Quackgrass is a problematic agricultural weed in the temperate zones of the world and is difficult to control without herbicides or intensive tillage. However, it may be possible to control quackgrass with less environmental impact by combining multiple low-intensity control methods. A pot experiment was conducted in July to October 2012 and repeated in June to September 2013 to investigate the effect of rhizome fragmentation, competition from white clover, shoot-cutting frequency, and cutting height on quackgrass. Rhizome fragmentation was expected to result in more, but weaker, quackgrass shoots that would be more vulnerable to shoot cutting and competition. However, by 20 d past planting, rhizome fragmentation did not change the total number of quackgrass shoots per pot, because an increase in main shoots was offset by a decrease in tiller numbers. Rhizome fragmentation did not reduce quackgrass biomass acquisition during the experimental period. Although rhizome fragmentation did reduce total fructan content, it did not enhance the effect of clover competition, shoot-cutting frequency, or shoot-cutting height. Clover competition by itself reduced quackgrass shoot numbers by 72%, rhizome biomass by 81%, and belowground fructan concentration by 10 percentage points, compared with no competition. The more frequently quackgrass shoots were cut, the less biomass quackgrass acquired, and a high shoot-cutting frequency (each time quackgrass reached 2 leaves) resulted in a lower belowground fructan concentration than a low shoot-cutting frequency (at 8 leaves). However, in pots without competition, a higher shoot-cutting frequency resulted in more quackgrass shoots. A lower shoot-cutting height (25 mm) had more impact when shoot cutting was more frequent. In conclusion, rhizome fragmentation did not reduce the number of quackgrass shoots or rhizome biomass, but competition from white clover, a high shoot-cutting frequency, and a low shoot-cutting height strongly suppressed quackgrass biomass and fructan acquisition.

Under field conditions, more photoassimilate moved to roots of Canada thistle at the bolt than at the bud, flower, or postflower stages. Similarly, greater photoassimilate accumulated in roots of Canada thistle in the greenhouse at the rosette and bolt than at the flower bud stage. Growth chamber experiments indicated that environmental conditions typical of fall, and possibly early spring, favored photoassimilate movement to the root and superseded growth stage control of assimilate partitioning. Allocation of assimilate within the root was strongly influenced by growth stage, with most assimilate being utilized for growth at the rosette stage and for fructan reserves in bolt and flower bud stages.

Roots of Canada thistle were excavated from the soil monthly from 1999 to 2001 near Scottsbluff, NE, to quantify the influence of changing soil temperature on free sugars and fructans in roots. Sucrose concentrations were low from May through August then increased in the fall and remained at high levels during winter and then declined in April as plants initiated spring growth. Changes in sucrose, 1-kestose (DP 3) and 1-nystose (DP 4) were shown to be closely associated with changes in soil temperature. During the second year of the study, average soil temperatures during the winter were colder than the first year and resulted in an increase of sucrose in Canada thistle roots. Experiments were conducted from 2001 to 2004 to determine whether there was a correlation between herbicide efficacy, time of herbicide application, and the resulting herbicide effect on root carbohydrate and Canada thistle control. Clopyralid applied in the fall reduced Canada thistle density 92% 8 months after treatment (MAT) whereas treatment made in the spring reduced plant density 33% 11 MAT. Fall application of clopyralid increased the activity of fructan 1-exohydrolase (1-FEH) in roots and was associated with a decline in sucrose, DP 4, and 1-fructofuranosyl-nystose (DP 5) 35 d after treatment (DAT). Spring application of clopyralid also resulted in a decrease of the same carbohydrates 35 DAT, but by 98 DAT, or early October, sucrose level in roots had recovered and was similar to nontreated plants. Fall application of 2,4-D or clopyralid reduced Canada thistle density 39 and 92% respectively, 8 MAT, but only clopyralid resulted in a reduction of sucrose, DP 4, DP 5, and total sugar and an increase of 1-FEH compared with nontreated plants.

