Higher Polyphenol Oxidase Activity Research Articles

Unraveling verticillium wilt resistance: insight from the integration of transcriptome and metabolome in wild eggplant

Verticillium wilt, caused by Verticillium dahliae, is a soil-borne disease affecting eggplant. Wild eggplant, recognized as an excellent disease-resistant resource against verticillium wilt, plays a pivotal role in grafting and breeding for disease resistance. However, the underlying resistance mechanisms of wild eggplant remain poorly understood. This study compared two wild eggplant varieties, LC-2 (high resistance) and LC-7 (sensitive) at the phenotypic, transcriptomic, and metabolomic levels to determine the molecular basis of their resistance to verticillium wilt. These two varieties exhibit substantial phenotypic differences in petal color, leaf spines, and fruit traits. Following inoculation with V. dahliae, LC-2 demonstrated significantly higher activities of polyphenol oxidase, superoxide dismutase, peroxidase, phenylalanine ammonia lyase, β-1,3 glucanase, and chitinase than did LC-7. RNA sequencing revealed 4,017 differentially expressed genes (DEGs), with a significant portion implicated in processes associated with disease resistance and growth. These processes encompassed defense responses, cell wall biogenesis, developmental processes, and biosynthesis of spermidine, cinnamic acid, and cutin. A gene co-expression analysis identified 13 transcription factors as hub genes in modules related to plant defense response. Some genes exhibited distinct expression patterns between LC-2 and LC-7, suggesting their crucial roles in responding to infection. Further, metabolome analysis identified 549 differentially accumulated metabolites (DAMs) between LC-2 and LC-7, primarily consisting of compounds such as flavonoids, phenolic acids, lipids, and other metabolites. Integrated transcriptome and metabolome analyses revealed the association of 35 gene–metabolite pairs in modules related to the plant defense response, highlighting the interconnected processes underlying the plant defense response. These findings characterize the molecular basis of LC-2 resistance to verticillium wilt and thus have potential value for future breeding of wilt-resistant eggplant varieties.

Control of Browning, Enzyme Activity, and Quality in Stored Fresh-cut Fruit Salads through Chitosan Coating Enriched with Bergamot Juice Powder.

In this study, fresh-cut fruit salads composed of apples, pears, kiwis, and pineapples were stored at +4 °C for 18 days under distinct conditions: non-coated (NC), chitosan-coated (CH), and bergamot juice powder extract-enriched chitosan-coated (CHBE). Storage endpoint decay percentages were as follows: NC group: 100%, CH group: 26.67-53.3%, CHBE group: 13.33-26.67%. CHBE had the highest moisture content (87.05-89.64%), soluble solids (12.40-13.26%), and chroma values (2.35-6.60). CHBE and NC groups had 2.10% and 6.61% weight loss, respectively. The NC group had the highest polyphenol oxidase activity (19.48 U mL-1) and browning index (0.70 A420/g); CH group: 0.85 U mL-1, 0.35 A420/g; CHBE group: 0.57 U mL-1, 0.27 A420/g. CHBE showed a titratable acidity of 1.33% and pH 3.73 post-storage, impeding microbial proliferation with the lowest counts (2.30-3.24 log CFU g-1). The microbial suitability of the NC group diminished after day 6, with an overall preference score of 1.00. Conversely, the CH and CHBE groups scored 3.15 and 4.56, highlighting the coatings' effectiveness. Bergamot juice powder extract further enhanced this, mitigating browning and enhancing quality. Results reveal tailored coatings' potential to extend shelf life, improve quality, and enhance fruit salads' acceptability. This study underscores the importance of edible coatings in addressing preservation challenges, emphasizing their role in enhancing food quality and consumer acceptability. Incorporating edible coatings is pivotal in mitigating deterioration issues and ensuring the overall success of fresh-cut fruit products in the market.

