Antioxidant Active Polysaccharides Extracted with Oxalate from Wild Blackthorn Fruits (Prunus spinosa L.)

Although several therapeutic effects have been attributed to wild blackthorn fruits, their use is still negligible. Purification of the antioxidant-active fraction, obtained from wild blackthorn fruits by hot ammonium oxalate extraction (Ao), yielded seven fractions after successive elution with water, sodium chloride and sodium hydroxide solutions. The purified fractions differ in carbohydrates, proteins, and phenolics. About 60% of the applied Ao material was recovered from the column, with the highest yields eluted with 0.25 M NaCl solution, accounting for up to 70 wt% of all eluted material. Analyses have shown that two dominant fractions (3Fa and 3Fb) contain 72.8-81.1 wt% of galacturonic acids, indicating the prevalence of homogalacturonans (HG) with a low acetyl content and a high degree of esterification. The low content of rhamnose, arabinose and galactose residues in both fractions indicates the presence of RG-I associated with arabinogalactan. In terms of yield, the alkali-eluted fraction was also significant, as a dark brown-coloured material with a yield of ~15 wt% with the highest content of phenolic compounds of all fractions. However, it differs from other fractions in its powdery nature, which indicates a high content of salts that could not be removed by dialysis.

Physicochemical Characterization of Pectic Polysaccharides from Rose Essential Oil Industry By-Products

The rose essential oil industry generates large quantities of solid byproducts yearly. These by-products, usually discarded, could yield valuable substances, such as pectic polysaccharides, widely used in the food industry as jelling agents. Seven industrial by-products were investigated as a source of pectic polysaccharides: four samples resulted from the treatment of Rosa damascena, two from Rosa alba, and one from Rosa centifolia. Three by-products were from steam-water distillation, two from CO2-supercritical extraction, and two after extraction with hexane and 1,1,1,2-tetrafluoroethane. The by-products were pretreated with 70% ethanol and extracted with 0.1 M HCl. The highest polysaccharide yield was observed for 1,1,1,2-tetrafluoroethane-extracted (RD_F) Rosa damascena by-products (13.98 ± 0.14%), followed by hexane (RD_X) and CO2-extracted (RD_CO2) Rosa damascena (12.68 ± 0.11 and 12.66 ± 0.10%, respectively). The polysaccharides were middle-methoxylated pectins, except RD_F and RD_X, having 26.68 ± 1.14 and 31.39 ± 1.39 mol % degree of methoxylation (low-methoxyl pectins). The polysaccharides had molecular masses in the 2.3-2.6 × 104 Da range. The rheological studies suggested RD_F formed a strong high-sucrose gel, while the others yielded weak gels. RD_F and RD_X formed strong Ca2+-mediated gels, comparable with commercial low-methoxylated citrus pectin. This study suggests that rose oil industry by-products could be successfully valorized and yield pectic polysaccharides with gelling properties, comparable with commercial citrus pectins.

Polysaccharides and Bioactive Phenolics from Aconitum septentrionale Roots

Aconitum septentrionale is known to contain toxic diterpene alkaloids, while other bioactive compounds in the plant remain unclear. The aim of this study was to explore the phenolic compounds and polysaccharides from the water extract of A. septentrionale roots. Fifteen phenolic compounds were isolated and identified by NMR and MS, including fourteen known and one new dianthramide glucoside (2-[[2-(β-D-glucopyranosyloxy)-5-hydroxybenzoyl]amino]-4,5-dihydroxybenzoic acid methyl ester, 14). One neutral (complex of glucans with minor amounts of mannans) and two acidic polysaccharide fractions (complexes of pectic polysaccharides and glucans) were also obtained. Hydroxytyrosol (1), hydroxytyrosol-1-O-β-glucoside (2) and bracteanolide A (7) inhibited the release of nitric oxide by dendritic cells. Magnoflorine (8) and 2-[[2-(β-D-glucopyranosyloxy)-5-hydroxybenzoyl]amino]-5-hydroxybenzoic acid methyl ester (12) inhibited 15-lipoxygenase, and bracteanolide A (7) was a moderate inhibitor of xanthine oxidase. This study is the first to describe the diversity of phenolics and polysaccharides from A. septentrionale and their anti-inflammatory and anti-oxidant activities.

