The structural organization of the outer tissues in the gametophytic stem of the umbrella moss Hypnodendron menziesii optimizes load bearing.

MAIN CONCLUSION: The ultrastructural design and biochemical organization of the significantly thickened outer tissues of the gametophytic stem of Hypnodendron menziesii optimizes load bearing of the stem. Hypnodendron menziesii is a bryoid umbrella moss growing in high humid conditions on the forest floors of New Zealand. The erect gametophyte bears up to eight whorls of branches in succession, spreading across the stem that bears the heavy weight of branches with highly hydrated leaves. Our investigation using a combination of light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and TEM-immunolabeling techniques provided novel information on the structural design and biochemical organization of greatly thickened cell walls of epidermal, hypodermal, and outermost cortical tissues, comparing underlying thin-walled cortical tissues in the gametophytic stem. Probing into the ultrastructure of the cell wall architecture of these target tissues by TEM and SEM revealed the cell walls to display a multilamellar organization, in addition to demonstrating the presence of an electron-dense substance in the cell wall, presumably flavonoids. The pattern of distribution and concentration of rhamnogalacturonan, homogalacturonan, and heteromannan, as determined by immunogold labeling, suggests that it is the combination of structural and molecular design of the cell wall that may optimize the mechanical function of the epidermal, hypodermal, and outer cortical tissues. Statistical relationships between the overall thickness of epidermal, hypodermal, and outer cortical cell walls, the lumen area of cells and the percentage area of cell wall occupied in these tissues at different heights of the stem, and thickness of secondary cell wall layers (L1-L4/5) were explored. The results of these analyses unequivocally support the contribution of outer tissues to the mechanical strength of the resilient stem.

Seasonal variation of vessel pits in sapwood: microscopical analyses of the morphology and chemical components of pit membrane encrustations in Fraxinus mandshurica.

BACKGROUND AND AIMS: Pit pairs and their filter-like partition, i.e. pit membranes, play important roles as water pathways, barriers and regulators in the water-conducting system of angiosperms. In Fraxinus species, the intervessel and vessel-parenchyma pit membranes in sapwood are normally encrusted during winter. Although these encrustations inevitably influence the performance of pits, their properties and functions remain unclear. This study aimed to reveal the morphological and chemical characteristics of encrustations in F. mandshurica in order to deepen understanding of the seasonal encrustation of pit membranes. METHODS: Seasonal and positional variations in the presence and morphology of encrustations were examined by field-emission scanning electron microscopy (FE-SEM). Cryo-FE-SEM for freeze-fixed greenwood samples was conducted to clarify whether encrustations were present in living trees. Chemical components were examined by histochemical staining using light and electron microscopies, immunofluorescence labelling and ultraviolet microspectroscopy. KEY RESULTS: Encrustations began to deposit in fall before leaf senescence and disappeared in spring before bud flushing. They infiltrated within the pit membranes, which suggested that they severely limit the permeation of pits. The encrustations differed in morphology among positions: they entirely filled the pit chambers in latewood, while they covered the pit membranes in earlywood. The encrustations were similarly observed in the samples that were freeze-fixed immediately after collection, indicating that they are present in living trees. The encrustations contained polysaccharides, including xyloglucan and homogalacturonan, and phenolic compounds, possibly including flavonoids and coumarins. These chemical components were also detected in droplets found in the latewood vessels with the encrustations, suggesting that the materials constituting encrustations were supplied through the vessel lumens. CONCLUSIONS: Encrustations undoubtedly cover the pit membranes in living F. mandshurica trees in winter and their morphology and chemical composition indicate that they are impermeable, have positional differences in function and are characterised by elaborate deposition/removal processes.

Effect of pectin structure on the in vitro bioaccessibility of carotenoids in simulated juice model.

