CiXTH29 and CiLEA4 Role in Water Stress Tolerance in Cichorium intybus Varieties

Drought causes massive crop quality and yield losses. Limiting the adverse effects of water deficits on crop yield is an urgent goal for a more sustainable agriculture. With this aim, six chicory varieties were subjected to drought conditions during seed germination and at the six week-old plant growth stage, in order to identify some morphological and/or molecular markers of drought resistance. Selvatica, Zuccherina di Trieste and Galatina varieties, with a high vegetative development, showed a major germination index, greater seedling development (6 days of growth) and a greater dehydration resistance (6 weeks of growth plus 10 days without water) than the other ones (Brindisina, Esportazione and Rossa Italiana). Due to the reported involvement, in the abiotic stress response, of xyloglucan endotransglucosylase/hydrolases (XTHs) and late embryogenesis abundant (LEA) multigene families, XTH29 and LEA4 expression profiles were investigated under stress conditions for all analyzed chicory varieties. We showed evidence that chicory varieties with high CiXTH29 and CiLEA4 basal expression and vegetative development levels better tolerate drought stress conditions than varieties that show overexpression of the two genes only in response to drought. Other specific morphological traits characterized almost all chicory varieties during dehydration, i.e., the appearance of lysigen cavities and a general increase of the amount of xyloglucans in the cell walls of bundle xylem vessels. Our results highlighted that high CiXTH29 and CiLEA4 basal expression, associated with a high level of vegetative growth, is a potential marker for drought stress tolerance.

The impact of chicory (Cichoriumintybus L.) on hemodynamic functions and oxidative stress in cardiac toxicity induced by lead oxide nanoparticles in male rats

BACKGROUND

A common environmental pollutant, lead can induce toxicity in several organ systems. A range of industrial and/or household materials and products contain lead, and food/liquid ingestion and inhalation are the mechanisms through which lead is introduced into the human body.

OBJECTIVE

Since knowledge about the cardiac toxicity of acute lead nanoparticles is limited, this work sought to shed more light on the issue by investigating the therapeutic effects of chicory extract based on rat models to elevate cardiac functions and oxidative stress.

METHODS

Four research groups were used, each consisting of ten albino rats of male sex and adult age. The groups were: control group, chicory group, lead oxide nanoparticle group, and lead oxide nanoparticle + chicory group.

RESULTS

Compared to the control and chicory groups, the lead oxide nanoparticle group displayed a notable increase in heart functions and oxidative stress markers as well as alterations in cardiac histological structure. On the other hand, cardiac function modifications were counteracted through four-week administration of lead oxide nanoparticles alongside chicory.

CONCLUSION

Heart damage caused by lead oxide nanoparticles may be attenuated by chicory through scavenging of free radicals.

Decreased expression of fructosyltransferase genes in asparagus roots may contribute to efficient fructan degradation during asparagus spear harvesting

Asparagus (Asparagus officinalis L.) accumulates inulin and inulin neoseries-type fructans in root, which are synthesized by three fructosyltransferases-sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100), and fructan:fructan 6^G-fructosyltransferase (6G-FFT, EC 2.4.1.243). Fructans in roots are considered as energy sources for emerging of spears, and it has been demonstrated that a gradual decrease in root fructan content occurs during the spear harvesting season (budding and shooting up period). However, the roles of certain three fructosyltransferases during the harvest season have not yet been elucidated. Here, we investigated the variation in enzymatic activities and gene expression levels of three fructosyltransferases and examined sugar contents in roots before and during the spear harvest period. Two cDNAs, aoft2 and aoft3, were isolated from the cDNA library of roots. The respective recombinant proteins (rAoFT2 and rAoFT3), produced by Pichia pastoris, were characterized: rAoFT2 showed 1-FFT activity (producing nystose from 1-kestose), whereas rAoFT3 showed 1-SST activity (producing 1-kestose from sucrose). These reaction profiles of recombinant proteins were similar to those of native enzymes purified previously. These results indicate that aoft2 and aoft3 encoding 1-FFT and 1-SST are involved in fructan synthesis in roots. A gradual downregulation of fructosyltransferase genes and activity of respective enzymes was observed in roots during the harvest period, which also coincided with the decrease in fructooligosaccharides and increase in fructose due to fructan exohydrolase activity. These findings suggest that downregulation of fructosyltransferases genes during harvest time may contribute to efficient degradation of fructan required for the emergence of spears.

