Pectin Methyl Research Articles

The ‘photosynthetic C1 pathway’ links carbon assimilation and growth in California poplar

Although primarily studied in relation to photorespiration, serine metabolism in chloroplasts may play a key role in plant CO2 fertilization responses by linking CO2 assimilation with growth. Here, we show that the phosphorylated serine pathway is part of a ‘photosynthetic C1 pathway’ and demonstrate its high activity in foliage of a C3 tree where it rapidly integrates photosynthesis and C1 metabolism contributing to new biomass via methyl transfer reactions, imparting a large natural 13C-depleted signature. Using 13CO2-labelling, we show that leaf serine, the S-methyl group of leaf methionine, pectin methyl esters, and the associated methanol released during cell wall expansion during growth, are directly produced from photosynthetically-linked C1 metabolism, within minutes of light exposure. We speculate that the photosynthetic C1 pathway is highly conserved across the photosynthetic tree of life, is responsible for synthesis of the greenhouse gas methane, and may have evolved with oxygenic photosynthesis by providing a mechanism of directly linking carbon and ammonia assimilation with growth. Although the rise in atmospheric CO2 inhibits major metabolic pathways like photorespiration, our results suggest that the photosynthetic C1 pathway may accelerate and represents a missing link between enhanced photosynthesis and plant growth rates during CO2 fertilization under a changing climate.

Effects of Thifluzamide Treatment on the Production of Cell Wall Degrading Enzymes in Rhizoctonia solani and Phenylpropane Metabolism in Pear Fruit

The study aimed to investigate the effects of thifluzamide (2.67 mg/L) on ‘Huangguan’ pear fruit rot caused by Rhizoctonia solani during storage, as well as the activities of polygalacturonase (PG), pectin methylesterase (PME), polygalacturonic acid trans-eliminase (PGTE), pectin methyl trans-eliminase (PMTE), xylanase, and pectate lyase (PL) secreted by R. solani. The results showed that thifluzamide treatment significantly inhibited the activities of PG, PME, PGTE, PMTE, xylanase, and PL secreted by R. solani after 3 days in vitro culture, compared to the control. Thifluzamide also increased the activities of phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate CoA ligase (4CL), and the contents of flavonoids and total phenolic compounds in pear fruit. Furthermore, thifluzamide increased the expression of PcPAL, PcC4H, Pc4CL, Pcβ-1,3-GA, PcLCH, PcF3H, and PcDFR involved in phenylpropanoid metabolism in pear fruit. In conclusion, thifluzamide treatment reduced the infection ability of R. solani by inhibiting the expression of the genes encoding cell wall-degrading enzymes in R. solani. At the same time, it inhibited the activities of cell wall-degrading enzymes induced resistance against R. solani infection in ‘Huangguan’ pears by promoting phenylpropane metabolism.

A QTL on chromosome 17 identified by Genome-Wide Association Mapping controls postharvest cold tolerance of Cucurbita pepo L.

The worldwide cultivated Cucurbita pepo L. is one of the most diverse species in the plant kingdom. In this study, chilling tolerance over a wide range of cultivars was characterized to discover the allelic variants to improving the postharvest quality of the immature fruit during cold storage. For this purpose, fruits from 126 accessions of worldwide origin have been evaluated for weight loss and chilling injury after 3, 7 and 14 days of cold storage, classifying them into tolerant, partially tolerant, and sensitive accessions. To verify this classification, antioxidant capacity and lipid peroxidation (MDA) of contrasting accessions (tolerant vs. sensitive) were assessed. The antioxidant capacity significantly decreased during cold storage in the sensitive accessions, while it was maintained in tolerant accessions. Additionally, the sensitive accessions presented a higher accumulation of MDA during this period. Finally, a GWAS analysis using GBS data available in CuGenDBv2, combined with weight loss percentage data, led to the identification of a candidate QTL located on chromosome 17 that regulates postharvest cold tolerance in zucchini. The region contains four SNPs whose alternative alleles were significantly associated with lower weight loss percentage and chilling injury indices during cold storage. Two SNPs are located in the 3' UTR region of the gene CpERS1, a gene involved in ethylene perception. The other two SNPs generate missense mutations in the coding region of a Pectin methyl esterase inhibitor gene (CpPMI). The role of this QTL and these variants in chilling tolerance is discussed.

