Activity Of Cell Wall Hydrolases Research Articles

Comparison of Fruit Texture and Storage Quality of Four Apple Varieties.

Fruit texture and storage properties of various apple varieties exhibit significant variation. The rate of fruit softening post-harvest plays a crucial role in determining fruit quality and shelf life. This research utilized four apple varieties as test subjects to investigate the internal factors influencing fruit texture changes among different varieties. By monitoring changes in relevant physiological indicators during the post-harvest texture softening process, the study examined fruit quality, cell wall material content, hydrolase activity, and gene transcription levels during storage of 'Orin', 'RX', 'RXH', and 'Envy' apples. Initial fruit softening was primarily linked to heightened post-harvest fruit respiration intensity, ethylene production, and rapid amylase activity. Subsequent softening was associated with increased activity of water-soluble pectin (WSP), cellulose (CEL), and other hydrolases. With the extension of the storage period, the fruit cells of the four varieties became more loosely arranged, resulting in larger intercellular gaps. Variations in WSP and cellulose content, CEL activity, and relative expression of Mdβ-gal were observed among the different apple varieties, potentially accounting for the disparities in fruit texture.

Isolation and Characterization of a Novel Virulent Phage ASG01 of Aeromonas salmonicida and Its Cell Wall Hydrolase Activity.

Aeromonas salmonicida is an important pathogen that causes furunculosis in trout and salmon with high morbidity and mortality, resulting in significant economic losses in aquaculture. Overuse of antibiotics has led to the continuous emergence of drug-resistant strains. Hence, there is an urgent need to find an alternative environmentally friendly antimicrobial agent. In this study, we isolated a virulent phage of A. salmonicida, named ASG01, which belongs to the Myoviridae family and maintains lytic activity at a pH value range from 4 to 12 and in the temperature range from 30 °C to 60 °C. The whole genomic sequence of ASG01 showed 82% similarity to Aeromonas phage pAh6-C. The cell wall hydrolase (Cwh)-encoding gene from the genome of ASG01 was predicted and heterologously expressed. Notably, in the absence of additional phage genes, endogenous expression of Cwh could lyse E. coli cells and greatly inhibit the growth of tested fish pathogenic bacteria. The lytic activity of Cwh was eliminated when the predicted active site was mutated. These results indicate that Cwh of ASG01 possessed excellent lytic activity and a wide antibacterial spectrum, suggesting its potential as an effective enzybiotic.

Pesticin-Like Effector VgrG3cp Targeting Peptidoglycan Delivered by the Type VI Secretion System Contributes to Vibrio cholerae Interbacterial Competition.

Vibrio cholerae can utilize a type VI secretion system (T6SS) to increase its intra- and interspecies competition. However, much still remains to be understood about the underlying mechanism of this intraspecies competition. In this study, we isolated an environmental V. cholerae strain E1 that lacked the typical virulence factors toxin-coregulated pilus and cholera toxin and that encoded a functional T6SS. We identified an evolved VgrG3 variant with a predicted C-terminal pesticin-like domain in V. cholerae E1, designated VgrG3cp. Using heterologous expression, protein secretion, and peptidoglycan-degrading assays, we demonstrated that VgrG3cp is a T6SS-dependent effector harboring cell wall muramidase activity and that its toxicity can be neutralized by cognate immunity protein TsiV3cp. Site-directed mutagenesis proved that the aspartic acid residue at position 867 is crucial for VgrG3cp-mediated antibacterial activity. Bioinformatic analysis showed that genes encoding VgrG3cp-like homologs are distributed in Vibrio species, are linked with T6SS structural genes and auxiliary genes, and the vgrG3cp-tsiV3cp gene pair of V. cholerae probably evolved from Vibrio anguillarum and Vibrio fluvialis via homologous recombination. Through a time-lapse microscopy assay, we directly determined that cells accumulating VgrG3cp disrupted bacterial division, while the cells continued to increase in size until the loss of membrane potential and cell wall breakage and finally burst. The results of the competitive killing assay showed that VgrG3cp contributes to V. cholerae interspecies competition. Collectively, our study revealed a novel T6SS E-I pair representing a new T6SS toxin family which allows V. cholerae to gain dominance within polymicrobial communities by T6SS. IMPORTANCE The type VI secretion system used by a broad range of Gram-negative bacteria delivers toxic proteins to target adjacent eukaryotic and prokaryotic cells. Diversification of effector proteins determines the complex bacterium-bacterium interactions and impacts the health of hosts and environmental ecosystems in which bacteria reside. This work uncovered an evolved valine-glycine repeat protein G3, carrying a C-terminal pesticin-like domain (VgrG3cp), which has been suggested to harbor cell wall hydrolase activity and is able to affect cell division and the integrity of cell wall structure. Pesticin-like homologs constitute a family of T6SS-associated effectors targeting bacterial peptidoglycan which are distributed in Vibrio species, and genetic loci of them are linked with T6SS structural genes and auxiliary genes. T6SS-delivered VgrG3cp mediated broad-spectrum antibacterial activity for several microorganisms tested, indicating that VgrG3cp-mediated antimicrobial activity is capable of conferring bacteria a competitive advantage over competitors in the same niches.