Antioxidants in Varieties of Chicory (Cichorium intybusL.) and Wild Poppy (Papaver rhoeasL.) of Southern Italy

We report the hydrophilic and lipophilic antioxidant activities, as well as the total phenol, flavonoid, tocochromanol (tocopherol and tocotrienol), and carotenoid contents in the edible portion of wild and cultivated varieties of chicory (Cichorium intybusL.) and in the basal rosette leaves of the wild species of poppy (Papaver rhoeasL.), known by natives as “paparina,” collected in the countryside of Salento (South Apulia, Italy). We analyzed (1) two cultivars of chicory, the “Catalogna” harvested in the area between S. Pietro Vernotico and Tuturano (Brindisi) and the “Otrantina” harvested in Otranto (Lecce); (2) two wild chicory ecotypes harvested in S. Pietro Vernotico (Brindisi) and Statte (Taranto), respectively; (3) the basal leaves of wild poppy harvested in Sternatia (Lecce). In all samples, our results showed that the hydrophilic antioxidant activity is, generally, higher than the lipophilic activity. Poppy leaves exhibited the highest hydrophilic and lipophilic antioxidant activities and the highest concentration of total phenols and flavonoids. Tocopherols were detected only as traces. Among the extracted carotenoids, lutein andβ-carotene were the most abundant in all analyzed samples. Total carotenoid content was greater in wild than in cultivated plants.

Manninotriose is a major carbohydrate in red deadnettle (Lamium purpureum, Lamiaceae)

BACKGROUND AND AIMS

There is a great need to search for natural compounds with superior prebiotic, antioxidant and immunostimulatory properties for use in (food) applications. Raffinose family oligosaccharides (RFOs) show such properties. Moreover, they contribute to stress tolerance in plants, acting as putative membrane stabilizers, antioxidants and signalling agents.

METHODS

A large-scale soluble carbohydrate screening was performed within the plant kingdom. An unknown compound accumulated to a high extent in early-spring red deadnettle (Lamium purpureum) but not in other RFO plants. The compound was purified and its structure was unravelled with NMR. Organs and organ parts of red deadnettle were carefully dissected and analysed for soluble sugars. Phloem sap content was analysed by a common EDTA-based method.

KEY RESULTS

Early-spring red deadnettle stems and roots accumulate high concentrations of the reducing trisaccharide manninotriose (Galα1,6Galα1,6Glc), a derivative of the non-reducing RFO stachyose (Galα1,6Galα1,6Glcα1,2βFru). Detailed soluble carbohydrate analyses on dissected stem and leaf sections, together with phloem sap analyses, strongly suggest that stachyose is the main transport compound, but extensive hydrolysis of stachyose to manninotriose seems to occur along the transport path. Based on the specificities of the observed carbohydrate dynamics, the putative physiological roles of manninotriose in red deadnettle are discussed.

CONCLUSIONS

It is demonstrated for the first time that manninotriose is a novel and important player in the RFO metabolism of red dead deadnettle. It is proposed that manninotriose represents a temporary storage carbohydrate in early-spring deadnettle, at the same time perhaps functioning as a membrane protector and/or as an antioxidant in the vicinity of membranes, as recently suggested for other RFOs and fructans. This novel finding urges further research on this peculiar carbohydrate on a broader array of RFO accumulators.

Chemical Constituents of Cichorium intybus and their Inhibitory Effects against Urease and α-Chymotrypsin Enzymes

Phytochemical investigation of the aerial parts of Cichorium intybus L. resulted in the isolation and identification of two new natural metabolites, 2,6-di[but-3( E)-en-2-onyl]naphthalene (1), and 3,3′,4,4′-tetrahydroxychalcone (2), along with nine known compounds. Their structures were determined by spectroscopic techniques including 1D and 2D NMR. The known compounds were identified as scopoletin (3), 4-hydroxyphenylacetic acid (4), 3-hydroxy-4-methoxybenzoic acid (5), 4,4′-dihydroxychalcone (6), 6,7-dihydroxycoumarine (7), 1-triacontanol (8), lupeol (9), β-sitosterol (10), and β-sitosterol-3- O-β-glucopyranoside (11). Compounds 4-6 and 8 are reported for the first time from C. intybus. Compounds 2 and 3 showed weak inhibitory activities against urease and α-chymotrypsin enzymes, respectively.