Sodium nitroprusside applications modulate cell wall degrading enzymes and preserves the postharvest quality of cold-stored mangoes

ABSTRACT Mango fruit undergoes various physiochemical changes after its harvest that affect consumer acceptability. The present research work was carried out to evaluate the preservation effect of sodium nitroprusside (SNP) treatments on the postharvest quality of mango cv. Langra fruits at 12 ± 1°C for 35 days. The results revealed that SNP 1.0 mM treated fruits exhibited reduced weight loss (6.94%), decay incidence (8.05%), and activities of cell wall degrading enzymes like polygalacturonase and pectin methyl esterase in comparison to uncoated fruits on the last day of storage. Furthermore, the treatment maintained higher fruit firmness (56.77 N) along with fruit quality parameters like soluble solid content (16.24%), titratable acidity (0.20%), starch (4.99%), and, total flavonoid content (12.92 mg/100 g). Overall, SNP 1.0 mM combined with low-temperature storage was proved to be the most effective in extending the shelf life and preserving the quality characteristics of mango fruits.

Carvacrol enhances antioxidant activity and slows down cell wall metabolism by maintaining the energy level of 'Guifei' mango.

Postharvest mango fruit are highly susceptible to rapid ripening, softening and senescence, greatly limiting their distribution. In this study, we evaluated the potential effects of carvacrol (0.06 g L-1) on mango (25 ± 1 °C) and the mechanisms by which it regulates antioxidant activity, energy and cell wall metabolism. The results showed that carvacrol treatment delayed the 'Guifei' mango color transformation (from green to yellow) and the decrease in firmness, titratable acidity, weight loss and soluble solids content, and suppressed the increase in relative conductivity, malondialdehyde content and reactive oxygen species (H2O2 and O2 ·-) as well as enhancing antioxidant activity. In addition, carvacrol treatment increased ascorbic acid and reduced glutathione levels, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase activities in mango. Meanwhile, energy level (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate and energy charge) content and energy metabolizing enzyme activities (H+-ATPase, Ca2+-ATPase, succinate dehydrogenasepears and cytochrome C oxidase) were increased on carvacrol treatment, which resulted in the maintenance of higher energy levels. Finally, the application of carvacrol was effective in maintaining firmness and cell wall components by inhibiting the activities of polygalacturonase, cellulase, pectin methyl esterase and β-galactosidase. The current study demonstrates that carvacrol effectively delays the ripening and softening of mangoes by modulating energy metabolism and cell wall dynamics through the attenuation of oxidative stress. © 2024 Society of Chemical Industry.

Postharvest application of sodium nitroprusside improves the quality of ‘Umran’ ber fruit under cold storage conditions by regulating enzyme activities

ABSTRACT Ber fruit is highly perishable, with a storage life of only 3–5 days under ambient conditions, which makes it difficult to transport the fruit even to domestic markets. An experiment was conducted to study the effect of postharvest treatment with sodium nitroprusside (50, 100 and 150 µM) on the storage life, quality attributes, bioactive composition and antioxidant enzyme contents of ‘Umran’ ber fruit. The treated fruit were stored for 28 days to investigate the effects of sodium nitroprusside after 7 days of cold storage at 7.5°C and 90–95% RH. It was found that fruit treated with 100 μM sodium nitroprusside experienced lower fruit weight loss and spoilage, maintained fruit firmness, and had a higher sensory quality, phenolic content, carotenoid content, soluble solids content, sugar content, ascorbic acid and antioxidant activity than the control. Furthermore, the activities of the cell wall degrading enzymes polygalacturonase, polyphenol oxidase, pectin methyl esterase and catalase were lower, while the activities of superoxide dismutase and peroxidase enzymes were higher in the treated fruit. Therefore, treatment with 100 μM sodium nitroprusside shows high potential for improving the storage life and maintaining the quality attributes of ber fruit for up to 21 days under cold storage.