RG-I Domain Matters to the In Vitro Fermentation Characteristics of Pectic Polysaccharides Recycled from Citrus Canning Processing Water

Canned citrus is a major citrus product that is popular around the world. However, the canning process discharges large amounts of high-chemical oxygen demand wastewater, which contains many functional polysaccharides. Herein, we recovered three different pectic polysaccharides from citrus canning processing water and evaluated their prebiotic potential as well as the relationship between the RG-I domain and fermentation characteristics using an in vitro human fecal batch fermentation model. Structural analysis showed a large difference among the three pectic polysaccharides in the proportion of the rhamnogalacturonan-I (RG-I) domain. Additionally, the fermentation results showed that the RG-I domain was significantly related to pectic polysaccharides' fermentation characteristics, especially in terms of short-chain fatty acid generation and modulation of gut microbiota. The pectins with a high proportion of the RG-I domain performed better in acetate, propionate, and butyrate production. It was also found that Bacteroides, Phascolarctobacterium, and Bifidobacterium are the main bacteria participating in their degradation. Furthermore, the relative abundance of Eubacterium_eligens_group and Monoglobus was positively correlated with the proportion of the RG-I domain. This study emphasizes the beneficial effects of pectic polysaccharides recovered from citrus processing and the roles of the RG-I domain in their fermentation characteristics. This study also provides a strategy for food factories to realize green production and value addition.

RGI-Type Pectic Polysaccharides Modulate Gut Microbiota in a Molecular Weight-Dependent Manner In Vitro

In this study, the fermentation characteristics of high rhamnogalacturonan I pectic polysaccharides (RGI) and free-radical degraded RGI (DRGI) were evaluated by a human fecal batch-fermentation model, and their structural properties were also investigated. As a result, the M_w of RGI decreased from 246.8 to 11.6 kDa, and the branches were broken dramatically. Fermentation showed that RGI degraded faster and produced more acetate and propionate than DRGI. Both of them reduced the Firmicutes/Bacteroidetes ratio and promoted the development of Bacteroides, Bifidobacterium, and Lactobacillus, bringing benefits to the gut ecosystem. However, the composition and metabolic pathways of the microbiota in RGI and DRGI were different. Most of the dominant bacteria of RGI (such as [Eubacterium]_eligens_group) participated in carbohydrate utilization, leading to better performance in glucolipid metabolism and energy metabolism. This work elucidated that large molecular weight matters in the gut microbiota modulatory effect of RGI-type pectic polysaccharides in vitro.

Pectic polysaccharides derived from Hainan Rauwolfia ameliorate NLR family pyrin domain-containing 3-mediated colonic epithelial cell pyroptosis in ulcerative colitis

Pectic polysaccharides (PPs) could exert functions on ulcerative colitis (UC), which is classified as a nonspecific inflammatory disorder. This study investigated the molecular mechanism of PPs derived from Rauwolfia in UC. First, the dextran sodium sulfate (DSS)-induced mouse colitis models and lipopolysaccharide (LPS)-treated colonic epithelial cell (YAMC) models were established and treated with PP. Subsequently, the effects of PPs on mucosal damages in DSS mice were detected, and the levels of inflammatory cytokines, pyroptosis-related factors, oxidative stress-related markers, and the tight junction-related proteins in the tissues or cells were examined, and the results suggested that PPs ameliorated colonic mucosal damages and cell pyroptosis in DSS mice, and limited colonic epithelial cell pyroptosis in in vitro UC models. Subsequently, the binding relations of retinol-binding protein 4 (RBP4) to miR-124-3p and NLR pyrin domain-containing 3 (NLRP3) were analyzed. miR-124-3p targeted RBP4 and reduced the binding of RBP4 to NLRP3, thus inhibiting NLRP3-mediated pyroptosis. Finally, functional rescue experiments revealed that miR-124-3p suppression or RBP4 overexpression promoted colonic epithelial cell pyroptosis. Collectively, Rauwolfia-derived PPs limited miR-124-3p and targeted RBP4 and reduced the binding potency of RBP4 to NLRP3 to inhibit NLRP3-mediated pyroptosis, resulting in the alleviation of colonic epithelial cell pyroptosis and mucosal damages in UC.

