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PubMed2006

Dissecting the regulation of fructan metabolism in perennial ryegrass (Lolium perenne) with quantitative trait locus mapping.

Quantitative trait locus (QTL) mapping, which can be a useful tool for dissecting complex traits, has been used here to study the regulation of fructan metabolism in temperate forage grasses. An F2 mapping family, derived from a high water-soluble carbohydrate (WSC) x low WSC cross, was used to map fructans and the other components of WSC (sucrose, glucose and fructose) in leaves and tiller bases of perennial ryegrass (Lolium perenne) in spring and autumn. To characterize regions of the genome that control basic carbohydrate metabolism, a strategy to minimize the impact of genotype (G) x environment (E), and E-effects on the characterization of G-effects, was adopted. Most traits were highly variable within the family. There was also considerable year-to-year environmental variation. However, significant genetic effects were detected, and several traits had high broad-sense heritability. QTL were identified on chromosomes 1, 2, 5 and 6. Leaf and tiller base QTL did not coincide. Individual QTL explained between 8 and 59% of the total phenotypic variation in the traits. Fructan turnover, metabolism and their genetic control, and the effect of environment, are discussed in the context of the results.

Biomarkers↗

PubMed2003

Nutrient digestibilities, microbial populations, and protein catabolites as affected by fructan supplementation of dog diets.

Fructans are fermentable carbohydrates and include short-chain fructooligosaccharides (scFOS), inulin, and hydrolyzed inulin (oligofructose, OF). Two studies with dogs were designed to examine the effects of low concentrations of fructans on nutrient digestibilities, fecal microbial populations, and endproducts of protein fermentation, and fecal characteristics. In Exp. 1, 11 adult male beagles were fed corn-based, kibbled diets supplemented with or without OF to provide 1.9 +/- 0.6 g/d. Dietary inclusion of OF decreased (P < 0.05) nutrient digestibilities, but did not affect fecal characteristics. Increasing OF concentration tended (P < 0.06) to linearly decrease fecal ammonia concentrations, but not those of branched-chain fatty acids (BCFA), amines, indole, or phenols. Fecal concentrations of total short-chain fatty acids (SCFA) and butyrate tended to be higher in OF-supplemented dogs (P < 0.10), as was the ratio of bifidobacteria to total anaerobes (P = 0.15). In Exp. 2, ileally cannulated adult female hounds were fed a meat-based kibbled diet and were assigned to four scFOS treatments (0, 1, 2, or 3 g/d) in a 4 x 4 Latin square design. Ileal nutrient digestibilities tended to increase (P < 0.15) with increasing concentrations of scFOS. On a DMI basis, fecal output tended to decrease linearly (P < 0.10) in response to increasing scFOS supplementation, whereas fecal score tended to exhibit a quadratic response (P = 0.12). In general, fecal concentrations of SCFA, BCFA, ammonia, phenols, and indoles were not altered by supplemental scFOS. Supplementation of scFOS increased fecal concentrations of total aerobes (P < 0.05) and decreased concentrations of Clostridium perfringens (P < 0.05). From these data, it seems that low levels of supplemental fructans have divergent effects on nutrient digestibility and fermentative endproducts, but do not adversely affect nutrient digestibility or fecal characteristics and may improve colonic microbial ecology in dogs.

Ammonia↗

PubMedDate not supplied

Measurement of total fructan in foods by enzymatic/spectrophotometric method: collaborative study.

An AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measuring oligofructans and fructan polysaccharide (inulins) in mixed materials and food products. The sample is extracted with hot water, and an aliquot is treated with a mixture of sucrase (a specific sucrose-degrading enzyme), alpha-amylase, pullulanase, and maltase to hydrolyze sucrose to glucose and fructose, and starch to glucose. These reducing sugars are then reduced to sugar alcohols by treatment with alkaline borohydride solution. The solution is neutralized, and excess borohydride is removed with dilute acetic acid. The fructan is hydrolyzed to fructose and glucose using a mixture of purified exo- and endo-inulinanases (fructanase mixture). The reducing sugars produced (fructose and glucose) are measured with a spectrophotometer after reaction with para-hydroxybenzoic acid hydrazide. The samples analyzed included pure fructan, chocolate, low-fat spread, milk powder, vitamin tablets, onion powder, Jerusalem artichoke flour, wheat stalks, and a sucrose/cellulose control flour. Repeatability relative standard deviations ranged from 2.3 to 7.3%; reproducibility relative standard deviations ranged from 5.0 to 10.8%.

