Polyphenol Oxidase Activity Research Articles

Effects of baculovirus-killed cadavers on plant defenses and insect behavior

Baculoviruses are a group of entomopathogenic viruses that are important natural enemies of insects, particularly lepidopteran larvae. An important component of baculovirus transmission efficiency is the frequency with which hosts encounter patchily distributed virions on plants. Little is known about the ecology and bacterial composition of virus-killed cadavers. We used a baculovirus and host Trichoplusia ni caterpillars to study the effects of virus-killed cadavers on tomato plant defenses and T. ni behavior. We also compared bacterial communities associated with virus-killed and uninfected (freeze-killed) cadavers and found that there was no significant difference in community composition and membership between tomato-fed virus-killed or freeze-killed cadavers. Comparison of virus-killed cadavers from two separate experiments revealed significant differences in bacterial community composition, suggesting that host plant could play a more important role in shaping bacterial communities than virus infection status. Culture-dependent plating indicated that virus-killed cadavers had significantly higher bacterial titers compared with uninfected cadavers. We found that virus-killed cadavers suppressed polyphenol oxidase activity, an important plant defense protein, in mechanically damaged plants, but not in plants damaged by herbivory. Although cadavers did not influence plant defenses induced by feeding damage inflicted by healthy or infected T. ni, this study provides the first evidence that baculoviruses could influence plant defenses through host cadavers. When applied to intact plants, neither virus-killed or freeze-killed cadavers influenced T. ni oviposition, larval choice, or larval consumption, indicating these insects did not discriminate cadaver cues. Virus-killed cadavers could play important roles in mediating interactions between plants, herbivores, and other trophic levels, with potential implications for viral transmission dynamics.

Fortifying plant fortresses: siderophores in defense against Cercospora leaf spot disease in Vigna radiata L.

Siderophores, specialized iron-chelating molecules produced by Bacillus amyloliquefaciens D5, were investigated for their role in enhancing plant defense mechanisms against Cercospora canescens in mung bean (Vigna radiata L.). Siderophores were extracted and purified using Amberlite XAD-4 and applied to plants at concentrations of 5, 10, and 15 µg/mL, followed by pathogen inoculation. The treatments significantly influenced enzymatic activities and defense-related gene expression. On Day 6, peroxidase (POD) activity reached its highest value of 0.563 in the SP15 (siderophore + pathogen at 15 µg/mL) treatment, with S15 (siderophore-only at 15 µg/mL) showing a lower but significant increase of 0.453, while control groups remained unchanged. Polyphenol oxidase (PPO) activity peaked in SP15 (0.10 U/mL), followed by S15 (0.08 U/mL), highlighting the role of these treatments in enhancing stress responses. Chitinase activity was significantly elevated in SP15 on Day 6, with a sustained response through Day 8, while no significant change was observed in the control group. Total phenolic content was highest in SP15 (100 µg/mL), showing a a ramified immune response whereas S15 recorded 80 µg/mL, significantly above the control. Gene expression analysis further demonstrated the effectiveness of siderophore and siderophore + pathogen treatments. Catalase expression was upregulated by 21.1-fold in siderophore-only treatment and amplified to 25.9-fold in SP15. Epoxide hydrolase (EH) gene expression increased by 77.3-fold in S15 and further synergized to over 90-fold in SP15. Similarly, PR10 expression showed moderate upregulation in S15 and significantly higher levels in SP15, reflecting enhanced pathogen defense. Calmodulin (CAL) gene expression was moderately regulated in S15 but significantly amplified in SP15. These findings underscore the dual role of siderophores in nutrient acquisition and as potent elicitors of plant defenses, highlighting their potential as bio-stimulants. Field trials are essential to validate these results under natural conditions and optimize their use in agriculture.

