Phenol Peroxidase Research Articles

Morinda citrifolia Essential Oil: A Plant Resistance Biostimulant and a Sustainable Alternative for Controlling Phytopathogens and Insect Pests.

With the growing demand for sustainable and safe agricultural practices, plant compounds emerge as a solution for biological activities. Here, we evaluated the potential of using Morinda citrifolia essential oil to induce plant resistance and to control phytopathogens (Curvularia lunata) and insect pests (Daubulus maidis). We conducted a chromatographic analysis to unveil the essential oil components. We also quantified the activity levels of antioxidant enzymes and chitinase for resistance induction. The antifungal action was evaluated through disease progression and the inhibition of mycelial growth in addition to in silico studies that made it possible to predict the interaction site between the fungal protein and the compounds. We assessed the toxicity and repellent actions towards the D. maidis. Octanoic acid (58.43%) was identified as the essential oil major compound. Preventive treatment with essential oil and octanoic acid (25.0 µL mL-1) increased not only the plant defense activities (i.e., the activity of the enzymes superoxide dismutase, catalase, phenol peroxidase, ascorbate peroxidase, and chitinase) but also controlled Curvularia leaf spot. The stable interactions between octanoic acid and tyrosine-tRNA ligase from C. lunata suggested protein synthesis inactivation. The essential oil inhibited 51.6% of mycelial growth, and this effect was increased to 75.9% with the addition of adjuvants (i.e., angico gum). The essential oil reduced 76% of the population of D. maidis adults and repelled 50% of the number of D. maidis after 48 h under field conditions. The repellency effect in the field reduced the population of D. maidis adults, transmitters of the stunting complex, by 50%. The results highlight the potential of M. citrifolia as a resistance activator, fungicide, insecticide, and an effective biorational alternative.

Heat shock combined with salinity impairs photosynthesis but stimulates antioxidant defense in rice plants

The interactive mechanisms that occur between heat shock and salt stress and their reflexes on photosynthesis and redox metabolism in plants are little understood yet. We tested the hypothesis that heat shock negatively interacts with salt stress, affecting most intensely K+/Na+ homeostasis, stomatal closure, and CO2 assimilation, in comparison to PSII activity and oxidative stress in rice leaves. 31-day old rice plants were previously exposed to 0 and 100 mM NaCl for eight days at 27 °C and afterwards two groups were transferred to high temperature (42 °C, heat shock) for 10 hours (heat and heat + salt) whereas two other groups remained at 27 °C (control and single salt treatments). Heat-salinity interaction greatly stimulated Na+ accumulation in leaves causing intense decrease in K+/Na+ ratios, inducing significant osmotic and ionic alterations. Stomata were closed intensely causing drastic impairment in CO2 assimilation and decrease in water use efficiency. In contrast, the PSII activity was much lesser affected, corroborated by a low increase in the fraction of closed reaction centers of PSII and slight decrease in electron transport rates. Despite that unbalance in photosynthesis, combined stress partially favored oxidative protection as indicated by a reduction in the levels of H2O2 and lipid peroxidation associated with reduction in the contents of reduced forms of ascorbate and glutathione. These favorable antioxidant responses were accompanied by increases in the activities of ascorbate peroxidases, superoxide dismutases, glutathione peroxidases, and phenol peroxidases whereas catalases and glycolate oxidases decreased. These antioxidant responses were not enough to mitigate overall physiological damages caused by combined stress, as indicated by drastic increase in membrane damage and decrease in relative water content in leaves. Heat shock drastically aggravates the negative effects caused by salt stress on the photosynthetic efficiency, especially CO2 assimilation, despite the heat – salinity interaction has partially favored the antioxidant defense.