Borohydrides↗

PubMedDate not supplied

[Fermentative synthesis and hydrolysis of fructans].

The review of the experimental papers dealing with some aspects of fermentative biosynthesis of fructans with different degrees of polymerization from microorganisms and plants is presented. The role of sucrose 1F-fructosyltransferase and 1,2-beta-fructan 1F-fructosyltransferase in the biosynthesis and hydrolysis of fructans, the influence of different stresses (water, temperature, oxygen and others) on these process are discussed.

Fermentation↗

PubMed1992

The structure of the fructan sinistrin from Urginea maritima.

The structure of sinistrin from red squill (Urginea maritima) was determined by methylation analysis and 13C NMR spectroscopy, using the fructans from Pucinella peisonis and quack-grass (Agropyron repens) as reference substances. Application of the reductive cleavage method showed that, of the beta-D-fructofuranosyl residues in sinistrin, 33% were 1-linked, 19% were 6-linked, 25% were terminal, and 19% were 1,6-linked. The average dp was 31 and, of the 3.24% of alpha-D-glucopyranosyl residues, 0.54% were terminal and 2.70% were 6-substituted. The fructan of quack grass was also highly branched with a (2-->6)-linked backbone, terminal alpha-D-glucopyranosyl residues, and a dp of approximately 45. The fructan from Pucinella peisonis was slightly branched, with a dp of approximately 10 and a (2-->6)-linked backbone.

Carbohydrate Conformation↗

PubMed2005

Mechanisms underlying the effects of inulin-type fructans on calcium absorption in the large intestine of rats.

Inulin-type fructans (inulin, oligofructose, fructooligosaccharides) in the diet do increase intestinal calcium absorption in animals and humans, but the underlying mechanism has not been identified. We therefore assessed the effects of fermentation of inulin-type fructans on transepithelial calcium transport in rat large intestine. Transepithelial calcium fluxes in vitro (Ussing chamber), effects on gene expression, mucosal morphology, and composition of luminal contents were determined in rats fed a standard diet and/or a diet containing 10% (w/w) 1/1 inulin-oligofructose mixture (INOF). Net transepithelial calcium transport in large intestine of rats fed a standard diet was increased by high mucosal calcium concentrations, the presence of 100 mmol/L mucosal short-chain fatty acids (SCFAs), the presence of 10 g/L INOF at the mucosal side, but not by reducing mucosal pH. Tissues from rats fed INOF did not show altered calcium transport when compared to controls. However, when flux data were based on the total caecal surface area, INOF-fed rats nearly doubled absorption rate in caecum. INOF feeding altered transcript levels of several mucosal genes that can be linked to transcellular and paracellular calcium transport processes. In addition, a decreased luminal pH in caecum with markedly increased caecal pools of total, soluble, and ionized calcium resulted from INOF ingestion. Thus, inulin-type fructans increase the large intestinal calcium absorption by different mechanisms including enhanced pools of soluble and ionized calcium, an increase in the absorptive surface predominantly in caecum, the increased concentrations of SCFAs, and by direct interaction with the intestinal tissue.

Animals↗

PubMed2002

Rubisco small subunit, chlorophyll a/b-binding protein and sucrose:fructan-6-fructosyl transferase gene expression and sugar status in single barley leaf cells in situ. Cell type specificity and induction by light.

We describe a highly efficient two-step single-cell reverse transcriptase-polymerase chain reaction technique for analyzing gene expression at the single-cell level. Good reproducibility and a linear dose response indicated that the technique has high specificity and sensitivity for detection and quantification of rare RNA. Actin could be used as an internal standard. The expression of message for Rubisco small subunit (RbcS), chlorophyll a/b-binding protein (Cab), sucrose (Suc):fructan-6-fructosyl transferase (6-SFT), and Actin were measured in individual photosynthetic cells of the barley (Hordeum vulgare) leaf. Only Actin was found in the non-photosynthetic epidermal cells. Cab, RbcS, and 6-SFT genes were expressed at a low level in mesophyll and parenchymatous bundle sheath (BS) cells when sampled from plants held in dark for 40 h. Expression increased considerably after illumination. The amount of 6-SFT, Cab, and RbcS transcript increased more in mesophyll cells than in the parenchymatous BS cells. The difference may be caused by different chloroplast structure and posttranscriptional control in mesophyll and BS cells. When similar single-cell samples were assayed for Suc, glucose, and fructan, there was high correlation between 6-SFT gene expression and Suc and glucose concentrations. This is consistent with Suc concentration being the trigger for transcription. Together with earlier demonstrations that the mesophyll cells have a higher sugar threshold for fructan polymerization, our data may indicate separate control of transcription and enzyme activity. Values for the sugar concentrations of the individual cell types are reported.