Novel Pectic Polysaccharides Isolated from Immature Honey Pomelo Fruit with High Immunomodulatory Activity

A novel pectic polysaccharide (HPP-1) with high immunomodulatory activity was extracted and isolated from the immature honey pomelo fruit (Citrus grandis). Characterization of its chemical structure indicated that HPP-1 had a molecular weight of 59,024 D. In addition, HPP-1 was primarily composed of rhamnose, arabinose, fucose, mannose, and galactose at a molar ratio of 1.00:11.12:2.26:0.56:6.40. Fourier-transform infrared spectroscopy, periodic acid oxidation, and Smith degradation results showed that HPP-1 had α- and β-glycosidic linkages and 1 → 2, 1 → 4, 1 → 6, and 1 → 3 glycosidic bonds. ¹³C NMR and ¹H NMR analyses revealed that the main glycogroups included 1,4-D-GalA, 1,6-β-D-Gal, 1,6-β-D-Man, 1,3-α-L-Ara, and 1,2-α-L-Rha. Immunomodulatory bioactivity analysis using a macrophage RAW264.7 model in vitro revealed that NO, TNF-α, and IL-6 secretions were all considerably increased by HPP-1. Moreover, RT-PCR results showed that HPP-1-induced iNOS, TNF-α, and IL-6 expression was significantly increased in macrophages. HPP-1-mediated activation in macrophages was due to the stimulation of the NF-κB and MAPK signaling pathways based on western blot analyses. HPP-1 extracted from immature honey pomelo fruit has potential applications as an immunomodulatory supplement.

Preliminary Characterization of Phytochemicals and Polysaccharides in Diverse Coffee Cascara Samples: Identification, Quantification and Discovery of Novel Compounds

Coffee cascara is the first and most significant by-product of the coffee processing industry, whose valorization has become an urgent priority to reduce harmful environmental impacts. This work aimed to provide an improved understanding of phytochemicals and polysaccharides in coffee cascara in order to offer information for the better evaluation of potential applications. Phytochemicals in 20 different coffee cascara samples were ultrasonically extracted and analyzed by HPLC-UV and HPLC-MS/MS. Four novel compounds were isolated for the first time from coffee cascara, including two still unknown tautomers (337 Da), and two dihydroflavonol glycosides (dihydromyricetin glycoside and dihydromyricetin rhamnosylglycoside). Their presence can contribute to the design of new value-added applications of coffee cascara. Chemical characterization of two polysaccharides from two of the coffee cascara pulp samples showed that they were mainly composed of homogalacturonan, with rhamnose and arabinose as minor neutral sugars. In addition, principal component analysis results indicated that coffee cultivar and/or country significantly impacted the phytochemical composition of coffee cascara, although differences may be reduced by the external environment and processing method. It is suggested that processing method should be carefully designed when generating coffee cascara from the same cultivar and country/farm.

New pectic polysaccharides from Codonopsis pilosula and Codonopsis tangshen: structural characterization and cellular antioxidant activities

BACKGROUND

Codonopsis pilosula and Codonopsis tangshen are plants widely used in traditional Chinese medicine. Two pectic polysaccharides from the roots of C. pilosula and C. tangshen named as CPP-1 and CTP-1 were obtained by boiling water extraction and column chromatography.

RESULTS

The core structures of both CPP-1 and CTP-1 comprise the long homogalacturonan region (HG) as the backbone and the rhamnogalacturonan I (RG-I) region as the side chains. CPP-1 has methyl esterified galacturonic acid units and a slightly lower molecular weight than CTP-1. Biological testing suggested that CPP-1 and CTP-1 can protect IPEC-J2 cells against the H₂ O₂ -induced oxidative stress by up-regulating nuclear factor-erythroid 2-related factor 2 and related genes in IPEC-J2 cells. The different antioxidative activities of polysaccharides from different source of C. pilosula may be result of differences in their structures.

