Nutrient media for plant parasitic nematodes. 3. Carbohydrate investigations on Aphelenchoides sp

Total carbohydrates of Aphelenchoides sp., harvested from 10-week-old cultures, ranged from 2.54 to 4.38% with a mean of 3.20% dry weight. Approximately 86% was glycogen. The presence of free sugars, trehalose and mannose, were determined by thin-layer chromatography. Mannose was synthesized by the nematodes while trehalose was obtained during feeding from the fungal host.     

Over-expression of OsUGE-1 altered raffinose level and tolerance to abiotic stress but not morphology in Arabidopsis

OsUGE-1 is known to be induced by various abiotic stresses, but its exact function in plants is unclear. In the present study, OsUGE-1 was over-expressed in Arabidopsis, transgenic plants conferred tolerance to salt, drought and freezing stress without altering plant morphology. In addition, transgenic plants showed a higher level of the soluble sugar raffinose than did wild-type plants. Our results suggest that elevated level of raffinose with over-expressed OsUGE-1 resulted in enhanced tolerance to abiotic stress. Thus, the gene may be applied to improve tolerance to abiotic stress in crops.     

α-Galactosidase/sucrose kinase (AgaSK), a novel bifunctional enzyme from the human microbiome coupling galactosidase and kinase activities

α-Galactosides are non-digestible carbohydrates widely distributed in plants. They are a potential source of energy in our daily food, and their assimilation by microbiota may play a role in obesity. In the intestinal tract, they are degraded by microbial glycosidases, which are often modular enzymes with catalytic domains linked to carbohydrate-binding modules. Here we introduce a bifunctional enzyme from the human intestinal bacterium Ruminococcus gnavus E1, α-galactosidase/sucrose kinase (AgaSK). Sequence analysis showed that AgaSK is composed of two domains: one closely related to α-galactosidases from glycoside hydrolase family GH36 and the other containing a nucleotide-binding motif. Its biochemical characterization showed that AgaSK is able to hydrolyze melibiose and raffinose to galactose and either glucose or sucrose, respectively, and to specifically phosphorylate sucrose on the C6 position of glucose in the presence of ATP. The production of sucrose-6-P directly from raffinose points toward a glycolytic pathway in bacteria, not described so far. The crystal structures of the galactosidase domain in the apo form and in complex with the product shed light onto the reaction and substrate recognition mechanisms and highlight an oligomeric state necessary for efficient substrate binding and suggesting a cross-talk between the galactose and kinase domains.     

Glass transition and time-dependent crystallization behavior of dehydration bioprotectant sugars

It has been suggested that the crystallization of a sugar hydrate can provide additional desiccation by removing water from the amorphous phase, thereby increasing the glass transition temperature (T_g). However, present experiments demonstrated that in single sugar systems, if relative humidity is enough for sugar crystallization, the amorphous phase will have a short life. In the conditions of the present experiments, more than 75% of amorphous phase crystallized in less than one month. The good performance of sugars that form hydrated crystals (trehalose and raffinose) as bioprotectants in dehydrated systems is related to the high amount of water needed to form crystals, but not to the decreased water content or increased T_g of the amorphous phase. The latter effect is only temporary, and presumably shorter than the expected shelf life of pharmaceuticals or food ingredients, and is related to thermodynamic reasons: if there is enough water for the crystal to form, it will readily form.     

Reactivity of melezitose and raffinose under Mitsunobu reaction conditions

The reactivity of melezitose and raffinose under Mitsunobu conditions was studied within the scope of the use of trisaccharides for the synthesis of fatty acid esters. Melezitose led to esters with preferential substitution at primary positions following the order of reactivity 6'>6>6'. Raffinose proved to be very reluctant toward ester formation in these conditions, leading mainly to the new 3',6'-anhydroraffinose.     