The impact of pectin structure on carotenoid bioaccessibility is still uncertain. This study aims to investigate how the different pectic polymers affected the bioaccessibility of carotenoids in a simulated juice model during static in vitro digestion. This study includes homogalacturonan (HG), which is a linear pectic polymer, rhamnogalacturonan-I (RG-I), which is a branched pectic polymer, and rhamnogalacturonan (RG), which is a diverse pectic polymer rich in RG-I, rhamnogalacturonan-II (RG-II), and xylogalacturonan domains. Juice models without pectin had the highest carotenoid bioaccessibility, suggesting pectin has negative effects on carotenoid bioaccessibility. During the intestinal phase, systems with HG showed the highest viscosity, followed by systems with RG and systems with RG-I. Systems with RG-I had lower carotenoid bioaccessibility than systems with HG and RG-II. Both the percentage of RG-I and the average side chain length of RG-I had negative correlations with carotenoid bioaccessibility. RG-I side chains with more arabinose and/or galactose might cause lower carotenoid bioaccessibility in this juice model system. This study offers valuable insights into the relationship between pectin structure and carotenoid bioaccessibility in a simulated juice model, highlighting the importance of considering pectin composition for maximizing carotenoid bioaccessibility and potential health benefits in fruit-based beverages.

The radiation of nodulated Chamaecrista species from the rainforest into more diverse habitats has been accompanied by a reduction in growth form and a shift from fixation threads to symbiosomes.

All non-Mimosoid nodulated genera in the legume subfamily Caesalpinioideae confine their rhizobial symbionts within cell wall-bound 'fixation threads' (FTs). The exception is the large genus Chamaecrista in which shrubs and subshrubs house their rhizobial bacteroids more intimately within symbiosomes, whereas large trees have FTs. This study aimed to unravel the evolutionary relationships between Chamaecrista growth habit, habitat, nodule bacteroid type, and rhizobial genotype. The growth habit, bacteroid anatomy, and rhizobial symbionts of 30 nodulated Chamaecrista species native to different biomes in the Brazilian state of Bahia, a major centre of diversity for the genus, was plotted onto an ITS-trnL-F-derived phylogeny of Chamaecrista. The bacteroids from most of the Chamaecrista species examined were enclosed in symbiosomes (SYM-type nodules), but those in arborescent species in the section Apoucouita, at the base of the genus, were enclosed in cell wall material containing homogalacturonan (HG) and cellulose (FT-type nodules). Most symbionts were Bradyrhizobium genotypes grouped according to the growth habits of their hosts, but the tree, C. eitenorum, was nodulated by Paraburkholderia. Chamaecrista has a range of growth habits that allow it to occupy several different biomes and to co-evolve with a wide range of (mainly) bradyrhizobial symbionts. FTs represent a less intimate symbiosis linked with nodulation losses, so the evolution of SYM-type nodules by most Chamaecrista species may have (i) aided the genus-wide retention of nodulation, and (ii) assisted in its rapid speciation and radiation out of the rainforest into more diverse and challenging habitats.

Purification, structural characterization, and immunomodulatory activity of two polysaccharides from Portulaca oleracea L.

In present study, two water-soluble polysaccharides designated as POL-1 and POL-2 were purified from purslane and their structural characteristics as well as immunomodulatory activity were investigated. The weight-average molecular weight (Mw) of POL-1 and POL-2 were determined to be 64,100 Da and 21,000 Da, respectively. Comprehensive techniques including UV, IR, GC-MS, and NMR were applied to deduced that POL-1 was a pectin polysaccharide homogalacturonan (HG) consisting of →4)-α-GalpA-(1→ with methyl ester degree of 9.71 % and acetylation degree of 0.34 %, while POL-2 was composed of a 1, 4-linked ß-Galp backbone substituted by short side chain →4)-α-Glcp-(1→ and →6)-α-Glcp-(1→. The →4)-α-Glcp-(1→ was attached at the O-6 position of →4)-ß-Galp-(1→. TEM further revealed that POL-1 was non-branched single chains, while POL-2 was entangled microstructure with side chains. Moreover, POL-2 significantly promoted macrophage phagocytosis as well as the secretion of NO and cytokines (TNF-α, IL-6) through activating NF-κB signaling pathway, thus demonstrating potential immunomodulatory activity. These findings suggested that purslane may be exploited as a potential adjuvant and dietary supplement with immunostimulatory purpose.

A novel pectin methylesterase inhibitor, PMEI3, in common bean suggests a key role of pectin methylesterification in Pseudomonas resistance.