CONCLUSION

All of the results indicated that pectic polysaccharides CPP-1 and CTP-1 from different species of C. pilosula roots could be used as a potential natural antioxidant source. These findings will be valuable for further studies and new applications of pectin-containing health products. © 2021 Society of Chemical Industry.

Structural Characterization of Pectic Polysaccharides in the Cell Wall of Stevens Variety Cranberry Using Highly Specific Pectin-Hydrolyzing Enzymes

The potential of poly- and oligosaccharides as functional ingredients depends on the type and glycosidic linkages of their monosaccharide residues, which determine their techno-functional properties, their digestibility and their fermentability. To isolate the pectic polysaccharides of cranberry, alcohol insoluble solids were first obtained from pomace. A sequential extraction with hot phosphate buffer, chelating agents (CH), diluted (DA) and concentrated sodium hydroxide was then carried out. Pectic polysaccharides present in CH and DA extracts were purified by anion exchange and gel filtration chromatography, then sequentially exposed to commercially available pectin-degrading enzymes (endo-polygalacturonase, pectin lyase and endo-arabinanase/endo-galactanase/both). The composition and linkages of the generated fragments revealed important characteristic features, including the presence of homogalacturonan with varied methyl esterification extent, branched type I arabinogalactan and pectic galactan. The presence of arabinan with galactose branches was suggested upon the analysis of the fragments by LC-MS.

Macromolecular Model of the Pectic Polysaccharides Isolated from the Bark of Norway Spruce (Picea abies)

The bark of Norway spruce (Picea abies) contains up to 13% pectins that can be extracted by pressurized hot water, which constitute a valuable renewable resource in second-generation lignocellulosic biorefineries. This article proposes, for the first time, structural molecular models for the pectins present in spruce bark. Pectin fractions of tailored molar masses were obtained by fractionation of the pressurized hot water extract of the inner bark using preparative size-exclusion chromatography. The monosaccharide composition, average molar mass distribution, and the glycosidic linkage patterns were analyzed for each fraction. The pectin fraction with high molecular weight (M_w of 59,000 Da) contained a highly branched RG-I domain, which accounted for 80% of the fraction and was mainly substituted with arabinan and arabinogalactan (type I and II) side chains. On the other hand, the fractions with lower molar masses (M_w = 15,000 and 9000 Da) were enriched with linear homogalacturonan domains, and also branched arabinan populations. The integration of the analytical information from the macromolecular size distributions, domain composition, and branch lengths of each pectin fraction, results in a comprehensive understanding of the macromolecular architecture of the pectins extracted from the bark of Norway spruce. This paves the way for the valorization of spruce bark pectic polymers in targeted applications based on their distinct polymeric structures and properties.

Migration of Tannins and Pectic Polysaccharides from Natural Cork Stoppers to the Hydroalcoholic Solution

Ellagitannins, condensed tannins, and pectic-derived polysaccharides were removed from natural cork stoppers using hydroalcoholic solution. Two main populations of migrated compounds were determined; the major one with molecular weight (MW) between 0.2 and 1 kDa and the second with 2.1 kDa and polydispersity of 1.3. Two residual populations mainly composed of condensed tannins were also observed between 2.5 and 4.5 kDa and higher than 15 kDa. Simple, C-glycosidic, complex, and oligomeric ellagitannins were identified by high-performance liquid chromatography-diode array detection/electrospray ionization-mass spectrometry (HPLC-DAD/ESI-MS). Ellagitannins linked to condensed tannins and some pectic-derived polysaccharides were also tentatively identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS). This preliminary work opens an opportunity for the cork stoppers industry due to the relevance of this type of compounds on the astringency and bitterness of wines.

