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Introduction: Blackberry (Rubus subgenus Rubus) is a soft-fruited specialty crop that often suffers economic losses due to degradation in the shipping process. During transportation, fresh-market blackberries commonly leak, decay, deform, or become discolored through a disorder known as red drupelet reversion (RDR). Over the past 50 years, breeding programs have achieved better fruit firmness and postharvest quality through traditional selection methods, but the underlying genetic variation is poorly understood. Methods: We conducted a genome-wide association of fruit firmness and RDR measured in 300 tetraploid fresh-market blackberry genotypes from 2019-2021 with 65,995 SNPs concentrated in genic regions of the R. argutus reference genome. Results: Fruit firmness and RDR had entry-mean broad sense heritabilities of 68% and 34%, respectively. Three variants on homologs of polygalacturonase (PG), pectin methylesterase (PME), and glucan endo-1,3-b-glucosidase explained 27% of variance in fruit firmness and were located on chromosomes Ra06, Ra01, and Ra02, respectively. Another PG homolog variant on chromosome Ra02 explained 8% of variance in RDR, but it was in strong linkage disequilibrium with 212 other RDR-associated SNPs across a 23 Mb region. A large cluster of six PME and PME inhibitor homologs was located near the fruit firmness quantitative trait locus (QTL) identified on Ra01. RDR and fruit firmness shared a significant negative correlation (r = -0.28) and overlapping QTL regions on Ra02 in this study. Discussion: Our work demonstrates the complex nature of postharvest quality traits in blackberry, which are likely controlled by many small-effect QTLs. This study is the first large-scale effort to map the genetic control of quantitative traits in blackberry and provides a strong framework for future GWAS. Phenotypic and genotypic datasets may be used to train genomic selection models that target the improvement of postharvest quality. [ABSTRACT FROM AUTHOR]

IntroductionBlackberry (Rubus subgenus Rubus) is a soft-fruited specialty crop that often suffers economic losses due to degradation in the shipping process. During transportation, fresh-market blackberries commonly leak, decay, deform, or become discolored through a disorder known as red drupelet reversion (RDR). Over the past 50 years, breeding programs have achieved better fruit firmness and postharvest quality through traditional selection methods, but the underlying genetic variation is poorly understood.MethodsWe conducted a genome-wide association of fruit firmness and RDR measured in 300 tetraploid fresh-market blackberry genotypes from 2019-2021 with 65,995 SNPs concentrated in genic regions of the R. argutus reference genome.ResultsFruit firmness and RDR had entry-mean broad sense heritabilities of 68% and 34%, respectively. Three variants on homologs of polygalacturonase (PG), pectin methylesterase (PME), and glucan endo-1,3-β-glucosidase explained 27% of variance in fruit firmness and were located on chromosomes Ra06, Ra01, and Ra02, respectively. Another PG homolog variant on chromosome Ra02 explained 8% of variance in RDR, but it was in strong linkage disequilibrium with 212 other RDR-associated SNPs across a 23 Mb region. A large cluster of six PME and PME inhibitor homologs was located near the fruit firmness quantitative trait locus (QTL) identified on Ra01. RDR and fruit firmness shared a significant negative correlation (r = -0.28) and overlapping QTL regions on Ra02 in this study.DiscussionOur work demonstrates the complex nature of postharvest quality traits in blackberry, which are likely controlled by many small-effect QTLs. This study is the first large-scale effort to map the genetic control of quantitative traits in blackberry and provides a strong framework for future GWAS. Phenotypic and genotypic datasets may be used to train genomic selection models that target the improvement of postharvest quality.

The de-methylesterification of the pectic polysaccharide homogalacturonan (HG) by pectin methylesterases (PMEs) is a critical step in the control of plant cell expansion and morphogenesis. Plants have large gene families encoding PMEs but also PME inhibitors (PMEIs) with differ in their biochemical properties. The Arabidopsis thaliana PECTIN METHYLESTERASE INHIBITOR 3 (PMEI3) gene is frequently used as a tool to manipulate pectin methylesterase activity in studies assessing its role in the control of morphogenesis. One limitation of these studies is that the exact biochemical activity of this protein has not yet been determined. In this manuscript we produced the protein in Pichia pastoris and characterized its activity in vitro. Like other PMEIs, PMEI3 inhibits PME activity at acidic pH in a variety of cell wall extracts and in purified PME preparations, but does not affect the much stronger PME activity at neutral pH. The protein is remarkable heat stable and shows higher activity against PME3 than against PME2, illustrating how different members of the large PMEI family can differ in their specificities towards PME targets. Finally, growing Arabidopsis thaliana seedlings in the presence of purified PMEI3 caused a dose-dependent inhibition of root growth associated with the overall inhibition of HG de-methylesterification of the root surface. This suggests an essential in vivo role for PME activity at acidic pH in HG de-methylesterification and growth control. These results show that purified recombinant PMEI3 is a powerful tool to study the connection between pectin de-methylesterification and cell expansion.

