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1.
Regulation of developmental pathways in cultured microspores of tobacco and snapdragon by medium pH 总被引:3,自引:0,他引:3
Barinova I Clément C Martiny L Baillieul F Soukupova H Heberle-Bors E Touraev A 《Planta》2004,219(1):141-146
The regulation of developmental pathways in cultured microspores of tobacco (Nicotiana tabacum L) and snapdragon (Antirrhinum majus L) by medium pH is described for the first time. Unicellular tobacco and snapdragon microspores developed into normal, fertile pollen when cultured in media T1 and AT3 at pH 7.0 and 25°C for 6 and 8 days, respectively. First, pollen mitosis was asymmetric and mature pollen grains were filled with starch granules and germinated upon transfer to a germination medium. However, when tobacco and snapdragon microspores were cultured in media T1 and AT3, respectively, at pH 8.0–8.5 for 4–6 days at 25 °C, the frequency of symmetric division increased significantly with the formation two nuclei of equal size, and the gametophytic pathway was blocked, as seen by the lack of starch accumulation and the inhibition of pollen germination. The transfer of these microspores to embryogenesis medium AT3 at pH 6.5 resulted in the formation of multicellular structures in both species and, in tobacco, in the formation of embryos and plants. In order to understand the possible mechanisms of the action of high pH, sucrose metabolism was analysed in isolated microspores of tobacco cultured at various pH values. Invertase (EC 3.2.1.26) activity in microspores was maximal at pH 5.0 and strongly decreased at higher pH, leading to a slow-down of sucrose cleavage. At the same time the incorporation of 14C-labelled sucrose from the medium into microspores was drastically reduced at high pH. These data suggest that isolated microspores are not able to metabolise carbohydrates at high pH and thus undergo starvation stress, which was shown earlier to block the gametophytic pathway and trigger sporophytic development. 相似文献
2.
The metabolism of wild-type Arabidopsis thaliana L. and its mutant TC265 were compared in order to reveal the role of the chloroplast glucose transporter. Plants were grown in a 12-h photoperiod. From 20 to 40 days after germination, starch per gram fresh weight of shoot in the mutant was four times that in the wild type. The extent of this difference did not alter during this period. Stereological analysis showed that the chloroplasts in the mutant were larger than those in the wild type; the thylakoids appeared to be distorted by the high starch content. [U-14C]Glucose and [U-14C]glycerol were supplied, separately, to excised leaves in the dark. [U-14C]Glucose was a good precursor of sucrose in the wild type and mutant; [U-14C]glycerol was a poor precursor of sucrose in both. The distribution of 14C in the wild type was used to calculate that the net flux was from hexose monophosphates to triose phosphates, not vice versa. During the first 4 h of the night the sugar content (75% sucrose, 20% glucose) of the leaves of the mutant dropped sharply, and at all times during the night it was less than that of the wild-type leaves. This drop in sugar coincided with a decrease in the rate of respiration. The growth rate of the mutant was less than that of the wild type. Addition of sucrose restored the rate of respiration at night and increased the rate of growth. It is argued that a major function of the glucose transporter in Arabidopsis chloroplasts is export of the products of starch breakdown that are destined for sucrose synthesis at night.We thank Professor C.R. Somerville for his generous gift of seed of the Arabidopsis mutant TC265. We are also grateful to Mr B. Chapman for assistance with the preparation of the sections for electron microscopy. R.N.T. thanks the Science and Engineering Research Council for a studentship. 相似文献
3.
The effect of different carbohydrate sources upon the initiation of embryogenesis from barley microspores 总被引:5,自引:0,他引:5
Isolated microspores of Hordeum vulgare L. cv. Igri were incubated in the presence of different sugars. In the presence of maltose, the optimum concentration for the development of embryoids or calluses from the microspores was 175 mM. At this concentration 0.2% of the cells developed into embryoids or calluses. Microspores cultured without a carbohydrate source died after three days' incubation. In contrast microspores incubated in the presence of sucrose, glucose or fructose died within three days. Moreover, microspores also died when incubated in the presence of a combination of 175 mM maltose with varying concentrations of either sucrose, glucose or fructose. It is concluded that incubation of microspores in the presence of sucrose, glucose or fructose results in the death of the cells via some unknown mechanism. In contrast to this, maltose can sustain development of embryoids and calluses from cultured microspores. 相似文献
4.