The mechanisms underlying susceptibility to and defense against Pseudomonas syringae (Pph) of the common bean (Phaseolus vulgaris) have not yet been clarified. To investigate these, 15-day-old plants of the variety Riñón were infected with Pph and the transcriptomic changes at 2 h and 9 h post-infection were analysed. RNA-seq analysis showed an up-regulation of genes involved in defense/signaling at 2 h, most of them being down-regulated at 9 h, suggesting that Pph inhibits the transcriptomic reprogramming of the plant. This trend was also observed in the modulation of 101 cell wall-related genes. Cell wall composition changes at early stages of Pph infection were associated with homogalacturonan methylation and the formation of egg boxes. Among the cell wall genes modulated, a pectin methylesterase inhibitor 3 (PvPMEI3) gene, closely related to AtPMEI3, was detected. PvPMEI3 protein was located in the apoplast and its pectin methylesterase inhibitory activity was demonstrated. PvPMEI3 seems to be a good candidate to play a key role in Pph infection, which was supported by analysis of an Arabidopsis pmei3 mutant, which showed susceptibility to Pph, in contrast to resistant Arabidopsis Col-0 plants. These results indicate a key role of the degree of pectin methylesterification in host resistance to Pph during the first steps of the attack.

Acetylation of homogalacturonan and rhamnogalacturonan-I is catalyzed by a suite of trichome birefringence-like proteins.

Plant cell wall polysaccharides, including xylan, mannan, xyloglucan, and pectins, are often acetylated and members of the domain of unknown function 231 (DUF231)/trichome birefringence-like (TBL) family have been shown to be O-acetyltransferases mediating the acetylation of xylan, mannan, and xyloglucan. However, little is known about the O-acetyltransferases responsible for pectin acetylation. In this report, we biochemically characterized a suite of Arabidopsis DUF231/TBL proteins for their roles in pectin acetylation. We generated 24 TBL recombinant proteins in mammalian cells and demonstrated that 10 of them were able to transfer acetyl groups from acetyl-CoA onto the pectins homogalacturonan (HG) or rhamnogalacturonan-I (RG-I), and thus were named pectin O-acetyltransferase 1 to 10 (POAT1 to 10). It was found that POAT2,4,9,10 specifically acetylated HG and POAT5,6 acetylated RG-I, whereas POAT1,3,7,8 could act on both HG and RG-I. The acetylation of HG and RG-I by POATs was further corroborated by hydrolysis with pectin acetylesterases and by nuclear magnetic resonance spectroscopy. In addition, mutations of the conserved GDS and DXXH motifs in POAT3 and POAT8 were shown to lead to a loss of their ability to acetylate HG and RG-I. Furthermore, simultaneous RNA interference downregulation of POAT1,3,6,7,8 resulted in reduced cell expansion, impaired plant growth, and decreased pectin acetylation. Together, our findings indicate that these POATs are pectin O-acetyltransferases involved in acetylation of the pectin polysaccharides HG and RG-I.

Properties of lime peel pectin as mainly influenced by ethanol and protein-based purification methods.

BACKGROUND: Lime peel, obtained from juice factory waste, is considered as a source of pectin. Lime peel pectin samples, extracted by three extraction procedures of 90 °C heating for 120 min, 90 °C heating for 90 min and then 32 min of ultrasound, and 80 °C heating for 60 min and then 22 min of ultrasound, and purified by two methods using ethanol and sodium caseinate (SC), were prepared and characterized. RESULTS: The results showed that the purification method significantly affected the lime pectin samples properties. Pectin samples purified with SC had a transparent and film-like appearance, whereas the ethanol-purified pectin samples showed an amorphous and opaque appearance. Pectin samples purified with ethanol showed higher extraction recovery (approximately 20%), whereas the lowest pectin yield was observed for the purification with SC (approximately 10%). Although SC purification did not enhance the pectin yield, it diminished the level of 'non-pectin' components and resulted in purer pectin. The bands at 1045-1076 cm-1 , relating to neutral sugars, had higher intensities in ethanol-purified pectin samples, indicating their higher sugar contents. Also the samples purified with SC exhibited more thermal stability, probably as a result of the presence of protein in their structure. CONCLUSION: In the present study, under the same or varying extraction conditions, the most important element distinguishing pectins in terms of appearance, physicochemical, thermal and Fourier transform infrared characteristics was the type of purification method. Purification with SC may result in pectins with more non-esterified galacturonic acids from the homogalacturonan fraction. © 2023 Society of Chemical Industry.