Glucosylation of raffinose via alternansucrase acceptor reactions

The glucansucrase known as alternansucrase [EC 2.4.1.140] can transfer glucosyl units from sucrose to raffinose to give good yields of oligosaccharides, which may serve as prebiotics. The main products were the tetrasaccharides α-d-Glcp-(1→3)-α-d-Galp-(1→6)-α-d-Glcp-(1↔2)-β-d-Fruf and α-d-Glcp-(1→4)-α-d-Galp-(1→6)-α-d-Glcp-(1↔2)-β-d-Fruf in ratios ranging from 4:1 to 9:1, along with lesser amounts of α-d-Glcp-(1→6)-α-d-Galp-(1→6)-α-d-Glcp-(1↔2)-β-d-Fruf. Ten unusual pentasaccharide structures were isolated. Three of these arose from glucosylation of the major tetrasaccharide product, two each from the minor tetrasaccharides, and three were the result of glucosylations of the fructose acceptor product leucrose or isomaltulose. The major pentasaccharide product arose from glucosylation of the major tetrasaccharide at position 4 of the fructofuranosyl unit, to give a subunit structure analogous to that of maltulose. A number of hexasaccharides and higher oligosaccharides were also produced. Unlike alternansucrase, dextransucrase [EC 2.4.1.5] gave only a single tetrasaccharide product in low yield, and no significant amounts of higher oligosaccharides. The tetrasaccharide structure from dextransucrase was found to be α-d-Glcp-(1→4)-α-d-Galp-(1→6)-α-d-Glcp-(1↔2)-β-d-Fruf, which is at odds with the previously published structure.     

Changes in the sugarcane metabolome with stem development. Are they related to sucrose accumulation?

Sucrose content increases with internode development down the stem of sugarcane. In an attempt to determine which other changes in metabolites may be linked to sucrose accumulation gas chromatography-mass spectrometry was used to obtain metabolic profiles from methanol/water extracts of four samples of different age down the stem of cultivar Q117. Extracts were derivatized with either N-methyl-N-(trimethylsilyl) trifluoracetamide (TMS) or N-methyl N-(tert-butyldimethylsilyl) trifluoroacetamide (TBS) separately in order to increase the number of metabolites that could be detected. This resulted in the measurement of 121 and 71 metabolites from the TMS and TBS derivatization, respectively. Fifty-five metabolites were identified using commercial and publicly available libraries. Statistical analysis of the metabolite profiles resulted in clustering of tissue types. Particular metabolites were correlated with the level of sucrose accumulation, which as expected increased down the stem. Metabolites, such as tricarboxylic acid cycle intermediates and amino acids, were more abundant in the M2 sample (meristem to internode 2) that was actively growing and decreased in an apparently coordinated developmentally programmed manner in more mature internodes down the stem. However, other metabolites such as trehalose and raffinose showed positive correlations with sucrose concentration. Here we discuss the technique used to measure metabolites in sugarcane and the changes in metabolite abundance down the sugarcane stem.     

Sorbitol accumulation during natural and accelerated ageing of pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.) seeds

The aim of the present study was to determine the effect of accelerated ageing on the composition and content of the soluble carbohydrates in pea seeds of six genotypes differing in the composition of raffinose family oligosaccharides. A gradual decrease in the concentration of higher homologues of raffinose was observed along with seed ageing. At the same time the seeds lost vigor, viability and germination capacity. No increase in the concentration of reducing sugars was recorded, but sorbitol accumulated in pea embryos. Sorbitol accumulation may indicate seed quality deterioration during storage.     

Oat β-glucan and xylan hydrolysates as selective substrates for Bifidobacterium and Lactobacillus strains

Novel oligomers that resist digestion in the upper gut were prepared from oat mixed-linked β-glucan and xylan by enzymatic hydrolysis with lichenase of Bacillus subtilis and xylanase of Trichoderma reesei respectively. The low-molecular-mass hydrolysis products of β-glucan and xylan were compared with fructooligomers and raffinose in their ability to provide growth substrates for probiotic (Lactobacillus and Bifidobacterium) and intestinal (Bacteroides, Clostridium and Escherichia coli) strains in vitro. A degradation profile of each carbohydrate and total sugar consumption were analysed with HPLC, and bacterial growth rate with an automatic turbidometer, the Bioscreen C system. β-Glucooligomers and xylooligomers both enhanced the growth of health-promoting probiotic strains as compared with intestinal bacterial growth, but not to a significant level. Raffinose stimulated the probiotic strains significantly, whereas fructooligomers induced high average growth for intestinal bacteria also. Received: 16 May 1997 / Received revision: 12 September 1997 / Accepted: 19 September 1997