The effects of a penetrating (NEM) and a non-penetrating (PCMBS) sulfhydryl-specific reagent on proton extrusion, 86Rb and [U-14C]sucrose uptake by Vicia faba leaves have been studied. Proton extrusion was strongly or completely inhibited by 0.1 mM NEM. 86Rb and [U-14C]sucrose uptake were markedly reduced by NEM concentrations equal to or higher than 0.5 mM. Under our experimental conditions, PCMBS (1 mM) exerted a strong inhibition on [14C]sucrose uptake but did not inhibit proton extrusion and 86Rb uptake. The sensitivity of phloem loading to PCMBS is thought to be a consequence of sugar-carrier blockage and not of inhibition of the proton pump.Abbreviations CCCP
carbonylcyanide-m-chlorophenylhydrazone
- DES
diethylstilbestrol
- DCCD
dicyclohexylcarbodiimide
- FC
Fusicoccin
- NEM
N-ethylmaleimide
- PCMBS
p-chloromercuribenzenesulfonic acid 相似文献
5.
The aim of this work was to discover the products of carbohydrate fermentation in alder roots. Experiments were done with roots of trees growing in naturally wet soils. Detached, anaerobic roots accumulated ethanol, and ethanol was the major labelled product of metabolism of [U-14C]sucrose. Glycerol was not labelled from [U-14C]sucrose, and did not accumulate in detached or attached roots. In both winter and summer, roots in the field contained little or no glycerol, and the amount was less than that in the aerobic parts of the tree. Roots in the field contained substantial amounts of ethanol. We conclude that ethanol is the major product of fermentation in alder roots, and that glycerol is not a significant product. These results are not consistent with Crawford's metabolic theory of flooding tolerance. 相似文献
6.
Summary Breeding and selection was used to generate a population of white clover (Trifolium repens L.) from cultivar Osceola with a high embryogenic capacity. Somatic embryos were obtained from immature cotyledons of white clover placed onto EC6 basal medium containing 40 mg L–1 of 2,4-D and 6% sucrose. The effects of 2,4-D at 20 and 40 mg L–1 and of the carbohydrates, sucrose and maltose, were evaluated for their influence in the establishment of repetitive somatic embryogenesis. To determine the optimal protocol for plant recovery from somatic embryos, the effects of MS vs. EC6 basal salts, sucrose vs. maltose, B5 vitamins vs. yeast extract, and inclusion or exclusion of activated charcoal were evaluated. Repeated subculture of white clover somatic embryos on EC6 basal medium containing 6% sucrose with 2,4-D at 20 or 40 mg L–1 effectively maintains repetitive embryogenesis. Medium containing MS salts with 6% maltose as the carbohydrate source was the most efficient for plant recovery. 相似文献
7.
The aim of this work was to discover how leucoplasts from suspension cultures of soybean (Glycine max L.) oxidize hexose monophosphates. Leucoplasts were isolated from protoplast lysates on a continuous gradient of Nycodenz with a yield of 28% and an intactness of 80%. Incubation of the leucoplasts with 14C-labelled substrates led to 14CO2 production, that was dependent upon leucoplast intactness, from [U-14C]glucose 6-phosphate, [U-14C]glucose 1-phosphate, [U-14C] fructose 6-phosphate and [U-14C]glucose+ATP, but not from [U-14C]fructose-1,6-bisphosphate or [U-14C]triose phosphate. The yield from [U-14C]glucose 6-phosphate was at least four times greater than that from any of the other substrates. When [1-14C]-, [2-14C]-, [3,4-14C]-, and [6-14C]glucose 6-phosphate were supplied to leucoplasts significant 14CO2 production that was dependent upon leucoplast intactness was found only for [1-14C]glucose 6-phosphate. It is argued that soybean cell leucoplasts oxidize glucose 6-phosphate via the oxidative pentose phosphate pathway with very little recycling, and that in these plastids glycolysis to acetyl CoA is negligible.S.A.C. thanks the Science and Engineering Research Council for a research studentship. 相似文献
8.
