Polygalacturonase Research Articles

ABA accelerates blackberry (Rubus spp.) fruit ripening by positively affecting ripening-related gene expression and metabolite profiles

BACKGROUND: The softness of blackberry fruits limits their postharvest shelf-life and commercial use, and abscisic acid (ABA) is considered one of the key hormones involved in fruit ripening. OBJECTIVE: This study aimed to explore the underlying physiological and molecular actions of ABA on blackberry fruit ripening and softening. METHODS: Various physiological indices of and plant hormone levels in treated and untreated blackberry fruits were determined simultaneously. The differentially expressed genes (DEGs) were analyzed by RNA-sequencing, and their expression profiles were detected. The ripening mechanism was elucidated by UHPLC-MS using two groups of fruits at 28 d. RESULTS: After 25 d, the ABA concentration and polygalacturonase (PG) and beta-1,4-endoglucanase (EG) activities in ABA-treated fruits were significantly higher than those in untreated fruits. Large differences in the expression profiles were detected at 28 d. The expression of DEGs related to cell wall softening and ABA synthesis was largely triggered after 25 or 28 d. Sixty-nine differentially accumulated metabolites were ultimately annotated as related to fruit ripening. CONCLUSIONS: ABA stimulates blackberry fruit ripening by promoting cell wall enzyme activities, the expression of various ripening-related genes and metabolite accumulation.

Polygalacturonase activity promotes aberrant cell separation in the quasimodo2 mutant of Arabidopsis thaliana

In plants, cell adhesion relies on balancing the integrity of the pectin-rich middle lamella with wall loosening during tissue expansion. Mutation of QUASIMODO2 (QUA2), a pectin methyltransferase, causes defective hypocotyl elongation and cell adhesion in Arabidopsis thaliana hypocotyls. However, the molecular function of QUA2 in cell adhesion is obscured by complex genetic and environmental interactions. To dissect the role of QUA2 in cell adhesion, we investigated a qua2 loss-of-function mutant and a suppressor mutant with restored cell adhesion, qua2 esmeralda1, using a combination of imaging and biochemical techniques. We found that qua2 hypocotyls have reductions in middle lamellae integrity, pectin methyl-esterase (PME) activity, pectin content and molecular mass, and immunodetected Ca2+-crosslinking at cell corners, but increased methyl-esterification and polygalacturonase (PG) activity, with qua2 esmd1 having wild type-like or intermediate phenotypes. Our findings suggest that excessive pectin degradation prevents pectin accumulation and the formation of a sufficiently Ca2+-crosslinked network to maintain cell adhesion in qua2 mutants. We propose that PME and PG activities balance tissue-level expansion and cell separation. Together, these data provide insight into the cause of cell adhesion defects in qua2 mutants and highlight the importance of harmonizing pectin modification and degradation during plant growth and development.

Construction of a TRFIC strip for rapid and sensitive detection of Ralstoniasolanacearum

The development of a sensitive and rapid screening method for Ralstonia solanacearum is critical for the control of tobacco wilt. In the present study, tissue homogenates of three tobacco varieties (Honda, Yunnan 87 and K326) with different resistance to R. solanacearum, were individually used as additives to the bacteria culture medium. The changes in R. solanacearum secretome were investigated and one of the most abundant secretary proteins with increased expression, polygalacturonase (PG), was selected as a marker for R. solanacearum identification. Then PG gene was cloned into E. coli, and the expressed protein was used as the immunogen to develop monoclonal antibodies. Subsequently, the monoclonal antibody against PG was coupled with synthesized polystyrene microspheres, and a rapid test strip system was developed for the detection of R. solanacearum based on time-resolved fluorescent immunochromatographic (TRFIC) method. Under optimal conditions, the detection limit of the strips could reach 72 cells/mL; while it was 422 cells/mL with a linear range from 4 × 102 to 5.12 × 104 cells/mL when testing tobacco samples, which is 1000 times lower than that of colloidal gold-labeled strips. Notably, no cross-reactivity was observed with nine tobacco-related pathogens. Finally, this TRFIC strips was applied to detect R. solanacearum existed in the tobacco and soils of fields with or without bacterial wilt. The results demonstrated that this TRFIC strips could distinguish the difference in bacterial concentration existed in tobacco and soil between the two fields. In summary, this test strip is suitable for sensitive, quick screening of R. solanacearum in tobacco.