Prediction of Pasta Colour Considering Traits Involved in Colour Expression of Durum Wheat Semolina

Colour plays an important role among the quality traits of durum wheat, attracting consumer attention for the pasta market. The traits involved in colour expression are affected by genotype, environment, and processing. In the present study, based on eighteen durum wheat genotypes grown in eight environments, the effects of different traits related to colour expression were evaluated. Carotenoid pigments, such as lutein and β-carotene content; yellow and brown indices; and lipoxygenase, peroxidase, and polyphenoloxidase activities were analysed in semolina. The effects of processing were evaluated by measuring both the content of carotenoid pigments and colorimetric indices in pasta. The genotype, the environment, and their interaction were significant for all traits, although with a strong prevalence of genotypic effects, except for the brown index. After processing, a decrease in carotenoid content and the yellow index (86.7% and 16.0%, respectively) was observed, while the brown index increased (8.2%). A multiple regression analysis was performed on semolina traits, and the yellow index emerged as the main predictor for pasta colour, strengthening this trait as a fast and reliable criterion of selection. A High-Performance Index tool was also used to identify the genotype and environment that better combine all traits, positively influencing colour expression. All this information can be used in durum wheat breeding programmes for the prediction of pasta colour.

Relevance of plant growth-promoting bacteria in reducing the severity of tomato wilt caused by Fusarium oxysporum f. sp. lycopersici by altering metabolites and related genes

Among the biotic stresses, wilt disease severely affects tomato quality and productivity globally. The causal organism of this disease is Fusarium oxysporum f. sp. lycopersici (Fol), which is very well known and has a significant impact on the productivity of other crops as well. Efforts have been made to investigate the effect of plant growth-promoting bacteria (PGPB) on alleviating tomato wilt disease. Four PGPB strains, such as Pseudomonas aeruginosa BHUPSB01 (T1), Pseudomonas putida BHUPSB04 (T2), Paenibacillus polymyxa BHUPSB16 (T3), and Bacillus cereus IESDJP-V4 (T4), were used as inocula to treat Fol-challenged plants. The results revealed that PGPB treatments T1, T2, T3, and T4 were able to decrease the severity of Fusarium wilt in the tomato plants at different levels. Among the treatments, T3 displayed the strongest protective effect, with the lowest disease frequency, which was 15.25%. There were no significant differences observed in parameters such as fruit yield and relative water content in the PGPB-inoculated plants, although T3 and T4 showed minimal electrolyte leakage. Significant changes in chlorophyll fluorescence were also recorded. A lower level of H2O2 and malondialdehyde (MDA) was observed in the T3 and T4 treatments. In addition, proline accumulation was highest in the T3-treated plants. Antioxidative enzyme activities, such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), significantly increased in the PGPB-treated plants. Furthermore, the highest phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activity was reported in the T3 and T4 plants, respectively. The PGPB-treated plants showed elevated expression of the PAL, PPO, PR3, PR2, SOD, CAT, and PO genes. This study’s results reveal that PGPB strains can be utilized as biocontrol agents (BCAs) to enhance tomato resistance against Fusarium wilt.

Biochar Application and Mowing Independently and Interactively Influence Soil Enzyme Activity and Carbon Sequestration in Karst and Red Soils in Southern China

Soil organic carbon (SOC), a critical component of the global carbon cycle, represents the largest terrestrial carbon reservoir, and is thus a major component of influencing climate regulation and ecosystem health. Grasslands store substantial carbon in their soils, but this carbon reservoir is easily degraded by both grazing and mowing, particularly in vulnerable karst landscapes. This study investigates the potential of biochar, a carbon-rich soil amendment, as a management tool to maintain SOC or mitigate the degradation of SOC during mowing in karst grasslands in Southern China, using both red acidic and calcareous soils as experimental variables. T SOC fractions, soil enzyme activities, and soil pH were measured to determine the effect of mowing and biochar application on carbon stability and microbial activity. Consistent with expectations, mowing increases belowground biomass and promotes carbon loss through increased microbial activity, particularly in calcareous soils where mowing also decreases soil pH, increasing acidity and reducing the stability of Ca–carbon complexes. Biochar, however, counteracted these effects, increasing both particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), especially in red soils where the addition of biochar greatly increased soil pH (from 5.4 to 6.33) (an effect not observed in the already-alkaline karst soils). Enzyme activities related to carbon degradation, such as β-D-Glucosidase and peroxidase, increased in biochar-amended soils (β-D-Glucosidase increased from 12.77 to 24.53 nmol/g/h and peroxidase increased from 1.1 to 2.36 mg/g/2h), each of which contribute to the degradation of carbon containing organic matter so that it may be ultimately stored in more recalcitrant forms. Mowing led to reduced polyphenol oxidase activity, but the presence of biochar mitigated these losses, protecting SOC pools (increased from 0.03 to 0.79 mg/g/2h). This study highlights biochar as an effective tool for enhancing SOC stability in karst grasslands, particularly in acidic soils, and suggests that integrating biochar into mowing regimes may optimize carbon sequestration while reducing fire risk. These findings offer valuable theoretical guidance for developing sustainable land management in sensitive ecosystems.

