Higher Peroxidase Levels Research Articles

Genotype-specificity in putative competitive endophytes modulated by root exudation of rice

The putative competitive endophytic bacteria with plant-growth-promoting attributes could be potential bio inputs to enhance agricultural sustainability. These special rhizosphere colonizing bacteria possess distinct strategies to enter and colonize the host plant asymptomatically and offer several plant growth-promoting benefits. However, the molecular interaction between the endophyte and host plant remains unclear in many crop spheres. In this study, we categorize putative endophytes in rice into two groups—common endophytes and genotype-specific endophytes—based on their ability to colonize alternative hosts. The putative competitive endophytes of rice landrace Norungan and high-yielding cultivar Co51 were cross-inoculated with each other under gnotobiotic conditions and attempted to re-isolate from the inoculated plants. Two Norungan endophytes (Priestia endophytica NE14 and NE21) and one Co51-endophyte (Peribacillus endoradicis CE10) could not colonize the internal tissues of the alternate hosts, and they were considered as genotype-specific endophytes. In contrast, the rest of the strains could colonize both genotypes (common endophytes). The bait trap assay with flow cytometry revealed that the Norungan root exudate significantly enhanced the chemotactic movement of NE14 and NE21 compared to Co51-endophyte (CE10) and common endophytes (NE09 and CE07). Likewise, the Co51-root exudate triggered high levels of chemotaxis of CE10 but not the others. The root exudates did not alter the growth and biofilm-producing capability of genotype-specific and common endophytes. The cell wall degrading enzyme, pectinase of genotype-specific endophytes (NE14 and NE21), had positively enhanced due to Norungan root exudate but not with Co51 exudate. When the genotype-specific endophytes were inoculated to alternate host, a strain-level difference was observed in the induction of rice defense enzymes. NE14 inoculation in Co51 rice had high levels of peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, and glutathione reductase; NE21 induced high levels of glutathione reductase and peroxidase alone in Co51. Likewise, CE10 triggered relatively high levels of catalase, glutathione reductase, peroxidase, and polyphenol oxidase in Norungan rice. No apparent difference between the two rice genotypes in defense enzymes’ levels was observed due to common endophytes (NE09 and CE07). These results authenticate the occurrence of genotype-specific putative competitive endophytes in rice, and exploring them for crop growth and yield would be a better choice for rice sustainability.

Potential role of root-associated bacterial communities in adjustments of desert plant physiology to osmotic stress

Plants possess the ability to adapt to osmotic stress by adjusting their physiology and morphology and by cooperating with their root-associated (rhizosphere and endosphere) microbial communities. However, the coordination of host self-regulation with root-associated microorganisms at the community level, especially for desert plants, remains unclear. This study investigated the morphophysiological responses of seedlings from the desert plant Alhagi sparsifolia Shap to osmotic stress, as well as the relationships between these adaptations and their root-associated bacterial communities. The results indicated that osmotic stress contributed to a reduction in height and increased levels of reactive oxygen species (ROS) and malondialdehyde (MDA). In response, A. sparsifolia exhibited a series of morphophysiological adjustments, including increased ratio of root to shoot biomass (R/S) and the number of root tip, enhanced vitality, high levels of peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), as well as osmolytes (proline, soluble protein, and soluble sugar) and modification in phytohormones (abscisic acid (ABA) and jasmonic acid (JA)). Additionally, osmotic stress resulted in alterations in the compositions and co-occurrence patterns of root-associated bacterial communities, but not α-diversity (Chao1). Specifically, the rhizosphere Actinobacteria phylum was significantly increased by osmotic stress. These shifts in root-associated bacterial communities were significantly correlated with the host's adaptation to osmotic stress. Overall, the findings revealed that osmotic stress, in addition to its impacts on plant physiology, resulted in a restructuring of root-associated microbial communities and suggested that the concomitant adjustment in plant microbiota may potentially contribute to the survival of desert plants under extreme environmental stress.

Inhibition activity of tomato endophyte Bacillus velezensis FQ-G3 against postharvest Botrytis cinerea.