A Novel Method of a High Pressure Processing Pre-Treatment on the Juice Yield and Quality of Persimmon.

This study investigates the effects of a high pressure processing pre-treatment (pre-HPP) on the juice yield of persimmon (Diospyros kaki L.) pulp and the pre-HPP plus HPP or thermal processing (TP) on microorganism inactivation and quality changes of the persimmon juice. The “Gongcheng” persimmon was selected with the highest juice yield (48.9%), and the pre-HPP set at 300 MPa/8 min increased the juice yield by 60% through an increasing pectin methylesterase (PME) activity of 25.03% and by maintaining polygalacturonase (PG) activity. For different processing modes, namely, pre-HPP plus HPP at 550 Mpa/5 min and pre-HPP plus TP treatment at 95 °C/5 min, both of the guaranteed microorganisms in the juice were below 2.0 lg CFU/mL; however, the persimmon juice treated by the pre-HPP plus HPP had higher contents of total phenol and ascorbic acid which were 16.07 mg GAE/100 g and 17.92 mg/100 mL, respectively, a lower content of soluble tannin which was 55.64 μg/mL, better clarity which was 18.6% and less color change where the ΔE was only 2.68.

Cloning and Functional Identification of SlPG49 in Solanum lycopersicum

The modification and degradation of pectin in cell walls are necessary for the fruit softening process, which involves a series of pectin-modifying enzymes. Polygalacturonases (PGs) are a major group of pectin-hydrolyzing enzymes, which participate in fruit maturation, organ shedding, pollen development, and other processes by catalyzing the degradation of polygalacturonic acid. However, their function in plants has not yet been fully elucidated. In this paper, a full-length cDNA encoding SlPG49 was cloned from a tomato. Sequence alignment and phylogenetic analysis demonstrated that SlPG49 contains four typical conserved domains and belongs to clade E in PG classification. Quantitative real-time PCR analysis showed that SlPG49 was highly expressed in fruits during the softening stage, indicating that SlPG49 may be involved in fruit softening. Subcellular localization results revealed that SlPG49 was located in the cell membrane and the cell wall. In addition, an in vitro enzymatic activity assay confirmed that SlPG49 does have the ability to catalyze the hydrolysis of polygalacturonic acid. These results indicate that SlPG49 is a newly discovered PG gene involved in tomato fruit softening, and provide an experimental basis for elucidating the biological functions of plant PGs during fruit softening.

Application of γ-Aminobutyric Acid Treatment Differently Affects Physicochemical Characteristics of Tomato Fruits during Post-harvest Storage

The quality of tomato fruit, from harvest to human consumption, requires a lengthy period for shipping, storing, and marketing. γ-aminobutyric acid (GABA) is a good candidate because it is a natural substance produced by plants to defend themselves against stress conditions. In this study, the effect of post-harvest GABA treatments at 0 (control), 5 mM and, 20 mM on the physical and biochemical properties and the polysaccharide content of tomatoes during 28 days of storage were investigated. Our results indicated that 5 mM of GABA treatment increased firmness and shelf-life by maintaining the integrity of fruits compared to control and 20 mM of GABA treated fruits. The fruits treated with 5 mM of GABA decreased the amount of WSP and the expression of cell wall related genes Pectate lyase (PL) and Polygalacturonase (PG). There was not a clear difference in colour index (CI) values among all treated groups at the end of post-harvest storage. Moreover, the tomato fruits treated with 5 mM GABA also showed somewhat less ethylene production, respiration rate and expression level of two ethylene synthesis genes ACS2 and ACS4 towards the end of storage. These results suggested that treatment with 5 mM GABA could be a beneficial strategy for maintaining the morphological and biochemical quality of tomato under post-harvest storage conditions.

Genome-Wide Identification of the Xyloglucan endotransglucosylase/Hydrolase (XTH) and Polygalacturonase (PG) Genes and Characterization of Their Role in Fruit Softening of Sweet Cherry.