The effects of fructans in the diet on the mucosal morphometry (height of villi, depth of the crypts, number of goblet cells), the thickness of the epithelial mucus layer and the histochemical composition of intestinal mucosubstances in the distal jejunum and the distal colon were investigated by comparing germ-free (GF) rats, rats harbouring Bacteroides vulgatus and Bifidobacterium longum (diassociated (DA) rats), and rats with a human faecal flora (HFA). The rats were fed either a commercial standard diet (ST) or ST + (50 g oligofructose (OF)–long-chain inulin (lcIN))/kg. Changes in total bacteria, bifidobacteria and Bacteroides–Prevotella in response to feeding these diets were investigated by fluorescent in situ hybridization with 16S rRNA-targeted probes both in intestinal contents (lumen bacteria) and tissue sections (mucosa-associated bacteria). The OF–lcIN-containing diet resulted in higher villi and deeper crypts in bacteria-associated, but not in GF rats. In DA and HFA rats, the colonic epithelial mucus layer was thicker and the numbers of the goblet cells were greater than in GF rats. These effects were enhanced by the OF–lcIN-containing diet. In both dietary groups, bacterial colonization of GF rats caused an increase in neutral mucins in the distal jejunum and colon. Bacteria-associated rats had more acidic mucins in the colon than GF rats, and the OF–lcIN-containing diet stimulated sulfomucins as the predominant type of acidic mucins, while sialomucins dominated in the ST-fed groups. The number of mucosa-associated bifidobacteria detected in the colon of DA and HFA rats was greater with OF–lcIN than ST (4·9 and 5·4 v. 3·5 and 4·0 log10/mm2 mucosal surface respectively), whereas the number of luminal bifidobacteria was only affected by fructans in DA rats. Bacteroides did not differ between the groups. The stabilisation of the gut mucosal barrier, either by changes in the mucosal architecture itself, in released mucins or by stimulation of mucosal bifidobacteria with fructans, could become an important topic in the treatment and prophylaxis of gastrointestinal disorders and health maintenance.

Simulated swards of perennial ryegrass (Lolium perenne) growing in 1-m3 soil blocks in the glasshouse were either well watered or deprived of water for 57 d and then rewatered. The first aim was to measure effects of drought on sugar (water-soluble carbohydrate) composition of laminae and sheaths of mature laminae, and bases and laminae of young (growing) leaves. The second aim was to use pulse labelling with 14CO2 to follow the partitioning of recently-fixed assimilates, and the assembly and consumption of reserve sugars (fructans). Over the last 7 d of drought growth almost stopped, old leaves died faster than they were replaced, and total sugar (which had doubled in concentration during drought) was rapidly consumed. Leaf laminae had lower content of total sugars and of large fructan (DP>5) than did growing bases and sheaths. Drought greatly reduced the rate at which sugar was exported from the laminae to the sheaths and growing leaf bases, and the rate at which it was converted to fructan. Nevertheless, fructan accumulated over the first 50 d of drought. Rewatering did not result in depolymerization and remobilization of sugars that had been formed during the last 7 d of drought, but stimulated their further assembly into high-DP fructans. Our hypothesis, that accumulation of neo-kestose (a DP-3 fructan) in droughted laminae was a symptom of sugar remobilization just before death, was disproved. It is concluded that sugar reserves contribute to drought resistance only under extreme conditions. The specific role of fructan in dry environments might be to improve regrowth when drought is relieved, rather than to enhance growth during drought.