Biochemical Alterations in Different Pigeon Pea Genotypes due to Sterility Mosaic Disease

Background: The sterility mosaic disease in pigeon pea caused by pigeon pea sterility mosaic virus is a serious threat to pigeon pea cultivation in India. A little information is available on the biochemical changes in pigeon pea plant against the SMD disease. Hence present study was taken to know the biochemical alterations in different pigeon pea genotypes due to sterility mosaic disease. Methods: Studies were conducted on the composition of the chlorophyll pigment, total soluble protein (%), total sugars, phenol, tannins, peroxidase and phenol peroxidase in six different genotypes. Result: The results of the study showed that there was a reduction in chlorophyll pigment composition, total soluble protein (%) and total sugars in all infected genotypes, but the reduction in resistant genotypes was less compared to other genotypes. In resistant genotypes, the amounts of phenols, tannins, peroxidase and phenol peroxidase were increased, where as in susceptible genotypes, they were roughly equal to the amounts in uninoculated genotypes. The increase in phenols, tannins, peroxidase and phenol peroxidase in resistant genotypes can be correlated with disease resistance.

Effects of different forms of nitrogen addition on microbial extracellular enzyme activity in temperate grassland soil

BackgroundNitrogen (N) deposition alters litter decomposition and soil carbon (C) sequestration by influencing the microbial community and its enzyme activity. Natural atmospheric N deposition comprises of inorganic N (IN) and organic N (ON) compounds. However, most studies have focused on IN and its effect on soil C cycling, whereas the effect of ON on microbial enzyme activity is poorly understood. Here we studied the effects of different forms of externally supplied N on soil enzyme activities related to decomposition in a temperate steppe. Ammonium nitrate was chosen as IN source, whereas urea and glycine were chosen as ON sources. Different ratios of IN to ON (Control, 10:0, 7:3, 5:5, 3:7, and 0:10) were mixed with equal total amounts of N and then used to fertilize the grassland soils for 6 years.ResultsOur results show that IN deposition inhibited lignin-degrading enzyme activity, such as phenol oxidase (POX) and peroxidase (PER), which may restrain decomposition and thus induce accumulation of recalcitrant organic C in grassland soils. By contrast, deposition of ON and mixed ON and IN enhanced most of the C-degrading enzyme activities, which may promote the organic matter decomposition in grassland soils. In addition, the β-N-acetyl-glucosaminidase (NAG) activity was remarkably stimulated by fertilization with both IN and ON, maybe because of the elevated N availability and the lack of N limitation after long-term N fertilization at the grassland site. Meanwhile, differences in soil pH, soil dissolved organic carbon (DOC), and microbial biomass partially explained the differential effects on soil enzyme activity under different forms of N treatments.ConclusionsOur results emphasize the importance of organic N deposition in controlling soil processes, which are regulated by microbial enzyme activities, and may consequently change the ecological effect of N deposition. Thus, more ON deposition may promote the decomposition of soil organic matter thus converting C sequestration in grassland soils into a C source.

Bacillus subtilis suppresses the charcoal rot disease by inducing defence responses and physiological attributes in soybean.

Endophytes can induce the defence responses and modulates physiological attributes in host plants during pathogen attacks. In the present study, 127 bacterial endophytes (BEs) were isolated from different parts of healthy soybean plant. Among them, two BEs (M-2 and M-4) resulted a significant antagonistic property against Macrophomina phaseolina, causes charcoal rot disease in soybean. The antagonistic potential was evaluated through dual culture plate assay, where M-4 expressed higher antifungal activity than M-2 against M. phaseolina. The M-4 produces cell wall degrading enzymes viz. cellulase (145.71 ± 1.34 μgmL-1), chitinase (0.168 ± 0.0009 unitmL-1) and β,1-3 endoglucanase (162.14 ± 2.5 μgmL-1), which helps in cell wall disintegration of pathogens. Additionally, M-4 also can produce siderophores, indole-3-acetic acid (IAA) (17.03 ± 1.10 μgmL-1) and had a phosphate solubilization potential (19.89 ± 0.26 μgmL-1). Further, GC-MS profiling of M-4 has been carried out to demonstrate the production of lipophilic secondary metabolites which efficiently suppress the M. phaseolina defensive compounds under co-culture conditions. Bio-efficacy study of M-4 strain shown a significant reduction in disease incidence around 60 and 80% in resistant and susceptible varieties of soybean, respectively. The inoculation of M-4 potentially enhances the physiological attributes and triggers various defence responsive enzymes viz. superoxide dismutase (SOD), phenol peroxidase (PPO), peroxidase (PO) and catalase (CAT). The histopathological study also confirmed that M-4 can reduce the persistence of microsclerotia in root and shoot tissue. Conclusively, M-4 revealed as an efficient biocontrol agent that can uses multifaceted measures for charcoal rot disease management, by suppress the M. phaseolina infection and enhance the physiological attributes of soybean.