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Phosphorus (P) starvation leads to increased reutilization of cell wall P in rice (Oryza sativa). Carbon dioxide (CO2) is involved not only in plant growth and development but also in the response to abiotic stresses. However, it remains unclear whether CO2 affects the reutilization of cell wall P in rice when subjected to P deficiency. In the present study, elevated CO2 (600 μl·L−1) significantly increased the soluble P content in shoots when compared with ambient CO2 (400 μl·L−1). This positive effect was accompanied by an increase of pectin content, as well as an increase of pectin methylesterase (PME) activity, which results in P release from the shoot cell wall, making it available for plant growth. P deficiency significantly induced the expression of phosphate transporter genes (OsPT2, OsPT6, and OsPT8) and decreased the P content in the xylem sap, but elevated CO2 had no further effect, indicating that the increased soluble P content observed in shoots under elevated CO2 is attributable to the reutilization of shoot cell wall P. Elevated CO2 further increased the P deficiency-induced ethylene production in the shoots, and the addition of the ethylene precursor 1-amino-cyclopropane-1-carboxylic acid (ACC) mimicked this effect, while the addition of the ethylene inhibitor aminoethoxyvinylglycine (AVG) abolished this effect. These results further support the role of ethylene in the alleviation of P deficiency under elevated CO2. Taken together, our results indicate that the improvement of P nutrition in rice by elevated CO2 is mediated by increasing the shoot cell wall pectin content and PME activity, possibly via the ethylene signaling pathway.

Phosphorus (P) starvation leads to increased reutilization of cell wall P in rice (Oryza sativa). Carbon dioxide (CO2) is involved not only in plant growth and development but also in the response to abiotic stresses. However, it remains unclear whether CO2 affects the reutilization of cell wall P in rice when subjected to P deficiency. In the present study, elevated CO2 (600 μl·L−1) significantly increased the soluble P content in shoots when compared with ambient CO2 (400 μl·L−1). This positive effect was accompanied by an increase of pectin content, as well as an increase of pectin methylesterase (PME) activity, which results in P release from the shoot cell wall, making it available for plant growth. P deficiency significantly induced the expression of phosphate transporter genes (OsPT2 , OsPT6 , and OsPT8) and decreased the P content in the xylem sap, but elevated CO2 had no further effect, indicating that the increased soluble P content observed in shoots under elevated CO2 is attributable to the reutilization of shoot cell wall P. Elevated CO2 further increased the P deficiency-induced ethylene production in the shoots, and the addition of the ethylene precursor 1-amino-cyclopropane-1-carboxylic acid (ACC) mimicked this effect, while the addition of the ethylene inhibitor aminoethoxyvinylglycine (AVG) abolished this effect. These results further support the role of ethylene in the alleviation of P deficiency under elevated CO2. Taken together, our results indicate that the improvement of P nutrition in rice by elevated CO2 is mediated by increasing the shoot cell wall pectin content and PME activity, possibly via the ethylene signaling pathway. [ABSTRACT FROM AUTHOR]