Dynamic Changes in Cell Wall Polysaccharides during Fruit Development and Ripening of Two Contrasting Loquat Cultivars and Associated Molecular Mechanisms.

Loquats have drawn much attention due to their essential nutrients and unusual phenology, which fills a market gap in early spring. Fruit firmness (FF) is one of the most important quality attributes. Dynamic changes in FF, cell wall (CW) polysaccharides, CW hydrolase activity, and expression of CW metabolism-related genes during the fruit development and ripening stages of two contrasting loquat cultivars were compared. Although the two cultivars possessed similar FF at the initial fruitlet stage, Dawuxing was significantly firmer than Ninghaibai at all subsequent time points. FF was positively correlated with the contents of covalent-soluble pectin and hemicellulose, activity of peroxidase, and gene expressions of PME, EG, CAD6, and POD; and negatively correlated with the contents of water-soluble pectin, activities of polygalacturonase, endo-glucanase, cellobiohydrolase, and xylanase, and gene expressions of PG, EG2, PAL1, PAL3, and CAD5. Identifying molecular mechanisms underlying the differences in FF is useful for fundamental research and crop improvement in future.

Nitric oxide alleviates chilling injury by regulating the metabolism of lipid and cell wall in cold-storage peach fruit

Peach fruit are prone to development of chilling injury during cold storage at around 0–7 °C. Nitric oxide (NO) has been proven to alleviate chilling injury, but the mechanism was still unclear. In this study, peach fruit were immersed in a NO donor (sodium nitroprusside, SNP) solution for 10 min, then stored at 0 °C. The SNP alleviated chilling injury, including decreasing the internal browning index, malondialdehyde content, electrolyte leakage, and lipoxygenase activity, and maintaining firmness. Furthermore, SNP maintenance of fruit firmness was associated with reduction of xyloglucan endotransglycosylase/hydrolase family member gene expression and decrease of cell wall hydrolase activity, especially the activities of polygalacturonase, xyloglucan endoglycosyl transferase, cellulase, and β-galactosidase. Meanwhile, SNP regulated the lipid metabolism by up-regulating the expression of genes encoding glycerol-3-phosphate acyltransferase, ketoacy-ACP synthase, phosphatidylinositol bisphosphate and long-chain acyl-CoA. Thus, the results of this study indicate that SNP alleviates chilling injury of post-harvest peach fruit by regulating cell wall and lipid metabolism.

Effects of 1-Methylcyclopropene Treatment on Fruit Quality during Cold Storage in Apple Cultivars Grown in Korea