Grey mold, caused by Botrytis cinerea, is a widespread and harmful disease of tomato. Biocontrol agents derived from endophytic bacteria are known to hold great potential for inhibition of phytopathogen. We conducted this study to explore the tomato endophytic strains with inhibition activity against B. cinerea. Endophytic strain Bacillus velezensis FQ-G3 exhibited excellent inhibition activity against B. cinerea. Inhibitory effects against B. cinerea were investigated both in vitro and in vivo. The in vitro assays displayed that FQ-G3 could significantly inhibit mycelia growth with inhibition rate of 85.93%, and delay conidia germination of B. cinerea. Tomato fruit inoculated with B. velezensis FQ-G3 revealed lower grey mold during treatment. The antifungal activity was attributed to activation of defense-related enzymes, as evidenced by the higher levels of peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase in tomatoes after inoculation. In addition, scanning electron microscope was applied to elucidate the interaction between endophytes and pathogen, and bacterial colonization and antibiosis appeared to be the underlying mechanisms that FQ-G3 could suppress growth of B. cinerea. Collectively, our present results suggested that FQ-G3 may potentially be useful as a biocontrol agent in postharvest tomatoes.

Genetics of novel leaf curl virus disease resistant pepper genotypes and antioxidative profile analysis of their progenies

Pepper/Chilli leaf curl virus disease (PepLCVD/ChiLCVD) is the most destructive disease of pepper that seriously reduced pepper production. The LCVD is transmitted by vector whitefly (Bemisia tabaci) so efficiently that even single whitefly is able to transmit the virus. The effective way to manage the LCVD in pepper is to introduce LCVD resistance into agronomically desired cultivars, but the lack of resistant sources is a major hurdle in this technique. So with this objective, we identified new resistant sources against LCVD using astringent artificial screening techniques. The genetics of these new sources was confirmed using artificial inoculation methods on parental lines and their progenies that developed by using susceptible bell pepper genotype PAU SM-1. The progenies of crosses S-343 and SL 475 with susceptible genotype reveal monogenic dominant control of LCVD resistance while progenies of crosses SL 492 and JL 282 reveal monogenic recessive gene control for LCVD resistance. Moreover, antioxidative and biochemical parameter analysis demonstrate high levels of peroxidase (PO), polyphenol oxidase (PPO), ascorbate peroxidase (APX), phenylalanine ammonia-lyase (PAL), tyrosine ammonia lyase (TAL) and superoxide dismutase (SOD) and phenolic compounds in leaves of resistant plants than susceptible plants. Furthermore, all the studied traits and treatments were subjected to principal component analysis (PCA), correlation, and clustering analysis. The first three PCA components describe 70.55% variation for both studied traits and treatments. Hence, the newly identified sources could be further used for resistant breeding programs, and their antioxidative profile data could be used as biochemical markers for studying further plant-virus interactions.

The Endophytic Strain ZS-3 Enhances Salt Tolerance in Arabidopsis thaliana by Regulating Photosynthesis, Osmotic Stress, and Ion Homeostasis and Inducing Systemic Tolerance.

Soil salinity is one of the main factors limiting agricultural development worldwide and has an adverse effect on plant growth and yield. To date, plant growth-promoting rhizobacteria (PGPR) are considered to be one of the most promising eco-friendly strategies for improving saline soils. The bacterium Bacillus megaterium ZS-3 is an excellent PGPR strain that induces growth promotion as well as biotic stress resistance and tolerance to abiotic stress in a broad range of host plants. In this study, the potential mechanisms of protection against salinity stress by B. megaterium ZS-3 in Arabidopsis thaliana were explored. Regulation by ZS-3 improved growth in A. thaliana under severe saline conditions. The results showed that ZS-3 treatment significantly increased the biomass, chlorophyll content and carotenoid content of A. thaliana. Compared to the control, the leaf area and total fresh weight of plants inoculated with ZS-3 increased by 245% and 271%, respectively; the chlorophyll a, chlorophyll b, and carotenoid contents increased by 335%, 146%, and 372%, respectively, under salt stress. Physiological and biochemical tests showed that ZS-3 regulated the content of osmotic substances in plants under salt stress. Compared to the control, the soluble sugar content of the ZS-3-treated group was significantly increased by 288%, while the proline content was significantly reduced by 41.43%. Quantification of Na+ and K+ contents showed that ZS-3 treatment significantly reduced Na+ accumulation and increased the K+/Na+ ratio in plants. ZS-3 also isolated Na+ in vesicles by upregulating NHX1 and AVP1 expression while limiting Na+ uptake by downregulating HKT1, which protected against Na+ toxicity. Higher levels of peroxidase and catalase activity and reduced glutathione were detected in plants inoculated with ZS-3 compared to those in uninoculated plants. In addition, it was revealed that ZS-3 activates salicylic acid (NPR1 and PR1) and jasmonic acid/ethylene (AOS, LOX2, PDF1.2, and ERF1) signaling pathways to induce systemic tolerance, thereby inducing salt tolerance in plants. In conclusion, the results of this study indicate that ZS-3 has the potential to act as an environmentally friendly salt tolerance inducer that can promote plant growth in salt-stressed environments.