Passion fruit juicing with or without seeds treated by high-pressure processing and thermal pasteurization: Effects on the storage stability of enzymes and quality properties

This study evaluated the changes of enzymes and quality properties of passion fruit juice juicing with (PFJ-1) and without seeds (PFJ-2) treated by high-pressure processing (HPP, 600 MPa/5 min) and thermal pasteurization (TP, 85 °C /30 s) during storage at 4 °C for 35 days. Juicing with seeds resulted in PFJ-1 with 76.83, 68.25 and 28.12% higher activities of polyphenol oxidase, peroxidase and superoxide dismutase than PFJ-2, respectively, and its apparent viscosity at 10−1 s and L* were also 148.60 and 1.47% higher, respectively. The total sugars, organic acids, and volatile compounds in PFJ-1 were 9.16, 4.97 and 53.85% higher than PFJ-2, respectively. Quality properties, including sugars, organic acids, volatile compounds in PFJ-1-HPP were all more susceptible towards degradation than PFJ-2-HPP under storage, which were decreased by 21.93, 26.14 and 18.47% after storage. This research provided new insights for production of high-quality passion fruit juice. Industrial relevanceAt present, the passion fruit juice is the dominated product in passion fruit industry, but there are few studies reported on the difference between the juice quality under different juicing methods by juicing with or without seeds. The seeds in passion fruit contains a great variety of substances such as oxidative browning enzymes, unsaturated fatty acids, which can significantly affect the quality of passion fruit juice after entering in juice. This research is of great significance as a theoretical basis to further research on the influence mechanism of enzyme and phytochemicals in seeds on the quality of passion fruit juice, and also provides a guide to production for quality orientated passion fruit juice based on consumer and producer demands.

Transcriptome and physiological analysis revealed the difference of resistance to fresh-cut browning among sweetpotato genotypes

Sweetpotato [Ipomoea batatas (L.) Lam.] storage roots tend to become brown due to damage incurred during harvest, transportation, processing and storage. Understanding the mechanism of sweetpotato browning is of great significance for breeding varieties with low browning, which have greater economic value. In this study, after analysis of the Browning Degree (BD) of 76 sweetpotato genotypes and analyzing the correlations between BD, the activities and contents of phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) for 21 genotypes, two genotypes, S07 (browning-resistant) and S28 (easily browned), were selected to elucidate the differences in the browning mechanism after fresh-cutting by physiological and transcriptome analyses. Genotype S28 had higher PAL, POD and PPO activities and a higher phenolic content after fresh-cutting compared with the basal level and genotype S07. Cell compartmentalization was severely damaged in fresh-cut S28. An RNA-Seq analysis showed that the phenylpropanoid biosynthesis in S28 was more active and gene families of related enzymes were more actively expressed. In conclusion, sweetpotato browning is due to a high content of phenolic compounds, and the high activity of PPO and POD resulting from the up-regulation of related genes. This study provided high quality breeding materials and a relevant theoretical basis for breeding browning-resistant sweetpotato varieties.

Catechol detection based on a two-dimensional copper-based metal-organic framework with high polyphenol oxidase activity

In this work, a novel sensing strategy for catechol was successfully developed based on a two-dimensional copper-based metal-organic framework (2D Cu-MOF) with high polyphenol oxidase activity. The 2D Cu-MOF was prepared from dimethylimidazole and Cu 2+ by stirring in a mixture solvent of methanol and water. We firstly found that the 2D Cu-MOF exhibited high polyphenol oxidase (PPO) activity by catalyzing the typical PPO substrate to produce a red color. And the PPO activity of the 2D Cu-MOF was higher than those of the other two reported PPO-mimicking enzymes at the same mass concentration. Subsequently, based on the effective PPO activities of the 2D Cu-MOF, we established a simple and rapid colorimetric method for detecting catechol with a detection limit of 0.35 μg·mL −1 . This method was also used to detect catechol in city water with satisfying results.