Fruit firmness is an important economical trait in sweet cherry (Prunus avium L.) where the change of this trait is related to cell wall degradation. Xyloglucan endotransglycosylase/hydrolase (XTH) and polygalacturonases (PGs) are critical cell-wall-modifying enzymes that occupy a crucial position in fruit ripening and softening. Herein, we identified 18 XTHs and 45 PGs designated PavXTH1-18 and PavPG1-45 based on their locations in the genome of sweet cherry. We provided a systematical overview of PavXTHs and PavPGs, including phylogenetic relationships, conserved motifs, and expression profiling of these genes. The results showed that PavXTH14, PavXTH15 and PavPG38 were most likely to participated in fruit softening owing to the substantial increment in expression during fruit development and ripening. Furthermore, the phytohormone ABA, MeJA, and ethephon significantly elevated the expression of PavPG38 and PavXTH15, and thus promoted fruit softening. Importantly, transient expression PavXTH14, PavXTH15 and PavPG38 in cherry fruits significantly reduced the fruit firmness, and the content of various cell wall components including hemicellulose and pectin significantly changed correspondingly in the transgenic fruit. Taken together, these results present an extensive analysis of XTHs and PGs in sweet cherry and provide potential targets for breeding softening-resistant sweet cherry cultivars via manipulating cell wall-associated genes.

On the Biochemical and Physiological Responses of ‘Crimson Seedless’ Grapes Coated with an Edible Composite of Pectin, Polyphenylene Alcohol, and Salicylic Acid

The ‘Crimson seedless’ grape encountered several difficulties during shelf life, including weight loss, rachis browning, and berry shattering. The effect of exogenous pectin (PE) and polyphenol alcohol (PVA) with supporting salicylic acid (SA) at different concentrations (0, 1, and 2 mM) was applied. The coating was applied to bunches for 5 min and stored at room temperature (26 ± 1 °C and RH 65 ± 3%) for 4 days. In this study, postharvest application of PE + PVA-SA can significantly reduce the cell wall degradation enzyme activities of ‘Crimson seedless’ grape during shelf life. ‘Crimson seedless’ bunches, treated with PE + PVA-SA 2 mmol L−1, had a lowered rachis browning index (RB index), weight loss (WL%), and berry shattering percentage (BS%) and preserved berry color hue angle (ho) compared to untreated bunches during shelf-life duration. Moreover, the PE + PVA-SA 2 mM improved berry firmness (BF) and removal force (BRF). It also improved the soluble solid content (SSC%), titratable acidity (TA%), and SSC: TA-ratio, for assessing berry maturity. The cellular metabolism enzyme activities (CMEAs) of the cell wall such as polygalacturonase (PG), cellulase (CEL), xylanase (XYL), and pectinase (PT) were minimized by applying PE + PVA-SA 2 mM coatings throughout storage duration. The accumulation of malondialdehyde (MDA) and cell wall damage, as well as the electrolyte leakage percentage (EL%), was reduced. PE + PVA-SA 2 mM maintained DPPH radical quenching activities and minimized O2− and H2O2 production rates. Collectively, these findings suggest that PE + PVA with the presence of SA as a coating treatment preserved ‘Crimson seedless’ bunches during shelf life. PE + PVA-SA 2 mM might be at least partially ascribed to the enhancement of bunches’ quality traits as well as inhibiting cell wall damage during the shelf-life period.

Production of an endo-polygalacturonase from Fusarium proliferatum isolated from agro-industrial waste

In this bioprospection survey, a pectinolytic fungal strain, identified as Fusarium proliferatum, was isolated from agro-industrial residues (banana peels) from among 87 microbial isolates. F. proliferatum P6 was detected as a polygalacturonase (PGAse) producer with enzymatic activity on all the incubation days tested (days 1–10) by determination of the reducing sugars, with maximum activity at 96h (83.05 U/mL). Moreover, the presence of citrus pectin in the medium was crucial for the PGAse production. Central Composite Rotatable Design (CCRD) demonstrated that PGAse activity of F. proliferatum P6 was influenced mainly by temperature, with optimal activity of 137.36 ± 2.21U/mL with pH 3.6 at 43.4°C. Furthermore, High Performance Thin Layer Chromatography (HPTLC) inferred that the F. proliferatum P6 strain secretes endo-PGAse enzymes, due oligogalacturonate and monogalacturonate products of enzymatic hydrolysis. This is the first time that this enzyme has been described in F. proliferatum. Endo-PGAse produced by F. proliferatum P6 presents an optimal activity for some industries, such as wine production as well as the processing of fruits and vegetables.