Abstract Pectin methylesterases (PMEs) catalyze pectin demethylation and facilitate the determination of the degree of methyl esterification of cell wall in higher plants. The regulation of PME activity through endogenous proteinaceous PME inhibitors (PMEIs) alters the status of pectin methylation and influences plant growth and development. In this study, we performed a PMEI screening assay using a chemical library and identified a strong inhibitor, phenylephrine (PE). PE, a small molecule, competitively inhibited plant PMEs, including orange PME and Arabidopsis PME. Physiologically, cultivation of Brassica campestris seedlings in the presence of PE showed root growth inhibition. Microscopic observation revealed that PE inhibits elongation and development of root hairs. Molecular studies demonstrated that R oot H air S pecific 12 (RHS12) encoding a PME, which plays a role in root hair development, was inhibited by PE with a Ki value of 44.1 μM. The biochemical mechanism of PE-mediated PME inhibition as well as a molecular docking model between PE and RHS12 revealed that PE interacts within the catalytic cleft of RHS12 and interferes with PME catalytic activity. Taken together, these findings suggest that PE is a novel and non-proteinaceous PME inhibitor. Furthermore, PE could be a lead compound for developing a potent plant growth regulator in agriculture. Highlights • Phenylephrine (PE) inhibits Pectin methylesterases (PMEs). • Phenylephrine (PE) serves as a competitive inhibitor of active PMEs. • Phenylephrine (PE) is a non-proteinaceous PME inhibitor. • Phenylephrine (PE) inhibits the growth of Brassica campestris seedlings. • Phenylephrine (PE) inhibits RHS12 (R oot H air S pecific 12), which PME plays a role in root hair development. [ABSTRACT FROM AUTHOR]

Pectin methylesterase is an enzyme with an important in vivo role in plants as well as in food industry. This enzyme catalyzes the hydrolysis of methyl ester bounds in pectin which is one of the main components of cell wall in plants, producing methanol and free carboxylic groups. The effect of pectin methylesterase in food quality has been extensively studied, producing desirable effects in texture improvement as well as undesirable effects in some beverages. Likewise, the low methoxyl pectin produced by this enzyme has characteristics that contribute to formulate best quality food products. Pectin methylesterase is a ubiquitously enzyme that presents multiple isoforms, but is not only present in plants; it is also found in fungi, bacteria, and yeast, which have specific chemical and physical characteristics. The latter makes the task of analyzing the wide variety of these enzymes with its specific characteristics difficult. Based on this enzyme relevance and the aforementioned, multiple methods have been developed in order to evaluate pectin methylesterase activity with different research objectives. In this paper, the importance of the enzyme as well as advantages and drawbacks of the different methods will be discussed besides applications and evolution of these will be mentioned. Additionally, this paper will improve the understanding of the systems used in pectin methylesterase activity analysis. [ABSTRACT FROM AUTHOR]

Non-thermal pasteurization of orange juices using a continuous pressure change technology (PCT) device was investigated on pilot plant scale for the first time. PCT treatment was conducted by pressurizing orange juice and nitrogen at moderately high pressures ( P = 25 or 50 MPa) in a tubular continuous reactor. Abrupt decompression was achieved by a relief valve at the end of the tubular system. As compared to freshly squeezed juice, PCT treatment slightly reduced levels of carotenoids, vitamin C and hesperidin by 19, 5, and 14 %, respectively. Peroxidase was completely inactivated, whereas residual pectin methylesterase activities amounted to 26-27 %. Simultaneously, total aerobic plate counts were substantially reduced by at least 3.4 log cfu/mL. The mean volume-weighed particle diameter d was drastically reduced from 652 μm in freshly squeezed juice to 6 and 31 μm at 25 and 50 MPa, respectively. Concomitantly, CIE- L* a* b* color values indicated a brighter and more intense yellow color of PCT-treated juices. While cloud separation in freshly squeezed juice was completed within 3 days, cloud stability in PCT-treated juices was retained for 5 days. [ABSTRACT FROM AUTHOR]

Fungi are important natural product sources that have enormous potential for the production of novel compounds for use in pharmacology, agricultural applications and industry. Compared with other natural sources such as plants, fungi are highly diverse but understudied. However, research on Cladosporium cladosporioides revealed the existence of bioactive products such as p-methylbenzoic acid, ergosterol peroxide (EP) and calphostin C as well as enzymes including pectin methylesterase (PME), polygalacturonase (PG) and chlorpyrifos hydrolase. p-Methylbenzoic acid has ability to synthesise 1,5-benzodiazepine and its derivatives, polyethylene terephthalate and eicosapentaenoic acid. EP has anticancer, antiangiogenic, antibacterial, anti-oxidative and immunosuppressive properties. Calphostin C inhibits protein kinase C (PKC) by inactivating both PKC-epsilon and PKC-alpha. In addition, calphostin C stimulates apoptosis in WEHI-231 cells and vascular smooth muscle cells. Based on the stimulation of endoplasmic reticulum stress in some types of cancer, calphostin C has also been evaluated as a potential photodynamic therapeutic agent. Methylesterase (PME) and PG have garnered attention because of their usage in the food processing industry and significant physiological function in plants. Chlorpyrifos, a human, animal and plant toxin, can be degraded and eliminated by chlorpyrifos hydrolase. [ABSTRACT FROM AUTHOR]