The effect of 1-methylcyclopropene (1-MCP) treatment on improving the storability of four apple cultivars (‘Hwangok’, ‘Picnic’, ‘Gamhong’, and ‘Fuji’) was investigated by analyzing the physiological and biochemical factors associated with their postharvest quality attributes. The flesh firmness, titratable acidity, and soluble solids content of the cultivars were higher in treated fruits than untreated fruits, while the opposite results were observed for ethylene production. In the treated fruits, the traits affected by 1-MCP varied depending on the cultivars used. Higher firmness and lower ethylene production were observed in the ‘Hwangok’ and ‘Picnic’ than ‘Gamhong’ and ‘Fuji’ cultivars. However, 1-MCP only affected weight loss in the ‘Gamhong’ cultivar, while the sugar content was affected in all of the cultivars except ‘Hwangok’. When analyzing cell wall hydrolase activities, 1-MCP differently affected the activities (β-galactosidase, α-galactosidase, β-glucosidase, α-mannosidase, β-xylosidase, and β-arabinosidase), with greater effects in the ‘Fuji’ and ‘Picnic’ cultivars and moderate effects in the ‘Gamhong’ and ‘Hwangok’ cultivars. In this study, the suppression of ethylene production by 1-MCP was positively associated with a transcriptional decrease in the ethylene biosynthesis genes MdACS1 and MdACO1. Overall, this study suggests that 1-MCP distinctly enhanced the storability of all apple cultivars, with a greater effect on ‘Hwangok’.

Diversification of LytM Protein Functions in Polar Elongation and Cell Division of Agrobacterium tumefaciens.

LytM-domain containing proteins are LAS peptidases (lysostaphin-type enzymes, D-Ala-D-Ala metallopeptidases, and sonic hedgehog) and are known to play diverse roles throughout the bacterial cell cycle through direct or indirect hydrolysis of the bacterial cell wall. A subset of the LytM factors are catalytically inactive but regulate the activity of other cell wall hydrolases and are classically described as cell separation factors NlpD and EnvC. Here, we explore the function of four LytM factors in the alphaproteobacterial plant pathogen Agrobacterium tumefaciens. An LmdC ortholog (Atu1832) and a MepM ortholog (Atu4178) are predicted to be catalytically active. While Atu1832 does not have an obvious function in cell growth or division, Atu4178 is essential for polar growth and likely functions as a space-making endopeptidase that cleaves amide bonds in the peptidoglycan cell wall during elongation. The remaining LytM factors are degenerate EnvC and NlpD orthologs. Absence of these proteins results in striking phenotypes indicative of misregulation of cell division and growth pole establishment. The deletion of an amidase, AmiC, closely phenocopies the deletion of envC suggesting that EnvC might regulate AmiC activity. The NlpD ortholog DipM is unprecedently essential for viability and depletion results in the misregulation of early stages of cell division, contrasting with the canonical view of DipM as a cell separation factor. Finally, we make the surprising observation that absence of AmiC relieves the toxicity induced by dipM overexpression. Together, these results suggest EnvC and DipM may function as regulatory hubs with multiple partners to promote proper cell division and establishment of polarity.

The pH Signaling Transcription Factor PAC-3 Regulates Metabolic and Developmental Processes in Pathogenic Fungi.

The zinc finger transcription factor PAC-3/RIM101/PacC has a defined role in the secretion of enzymes and proteins in response to ambient pH, and also contributes to the virulence of species. Herein we evaluated the role of PAC-3 in the regulation of Neurospora crassa genes, in a model that examined the plant-fungi interactions. N. crassa is a model fungal species capable of exhibiting dynamic responses to its environment by employing endophytic or phytopathogenic behavior according to a given circumstance. Since plant growth and productivity are highly affected by pH and phosphorus (P) acquisition, we sought to verify the impact that induction of a Δpac-3 mutation would have under limited and sufficient Pi availability, while ensuring that the targeted physiological adjustments mimicked ambient pH and nutritional conditions required for efficient fungal growth and development. Our results suggest direct regulatory functions for PAC-3 in cell wall biosynthesis, homeostasis, oxidation-reduction processes, hydrolase activity, transmembrane transport, and modulation of genes associated with fungal virulence. Pi-dependent modulation was observed mainly in genes encoding for transporter proteins or related to cell wall development, thereby advancing the current understanding regarding colonization and adaptation processes in response to challenging environments. We have also provided comprehensive evidence that suggests a role for PAC-3 as a global regulator in plant pathogenic fungi, thus presenting results that have the potential to be applied to various types of microbes, with diverse survival mechanisms.

Cell wall hydrolases act in concert during aerenchyma development in sugarcane roots.