Resistance of Cowpea Genotypes to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Its Relationship to Resistance-Related Enzymes.

Spodoptera frugiperda (J.E. Smith) can attack cowpea plants (Vigna unguiculata [L.] Walp.) (Fabales: Fabaceae) in any growth stage but attacks primarily in the first days after plant emergence, when the plants are more sensitive to defoliation. This study was carried out to evaluate the resistance to S. frugiperda in six cowpea genotypes, of which four were cultivars (BRS Tapahium, BRS Tumucumaque, Fradinho, and Miranda), and two were landraces (Juti and Nioaque), in three different experiments. In the first experiment, adult emergence, adult weight, adult longevity, larva to adult period, numbers of injured leaves per plant canopy (upper, middle, and lower), and reduction in plant dry matter were assessed. In the second experiment, the oviposition preference of S. frugiperda for the different cowpea genotypes was evaluated under free-choice conditions. In the third experiment, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in cowpea leaves were assessed. Insects fed on landrace Juti plants showed low adult emergence, yielded a lower fitness index, and caused less plant dry matter reduction. In addition, plants of landrace Juti were less preferred for oviposition. Overall, Juti plants showed higher resistance levels in all three resistance categories and higher levels of POD and SOD in S. frugiperda injured leaves, in addition to a lower protein content. Juti will be tested in field conditions, followed by molecular characterization. This will provide additional information about its potential as an S. frugiperda resistance source in plant breeding programs.

Neutrophil activation identifies patients with active polyarticular gout

BackgroundGout is the most prevalent inflammatory arthritis in developed countries. A gout flare is mediated by phagocytosis of monosodium urate crystals by macrophages and neutrophils leading to subsequent activation of neutrophils contributing to synovitis, local joint destruction, and systemic inflammation. We hypothesize that biomarkers from activated neutrophils reflect gout disease activity.The objective of this study therefore was to investigate the clinical utility of neutrophil-derived biomarkers in gout disease activity.MethodsPlasma samples from 75 gout patients participating in the “Reade gout cohort Amsterdam” were compared with 30 healthy controls (HC). Levels of neutrophil extracellular traps (NETs) and neutrophil activation markers (calprotectin and peroxidase activity) were analyzed by ELISA and fluorimetry, compared to healthy controls, and related to markers of inflammation and disease activity.ResultsLevels of NETs, as well as neutrophil activation markers, were increased in gout patients compared to HC (p < 0.01). No associations were found between markers of cell death (cell-free DNA and NETs) and disease activity. Cell-free levels of genomic DNA were elevated among gout patients compared to HC (p < 0.05) and related to the number of gout attacks in the last year (β = 0.35, p < 0.01). Peroxidase activity correlated with disease activity (RAPID score: β = 0.49, p < 0.01, MHAQ: β = 0.66, p < 0.01) and inflammation markers (CRP: β = 0.25, p = 0.04, and ESR: β = 0.57, p < 0.001). Involvement of ankle or wrist resulted in significant higher peroxidase levels compared to mono-articular disease (β = 0.34, p < 0.01), indicating that peroxidase activity is a marker of poly-articular gout. Calprotectin (S100A8/A9) correlated with the inflammation marker CRP (β = 0.23, p = 0.05) and morning stiffness, especially in patients with chronic poly-articular gout (β = 0.71, p < 0.01).ConclusionsNeutrophil activation markers are associated with characteristics of active, polyarticular gout. Furthermore, NETs are present in the peripheral blood of gout patients. However, NETs do not associate with markers of disease activity or inflammation. Future research should point out if peroxidase and calprotectin could be used in clinical practice as biomarkers for monitoring gout disease activity.