In the present work, the role of calcium ions (Ca2+) in the rheological behaviour of carrot-derived purées was investigated. Therefore, purées based on carrots containing pectin with different degree of methoxylation were prepared and the effects of Ca2+ addition in excess on the rheological properties of these purées were studied at different pH. More specifically, it was assessed if the purée stiffness and strength could be influenced by Ca2+ addition. Ion addition caused a decrease in both network stiffness and strength, in particular at pH values above 4.5. By separating the particle phase from the serum, and characterizing the rheology of both phases as a function of pectin degree of methoxylation, Ca2+ addition in excess and pH, it was concluded that the particle phase rather than the serum phase is affected by ion addition. Immunolabeling of the carrot-derived particles with anti-pectin antibodies showed the presence of non-methoxylated residues at the particle surfaces, which will be charged at specific pH. Hence, the calcium ions may compress the electrical double layer around the particles whereby they can approach each other more closely. The latter mechanism was confirmed by the relation between the phase volume and the rheological parameters. Rather than being involved in Ca2+ cross-link formation thus enhancing the pectin network in carrot-derived purées, it turned out that Ca2+ screens the negatively charged pectin at the surface of the particles whereby the rheological characteristics of these suspensions, such as the yield stress and storage modulus, are reduced and the flow is facilitated. [ABSTRACT FROM AUTHOR]

The activity of endogenous deteriorative enzymes together with microbial growth (with associated enzymatic activity) and/or other non-enzymatic (usually oxidative) reactions considerably shorten the shelf life of fruits and vegetable products. Thermal processing is commonly used by the food industry for enzyme and microbial inactivation and is generally effective in this regard. However, thermal processing may cause undesirable changes in product's sensory as well as nutritional attributes. Over the last 20 years, there has been a great deal of interest shown by both the food industry and academia in exploring alternative food processing technologies that use minimal heat and/or preservatives. One of the technologies that have been investigated in this context is high-pressure processing (HPP). This review deals with HPP focusing on its effectiveness for controlling quality-degrading enzymes in horticultural products. The scientific literature on the effects of HPP on plant enzymes, mechanism of action, and intrinsic and extrinsic factors that influence the effectiveness of HPP for controlling plant enzymes is critically reviewed. HPP inactivates vegetative microbial cells at ambient temperature conditions, resulting in a very high retention of the nutritional and sensory characteristics of the fresh product. Enzymes such as polyphenol oxidase (PPO), peroxidase (POD), and pectin methylesterase (PME) are highly resistant to HPP and are at most partially inactivated under commercially feasible conditions, although their sensitivity towards pressure depends on their origin as well as their environment. Polygalacturonase (PG) and lipoxygenase (LOX) on the other hand are relatively more pressure sensitive and can be substantially inactivated by HPP at commercially feasible conditions. The retention and activation of enzymes such as PME by HPP can be beneficially used for improving the texture and other quality attributes of processed horticultural products as well as for creating novel structures that are not feasible with thermal processing. [ABSTRACT FROM AUTHOR]

Highlights: [•] This is the first molecular study of Moniliophthora perniciosa polygalacturonases. [•] MpPG genes present different expression pattern and regulation. [•] MpPG genes are regulated by fermentable carbon sources. [•] PG are possibly regulated by post-translational modifications. [•] Systems biology identified key proteins interacting with MpPG. [Copyright &y& Elsevier]

Plant cell growth is controlled by the balance between turgor pressure and the extensibility of the cell wall. Several distinct classes of wall polysaccharides and their interactions contribute to the architecture and the emergent features of the wall. As a result, remarkable tensile strength is achieved without relinquishing extensibility. The control of growth and development does not only require a precisely regulated biosynthesis of cell wall components, but also constant remodeling and modification after deposition of the polymers. This is especially evident given the fact that wall deposition and cell expansion are largely uncoupled. Pectins form a functionally and structurally diverse class of galacturonic acid-rich polysaccharides which can undergo abundant modification with a concomitant change in physicochemical properties. This review focuses on homogalacturonan demethylesterification catalyzed by the ubiquitous enzyme pectin methylesterase (PME) as a growth control module. Special attention is drawn to the recently discovered role of this process in primordial development in the shoot apical meristem. [ABSTRACT FROM AUTHOR]