Residual polyphenol oxidase and peroxidase activities in high pressure processed bok choy (Brassica rapa subsp. chinensis) juice did not accelerate nutrient degradation during storage

Polyphenol oxidase (PPO) and peroxidase (POD) cannot be fully inactivated by commercial high pressure processing (HPP) operations, and their residual activities may accelerate nutrient degradation during storage. This study hence aimed to establish the effect of residual enzyme activity on nutrient preservation in bok choy (Brassica rapa subsp. chinensis) juice. Bok choy juice was treated at 600 MPa for up to 20 min and enzyme inactivation, nutrient retention immediately after treatment and nutrient preservation during storage were determined. High residual PPO (85.1 ± 2.6%) and POD (68.5 ± 1.0%) activities remained after 20 min of treatment. Increasing the pressure holding time to enhance enzyme inactivation did not compromise total antioxidant capacity, vitamin C, carotenoids, isothiocyanates and vitamin K levels. Neither did it significantly reduce the vitamin C degradation rate during refrigerated storage. Maximising enzyme inactivation may thus not be necessary for nutrient preservation during the storage of HPP-treated bok choy juice. Industrial relevance textWith HPP, an increase in pressure or holding time is required to achieve higher levels of enzyme inactivation. Without the need to maximize PPO and POD inactivation, juice processors may employ the minimum pressure and holding time required for microbial inactivation. As vegetative bacteria are typically less resistant to HPP inactivation than these enzymes, this could translate to reduced energy costs and increased throughput.

A chemometric approach to evaluate the effects of probe-type ultrasonication on the enzyme inactivation and quality attributes of fresh amla juice

The enzymatic browning induced in amla juice due to the high activity of polyphenol oxidase (PPO) and peroxidase (POD) is one of the critical issues faced by the industry. The present study assessed the suitability of non-thermal, high-intensity ultrasound (US) on the inactivation of PPO and POD in fresh Indian Gooseberry juice. Ultrasonic waves, using a 6mm titanium alloy probe were irradiated in the juice at a maximum power of 455W and frequency of 20kHz. The subsequent effects on biochemical attributes were studied using response surface methodology. Inactivation rates of 90.72% and 73.18%, respectively, for PPO and POD enzymes, were observed at the highest US intensity and exposure time. Numerical optimisation using the three-factor, three-level Box-Behnken design suggested that an optimum process at 70% (energy density: 1610 Wcm-2) pulsed at 5s on and 5s off for 7min 30s resulted in PPO and POD inactivation of the order of 76.42% and 64.57% respectively. At these experimental conditions, the optimized levels of biochemical attributes i.e., ascorbic acid (738.50mg/100mL), total phenols (17.10mg/mL), DPPH antioxidant activity (58.47%), tannins (7.11µg/mL), colour change (ΔE=9.04) and flavonoids (6.14mg/mL) were achieved. The overall statistical models were significant for all the responses except for reducing sugars. Furthermore, the approximation equations for individual responses indicated that the goodness of fit was adequate (R2>0.90). The results suggested that ultrasound is a suitable processing technique for amla juice stabilisation compared to thermal treatments that result in the loss of quality.

Impact of polyphenol oxidase on the bioavailability of flavan-3-ols in fruit smoothies: a controlled, single blinded, cross-over study.

Flavan-3-ols are bioactive compounds found in a variety of fruits and vegetables (F&V) that have been linked to positive health benefits. Increasing habitual flavan-3-ol intake is challenged by the generally low consumption of F&V. While smoothies are a commonly endorsed, consumer-accepted means to increase the daily intake of these important foods, fruits used for smoothie preparation can have a high polyphenol oxidase (PPO) activity and thus potentially affect the content and bioavailability of flavan-3-ols. To assess whether or not consuming freshly prepared smoothies made with different PPO-containing fruit impacts the bioavailability of the flavan-3-ols, a controlled, single blinded and cross-over study was conducted in healthy men (n = 8) who consumed a flavan-3-ol-containing banana-based smoothie (high-PPO drink), a flavan-3-ol-containing mixed berry smoothie (low-PPO drink) and flavan-3-ols in a capsule format (control). The peak plasma concentration (Cmax) of flavan-3-ol metabolites after capsule intake was 680 ± 78 nmol L-1, which was similar to the levels detected after the intake of the low PPO drink. In contrast, the intake of the high PPO drink resulted in a Cmax of 96 ± 47 nmol L-1, 84% lower than that obtained after capsule intake. In a subsequent study (n = 11), flavan-3-ols were co-ingested with a high-PPO banana drink but contact prior to intake was prevented. In this context, plasma flavan-3-ol levels were still reduced, suggesting an effect possibly related to post-ingestion PPO activity degrading flavan-3-ols in the stomach. There was a substantial range in the PPO activity detected in 18 different fruits, vegetables and plant-derived dietary products. In conclusion, bioavailability of flavan-3-ols, and most likely other dietary polyphenol bioactives, can be reduced substantially by the co-ingestion of high PPO-containing products, the implications of which are of importance for dietary advice and food preparation both at home and in industrial settings.