Heavy Metal Tolerance and Accumulation Potential of a Rare Coastal Species, Anthyllis vulneraria subsp. maritima

The aim of the present study was to explore heavy metal tolerance and accumulation potential in Anthyllis vulneraria subsp. maritima plants from coastal sand dunes in controlled conditions. Plants were established from seeds collected in coastal sand dunes and cultivated in substrates in greenhouse conditions. A gradual treatment with CdCl2, PbOAc, CuSO4, MnSO4, and ZnSO4 was performed until three final concentrations for each metal were reached. The number of leaves, their biomass, and biomass of roots were negatively affected by increasing concentrations of lead (Pb) and manganese (Mn) in substrate, but no negative effect was evident for cadmium (Cd), copper (Cu), and zinc (Zn). Visible effects of metal toxicity were evident for Pb-treated plants (appearance of thinner leaves, yellowing of older leaves), as well as for Mn-treated plants (reduced leaf size, curled leaves, red leaf venation). There was a significant decrease in water content in old leaves at high Pb and increasing Mn concentration, indicating accelerated leaf senescence. Increase in polyphenol oxidase activity in leaves was evident in all the plants treated with heavy metals. In contrast, an increase in peroxidase activity was evident only for plants treated with 50 and 100 mg L−1 Cd, 500 mg L−1 Pb, 200–1000 mg L−1 Mn, and 500 mg L−1 Zn. Metal accumulation potential for Cd and Cu was the highest in the roots, but for Pb, Mn, and Zn, more metal accumulated in old leaves. It can be concluded that A. vulneraria subsp. maritima plants are tolerant to high Cd, Cu, and Zn, but moderately susceptible to Pb and Mn. However, oxidative enzyme activity cannot be unequivocally used as a specific indicator of metal tolerance. In respect to phytoremediation potential, the plants have very good accumulation capacity for Pb, Mn, and Zn.

1-Methylcyclopropene Delays Browning and Maintains Aroma in Fresh-Cut Nectarines.

The color and aroma of nectarines experience adverse effects from cutting, resulting in the fast senescence of fruit tissue. Therefore, 1-methylcyclopropene (1-MCP) was used to treat postharvest nectarines before cutting, and its effect on the surface browning and aroma alteration were investigated. The results indicated that 1-MCP restrained the soluble quinone (SQC) accumulation in fresh-cut nectarines by regulating the peroxidase (POD) and polyphenol oxidase (PPO) activities and the metabolism of phenolic compounds. Compared with the control, 1-MCP pre-cutting treatment maintained the ultrastructural integrity of the cell wall in fresh-cut nectarines, which also showed reduced malondialdehyde (MDA) content and reactive oxygen species (ROS) and enhanced the 1,1-Diphenyl-2-Picrylhydrazyl (DPPH) radical scavenging activities. Electronic nose and GC-MS analysis revealed that the aroma profiles presented significant differences in the control and 1-MCP treatment during the storage at 0 °C for 10 days. The browning value of the 1-MCP pre-cutting treatment was 29.95% lower than the control, which prevented the loss of aroma on day 10. The fresh-cut nectarines could still maintain the characteristic flavor, while the flesh maintains its firmness. The 1-MCP pre-cutting treatment improves the sensory and aroma characteristics of fresh-cut fruits, which is beneficial to the preservation of fresh-cut fruits, improves transportation efficiency, and then improves the overall quality and market attractiveness of the fruit.