Pectin-based encapsulation systems for the protection of beneficial bacterial species and impact on intestinal barrier function in vitro

Pectin is a complex polysaccharide important to the pharmaceutical and food industry, and due to its versatility, cheapness, and notable health benefits, it is proposed to be investigated as an encapsulation material to protect sensitive food components such as living bacteria during their passage through the gastrointestinal tract. The main objective of this study was to evaluate both, the ability of pectin-based beads to maintain the viability and functionality of L. plantarum WCFS1 and the protective effect on intestinal epithelial barrier disruption in vitro. Pectin isolated from lemon with two degrees of methylation (DM18 and DM88) was used to form microbeads with either alginate or chitosan, producing four bead types, which were alginate/pectin DM18 (AlgDM18), alginate/pectin DM88 (AlgDM88), chitosan/pectin DM18 (ChitoDM18), and chitosan/pectin DM88 (ChitoDM88).The beads were loaded with L. plantarum, and it was demonstrated that all pectin-based beads could preserve the viability of L. plantarum after encapsulation. While some differences in metabolism was observed, the alginate-pectin beads exhibited higher activity and loading capacity. Then these beads were tested on intestinal epithelial cells to assess their protective impact in the presence of a barrier disruptor A23187. The effect on gut barrier function demonstrates that the composition of the microbeads significantly affected their protective effects. Empty ChitoDM88 beads demonstrated protective effects by delaying barrier disruption and modulating the release of gut epithelial cell-specific cytokines. They increased the production of CCL20 while reducing levels of IL-8 and IL-13, which are markers of inflammation.L. plantarum WCFS1-loaded Chitosan DM88-pectin microbeads provided the strongest protection. These beads not only delayed disruption of the gut epithelial barrier but also increased epithelial barrier function before and after treatment of the monolayer with the A23187 disruptor. Additionally, the loaded ChitoDM88 beads upregulated key genes associated with the tight junction integrity of the intestinal epithelium, including ZO-1, Occludin, and Claudin-1, further supporting their protective role. The immune response was also modulated by the loaded ChitoDM88 beads, as they increased CCL20 production and reduced IL-8 levels, highlighting a bead-type-dependent impact on epithelial immune signaling.This study demonstrates that pectin-based microbeads can preserve the viability and functionality of encapsulated L. plantarum, protecting against gut barrier impairment. The results highlight pectin's potential as a promising polymer for probiotic delivery, with encapsulation effectiveness depending on the pectin's methylation degree and the stabilizing agent used.

Effect of magnetic field treatment on the softening of green chilies (Capsicum annuum L.) during storage

In this study, effects of magnetic field treatment on the softening of green chilies during storage (0–30 d at 10 °C) were investigated, and the cell wall polysaccharide content, modifying enzyme activities, water distribution, and cell wall structure were determined. After 30 d of storage, the weight loss of the green chilies in conventional refrigeration (CR) group reached 35.40 %, whereas it was 20.96 % and 29.85 % in the static (SMF; 4 mT) and alternating magnetic field (AMF; 4 mT, 1 Hz) groups, respectively. Furthermore, magnetic field treatment maintained low levels of water-soluble pectin (WSP) and high levels of chelate-soluble pectin (CSP) and sodium carbonate-soluble pectin (NSP) in the green chilies. The degree of methylation (DE) values of WSP and NSP in the pre-treated samples were 0.37 and 0.18, respectively. Conversely, at the end of storage, the DE values of WSP and NSP in the CR, SMF, and AMF groups decreased to 0.12 and 0.05, 0.25 and 0.11, and 0.18 and 0.07, respectively, suggesting that magnetic field treatment had a negative influence on the demethylation of pectin. Magnetic field treatment also decreased the activities of pectin methyl esterase, polygalacturonase, and β-galactosidase in the green chilies, maintaining them at a low level. The magnetic field treatment resulted in a higher free water content in green chilies compared to the CR, exceeding the CR group’s content by 1.79 % and reaching 88.18 % at the terminal storage. Scanning electron microscopy results revealed that magnetic field treatment maintained the structural integrity of the cell wall in the green chilies. The results of this study confirmed the applicability of magnetic field treatment in maintaining the firmness and reducing the weight loss of the green chilies, thus prolonging their shelf life.

