification. Explants of storage tissue of Helianthus tuberosus L. were cultured under conditions which caused extensive lignification. 14CO 2 production from [1- 14C]-, [3,4- 14C]-, and [6- 14C]glucose indicated activity of the pentose phosphate pathway during tracheid formation. We suggest that lignification is accompanied by appreciable activity of the pentose phosphate pathway and that this could provide the reducing power for lignin synthesis.Abbreviations NADP
nicotinamide-adenine dinucleotide phosphate
- IAA
indoleacetic acid 相似文献
10.
Abstract: The molecular basis of the close linkage between oxidative metabolism and acetylcholine (ACh) synthesis is still unclear. We studied this problem in slices and synaptosomes by measurement of ACh synthesis from [U- 14C]glucose, and 14CO 2 production from [3,4- 14C]- and [2- 14C]glucose, an index of glucose decarboxylation by the pyruvate dehydrogenase complex (PDH) and the enzymes of the Krebs cycle, respectively. We examined both under conditions that either inhibited (low O 2 or antimycin) or stimulated (2,4- dinitrophenol [DNP] or 35 mm -K +) 14CO 2 production from [2- 14C]- or [3,4- 14C]glucose. Incorporation of [U- 14C]glucose into ACh was reduced under low O 2 and by antimycin or DNP (by 51-93%) and stimulated by 35 mm -K + (by 30-60%). Under all of these conditions, ACh synthesis and the decarboxylation of [3,4- 14C]- and [2- 14C]glucose were linearly related ( r= 0.741 and 0.579, respectively). The difference in the rate of 14CO 2 production from [3,4- 14C]- and [2- 14C]glucose was used as a measure of the amount of glucose that was not oxidatively decarboxylated (efflux). We found that efflux was reduced (low 0 2 and antimycin), unchanged (DNP in slices), or increased (DNP in synaptosomes and K + stimulation in slices) compared with control values under 100% O 2. ACh synthesis and efflux were more closely related ( r= 0.860) than ACh synthesis and 14CO 2 production from variously labeled glucoses. 相似文献
11.
The aim of this work was to investigate the extent of glycolysis during gluconeogenesis in the germination of marrow ( Cucurbita pepo L. var. medullosa Alef.). The activities of phosphofructokinase (E.C. 2.7.1.11) in extracts of cotyledons, of seeds, and seedlings grown in the dark for 2, 5, and 8 days were 3·5, 4·8, 9·4, and 11·8 nmol substrate consumed per cotyledon per min, respectively. The comparable figures for pyruvate kinase (E.C. 2.7.1.41) were 16·3, 72·3, 974, and 1485. The patterns of 14CO 2 production from [1- 14C], [2- 14C], [3,4- 14C], and [6- 14C]glucose indicated that at all the above stages of germination glycolysis was appreciable and predominated over the pentose phosphate pathway. These patterns, and the distribution of label from [1- 14C], and [3- 14C]pyruvate supplied to 5-day-old cotyledons, indicated that the pyruvate formed in glycolysis was converted to acetyl units that were used primarily in biosyntheses. It is concluded that glycolysis occurred at all the stages of germination examined and was particularly active during gluconeogenesis. It is suggested that the significance of this glycolysis is the provision of intermediates for biosyntheses, a need that may not be met by corresponding gluconeogenic intermediates as these may be retained within organelles. 相似文献
12.
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
14.
γ-Irradiation of preclimacteric banana resulted in a gradual increase in fructose content, which reached a maximum in 6 days. Although the catabolism of glucose-U- 14C was less in irradiated banana, incorporation of label into fructose was high. Initial fructose accumulation in irradiated banana may be due to a shift in glucose utilization from the glycolytic to the pentose phosphate pathway. The ratio of resporatory CO 2 from glucose-6- 14C and glucose-1- 14C was halved in irradiated bananas indicating predominance of the pentose phosphate pathway. The radioactivity of fructose derived from glucose-6- 14C was almost twice that from glucose-1- 14C in irradiated bananas, whilst in control both fruit the labelled precursors yielded equal amounts. Studies on individual enzymes in these two pathways showed an increase in phosphorylase, phosphoglucomutase, glucose-6-phosphate dehydrogenase and fructose-6-phosphatase and a decrease in hexokinase in irradiated banana. 相似文献
15.