Biochemical characterization of Arabidopsis clade F polygalacturonase shows a substrate preference toward oligogalacturonic acids

Polygalacturonases (PGs) hydrolyze α-1,4-linked d-galacturonic acid (GalUA) in polygalacturonic acid. Previously, PG activity in pea seedlings was found in the Golgi apparatus, where pectin biosynthesis occurs. However, the corresponding genes encoding Golgi-localized PG proteins have never been identified in the higher plants. In this study, we cloned the 5 Arabidopsis genes encoding putative membrane-bound PGs from clade F PGs (AtPGFs) as the first step for the discovery of the Golgi-localized PGs. Five AtPGF proteins (AtPGF3, AtPGF6, AtPGF10, AtPGF14 and AtPGF16) were heterologously produced in Schizosaccharomyces pombe. Among these, only the AtPGF10 protein showed invitro exo-type PG activity toward fluorogenic pyridylaminated-oligogalacturonic acids (PA-OGAs) as a substrate. The optimum PG activity was observed at pH 5.5 and 60°C. The recombinant AtPGF10 protein showed the maximum PG activities toward PA-OGA with 10 degrees of polymerization. The apparent Km values for the PA-OGAs with 7, 11 and 14 degrees of polymerization were 8.0, 22, and 5.9μM, respectively. This is the first report of the identification and enzymatic characterization of AtPGF10 as PG carrying putative membrane-bound domain.

Effects of procyanidin treatment on the ripening and softening of banana fruit during storage

Cell wall degradation accompanied with softening is very common in harvested fruit. To develop a facile postharvest approach, which can be used at ambient temperature, for suppressing softening and maintaining quality of banana fruit, influences of 1% procyanidin (PA) solution treatment on pulp firmness, total soluble solids (TSS) in pulp, peel hue value, chlorophyll content of peel, fruit ethylene production, fruit respiration rate, malondialdehyde (MDA) concentration in peel, peel ion leakage, activities and expression levels of enzymes related with fruit softening during storage at 23 ± 2°C were investigated. Results indicated that PA treatment effectively inhibited ripening-associated processes, as compared to the control banana fruit, PA-treated fruit exhibited higher firmness, hue value and chlorophyll content, lower TSS content, ethylene production, respiration rate, MDA concentration, and ion leakage. Besides, lower activities of cell wall-degrading enzymes polygalacturonase (PG), pectin methyl esterase (PME), pectate lyase (PL), and cellulase (CX) and expression levels of PG, PME, PL were also observed in PA-treated fruit. These results would provide theoretical basis to help solve fruit quality decline of banana fruit during storage in further research.

Combining natamycin and 1-methylcyclopropene with modified atmosphere packaging to evaluate plum (Prunus salicina cv. ‘Cuihongli’) quality

This study aimed to investigate the effect of combining natamycin (NT) and 1-methylcyclopropene (1-MCP) with modified atmosphere packaging (MAP) (NT+1-MCP+MAP) on plums stored at 4 °C and 25 °C. Plums packed in a polypropylene (PP) box were used as a control. Parameters such as the decay incidence, respiration rate, weight loss, firmness, malondialdehyde (MDA) content, pectin, enzyme activity, total soluble solids (TSS), and titratable acidity (TA) of the plums were compared to identify an appropriate preservation method. The storage period (decay incidence ≤ 50 %) of plums treated with NT+1-MCP+MAP was extended from 80 d to 120 d at 4 °C and from 12 d to 21 d at 25 °C compared to PP plums. The treated fruit exhibited less weight loss, lower respiration rate peaks, and a higher firmness than PP plums. Moreover, the efficiency of NT+1-MCP+MAP treatment exceeded that of NT and MAP (NT+MAP) or 1-MCP and MAP (1-MCP+MAP) alone. Furthermore, NT+1-MCP+MAP treatment significantly reduced MDA accumulation while inhibiting pectin methylesterase (PME) and polygalacturonase (PG) activity. The results suggested that NT+1-MCP+MAP was an effective strategy for improving the postharvest quality and prolonging the shelf life of plums.