Narrow-Band 311 nm Ultraviolet-B Radiation Evokes Different Antioxidant Responses from Broad-Band Ultraviolet.

Supplemental narrow-band 311 nm UV-B radiation was applied in order to study the effect of this specific wavelength on tobacco as a model plant. UV-B at photon fluxes varying between 2.9 and 9.9 μmol m−2 s−1 was applied to supplement 150 μmol m−2 s−1 photosynthetically active radiation (PAR) for four hours in the middle of the light period for four days. Narrow-band UV-B increased leaf flavonoid and phenolic acid contents. In leaves exposed to 311 nm radiation, superoxide dismutase activity increased, but phenolic peroxidase activity decreased, and the changes were proportional to the UV flux. Ascorbate peroxidase activities were not significantly affected. Narrow-band UV-B caused a dose-dependent linear decrease in the quantum efficiency of photosystem II, up to approximately 10% loss. A parallel decrease in non-regulated non-photochemical quenching indicates potential electron transfer to oxygen in UV-treated leaves. In addition to a flux-dependent increase in the imbalance between enzymatic H2O2 production and neutralization, this resulted in an approximately 50% increase in leaf H2O2 content under 2.9–6 μmol m−2 s−1 UV-B. Leaf H2O2 decreased to control levels under higher UV-B fluxes due to the onset of increased non-enzymatic H2O2- and superoxide-neutralizing capacities, which were not observed under lower fluxes. These antioxidant responses to 311 nm UV-B were different from our previous findings in plants exposed to broad-band UV-B. The results suggest that signaling pathways activated by 311 nm radiation are distinct from those stimulated by other wavelengths and support the heterogeneous regulation of plant UV responses.

Endophytic halotolerant Bacillus velezensis FMH2 alleviates salt stress on tomato plants by improving plant growth and altering physiological and antioxidant responses

Salinity stress has significant deleterious effects on agricultural lands and plant yields. Plants undergo a series of physiological and molecular changes to reduce salt-induced damage. However, these mechanisms remain insufficient. The inoculation of plant growth promoting bacteria to improve plant health under stress conditions offers promise. Bacillus velezensis FMH2 has been shown to protect tomato fruits against black mold disease and to improve seed tolerance to abiotic stresses. During this study, the major physiological and metabolic changes connected with FMH2 mitigation of abiotic stress tolerance in tomato plants were explored. In presence of different salt levels, FMH2 showed a high potentiality to colonize internal plant tissues and to produce several plant growth promoting metabolites such as siderophores, indole acetic acid, and hydrolytic enzymes. FMH2-treatment promoted plant growth (root structure, plant elongation, leaf emission, fresh and dry weights, water content, etc.) in absence as well as in presence of salt stress. FMH2 treatment decreased endogenous Na+ accumulation and increased K+ and Ca2+ uptake. Furthermore, B. velezensis FMH2-treatment improved chlorophyll contents, membrane integrity and phenol peroxidase concentrations, and reduced malondialdehyde and hydrogen peroxide levels under saline conditions with a significant salinity × strain interaction. The present study suggests the endophytic strain FMH2 involved different mechanisms and regulatory functions to enhance plant oxidative systems and regulate ion uptake mechanisms supporting both growth and stress management.

Halotolerant Bacillus spizizenii FMH45 promoting growth, physiological, and antioxidant parameters of tomato plants exposed to salt stress.