Carbohydrate Metabolism↗

PubMed1986

Labeling of fructans in winter wheat stems.

Fructans synthesized from newly formed assimilates accumulate in wheat stems as nonstructural carbohydrates. Experiments performed tested the hypothesis that the fructose moiety from translocated sucrose is used preferentially in biosynthesis of these fructans. Results indicated: (a) a large percentage of labeled sucrose was translocated and unloaded in an unaltered state; and (b) sucrose contributed its fructose moiety to fructan synthesis in stems.

Journal Article↗

PubMed1987

Enzymology of Fructan Synthesis in Grasses: Properties of Sucrose-Sucrose-Fructosyltransferase in Barley Leaves (Hordeum vulgare L. cv Gerbel).

Fructan synthesis was induced in excised primary leaf blades of Hordeum vulgare L. cv Gerbel by illumination in 30 millimolar fructose. This treatment induced a 26-fold increase of sucrose-sucrose-fructosyltransferase (SST, EC 2.4.1.99) activity within 24 hours. Acid invertase (EC 3.2.1.26) activity remained about constant. By preparing protoplasts from induced leaves, approximately 80% of the invertase activity was removed with the cell walls while SST was retained. The protoplast homogenate was used to partially purify and characterize SST. Acid precipitation (pH 4.75) and anion exchange chromatography (fast protein liquid chromatography on Mono ;Q') resulted in a recovery of about 80% of total SST activity. The principal activity (SST 1), accounting for 85% of the activity recovered, was purified about 200-fold. It was essentially free of invertase activity and catalyzed the synthesis of a trisaccharide which co-chromatographed with isokestose (1F-beta-fructosylsucrose). The remaining 15% of SST activity (SST 2) was purified about 35-fold. It retained substantial invertase activity and catalyzed the synthesis of only one trisaccharide which co-chromatographed with kestose (6F-beta-fructosylsucrose). It is concluded that barley leaves which store mainly fructan of the phlein type (beta-2-6 polyfructosylsucrose), nevertheless contain sucrose-sucrose 1F-beta-d-fructosyltransferase as the key enzyme of fructan synthesis.

Journal Article↗

PubMed2004

Sugar and fructan accumulation during metabolic adjustment between respiration and fermentation under low oxygen conditions in wheat roots.

In terms of gene expression and carbohydrate metabolism, the response of wheat seedlings to hypoxia is dramatically different from the anoxic response. Total carbohydrate content of roots increased 4-fold during 6 days of hypoxia, with a 17-fold increase in fructans. In contrast, anoxically treated roots depleted all soluble carbohydrates and died within 72 h. Gas exchange measurements (CO(2) release vs. O(2) uptake) demonstrate that hypoxia establishes a new balance between fermentation and aerobic respiration in the roots without altering the flux of carbon through glycolysis. Furthermore, the respiratory component of this new balance is 55% higher in roots that have been hypoxically pretreated compared to non-hypoxically pretreated roots. The establishment of this new homeostasis under hypoxia involves the induction of glycolytic (aldolase and enolase) and fermentative enzymes (pyruvate decarboxylase, alcohol dehydrogenase, and lactate dehydrogenase). Enzyme induction is generally complete within 24 h with mRNA induction occurring primarily during Period I (0-6 h of hypoxia), and maximal enzymes activities attained during Period II (6-24 h of hypoxia). Accumulation rates of Suc, hexoses, and fructans also change during Periods I and II. By the start of Period III (24-144 h of hypoxia), the metabolic adjustments are complete and fructans are the major carbohydrate accumulated. In anoxia, the pattern of enzyme induction was dramatically different: aldolase was not induced and declined throughout the treatment. Alcohol dehydrogenase, pyruvate decarboxylase, and lactate dehydrogenase were induced as in hypoxia, but rapidly declined within 72 h of anoxia. Only enolase exhibited a similar expression pattern in both anoxia and hypoxia.