Effects of Shade Stress on the Synthesis of Cellulose and Lignin in Maize Nodal Roots

ABSTRACTLow solar radiation is an important factor affecting maize root growth and development. Roots have an anchoring function, and their important components are cellulose and lignin. Here, shade experiments were conducted using shade nets with 50% light transmittance (L50). The experiment was conducted in 2021 and 2022 using the ‘Xianyu 335’ maize variety under two nitrogen conditions (N1 = 180 kg ha−1 and N2 = 240 kg ha−1) to investigate the effect of shading on the structural carbohydrate content of maize nodal roots. The results showed that light had a highly significant effect on cellulose and lignin contents. Compared with normal light (L100), the cellulose content significantly decreased by 10.36%–13.87% and the lignin content significantly decreased by 12.96%–18.68% under shading (L50). Shading decreased the sucrose and soluble sugar contents and the cellulose and lignin‐related enzyme activities. The cellulose and lignin contents were significantly positively correlated with the sucrose content. The cellulose content at the silking (R1) stage was significantly positively correlated with the soluble sugar content and sucrose synthase (SS) and sucrose phosphate synthase activities at the 15th leaf (V15) stage; the lignin content at R1 was significantly positively correlated with the soluble sugar content and SS, acid invertase, tyrosine ammonia‐lyase, cinnamyl alcohol dehydrogenase, polyphenol oxidase and peroxidase activities at V15. Genes related to cellulose synthesis, including sucrose synthase (SS), cellulose synthase (CESA), cellulose synthase‐interactive protein 1 (CSI1), Chitinase‐Like1 (CTL1) and STELLO2 (STL2), were downregulated under shading, as were the lignin synthesis‐related phenylalanine/tyrosine ammonia‐lyase (PTAL), 4‐coumarate‐CoA ligase (4CL) and peroxidase (POD) genes. Auxin and jasmonic acid were significantly affected by light and decreased under shading, thereby reducing cellulose and lignin synthesis. These findings provide theoretical support for the development of appropriate maize cultivation practices under reduced solar radiation.

Inactivation of polyphenol oxidase and peroxidase activity in mangosteen pericarp via blanching: correlation between anthocyanins and enzyme activities

Inactivation of polyphenol oxidase and peroxidase activity in mangosteen pericarp via blanching: correlation between anthocyanins and enzyme activities

Chrysanthemum morifolium Ramat. as a traditional tea material: Unraveling the influence of kill-green process on drying characteristics, phytochemical compounds, and volatile profile

The dried capitulum of chrysanthemums is a traditional material in scented tea, and the kill-green process is a critical step in determining their quality. However, the changes in the physicochemical properties during kill-green and the mechanisms by which these changes affect drying characteristics, metabolic components, and aroma profiles remain unclear. Therefore, this study investigated the changes in water status, polyphenol oxidase and peroxidase activities, and microstructure during high-humidity air impingement kill-green (HHAIK) and steam kill-green (SK), and their effects on drying behavior, color, phytochemicals, and volatile profile of dried chrysanthemums. Results showed that the kill-green process increased the freedom degree of immobile water, reduced the relative content of free water, and induced microstructure alterations, thus enhancing the water diffusion and shortening the subsequent drying time by up to 46.15 %. Compared to SK, HHAIK more rapidly inactivated PPO and POD, causing an improved color profile of dried samples. Dried samples treated with HHAIK for 60 s exhibited higher retention of 9 individual phenolics, total sugar, amino acids, and volatile compounds, thus resulting in higher sensorial acceptance than those treated with SK for 60 s. This study offers theoretical insights and technical support for the future development of high-quality chrysanthemum products.

Histopathological and biochemical variations in resistant and susceptible black pepper cultivars infected with Meloidogyne incognita

Plant-parasitic nematodes cause yield losses ranging from 30 to 65% in black pepper. Root-knot nematodes are a bottleneck in production of black pepper in Kerala, India. Identifying resistant cultivars have gained attention, as they provide an eco-friendly alternative to chemical nematicides. This study aimed to identify a root-knot nematode-resistant black pepper cultivar and determine the biochemical and histopathological changes caused by the nematode. Twenty-six black pepper cultivars (10 KAU released, 2 wild and 14 local) were screened for nematode resistance under pot culture conditions. The local cultivar Koshinadan exhibited resistance to Meloidogyne incognita (gall index 2), while the hybrid variety Panniyur 1 showed high susceptibility (gall index 5). Analysis of the biochemical basis of resistance revealed enhanced level of phenol content and activity of peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase in leaves and roots of Koshinadan compared to susceptible cultivar, Panniyur 1. Histopathological studies of the most resistant (Koshinadan) and susceptible (Panniyur 1) cultivars revealed that giant cells formed near the vascular region at different inoculum levels (0, 100, 500, 1000, 5000, 10000 J2 pot-1). The number and size of giant cells were lower in Koshinadan compared to Panniyur 1 and complete disorganization of xylem and phloem vessels was observed in the susceptible Panniyur 1. The resistant cultivar identified can serve as rootstock for grafting high-yielding varieties, resulting in nematode free seedlings.