Cell wall disassembly occurs naturally in plants by the action of several glycosyl-hydrolases during different developmental processes such as lysigenous and constitutive aerenchyma formation in sugarcane roots. Wall degradation has been reported in aerenchyma development in different species, but little is known about the action of glycosyl-hydrolases in this process. In this work, gene expression, protein levels and enzymatic activity of cell wall hydrolases were assessed. Since aerenchyma formation is constitutive in sugarcane roots, they were assessed in segments corresponding to the first 5 cm from the root tip where aerenchyma develops. Our results indicate that the wall degradation starts with a partial attack on pectins (by acetyl esterases, endopolygalacturonases, β-galactosidases and α-arabinofuranosidases) followed by the action of β-glucan-/callose-hydrolysing enzymes. At the same time, there are modifications in arabinoxylan (by α-arabinofuranosidases), xyloglucan (by XTH), xyloglucan-cellulose interactions (by expansins) and partial hydrolysis of cellulose. Saccharification revealed that access to the cell wall varies among segments, consistent with an increase in recalcitrance and composite formation during aerenchyma development. Our findings corroborate the hypothesis that hydrolases are synchronically synthesized, leading to cell wall modifications that are modulated by the fine structure of cell wall polymers during aerenchyma formation in the cortex of sugarcane roots.

A switch in surface polymer biogenesis triggers growth-phase-dependent and antibiotic-induced bacteriolysis.

Penicillin and related antibiotics disrupt cell wall synthesis to induce bacteriolysis. Lysis in response to these drugs requires the activity of cell wall hydrolases called autolysins, but how penicillins misactivate these deadly enzymes has long remained unclear. Here, we show that alterations in surface polymers called teichoic acids (TAs) play a key role in penicillin-induced lysis of the Gram-positive pathogen Streptococcus pneumoniae (Sp). We find that during exponential growth, Sp cells primarily produce lipid-anchored TAs called lipoteichoic acids (LTAs) that bind and sequester the major autolysin LytA. However, penicillin-treatment or prolonged stationary phase growth triggers the degradation of a key LTA synthase, causing a switch to the production of wall-anchored TAs (WTAs). This change allows LytA to associate with and degrade its cell wall substrate, thus promoting osmotic lysis. Similar changes in surface polymer assembly may underlie the mechanism of antibiotic- and/or growth phase-induced lysis for other important Gram-positive pathogens.

The Starch Is (Not) Just Another Brick in the Wall: The Primary Metabolism of Sugars During Banana Ripening.

The monocot banana fruit is one of the most important crops worldwide. As a typical climacteric fruit, the harvest of commercial bananas usually occurs when the fruit is physiologically mature but unripe. The universal treatment of green bananas with ethylene or ethylene-releasing compounds in order to accelerate and standardize the ripening of a bunch of bananas mimics natural maturation after increasing the exogenous production of ethylene. The trigger of autocatalytic ethylene production regulated by a dual positive feedback loop circuit derived from a NAC gene and three MADS genes results in metabolic processes that induce changes in the primary metabolism of bananas. These changes include pulp softening and sweetening which are sensorial attributes that determine banana postharvest quality. During fruit development, bananas accumulate large amounts of starch (between 15 and 35% w/w of their fresh weight, depending on the cultivar). Pulp softening and sweetening during banana ripening are attributed not only to changes in the activities of cell wall hydrolases but also to starch-to-sugar metabolism. Therefore, starch granule erosion and disassembling are key events that lead bananas to reach their optimal postharvest quality. The knowledge of the mechanisms that regulate sugar primary metabolism during banana ripening is fundamental to reduce postharvest losses and improve final product quality, though. Recent studies have shown that ethylene-mediated regulation of starch-degrading enzymes at transcriptional and translational levels is crucial for sugar metabolism in banana ripening. Furthermore, the crosstalk between ethylene and other hormones including indole-3-acetic acid and abscisic acid also influences primary sugar metabolism. In this review, we will describe the state-of-the-art sugar primary metabolism in bananas and discuss the recent findings that shed light on the understanding of the molecular mechanisms involved in the regulation of this metabolism during fruit ripening.