GhPME36 aggravates susceptibility to Liriomyza sativae by affecting cell wall biosynthesis in cotton leaves

BackgroundCotton is an important economic crop and a host of Liriomyza sativae. Pectin methylesterase (PME)-mediated pectin metabolism plays an indispensable role in multiple biological processes in planta. However, the pleiotropic functions of PME often lead to unpredictable effects on crop resistance to pests. Additionally, whether and how PME affects susceptibility to Liriomyza sativae remain unclear.ResultsHere, we isolated GhPME36, which is located in the cell wall, from upland cotton (Gossypium hirsutum L.). Interestingly, the overexpression of GhPME36 in cotton caused severe susceptibility to Liriomyza sativae but increased leaf biomass in Arabidopsis. Cytological observations revealed that the cell wall was thinner with more demethylesterified pectins in GhPME36-OE cotton leaves than in WT leaves, whereas the soluble sugar content of GhPME36-OE cotton leaf cell walls was accordingly higher; both factors attracted Liriomyza sativae to feed on GhPME36-OE cotton leaves. Metabolomic analysis demonstrated that glucose was significantly differentially accumulated. Transcriptomic analysis further revealed DEGs enriched in glucose metabolic pathways when GhPME36 was overexpressed, suggesting that GhPME36 aggravates susceptibility to Liriomyza sativae by affecting both the structure and components of cell wall biosynthesis. Moreover, GhPME36 interacts with another pectin-modifying enzyme, GhC/VIF1, to maintain the dynamic stability of pectin methyl esterification.ConclusionsTaken together, our results reveal the cytological and molecular mechanisms by which GhPME36 aggravates susceptibility to Liriomyza sativae. This study broadens the knowledge of PME function and provides new insights into plant resistance to pests and the safety of genetically modified plants.

Chemical structure, morphology, and physicochemical properties of highly methylated pectin functionalized by amidation in homogeneous and heterogeneous medium

Chemical structure, morphology, and physicochemical properties of highly methylated pectin functionalized by amidation in homogeneous and heterogeneous medium

Preharvest methyl jasmonate application delays cell wall degradation and upregulates phenolic metabolism and antioxidant activities in cold stored raspberries

The effects of preharvest methyl jasmonate (MeJA) spray application on the physicochemical quality, metabolism of phenolics, and cell wall components in raspberries were investigated during a 10-day cold storage period. MeJA spray reduced firmness loss, decay incidence, and weight loss, while maintained higher levels of soluble solids content, ascorbic acid, anthocyanins and flavonoids in raspberries. Furthermore, MeJA application resulted in increased total pectin and protopectin levels, as well as lowered water-soluble pectin, and activities of pectin methyl esterase, polygalacturonase and cellulase enzymes. Additionally, MeJA treatment upregulated the phenylpropanoid pathway, leading to higher endogenous phenolics and activities of phenylalanine-ammonia lyase and shikimate dehydrogenase. In conclusion, preharvest MeJA spray application could be adopted to enhance the storage potential of cold-stored raspberries for 10 days by maintaining higher firmness, assuring better physicochemical quality, and increasing phenolic metabolism, while reducing cell wall hydrolysis.

Fabrication of hydrogen-bonded crosslinked hydrogel vitrimer with enhanced self-healing and printability via K+ induced low methyl apple pectin