Effects of extraction methods on the physicochemical properties and functionalities of pectic polysaccharides from burdock (Arctium lappa L.).

In this work, the effects of four different extraction methods, acid (HCl), alkali (NaOH), enzymes (cellulase/pectinase), and buffer (pH 7.0) on the physicochemical properties and functionalities of burdock pectin were systematically investigated and compared. Buffer extraction gave a low yield (2.8 %) and is therefore limited in its application. The acid treatment hydrolyzed the neutral sidechains and gave a homogalacturonan content of 72.6 %. By contrast, alkali and enzymes preserved the sidechains while degrading the polygalacturonan backbone, creating a rhamnogalacturonan-I dominant structure. The branched structure, low molecular weight, and high degree of methylation (42.3 %) contributed to the interfacial adsorption, emulsifying capacity, and cellular antioxidant activity of the enzyme-extracted product. For the acid-extracted product, the strong intramolecular electrostatic repulsion restricted the formation of a contact interface to prevent coalescence of the emulsion. In addition, they did not have sufficient reducing ends to scavenge free radicals. Although a high branching size (5.0) was adopted, the low degree of methylation (19.5 %) affected the emulsifying capacity of the alkali-extracted products. These results provide useful information for pectic polysaccharides production with tailored properties.

Water-soluble polysaccharides from Piper regnellii (Pariparoba) leaves: Structural characterization and antinociceptive and anti-inflammatory activities.

Piper regnellii is a plant popularly known as "Pariparoba" and it is widely used in folk medicine to treat pain, inflammation, among others. This work presents the extraction, purification and characterization of polysaccharides present in the plant leaves and evaluation of their anti-inflammatory and antinociceptive activities. From the crude aqueous extract of P. regnellii leaves, a polysaccharide fraction named PR30R, predominantly constituted of arabinose, galactose and galacturonic acid monosaccharide units, was obtained. Methylation and NMR analysis showed that the main polysaccharides of PR30R are a type II arabinogalactan, formed by a ß-D-Galp-(1 â†’ 3) main chain, substituted at O-6 by side chains of ß-D-Galp-(1 â†’ 6), which are substituted at O-3 by non-reducing α-L-Araf ends, and a homogalacturonan, formed by →4)-α-D-GalpA-(1→ units. Intraperitoneal administration of the crude polysaccharide fraction PRSF reduced significantly nociception induced by acetic acid in mice at the doses tested, and the PR30R fraction, derived from PRSF, presented antinociceptive and anti-inflammatory effects at a dose of 0.1096 mg/kg (PRSF ED50). These data support the use of the plant leaves in folk medicine as an herbal tea to treat pain and inflammation.

Response of Prolyl 4 Hydroxylases, Arabinogalactan Proteins and Homogalacturonans in Four Olive Cultivars under Long-Term Salinity Stress in Relation to Physiological and Morphological Changes.

Olive (Olea europeae L.) salinity stress induces responses at morphological, physiological and molecular levels, affecting plant productivity. Four olive cultivars with differential tolerance to salt were grown under saline conditions in long barrels for regular root growth to mimic field conditions. Arvanitolia and Lefkolia were previously reported as tolerant to salinity, and Koroneiki and Gaidourelia were characterized as sensitive, exhibiting a decrease in leaf length and leaf area index after 90 days of salinity. Prolyl 4-hydroxylases (P4Hs) hydroxylate cell wall glycoproteins such as arabinogalactan proteins (AGPs). The expression patterns of P4Hs and AGPs under saline conditions showed cultivar-dependent differences in leaves and roots. In the tolerant cultivars, no changes in OeP4H and OeAGP mRNAs were observed, while in the sensitive cultivars, the majority of OeP4Hs and OeAGPs were upregulated in leaves. Immunodetection showed that the AGP signal intensity and the cortical cell size, shape and intercellular spaces under saline conditions were similar to the control in Arvanitolia, while in Koroneiki, a weak AGP signal was associated with irregular cells and intercellular spaces, leading to aerenchyma formation after 45 days of NaCl treatment. Moreover, the acceleration of endodermal development and the formation of exodermal and cortical cells with thickened cell walls were observed, and an overall decrease in the abundance of cell wall homogalacturonans was detected in salt-treated roots. In conclusion, Arvanitolia and Lefkolia exhibited the highest adaptive capacity to salinity, indicating that their use as rootstocks might provide increased tolerance to irrigation with saline water.