Various solutions of labeled precursors were absorbed by the cotyledons of etiolated Euphorbia lathyris L. seedlings. Incorporation of 14C into triterpenes from [2-14C]mevalonic acid, [1-14C]acetate, [3-14C]pyruvate, [U-14C]glyoxylate, [U-14C]glycerol, [U-14C]serine, [U-14C]xylose, [U-14C]glucose, and [U-14C]sucrose was obtained. The [14] triterpenes synthesized from [14C] sugars were mainly of latex origin. [14C]mevalonic acid was only involved in terpenoid synthesis outside the laticifers. Exogenously supplied glyoxylate, serine, and glycerol were hardly involved in lipid synthesis at all. The 14C-distribution over the various triterpenols was consistent with the mass distribution of these constituents in gas liquid chromatography when [14C]sugars, [14C]acetate, and [14C]pyruvate were used. These precursors were supplied to the seedlings in the presence of increasing amounts of unlabeled substrates. The amount of substrate directly involved in lipid synthesis as well as the absolute triterpenol yield was calculated from the obtained [14C]triterpenols. The highest yield was obtained in the sucrose incorporated seedlings, being 25% of the daily increase of latex triterpenes in growing seedlings. 相似文献
9.
The biosynthesis of myo-inositol (MI) and its role as a precursor of cell-wall polysaccharides was studied in supension cultures of wild carrot (Daucus carota L.) cells. Suspension cultures, grown in the presence or absence of 2,4-dichlorophenoxyacetic acid for 7 and 14d were incubated with [U-14C]glucose and [2-3H]MI in the presence of different concentrations of unlabeled MI. Synthesis of [14C]MI from [U-14C]glucose occurred under all conditions. The amount of MI synthesized from glucose was sharply reduced when 10 mM MI was provided in the medium. Substantial quantities of 3H were incorporated in arabinose, xylose and galacturonic acid isolated and purified from the cell-wall polysaccharides of the cell cultures in various stages of growth or embryogenesis. No 3H was present in the glucose or galactose units of cell-wall polysaccharides. At the four stages of growth and states of development of the carrot cultures used, the MI oxidation pathway contributed to the synthesis of pentosyl and galacturonosyl units of the cell wall. However, the data indicate that the contribution of the MI oxidation pathway to pentosyl and galacturonosyl units is small.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- MI
myo-inositol 相似文献
10.
L. Cistué A. Ziauddin E. Simion K. J. Kasha 《Plant Cell, Tissue and Organ Culture》1995,42(2):163-169
Pretreatment of anthers in mannitol prior to isolation of microspores by glass rod homogenization was effective for in vitro induction of embryogenesis in barley cv. Igri. A procedure for separation of viable microspores using centrifugation on 20% maltose was developed. The concentration of microspores was important and greatly increased the number of developing structures. Initial culture of microspores on FHG medium containing 62 g l-1 maltose, 4.4 M (1 mg l-1) BA and 200 g l-1 Ficoll-400 resulted in high frequencies of plant regeneration. Albino plant frequency was correlated to length of time in culture. Stock plant condition appeared to be a major factor influencing induction frequency. From 868 to 1738 green plants per 100 anthers were produced. The number of calli and embryos obtained and the number of green plantlets regenerated were improved by increasing the Ficoll concentration from 100 g l-1 to 400 g l-1 during the culture period compared to continuous culture on FHG Ficoll 200 g l-1.Abbreviations BA
benzyladenine 相似文献
11.
A quantitative triterpene analysis was made of latex stem tissue of Euphorbia lathyris. Young plants seedlings of E. lathyris were incubated with various labelled precursors. Incorporation into triterpenes was obtained from [2-14C]mevalonic acid, [1-14C]acetate, [3-14C]pyruvate, [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose, [U-14C]glyoxylate, [2,3-14C]succinic acid, [1-14C]glycerol [U-14C]serine. Both sugars tyrosine appeared to be effective precursors in DOPA synthesis inside the laticifers. Exogenously supplied mevalonic acid was only involved in triterpene synthesis outside the laticifers. GC-RC of triterpenes synthesized from [U-14C]glucose revealed the origin of these compounds in the latex. The labelled triterpenes obtained after incorporation of the other mentioned labelled precursors were only partly synthesized in the laticifers. For quantitative data on latex triterpene synthesis seedlings were incubated with [U-14C]sucrose, [U-14C]glucose, [U-14C]xylose [1-14C]acetate in the presence of increasing amounts of unlabelled substrate. From the amount of 14C incorporated into the triterpenes the amount of substrate directly involved in triterpene synthesis was calculated, as was the absolute triterpene yield. Sucrose showed the highest triterpene yield, equivalent to the daily increase of the triterpene content of growing seedlings. The possible significance of the other precursors in triterpene synthesis in the laticifers is discussed. 相似文献
12.