Low methyl pectin, conventionally extruded as sols and shaped through Ca2+ post-curing, face complexity and high production costs, limiting their application in 3D printing. We developed apple pectin (AP) vitrimer inks with shear-thinning behavior at elevated temperatures and self-supporting properties at low ones, via pectin methyl esterase (PME) modification and K+ induction, aiming to facilitate simpler extrusion 3D printing. PME-modified AP (PME-AP) exhibits a higher affinity for K+ compared to AP, attributed to an 8.76 % reduction in the degree of methyl esterification and a 9.72 % increase in the degree of blockiness. Consequently, 1 % PME-AP forms a robust hydrogel vitrimer characterized by a hardness of 121.33 g and a water holding capacity of 99.50 % at 150 mM K+, a 68 % reduction in K+ concentration requirement over AP gels. Through electrostatic shielding, K+ induces hydrogen-bonded crosslinked vitrimers with stress relaxation within 53 s at 80 °C and self-healing properties with minimal texture reduction (~2 g). These characteristics suggest that the hydrogen bond crosslinked vitrimer network can dynamically reorganize in response to temperature variations, making PME-AP gel ideal for 3D printing applications. This study establishes the groundwork for cost-efficient AP-based extrusion 3D printing.

Cloning, Expression and Enzymatic Characterization of Pectin Methyl Esterase from Populus trichocarpa and Its Application

Cloning, Expression and Enzymatic Characterization of Pectin Methyl Esterase from Populus trichocarpa and Its Application

The influence of the pectin structure on the properties of hydrogel dressings doped with octenidine-containing antiseptic

This article presents a method for producing hydrogel dressings using high methylated pectin from apples or citrus, doped with the antiseptic agent, octenidine dihydrochloride. Octenidine was incorporated in-situ during the polymer crosslinking. The pectins were characterized by their varying molecular weight characteristics, monosaccharide composition, and degree of esterification (DE). The study assessed the feasibility of producing biologically active hydrogels with pectin and delved into how the polymer's characteristics affect the properties of the resulting dressings. The structure evaluation of hydrogel materials showed interactions between individual components of the system and their dependence on the type of used pectin. Both the antimicrobial properties and cytotoxicity of the dressings were evaluated. The results suggest that the primary determinants of the functional attributes of the hydrogels are the molecular weight characteristics and the DE of the pectin. As these values rise, there is an increase in polymer-polymer interactions, overshadowing polymer-additive interactions. This intensification strengthens the mechanical and thermal stability of the hydrogels and enhances the release of active components into the surrounding environment. Biological evaluations demonstrated the ability of octenidine to be released from the dressings and effectively inhibit the growth of microbial pathogens.

Cinnamic acid derivatives played a major role in the resistance of peach leaves to Xanthomonas arboricola pv. pruni infection

AbstractPeach bacterial shot hole is a common global disease of peach trees caused by the pathogen Xanthomonas arboricola pv. pruni (Xap). To preliminarily explore the resistance mechanism of peach bacterial shot hole, leaves of the resistant variety ‘Yanbao’ and the susceptible variety ‘Frederic’ were used as test materials. The contents of total phenols, total flavonoids and lignin were analysed after 1 day of inoculation treatment, and the activities of defence enzymes and cell wall degradation enzymes in the leaves were determined. Furthermore, the resistant substances were screened by combining broad‐target metabolomics technology and in vitro antibacterial activity. The results showed that the contents of total phenols, total flavonoids and lignin in peach leaves were related to resistance. The resistant varieties resisted infection by inhibiting the activities of polygalacturonase (PG) and pectin methyl trans‐eliminase (PMTE) produced by Xap in peach leaves and increasing the activities of 4‐coumarate:coenzyme A ligase (4CL), cinnamic acid‐4‐hydroxylase (C4H), phenylalanine ammonia lyase (PAL) and peroxidase (POD). A total of six resistant compounds were screened from 85 differential metabolites. The minimum inhibitory concentrations of methyl ferulate (MF), p‐coumaric acid (p‐CA) and methyl caffeate (MC) on Xap were 0.0625, 00625 and 0.125 mg/mL, respectively, while that of the positive control drug oxytetracycline (OTC) was 0.125 mg/mL. The antibacterial activities of MF and p‐CA were better than that of OTC, and MF was equivalent to OTC. In addition, homoeriodictyol, hesperetin and fraxin have certain antibacterial effects. Before inoculation treatment, the contents of MF, p‐CA and MC in ‘Yanbao’ were 1.13, 1.24 and 1.96 times higher than those in ‘Frederic’, respectively, while they were 1.29, 1.80 and 1.94 times after inoculation treatment, respectively. During the process of pathogen infection, MF and p‐CA in the leaves of resistant peach varieties played a role in inducing resistance, while MC was a component of resistance. The above three cinnamic acid derivatives play an important roles in the resistance of peach bacterial shot hole and are potential control drugs.