Induction of resistance in grapevines against powdery mildew by Bacillus strains

Table grape cultivars are highly susceptible to powdery mildew disease and frequent use of single site action fungicides has led to the development of fungicide resistance in the pathogen and detection of fungicide residues in grapes at harvest. A systematic study was conducted to identify bacteria which can induce resistance in grapevines against the powdery mildew. Two hundred and ninety three bacteria from the grapevine ecosystem were screened in vitro for their growth promoting activities. The twenty two positive isolates, identified as Bacillus species were further screened in vivo for their ability to reduce disease severity and eleven promising isolates which reduced disease severity by 35 per cent or more were identified. These Bacillus species induced higher levels of peroxidase, polyphenol oxidase, total phenols and total proteins in leaves of treated plants and also tested positive for IAA, NH3, HCN and siderophore production, which are implicated in plant growth promotion. The most promising of these, TS-45, DR-92, TL-171, and TP-232 were evaluated, alone or in binary combination, on field grown grapevines for three consecutive seasons during 2015 to 2017. All treatments reduced the powdery mildew severity as compared to the control in all the three trials. Combined applications, of TP-232+TL-171 and TS-45+DR-92 were more effective. Treated vines showed higher level of chitinase, β 1,3-glucanase, peroxidase and polyphenol oxidase activities. In morphological and 16S rDNA gene analysis, isolates TS-45, DR-92, TL-171, and TP-232 showed close homology to Bacillus subtilis, B. endophyticus, B. licheniformis and B. flexus, respectively. This study has shown that soil application of selected efficient Bacillus species can enhance grapevine resistance to powdery mildew disease.

The combined effect of ozone treatment and polyethylene packaging on postharvest quality and biodiversity of Toona sinensis (A.Juss.) M.Roem

The young leaves and sprouts of the Toona sinensis (TS) are nutritious and popular in Asia, however they are highly perishable and, thus, have a short shelf life, which impacts negatively on their market performance. This study investigated the effects of ozone (OZ) and polyethylene (PE) treatments on the postharvest quality of TS during near-freezing temperature storage. The results revealed that TS subjected to OZ + PE treatment had higher levels of peroxidase, superoxidase dismutase, catalase, thiophenes, CIS, TRANS, malondialdehyde and hue angle, and lower levels of weight loss, respiration rate, ethylene production rate, total chlorophyll content, vitamin C, total plate count, coliforms, yeast and mold, and polyphenol oxidase compared to the control (CK) and PE treatments. In the next-generation sequencing analysis of TS biodiversity, microbial communities of TS treated with OZ +PE were found to differ significantly from those treated with CK and PE. The combination treatment inhibited most order bacteria, however, the fungal communities present in TS, such as orders of Dothideales, Agaricales, Erysiphales and Filobasidiales, proved resistant to OZ treatments. The results of the principal components analysis and co-occurrence network patterns further confirmed that OZ, used in combination with PE, could improve postharvest quality and extended the shelf life of TS.