The effects of three conditions likely to affect soluble carbohydrate pools, namely drought, expression of barley sucrose: fructan 6-fructosyl transferase (6-SFT, EC 2.4.1.10) and the establishment of the arbuscular mycorrhizal symbiosis with Glomus mosseae were studied in a multifactorial experiment using tobacco (Nicotiana tabacum). Tobacco, a plant naturally unable to form fructan, accumulated fructan in leaves, and to a larger extent in the roots, when transformed with 6-SFT. Under drought conditions, growth was considerably reduced, but neither expression of 6-SFT nor mycorrhiza formation had an effect on growth rate. However, in response to drought, carbon partitioning was significantly altered towards accumulation of soluble sugars. In plants exposed to drought, pools of sucrose were greater than those of unstressed plants, particularly in their roots. In the transgenic plants expressing 6-SFT, there were also increased contents of the products of 6-SFT, namely fructan, most probably because of the increased availability of the substrate, sucrose. These effects were the same in the presence or absence of mycorrhiza. Hexoses (glucose and fructose) also increased in response to drought, primarily in the leaves. This effect of drought was little affected by the expression of 6-SFT, except that it slightly enhanced drought-induced glucose accumulation in roots. However, the presence of mycorrhiza led to a considerable reduction in drought-induced accumulation of hexoses in the leaves. The content of the fungal disaccharide trehalose was greatly increased in the roots of all mycorrhizal plants upon exposure to drought, particularly in some of the transgenic plants expressing 6-SFT.

The major soluble carbohydrates in the desiccation-tolerant leafy liverwort Porella platyphylla (L.) Lindb. are sucrose and a homologous series of fructans including the trisaccharide 1-kestose. Exogenous glucose and fructose (10 mol m−3) did not affect the composition of the soluble carbohydrate pool. Sucrose caused an increase in the fructan pool. Sucrose also inhibited photosynthetic oxygen evolution and respiration. The fructan pool was maintained in preference to sucrose during dark starvation. Low temperature and low water potential increased the fructan pool whereas desiccation increased the proportion of high molecular weight fructan. Acid invertase activity was detected in a taxonomically diverse range of liverworts but was very low or undetectable in a range of mosses. The invertase activity from P. platyphylla was partially purified by ammonium sulphate precipitation. The reaction products of the partially purified enzyme were equimolar glucose and fructose. Kestose and higher DP fructans were not detected suggesting that, at least under the assay conditions used, the enzyme does not have sucrose[ratio ]sucrose fructosyl transferase activity. The pH optimum was 4·5–5 and the Km for sucrose was 1·7 mol m−3. Pyridoxal hydrochloride (5 mol m−3) caused 50% inhibition. The coexistence of sucrose and invertase suggests that either the invertase is inactive in vivo or is in a different subcellular compartment from sucrose. The pH response shows that it would have very low activity at cytosolic pH. A large acidic vacuole was detected in P. platyphylla leaf cells by neutral-red staining in which either invertase or sucrose could be sequestered. Rehydrating desiccated P. platyphylla for 10 min resulted in a 60% loss of extractable invertase activity. By contrast, extractable malate dehydrogenase activity increased during rehydration. Rehydrating desiccated leaves caused an increase in glucose and fructose suggesting that the sucrose pool was susceptible to invertase at this time. It is suggested that the partial inactivation of invertase during rehydration minimizes sucrose hydrolysis while membrane structure and subcellular compartmentation are re-established.

Barley (Hordeum vulgare L. cv. Agneta) was cultivated hydroponically under continuous light, constant temperature and relative humidity. The relative growth rate (RGR) was kept at 25% by an exponential supply of complete medium for 2 wk. The cultures were then transferred to phosphorus-free media and the amounts of total P, fructans, starch, sucrose, glucose and fructose in sink and source leaves were measured at 0, 12, 24, 48, 72, 120 and 156 h. The capacity of net fructan synthesis (i.e. total activity of sucrose[ratio ]sucrose 1-fructosyltransferase (1-SST) and sucrose[ratio ]fructan 6-fructosyltransferase (6-SFT)), the activity of fructan exohydrolase (FEH), as well as the activity of acid invertase were also measured in the two types of leaves. Omission of P from the growth medium caused a decrease in the P content in both sink and source leaves, whereas the RGR was not affected during the 156 h of the experiment. The fructan concentration increased in low-P plants whilst there was little or no effect on the concentrations of starch, sucrose, glucose and fructose. There was a slight increase in the capacity of net fructan synthesis in both sink and source leaves at 156 h after the onset of P-starvation. There was no change in the activity of FEH or acid invertase. The results indicate that in barley leaves the mechanism for carbon partitioning into fructans is more sensitive towards low P conditions than the mechanism for carbon partitioning into starch.