Changes in pericarp morphology, physiology and cell wall composition account for flesh firmness during the ripening of blackberry (Rubus spp.) fruit

Fruit flesh firmness plays a critical role in controlling blackberry (Rubus spp.) postharvest shelf life. This work aimed to identify the underlying characteristics in pericarp morphology, cell wall hydrolase activity and cell wall composition that account for flesh firmness in soft-fruited ‘Boysen’ and firm-fruited ‘Arapaho’ cultivars that have a similar ripening time of 39 days after flowering (DAF). The fruit firmness of both fruits decreased noticeably at the onset of color change, and this decrease hastened from 33 DAF to ripening despite considerable differences in their temporal changes. The evaluation of pericarp cellular morphology revealed that the disassembly of the cell wall in both fruits was likely initiated at 33 DAF, followed by extreme degradation at 39 DAF. Cell wall hydrolase activity assays indicated that increases in polygalacturonase (PG) and cellulase activity also dramatically occurred in the late softening stages of both fruits. Notably, appreciably higher levels of cellulase, and significant increases in pectin methylesterase (PME), α-L-arabinofuranosidase (α-L-Af) and xyloglucan endotransglycosylase (XET) were only detected in the late ripening stages of ‘Boysen’. In terms of cell wall components, the levels of cell wall material (CWM), cellulose and hemicellulose declined similarly during ripening in both fruits. Comparatively, lower levels of CWM, chelator soluble pectin (CSP), sodium carbonate soluble pectin (SSP), and hemicellulose as well as higher levels of water soluble pectin (WSP) were found in ‘Boysen’ than those in ‘Arapaho’ during maturation and ripening. Overall, the loss of fruit firmness during ripening in blackberry fruit is correlated closely with biochemical changes in cell wall fractions that involve hydrolytic processes, resulting in the breakdown of cell-wall polymers. The low firmness of ‘Boysen’, as determined by cell wall degradation, could be of particular relevance to the function of cell wall degrading enzymes and to the more drastic degradation of cell wall components than that in the firm cv. ‘Arapaho’.

Effect of packaging films on cell wall hydrolyzing enzymes in relation to shelf life enhancement of tomatoes stored under ambient conditions

The effect of packaging films on post-harvest life span of tomato in relation to their effect on the activities of potential cell wall hydrolyzing enzymes were investigated. Tomato cv. ‘Punjab Upma’ and ‘Punjab Ratta’ picked at pink stage were placed in open trays, high density polyethylene (HDPE)-, low density polyethylene (LDPE)- and polypropylene (PP)-bags and stored under ambient conditions till their edible state. Irrespective of the variety, there was enhancement in the activities of cell wall hydrolyzing enzymes i.e. polygalacturonase, pectin methylesterase, cellulase and β-galactosidase. Further, there was decrease in firmness with increase in storage period. However, less changes were noticed in tomatoes packaged in polythene bags in comparison to those kept in open trays. Tomato cv. ‘Punjab Ratta’ displayed slow increase in the activities of cell wall hydrolases and less decrease in firmness as compared to cv. ‘Punjab Upma’. In both the varieties, LDPE packaging showed slowest changes in enzymatic activities and firmness and were efficient in enhancing the shelf life of tomatoes.

Loss in photosynthesis during senescence is accompanied by an increase in the activity of β-galactosidase in leaves of Arabidopsis thaliana: modulation of the enzyme activity by water stress.

The precise nature of the developmental modulation of the activity of cell wall hydrolases that breakdown the wall polysaccharides to maintain cellular sugar homeostasis under sugar starvation environment still remains unclear. In this work, the activity of β-galactosidase (EC 3.2.1.23), a cell-wall-bound enzyme known to degrade the wall polysaccharides, has been demonstrated to remarkably enhance during senescence-induced loss in photosynthesis in Arabidopsis thaliana. The enhancement in the enzyme activity reaches a peak at the terminal phase of senescence when the rate of photosynthesis is at its minimum. Although the precise nature of chemistry of the interface between the decline in photosynthesis and enhancement in the activity of the enzyme could not be fully resolved, the enhancement in its activity in dark and its suppression in light or with exogenous sugars may indicate the involvement of loss of photosynthetic production of sugars as a key factor that initiates and stimulates the activity of the enzyme. The hydrolase possibly participates in the catabolic network of cell wall polysaccharides to produce sugars for execution of energy-dependant senescence program in the background of loss of photosynthesis. Drought stress experienced by the senescing leaves accelerates the decline in photosynthesis with further stimulation in the activity of the enzyme. The stress recovery of photosynthesis and suppression of the enzyme activity on withdrawal of stress support the proposition of photosynthetic modulation of the cell-wall-bound enzyme activity.