Metabolism of galactosyl-oligosaccharides in Stellaria media--discovery of stellariose synthase, a novel type of galactosyltransferase

The raffinose family oligosaccharides (RFOs), including raffinose (Gal-alpha(1-->6)-Glc-alpha(1-->2)beta-Fru), stachyose (Gal-alpha(1-->6)-Gal-alpha(1-->6)-Glc-alpha(1-->2)beta-Fru) and higher degree of polymerization RFOs are the most widespread galactosyl-oligosaccharides (GOS) in the plant kingdom. Stellaria media is a typical representative of the Caryophyllaceae, a plant family lacking stachyose and the typical galactosyl extensions of stachyose. During cold treatment raffinose, lychnose (Gal-alpha(1-->6)-Glc-alpha(1-->2)beta-Fru-alpha(1-->1)-Gal) and stellariose (Gal-alpha(1-->6)-[Gal-alpha(1-->4)]-Glc-alpha(1-->2)beta-Fru-alpha(1-->1)-Gal) were found to accumulate in S. media stems. Next to these prominent oligosaccharides, two extra GOS were discovered. Biochemical analyses (enzymatic incubations and mild acid hydrolysis) and mass spectrometry identified the first, most abundant oligosaccharide as Glc-alpha(1-->2)beta-Fru-alpha(1-->1)-Gal, a breakdown product of lychnose. The structure of this trisaccharide was confirmed by full NMR characterization. The second, less abundant compound (termed mediose) was identified as Gal-alpha(1-->6)-[Gal-alpha(1-->4)]Glc-alpha(1-->2)beta-Fru after biochemical analyses. By partial enzyme purification the presence of discrete lychnose synthase (raffinose:raffinose 1(Fru) galactosyltransferase) and stellariose synthase (raffinose:lychnose 4(Glc) galactosyltransferase) activities were shown. A model is presented explaining the structural diversity of GOS in S. media. In the absence of stachyose, raffinose is further elongated by lychnose synthase and stellariose synthase to produce lychnose, mediose and stellariose. Most likely, these compounds are also subject to partial trimming by endogenous alpha-galactosidases.

Banisteriopsis caapi, a unique combination of MAO inhibitory and antioxidative constituents for the activities relevant to neurodegenerative disorders and Parkinson's disease

AIM OF THE STUDY

Parkinson's disease is a neurological disorder mostly effecting the elder population of the world. Currently there is no definitive treatment or cure for this disease. Therefore, in this study the composition and constituents of the aqueous extract of Banisteriopsis caapi for monoamine oxidases (MAO) inhibitory and antioxidant activities were assessed, which are relevant to the prevention of neurological disorders, including Parkinsonism.

MATERIALS AND METHODS

The aqueous extract of Banisteriopsis caapi stems was standardized and then fractionated using reversed-phase (RP) chromatography. Pure compounds were isolated either by reversed-phase (RP) chromatography or centrifugal preparative TLC, using a Chromatotron. Structure elucidation was carried out by 1D and 2D NMR, Mass, IR and Circular Dichroism spectroscopy and chemical derivatization. Chemical profiling of the extract was carried out with RP-HPLC. The inhibitory activity of MAO-A, MAO-B, acetylcholinesterase, butyrylcholinesterase and catechol-O-methyl transferase enzymes, as well as antioxidant and cytotoxic activities of both Banisteriopsis caapi extract and isolated compounds was evaluated.

RESULTS

An examination of the aqueous extracts of Banisteriopsis caapi cultivar Da Vine yielded two new alkaloidal glycosides, named banistenoside A (1) and banistenoside B (2), containing "azepino[1,2-a]tetrahydro-beta-carboline" unique carbon framework. One additional new natural tetrahydronorharmine (4), four known beta-carbolines harmol (3), tetrahydroharmine (5), harmaline (6) and harmine (7), two known proanthocyanidines (-)-epicatechin (8) and (-)-procyanidin B2 (9), and a new disaccharide beta-d-fructofuranosyl-(2-->5)-fructopyranose (14) together with known sacharose (15) and beta-d-glucose (16) were also isolated. In addition, the acetates of 1, 2, 8, 9, 14 and 15 (compounds 10-13, 17, 18) were also prepared. Harmaline (6) and harmine (7) showed potent in vitro inhibitory activity against recombinant human brain monoamine oxidase (MAO)-A and -B enzymes (IC(50) 2.5 and 2.0 nM, and 25 and 20 microM, respectively), and (-)-epicatechin (8) and (-)-procyanidin B2 (9) showed potent antioxidant and moderate MAO-B inhibitory activities (IC(50)<0.13 and 0.57 microg/mL, and 65 and 35 microM). HPLC analysis revealed that most of the dominant chemical and bioactive markers (1, 2, 5, 7-9) were present in high concentrations in dried bark of large branch. Analysis of regular/commercial Banisteriopsis caapi dried stems showed a similar qualitative HPLC pattern, but relatively low content of dominant markers 1, 2, 7, and 9, which led to decreased MAO inhibitory and antioxidant potency.