Chemical and Enzymatic Characterization of Leaves from Spanish Table Olive Cultivars

Olive leaves are generated as by-products in the olive industry and contain substances with biological properties that provide health benefits. Although these compounds have been characterized in many leaves from olive cultivars devoted to olive oil extraction, few data are available on leaves from the processing of table olives. In this study, the concentration of polyphenols, triterpenic acids, sugars and enzymatic activities (polyphenol oxidase, peroxidase, β-glucosidase and esterase) were determined in the leaves of the olive tree (Olea europaea L.) of cvs. Aloreña, Cacereña, Empeltre, Hojiblanca, Manzanilla, Verdial, Gordal and Morona. The mean total phenolic content in olive leaves reached 75.58 g/kg fresh weight, and oleuropein was the main polyphenol identified (89.7-96.5%). The main triterpenic acid identified was oleanolic acid, and the main sugar was mannitol, with mean values of 15.83 and 22.31 g/kg, respectively. However, the content of these biocompounds was influenced by the type of cultivar and the orchards of origin. The highest oleuropein content was found in the Manzanilla variety, while the Gordal had the highest triterpene and mannitol content. In particular, the phenolic content could also be affected by endogenous enzymatic activities. High polyphenol oxidase, peroxidase and β-glucosidase activity and low esterase activity were detected, compared to the fruit. Similar to the phenolic compounds, enzymatic activities varied with the harvesting season. The lowest phenolic content corresponded to the highest polyphenol oxidase activity detected during spring. The rest of the enzymatic activities also varied throughout the year, but no common trend was observed.

Burkholderia ambifaria XN08: A plant growth-promoting endophytic bacterium with biocontrol potential against sharp eyespot in wheat.

Plant growth-promoting bacteria (PGPB) have been considered promising biological agents to increase crop yields for years. However, the successful application of PGPB for biocontrol of sharp eyespot in wheat has been limited, partly by the lack of knowledge of the ecological/environmental factors affecting the colonization, prevalence, and activity of beneficial bacteria on the crop. In this study, an endophytic bacterium XN08 with antagonistic activity against Rhizoctonia cerealis (wheat sharp eyespot pathogenic fungus), isolated from healthy wheat plants, was identified as Burkholderia ambifaria according to the sequence analysis of 16S rRNA. The antibiotic synthesis gene amplification and ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analyses were used to characterize the secondary metabolites. The results showed that the known powerful antifungal compound named pyrrolnitrin was produced by the strain XN08. In addition, B. ambifaria XN08 also showed the capacity for phosphate solubilization, indole-3-acetic acid (IAA), protease, and siderophore production in vitro. In the pot experiments, a derivate strain carrying the green fluorescent protein (GFP) gene was used to observe its colonization in wheat plants. The results showed that GFP-tagged B. ambifaria could colonize wheat tissues effectively. This significant colonization was accompanied by an enhancement of wheat plants' growth and an induction of immune resistance for wheat seedlings, which was revealed by the higher activities of polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonia-lyase (PAL). As far as we know, this is the first report describing the colonization traits of B. ambifaria in wheat plants. In addition, our results indicated that B. ambifaria XN08 might serve as a new effective biocontrol agent against wheat sharp eyespot disease caused by R. cerealis.

Determination of optimum humidity for air-curing of cigar tobacco leaves during the browning period