Homogalacturonan enriched pectin based hydrogel enhances 6-gingerol's colitis alleviation effect via NF-κB/NLRP3 axis.

A nanolipidcarrier (NLC) loaded homogalacturonan enriched pectin (citrus modified pectin, MCP4) hydrogel was designed as a novel colon inflammation site-specific oral delivery system for 6-gingerol (6G) (6G-NLC/MCP4 hydrogel) administration, and its colitis alleviation effect were investigated. 6G-NLC/MCP4 exhibited typical "cage-like" ultrastructure with 6G-NLC embedded in the hydrogel matrix as observed by cryoscanning electron microscope. And due to the homogalacturonan (HG) domain in MCP4 specifically combined with Galectin-3, which is overexpressed in the inflammatory region, the 6G-NLC/MCP4 hydrogel targeted to severe inflammatory region. Meanwhile, the prolonged-release characteristics of 6G-NLC provided sustained release of 6G in severe inflammatory regions. The matrix of hydrogel MCP4 and 6G achieved synergistic alleviation effects for colitis through NF-κB/NLRP3 axis. Specifically, 6G mainly regulated the NF-κB inflammatory pathway and inhibited the activity of NLRP3 protein, while MCP4 regulated the expression of Galectin-3 and peripheral clock gene Rev-Erbα/ß to prevent the activation of inflammasome NLRP3.

Comparison of structures and emulsifying properties between water-extracted pectins from Fructus aurantii.

The structural characteristics of two water-extracted pectic polysaccharides from Fructus aurantii were investigated, and the impacts of their structures on the emulsifying stability were evaluated. FWP-60 (extracted by cold water and followed 60 % ethanol precipitation) and FHWP-50 (extracted by hot water and followed 50 % ethanol precipitation) were both high methyl-esterified pectins, which were composed of homogalacturonan (HG) and highly branched rhamnogalacturonan I (RG-I) regions. The weight-average molecular weight, methyl-esterification degree (DM) and HG/RG-I ratio of FWP-60 were 1200 kDa, 66.39 % and 4.45, respectively, which were 781 kDa, 79.10 % and 1.95 for FHWP-50. The methylation and NMR analysis of FWP-60 and FHWP-50 demonstrated that the main backbone consisted of different molar ratios of →4)-α-GalpA-(1 â†’ and →4)-α-GalpA-6-O-methyl-(1 →, and the side chains contained arabinan and galactan. Moreover, the emulsifying properties of FWP-60 and FHWP-50 were discussed. Compared with FHWP-50, FWP-60 had better emulsion stability. Overall, pectin had a linear HG domain and a small number of RG-I domain with short side chains to facilitate the stabilization of emulsions in Fructus aurantii. A comprehensive knowledge of the structure characteristic and emulsifying property would enable us to provide more information and theoretical guidance for the structure and emulsion preparation of Fructus aurantii pectic polysaccharides.

Elucidation of the GAUT gene family in eight Rosaceae species and function analysis of PbrGAUT22 in pear pollen tube growth.