Bacillus spizizenii is for the first time described as a plant growth salt-tolerant bacterium able to alleviate salt stress in crop plants by improving physiological parameters and antioxidant defense mechanisms. Agricultural soil salinization is a serious issue worldwide affecting agricultural yield. Plant growth promoting bacteria can enhance salt tolerance and plant yield. Bacillus spizizenii FMH45 has been shown to inhibit fungal attacks in tomato fruits and to augment tomato seed germination in presence of abiotic stresses. During this study, we reported for the first time B. spizizenii as a salt-tolerant bacterium able to alleviate salt stress in tomato plants. B. spizizenii FMH45 was examined in vitro for its potential to produce several plant growth promoting characters (siderophores, IAA, and phosphate solubilization) and hydrolytic enzymes (cellulase, glucanase and protease) in the presence of saline conditions. FMH45 was also investigated in vivo in pot experiments to evaluate its ability to promote tomato plant growth under salt stress condition. FMH45 inoculation, enhanced tomato seedling length, vigor index, and plant fresh and dry weights when compared to the non-inoculated controls exposed and not exposed to a regular irrigation with salt solutions containing: 0; 3.5; 7; and 10g L-1 of NaCl. FMH45-treated plants also presented improved chlorophyll content, membrane integrity (MI), and phenol peroxidase (POX) concentrations, as well as reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels under saline conditions with a significant salinity × strain interaction. Furthermore, FMH45 inoculation significantly decreased endogenous Na+ accumulation, increased K+ and Ca2+ uptake, and thereby improved K+/Na+ and Ca2+/Na+ ratios. This study proves that bio-inoculation of FMH45 efficiently increases salt tolerance in tomato plants. This sustainable approach can be applied to other stressed plant species in affected soils.

Tillage, green manure and residue management accelerate soil carbon pools and hydrolytic enzymatic activities for conservation agriculture based rice-wheat systems

ABSTRACT We studied the effects of tillage, crop residues, and green manure on soil carbon pools and hydrolytic enzyme activity in a sandy loam after five cycles of the rice-wheat system (RWS). Four main plot treatments in rice were combinations of wheat straw and Sesbania green manure (GM) management: (1) puddled transplanted rice (PTR) with no wheat straw, (2) PTR with 25% wheat stubbles (12–15 cm long) retained, (3) PTR with no wheat straw plus GM, and (4) PTR with 25% wheat stubbles plus GM. Three subplots treatments in subsequent wheat were (1) conventional tillage with rice straw removed, (2) zero tillage (ZT) with rice straw removed, and (3) ZT with 100% rice straw retained as a surface mulch. The results showed that PTR with wheat stubbles retained plus GM and ZT wheat with rice straw retained (ZTWRS100) significantly (p< 0.05) increased all the carbon pools and hydrolytic enzymes except phenol oxidase and peroxidase activities. The carbon management index under ZTWRS100 retained was significantly higher than zero-till or conventional till wheat without residue. The principal component analysis identified active carbon, less labile carbon pools; xylanase and dehydrogenase hydrolytic enzymes as the most reliable sensitive indicators for assessing soil quality for conservation agriculture (CA) – based practices in RWS. The study showed that adoption of PTR with 25%-anchored wheat stubbles retained plus GM in rice followed by ZTWRS100 in wheat was the best crop production strategy for enhanced carbon pools, hydrolytic enzymatic activities and gives an idea of its overall fitness for carrying out ecosystem functions.

Influence of exogenous jasmonic acid on the functioning of a defense system of potato seedlings (&lt;i&gt;Solanum tuberosum&lt;/i&gt; L.) grown on artificial ion exchange substrate and infected with potato virus X

The content of reactive oxygen species, the activities of ascorbate-glutathione cycle enzymes, the content of low molecular weight antioxidants: ascorbate and glutathione, the activity of phenolic peroxidase, the content of water-soluble phenols and the expression level of the hypersensitive response marker gene (HSR) and PR protein genes (Chit, Glu and TLP) in potato seedlings grown on an ion-exchange substrate in the presence of jasmonic acid at a concentration of 10 -8 and 10 -6 M and infected with potato virus X were studied. Accumulation of reactive oxygen species, an increase in the content of reduced ascorbate and an intensive consumption of reduced glutathione upon action of jasmonic acid, as well as a sharp increase in the expression of HSR, Chit, Glu, and TLP genes in the leaves of potato seedlings grown on a substrate with the addition of 10 -6 M jasmonic acid before infection were shown. In control plants, the expression of the HSR and TLP genes increased only after infection with potato virus X.