Hainan is a natural air-curing barn for cigar leaves. Humidity has a marked influence on the air-curing of cigar leaves. The browning stage is a key period, which determines the degree and quality of cigar tobacco leaf browning. To understand the effects of humidity in the browning stage on tobacco leaf quality, we examined the malondialdehyde and polyphenol contents, polyphenol oxidase activity, moisture, chemical composition, and appearance of tobacco leaves that were air cured at humidities of 60%, 70%, and 80% during the browning stage. High humidity (80%) during curing led to a high moisture content and polyphenol oxidase activity in leaves. With regard to malondialdehyde content, a minute differences between moderate-humidity (70%) and high-humidity (80%) air-curing were observed. During the browning stage, the chlorogenic acid content was reduced by 85.32% when tobacco leaves were air-cured at 80% humidity, which means that it underwent a more comprehensive oxidized process compared to the other two treatments, whereas rutin and scopoletin experienced a more thorough oxidation at 60% humidity. 70% Humidity was found to be the most suitable humidity for the appearance of air-cured leaves than others, producing the optimum appearance of the cigar leaves. At the end of air-curing, the treatment with 70% curing humidity had a more coordinated chemical composition compared to the other treatments, for instance, it had a starch content of 1.14% and a potassium-chloride ratio of 7.65, which indicated a much better quality of cigar tobacco leaves. In summary, these findings indicate that air-curing at 70% humidity during the browning stage was the most favorable choice for improving tobacco leaf quality for cigar production.

The R2R3 Transcription Factor CsMYB59 Regulates Polyphenol Oxidase Gene CsPPO1 in Tea Plants (Camellia sinensis).

Polyphenol oxidase (PPO) plays a role in stress response, secondary metabolism, and other physiological processes during plant growth and development, and is also a critical enzyme in black tea production. However, the regulatory mechanisms of PPO genes and their activity in tea plants are still unclear. In this study, we measured PPO activity in two different tea cultivars, Taoyuandaye (TYDY) and Bixiangzao (BXZ), which are commonly used to produce black tea and green tea, respectively. The expression pattern of CsPPO1 was assessed and validated via transcriptomics and quantitative polymerase chain reaction in both tea varieties. In addition, we isolated and identified an R2R3-MYB transcription factor CsMYB59 that may regulate CsPPO1 expression. CsMYB59 was found to be a nuclear protein, and its expression in tea leaves was positively correlated with CsPPO1 expression and PPO activity. Transcriptional activity analysis showed that CsMYB59 was a transcriptional activator, and the dual-luciferase assay indicated that CsMYB59 could activate the expression of CsPPO1 in tobacco leaves. In summary, our study demonstrates that CsMYB59 represents a transcriptional activator in tea plants and may mediate the regulation of PPO activity by activating CsPPO1 expression. These findings provide novel insights into the regulatory mechanism of PPO gene in Camellia sinensis, which might help to breed tea cultivars with high PPO activity.

Packaging of Fresh Sliced Mushrooms with Essential Oils Vapours: A New Technology for Maintaining Quality and Extending Shelf Life.

The use of vapour of essential oils (EOs) through an innovative pilot-plant packaging device was studied to preserve the quality of sliced mushrooms during storage. A mix of EOs (eugenol, bergamot EO, and grapefruit EO) was vaporized (100 and 125 µL L−1) and applied during packaging of sliced mushrooms under modified atmosphere packaging (MAP); then, the product quality was studied during cold storage up to 12 days. The highest colour changes of EOs125 samples, which were observed in the mushroom stipe, were not observed with the EOs100 atmosphere. Thus, the high polyphenoloxidase activity observed in untreated samples after 5–7 days was highly controlled with the vapour EOs atmospheres. Furthermore, the visual appearance scores of EOs100 samples were still over the limit of usability, while untreated samples were already below this threshold after 5 days of storage. A strong bacteriostatic effect was achieved with vapour EOs, reducing the Pseudomonas spp. (the main microbial genus in cultivated mushrooms) growth by ≈1.7 log CFU g−1, regardless of the EOs dose, after 12 days. The activity of phenyl ammonia lyase was also reduced up to ≈0.4 enzymatic units with the EOs100 treatment. Conclusively, packaging of sliced mushrooms under an atmosphere enriched with 100 µL L−1 EOs vapour highly controlled the quality loss of sliced mushrooms owing to their enzymatic inhibition and high bacteriostatic effect.