Abstract: One of the major causes of ‘Fuyu’ persimmon loss after cold storage (CS) is the breakdown of its flesh, which results in the production of a translucent fruit (a water-soaked fruit). It is believed that the cause of this disturbance is linked to disorganization of the cytoskelet and endomembrane system, which changes the synthesis and transport of proteins and metabolites, resulting in incomplete ripening. To test this hypothesis, ‘Fuyu’ persimmon was subjected to three different postharvest treatments (T): Control – harvested and kept at 23±3°C and relative humidity (RH) of 85±5% (room temperature, RT) for 12 days, T1 – harvested and kept under cold storage (CS) (1±1°C and RH of 85±5%) for 30 days followed by RT storage for 2 days, T2 – kept under RT for 2 days (acclimatization) followed by CS for 30 days. Control and T2 resulted in fruit with decreased flesh firmness (FF), and increased soluble solids (SS) and ascorbic acid (AA) contents. In these fruit the activity of endo-1,4-ß-glucanase (endo-1,4-ß-gluc), pectin methylesterase (PME), polygalacturonase (PG) and ß-galactosidase (ß-gal) increased. T1 resulted in translucent fruit with decreased FF, without any enzymatic activity changes, probably due to the physical disruption of the cytoskeleton. Further, there was an increased content of proteins corresponding to expansins in fruit kept under Control and T2 conditions, which suggests that these conditions do contribute to the synthesis and/or transport of proteins involved in the process of solubilization of the cell wall. In these fruit, there was also a major accumulation of gene transcripts corresponding to heat shock proteins (HSPs) of organelles related to endomembrane, which suggests participation of these genes in the prevention of damage caused by cold conditions. These data proved the hypotheses that acclimatization contributes to the expression of HSPs, and synthesis and transportat of proteins involved in the solubilization of the cell wall. The expression of these genes results in the normal ripening of the persimmon, as confirmed by the evolution of ethylene production. [Copyright &y& Elsevier]

Abstract: Pectin methylesterase (PME) catalyses the demethoxylation of pectin, a major plant cell wall polysaccharide. Through modification of the number and distribution of methyl-esters on the pectin backbone, PME affects the susceptibility of pectin towards subsequent (non-) enzymatic conversion reactions (e.g., pectin depolymerisation) and gel formation, and, hence, its functionality in both plant cell wall and pectin-containing food products. The enzyme plays a key role in vegetative and reproductive plant development in addition to plant–pathogen interactions. In addition, PME action can impact favourably or deleteriously on the structural quality of plant-derived food products. Consequently, PME and also the proteinaceous PME inhibitor (PMEI) found in several plant species and specifically inhibiting plant PMEs are highly relevant for plant biologists as well as for food technologists and are intensively studied in both fields. This review paper provides a structured, comprehensive overview of the knowledge accumulated over the years with regard to PME and PMEI. Attention is paid to both well-established and novel data concerning (i) their occurrence, polymorphism and physicochemical properties, (ii) primary and three-dimensional protein structures, (iii) catalytic and inhibitory activities, (iv) physiological roles in vivo and (v) relevance of (endogenous and exogenous) enzyme and inhibitor in the (food) industry. Remaining research challenges are indicated. [ABSTRACT FROM AUTHOR]

Abstract: Two surface plasmon resonance (SPR)-based interaction analysis methods were successfully implemented to explore the binding between plant PME and kiwi PMEI. In a first method, plant PMEs were immobilised on a chip surface via amine coupling. This experimental setup allowed studying the effect of pH and ionic strength on the PME–PMEI interaction kinetics. Strong binding was obtained at pH<7 and at low salt concentrations, whereas both pH⩾8 and [NaCl] of ca. 1.0M effectively caused dissociation. In a second method, kiwi PMEI was immobilised on a chip surface to which streptavidin had been covalently attached. Hereto, PMEI was biotinylated by means of a NHS-biotin reagent. With this immobilisation strategy, the effect of (partial) thermal or high pressure-induced denaturation of PME on its affinity towards PMEI was investigated. A notable degree of enzyme inactivation was required before interaction characteristics were significantly altered. Any incomplete inactivation of PME resulted in binding to the PMEI surface. [Copyright &y& Elsevier]