Involvement of endogenous IAA and ABA in the regulation of arbuscular mycorrhizal fungus on rooting of tea plant (Camellia sinensis L.) cuttings

BackgroundAdventitious root (AR) formation is the key step for successful cutting propagation of tea plants (Camellia sinensis L.). Studies showed that arbuscular mycorrhizal fungus (AMF) can promote the rooting ability, and auxin pathway in basal stem of cuttings was involved in this process. However, auxin and abscisic acid (another important regulator on AR formation) in the other parts of cuttings at different rooting stages responding to AMF inoculation are not well studied. Therefore, in this paper, contents, enzymes and genes related to these two plant hormones were comprehensively determined aiming to unveil how endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) involve in the AMF regulating AR development of tea cuttings.ResultsInoculating with AMF significantly increased the proportion of cuttings at S2 stage (AR formation), which was more than twice as much as the control. And the total rooting rate in mycorrhizal treatment was also higher than that in the control with an increase of 8.66%. Enzyme activity assays showed that except for decreased polyphenol oxidase (PPO) activity at the S3 stage and peroxidase (POD) activity in middle stem of S3 stage, AMF inoculation increased activities of POD, PPO, superoxide dismutase (SOD) and catalase (CAT) to varying degrees in leaf, middle stem and basal stem of tea cuttings. After inoculation with AMF, the indoleacetic acid oxidase (IAAO) activity decreased to a certain extent in the first three stages of tea cuttings, which showed a trend of ‘low-high-low’ in the basal stem of all treatments. Besides, there was a significantly positive correlation between SOD activity and AR formation, especially for the proportion of cuttings at S2 and S3 stages. Higher IAA level and IAA/ABA ratio was found in basal stem of cuttings at S1 stage induced by AMF, which promoting the AR formation as revealed by correlation analysis. At the same time, AMF significantly elevated the level of IAA in leaf at S1 stage. By screening differentially expressed genes (DEGs) related to IAA and ABA pathways, together with redundant analysis, it was indicated that auxin biosynthesis and transport, as well as ABA transport and signal transduction, were involved in AMF regulating the rooting of tea cuttings.ConclusionsOverall, both endogenous IAA and ABA played roles in the regulation of AR formation of tea cuttings by AMF inoculating, enriching the theoretical basis of AMF regulating rooting of cuttings and providing foundations for cutting propagation of tea plants.

Bacillus endophytes for sustainable management of tomato spotted wilt virus and yield production.

Tomato-spotted wilt virus (TSWV) from the Tospovirus genus affects over 1000 plant species, including key crops, and traditional control methods often prove inadequate. This study investigates the effectiveness of Bacillus amyloliquefaciens and Bacillus subtilis in reducing TSWV infection, enhancing plant growth, and strengthening defense in Nicotiana benthamiana. The aim is to assess Bacillus as a sustainable biocontrol alternative, offering an eco-friendly solution for managing TSWV disease in agriculture. Here, we report the efficacy of five Bacillus isolates (out of 15 tested) - B. amyloliquefaciens (DJB5, YN48, YN28, Mg6) and B. subtilis L1-21 - significantly reducing TSWV copies per gram in N. benthamiana leaves, using a half-leaf assay. In glasshouse trials, isolates DJB5, YN48, and Mg6 decreased TSWV copies per gram by 75.7%, 83.6%, and 88.2%, with biocontrol efficacy rates of 91.2%, 94.1%, and 95.7% respectively. All the isolates consistently mitigated the symptoms of TSWV, reduced the disease severity, and area under the disease progress curve (AUDPC) at 21 days post-inoculation. Additionally, these isolates enhanced plant growth parameters, including shoot and root length, leaf number, area, and biomass. The application of endophytes in the infected plants activated antioxidant defense enzymes by elevating the activities of polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), and chitinase. However, defense-related enzymes, such as malondialdehyde (MDA), catalase (CAT), phenylalanine ammonia-lyase (PAL), total phenol, and β-1,3-glucanase decreased as TSWV infection reduced in the leaves. Our findings indicate that B. amyloliquefaciens isolates, DJB5, YN48, and Mg6, effectively manage TSWV by activating plant defense, reducing virus load, reducing TSWV symptoms, and promoting plant growth. © 2024 Society of Chemical Industry.