Locating Methyl-Etherified and Methyl-Esterified Uronic Acids in the Plant Cell Wall Pectic Polysaccharide Rhamnogalacturonan II

Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide that exists as a borate ester cross-linked dimer in the cell walls of all vascular plants. The glycosyl sequence of RG-II is largely conserved, but there is evidence that galacturonic acid (GalA) methyl etherification and glucuronic acid (GlcA) methyl esterification vary in the A sidechain across plant species. Methyl esterification of the galacturonan backbone has also been reported but not confirmed. Here we describe a new procedure, utilizing aq. sodium borodeuteride (NaBD₄)-reduced RG-II, to identify the methyl esterification status of backbone GalAs. Our data suggest that up to two different GalAs are esterified in the RG-II backbone. We also adapted a procedure based on methanolysis and NaBD₄ reduction to identify 3-, 4-, and 3,4-O-methyl GalA in RG-II. These data, together with matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF) MS analysis of sidechain A generated from selected RG-IIs and their NaBD₄-reduced counterparts, suggest that methyl etherification of the β-linked GalA and methyl esterification of the GlcA are widespread. Nevertheless, the extent of these modifications varies between plant species. Our analysis of the sidechain B glycoforms in RG-II from different dicots and nonpoalean monocots suggests that this sidechain has a minimum structure of an O-acetylated hexasaccharide (Ara-[MeFuc]-Gal-AceA-Rha-Api-). To complement these studies, we provide further evidence showing that dimer formation and stability in vitro is cation and borate dependent. Taken together, our data further refine the primary sequence and sequence variation of RG-II and provide additional insight into dimer stability and factors controlling dimer self-assembly.

Surfactant-Induced Competitive Displacement of Potato Pectin-Protein Conjugate from the Air-Water Interface

Potato pectin contains some proteinaceous components and exhibits emulsifying and emulsion stabilizing abilities. The objective of this study was to elucidate the effect of the pectin moiety of the pectin-protein conjugate present in pectic extracts from potato tubers on their interfacial properties. Potato pectin was extracted from highly purified cell wall materials to avoid the contamination of unconjugated proteins. The abilities of the potato pectin to adsorb to graphite surfaces and to resist surfactant-induced competitive displacement from the air-water interface were investigated using atomic force microscopy. The pectin moiety of the potato pectin was capable of adsorbing to graphite surfaces even after alkali treatment. Furthermore, the potato pectin exhibited enhanced resistance to surfactant-induced competitive displacement from the interface as a result of the formation of network structures of self-assembled pectin moieties at the interface. The present results suggest the importance of the pectin moiety with regard to the interfacial properties of potato pectin.

Utilization of Complex Pectic Polysaccharides from New Zealand Plants (Tetragonia tetragonioides and Corynocarpus laevigatus) by Gut Bacteroides Species

Pectic polysaccharides from New Zealand (NZ) spinach (Tetragonia tetragonioides) and karaka berries (Corynocarpus laevigatus) were extracted and analyzed. NZ spinach polysaccharides comprised mostly homogalacturonan (64.4%) and rhamnogalacturonan I (5.8%), with side chains of arabinan (8.1%), galactan (2.2%), and type II arabinogalactan (7.1%); karaka berry polysaccharides comprised homogalacturonan (21.8%) and rhamnogalacturonan I (10.0%), with greater proportions of side chains (arabinan, 15.6%; galactan, 23.8%; and type II arabinogalactan, 19.3%). Screening of gut commensal Bacteroides showed that six were able to grow on the NZ spinach extract, while five were able to grow on the karaka berry extract. Analysis of the polysaccharides remaining after fermentation, by size-exclusion chromatography and constituent sugar analysis, showed that the Bacteroides species that grew on these two substrates showed preferences for the different pectic polysaccharide types. Our data suggest that, to completely degrade and utilize the complex pectin structures found in plants, members of Bacteroides and other bowel bacteria work as metabolic consortia.

Physiologically induced changes in bound phenolics and antioxidants, DNA/cytoprotective potentials in pectic poly/oligosaccharides of tomato (Solanum lycopersicum)

BACKGROUND

Antioxidant, cyto/DNA protective potentials are known to offer significant protection against free radical induced injury to cells or tissues and cellular damages that are envisaged in various diseases including chronic diseases like cancer, diabetes, etc, while galectin-3 inhibitory potentials are known to block or delay the process of metastasis in cancer. Antioxidant, cyto/DNA protection and galectin-3 inhibitory potentials were examined in pectic polysaccharides (PPs) and pectic oligosaccharides (POs) from four types of two varieties of tomatoes such as Sour (Mallika local variety) raw (SrRT-SrRTPP, SrRTPO), Sour ripe (SrRIT-SrRITPP, SrRITPO), Sweet (Rashmi local variety) raw (SwRT-SwRTPP, SwRTPO) and Sweet ripe (SwRIT-SwRITPP and SwRITPO).