CONCLUSION

Collectively, these results give additional basis to the existing claim of Banisteriopsis caapi stem extract for the treatment of Parkinsonism, including other neurodegenerative disorders.

Isolation and Structural Analysis In Vivo of Newly Synthesized Fructooligosaccharides in Onion Bulbs Tissues (Allium cepa L.) during Storage

Fructooligosaccharides are involved in physiological activities and quality attributes of onion bulbs. This work describes structures of newly synthesized oligosaccharides formed by fructose moieties in onion bulb tissues during storage. Onion bulbs were stored for four weeks at 10. HPAEC-PAD analysis showed that saccharide 1 was eluted after 1-kestose while saccharide 2 was eluted after nystose . Saccharides 1 and 2 have R-sucrose values of 1.55 and 2.15 by HPAEC, a reducing terminal, a reducing sugar-to-fructose ratio of 0.5 and 0.3, and a degree of polymerization of 2 and 3 by TOF-MS, respectively. GLC analysis of the methyl derivatives and NMR measurement of the saccharides confirmed the presence of two different structures: the structure of saccharide 1 is composed by two fructose moieties and linked by linkage and was identified as inulobiose [-D-fructofuranosyl---D-fructopyranose]. The structure of saccharide 2 consists of three units of fructose linked by linkage and was identified as inulotriose [-D-fructofuranosyl---D-fructofuranosyl---D-fructopyranose]. The spectra also showed that 70 to 80% of the terminal fructose residue of the two saccharides is of pyranosyl form, while 20 to 30% is of furanosyl form. This finding demonstrated that these newly produced saccharides, catalyzed by onion-purified 6G-FFT, were synthesized by the action of 1-FFT fructosyltransfer from 1-kestose to free fructopyranose yielding inulobiose and sucrose, while elongation of fructofuranosyl units occurs at this transferred fructofuranosyl residue to produce inulooligosaccharide having an additional unit of fructofuranose.

Isolation and characterization of a pentasaccharide from Stellaria media

While classic raffinose family oligosaccharides (RFOs) such as raffinose and stachyose are common in plants, stachyose is absent in the Caryophyllaceae. Instead the tetrasaccharide lychnose α-d-Gal-(1→6)α-d-Glc-(1→2)β-d-Fru-(1→1)α-d-Gal can accumulate. Stellaria media, a representative member of this family, was used to isolate α-d-Gal-(1→6)-[α-d-Gal-(1→4)]α-d-Glc-(1→2)β-d-Fru-(1→1)α-d-Gal, a novel pentasaccharide with a lychnose backbone. Complete NMR characterization using COSY, HSQC, HSQC-TOCSY, HMBC, and NOESY experiments was performed to unequivocally resolve its structure. This is the first report of a natural compound containing a Gal α(1→4)Glc linkage. The trivial name stellariose is proposed for this new pentasaccharide.

Purification, cloning and functional differences of a third fructan 1-exohydrolase (1-FEHw3) from wheat (Triticum aestivum)

A third fructan exohydrolase isoform (1-FEHw3) was purified from wheat stems by a combination of ammonium sulfate precipitation, ConA affinity and ion-exchange chromatography. Homogeneity of the preparation was indicated by the presence of a single band (70 kDa) after SDS-PAGE. The enzyme hydrolyzed mainly beta2-1 linkages in fructans and was inhibited by sucrose. A cDNA could be obtained after reverse transcriptase polymerase chain reaction (RT-PCR)-based strategies and screening of a cDNA library. Functionality tests of the cDNA performed after heterologous expression in the yeast Pichia pastoris showed that the encoded protein has essentially the same characteristics as the native enzyme. Homology with previously described 1-FEH isoforms from wheat was high (97% identity), and the enzyme showed minor differences to the previously published enzymes. The relative abundance of 1-FEH transcripts in different tissues was investigated by using quantitative RT-PCR.