The pathway (s) of glucose degradation in detached senescent and non-senescent tobacco leaves from plants approximately 100 days old were studied utilizing‘Relabeled carbohydrates. Comparable samples of each tissue were allowed to metabolize glucose-1- and glucose-6- 14C and C 6/C 1 ratios were computed from the radioactivity of 14CO 2 collected. Two methods of calculation were compared. Hexose monophosphate pathway activity was also compared in both ages of tissue by measuring 14CO 2 respired from substrate ribose-1-, xylose-1- and gluconic acid-6- 14C. The results indicate that the hexose monophosphate pathway accounts for approximately 25 percent of the respired CO 2 in both senescent and non-senescent tissues. Both types of tissue were equally efficient in degrading HMP shunt intermediates to CO 2. 相似文献
16.
Summary Rust infected leaves of wheat plants were incubated with glucose- 14C. Uredospores which were formed during the application of the tracer were analyzed. All isolated compounds were labeled with 14C. When germinating uredospores were incubated directly with 14C-glucose, the isolated glutamic acid, arginine and lysine had practically no radioactivity. These compounds did, however, contain considerable 14C-activity when they were isolated from uredospores formed on leaves that had been treated with the tracer. We therefore conclude that these amino acids were synthesized in the host and were taken up by the haustoria of the mycelium.High 14C-radioactivity was also found in all carbohydrates (chitin, glucomannan, polyols etc.). Hexoses isolated from the spore constituents chitin and glucomannan showed the same distribution of radioactivity as the applied glucose-1- 14C or glucose-6- 14C. It follows that the rust mycelium takes up glucose or a similar monosaccharide from the wheat plant. The C-6-skeleton is not degraded to smaller metabolites before it is taken up. 相似文献
17.
Phanerochaete chrysosporium metabolized the radiolabeled lignin model compounds [γ- 14C]guaiacylglycerol-β-guaiacyl ether and [4- methoxy- 14C]veratrylglycerol-β-guaiacyl ether (VI) to 14CO 2 in stationary and in shaking cultures. 14CO 2 evolution was greater in stationary culture. 14CO 2 evolution from [γ- 14C]guaiacyl-glycerol-β-guaiacyl ether and [4- methoxy- 14C]veratrylglycerol-β-guaiacyl ether in stationary cultures was two- to threefold greater when 100% O 2 rather than air (21% O 2) was the gas phase above the cultures. 14CO 2 evolution from the metabolism of the substrates occurred only as the culture entered the stationary phase of growth. The presence of substrate levels of nitrogen in the medium suppressed 14CO 2 evolution from both substrates in stationary cultures. [ 14C]veratryl alcohol and 4-ethoxy-3-methoxybenzyl alcohol were formed as products of the metabolism of VI and 4-ethoxy-3-methoxyphenylglycerol-β-guaiacyl ether, respectively. 相似文献
18.