Embryogenesis and plant regeneration of hot pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) through isolated microspore culture 总被引:1,自引:0,他引:1
We report high frequencies of embryo production and plant regeneration through isolated microspore culture of hot pepper (Capsicum annuum L.). Microspores cultured in modified NLN medium (NLNS) divided and developed to embryos. Globular and heart-shaped embryos
were observed from 3 weeks after the beginning of culture, and many embryos reached the cotyledonary stage after 4 weeks of
culture. These cotyledonary embryos developed to plantlets after transfer to solid B5 basal medium. We also optimized conditions
for embryo production by varying the pretreatment media, the carbon sources, and culture densities. Heat shock treatment in
sucrose-starvation medium was more effective than in B5 medium. Direct comparisons of sucrose and maltose as carbon sources
clearly demonstrated the superiority of sucrose compared to maltose, with the highest frequency of embryo production being
obtained in 9% (w/v) sucrose. Microspore plating density was critical for efficient embryonic induction and development, with
an optimal plating density of 8 × 104–10 × 104/ml. Under our optimized culture conditions, we obtained over 54 embryos, and an average of 5.5 cotyledonary embryos when
10 × 104 microspores were grown on an individual plate. 相似文献
13.
Replacement of mannitol with sucrose decreases the binding of [203Hg]-p-chloromercuribenzenesulphonic acid (PCMBS) to Vicia faba leaf discs without epidermis. This decrease is optimal for 20 minutes on incubation, is concentration-dependent, and is also found with maltose and raffinose. In parallel experiments, the addition of sucrose, maltose, and raffinose during PCMBS pretreatment was shown to increase subsequent uptake of [U-14C]sucrose. In contrast, d- or l-glucose, 3-O-methylglucose, galactose, fructose, palatinose, turanose, or melibiose had no effect either on PCMBS binding or on [14C]sucrose uptake. The sucrose-induced decrease of PCMBS binding is retained after a cold and ionic shock. Measurements of specific activities of membrane fractions prepared from tissues incubated in labeled PCMBS show that the decrease concerns the 120,000 gravity pellet, but that very mild procedures must be chosen to prevent redistribution of label in the supernatant. Altogether, the data provide new support to the hypothesis that the active site of the sucrose carrier contains a group sensitive to PCMBS. 相似文献
14.
Fluoride-Induced Inhibition of Starch Biosynthesis in Developing Potato, Solanum tuberosum L., Tubers Is Associated with Pyrophosphate Accumulation 总被引:1,自引:1,他引:0
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Pretreatment of discs excised from developing tubers of potato (Solanum tuberosum L.) with 10 millimolar sodium fluoride induced a transient increase in 3-phosphoglycerate content. This was followed by increases in triose-phosphate, fructose 1,6-bisphosphate and hexose-phosphate (glucose 6-phosphate + fructose 6-phosphate + glucose 1-phosphate). The effect of fluoride is attributed to an inhibition of glycolysis and a stimulation of triose-phosphate recycling (the latter confirmed by the pattern of 13C-labeling [NMR] in sucrose when tissue was supplied with [2-13C]glucose). Fluoride inhibited the incorporation of [U-14C] glucose, [U-14C]sucrose, [U-14C]glucose 1-phosphate, and [U-14C] glycerol into starch. The incorporation of [U-14C]ADPglucose was unaffected. Inhibition of starch biosynthesis was accompanied by an almost proportional increase in the incorporation of 14C into sucrose. The inhibition of starch synthesis was accompanied by a 10-fold increase in tissue pyrophosphate (PPi) content. Although the subcellular localization of PPi was not determined, a hypothesis is presented that argues that the PPi accumulates in the amyloplast due to inhibition of alkaline inorganic pyrophosphatase by fluoride ions. 相似文献
15.
Muller AP Rotta LN Kawano C Leszczinski DN Schweigert ID Londero LG Gravina FS da Silveira CK de Souza CG Battu CE Gonçalves CA de Souza DO Perry ML 《Neurochemical research》2006,31(3):417-422
We studied the effect of different concentrations of 2-deoxy-d-glucose on the l-[U-14C]leucine, l-[1-14C]leucine and [1-14C]glycine metabolism in slices of cerebral cortex of 10-day-old rats. 2-deoxy-d-glucose since 0.5 mM concentration has inhibited significantly the protein synthesis from l-[U-14C]leucine and from [1-14C]glycine in relation to the medium containing only Krebs Ringer bicarbonate. Potassium 8.0 mM in incubation medium did not stimulate the protein synthesis compared to the medium containing 2.7 mM, and at 50 mM diminishes more than 2.5 times the protein synthesis compared to the other concentration. Only at the concentration of 5.0 mM, 2-deoxy-d-glucose inhibited the CO2 production and lipid synthesis from l-[U-14C] leucine. This compound did not inhibit either CO2 production, or lipid synthesis from [1-14C]glycine. Lactate at 10 mM and glucose 5.0 mM did not revert the inhibitory effect of 2-deoxy-d-glucose on the protein synthesis from l-[U-14C]leucine. 2-deoxy-d-glucose at 2.0 mM did not show any effect either on CO2 production, or on lipid synthesis from l-[U-14C]lactate 10 mM and glucose 5.0 mM. 相似文献
16.