MAIN CONCLUSION: The phylogenetic relationship and evolutionary history of the GAUT gene family were identified in 8 Rosaseae species. PbrGAUT22 was involved in controlling pollen tube growth by regulating the content of pectins. In plants, galacturonosyltransferases (GAUTs) were involved in homogalacturonan biosynthesis and functioned in maintaining pollen tube cell wall integrity. However, the feature and evolutionary history of the GAUT gene family in Rosaceae species and candidates in pear pollen tube growth remain unclear. Here, we identified 190 GAUT genes in 8 Rosaceae species, including Chinese white pear (Pyrus bretschneideri), European pear (Pyrus communis), apple (Malus × domestica), peach (Prunus persica), Japanese apricot (Prunus mume), sweet cherry (Prunus avium), woodland strawberry (Fragaria vesca) and black raspberry (Rubus occidentalis). Members in GAUT gene family were divided into 4 subfamilies according to the phylogenetic and structural analysis. Whole-genome duplication events and dispersed duplicates drove the expansion of the GAUT gene family. Among 23 pollen-expressed PbrGAUT genes in pear, PbrGAUT22 showed increased expression level during 1-6 h post-cultured pollen tubes. PbrGAUT22 was localized to the cytoplasm and plasma membrane. Knockdown of PbrGAUT22 expression in pollen tubes caused the decrease of pectin content and inhibited pear pollen tubes growth. Taken together, we investigated the identification and evolution of the GAUT gene family in Rosaceae species, and found that PbrGAUT22 played an essential role in the synthesis of pectin and the growth of pear pollen tubes.

GoSAMTs are required for pectin methyl-esterification and mucilage release in seed coat epidermal cells.

Introduction: GoSAMTs play a role in the methylation of polysaccharides synthesized by the Golgi. Pectin homogalacturonan (HG) methyl-esterification is essential for the proper function of this polysaccharide in cell walls. In order to better understand the role of GoSAMTs in HG biosynthesis, we analyzed mucilage methyl-esterification in gosamt mutants. Methods: To determine the function of GoSAMT1 and GoSAMT2 in HG methyl-esterification we utilized epidermal cells of seed coats, as these structures produce mucilage, which is a pectic matrix. We evaluated differences in seed surface morphology and quantified mucilage release. We measured methanol release, and used antibodies and confocal microscopy to analyze HG methyl-esterification in mucilage. Results: We observed morphological differences on the seed surface and delayed, uneven mucilage release in gosamt1-1gosamt2-1 double mutants. We also found changes in the distal wall length indicating abnormal cell wall breakage in this double mutant. Using methanol release and immunolabeling, we confirmed that GoSAMT1 and GoSAMT2 are involved in HG methyl-esterification in mucilage. However, we did not find evidence of decreasing HG in the gosamt mutants. Confocal microscopy analyses detected different patterns in the adherent mucilage and a greater number of low-methyl-esterified domains near the seed coat surface, which correlates with a greater number of "egg-box" structures in this region. We also detected a shift in the partitioning between the Rhamnogalacturonan-I soluble and adherent layers of the double mutant, which correlated with increased amounts of arabinose and arabinogalactan-protein in the adherent mucilage. Discussion: The results show that the HG synthesized in gosamt mutant plants is less methyl esterified, resulting in more egg-box structures, which stiffen the cell walls in epidermal cells and change the rheological properties of the seed surface. The increased amounts of arabinose and arabinogalactan-protein in adherent mucilage, also suggests that compensation mechanisms were triggered in the gosamt mutants.

Insights into pectin O-acetylation in the plant cell wall: structure, synthesis, and modification.

O-Acetyl esterification is an important structural and functional feature of pectins present in the cell walls of all land plants. The amount and positions of pectin acetyl substituents varies across plant tissues and stages of development. Plant growth and response to biotic and abiotic stress are known to be significantly influenced by pectin O-acetylation. Gel formation is a key characteristic of pectins, and many studies have shown that gel formation is dependent upon the degree of acetylation. Previous studies have indicated that members of the TRICHOME BIREFRINGENCE-LIKE (TBL) family may play a role in the O-acetylation of pectin, however, biochemical evidence for acceptor specific pectin acetyltransferase activity remains to be confirmed and the exact mechanism(s) for catalysis must be determined. Pectin acetylesterases (PAEs) affect pectin acetylation as they hydrolyze acetylester bonds and have a role in the amount and distribution of O-acetylation. Several mutant studies suggest the critical role of pectin O-acetylation; however, additional research is required to fully understand this. This review aims to discuss the importance, role, and putative mechanism of pectin O-acetylation.