Analysis of spatiotemporal changes mechanism of cell wall biopolymers and monosaccharide components in kiwifruit during Botryosphaeria dothidea infection

To further reveal the interaction mechanism between plants and pathogens, this study used confocal Raman microscopy spectroscopy (CRM) combined with chemometrics to visualize the biopolymers distribution of kiwifruit cell walls at different infection stages at the cellular micro level. Simultaneously, the changes in the content of various monosaccharides in fruit were studied at the molecular level using high-performance liquid chromatography (HPLC). There were significant differences in the composition of various nutrient components in the cell wall structure of kiwifruit at different infection times after infection by Botryosphaeria dothidea. PCA could cluster samples with infection time of 0–9 d into different infection stages, and SVM was used to predict the PCA classification results, the accuracy >96 %. Multivariate curve resolution-alternating least squares (MCR-ALS) helped to identify single substance spectra and concentration signals from mixed spectral signals. The pure substance chemical imaging maps of low methylated pectin (LMP), high methylated pectin (HMP), cellulose, hemicellulose, and lignin were obtained by analyzing the resolved concentration data. The imaging results showed that the lignin content in the kiwifruit cell wall increased significantly to resist pathogens infection after the infection of B. dothidea. With the development of infection, B. dothidea decomposed various substances in the host cell walls, allowing them to penetrate the interior of fruit cells. This caused significant changes in the form, structure, and distribution of various chemicals on the fruit cell walls in time and space. HPLC showed that glucose was the main carbon source and energy substance obtained by pathogens from kiwifruit during infection. The contents of galactose and arabinose, which maintained the structure and function of the fruit cell walls, decreased significantly and the cell wall structure was destroyed in the late stage of pathogens infection. This study provided a new perspective on the cellular structure changes caused by pathogenic infection of fruit and the defense response process of fruit and provided effective references for further research on the mechanisms of host-pathogen interactions in fruit infected by pathogens.

In Silico Determination of The Antifungal Effect of Plant Active Molecules Against Botrytis Cinerea by Molecular Docking

Botrytis cinerea, which has developed many strategies to infect plants, can survive in harsh environmental conditions, and has a wide host range, has become an important problem both economically and ecologically by causing tons of crop losses for many years. The residues in soil and crops caused by chemical pesticides used to get rid of agricultural pests pose serious threats to human and environmental health, such as hormonal abnormalities and acute respiratory poisoning, especially in children. The most critical step to avoid these hazards will be to replace chemical pesticides with plant-active molecules. At the same time, these studies primarily in silico will provide a return in terms of both time and cost. Inhibition of pectin methyl esterase, an important virulence factor of B. cinerea, will ensure the organism is controlled. In order to determine candidate biofungicide effector molecules, QSAR parameter values of 409 plant active molecules were calculated. Firstly, conformer distribution and geometry optimizations were performed with Spartan 14’ software. Docking studies of the optimized molecules were carried out through Autodock Vina software, while visualization studies to make sense of the interactions between the target receptor structure and effector molecules were used by BIOVIA Discovery Studio software. As a result of all the analyses, the molecules that are alternatives to chemical pesticides as biofungicides were determined to be the following molecules: Podolactone B, Repin, Sandaracopimaradienediol, 6-Hydrogenistein, Artemisinin, Lycoricidine, 6-Methoxygossypol, Viscidulin, Ciprofloxacin, and 7,4’-Dihydroxyflavan.