Roberto Viola 《Planta》1996,198(2):186-196
Metabolism of radiolabelled hexoses by discs excised from developing potato (Solanum tuberosum L.) tubers was been investigated in the presence of acid invertase to prevent accumulation of labelled sucrose in the bathing medium (Viola, 1996, Planta 198: 179–185). When the discs were incubated with either [U-14C]glucose or [U-14C]fructose without unlabelled hexoses, the unidirectional rate of sucrose synthesis was insignificant compared with that of sucrose breakdown. The inclusion of unlabelled fructose in the medium induced a dramatic increase in the unidirectional rate of sucroses synthesis in the tuber discs. Indeed, the decline in the sucrose content observed when discs were incubated without exogenous sugars could be completely prevented by including 300 mM fructose in the bathing medium. On the other hand, the inclusion of unlabelled glucose in the medium did not significantly affect the relative incorporation of [U-14C]glucose to starch, sucrose or glycolytic products. Substantial differences in the intramolecular distribution of 13C enrichment in the hexosyl moieties of sucrose were observed when the discs were incubated with either [2-13C]fructose or [2-13C]glucose. The pattern of 13C enrichment distribution in sucrose suggested that incoming glucose was converted into sucrose via the sucrose-phosphate synthase pathway whilst fructose was incorporated directly into sucrose via sucrose synthase. Quantitative estimations of metabolic fluxes in vivo in the discs were also provided. The apparent maximal rate of glucose phosphorylation was close to the extractable maximum catalytic activity of glucokinase. On the other hand, the apparent maximal rate of fructose phosphorylation was much lower than the maximum catalytic activity of fructokinase, suggesting that the activity of the enzyme (unlike that of glucokinase) was regulated in vivo. Although in the discs incubated with or without fructose the rates of starch synthesis or glycolysis were similar, the relative partitioning of metabolic intermediates into sucrose was much higher in discs incubated with fructose (0.6% and 32.6%, respectively). It is hypothesised that the equilibrium of the reaction catalysed by sucrose synthase in vivo is affected in discs incubated with fructose as a result of the accumulation of the sugar in the tissue. This results in the onset of sucrose cycling. Incubation with glucose enhanced all metabolic fluxes. In particular, the net rate of starch synthesis increased from 2.0 mol · hexose · g FW–1 · h–1 in the absence of exogenous glucose to 3.7 mol · hexose · g FW–1 · h–1 in the presence of 300 mM glucose. These data are taken as an indication that the regulation of fructokinase in vivo may represent a limiting factor in the utilisation of sucrose for biosynthetic processes in developing potato tubers.Abbreviations ADPGlc
adenosine 5-diphosphoglucose
- Glc6P
glucose-6-phosphate
- hexose-P
hexose phosphate
- NMR
nuclear magnetic resonance
- UDPGlc
uridine 5-diphosphoglucose
Many thanks to L. Sommerville for skillfull assistance and to J. Crawford and J. Liu for useful discussions on flux analysis. The research was funded by the Scottish Office Agriculture and Fisheries Department. 相似文献
17.