Effect of chitosan coating incorporated with pomegranate peel extract on pear fruit softening, quality, and cell wall degrading enzymes during cold storage

Pear fruit is vulnerable to textural softening and quality loss during long-term storage. Therefore, in the present studies, the effect of chitosan coatings (CH 1% and CH 2%), pomegranate peel extract, and chitosan-enriched pomegranate peel extract (CH 1%+PPE and CH 2%+PPE) coatings was investigated on pear fruits stored at 01°C and 90%95% relative humidity for 67 day. The results revealed that the combination of chitosan coating with pomegranate peel extract (CH 2%+PPE) markedly reduced the mass loss, spoilage, and maintained the firmness of pear fruit during the storage. In addition, the combined CH +PPE coatings resulted in higher sensory quality, soluble solid content (SSC), pH, and solid acid ratio as compared to the control fruit. Further, the CH+PPE coatings resulted in the lower activities of polygalacturonase (PG), pectinmethylestarase (PME), and cellulase enzymes in the stored pear fruits. The lower cell wall metabolism of treated fruits was associated with the reduced membrane permeability as well as the malondialdehyde content (MDA) which contributed to higher fruit firmness during storage. Thus, among all the treatments, CH 2%+PPE was most effective in retaining fruit firmness and quality by lowering the activity of cell wall degrading enzymes during long-term storage. Practical applications Pear fruits cv. Punjab Beauty tends to soften and deteriorate rapidly during the long-term storage. Chitosan coating enriched with pomegranate peel extract has been reported to preserve postharvest quality in fruits. This study reported that combined CH +PPE coatings could be explored as a potential approach for maintaining the fruit firmness and postharvest quality in pears during a low-temperature storage.

Valeric acid suppresses cell wall polysaccharides disassembly to maintain fruit firmness of harvested ‘Waizuili’ plum (Prunus salicina Lindl)

Cell wall polysaccharides are closely related to fruit firmness. Firmness loss results in softening and restricts postharvest storage of plum fruit at ambient temperature. This study aimed to investigate the effects of valeric acid (VA) treatment on fruit firmness and cell wall polysaccharides metabolism in plum fruit. Results showed that 10 mg L−1 VA treatment delayed the decline of plum fruit firmness. VA-treated plum maintained higher contents of protopectin, cellulose, hemicelluloses, and lignin but lower water-soluble pectin (WSP) amount. Lower activities of polygalacturonase (PG), pectinate lyases (PL), pectinesterase (PE), β-galactosidase (β-GAL), cellulase, hemicellulase but higher activities of phenylalanine ammonia lyase (PAL), 4-coumaroyl-CoA ligase (4CL) and peroxidase (POD) were observed in VA-treated fruit. These results suggested that VA treatment delayed the depolymerization of cell wall polysaccharides via inhibiting activities of degrading-enzymes. Moreover, lignin metabolism was regulated by VA treatment. Altogether, VA treatment regulated cell wall polysaccharides metabolism, then subsequently alleviated firmness loss and prolong storage-life of postharvest plum fruit.

Daucus carota DcPSY2 and DcLCYB1 as Tools for Carotenoid Metabolic Engineering to Improve the Nutritional Value of Fruits.