Root Activity and Antioxidant Enzyme Activities of Rice Cultivars under Different Iron Toxicity Mitigation Options

Iron (Fe) toxicity is a widespread environmental problem of rice growing area in many parts of the world. Amendments and genotypes can be used to mitigate the Fe toxicity. Several strategies may be adopted by higher plants to cope up with high levels of soluble Fe in their environment. A field experiment was carried out in acidic laterite soil having 400 mg kg−1 di-ethylene tri-amine-penta-acetic acid extractable Fe (DTPA-Fe) to assess the root activity and antioxidant enzyme activities of rice cultivars under different soil management options in Fe toxic soil. The treatments comprised of four cultivars (two each tolerant and susceptible) and six amendments. The amendments resulted into the increase in soil pH as compared to the control, which helps in mitigation of Fe toxicity. Tolerant cultivars recorded significantly higher rice root oxidation and Fe plaque deposition as compared to sensitive cultivars under all the soil management treatments. Cultivars also differed significantly in the amount of Fe plaque on the roots under control. Iron concentration in the roots showed a reverse trend as compared to Fe oxidation and Fe plaque for all the cultivars and soil management treatments. Under high toxic Fe level (control), due to high activity of peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) mechanisms of antioxidative defense were more active for tolerant cultivars as compared to susceptible cultivars. The effect of defense mechanism of the tolerant cultivars is manifested in yield and under control condition, higher yield were reported for tolerant cultivars as compared to susceptible. Lime application is the most effective way to overcome the Fe toxicity, which increased the yield of both the tolerant and susceptible rice cultivars. Rice roots plays important role in alleviating the Fe toxicity by oxidizing the Fe2+ and excluding its uptake. Iron resistance of the tolerant cultivars is also attributed to the comparatively high levels of POD, CAT, and SOD activities in the leaf tissues. The differential response of the cultivars to the Fe-toxicity is due to differential ability of Fe compartmentation, root oxidation power and ability of cultivars to produce antioxidative stress enzymes. The mechanisms of Fe toxicity tolerance both in plant and soil are result of combined effect of genetics of the crop plant and management interventions.

Comparative analysis of the humoral immunity of skin mucus from several marine teleost fish

Fish skin mucus contains several immune substances that provide the first line of defence against a broad spectrum of pathogens although they are poorly studied to date. Terminal carbohydrate composition and levels of total IgM antibodies, several immune-related enzymes (lysozyme, peroxidase, alkaline phosphatase, esterases, proteases and antiproteases) as well as the bactericidal activity (against fish pathogenic Vibrio harveyi, Vibrio angillarum, Photobacterium damselae and non-pathogenic bacteria Escherichia coli, Bacillus subtilis, Shewanella putrefaciens) were identified and measured in the skin mucus of five marine teleosts: gilthead seabream (Sparus aurata), European sea bass (Dicentrarchus labrax), shi drum (Umbrina cirrosa), common dentex (Dentex dentex) and dusky grouper (Epinephelus marginatus). First, lectin binding results suggests that skin mucus contain, in order of abundance, N-acetylneuraminic acid, glucose, N-acetyl-glucosamine, N-acetyl-galactosamine, galactose and fucose residues. Second, results showed that while some immune activities were very similar in the studied fish (e.g. IgM and lysozyme activity) other such as protease, antiprotease, alkaline phosphatase, esterase and peroxidase activities varied depending on the fish species. High levels of peroxidase and protease activity were found in U. cirrosa respect to the values obtained in the other species while E. marginatus and S. aurata showed the highest levels of alkaline phosphatase and esterase activities, respectively. Moreover, skin mucus of S. aurata revealed higher bactericidal activity against pathogenic bacteria, contrarily, to what happened with non-pathogenic bacteria (E. coli, B. subtilis). Thus, study of the variations in the carbohydrate profile and immune-related components of the fish skin mucus could help to understand the fish resistance as well as the presence and distribution of pathogens and magnitude of infections, aspects that are of major importance for the aquaculture industry.

Different eco-physiological responses between male and female Populus deltoides clones to waterlogging stress