Space electric field impacts on softening and cell wall modification of strawberry during cold storage

As an emerging non-contact cold chain preservation technology, the impact of the DENBA+ on plant cell wall metabolism and its mechanism of inhibiting softening have not been addressed. In this study, strawberries were used as an experimental model to investigate the effect of space electric field storage on cell wall metabolism. Compared with the control, 500 V DENBA+ treatment was able to reduce the firmness loss of strawberries by 18.3 % on 18 d. Additionally, the DENBA+ exhibited a pronounced ability to suppress fruit softening enzyme (FaPG1 and FaβGal4) expression, delay the rise in polygalacturonates (PG), pectin methyl esterase (PME), cellulase (Cx), and β-galactosidase (β-Gal) activities, postpone the decline in cell wall matrix (CWM), insoluble solid pectin (ISP), and colloidal soluble pectin (CSP) content along with hemicellulose and cellulose levels while attenuating water-soluble pectin (WSP) accumulation during cold storage period. These findings contribute to the maintenance of fruit cell wall structural integrity with the aim of sustaining strawberry firmness and retarding the progression of aging.

Unravelling physiological and histochemical changes in two popular dessert and cooking bananas of India during fruit ripening

The physicochemical and histochemical characteristics of two consumingly divergent commercial varieties of Musaceae (Musa cv. Kanthali and Musa cv. Kacha Kela) were investigated during their postharvest ripening. The fruit peels from both cultivars were characterised by a reduction in chlorophyll contents, loosening of cortical tissues, and shrinkage of parenchymatous cells. The pulp-to-peel ratio, total soluble sugars, reducing sugar, fruit firmness, electrolyte leakage, and respiration rate were investigated along with activities of a few enzymes involved in fruit softening, namely cellulase, xylanase, invertase and glucanase. Additionally, semi-quantitative gene expression analyses with a few ripening-related genes, including ethylene biosynthesis (MaACS and MaACO), carbohydrate metabolism viz. sucrose synthase (MaSUS), sucrose phosphate synthase (MaSPS), glucanase (MaGLU), invertase (MaINV) and pectin methyl esterase (MaPME) were also carried out along with chitinase (MaCHT) in both cultivars during postharvest ripening. A faster postharvest ripening of ‘Kanthali’ than ‘Kacha Kela’ was evidenced as an outcome of the above studies.The peel histology and surface ultrastructure were examined through light microscopy and scanning electron microscopy (SEM), respectively. In light microscopy, substantial variations were noted between the cultivars, especially on peel-tissue degradation and accumulation of metabolites. The surface ultrastructure revealed temporal variations in the peel stomatal opening along with gradual depletion of surface wax. Such temporal opening of stomata was found to coincide with our earlier recorded postharvest volatiles emission patterns of respective cultivars suggesting it to be a legible vent for aroma emission.

Dicyclohexylcarbodiimide and disodium succinate regulate the pulp softening and breakdown in fresh longan by modulating the metabolism of cell wall polysaccharides

Cell wall polysaccharides (CWP) are an important component of cell structure, and its content variation is a primary factor affecting the texture of fresh longan. The influences of dicyclohexylcarbodiimide (DCC) and disodium succinate (DS) treatments on the pulp softening and pulp breakdown, and their relation to CWP metabolism in pulp of longan fruit were explored. Compared with the control longan, DCC-treated fruit showed lower value of pulp firmness, higher index of pulp breakdown, higher expression levels of cell wall disassembly enzymes (CWDEs)-related genes (DlPME1, DlPME3, DlPG1, Dlβ-Gal1, Dlβ-Gal16, DlCx7, DlXET3, DlXET27), and higher activities of CWDEs including pectin methyl esterase (PME), polygalacturonase (PG), β-galactosidase (β-Gal), cellulase (Cx), xyloglucan endotransglycosylase (XET), lower values of cell wall materials, and lower levels of CWP including ionic-soluble pectin, covalent-soluble pectin, cellulose, and hemicellulose. Whereas, the opposite effects were exhibited in DS-treated fruit. The above data indicate that DCC-hastened longan pulp softening and pulp breakdown was due to the up-regulating expressions of CWDEs-related genes, the activating activities of CWDEs, and the accelerating CWP disassembly by DCC treatment. Whereas, DS repressed longan pulp softening and pulp breakdown through down-regulating the expressions of CWDEs-related genes, inhibiting CWDEs activities, and reducing CWP degradation.