In the present work we compare responses to hypoxia of the carbohydrate content of related plant species, which grow naturally on sites prone to flooding (Senecio aquaticus Hill., Myosotis palustris (L.) Lehm. Rchb.) with plants from habitats with only a low risk of oxygen shortage (Senecio jacobaea L., Myosotis arvensis (L.) Hill.). Whilst the amounts of glucose, fructose and sucrose changed only slightly following hypoxia and peaked at a maximum approximately double that of the aerated control specimens, the fructan content increased fivefold to tenfold. In nearly all the plants studied, fructan became the main polysaccharide reserve. For example, the flooding-tolerant Senecio aquaticus accumulated the highest amount, in particular fructans with a degree of polymerization up to 35 compared with 10 under control conditions. Nearly 70% of the soluble carbohydrates were fructans, compared with 30% under aerated conditions.

In all species tested the starch fraction marginally increased or remained constant.

Fructans were found to accumulate as a response to oxygen deficiency in both flooding-tolerant and intolerant species but with higher absolute values and ratios between fructan and starch in the flooding-tolerant species. At 24 h after the onset of hypoxic treatment, the sugar content rose, in spite of the diminished photosynthetic rates. The ability to accumulate fructans seems to vary in plants coping with oxygen shortage but could be interpreted as advantageous in comparison to starch synthesis in terms of (i) the location of the fructan metabolism in the vacuoles, with no negative feedback in the photosynthetic apparatus and (ii) the possibility of storage of sucrose in the form of fructose polymers without the intermediate stages and energy-using processes which are indispensable for starch synthesis. These results might indicate that fructan metabolism could play a role in the tolerance of oxygen deficiency.

Two species of Bromus adapted to different climatic conditions were studied to determine their responses to chilling and water stress. Enzymes of sucrose and fructan metabolism as well as fructoside content were measured in roots and shoots. The results indicate that Bromus pictus (adapted to a cold desert area) has a constitutive fructan synthesis, whilst B. auleticus (adapted to a warmer northern climate) only accumulated fructan under cold stress. Microscopic observations of roots exposed to fluorescent probes ascertained cell viability and showed that the apex of roots in the northern species were more affected by the water-deficit treatment than the southern species. The presence of fructans in B. pictus and their absence in B. auleticus support the hypothesis that fructans play a role in plant tolerance to environmental stress.

To test the hypothesis that fructan structure can be used as a taxonomic character for the Poaceae we examined the accumulation of the linear, β-2,6-linked fructan series with a terminal glucose residue within the tribes Aveneae and Poeae. Only Dactylis glomerata L. (Poeae) has been shown to contain this series, making it unique among fructan structures and a potential taxonomic marker. To this end, 13 members of the tribes Aveneae and Poeae were surveyed for the presence of this fructan series by comparing extracts of water-soluble carbohydrate by TLC with an extract of D. glomerata. The fructans of four species were similar to those of D. glomerata, as determined by TLC. Further comparison by anion-exchange chromatography and linkage analysis demonstrated that Phalaris aquatica L., Puccinellia stricta (Hook. f.) C. H. Blom and Holcus lanatus L. contained a linear, β-2,6-linked series of fructan with a terminal glucose residue but that Lagurus ovatus L., although containing predominantly β-2,6-linked fructan was composed of more than one series of fructan, one with a terminal glucose residue and one with an internal glucose residue. A linear β-2,6-linked series of fructans with a terminal glucose residue was the dominant fructan accumulated by some species of genera belonging to both the Aveneae (Phalaris and Holcus) and the Poeae (Dactylis and Puccinellia). As both of these tribes also contain genera that accumulate fructans with an internal glucose residue, e.g. Avena and Lagurus (Aveneae) and Lolium (Poeae), structure of fructan cannot be used to distinguish these tribes. Review of the literature, however, showed that it is possible to separate the supertribes Triticodae and Poodae on the basis of the structure of the fructan that they accumulate.