Sex-related variations in response to waterlogging stress between male clones ( Populus deltoides CL. ‘Juba’) and female clones ( P. deltoides CL. ‘Danhong’) in a semi-controlled environment were investigated. All tested plants survived after a ten-week waterlogging treatment with 5 cm of water above the soil surface. This suggests that the two clones belonged to waterlogging-tolerant species, so that they can be applied in the construction of riparian protection forests and the restoration of wetlands. Compared with well-watered treatment, waterlogging treatment significantly decreased shoot height, stem diameter, leaf number, mean leaf area, total leaf area, relative water content (RWC), specific leaf area (SLA), total chlorophyll concentration (chlorophyll a + b, TC), carotenoids (Caro), net photosynthetic rate ( A), stomatal conductance ( gs), instantaneous water use efficiency (WUEi), maximum efficiency of PSII ( F v/ F m), maximum effective quantum yield of PSII (Yield), and soluble sugar content and significantly increased levels of superoxide anion radical ( O 2 - ), hydrogen peroxide (H 2O 2), proline, reducing sugar, peroxidase (POD) activity, and superoxide dismutase (SOD) activity. The effects of waterlogging on chlorophyll a/chlorophyll b ratio, TC/Caro ratio, intercellular CO 2 concentration ( Ci), transpiration ( E), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were not significant. In well-watered conditions, females had significantly faster growth rate and higher TC, Caro, and A than males. In contrast, males exhibited higher values of RWC and WUEi; less reductions in SLA, TC, Caro, and A; higher levels of POD and SOD activities; higher proline and reducing sugar contents; and lower O 2 - and H 2O 2 levels than females under waterlogging conditions. Findings indicate that males have better cellular defense mechanisms against damage caused by waterlogging stress than females, whereas females were more responsive to waterlogging stress than males.

Ligninolytic enzymes production and Remazol brilliant blue R decolorization by tropical brazilian basidiomycetes fungi

Remazol Brilliant Blue R (RBBR) dye was used as substrate to evaluate ligninolytic activity in 125 basidiomycetous fungi isolated from tropical ecosystems. The extracellular RBBR decolorizing activity produced when selected fungi were grown in solid media and in soil contaminated with organochlorines was also evaluated. A total of 106 fungi decolorized the RBBR during the growth in malt extract agar (MEA, 2%); 96 fungi showed a mycelia growth and decolorization activity stronger than the P. chrysosporium used as reference. Extracellular extracts of 35 selected fungi grown on solid medium with sugar cane bagasse (BGS) were evaluated for RBBR decolorization and peroxidase activity. All fungi showed peroxidase activities, but 5 of those were unable to decolorize the RBBR. Different patterns of ligninolytic enzymes were detected in 12 fungi extracts. Mn-dependent peroxidase (MnP) was produced by Peniophora cinerea, Psilocybe castanella, three strains of Trametes villosa, T. versicolor, Melanoporia nigra and Trichaptum byssogenum. All 12 fungi had laccase activity. Trogia buccinalis showed the highest RBBR decolorization and did not produce MnP activity. RBBR decolorization without MnP production was also observed for three strains of Lentinum tested. Higher levels of peroxidase and laccase cannot be related to high RBBR decolorization. RBBR decolorization by extracellular extract was also detected during the growth of P. castanella, L. crinitus, P. cinerea and two strains of T. Villosa in pentachlorophenol- and hexachlorobenzene-contaminated soils. These fungi showed higher RBBR decolorization when grown in the presence of organochlorine compounds than when in non contaminated soil.

Peroxidase production from hairy root cultures of red beet (Beta vulgaris)

The genetically transformed roots of red beet have been shown, for the first time, to produce very high levels of peroxidase (POD; EC 1.11.1.7) accounting for 1.21 x 10 6 Units L -1 . Of the ten clones established using different strains of Agrobacterium rhizogenes , one was that from the strain LMG-150, three each from A 2/83, A 20/83 and A4. All the clones showed true integration of T-DNA when tested by PCR and Southern hybridization methods. Each clone differed significantly from the others in growth, hormone dependency and POD production where LMG-150 produced highest biomass (140 g FW L -1 ) as well as POD (ranging from 8000-9000 U g -1 FW and 1.18 x 10 6 U L -1 with a specific activity of 600 U mg -1 protein) on hormone-free medium, both in shake-flask as well as in bioreactor with a further enhancement to 1.21 x 10 6 U L -1 upon the addition of extra calcium chloride (5 mM). PAGE with active staining showed 4 distinct bands of R m 0.06, 0.16, 0.25, 0.38 and 0.46 in the biomass and bands at R m 0.06, 0.16, 0.25 and one extra band of R m 0.575 in the spent medium where isozymes of R m 0.38 and 0.46 were totally absent. The pH optima and other properties were grossly comparable with the standard horse-radish POD (HRP) with better thermal stability than HRP and therefore, the present source appears to offer a cheaper and additional alternative for the commercial production of POD.