Pectin, one of the main components of plant cell wall, is deesterified by the pectin methylesterase (PME). PME activity is regulated by inhibitor proteins known as the pectin methylesterase inhibitor (PMEI), which plays a key role in wounding, osmotic stress, senescence and seed development. However, the role of PMEI in many plant species still remains to be elucidated, especially in wheat. To facilitate the expression analysis of the TαPMEI gene, RT-PCR was performed using leaf, stem and root tissues that were treated with exogeneous application of phytohormones and abiotic stresses. High transcription was detected in salicylic acid (SA) and hydrogen peroxide treatments. To elucidate the subcellular localization of the TαPMEI protein, the TαPMEI:GFP fusion construct was transformed into onion epidermal cells by particle bombardment. The fluorescence signal was exclusively detected in the cell wall. Using an enzyme assay, we confirmed that PME was completely inhibited by TαPMEI. These results indicated that TαPMEI was involved in inhibition of pectin methylesterification and may play a role in the plant defense mechanism via cell wall fortification. [ABSTRACT FROM AUTHOR]

Abstract: Carrot pectin methylesterase (PME) and its inhibitor (PMEI) from kiwi fruit were successfully purified by affinity chromatography. Enzyme and inhibitor activity and stability and PME–PMEI complex formation, as influenced by intrinsic product factors (pH and NaCl) and extrinsic process factors (temperature and pressure), were studied. The effect of temperature- or pressure-induced denaturation of PME and PMEI on their respective activities was assessed by estimating inactivation kinetic parameters. PME inactivation obeyed first-order kinetics. The enzyme was rather heat-labile but pressure-stable. PMEI inactivation was best described by a model taking into account a processing-stable PMEI intermediate. The behavior of PME and the PME–PMEI complex at elevated temperature or pressure in the presence of pectin was explored by following methanol formation as a function of treatment time. PME catalytic activity was stimulated up to a certain temperature or pressure level before declining. No conclusive evidence was obtained for a temperature-induced dissociation of the PME–PMEI complex, whereas high pressure exposure caused the complex to separate. Industrial relevance: PME activity control is a major point of interest in the quest of obtaining high quality plant-derived food products. The current study demonstrates that both traditional thermal processing and novel high hydrostatic pressure processing allow stimulation as well as inactivation of PME and, hence, directing the PME-catalyzed pectin hydrolysis. An alternative or additional approach to control endogenous PME activity (e.g. to obtain cloud-stable juices) is through enzyme inhibition using kiwi PMEI. In this context, pH and NaCl boundaries for application were established, the existence of a temperature- and pressure-stable PMEI intermediate was shown and the PME–PMEI complex was proven not to be dissociated at mild temperature and pressure levels. These observations endorse the possibility of inhibiting undesirable PME activity remaining after mild processing. [Copyright &y& Elsevier]

Abstract: High- and low-methoxyl pectins were treated with pectin methylesterase (PME) and the functional properties of the resulting pectin gels were characterized. The degree of esterification of high- and low-methoxyl pectins decreased from 74.5% to 6.3% and 40.0% to 6.5%, respectively while not changing their molecular weight. Also, the addition of glucono-delta-lactone (GDL) dramatically affected the gel strength and the pH reduction by the GDL led to the increased syneresis of the pectin gels, which was also observed in the PME-treated samples. When flavor compounds were incorporated into the pectin gels, the flavor release from the gels increased with decreasing the degree of esterification due to increased hydrophilic properties. [Copyright &y& Elsevier]

Abstract: Ultraviolet (UV) with a wavelength of 254 nm tends to inactivate most types of microorganisms. Most juices are opaque to UV due to the high-suspended solids in them and hence the conventional UV treatment, usually used for water treatment, cannot be used for treating juices. In order to make the process efficient, a thin film reactor was designed and constructed from glass with the juice flowing along the inner surface of a vertical glass tube as a thin film. The decimal reduction doses required for the reconstitute orange juices (OJ; 10.5° Brix) were 87±7 and 119±17 mJ/cm2 for the standard aerobic plate count (APC) and yeast and moulds, respectively. The shelf life of fresh squeezed orange juice was extended to 5 days with a limited exposure of UV (73.8 mJ/cm2). The effect of UV on the concentration of Vitamin C was investigated using both HPLC and titration methods of measurements. The degradation of Vitamin C was 17% under high UV exposure of 100 mJ/cm2, which was similar to that usually found in thermal sterilization. Enzyme pectin methylesterase (PME) activity, which is the major cause of cloud loss of juices, was also measured. In contrast to the heat treatment, UV processing does not inactivate enzyme pectin methylesterase. The energy required for UV treatment of orange juice (2.0 kW h/m3) was much smaller than that required in thermal treatment (82 kW h/m3). The color and pH of the juice were not significantly influenced by the treatment. [Copyright &y& Elsevier]