Effect of soil carbon amendments in reversing the legacy effect of plant invasion

Abstract Invasive plants are key drivers of global environmental changes leading to the disruption of ecosystems. Many invasive species engage in novel niche construction through plant–soil feedbacks that are driven by plant secondary compounds. These compounds can persist in the soil even after removing the invader, thus creating a legacy effect that inhibits the return of native flora and fauna. The formulation of active intervention strategies that can reverse niche construction is therefore critical for the restoration of these invaded ecosystems. We conducted this study in an old‐field in Massachusetts, USA, that has been invaded by Japanese knotweed (Polygonum cuspidatum) for &gt;20 years. We chose knotweed as a model system as it alters soil chemistry and microbial community through the input of polyphenols such as tannins that creates a legacy effect. Following the removal of knotweed biomass, we investigated the effect of two soil carbon (C) amendments (biochar and activated carbon) on the growth and establishment of newly seeded native and prairie species. We measured the percent plant cover and above‐ground biomass to assess the establishment of the native and prairie species. We also measured soil and microbial characteristics including nutrient availability, extracellular enzyme activities and fungal biomass to elucidate the effect of C amendments in reversing the legacy effect. Eventhough the native species did not respond positively to C amendments, the biomass of the prairie species was 80% higher in activated carbon and biochar amended plots than the non‐amended control plots. The nitrate content of the C amended plots was five times higher than the non‐amended plots indicating an increased N mineralisation in the C amended plots. This could be potentially due to the amelioration of phenolic compounds by activated carbon and biocharthrough sorption. The phenol peroxidase activity also increased in the activated carbon and biochar amended plots potentially due to the less inhibition by phenolic compounds. With the decrease in polyphenols, the fungal biomass decreased in C amended plots that may have resulted in faster nutrient cycling and increased availability of soil N. Synthesis and applications. The phenolic compounds from the litter of invasive species that persist in soil C fractions can negatively affect the germination and growth of the native or non‐invasive plant species. The polyphenols such as tannins from the litter can complex nitrogenous compounds in soils making the N unavailable to the native or non‐invasive species. Our results revealed the potential of soil C amendments in reversing niche construction and legacy effects of polyphenol‐rich invasive species and indicated that biochar could be a more economically feasible alternative to activated carbon in restoring invaded ecosystems. These results also emphasise thatunderstanding the mechanisms through which invasive species create a legacy effect is pivotal in formulating suitable knowledge‐based practices for restoring invaded ecosystems.

Ultraviolet-B acclimation is supported by functionally heterogeneous phenolic peroxidases

Tobacco plants were grown in plant chambers for four weeks, then exposed to one of the following treatments for 4 days: (1) daily supplementary UV-B radiation corresponding to 6.9 kJ m−2 d−1 biologically effective dose (UV-B), (2) daily irrigation with 0.1 mM hydrogen peroxide, or (3) a parallel application of the two treatments (UV-B + H2O2). Neither the H2O2 nor the UV-B treatments were found to be damaging to leaf photosynthesis. Both single factor treatments increased leaf H2O2 contents but had distinct effects on various H2O2 neutralising mechanisms. Non-enzymatic H2O2 antioxidant capacities were increased by direct H2O2 treatment only, but not by UV-B. In contrast, enzymatic H2O2 neutralisation was mostly increased by UV-B, the responses showing an interesting diversity. When class-III peroxidase (POD) activity was assayed using an artificial substrate (ABTS, 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)), both treatments appeared to have a positive effect. However, only UV-B-treated leaves showed higher POD activities when phenolic compounds naturally occurring in tobacco leaves (chlorogenic acid or quercetin) were used as substrates. These results demonstrate a substrate-dependent, functional heterogeneity in POD and further suggest that the selective activation of specific isoforms in UV-B acclimated leaves is not triggered by excess H2O2 in these leaves.