Involvement of a novel peroxidase isozyme and lignification in hydathodes in resistance to black rot disease in cabbage

The physiological mechanisms associated with resistance of cabbage to black rot disease seem to be associated with the hydathodes. To investigate the role of hydathodes in disease resistance, total peroxidase activities, anionic peroxidase isozyme expression, and lignin deposition were determined in hydathodes of resistant (Hancock and Green Cup), partially resistant (Cheers), and susceptible (Strukton and Perfect Ball) cabbage varieties (Brassica oleracea L.) during pathogenesis with Xanthomonas campestris pv. campestris. Four-week-old plants were petiole-inoculated with a highly virulent strain of X. campestris pv. campestris (FD91L). Hydathodal fluids were collected daily over a 14-day period from infected plants as well as noninfected, mock-inoculated control plants. Hydathodal fluids of resistant varieties had greater peroxidase activity when compared to susceptible ones, with infected plants having higher peroxidase levels than noninfected plants. Isoelectric focusing revealed the presence of four anionic peroxidase isozymes in hydathodal fluids, with the most anionic one (pI of 3.6) accumulating only upon infection. Lignin deposition in and around the hydathodes was associated with the accumulation of this particular isozyme in hydathodal fluids. The evidence suggests that a rapid, systemic response is associated with resistance to the bacterial pathogen.Key words: peroxidases, hydathodes, isozymes, black rot disease, cabbage, Xanthomonas campestris pv. campestris.

Expression of theShpx2peroxidase gene ofStylosanthes humilisin transgenic tobacco leads to enhanced resistance toPhytophthora parasiticapv.nicotianaeandCercospora nicotianae

Abstract Previous research indicated that the constitutive expression of a pathogen-inducible peroxidase gene (Shpx6a) from Stylosanthes humilis in transgenic plants resulted in enhanced resistance to fungal pathogens ( Kazan, K., Goulter, K.C., Way, H.M. and Manners, J.M. (1998) Expression of a pathogenesis-related peroxidase of Stylosanthes humilis in transgenic tobacco and canola and its effect on disease development. Plant Sci. 136, 207-217). We have now investigated another pathogen-inducible peroxidase gene of S. humilis, termed Shpx2, which is highly divergent from Shpx6a. Constitutive expression of the Shpx2 cDNA was obtained in tobacco using the 35S CaMV promoter, and up to a 12-fold increase in total peroxidase activity was observed in the leaves of transgenic plants compared to nontransgenic controls. Disease development was evaluated after inoculations in T(1) and T(2) transgenic lines expressing Shpx2. Lesion expansion was significantly (P < 0.05) reduced by up to 25% and 50% on leaves and stems, respectively, of transgenic plants expressing high levels of peroxidase compared to nontransgenic controls, following inoculation with Phytophthora parasitica pv. nicotianae, the cause of black shank disease. In addition, plant survival and recovery were greatly enhanced in transgenic plants following stem inoculations of plants with this plant pathogen. A significant (55%, P < 0.05) reduction in lesion number was observed in transgenic plants with high levels of peroxidase activity following inoculation with the fungus Cercospora nicotianae, the cause of frog-eye disease. No significant differences in disease development were observed between the lines expressing Shpx2 and controls following inoculation with the bacterium Pseudomonas syringae pv. tabaci, the cause of wildfire disease. These results provide evidence for a role for this peroxidase gene in plant defence, and suggest that diverse peroxidase genes may be employed as components of strategies aimed at the engineering of disease resistance.