Ion exchange chromatography of water extracts was used to classify the fructans in leaves of 40 temperate dicots and 110 temperate grass species. Of the 150 species studied, only Poa ampla (Merrill) contained a single β-2,6 linked fructan series. All other species grown at 10/5°C day/night temperatures (16 h day) contained some β-1,2 linked oligofructans, even when the major fructan series was β-2,6 linked. Leaves of P. ampla plants grown at 15/10°C day/night temperatures contained some β-1,2 linked fructans and raffinose in addition to the dominant β-2,6 series, but did not contain significant amounts of 1-kestose or bifurcose (1&6-kestotetraose). Leaves of Poa arctica R.Br. and Poa bulbosa L. contained significant amounts of raffinose and various β-1,2 linked oligomers but no 1-kestose. In vivo synthesis of 6-kestose in leaves of P. ampla grown at 10/5°C proceeds in the absence of significant amounts of either 1-kestose or bifurcose. Thus P. ampla probably has a specific 6-SST (6-sucrose-sucrosefructosyl transferase) and might provide a ready source of β-2,6 linked grass fructan.

A novel extracellular fructanhydrolase was isolated from the culture filtrate of Lactobacillus paracasei ssp. paracasei P 4134 grown on a mineral medium supplemented with fructan extracted from Timothy (Phleum pratense L.) as the only carbon source. The enzyme was purified by a combination of ammonium sulphate precipitation, affinity chromatography, preparative isoelectric focusing and anion-exchange chromatography. As a result of these procedures, the specific enzyme activity increased 93-fold, with a final yield of 28·4%. The substrate-specific activities against different fructan types were determined by incubating the enzyme fractions with fructan extracted from Timothy (predominantly β-2,6 fructosyl-fructose linkages), inulin from Dahlia tubers (mostly β-2,1 fructosyl-fructose linkages) and sucrose. The purified enzyme catalysed the hydrolysis of β-2,6-linked fructan more rapidly than the β-2,1 linkages of inulin. Additionally, the enzyme showed low ability to hydrolyse sucrose. Fructose was the main product of the degradation of Timothy fructan and inulin, indicating a high exohydrolytic activity of the enzyme. It is proposed that the fructan-degrading enzyme from L. paracasei ssp. paracasei P 4134 is a β-D-fructan-fructohydrolase (EC 3.2.1.80). The enzyme preparation showed a single protein band in sodium dodecyl sulphate-polyacrylamide gel electrophoresis with a mobility corresponding to molecular weight of c. 42 kDa. It was concluded that only one molecular weight of fructan-degrading enzyme exists in L. paracasei ssp. paracasei P 4134.

To study the role of fructan in leaf development of barley seedlings, fructan contents and the activities of enzymes involved in fructan metabolism were measured in segments of the third leaf at the stage of maximal growth. Fructans amounted to more than 10% of the d. wt in the growth zone at the base of the developing leaf and decreased sharply in the zone above. The specific activities of sucrose[ratio ]sucrose 1-fructosyltransferase (1-SST) and sucrose[ratio ]fructan 6-fructosyltransferase (6-SFT), two key enzymes in fructan synthesis, also peaked in the growth zone but decreased more slowly in the zone above. By contrast, the specific activities of invertase and fructan exohydrolase (FEH) were low in the growth zone at the leaf base and had their peak just above it. The specific activity of fructan[ratio ]fructan 1-fructosyltransferase (1-FFT) was approx. constant over the whole leaf. These results indicate that transitory accumulation of fructans in the growth zone plays a key role in the development of barley leaves.