Increased hydrolase gene expression and hydrolase activity in the abscission zone involved in chilling-induced abscission of Dendrobium flowers

After 4days exposure to15°C and 5°C temperature, cut cv. Ear Sakul Dendrobium inflorescences were returned to 25°C.The exposure of open flowers and floral buds to 5°C induced more abscission than exposure to 15°C after transfer to 25°C. Ethylene production rates of floral buds and open flowers with and without 1-MCP treatment were comparatively low during exposure to to15°C and 5°C. Flower buds had a greater increase of ethylene production than open flowers after upon transfer to 25°C and flower buds stored at 5°C had a greater increase than that of flower buds stored at 15°C. 1-MCP treatment reduced significantly more ethylene production rates of floral buds stored at 5°C than those stored at 15°C compared with open flowers upon transfer to 25°C on the last 3days. The abscission zone (AZ) activities of pectin methylesterase (PME), polygalacturonase (PG), β-1,4 glucanase (cellulase, CEL) and β-galactosidase (β-GAL) increased after exposure to5°C, while β-GAL also increased after 15°C exposure. Treatment with 100nlL−1 1-MCP for 4h at 25°C, lower temperature exposure reduced abscission in both open flowers and floral buds. 1-MCP also prevented an increase in the activities of PME, PG, CEL and β-GAL in the AZ. Genes encoding a PME, a CEL, and a β-GAL were isolated from the AZ. In the absence of 1-MCP an early increase was found in the expression of the β-GAL and PME genes in the AZ, that was correlated with the abscission rates. An increase in the expression of the CEL gene was found later in abscission. 1-MCP prevented the increase in expression of the β-GAL, PME and CEL genes in the AZ. It was concluded that chilling-induced abscission was mediated by ethylene, that induced gene expression and increased the activity of cell wall hydrolases. The high correlation between abscission and gene expression of β-GAL and CEL suggests that they were involved relatively early and again in late stages of abscission. The role of PME and PG was less clear, but they were possibly involved in the abscission after the 5°C treatment.

The Influence of Hot Water and Calcium Chloride on the Changes in Cell Wall Composition and the Activities of Cell Wall Hydrolases during Storage inAgaricus bisporus

Mushrooms show significant losses in firmness due mainly to the changes in cell walls after harvest. This study was performed to determine the effects of CaCl2 and hot water dips on the changes in firmness, cell wall composition and hydrolase activities of mushrooms during storage. Mushrooms were treated with various concentrations of CaCl2 and hot water at various degrees and stored for 12 days at 10C. The results showed that the firmness of mushrooms decreased significantly and their cell walls have undergone significant changes during 12 days storage period after harvest. Polysaccharide content decreased significantly during storage. This decrease was mainly due to the decrease in the strong alkaline-soluble polysaccharides. Xyloglucanase and beta glucanase activities increased significantly during storage, possibly contributing significantly to the polysaccharide losses. CaCl2 and hot water treatments significantly reduced the changes in cell wall components and cell wall hydrolase activities. The results suggest that CaCl2 and hot water treatments could be used to reduce the changes in firmness and cell walls after harvest and extend the shelf life of mushroom. Practical Applications Mushrooms show rapid deterioration after harvest due mainly to changes in cell walls and have a very short shelf life. This significantly reduces their marketing period. The results demonstrate that both hot water and CaCl2 significantly delay cell wall degradation and prolong the shelf life of mushrooms. The results of the study have the potential to be used to decide on what treatments should be used to extend the shelf life and marketing period of mushrooms.