Carotenoids are pigments with important nutritional value in the human diet. As antioxidant molecules, they act as scavengers of free radicals enhancing immunity and preventing cancer and cardiovascular diseases. Moreover, α-carotene and β-carotene, the main carotenoids of carrots (Daucus carota) are precursors of vitamin A, whose deficiency in the diet can trigger night blindness and macular degeneration. With the aim of increasing the carotenoid content in fruit flesh, three key genes of the carotenoid pathway, phytoene synthase (DcPSY2) and lycopene cyclase (DcLCYB1) from carrots, and carotene desaturase (XdCrtI) from the yeast Xanthophyllomyces dendrorhous, were optimized for expression in apple and cloned under the Solanum chilense (tomatillo) polygalacturonase (PG) fruit specific promoter. A biotechnological platform was generated and functionally tested by subcellular localization, and single, double and triple combinations were both stably transformed in tomatoes (Solanum lycopersicum var. Microtom) and transiently transformed in Fuji apple fruit flesh (Malus domestica). We demonstrated the functionality of the S. chilense PG promoter by directing the expression of the transgenes specifically to fruits. Transgenic tomato fruits expressing DcPSY2, DcLCYB1, and DcPSY2-XdCRTI, produced 1.34, 2.0, and 1.99-fold more total carotenoids than wild-type fruits, respectively. Furthermore, transgenic tomatoes expressing DcLCYB1, DcPSY2-XdCRTI, and DcPSY2-XdCRTI-DcLCYB1 exhibited an increment in β-carotene levels of 2.5, 3.0, and 2.57-fold in comparison with wild-type fruits, respectively. Additionally, Fuji apple flesh agroinfiltrated with DcPSY2 and DcLCYB1 constructs showed a significant increase of 2.75 and 3.11-fold in total carotenoids and 5.11 and 5.84-fold in β-carotene, respectively whereas the expression of DcPSY2-XdCRTI and DcPSY2-XdCRTI-DcLCYB1 generated lower, but significant changes in the carotenoid profile of infiltrated apple flesh. The results in apple demonstrate that DcPSY2 and DcLCYB1 are suitable biotechnological genes to increase the carotenoid content in fruits of species with reduced amounts of these pigments.

Investigating the Molecular Mechanisms of Pepper Fruit Tolerance to Storage via Transcriptomics and Metabolomics

Pepper is one of the most important vegetable crops in China and has high economic value. However, the pepper fruit is easily softened and spoiled after harvest, which seriously affects its flavor, transportation, and economic value. In this study, we used pepper lines with different levels of storage resistance, A144 and A361, and performed physiological examination, transcriptomics, and metabolomics on them at 0 and 3 days after harvest in order to analyze their gene expression patterns and molecular regulatory mechanisms for storage tolerance. A total of 23,477 genes and 985 metabolites were identified. After comparing and analyzing each sample, we identified 7829 differentially expressed genes and 296 differential metabolites. We found that the genes such as ethylene-responsive transcriptional factor (ERFs), polygalacturonase (PG), cellulose synthase (CESA), abscisic acid insensitive (ABI), protein kinase 2 (SnRK2), and protein phosphatase 2C (PP2C) and metabolites such as phenylalanine and glycyl-tyrosine were differentially expressed between different storage times in the two materials. Through GO and KEGG enrichment analysis, we found that the differential genes were mainly enriched in carbohydrate metabolism, small molecule metabolism, and plant hormone signal transduction, and the differential metabolites were mainly enriched in flavonoid biosynthesis, glutathione metabolism, and cysteine and methionine metabolism pathways. This study provides a scientific basis for investigating the molecular mechanisms of storage tolerance and developing new pepper varieties with improved storage resistance.

Biochemical changes in pear fruits during storage at ambient conditions

‘Patharnakh’ (PN) (Pyrus pyrifolia Burm. Nakai) and ‘Punjab Beauty’ (PB) [Pyrus communis L. × Pyrus pyrifolia Burm. (Nakai)] are leading low-chill pear cultivars of subtropics of India. Diurnal temperature and relative humidity during fruit harvest period is high which considerably affect the shelf life of fruits. Fruits of ‘PN’ and ‘PB’ pear harvested at physiological maturity were stored for 12 days at ambient temperature and effects of storage temperature on physical and qualitative parameters were studied. Both cultivars showed reduction in fruit weight and firmness, reducing sugars, sucrose, starch and pectin content. However, total soluble solids and juice acid content increased during storage. Sucrose synthase activity and sucrose content showed significant positive correlation in ‘PN’ cultivar. Activities of fruit softening enzymes such as polygalacturonase (PG) and cellulase was enhanced; whereas, pectinmethylesterase (PME) was reduced during storage. Fruit firmness was negatively correlated with PG in both the cultivars. In ‘PN’ cultivar, fruit firmness was positively correlated with cellulase and negatively with PME enzyme but reverse trend was observed in ‘PB’ cultivar. Fruit minerals content didn’t show any substantial disparities in both the cultivars during storage. ‘Patharnakh’ and ‘Punjab Beauty’ fruits maintain desirable quality parameters up to 6-9 days and 3-6 days, respectively, during storage at ambient conditions.