Fructans are linear or branched polymers containing a single sucrose and repeating fructose residues. An early model for fructan biosynthesis in higher plants suggested that partial synthesis of the polymer occurred in the cell cytosol. The current model suggests that synthesis requires the interaction of two separate fructosyltransferases located in the vacuole. Tobacco lines containing a chemically induced promoter, directing expression of the Bacillus amyloliquefaciens SacB gene in the present study, provided an opportunity to regulate and target fructan synthesis to the cytosol of transgenic plants. Induced expression of the gene led to rapid destruction of leaf tissue. Amino acid substitution at a highly conserved site (Arg331) in the SacB gene reduced the fructosyltransferase efficiency without reducing the invertase activity of the enzyme. Expression of the mutant gene in transgenic tobacco also resulted in leaf damage. However, the appearance of necrotic tissue was greatly delayed. The results suggest that the phenotype is due to accumulation of fructan in the cytosol. Fructan metabolism in the cytosol of potato tubers was also detrimental to development. Tuber size and starch synthesis was significantly reduced in lines containing the untargeted gene. Transgenic tobacco and potato containing the SacB gene offer an opportunity to study the metabolism of fructan and the effect of accumulation on plant cell development.

Possible limitations of sink strength for fructan storage in tubers of Jerusalem artichoke (Helianthus tuberosus L. cv. Waldspindel) were studied in 2-yr field experiments. Treatments included the removing of side branches and the breaking of apical dominance in unbranched plants. Data from both treatments and the comparison of results obtained for 2 yr, which differed in temperature and total irradiance, indicated that fructan storage in tubers during the storage phase was not limited by supply of assimilate (sucrose). Moreover, fructan concentrations were very constant despite large variations in tuber yields and yield components (e.g. number of tubers per plant, tuber length). However, stimulation of cell expansion and diameter of tubers increased fructan concentrations, probably owing to a larger vacuolar volume in the storage cells. We concluded that fructan storage in tubers of Jerusalem artichoke is not source-limited as far as carbon import into tubers is concerned. However, a strong shoot control, most probably regulated via phytohormones, limits sink strength. Fructan concentrations in tubers might not only be increased by sink activity (fructan-synthesizing enzymes) but also by sink capacity (vacuolar volume). In this respect the shoot might play a decisive role not only as a temporary storage pool for carbohydrates but also as a source of native growth-regulators which control sink capacity.

The growth and fructan contents of plants of Vernonia herbacea (Vell.) Rusby regenerated from fragments of the underground organ (rhizophore) were analysed during two developmental cycles. When cultivated away from their natural ecosystem, these plants went through the same phenological phases as those naturally grown in the cerrado. The first aerial shoots started developing from initial fragments before the new underground system, the former acting as the main metabolic sink for the fructan present in the initial fragments. The new rhizophores started to develop by the sixth month, as photosynthates were transformed into fructans. Growth parameters measured reached higher values in the second growth cycle, exhibiting growth curves synchronized with those obtained for fructan contents in the new rhizophores. Fructo-oligosaccharides were available mostly during the period of fast growth of aerial organs whilst the fructo-polysaccharides were reduced. Fructan variation indicates that these compounds are metabolized during development. Additionally, the rapid growth, intense production of rhizophores and high fructan content make Vernonia herbacea a promising source of fructan for commercial use.