N-glycosylation affects substrate specificity of chicory fructan 1-exohydrolase: evidence for the presence of an inulin binding cleft

Recently, the three-dimensional structure of chicory (Cichorium intybus) fructan 1-exohydrolase (1-FEH IIa) in complex with its preferential substrate, 1-kestose, was determined. Unfortunately, no such data could be generated with high degree of polymerization (DP) inulin, despite several soaking and cocrystallization attempts. Here, site-directed mutagenesis data are presented, supporting the presence of an inulin-binding cleft between the N- and C-terminal domains of 1-FEH IIa. In general, enzymes that are unable to degrade high DP inulins contain an N-glycosylation site probably blocking the cleft. By contrast, inulin-degrading enzymes have an open cleft configuration. An 1-FEH IIa P294N mutant, introducing an N-glycosylation site near the cleft, showed highly decreased activity against higher DP inulin. The introduction of a glycosyl chain most probably blocks the cleft and prevents inulin binding and degradation. Besides cell wall invertases, fructan 6-exohydrolases (6-FEHs) also contain a glycosyl chain most probably blocking the cleft. Removal of this glycosyl chain by site-directed mutagenesis in Arabidopsis thaliana cell wall invertase 1 and Beta vulgaris 6-FEH resulted in a strong decrease of enzymatic activities of the mutant proteins. By analogy, glycosylation of 1-FEH IIa affected overall enzyme activity. These data strongly suggest that the presence or absence of a glycosyl chain in the cleft is important for the enzyme's stability and optimal conformation.

Complete NMR characterization of lychnose from Stellaria media (L.) Vill

Lychnose (alpha-D-Gal-(1-->6)-alpha-D-Glc-(1-->2)-beta-D-Fru-(1-->1)-alpha-D-Gal) was isolated from Stellaria media, a representative member of the Caryophyllaceae plant family. Weak acid hydrolysis, enzymatic hydrolysis and complete NMR characterization were performed to confirm the identity of the tetrasaccharide. All (1)H and (13)C resonances were unambiguously assigned and the conformation of the sugars was determined using one and two dimensional NMR techniques. Anomeric characterizations in lychnose were confirmed from HMBC and NOESY spectra.

Purification, cloning and functional characterization of a fructan 6-exohydrolase from wheat (Triticum aestivum L.)

Fructans, beta2-1 and/or beta2-6 linked polymers of fructose, are produced by fructosyltransferases (FTs) from sucrose. They are important storage carbohydrates in many plants. Fructan reserves, widely distributed in plants, are believed to be mobilized via fructan exohydrolases (FEHs). The purification, cloning, and functional characterization of a 6-FEH from wheat (Triticum aestivum L.) are reported here. It is the first FEH shown to hydrolyse exclusively beta2-6 bonds found in a fructan-producing plant. The enzyme was purified to homogeneity using ammonium sulphate precipitation, ConA affinity-, ion exchange-, and size exclusion chromatography and yielded a single band of 70 kDa following SDS-PAGE. Sequence information obtained by mass spectrometry of in-gel trypsin digests demonstrated the presence of a single protein. Moreover, these unique peptide sequences, together with some ESTs coding for them, could be used in a RT-PCR based strategy to clone a 1.7 kb cDNA. Functionality tests of the cDNA performed after heterologous expression in the yeast Pichia pastoris showed--as did the native enzyme from wheat--a very high activity of the produced protein against bacterial levan, 6-kestose, and phlein whilst sucrose and inulin were not used as substrates. Therefore the enzyme is a genuine 6-FEH. In contrast to most FEHs from fructan-accumulating plants, this FEH is not inhibited by sucrose. The relative abundance of 6-FEH transcripts in various tissues of wheat was investigated using quantitative RT-PCR.

Cloning, characterization and functional analysis of novel 6-kestose exohydrolases (6-KEHs) from wheat (Triticum aestivum)

Cereals accumulate graminan-type fructans which are subject to stress-related degradation by fructan 1-exohydrolases (1-FEHs) and fructan 6-exohydrolases (6-FEHs). To find new FEH genes related to freezing tolerance, a cold-hardened wheat crown cDNA library was screened. Here we report the cloning, purification and characterization of two novel 6-kestosidase (6-KEH) isoenzymes from wheat crowns (Triticum aestivum). Functional characterization in Pichia pastoris confirmed the extreme substrate selectivity for the fructan trisaccharide 6-kestose. Northern blotting showed that 6-KEH transcripts were constantly detected at the same level from autumn to winter in crown but not in leaf tissues. Apoplastic fluid isolations and activity measurements strongly suggest that 6-KEH is localized in the apoplast. It is proposed that 6-KEHs, together with other FEHs, might be involved in the breakdown of apoplastic fructans which may fulfil a role as membrane protectors under stress. Alternatively, a role in signalling processes, or in the degradation of exogenous 6-kestose from bacterial origin, cannot be excluded.