Relationship between the allelic variations at the<italic> Ppo-A1 </italic>and <italic>Ppo-D1</italic> loci and pre-harvest sprouting resistance in wheat

<p indent=0mm><italic>Ppo-A1</italic> and <italic>Ppo-D1</italic> are the major genes that control the activity of polyphenol oxidase (PPO) in wheat. It has been reported that the activity of polyphenol oxidase affects pre-harvest sprouting (PHS) resistance, but the effect of different alleles/allelic combinations at the <italic>Ppo-A1</italic> and <italic>Ppo-D1 </italic>loci on PHS resistance remains unclear. The current study was carried out to elucidate the effects based on the germination index obtained from 248 Chinese wheat cultivars in a three-year trial in combination with genotypic data at the <italic>Ppo-A1</italic> and <italic>Ppo-D1 </italic>loci. Analysis of variation for the<italic> Ppo-A1 </italic>and <italic>Ppo-D1</italic> loci showed that year,<italic> Ppo-A1</italic> locus and<italic> Ppo-A1</italic> × <italic>Ppo-D1 </italic>interaction had significant effects on germination index. At locus <italic>Ppo-A1</italic>, germination index of cultivars carrying the allele <italic>Ppo-A1b</italic> of low PPO activity was 5.22% lower than that carrying the allele<italic> Ppo-A1a</italic> of high PPO activity on average. In contrast, the cultivars carrying the allele <italic>Ppo-D1a</italic> of low PPO activity had higher germination index than that carrying the allele<italic> Ppo-D1b</italic> of high PPO activity at locus<italic> Ppo-D1</italic>, but no significant differences between two alleles. Among the four allelic combinations, the cultivars with the <italic>Ppo-A1bPpo-D1b</italic> had the lowest germination index. The relationship between the alleles at locus <italic>Ppo-A1</italic> and PHS resistance had been verified in the Lunxuan 13 × Jimai 20 F₂ and F_2:3 segregation populations. There were significantly positive correlations between PPO activity / relative expression level of <italic>Ppo-A1</italic> gene and germination index. This study suggests that functional markers of allele<italic> Ppo-A1b </italic>can be effectively applied in marker-assisted selection for PHS resistance.

Evaluating the Anti-Inflammatory and Antioxidant Effects of Broccoli Treated with High Hydrostatic Pressure in Cell Models.

Isothiocyanates (ITCs) are important functional components of cruciferous vegetables. The principal isothiocyanate molecule in broccoli is sulforaphane (SFN), followed by erucin (ERN). They are sensitive to changes in temperature, especially high temperature environments where they are prone to degradation. The present study investigates the effects of high hydrostatic pressure on isothiocyanate content, myrosinase activity, and other functional components of broccoli, and evaluates its anti-inflammatory and antioxidant effects. Broccoli samples were treated with different pressures and for varying treatment times; 15 min at 400 MPa generated the highest amounts of isothiocyanates. The content of flavonoids and vitamin C were not affected by the high-pressure processing strategy, whereas total phenolic content (TPC) exhibited an increasing tendency with increasing pressure, indicating that high-pressure processing effectively prevents the loss of the heat-sensitive components and enhances the nutritional content. The activity of myrosinase (MYR) increased after high-pressure processing, indicating that the increase in isothiocyanate content is related to the stimulation of myrosinase activity by high-pressure processing. In other key enzymes, the ascorbate peroxidase (APX) activity was unaffected by high pressure, whereas peroxidase (POD) and polyphenol oxidase (PPO) activity exhibited a 1.54-fold increase after high-pressure processing, indicating that high pressures can effectively destroy oxidases and maintain food quality. With regards to efficacy evaluation, NO production was inhibited and the expression levels of inducible nitric oxide synthase (iNOS) and Cyclooxygenase-2 (COX-2) were decreased in broccoli treated with high pressures, whereas the cell viability remained unaffected. The efficacy was more significant when the concentration of SFN was 60 mg·mL−1. In addition, at 10 mg·mL−1 SFN, the reduced/oxidized glutathione (GSH/GSSG) ratio in inflammatory macrophages increased from 5.99 to 9.41. In conclusion, high-pressure processing can increase the isothiocyanate content in broccoli, and has anti-inflammatory and anti-oxidant effects in cell-based evaluation strategies, providing a potential treatment strategy for raw materials or additives used in healthy foods.

