The acid hydrolysis of glycosides

Rhamnogalacturonan-I as a nematode chemoattractant from Lotus corniculatus L. super-growing root culture

INTRODUCTION

The soil houses a tremendous amount of micro-organisms, many of which are plant parasites and pathogens by feeding off plant roots for sustenance. Such root pathogens and parasites often rely on plant-secreted signaling molecules in the rhizosphere as host guidance cues. Here we describe the isolation and characterization of a chemoattractant of plant-parasitic root-knot nematodes (Meloidogyne incognita, RKN).

METHODS

The Super-growing Root (SR) culture, consisting of excised roots from the legume species Lotus corniculatus L., was found to strongly attract infective RKN juveniles and actively secrete chemoattractants into the liquid culture media. The chemo-attractant in the culture media supernatant was purified using hydrophobicity and anion exchange chromatography, and found to be enriched in carbohydrates.

RESULTS

Monosaccharide analyses suggest the chemo-attractant contains a wide array of sugars, but is enriched in arabinose, galactose and galacturonic acid. This purified chemoattractant was shown to contain pectin, specifically anti-rhamnogalacturonan-I and anti-arabinogalactan protein epitopes but not anti-homogalacturonan epitopes. More importantly, the arabinose and galactose sidechain groups were found to be essential for RKN-attracting activities. This chemo-attractant appears to be specific to M. incognita, as it wasn't effective in attracting other Meloidogyne species nor Caenorhabditis elegans.

DISCUSSION

This is the first report to identify the nematode attractant purified from root exudate of L corniculatus L. Our findings re-enforce pectic carbohydrates as important chemicals mediating micro-organism chemotaxis in the soil, and also highlight the unexpected utilities of the SR culture system in root pathogen research.

Glycosidically-Bound Volatile Phenols Linked to Smoke Taint: Stability during Fermentation with Different Yeasts and in Finished Wine

When wine grapes are exposed to smoke, there is a risk that the resulting wines may possess smoky, ashy, or burnt aromas, a wine flaw known as smoke taint. Smoke taint occurs when the volatile phenols (VPs) largely responsible for the aroma of smoke are transformed in grape into a range of glycosides that are imperceptible by smell. The majority of VP-glycosides described to date are disaccharides possessing a reducing β-d-glucopyranosyl moiety. Here, a two-part experiment was performed to (1) assess the stability of 11 synthesized VP-glycosides towards general acid-catalyzed hydrolysis during aging, and (2) to examine whether yeast strains differed in their capacity to produce free VPs both from these model glycosides as well as from grapes that had been deliberately exposed to smoke. When fortified into both model and real wine matrices at 200 ng/g, all VP-disaccharides were stable over 12 weeks, while (42–50 ng/g) increases in free 4-ethylphenol and p-cresol were detected when these were added to wine as their monoglucosides. Guaiacol and phenol were the most abundantly produced VPs during fermentation, whether originating from natural VP-precursors in smoked-exposed Pinot Noir must, or due to fortification with synthetic VP-glycosides. Significant yeast strain-specific differences in glycolytic activities were observed for phenyl-β-d-glycopyranoside, with two strains (RC212 and BM45) being unable to hydrolyze this model VP, albeit both were active on the guaiacyl analogue. Thus, differences in Saccharomyces cerevisiae β-glucosidase activity appear to be influenced by the VP moiety.

Root-knot nematode chemotaxis is positively regulated by l-galactose sidechains of mucilage carbohydrate rhamnogalacturonan-I

Root-knot nematodes (RKNs) are plant parasites and major agricultural pests. RKNs are thought to locate hosts through chemotaxis by sensing host-secreted chemoattractants; however, the structures and properties of these attractants are not well understood. Here, we describe a previously unknown RKN attractant from flaxseed mucilage that enhances infection of Arabidopsis and tomato, which resembles the pectic polysaccharide rhamnogalacturonan-I (RG-I). Fucose and galactose sidechains of the purified attractant were found to be required for attractant activity. Furthermore, the disaccharide α-l-galactosyl-1,3-l-rhamnose, which forms the linkage between the RG-I backbone and galactose sidechains of the purified attractant, was sufficient to attract RKN. These results show that the α-l-galactosyl-1,3-l-rhamnose linkage in the purified attractant from flaxseed mucilage is essential for RKN attraction. The present work also suggests that nematodes can detect environmental chemicals with high specificity, such as the presence of chiral centers and hydroxyl groups.

Chemical structure analysis of starch and cellulose derivatives

Starch and cellulose are the most abundant and important representatives of renewable biomass. Since the mid-19th century their properties have been changed by chemical modification for commercial and scientific purposes, and there substituted polymers have found a wide range of applications. However, the inherent polydispersity and supramolecular organization of starch and cellulose cause the products resulting from their modification to display high complexity. Chemical composition analysis of these mixtures is therefore a challenging task. Detailed knowledge on substitution patterns is fundamental for understanding structure-property relationships in modified cellulose and starch, and thus also for the improvement of reproducibility and rational design of properties. Substitution patterns resulting from kinetically or thermodynamically controlled reactions show certain preferences for the three available hydroxyl functions in (1→4)-linked glucans. Spurlin, seventy years ago, was the first to describe this in an idealized model, and nowadays this model has been extended and related to the next hierarchical levels, namely, the substituent distribution in and over the polymer chains. This structural complexity, with its implications for data interpretation, and the analytical approaches developed for its investigation are outlined in this article. Strategies and methods for the determination of the average degree of substitution (DS), monomer composition, and substitution patterns at the polymer level are presented and discussed with respect to their limitations and interpretability. Nuclear magnetic resonance spectroscopy, chromatography, capillary electrophoresis, and modern mass spectrometry (MS), including tandem MS, are the main instrumental techniques employed, in combination with appropriate sample preparation by chemical and enzymatic methods.

Structure of the capsular polysaccharide of Escherichia coli O9:K32(A):H19

The capsular polysaccharide of the bacterium Escherichia coli O9:K32(A):H19 was analyzed using chemical methods (hydrolysis, sequential Smith degradation, methylation analysis) together with 1H- and 13C-n.m.r. spectroscopy. 13C-N.m.r. spectroscopy and chemical analyses indicated that the K32 polysaccharide is composed of equimolar proportions of glucose, galactose, rhamnose, and glucuronic acid, and carries O-acetyl groups. 1H-N.m.r. analysis of native K32 polysaccharide revealed five resonances in the anomeric region (delta 5.52, 5.16, 5.12, 5.02, and 4.73) and the presence of an acetyl group (delta 2.18). O-Deacetylation of the polysaccharide resulted in the loss of the resonance at delta 2.18 and one of the resonances (delta 5.52) in the anomeric region. The "extra" anomeric resonance in the 1H-n.m.r. spectrum of the native K32 polymer was assigned to H-2 of rhamnose, which experiences a large downfield shift when the 2-position is O-acetylated. This was confirmed by a 2D-COSY n.m.r. experiment and studies of model compounds. The K32 capsular polysaccharide is of the "2 + 2" type, comprised of the following repeating unit: (sequence; see text) This structure is identical to that of Klebsiella K55 capsular polysaccharide.