Journal Article↗

PubMed2005

X-ray diffraction structure of a plant glycosyl hydrolase family 32 protein: fructan 1-exohydrolase IIa of Cichorium intybus.

Fructan 1-exohydrolase, an enzyme involved in fructan degradation, belongs to the glycosyl hydrolase family 32. The structure of isoenzyme 1-FEH IIa from Cichorium intybus is described at a resolution of 2.35 A. The structure consists of an N-terminal fivefold beta-propeller domain connected to two C-terminal beta-sheets. The putative active site is located entirely in the beta-propeller domain and is formed by amino acids which are highly conserved within glycosyl hydrolase family 32. The fructan-binding site is thought to be in the cleft formed between the two domains. The 1-FEH IIa structure is compared with the structures of two homologous but functionally different enzymes: a levansucrase from Bacillus subtilis (glycosyl hydrolase family 68) and an invertase from Thermotoga maritima (glycosyl hydrolase family 32).

Amino Acid Sequence↗

PubMed2001

Application of high performance anion exchange chromatography to study invertase-catalysed hydrolysis of sucrose and formation of intermediate fructan products.

Baker's yeast invertase was found to catalyse transfructosylation reactions in aqueous and anhydrous organic media with sucrose as a substrate, leading to the formation of five intermediate fructans in addition to the release of D-glucose (D-Glc)and D-fructose (D-Fru). All the reaction products were separated and quantitatively estimated using high performance anion exchange-pulsed amperometric detection equipment. The unknown products were subsequently identified by linkage analysis as beta-D-Fru-(2 --> 1)-beta-D-Fru-(2 --> 1)- alpha-D-glucopyranoside (1-kestose), beta-D-Fru- (2 --> 6)-alpha-D-glucopyranoside (6-beta-fructofuranosylglucose), beta-D-Fru-(2 -->1) -beta-D-fructofuranoside (inulobiose), beta-D-Fru-(2 --> 6)-beta-D-Fru-(2 --> 1)-alpha-D-glucopyranoside (6-kestose) and beta-D-Fru-(2 --> 6)-alpha-D-Glc-(1 --> 2)-beta-D-fructofuranoside (neokestose); and this last was eluted together with a disaccharide. The time-course of sucrose hydrolysis via fructan production in 2 ml of a 50 mM sodium acetate buffer (pH 4.5) containing 0.2 M sucrose and 25 U of invertase was different from that in 2 ml of anhydrous toluene with 1.46 M sucrose and 1,000 U of invertase as a suspended powder. Under the latter experimental conditions, invertase was found to exhibit cyclic behaviour, where sucrose was degraded and subsequently synthesised. This observation has not yet been reported, as far as we know.

Biotechnology↗

PubMed2006

Calcium is essential for fructan synthesis induction mediated by sucrose in wheat.

The role of Ca(2+) in the induction of enzymes involved in fructan synthesis (FSS) mediated by sucrose was studied in wheat (Triticum aestivum). Increase of FSS enzyme activity and induction of the expression of their coding genes by sucrose were inhibited in leaf blades treated with chelating agents (EDTA, EGTA and BAPTA). Ca(2+) channel blockers (lanthanum chloride and ruthenium red) also inhibited the FSS response to sucrose, suggesting the participation of Ca(2+) from both extra- and intra- cellular stores. Sucrose induced a rapid Ca(2+) influx into the cytosol in wheat leaf and root tissues, shown with the Ca(2+ )sensitive fluorescent probe Fluo-3/AM ester. Our results support the hypothesis that calcium is a component of the sucrose signaling pathway that leads to the induction of fructan synthesis.

Calcium↗

PubMed2001

Protein kinase and phosphatase activities are involved in fructan synthesis initiation mediated by sugars.

The induction of fructosylsucrose-synthesizing activity (FSS) by sugars was tested using detached primary leaf blades of several wheat (Triticum aestivum L.) cultivars, immersed in different sugars solutions for 24 h in the dark. The highest induction was brought about by sucrose, while glucose, fructose and maltose also caused significant induction. 5-Ketofructose, 3-methylglucose and 6-deoxyglucose, which cannot be metabolized by plants, produced no induction at all. The fact that mannose also failed to induce FSS and that mannoheptulose did not inhibit the induction by sucrose suggests that the hexokinase-sensing system may not be involved. The protein phosphatase inhibitor okadaic acid and the calmodulin-dependent protein kinase antagonist W7 inhibited FSS induction while some types of protein kinase inhibitors, such as staurosporine and genistein, had less or no effect, respectively. Cycloheximide and cordycepin completely inhibited the induction response, indicating that transcription and translation are necessary for the FSS induction. Northern blot experiments using a sucrose:fructan-6-fructosyl transferase probe gave a clear indication that the mRNA for this enzyme, which is almost absent in control leaves, is dramatically increased after a 24-h treatment with 500 mM sucrose, and confirmed the inhibition produced by protein kinase and protein phosphatase inhibitors. Our data indicate that protein kinase and protein phosphatase activities take part in the chain of events that intervenes in the induction of fructan synthesis by sugars.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed2005