The effect of elicitors of bacterial origin on the functioning of the protective system of potato (&lt;i&gt;Solanum Tuberosum&lt;/i&gt; L.) seedlings infected with X-virus

The reactive oxygen species content, the activity of phenolic peroxidase, and the expression levels of genes encoding certain defense proteins were studied in potato seedlings grown on a substrate with the addition of a preparation based on B. subtilis and infected with potato virus Х. The accumulation of reactive oxygen species and the induction of the defense system components in potato leaves treated with this preparation and infected are shown. Less viral material was detected in experimental samples of potato seedlings compared with control untreated with B. subtilis.

Effects of Oudemansiella radicata polysaccharide on postharvest quality of oyster mushroom (Pleurotus ostreatus) and its antifungal activity against Penicillium digitatum

The effects of a water-soluble polysaccharide from Oudemansiella radicata (ORWP) on the postharvest quality of Pleurotus ostreatus were investigated. In the present work, oyster mushroom was divided into four groups which were treated separately with distilled water (control), and ORWP at 5, 10 and 15 g L−1 concentration, respectively, and kept at 4 ℃ for 15 d. The results showed that treatment with ORWP was effective in maintaining the sensory quality of oyster mushrooms. Mushrooms that were ORWP-coated displayed, compared to the control, reduction in the following parameters: weight loss, relative electrolyte leakage, phenol peroxidase (PPO) activities and malondialdehyde (MDA) content. In addition, ORWP-coated mushrooms maintained activities of superoxide dismutase (SOD) and catalase (CAT), contents of ascorbic acid, carbohydrate, soluble protein and phenolic compounds which were all higher than those of the control. Furthermore, the antifungal activity and underlying mechanisms of ORWP against Penicillium digitatum were investigated. The minimum inhibitory concentration (MIC) was 0.25 g L-1 and the minimum fungicidal concentration (MFC) was 1.00 g L−1. A combination of hyphal membrane permeability analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the antifungal activity of ORWP was attributed to disruption of hyphal cell membrane integrity, leading to leakage of intracellular materials, and impaired cellular metabolism, thereby thwarting the growth of P. digitatum. Therefore, ORWP is a promising preservative agent for postharvest oyster mushrooms and could be used as an inhibitor of fungi in food and medicine.

Oxidative status of Moringa oleifera Lam. seeds during storage

The aim of this study was to evaluate oxidative damages and antioxidative defences during loss of viability and vigour in Moringa oleifera Lam. seeds stored under controlled conditions. Seeds were packed in semipermeable plastic bags, maintained in a refrigerator (4 ± 2 °C and 20–25% RH) or in a growth chamber (27 ± 2 °C and 60–65% RH) for 18 months, and harvested every 6 months. The seeds stored in the growth chamber lost viability and vigour earlier than those stored under refrigeration. Irrespective of the storage environment, the H2O2 levels did not increase, lipid peroxidation remained almost unchanged, and protein carbonylation decreased in the course of the experiment. The reduced glutathione levels and the phenol peroxidase activity decreased faster in the seeds maintained in the growth chamber than in those kept under refrigeration. The reduced ascorbate levels and the activities of ascorbate peroxidase and catalase increased during storage in both tested conditions. Hence, loss of viability and vigour in M. oleifera seeds during storage could not be attributed to oxidative damages, in terms of H2O2 accumulation, lipid peroxidation, and protein carbonylation. The preservation of antioxidative defences, specifically the reduced ascorbate levels and the activities of superoxide dismutase, ascorbate peroxidase, and catalase, does not result in the maintenance of seed vigour.

Supplementation of Trichoderma improves the alteration of nutrient allocation and transporter genes expression in rice under nutrient deficiencies