Properties of fructan:fructan 1-fructosyltransferases from chicory and globe thistle, two Asteracean plants storing greatly different types of inulin

Remarkably, within the Asteraceae, a species-specific fructan pattern can be observed. Some species such as artichoke (Cynara scolymus) and globe thistle (Echinops ritro) store fructans with a considerably higher degree of polymerization than the one observed in chicory (Cichorium intybus) and Jerusalem artichoke (Helianthus tuberosus). Fructan:fructan 1-fructosyltransferase (1-FFT) is the enzyme responsible for chain elongation of inulin-type fructans. 1-FFTs were purified from chicory and globe thistle. A comparison revealed that chicory 1-FFT has a high affinity for sucrose (Suc), fructose (Fru), and 1-kestose as acceptor substrate. This makes redistribution of Fru moieties from large to small fructans very likely during the period of active fructan synthesis in the root when import and concentration of Suc can be expected to be high. In globe thistle, this problem is avoided by the very low affinity of 1-FFT for Suc, Fru, and 1-kestose and the higher affinity for inulin as acceptor substrate. Therefore, the 1-kestose formed by Suc:Suc 1-fructosyltransferase is preferentially used for elongation of inulin molecules, explaining why inulins with a much higher degree of polymerization accumulate in roots of globe thistle. Inulin patterns obtained in vitro from 1-kestose and the purified 1-FFTs from both species closely resemble the in vivo inulin patterns. Therefore, we conclude that the species-specific fructan pattern within the Asteraceae can be explained by the different characteristics of their respective 1-FFTs. Although 1-FFT and bacterial levansucrases clearly differ in their ability to use Suc as a donor substrate, a kinetic analysis suggests that 1-FFT also works via a ping-pong mechanism.

Fructan 1-exohydrolases. beta-(2,1)-trimmers during graminan biosynthesis in stems of wheat? Purification, characterization, mass mapping, and cloning of two fructan 1-exohydrolase isoforms

Graminan-type fructans are temporarily stored in wheat (Triticum aestivum) stems. Two phases can be distinguished: a phase of fructan biosynthesis (green stems) followed by a breakdown phase (stems turning yellow). So far, no plant fructan exohydrolase enzymes have been cloned from a monocotyledonous species. Here, we report on the cloning, purification, and characterization of two fructan 1-exohydrolase cDNAs (1-FEH w1 and w2) from winter wheat stems. Similar to dicot plant 1-FEHs, they are derived from a special group within the cell wall-type invertases characterized by their low isoelectric points. The corresponding isoenzymes were purified to electrophoretic homogeneity, and their mass spectra were determined by quadrupole-time-of-flight mass spectrometry. Characterization of the purified enzymes revealed that inulin-type fructans [beta-(2,1)] are much better substrates than levan-type fructans [beta-(2,6)]. Although both enzymes are highly identical (98% identity), they showed different substrate specificity toward branched wheat stem fructans. Although 1-FEH activities were found to be considerably higher during the fructan breakdown phase, it was possible to purify substantial amounts of 1-FEH w2 from young, fructan biosynthesizing wheat stems, suggesting that this isoenzyme might play a role as a beta-(2,1)-trimmer throughout the period of active graminan biosynthesis. In this way, the species and developmental stage-specific complex fructan patterns found in monocots might be determined by the relative proportions and specificities of both fructan biosynthetic and breakdown enzymes.

Chemical syntheses of inulin and levan structures

A fructofuranosyl thiglycoside donor, ethyl 6-O-acetyl-3-O-benzyl-1,4-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-2-thio-beta-D-fructofuranoside (11), designed to yield stereospecifically beta-linkages and also to allow subsequent elongation in the 6- and/or 1-positions, was prepared and used in syntheses of levan and inulin structures. DMTST-promoted glycosylation between 11 (1.3 mol equiv) and methyl beta-D-fructofuranoside 6-OH and 1-OH acceptors (3 and 6) gave stereospecifically the protected methyl levanobioside 12 and inulinobioside 17 in excellent yields (80 and 86%), respectively. Protecting group manipulations on these afforded new disaccharide 6'-OH and 1'-OH acceptors (13 and 19), which were coupled again with donor 11 (1.0 mol equiv) to yield methyl levanotrioside 14 and inulinotrioside 20 in high yields, 65 and 67%, respectively. These were transformed into new acceptors and also fully deprotected to afford the methyl glycosides of levanotriose and inulinotriose, all structures that have earlier not been accessible by chemical synthesis.