The specificity of pectate lyase VdPelB from Verticilium dahliae is highlighted by structural, dynamical and biochemical characterizations.

Pectins, complex polysaccharides and major components of the plant primary cell wall, can be degraded by pectate lyases (PLs). PLs cleave glycosidic bonds of homogalacturonans (HG), the main pectic domain, by ß-elimination, releasing unsaturated oligogalacturonides (OGs). To understand the catalytic mechanism and structure/function of these enzymes, we characterized VdPelB from Verticillium dahliae. We first solved the crystal structure of VdPelB at 1.2 Å resolution showing that it is a right-handed parallel ß-helix structure. Molecular dynamics (MD) simulations further highlighted the dynamics of the enzyme in complex with substrates that vary in their degree of methylesterification, identifying amino acids involved in substrate binding and cleavage of non-methylesterified pectins. We then biochemically characterized wild type and mutated forms of VdPelB. Pectate lyase VdPelB was most active on non-methylesterified pectins, at pH 8.0 in presence of Ca2+ ions. The VdPelB-G125R mutant was most active at pH 9.0 and showed higher relative activity compared to native enzyme. The OGs released by VdPelB differed to that of previously characterized PLs, showing its peculiar specificity in relation to its structure. OGs released from Verticillium-partially tolerant and sensitive flax cultivars differed which could facilitate the identification VdPelB-mediated elicitors of defence responses.

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage.

INTRODUCTION: Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant. OBJECTIVES: This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness. METHODS: The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca2+ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit. RESULTS: The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0 °C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca2+ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals. CONCLUSION: PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca2+ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Multi-microscopy techniques combined with FT-IR spectroscopy reveals the histological and biochemical causes leading to fruit texture difference in oriental melon (Cucumis melo var. Makuwa Makino).

Multi-microscopy techniques and Fourier transform infrared (FT-IR) spectroscopy were used in this study to investigate the intrinsic causes leading to fruit texture difference between two cultivars of oriental melon 'HDB' (crisp) and 'HPM' (mealy). On the histological aspect, orderly arranged regular-shaped cells with tissue natural fracture pattern showed cell rupture in 'HDB' versus loosely arranged irregular-shaped cells with tissue natural fracture pattern showed cell-to-cell separation in 'HPM' of sarcocarp are histological causes for crisp and mealy fruit texture, respectively. On the biochemical aspect, FT-IR spectra (4000-850 cm-1) of sarcocarp tissue cell wall materials (CWM) happened a dramatic change at the mature stage in 'HPM', but not in 'HDB'. Insightly, the lower de-methyl-esterified homogalacturonan (HG) abundance with higher water-soluble pectin (WSP) ratio and lower hemicellulose (HC) content contribute a poor intercellular adhesion in 'HPM' middle lamella (ML) at the mature stage compared to 'HDB'.

A Homogalacturonan from Peel of Winter Jujube (Zizyphus jujuba Mill. cv. Dongzao): Characterization and Protective Effects against CCl4-Induced Liver Injury.

A homogalacturonan pectin (HG, designated as WJP-F80) was extracted from the peel of winter jujube (Zizyphus jujuba Mill. Cv. Dongzao) and separated via ethanol-graded precipitation. The structural and conformational features were elucidated through HPAEC-PAD, GC-MS, 2D NMR, and HPSEC-MALLS studies. In vivo assessments were carried out to evaluate the hepatoprotective effects of WJP-F80 against CCl4-induced injury of mice. Results showed that WJP-F80 was a linear 1,4-α-galacturonan with partially methyl-esterified at O-6 of GalpA and occasionally acetylation. The Mw of WJP-F80 was determined as 45.3 kDa, the polydispersity was calculated as 1.56, and the Rg was measured as 22.7 nm in 0.1 M NaNO3. The conformational analysis revealed that WJP-F80 exhibited as rigid stiff chain in low Mw range, while aggregation by self-assembly of HG chains lead to high Mw and random coil conformation. In vivo studies indicated that WJP-F80 can protect the livers of mice from acute injury induced via CCl4 by decreasing the serum biochemical markers of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) to normal levels. This work provides a theoretical basis for the value-added deep processing of winter jujube.