RESULTS

Results indicate that unripe PPs and POs show approximately four- to five-fold better galectin-3 inhibitory property than ripe ones. An approximately nine- to 10-fold increase in galectin-3 inhibitory activity in sour variety was observed. The IC₅₀ as determined by free radical scavenging (FRS), red blood cell (RBC) and DNA protection assays revealed reduction in FRS and RBC protective potencies in pectic oligosaccharides (POs) than pectic polysaccharides (PPs), supporting the fact that phenolics contribute towards these activities. Loss of activity could be attributed to the hydrolysis of certain phenolics during the ripening process as well as during conversion of PPs to POs.

CONCLUSION

This study, for the first time, showed changes in bioactivity profiling in unripened and ripened conditions in tomato. Precise alterations in biomolecular components, such as bound cinnamyl/ferulyl and vanillic acid derivatives, along with alterations in sugar composition that reflect changes in antioxidants, cyto/DNA protective and antimetastatic potentials, have been delineated. © 2016 Society of Chemical Industry.

The chemical identity of intervessel pit membranes in Acer challenges hydrogel control of xylem hydraulic conductivity

Ion-mediated enhancement of the hydraulic conductivity of xylem tissue (i.e. the ionic effect) has been reported for various angiosperm species. One explanation of the ionic effect is that it is caused by the swelling and shrinking of intervessel pit membranes due to the presence of pectins and/or other cell-wall matrix polymers such as heteroxylans or arabinogalactan-proteins (AGPs) that may contain acidic sugars. Here, we examined the ionic effect for six Acer species and their pit membrane chemistry using immunocytochemistry, including antibodies against glycoproteins. Moreover, anatomical features related to the bordered pit morphology and vessel dimensions were investigated using light and electron microscopy. The ionic effect varied from 18 % (± 9) to 32 % (± 13). Epitopes of homogalacturonan (LM18) and xylan (LM11) were not detected in intervessel pit membranes. Negative results were also obtained for glycoproteins (extensin: LM1, JIM20; AGP glycan: LM2), although AGP (JIM13)-related epitopes were detected in parenchyma cells. The mean vessel length was significantly correlated with the magnitude of the ionic effect, unlike other pit or vessel-related characteristics. Our results suggest that intervessel pit membranes of Acer are unlikely to contain pectic or other acidic polysaccharides. Therefore, alternative explanations should be tested to clarify the ionic effect.

Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method

BACKGROUND AND AIMS

Many fruits soften during ripening, which is important commercially and in rendering the fruit attractive to seed-dispersing animals. Cell-wall polysaccharide hydrolases may contribute to softening, but sometimes appear to be absent. An alternative hypothesis is that hydroxyl radicals ((•)OH) non-enzymically cleave wall polysaccharides. We evaluated this hypothesis by using a new fluorescent labelling procedure to 'fingerprint' (•)OH-attacked polysaccharides.

METHODS

We tagged fruit polysaccharides with 2-(isopropylamino)-acridone (pAMAC) groups to detect (a) any mid-chain glycosulose residues formed in vivo during (•)OH action and (b) the conventional reducing termini. The pAMAC-labelled pectins were digested with Driselase, and the products resolved by high-voltage electrophoresis and high-pressure liquid chromatography.

KEY RESULTS

Strawberry, pear, mango, banana, apple, avocado, Arbutus unedo, plum and nectarine pectins all yielded several pAMAC-labelled products. GalA-pAMAC (monomeric galacturonate, labelled with pAMAC at carbon-1) was produced in all species, usually increasing during fruit softening. The six true fruits also gave pAMAC·UA-GalA disaccharides (where pAMAC·UA is an unspecified uronate, labelled at a position other than carbon-1), with yields increasing during softening. Among false fruits, apple and strawberry gave little pAMAC·UA-GalA; pear produced it transiently.