Rhamnolipid Modified Silica Nanoparticles Control Rice Blast Disease by Enhancing Antifungal Activity In Vivo and Antioxidant Defense System of Rice (Oryza sativa L.).

Blast disease caused by Magnaporthe oryzae is a devastating disease that limits rice grain production. Here, we synthesized rhamnolipid (RL) modified silica nanoparticles (SiO2NPs) based on the excellent antimicrobial activity of RL against various phytopathogens and the role of SiO2NPs in alleviating plant diseases and investigated the roles and mechanisms of RL@SiO2NPs application in controlling rice blast disease. Two-week-old rice seedlings were sprayed with 100 mL/L of different materials before pathogen inoculation, and blast incidence was investigated 5 days after inoculation. The results showed that RL0.1@SiO2NPs were the most suitable mixture ratio in suppressing blast and enhanced plant resistance. Compared with the control, application of RL0.1@SiO2NPs significantly reduced rice blast disease incidence by 10.80% and the relative growth of fungus by 97.05% and increased the shoot dry biomass by 13.33%, which alleviated the infection pressure of rice blast fungus. Additionally, after RL0.1@SiO2NPs treatment, peroxidase, ascorbate peroxidase, and polyphenol oxidase activities in rice leaves were significantly increased by 47.02%, 34.26%, and 44.36%, respectively, the total phenolics content was significantly increased by 24.14%, and the malondialdehyde and hydrogen peroxide content was decreased by 5.28% and 14.58%, respectively. RL0.1@SiO2NPs also improved plant nutrient status and enhanced disease resistance of infected plants by restoring nutrient balance or ion homeostasis, including increased potassium concentration (23.84%) in leaves and Si concentration (60.34%) in roots and decreased magnesium (11.89%) and iron concentrations (30.55%) in rice leaves. In summary, our results suggest that RL0.1@SiO2NPs enhance rice plant resistance against blast by enhancing the antifungal activity in vivo, activating the antioxidant defense system, and affecting nutrient acquisition in rice seedlings. RL@SiO2NPs have shown potential application as green and efficient agricultural chemical substitutes in plant disease management.

Effect of oil and diesel fuel pollution on enzymatic activity of meadow chernozem-like soil

In the laboratory experiment, the effect of oil pollution on the short-term dynamics of the activity of urease, phosphatase, catalase, peroxidase and polyphenol oxidase of the chernozem soil of the south of the Far East was studied. It was found that when soil was contaminated with oil and petroleum products, urease activity decreased by 20–44% at the end of incubation, peroxidase activity increased by 39–49% in the middle and end of incubation, polyphenol oxidase activity increased 1.6–2.0 times in the middle of incubation. The activity of phosphatase and catalase was stable at different levels of contamination throughout the experiment. Examining the effect of the incubation period, it was found that the maximum activity of urease was on the 10th day, phosphatase – on the 20th, peroxidase – on the 20th and 30th, polyphenol oxidase – on the 30th day of the experiment. Catalase activity was stable throughout all incubation periods. It was shown that in the case of contamination of chernozem-like soil with oil and diesel fuel in doses up to 5000 mg/kg, inhibition of enzymatic activity did not occur in the early stages.

Cold atmospheric plasma inactivation of polyphenol oxidase: Focus on the protective and boosting effect of mono- and disaccharides.