Caracterización físico-química y potencial para fritura de materiales genéticos de papa (Solanum tuberosum)

Breeding programs should consider, in addition to agronomic aspects (yield, crop cycle, resistance to diseases and pests, among others), aspects related to suitability for use and quality of the final product, since consumer acceptance depends on them. Therefore, the objective of this research was to characterize 24 potato (Solanum tuberosum) genetic materials, considered promising for frying, and a commercial control based on physical (dry matter content, specific gravity and color) and chemical (total polyphenols, total antioxidant capacity and polyphenol oxidase activity) quality parameters. Differences were found in dry matter content, where three genetic materials (07032.3, 10025.1 and 07062.1), with values less than 20 %, would not be suitable for frying, but for cooking. Specific gravity was similar among genetic materials, proving to be a parameter not as strict for selection as dry matter content. Differences were observed in polyphenol oxidase activity (2.1 to 101.43 U∙gprotein-1a in dry weight [DW]) and frying color. Of all materials analyzed, 10 are promising for frying, while the rest have problems with low dry matter content (15.5 to 17.19 %), high polyphenol oxidase activity (> 45 U∙gprotein-1a in DW) and non-golden or dark color, which would make them less attractive to both industry and consumers.

Responses of Hydrocharis dubia (Bl.) Backer and Trapa bispinosa roxb. to tetracycline exposure

The presence of tetracycline is ubiquitous and has adverse effects on aquatic systems. A hydroponic experiment was conducted to investigate the ecological sensitivity of Hydrocharis dubia (Bl.) Backer and Trapa bispinosa Roxb. Exposed to different concentrations of tetracycline (0, 0.1, 1, 10, 30 and 50 mg/L) for one day (1D) and 14 days (14D). The results showed that after 1D of tetracycline exposure, the physiological indices of H. dubia had no remarkable change except for proline which was significantly stimulated under 0.1 mg/L tetracycline. For T. bispinosa, guaiacol peroxidase (POD), polyphenol oxidase (PPO) and ascorbate peroxidase (APX) activity and protein and proline content were notably promoted under different concentrations of tetracycline, but PPO activity was significantly decreased in 50 mg/L. After 14D, tetracycline caused no harm to the growth and protein content of H. dubia, but negatively influenced lipid peroxidation product and chlorophyll content in H. dubia under high tetracycline concentrations. Superoxide dismutase (SOD) and POD activity of H. dubia significantly increased at high tetracycline concentrations, while catalase (CAT) and PPO activity significantly decreased. APX activity in H. dubia increased with tetracycline concentrations at low tetracycline concentrations. For T. bispinosa, high concentrations of tetracycline application significantly inhibited its growth and the content of protein and chlorophyll. SOD, POD, CAT, and PPO activity of T. bispinosa were induced under different concentrations of tetracycline and no lipid peroxidation was observed. APX activity in T. bispinosa was significantly inhibited at high tetracycline concentrations. The results suggest that tetracycline can cause oxidative damage in H. dubia but harm the metabolism process of T. bispinosa without inducing oxidative damage. Overall, the sensitivity of T. bispinosa exposed to tetracycline exposure is higher than that of H. dubia.

Fe2 O3 nanoparticles induced biochemical responses and expression of genes involved in rosmarinic acid biosynthesis pathway in Moldavian balm under salinity stress.

The effect of iron oxide nanoparticle (NP) at four concentrations (0, 30, 60 and 90 ppm) and salinity at three levels (0, 50 and 100 mM) were investigated on rosmarinic acid (RA) production in 5-week-old Moldavian balm (Dracocephalum moldavica L.) plants. Salinity and spraying iron oxide NPs significantly affected tyrosine (Tyr), phenylalanine (Phe) and proline (Pro) amino acids content, Phenylalanine Ammonia-Lyase (PAL), Tyrosine Aminotransferase (TAT) and Rosmarinic Acid Synthase (RAS) genes expression levels, RA content, Polyphenol Oxidase (PPO), PAL and Superoxide Dismutase (SOD) activities, malondialdehyde (MDA) content and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. PAL, TAT and RAS genes expression rate and content of RA were enhanced in Moldavian balm plants exposed by NaCl + NPs. The results of high performance liquid chromatography (HPLC) revealed that simultaneous application of 50 mM NaCl and 90 ppm NPs increases the RA content in leaf by 81.15% as compared to control plants. The Tyr and Phe contents decreased in Moldavian balm plants exposed to salt stress. Application of NPs had a positive effect on the content of these amino acids. Proline content increased under salinity stress and application of iron NPs induced a significant increase in the Pro content of leaf. The results revealed that PAL, PPO and SOD enzymes activities increased under salinity conditions. The highest activity of PPO and SOD was observed in 100 mM NaCl + 60 ppm NPs treatment. Simultaneous application of 100 mM NaCl + 90 ppm NPs increased the MDA content and DPPH radical scavenging activity compared to control plants. It can be concluded that the application of appropriate levels of NPs moderates the effect of salinity stress in D. moldavica L. and results in an increased amount of RA compared to control plants.