Traceability of tomatoes (Solanun lycopersicum) based on their enzymatic profile

This study aimed at evaluating the effect of organic and conventional farming systems on enzymatic profiles of tomatoes so as to find a biomarker for their safe traceability and certification. Three tomato varieties (Khaki, Italian and Cherry), officially certificated and sold in fruit shops, were collected in different seasons. The fruits of each variety were standardized in analytical samples in relation to their ripeness indicators (color, sugar/acidity rate). Assays used for determining enzymatic activities were previously standardized to invertases (INV), polygalacturonases (PG), peroxidases (PO), polyphenoloxidases (PPO), catalases (CAT) and phenylalanine ammonia lyase (PAL). Enzymatic activities were correlated with the farming systems by the Principal Component Analysis (PCA). Enzymatic activities of PO, PPO, CAT and PAL proved to be useful for tomato certification and traceability, since their correlation was above 0.9. The statistical analysis confirmed that PO and CAT activities were the most promising to find a model of response to the farming system. Enzymatic profiles of both Italian and Cherry varieties were the most affected by the farming system.

Cell wall break down of pitanga fruit (Eugenia uniflora L.) is associated with pectic solubilisation and softening

SummaryPitanga fruit stands out for its exotic flavour and antioxidant properties. The objective of this work was to evaluate changes in the physical, chemical and biochemical variables of red pitanga variety, in four stages of development (green, yellow, orange and red) and associate them to the cell wall break down. Analysis of pH, titratable acidity, soluble solids, firmness, soluble pectin, pectinamethylesterase (PME), polygalacturonase (PG), cell wall swelling and microstructure were performed. pH and levels of soluble solids and soluble pectin increased, in addition to the cell wall swelling and reduction of firmness, throughout the development of pitanga. From the SEM, it was possible to observe the degradation of the fruit cell wall during ripening, suggesting mainly the degradation of pectic polysaccharides, verified by the solubilisation of these substances. PG and PME enzymes were not active, which suggests that other enzymes may be associated with the cell wall break down.

The storage temperature affects flesh firmness and gene expression patterns of cell wall-modifying enzymes in stony hard peaches

Stony hard (SH) peaches undergo minimal softening on the tree or after harvest in air at room temperature. Instead, the firmness of SH peach fruit is reduced by treatments with ethylene or auxin or storage at 10 °C. In this study, the SH peach cultivar ‘Manami’ was stored at 0 °C, 5 °C, 8 °C, 10 °C, 15 °C, 18 °C, and 20 °C to characterize fruit softening with storage temperature. Fruit firmness was effectively reduced with storage at 8 °C, 10 °C, and 15 °C, with softening occurring, even in fruit with lower ethylene production, at 15 °C. In these fruit tissues, expression of a cell wall-modifying enzyme gene coding for polygalacturonase (PG) was identified (PpPGM), which is related to fruit firmness. The duration and sequence of different softening treatments were also examined. Fruit stored at 10 °C for 6 d prior to cold storage (0 °C) continued to soften after storage, and PpPGM was expressed in these tissues during cold storage. However, fruit stored at 0 °C or 20 °C for longer than 2 w did not soften during subsequent treatment at 10 °C. These results indicate that temperature-induced fruit softening, for example, within 7 d of treatment and during storage at 15 °C, occurred under conditions of lower ethylene production and may be partly attributed to ethylene-independent PG induction. Thus, PG expression might be an important factor for SH peach fruit softening during or after storage.