Polyphenol oxidase (PPO) is among the most detrimental enzymes in processed plant foods, being responsible for enzymatic browning. To propose a "mild" alternative to traditional enzymatic inactivation methods, this study investigated the effect of cold atmospheric plasma (CAP) on PPO inactivation and highlighted the role of different sugars on both inactivation and structural modification of this enzyme. Different model systems were prepared in phosphate buffer using a purified PPO either alone or added with glucose, fructose, sucrose, and trehalose at different concentrations. CAP treatments (6KV; 23KHz; duty cycle 10%) were applied at times ranging from 5 to 30min. Different spectroscopic analyses were conducted before and after treatments to evaluate the PPO activity and changes in tertiary and secondary structures. CAP induced a significant reduction (p<0.05) in PPO activity across all systems, ranging from 70% to 94% after 30min of treatment. Among sugars, fructose enhanced (p<0.05) the PPO inactivation (+23% on average with respect to the phosphate buffer system), possibly by promoting the loss of secondary structures containing the copper-binding site of the catalytic pocket. The effect of other sugars on PPO inactivation was strictly dependent on their type and concentration; specifically, disaccharides at the highest concentrations and treatment times showed a protective effect on the structure and functionality of the protein. Thus, the results of this study highlight that sugars can modulate the effectiveness of CAP, offering promising perspectives for optimizing this food processing technology. PRACTICAL APPLICATION: Cold atmospheric plasma (CAP) is a promising nonthermal technology for food preservation. In particular, surface dielectric barrier discharge (SDBD) CAP could be applied as an alternative to chemical and thermal treatments to inactivate polyphenol oxidase (PPO), an enzyme responsible for browning reactions and quality loss in most processed fruit and vegetable products. However, as shown by this study, PPO inactivation induced by CAP is affected by sugars. Specifically, fructose can positively influence the inactivation of this enzyme. Therefore, CAP potentially could find main applications for the PPO stabilization of high fructose-content plants (e.g., pears, apples, bananas, grapes, peppers, and squashes).

Trichoderma longibrachiatum (T6) Peptaibols Inhibiting the Monilia yunnanensis Growth and Inducing Pear Fruit Resistance in Its Infection.

Pear fruit brown rot, caused by Monilia yunnanensis, affects pear fruit yields and quality. The present study determined Trichoderma longibrachiatum T6 (T6) peptaibols as a biological control alternative to synthetic fungicides and assessed its efficacy against M. yunnanensis through dual plate culture and surface spraying at different concentrations. T6 peptaibols effectively inhibited M. yunnanensis growth, achieving an 85.99% inhibitory rate at 1250 µg/mL after inoculation on PDA medium for 5 days, and 84.57% control efficacy on pear fruit with the same concentration at 6 days. Treatment with T6 peptaibols significantly decreased the average contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2), as well as electrolyte leakage, by 31.99%, 27.93%, and 21.00% from days 1 to 9 post-inoculation, respectively, in comparison to the negative control. Additionally, the average antioxidant enzyme activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) increased by 86.27%, 56.76%, 25.94%, and 47.88%, respectively; the average defense enzyme activities of phenylalanine ammonia-lyase (PAL), lipoxygenase (LOX), chitinase (CHI), and β-1,3-glucanase (β-Glu) increased by 63.00%, 55.70%, 26.19%, and 16.34%, respectively. Moreover, the expression levels of the antioxidant and defense-related genes (CAT, SOD, POD, PPO, CHI, LOX, PAL, β-Glu) were significantly upregulated by 2.80, 2.81, 3.03, 2.79, 3.37, 2.49, 2.73, and 1.83-folds at 3 days after inoculation compared to the negative control. Thus, T6 peptaibols effectively reduced the pathogen infection through growth inhibition and antioxidant defenses, thereby boosting fruit immunity.

How does fertilizer management strategy in soilless blueberry cultivation change the phytochemical profile and phenoloxidases activity during fruit ripening?

Highbush blueberry fruits have attracted a lot of attention from consumers due to their exquisite taste and considerable quantities of bioactive compounds. This premium-class foodstuff also contains antioxidant enzymes (phenoloxidases) implicated in the degradation of polyphenols that lead to discoloration and loss of antioxidant activity during fruit ripening. Despite substantial progress in research focused on fruit quality, unanswered questions remain about the effect of fertilizer strategy in soilless blueberry cultivation on the phytochemical content and phenoloxidases activities. Therefore, this study aimed to compare the individual effect of mineral fertilizers (Min treatment) and combined application of organic and mineral fertilizers (Org-Min treatment) the content of targeted primary and secondary metabolites, as well as phenoloxidases activities of blueberry cultivar 'Bluecrop' grown in pots. The sugar content and sweetness index were not affected by the fertilizer treatment, while the predominant organic acids content (citrate and malate) increased significantly by the Org-Min treatment in both years studied. The Org-Min treatment also stimulated the synthesis of phenolic acids, primarily chlorogenic and p-coumaric acid, while the Min treatment contributed to significant increase in polyphenol oxidase (PPO) activity in both years of the study. The Org-Min treatment in annual amounts of 72 kg ha-1 nitrogen, 48 kg ha-1 phosphorus, and 68 kg ha-1 potassium had the most pronounced positive effect on the content of phenolic bioactives, which indicates that a partial replacement of mineral by organic fertilizers can be recommended in soilless cultivation of blueberries. © 2024 Society of Chemical Industry.