Effect of water stress on proline accumulation of genetically modified potatoes (Solanum tuberosum L.) generating fructans.

This study aimed to investigate the effect of water stress on the accumulation of proline in the leaves of transgenic potato lines generating fructans. The results of the series of bifactorial experiments in 2002 and 2003 indicated an increase of the proline level in leaves of all potato lines examined under water deficit. In addition, an increase in proline concentration during plant development was observed. The proline content was related to leaf water potential and relative water content (RWC), which indicates that proline could be involved in osmoregulation of potato plants under the experimental conditions. Surprisingly, under water deficit, the proline level was lowest in most of the transgenic SST/FFT-lines, which generate fructan molecules with a high degree of polymerization. Therefore, a pleiotropic effect can not be excluded as the reason for the divergence in behavior of these transgenic lines. The present results suggest that the modification of carbohydrate metabolism, especially the high content of soluble carbohydrates, may affect water stress-induced proline accumulation.

Fructans↗

PubMed2000

Characterisation of the high-molecular weight fructan isolated from garlic (Allium sativum L.).

A high molecular weight fructan was isolated from garlic and the structure determined by enzymatic, chemical and spectroscopic (NMR) methods. It was found that the garlic fructan belongs to the neokestose family. It has a (2 --> 1)-linked beta-D-Fruf backbone with (2 --> 6)-linked beta-D-Fruf side chains. A structural model was postulated for a degree of polymerisation of about 58. This model was substantiated using an endo-inulinase purified from Aspergillus ficuum and by 1H and 13C NMR spectroscopy.

Aspergillus↗

PubMed2000

Plant fructans stabilize phosphatidylcholine liposomes during freeze-drying.

Fructans have been implicated as protective agents in the drought and freezing tolerance of many plant species. A direct proof of their ability to stabilize biological structures under stress conditions, however, is still lacking. Here we show that inulins (linear fructose polymers) isolated from chicory roots and dahlia tubers stabilize egg phosphatidylcholine large unilamellar vesicles during freeze-drying, while another polysaccharide, hydroxyethyl starch, was completely ineffective. Liposome stability was assessed after rehydration by measuring retention of the soluble fluorescent dye carboxyfluorescein and bilayer fusion. Inulin was an especially effective stabilizer in combination with glucose. Analysis by HPLC showed that the commercial inulin preparations used in our study contained no low molecular mass sugars that could be responsible for the observed stabilizing effect of the fructans. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature of dry egg PtdCho by more than 20 degrees C in the presence of inulin. A direct interaction of inulin with the phospholipid in the dry state was also indicated by dramatic differences in the phosphate asymmetric stretch region of the infrared spectrum between samples with and without the polysaccharide.

Cichorium intybus↗

PubMed1990

Fructans of Jerusalem artichokes: intestinal transport, absorption, fermentation, and influence on blood glucose, insulin, and C-peptide responses in healthy subjects.

Fructans are naturally occurring plant oligosaccharides with sweetening properties. Fructans (FAs) isolated from Jerusalem artichokes (Helianthus tuberosus) were studied with respect to intestinal handling and influence on blood glucose (BG), insulin, and C-peptide responses in eight healthy subjects. The responses were compared with those for fructose ingestion. The effect of FAs added to a wheat-starch meal was also studied. Standardized breath-hydrogen excretion indicated that FAs were completely malabsorbed and, after a 20-g dose, traces of FA were detected in 24-h urine collections in one subject only. Orocecal transit times were longer for FAs than for lactulose and fructose. The BG and insulin increments were very low after FA ingestion, lower than after fructose ingestion, whereas hydrogen production was much higher. Areas under BG curves tended to be smaller when 10 g FA was added to a 50-g wheat-starch meal, but there was no apparent interference with starch absorption.

Absorption↗