A cDNA of a flax (Linum usitatissimum) pectin methylesterase (PME) gene, Lupme3, was isolated by RACE-PCR. A partial sequence of this cDNA was inserted in antisense orientation downstream the cauliflower mosaic virus 35S promoter and introduced into the flax genome via Agrobacterium tumefaciens. Transgenic calli derived from the cocultivated explants were analysed for the antisense sequence expression, and for their PME activity as well as their degree of pectin methylesterification and level of bound cations in the cell wall. Expression of the antisense sequence was correlated with a decrease of sense transcripts and a decrease of the PME enzyme activity of cell extracts at pH 8.5. In transgenic cells, a slight increase of activity was observed at acidic pH (5.5), possibly due to a compensation phenomenon and a moderately basic isoform appeared on IEF of transgenic lines. A decrease of the bound potassium level was also noted. [Copyright &y& Elsevier]

Alcobaca is commonly regarded as an abnormally ripening mutant of the tomato (Lycopersicon esculentum Mill.). Alcobaca fruits were found to be similar to cv. Rutgers fruits in the following characteristics: time between full anthesis and the onset of ripening, response to ethephon, flavor, pH and concentrations of titratable acids, total soluble solids and reducing sugars. The pattern of CO2 and ethylene climacteric are similar in the two plant types, but the peak levels were lower and occurred later in alcobaca than in 'Rutgers'. The mutant fruits differed from fruits of normal varieties in their greatly prolonged shelf life, their relatively low activity of polygalacturonase (PG) and polymethylgalacturonase (PMG), and their low level of endogenous ethylene. Fruits of the mutant harvested before the onset of ripening failed to reach normal pigmentation and remained yellow. Fruits harvested at the onset of ripening reached an orange color, while fruits ripened while attached to the plant reached almost normal pigmentation. These results suggest that alcobaca is a slow ripening mutant and does not belong to the category of non-ripening mutants. [ABSTRACT FROM AUTHOR]

Pectin methylesterases (PMEs) catalyze the demethylesterification of homogalacturonan domains of pectin in plant cell walls and are regulated by endogenous pectin methylesterase inhibitors (PMEIs). In Arabidopsis dark-grown hypocotyls, one PME (AtPME3) and one PMEI (AtPMEI7) were identified as potential interacting proteins. Using RT-quantitative PCR analysis and gene promoter::GUS fusions, we first showed that AtPME3 and AtPMEI7 genes had overlapping patterns of expression in etiolated hypocotyls. The two proteins were identified in hypocotyl cell wall extracts by proteomics. To investigate the potential interaction between AtPME3 and AtPMEI7, both proteins were expressed in a heterologous system and purified by affinity chromatography. The activity of recombinant AtPME3 was characterized on homogalacturonans (HGs) with distinct degrees/patterns of methylesterification. AtPME3 showed the highest activity at pH 7.5 on HG substrates with a degree of methylesterification between 60 and 80% and a random distribution of methyl esters. On the best HG substrate, AtPME3 generates long non-methylesterified stretches and leaves short highly methylesterified zones, indicating that it acts as a processive enzyme. The recombinant AtPMEI7 and AtPME3 interaction reduces the level of demethylesterification of the HG substrate but does not inhibit the processivity of the enzyme. These data suggest that the AtPME3·AtPMEI7 complex is not covalently linked and could, depending on the pH, be alternately formed and dissociated. Docking analysis indicated that the inhibition of AtPME3 could occur via the interaction of AtPMEI7 with a PME ligand-binding cleft structure. All of these data indicate that AtPME3 and AtPMEI7 could be partners involved in the fine tuning of HG methylesterification during plant development., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

Summary [ABSTRACT FROM AUTHOR]