Biocontrol potential of natamycin-producing Streptomyces lydicus JCK-6019 against soil-borne fungal diseases of cucumber and characterization of its biocontrol mechanism.

Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani AG-4 are the two most important fungal pathogens causing soil-borne fungal diseases of cucumber; they are difficult to control and cause serious economic losses. Given the detrimental effects of the indiscriminate use of chemical fungicides, biocontrol emerges as an efficient and ecofriendly alternative for managing soil-borne fungal diseases. Streptomyces lydicus JCK-6019 (hereafter, JCK-6019) was isolated from rhizosphere soil. Its fermentation filtrate and volatile organic compounds exhibited broad-spectrum antifungal activity against various phytopathogenic fungi and oomycetes. JCK-6019 produced natamycin as an agar-diffusible antifungal metabolite. It also produced indole-3-acetic acid and various hydrolytic enzymes. In vivo experiments revealed that a ten-fold-diluted optimized JCK-6019 fermentation broth exhibited 100% control efficiency against cucumber damping-off disease and 62.5% control efficiency against cucumber Fusarium wilt disease. Pretreatment of cucumber seedlings with 1000-fold-diluted optimized JCK-6019 fermentation broth resulted in 68.18% and 23.91% disease control values against cucumber damping-off and Fusarium wilt disease, respectively. Moreover, peroxidase activity in cucumbers after 1 day of treatment was 1.5-fold higher than that in the control. Similarly, polyphenol oxidase activity in cucumbers after 3 days of treatment was 2.34-fold higher than that in the control, indicating that JCK-6019 can induce plant resistance. The natamycin-producing strain JCK-6019 could effectively suppress the development of cucumber Fusarium wilt and damping-off disease by inducing plant resistance and producing antifungal metabolites, including natamycin and volatile organic compounds. Thus, JCK-6019 possesses high potential for application in the development of biocontrol agents against soil-borne fungal diseases of cucumber. © 2024 Society of Chemical Industry.

Drought intensity–responsive changes in photosynthesis‐related proteins, carbohydrate pools and forage quality in Kentucky bluegrass (Poa pratensis L.)

AbstractDrought is a major factor affecting annual forage production and quality. The present study aimed to characterize drought stress–responsive changes in carbohydrate composition and forage quality–related parameters as being linked to the responses of physiological parameters during the regrowth of Kentucky bluegrass (Poa pratensis L.). Drought treatment gradually decreased leaf water potential (Ψw) to a minimum value of −2.94 MPa at day 46. Drought‐responsive increases in H2O2 concentration and lipid peroxidation were significant from day 22 (Ψw = −1.38 MPa), accompanied by the decreased chlorophyll content. Drought stress repressed Rubisco large subunit and several thylakoid membrane protein complexes (PSI, PSII dimer, PSII monomer and cytochrome b6/f). Drought also increased glucose, fructose and sucrose concentrations from day 22. A distinct increase in monosaccharides and disaccharides coincided with a reduction of fructan, especially from day 36 onward, when the enzymatic activity of fructan exohydrolases (1‐FEH and 6‐FEH) became greatly enhanced. Significant changes in forage nutritional parameters also occurred from day 36 (Ψw = −2.74 MPa), as shown by increases in neutral detergent fiber, acid detergent fiber (ADF) and ADF‐lignin with enhanced activity of polyphenol oxidase, as well as a decrease in crude protein content. These drought‐responsive changes in nutritional parameters were strongly correlated with a decrease in in vitro dry matter digestibility (IVDMD). A correlation analysis revealed that drought‐induced accumulation of H2O2 along with decreasing Ψw was closely associated with increases in fiber compounds and ADF‐lignin leading to a decrease in IVDMD. Our results indicate that drought‐responsive reductions in forage quality mainly occurred under severe drought stress (day 36 to day 46, Ψw ≤ −2.74), when H2O2 accumulation and lipid peroxidation were high, were characterized by an accompanied increase in ADF.