CONCLUSIONS

GalA-pAMAC arises from pectic reducing termini, formed by any of three proposed chain-cleaving agents ((•)OH, endopolygalacturonase and pectate lyase), any of which could cause its ripening-related increase. In contrast, pAMAC·UA-GalA conjugates are diagnostic of mid-chain oxidation of pectins by (•)OH. The evidence shows that (•)OH radicals do indeed attack fruit cell wall polysaccharides non-enzymically during softening in vivo. This applies much more prominently to drupes and berries (true fruits) than to false fruits (swollen receptacles). (•)OH radical attack on polysaccharides is thus predominantly a feature of ovary-wall tissue.

Boron bridging of rhamnogalacturonan-II is promoted in vitro by cationic chaperones, including polyhistidine and wall glycoproteins

Dimerization of rhamnogalacturonan-II (RG-II) via boron cross-links contributes to the assembly and biophysical properties of the cell wall. Pure RG-II is efficiently dimerized by boric acid (B(OH)3 ) in vitro only if nonbiological agents for example Pb(2+) are added. By contrast, newly synthesized RG-II domains dimerize very rapidly in vivo. We investigated biological agents that might enable this. We tested for three such agents: novel enzymes, borate-transferring ligands and cationic 'chaperones' that facilitate the close approach of two polyanionic RG-II molecules. Dimerization was monitored electrophoretically. Parsley shoot cell-wall enzymes did not affect RG-II dimerization in vitro. Borate-binding ligands (apiose, dehydroascorbic acid, alditols) and small organic cations (including polyamines) also lacked consistent effects. Polylysine bound permanently to RG-II, precluding electrophoretic analysis. However, another polycation, polyhistidine, strongly promoted RG-II dimerization by B(OH)3 without irreversible polyhistidine-RG-II complexation. Likewise, partially purified spinach extensins (histidine/lysine-rich cationic glycoproteins), strongly promoted RG-II dimerization by B(OH)3 in vitro. Thus certain polycations, including polyhistidine and wall glycoproteins, can chaperone RG-II, manoeuvring this polyanionic polysaccharide domain such that boron-bridging is favoured. These chaperones dissociate from RG-II after facilitating its dimerization, indicating that they act catalytically rather than stoichiometrically. We propose a natural role for extensin-RG-II interaction in steering cell-wall assembly.

Sugar composition of the pectic polysaccharides of charophytes, the closest algal relatives of land-plants: presence of 3-O-methyl-D-galactose residues

BACKGROUND AND AIMS

During evolution, plants have acquired and/or lost diverse sugar residues as cell-wall constituents. Of particular interest are primordial cell-wall features that existed, and in some cases abruptly changed, during the momentous step whereby land-plants arose from charophytic algal ancestors.

METHODS

Polysaccharides were extracted from four charophyte orders [Chlorokybales (Chlorokybus atmophyticus), Klebsormidiales (Klebsormidium fluitans, K. subtile), Charales (Chara vulgaris, Nitella flexilis), Coleochaetales (Coleochaete scutata)] and an early-diverging land-plant (Anthoceros agrestis). 'Pectins' and 'hemicelluloses', operationally defined as extractable in oxalate (100 °C) and 6 m NaOH (37 °C), respectively, were acid- or Driselase-hydrolysed, and the monosaccharides analysed chromatographically. One unusual monosaccharide, 'U', was characterized by (1)H/(13)C-nuclear magnetic resonance spectroscopy and also enzymically.

KEY RESULTS

'U' was identified as 3-O-methyl-D-galactose (3-MeGal). All pectins, except in Klebsormidium, contained acid- and Driselase-releasable galacturonate, suggesting homogalacturonan. All pectins, without exception, released rhamnose and galactose on acid hydrolysis; however, only in 'higher' charophytes (Charales, Coleochaetales) and Anthoceros were these sugars also efficiently released by Driselase, suggesting rhamnogalacturonan-I. Pectins of 'higher' charophytes, especially Chara, contained little arabinose, instead possessing 3-MeGal. Anthoceros hemicelluloses were rich in glucose, xylose, galactose and arabinose (suggesting xyloglucan and arabinoxylan), none of which was consistently present in charophyte hemicelluloses.