Nutrients are the finite natural resources that are essential for productivity and development of rice and its deficiency causes compromised yield along with reduced immunity against several biotic and abiotic stresses. In this study, the potential of Trichoderma reesei has been investigated as a biofertilizer (BF) to ameliorate nutrient stress in different rice cultivars at physiological, biochemical and molecular levels. The results indicated that cultivar Heena is much more compatible with BF as compared to cultivar Kiran at 50% nutrient limiting condition. Enhancement in physiological attributes and photosynthetic pigments were observed in BF treated Heena seedlings. The localization of biofertilizer in treated roots was further validated by scanning electron micrographs. This result correlated well with the higher levels of Indole acetic acid and Gibberellic acid in biofertilizer treated rice. Similarly, the uptake of micro-nutrients such as Fe, Co, Cu and Mo was found to be 1.4–1.9 fold higher respectively in BF treated Heena seedlings under 50% nutrient deficient condition. Furthermore, different stress ameliorating enzymes Guaiacol peroxidase, Super oxide dismutase, Total Phenolic Content, Phenol Peroxidase, Phenylalanine ammonia lyase and Ascorbate peroxidase in Heena seedlings were also increased by 1.8, 1.4, 1.2, 2.4, 1.2, and 8.3-fold respectively, at 50% nutrient deficient condition. The up-regulation of different micro and macro-nutrients allocation and accumulation; metal tolerance related; auxin synthesis genes in BF treated Heena as compared to 50% nutrient deficient condition was further supported by our findings that the application of biofertilizer efficiently ameliorated the deficiency of nutrients in rice.

Intervention of bio-protective endophyte Bacillus tequilensis enhance physiological strength of tomato during Fusarium wilt infection

The plants in their natural environment face various biotic stresses due to invading phytopathogens. Their control measures primarily involve large scale applications of chemical fungicides. The excessive use of chemicals leads to the contamination of the environment by entering the food web. To address the above concern, in the present study six antagonistic bacterial strains were screened from 344 isolates and identified through 16S rRNA sequencing. Out of these six antagonistic bacterial endophytes, Bacillus tequilensis (PBE1) (MTCC25188) was proven most effective and an eco-friendly substitute of chemical fungicides against Fusarium oxysporum for tomato wilt disease management. The antagonistic effect of PBE1 was well corroborated by dual culture plate assay and SEM micrographs. The PBE1 also showed efficient plant growth-promoting traits as it produced indole acetic acid (IAA) (31.89 μg ml−1), hydroxymate type siderophore (5.00 μg ml−1) along with phosphate solubilizing (9.09 μg ml−1) ability. The bio-protective intervention of PBE1 demonstrated 60.00% reduction of disease incidence in comparison to the pathogen infected plants. Simultaneously, enhanced physical parameters such as root length, shoot length, number of branches, fresh weight and dry weight by 1.73, 1.43, 1.71, 5.35 and 2.74 folds respectively. All the studies were performed under greenhouse conditions at 25 ± 2 °C for 30 days. Plants were grouped into six different treatments. The pathogen infection was given to 30 days old seedlings post-transplantation and PBE1 treatment was given at 7 days post-infection. The prevention of vascular bundle disruption and uniform thickness of parenchymatous cortical layer was observed in PBE1 treated plants. The changes were distinguished in transverse sections of the collar region of tomato stems. Moreover, PBE1 also enhanced various antioxidant and defense-related responses including superoxide dismutase, phenol peroxidase, peroxidase, and catalase enzymes estimated (77.22 U/mg of protein; 0.04 U/mg of protein, 0.003ΔOD/min/mg of FW and 1098.90 U/mg of protein respectively). The lipid peroxidation was found to decrease in PBE1+P treated plants (2.74 nM of TBARS/gm FW) as compared to all other groups. Whereas, the secondary metabolites including total phenolics and flavonoids content were higher in PBE1+P treated plants than all other treatments. By the virtue of obtained results, the study may provide an efficient eco-friendly bio-protective tool for the Fusarium wilt disease management by replacing widely used chemical fungicides.