After cooling the roots and shoot apex of barley, there is a reduction in sucrose export from, and an increased total accumulation of carbohydrate and induction of fructan synthesis in, source leaves. We investigated carbohydrate accumulation in individual leaf cells. Using the microsampling technique and microfluorometric enzymatic assay, the amounts of various carbohydrates were measured in mesophyll, bundle sheath and epidermal cells. Epidermal cells take no part in carbohydrate partitioning and have very low concentrations of sugars even when leaf export is reduced. Even without cooling, however, there are remarkable changes in sucrose concentration (up to 200 mM) in mesophyll and bundle sheath cells during the photoperiod. The activity of acid invertase in samples from individual cells was very low, c. 3 μmol sucrose (g f. wt)−1 h−1. Interrelationships between these cell types and the control of fructan metabolism are discussed.

Wheat stems serve as a store for fructans to buffer the plant against nutritional and environmental influences. It has been suggested that fructan storage influences yield stability and tolerance of environmental factors. Near infra-red spectroscopy (NIR) analysis provides a rapid and accurate assessment of the fructan content of the wheat stem, as well as allowing detection of growth-limiting nutrient stresses, and so is proving to be a useful technique for making crop management decisions. Commercial laboratories using NIR analysis have been tissue-testing crops in the eastern Australian wheat belt since 1993. In healthy, normally developing crops not under stress there is a predictable relationship between nitrogen and fructan. Investigation of the nitrogen and fructan concentrations in commercial crops has confirmed an inverse relationship between these two constituents. The function: Fructan (%)=a+bN%+cN%2 accounted for up to 81% of variation in tissue fructan concentration. In commercial tissue-testing this relationship is used to detect crops under stresses other than nitrogen deficiency. If the fructan concentration deviates by more than 4%, cereal growers are advised that their crop might be subject to other stresses which might reduce its response to applied nitrogen.

Sucrose[ratio ]sucrose fructosyltransferase (SST) activity was partially purified from whole shoots of Lolium rigidum by a combination of affinity chromatography, gel filtration and anion-exchange chromatography. The SST activity co-eluted with some fructan[ratio ]fructan fructosyltransferase (FFT) and invertase activities and consequently the partially purified preparation was termed the fructosyltransferase (FT) preparation.

The SST-like activity in the FT preparation was purified 214-fold and had an apparent molecular mass of 84000. The FT preparation contained several peptides with an apparent pI of 4·6–4·7. When assayed with sucrose concentrations up to 600 mM, the FT preparation synthesized 1-kestose at all concentrations, and synthesized 6-kestose at concentrations of 150 mM and greater. The Km of 1-kestose production was 0·2 M. When the FT preparation was assayed at a concentration of activity approximately half that measured in fresh tissue with 100 mM sucrose, 1-kestose, or 6G-kestose as substrates, fructans of degree of polymerization (DP) [les ]5 were synthesized.

A partially purified FFT activity, free of SST and invertase activities, which synthesized β-2,1-glycosidic linked oligofructans of DP [les ]6, was combined in vitro with the FT preparation (FFT-FT preparation) to give a ratio of SST[ratio ]FFT activities similar to that measured in crude enzyme extracts from L. rigidum. The FFT-FT preparation synthesized oligofructans when assayed with 100 mM concentrations of sucrose, 1-kestose or 6G-kestose, but was not able to synthesize fructans of DP [ges ]6 even after extended assays of up to 10 h. The FFT-FT preparation was also assayed with 100 mM sucrose with small amounts of concentrated sucrose added periodically during the assay to maintain the substrate concentration. In this assay, the FFT-FT preparation synthesized fructans up to an apparent DP of 17 or greater. The fructans of DP [ges ]6 synthesized in the assay appeared to form two molecular series containing both β-2,1- and β-2,6-glycosidic linked fructosyl residues with terminal or internal glucosyl residues. The apparent rate of SST activity in the assay of the FFT-FT preparation was greater than that measured in a similar assay of the FT preparation alone which did not result in fructans with DP [ges ]6. It was concluded that the FFT-FT preparation, when assayed with a continual supply of sucrose, contained a factor which promoted synthesis of fructans of DP [ges ]6 and synthesis of β-2,6-glycosidic linkages between fructosyl residues.