CONCLUSIONS

Homogalacturonan is an ancient streptophyte feature, albeit secondarily lost in Klebsormidium. When conquering the land, the first embryophytes already possessed rhamnogalacturonan-I. In contrast, charophyte and land-plant hemicelluloses differ substantially, indicating major changes during terrestrialization. The presence of 3-MeGal in charophytes and lycophytes but not in the 'intervening' bryophytes confirms that cell-wall chemistry changed drastically between major phylogenetic grades.

Differences between easy- and difficult-to-mill chickpea (Cicer arietinum L.) genotypes. Part III: free sugar and non-starch polysaccharide composition

BACKGROUND

Parts I and II of this series of papers identified several associations between the ease of milling and the chemical compositions of different chickpea seed fractions. Non-starch polysaccharides were implicated; hence, this study examines the free sugars and sugar residues.

RESULTS

Difficult milling is associated with: (1) lower glucose and xylose residues (less cellulose and xyloglucans) and more arabinose, rhamnose and uronic acid in the seed coat, suggesting a more flexible seed coat that resists cracking and decortication; (2) a higher content of soluble and insoluble non-starch polysaccharide fractions in the cotyledon periphery, supporting a pectic polysaccharide mechanism comprising arabinogalacturonan, homogalacturonan, rhamnogalalcturonan, and glucuronan backbone structures; (3) higher glucose and mannose residues in the cotyledon periphery, supporting a lectin-mediated mechanism of adhesion; and (4) higher arabinose and glucose residues in the cotyledon periphery, supporting a mechanism involving arabinogalactan-proteins.

CONCLUSION

This series has shown that the chemical composition of chickpea does vary in ways that are consistent with physical explanations of how seed structure and properties relate to milling behaviour. Seed coat strength and flexibility, pectic polysaccharide binding, lectins and arabinogalactan-proteins have been implicated. Increased understanding in these mechanisms will allow breeding programmes to optimise milling performance in new cultivars.

Boron deficiency: how does the defect in cell wall damage the cells?

Boron (B) is an essential micronutrient for vascular plants. Boron plays a structural role in cell walls through binding to pectic polysaccharides. It still remains unclear how B deficiency, and hence probably alterations in cell wall structure, leads to various metabolic disorders and cell death. To understand the process, we analyzed the physiological changes in suspension- cultured tobacco (Nicotiana tabacum) BY-2 cells under B deficiency. The results indicated that the cells deprived of B did not undergo a typical programmed cell death process. Oxidative damage was proven to be the direct and major cause of cell death. We discuss possible mechanisms for the generation and accumulation of reactive oxygen species under B deprivation.

Intercellular pectic protuberances in Asplenium: new data on their composition and origin

BACKGROUND AND AIMS

Projections of cell wall material into the intercellular spaces between parenchymatic cells have been observed since the mid-19th century. Histochemical staining suggested that these intercellular protuberances are probably pectic in nature, but uncertainties about their origin, composition and biological function(s) have remained.

METHODS

Using electron and light microscopy, including immunohistochemical methods, the structure and the presence of some major cell wall macromolecules in the intercellular pectic protuberances (IPPs) of the cortical parenchyma have been studied in a specimen of the Asplenium aethiopicum complex.

KEY RESULTS

IPPs contained pectic homogalacturonan, but no evidence for pectic rhamnogalacturonan-I or xylogalacturonan epitopes was obtained. Arabinogalactan-proteins and xylan were not detected in cell walls, middle lamellae or IPPs of the cortical parenchyma, whereas xyloglucan was only found in its cell walls. Extensin (hydroxyproline-rich glycoproteins) LM1 and JIM11 and JIM20 epitopes were detected specifically in IPPs but not in their adjacent cell walls or middle lamellae.

CONCLUSIONS

It is postulated that IPPs do not originate exclusively from the middle lamellae because extensins were only found in IPPs and not in surrounding cell walls, intercellular space linings or middle lamellae, and because IPPs and their adjacent cell walls are discontinuous.