Antioxidant Protection of Photosynthesis in Two Cashew Progenies Under Salt Stress

The present work evaluated the indicators of photosynthetic efficiency and antioxidative protection in cashew tree seedlings subjected to salinity stress. The study was conducted with seedlings of two advanced dwarf cashew clones (CCP09 and CCP76) subjected to salt stress with increasing doses of NaCl (0, control; 25; 50; 75; 100 mM) in the nutrient solution for 30 days under greenhouse conditions. The variables of gas exchange, CO2 assimilation (PN), stomatal conductance (gS), transpiration (E), intercellular CO2 concentration (CI), photochemical activity, potential quantum efficiency (Fv/Fm), effective quantum efficiency (&amp;Delta;F/Fm&amp;rsquo;) of photosystem II (PSII), photochemical quenching (qP), non-photochemical quenching (NPQ) electron transport rate (ETR) as well as the indicators of damage and oxidative protection were measured. Under these conditions, there was an intense accumulation Na+ associated with a reduction in the K+/Na+ ratio in the leaves of both clones in response to salt, with higher values for this ratio in clone CCP09 than in CCP76 the highest concentration of NaCl (100 mM). Salinity reduced PN, gS and E in the two clones evaluated, with lower reductions in CCP09 than in CCP76 at the highest salt dose. Instantaneous carboxylation (PN/CI) and water use (PN/E) efficiencies were strongly restricted by salinity but were less affected in CCP09 than in CCP76. Salinity stress also increased hydrogen peroxide (H2O2) levels in CCP09, whereas lipid peroxidation decreased in both progenies. The clones presented specific antioxidant responses due to greater enzymatic and non-enzymatic activity in CCP76, in addition to the activity of phenol peroxidase (POX) in CCP09.

English

Secondary metabolites may play a number of roles, among them, is the activation of plant defense mechanisms, such as phytoalexins and the synthesis of antioxidative enzymes. This study aimed to test the eliciting activity of phytoalexins of Lippia sidoides Cham. and six endophytic fungi associated with it and to verify the synthesis of the enzymes, as a response to the antioxidative and antifungal system. The assays were performed using spectrophotometric methods. Of the concentrations of essential oil used, 7.5 mg mL-1 was 66.48% higher than the Acorda&reg; positive control for the induction of glyceollin. The endophytic fungus, Verticillium sp. showed the best result for 3-deoxythianocyanidine production. Excellent results were demonstrated by the LS-14 fungus for superoxide dismutase enzyme activity (130 U g-1 E-1 min-1); by L. sidoides for the activity of ascorbate peroxidase enzyme (3821 &mu;mol ASA g-1 E-1 min-1); by L. sidoides for the activity of catalase enzyme (2429 &mu;mol H2O2 g-1 E-1 min-1); by Fusarium sp. 2 for the activity of phenol peroxidase (87 &mu;mol H2O2 g-1 E-1 min-1) and by Fusarium sp. 1 for the activity of chitinase (0.214 U min-1). Both the essential oil of L. sidoides and the extracts of the endophytic fungi had a positive response to the induction of phytoalexin and presence of enzymes related to antioxidative activity were verified and shown. Key words: Catalase, superoxide dismutase, peroxidase phenols, ascorbate peroxidase, chitinase.

Soil application of rice husk as a natural silicon source to enhance some chemical defense responses against foliar fungal pathogens and growth performance of Bitter Gourd (&lt;em&gt;Momordica charantia L.&lt;/em&gt;)

Rice husk is a natural Silicon (Si) source. This study evaluated the effect of rice husk in two different forms; ground rice husk (GRH) and rice husk ash (RHA) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora sp. Rice husk was added to the growing medium to achieve the final concentration of 200 mg Si /kg soil. Si accumulation in leaves, disease severity, plant growth parameters, cuticle-epidermal layer thickness, chlorophyll content, total phenolic content, peroxidase (POD) and polyphenol oxidase (PPO) activity of leaves were measured. Husk treatment lowered the downy mildew severity significantly (p < 0.05) in leaves although the difference between the effects of two husk forms was insignificant. Numbers of leaves, flowers and fruits in husk-treated plants were significantly higher (p < 0.05) than those in control plants. Cuticle-epidermal layer thickness in GRH, RHA-treated and control plants were 16.8 ± 1.21, 18.2 ± 0.98 and 13.2 ± 1.27 μm respectively. Total phenol content, POD, PPO activity and chlorophyll content in rice husk-treated plants were significantly (p < 0.05) higher than that of control plants. The enhanced disease resistance in rice husk-treated plants appears to be positively associated with the higher accumulation of silicon and Si-enhanced phenolic content and increased activity of PPO and POD enzymes in leaves.