Large quantities of CO 2 are released within many photosynthesizing tissues in the light by the process of photorespiration. This CO 2 arises largely from the carboxylcarbon atom of glycolate, which is synthesized in chloroplasts during photosynthesis. Glyoxylate is then produced by the glycolate oxidase reaction. The glyoxylate may be directly decarboxylated to CO 2, but some investigators believe the glyoxylate must first be converted to glycine before CO 2 is released during photorespiration. Spinach chloroplasts with their envelope membranes removed in dilute buffer solution have now been shown to carry out the oxidative decarboxylation of [1- 14C]glyoxylate, in the presence of light and manganous ions in an atmosphere containing oxygen, to yield 1 mole each of 14CO 2 and formate. Rates of enzymatic decarboxylation exceeding 50 μmoles of 14CO 2 mg chlorophyll −1 hr −1 were obtained at pH 7.6; hydrogen peroxide is probably the oxidant in the reaction. Heated chloroplasts are inactive under the standard conditions and there is an almost absolute requirement for each of the components listed above. Conditions for some other nonenzymatic decarboxylations of glyoxylate have also been described. [1- 14C]Glycine is decarboxylated by the enzymatic system at only 1% of the rate of [1- 14C]glyoxylate. Maize chloroplast preparations are much less active than spinach chloroplasts. The high rates of CO 2 produced by the spinach system directly from glyoxylate, as well as the need for light and oxygen, suggest that this reaction functions in photorespiration, and that CO 2 arises during photorespiration without glycine as a mandatory intermediate. 相似文献
19.
Recycling of carbon in the oxidative pentose phosphate pathway (OPPP) of intact pea root plastids has been studied. The synthesis of dihydroxyacetone phosphate (DHAP) and evolution of CO 2 was followed in relation to nitrite reduction. A close coupling was observed between all three measured fluxes which were linear for up to 60 min and dependent upon the integrity of the plastids. However, the quantitative relationship between 1- 14CO 2 evolution from glucose 6-phosphate and nitrite reduction varied with available hexose phosphate concentration. When 10 mM glucose 6-phosphate was supplied to intact plastids a stoichiometry of 1.35 was observed between 14CO 2 evolution and nitrite reduction. As exogenous glucose 6-phosphate was decreased this value fell, becoming 0.47 in the presence of 0.2 mM glucose 6-phosphate, indicative of considerable recycling of carbon. This conclusion was reinforced when using [2- 14C]glucose-6-phosphate. The measured release of 2- 14CO 2 was consistent with the data for 1- 14CO 2, suggesting complete recycling of carbon in the OPPP. Ribose 5-phosphate was also able to support nitrite reduction and DHAP production. A stoichiometry of 2 NO 2 ? reduced: 1 DHAP synthesised was observed at concentrations of 1 mM ribose 5-phosphate or less. At concentrations of ribose 5-phosphate greater than 1 mM this stoichiometry was lost as a result of enhanced DHAP synthesis without further increase in nitrite reduction. It is suggested that this decoupling from nitrite reduction is a function of excess substrate entering directly into the non-oxidative reactions of the OPPP, and may be useful when the demand for OPPP products is not linked to the demand for reductant. The significance of recycling in the OPPP is discussed in relation to the coordination of nitrate assimilation with carbohydrate oxidation in roots and with the utilisation of carbohydrate by other pathways within plastids. 相似文献
20.
Application of levulinic acid (LA), a competitive inhibitor of δ-aminolevulinic acid (ALA) dehydratase, to greening plant tissues causes ALA to accumulate at the expense of chlorophyll. 4,6-Dioxoheptanoic acid (DA), which has been reported to be an effective inhibitor of this enzyme in animal systems, has a similar but more powerful effect on ALA and chlorophyll metabolism in greening leaves of Hordeum vulgare L. var. Larker. Both LA and DA also inhibit the uptake of [ 14C]amino acids into etiolated and greening barley leaves and reduce their incorporation into protein. Treatment of etiolated and greening leaves with these compounds results in the inhibition of 14CO 2 evolution from labeled precursors, including amino and organic acids. Inhibition of 14CO 2 evolution by these compounds is more effective in greening leaves than in etiolated leaves when [4- 14C]ALA or [1- 14C]glutamate are employed as precursors. Both LA and DA also inhibit the uptake and increase the incorporation of 32Pi into organophosphorus by etiolated barley leaves. These results indicate that LA and DA have more far-reaching effects upon plant metabolism than was previously believed. 相似文献
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