Jiahua Xie Mingwei Gao Qihua Cai Xiongying Cheng Yuwei Shen Zhuqing Liang 《Plant Cell, Tissue and Organ Culture》1995,42(3):245-250
The influence of maltose and growth regulators on microspore culture response was investigated in japonica rice. High frequency of callus induction of isolated microspores was obtained with liquid medium containing MS salts, 100 mg l–1 myo-inositol, 1 mg l–1 thiamine-HCl, 500 mg l–1 glutamine, 60 g l–1 maltose, and several growth regulators. The effect of maltose on promoting callus formation was associated with keeping a high proportion of swollen microspores after 5 day preculture and increasing the microspore division rate on the 3rd day after culture initiation. No significant effect of maltose in place of sucrose on plantlet regeneration was seen in regeneration medium. Among the growth regulators tested, the combination of auxin 2,4-dichlorophenoxyacetic acid (1 mg l–1), naphthaleneacetic acid (1 mg l–1), and cytokinin (6-benzyl-aminopurine 1 mg l–1) in the medium proved to be much better for callus formation than in the other media, and the percentage of callusing microspores of that medium reached 0.86%. Indole-3-acetic acid (0.5 mg l–1) and kinetin (2 mg l–1) in regeneration medium were beneficial for green plantlet differentiation. The results also showed that the frequencies of microspores initial division, callus formation and green plant regeneration varied among genotypes no matter what kind of growth regulator and sugar were used. Xiushui 117 was the best variety for callusing followed by 02428 & Taipei 309. Taipei 309 showed a good ability for green plantlet regeneration.Abbreviations 2,4-d
2,4-dichlorophenoxyacetic acid
- NAA
naphthaleneacetic acid
- 6-BA
6-benzylaminopurine
- KT
kinetin
- IAA
indole-3 acetic acid 相似文献
18.
Palmarosa inflorescence with partially opened spikelets is biogenetically active to incorporate [U-14C]sucrose into essential oil. The percent distribution of14C-radioactivity incorporated into geranyl acetate was relatively higher as compared to that in geraniol, the major essential
oil constituent of palmarosa. At the partially opened spikelet stage, more of the geraniol synthesized was acetylated to form
geranyl acetate, suggesting that majority of the newly synthesized geraniol undergoes acetylation, thus producing more geranyl
acetate.In vitro development of palmarosa inflorescence, fed with [U-14C]sucrose, resulted in a substantial reduction in percent label from geranyl acetate with a corresponding increase in free
geraniol, thereby suggesting the role of an esterase in the production of geraniol from geranyl acetate. At time course measurement
of14CO2 incorporation into geraniol and geranyl acetate substantiated this observation. Soluble acid invertase was the major enzyme
involved in the sucrose breakdown throughout the inflorescence development. The activities of cell wall bound acid invertase,
alkaline invertase and sucrose synthase were relatively lower as compared to the soluble acid invertase. Sucrose to reducing
sugars ratio decreased till fully opened spikelets stage, concomitant with increased acid invertase activity and higher metabolic
activity. The phenomenon of essential oil biosynthesis has been discussed in relation to changes in these physiological parameters. 相似文献
19.
Mycelium of Puccinia graminis was grown for 4 d on 200 mM D-[U-14C]glucose followed by a cold chase for 30 h. Analysis of cellular metabolites during the chase indicated significant turnover only in carbohydrates soluble in 80% (w/v) ethanol. A kinetic analysis of the depletion of [14C] in pools of free sugars and sugar alcohols indicated that the trehalose pools and a small proportion (12–16%) of the mannitol and glucitol pools did not turn over, whilst pools of glucose, fructose, and the remainder of the hexitols became totally,depleted of label during the chase. Because the [14C] was totally lost from the pools of glucose and fructose prior to the hexitols, it was deduced that both of these hexoses were precursors of the hexitols. Estimation of the carbon fluxes through pools indicated that 52, 36 and 16% of the carbon from glucose was assimilated via glucitol, fructose and mannitol respectively, demonstrating that glucitol could not have originated from fructose as sole precursor. After offering D-[U-14C]glucitol, [14C] was assimilated into trehalose phosphate, glucans and amino acids, but not into free glucose or fructose. These data indicate that hexitols are quantitatively important intermediates during the assimilation of glucose by Puccinia graminis. 相似文献
20.
Radioactive maltose with label in the reducing glucose moiety was prepared using a glucosyltransferase enzyme to catalyze exchange of [6-3H]glucose into unlabeled maltose. The enzyme was isolated from spinach by ammonium sulfate precipitation followed by DEAE column chromatography. A 77% yield of [6-3H]maltose was obtained after a reaction of 100 nmol of maltose with 0.0147 nmol of [6-3H]glucose was catalyzed by the most active column peak. The product was exclusively labeled in the reducing glucose moiety as indicated by the label occurring only in sorbitol following sodium borohydride reduction and sulfuric acid hydrolysis. Between 88.3 and 96.0% of the tritium in the synthesized preparation was present as [6-3H]maltose by Dowex 1-X4 chromatography. This column separates [6-3H]maltose-[U-14C]maltose mixtures and [6-3H]glucose-[U-14C]glucose mixtures apparently as a result of an isotope effect. 相似文献