Functional analysis of walnut polyphenol oxidase gene (JrPPO1) in transgenic tobacco plants and PPO induction in response to walnut bacterial blight

AbstractWalnut (Juglans regia) is economically important for both its wood and nut nutritional value, but it is susceptible to diseases such as walnut bacterial blight, caused by Xanthomonas arboricola pv. juglandis (Xaj). Walnuts contain many phenolic compounds, providing a good model on which to study polyphenol oxidase (PPO). We inoculated the detached walnut fruits of cultivars Ford, Chandler, Franquette, Robert Livermore, and Payne with Xaj and measured the induction of PPO activity in infected sites and adjacent to infected sites. Compared to infected and uninfected sites, PPO activity was induced significantly in areas adjacent to infected sites in all cultivars except Ford. Ford and Franquette, presenting the lowest and highest PPO activity, showed the largest and smallest mean diameter spots in response to Xaj, respectively. Polyacrylamide gel electrophoresis confirmed monophenol oxidase activity of walnut PPO in the assessed tissues. Then, we revealed the antipathogenic potential of walnut PPO through Agrobacterium tumefaciens‐mediated walnut JrPPO1 gene transfer into tobacco (Nicotiana tabacum). Two transformed tobacco lines overexpressing the JrPPO1 gene were regenerated successfully and challenged with Pseudomonas syringae pv. tabaci. Transgenic lines showed significantly higher PPO activity and lower disease severity to the pathogen compared to the control. However, a significant difference in disease severity and PPO activity level was observed between the two transgenic lines. Our results demonstrate a potential defence‐related role of PPO in transgenic tobacco and its induction in areas adjacent to infection sites in walnut cultivars treated with Xaj.

Flesh browning development of ‘Empire’ apple during a shelf life period after 1-methylcyclopropene (1-MCP) treatment and controlled atmosphere storage

Little information is known about metabolism of flesh browning disorders in apples after removal of fruit from cold storage. ‘Empire’ apples develop a firm flesh browning, a physiological disorder that is assumed to be a chilling injury because it occurs usually at 0.5 °C; however, incidence is increased in fruit at warmer storage temperatures (2–3 °C) if fruit have been treated with 1-methylcyclopropene (1-MCP). In this study, fruit were untreated or treated with 1-MCP and stored in controlled atmospheres at 0.5 or 3 °C for 40 weeks, followed by a 10 d shelf life period at 20 °C. The greatest increase of internal ethylene concentration (IEC) and softening occurred in the fruit that had been stored at 3 °C without 1-MCP, and the lowest in fruit from 0.5 °C plus 1-MCP. Flesh browning was present in 1-MCP treated fruit and in fruit stored at 0.5 °C at the time of removal, and low in fruit stored at 3 °C. Incidence and severity of the disorder in 1-MCP treated fruit stored at 3 °C increased greatly during the shelf life period. Electrolyte leakage was higher in 1-MCP treated fruit stored at 0.5 °C than in the other treatments. Polyphenol oxidase (PPO) activity was higher in 1-MCP treated fruit regardless of storage temperature but peroxidase (POX) activity was higher in fruit that had been stored at 0.5 °C regardless of 1-MCP treatment. The highest POX activity was measured in the fruit that had been stored at 0.5 °C without 1-MCP treatment. Overall, browning development during the shelf life is associated with higher PPO activity in 1-MCP treated fruit and higher POX activity at the lower storage temperature.