Chitosan coating with trans-cinnamaldehyde improves structural integrity and antioxidant metabolism of fresh-cut melon

This study evaluated a 2% chitosan-based coating with 500mgL−1trans-cinnamaldehyde on quality attributes, pro- and anti-oxidative metabolism, and structural integrity of biological membranes and cell wall of fresh-cut melon (Cucumis melo var. Cantalupensis Naud.) stored for 20 days at 4°C. Coating improved (P<0.05) samples’ firmness, colour, soluble solids, total vitamin C and carotenoid content for up to 15 days of storage, thereafter samples showed signs of decay with softening of processed melon resulting from structural changes in both biological membranes and cell walls. Coating also reduced hydrogen peroxide radical levels leading to lower antioxidant enzymatic activity and lipid peroxidation degree and electrolyte leakage levels compared with control. Coating improved produce visual quality due to reduction in the activity of browning-associated enzymes, G-POD and PPO. Results indicate that coating improved quality of fresh cut Cantaloupe melons by acting as a physical barrier to gas exchange decreasing respiration rate and consequently, O2-dependent processes, while trans-cinnamaldehyde acted as free radical scavenger and enzyme inhibitor. The lower respiration rate inhibited the establishment of an oxidative stress induced by fruit processing and senescence with less damage to biological membranes, lower cell wall hydrolase activities and loss of bioactive compounds.

Reduction in Hami melon (Cucumis melo var. saccharinus) softening caused by transport vibration by using hot water and shellac coating

The effects of transport vibration on Hami melon (Cucumis melo var. saccharinus) softening during storage (room temperature) were studied. Hot water (HW) and HW in combination with shellac coating (HW+shellac) were used to reduce melon softening caused by vibration. Changes in flesh firmness, hydrolase activities, cell wall constituents, cell membrane permeability and weight loss were monitored periodically in stored fruits for 28 days following vibration treatment. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) were used to assess the internal morphological characteristics, transverse relaxation times, and water distribution of Hami melons. The results revealed that vibration contributes to Hami melon softening during storage. Compared to HW treatment, HW+shellac was more effective in reducing melon softening by reducing cell wall hydrolase activity, cell membrane leakage, fruit weight loss, and loss of cell wall constituents. The results were confirmed by MRI and NMR.

Cell wall enzymes and changes in sugar content in pollinated orchids treated with ethylene inhibitors and sugars

The pollinated flowers of Dendrobium Pompadour orchids exhibited rapid morphological changes, which resulted in full flower closure. In contrast, unpollinated flowers remained fresh and turgid during the identical time period. The aim of this study was to examine the pollination-induced changes in the cell wall enzyme activity and sugar content. Cell wall hydrolase assays showed that pollination induces significant increases in polygalacturonase, pectate lyase and cellulase activity, whereas pectin methyl esterase showed insignificant changes in activity. Membrane leakage was rapid in pollinated flowers. The total and reducing sugar content increased in the pollinated flowers and was most profound in the column of the flowers. Treatment with ethylene inhibitors and sugars suppressed cell wall hydrolase activity and membrane leakage to a varying extent. The sugar content was more stable in the treated flowers. Altogether, the results show that ethylene inhibitors effectively delay pollination-induced floral destruction.

Effects of cold storage and 1-methylcyclopropene treatments on ripening and cell wall degrading in rabbiteye blueberry (Vaccinium ashei) fruit

The effect of postharvest 1-methylcyclopropene and/or cold storage application on texture quality parameters during storage was determined. The changes in fruit quality (including weight loss, firmness, total soluble solids content, and ethylene production), cell wall material (including water-soluble fraction, ethylenediaminetetraacetic acid-soluble fraction, Na2CO3-soluble fraction, 4% KOH-soluble fraction, and 14% KOH-soluble fraction), and cell wall hydrolase activities (including polygalacturonase, endo-1,4-beta-D-glucanase, pectinesterase, alpha-L-arabinofuranosidase, and beta-galactosidase) were periodically measured up to 25 days after postharvest treatments. The application of cold storage reduced weight loss, ethylene production, and delayed ripening of blueberry fruit. The inhibition of senescence was associated with suppressed increase in cell wall hydrolase activities and retarded solubilization of pectins and hemicelluloses. Furthermore, no obvious differences in firmness, weight loss, ethylene production, and cell wall hydrolase activities between fruits with or without 1-methylcyclopropene application were observed, while significant lower levels of the detected parameters were found in cold storage fruit compared with fruit stored in room temperature. Thus, cold storage can be viewed as an effective means to extend the shelf life of blueberry fruit.