Involvement of a novel peroxidase isozyme and lignification in hydathodes in resistance to black rot disease in cabbage

The physiological mechanisms associated with resistance of cabbage to black rot disease seem to be associated with the hydathodes. To investigate the role of hydathodes in disease resistance, total peroxidase activities, anionic peroxidase isozyme expression, and lignin deposition were determined in hydathodes of resistant (Hancock and Green Cup), partially resistant (Cheers), and susceptible (Strukton and Perfect Ball) cabbage varieties (Brassica oleracea L.) during pathogenesis with Xanthomonas campestris pv. campestris. Four-week-old plants were petiole-inoculated with a highly virulent strain of X. campestris pv. campestris (FD91L). Hydathodal fluids were collected daily over a 14-day period from infected plants as well as noninfected, mock-inoculated control plants. Hydathodal fluids of resistant varieties had greater peroxidase activity when compared to susceptible ones, with infected plants having higher peroxidase levels than noninfected plants. Isoelectric focusing revealed the presence of four a...

Antifungal effects of hydrogen peroxide and peroxidase on spore germination and mycelial growth ofPseudocercosporaspecies

Spore germination in Pseudocercospora abelmoschi (Ell. &amp; Ev.) Deighton USDB1312 and Pseudocercospora cruenta (Sacc.) Deighton USDB1313, pathogens of Hibiscus esculentus L. and Vigna sinensis ssp. sesquipedalis (L.) van Eseltine, was significantly inhibited when incubated with different levels of hydrogen peroxide (0.03 × 10-5- 4.59 × 10-5M H2O2) and 1-100 µg/mL peroxidase (equivalent to 1.06-106 enzyme units). Significant reduction in mycelial growth was also observed in both fungi at different levels of H2O2(0.03 × 10-5- 7.71 × 10-5M) and 1-1000 µg/mL peroxidase. The spores and mycelium of P. cruenta USDB1313 could tolerate higher levels of H2O2(0.03 × 10-5- 2.61 × 10-5M) compared with that of P. abelmoschi USDB1312. The effects of peroxidase on spore germination and mycelial growth were similar in both P. abelmoschi and P. cruenta isolates. Spore germination and mycelial growth were inhibited significantly at higher levels of peroxidase. The results of this study complemented earlier field observations on the resistance or susceptibility of H. esculentus and V. sinensis ssp. sesquipedalis to both fungi.Key words: hydrogen peroxide, peroxidase, Pseudocercospora spp.

Evaluation of Elicitor- and High-Pressure-Induced Enzymatic Browning Utilizing Potato (Solanum tuberosum) Suspension Cultures as a Model System for Plant Tissues

Potato (Solanum tuberosum) suspension cultures were used as a model to obtain basic information regarding the occurrence of enzymatic browning reactions. The cultures were subjected to chitosan, an established stress factor, at concentrations from 2.5 to 100 μg/mL to examine stress reactions and to pressure treatments from 100 to 400 MPa for 10 min at 25 °C to monitor the impact of minimal processing on plant systems. The release of hydrogen peroxide from chitosan or high- pressure-treated potato cells, which constitutes an initial stress response, was correlated with activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO), and polyphenol oxidase (PPO) as well as with polyphenol production in cell free extracts. Chitosan-induced browning was related to PAL induction and corresponded to the concentration of phenols within the cells. Sensitivity of plant cells to these stress factors was affected by the amount of PO present in the cells. High PO levels in the potato cells resulted in a fast degrada...

Glutathione and β‐amylase, peroxidase and o‐diphenolase activities during sprouting of minisett yams (Dioscorea sp)

AbstractGlutathione, β‐amylase, o‐diphenolase (EC 1.10.3.1) and peroxidase (EC 1.11.1.7) activities were assayed in minisetts derived from the head, middle and tail sections of sprouted Dioscorea alata (cv Sweet Yam) and D cayenensis (cv Round Leaf) yam tubers. In both tubers the head portions exhibited highest initial activities followed by the middle and tail, respectively. Minisetts obtained from the head, middle and tail sections of D alata sprouted uniformly whereas those obtained from D cayenensis tubers showed a much slower, sporadic sprouting pattern, with the head portions displaying dominant sprouting, The results revealed that sprouting initiation of the minisetts from both species correlated well with increased glutathione levels. High levels of peroxidase and reduced levels of o‐diphenolase seemed to enhance the sprouting of the minisetts.