Guaiacol-dependent Peroxidase Research Articles

Salicylic Acid Improves Cold Resistance of Solanum tuberosum Regenerants via Regulation of the Antioxidant System

Pretreatment of roots with salicylic acid (SA) and its role in control over morphophysiological parameters characterizing cold resistance of plant regenerants were examined in potato (Solanum tuberosum L.). It was found that potato plants exposed to low above-zero temperatures (4°C, 3 days) failed to restore initial growth parameters (plant height, leaf surface area, number of stolons, and weight of the organs) and oxidative status (intensity of lipid peroxidation) of the roots and leaves after transfer to favorable conditions (22°C, 10 days). A short-term (4-h-long) pretreatment of the roots with 0.1 μM SA minimized the adverse effect of deferred chilling. SA treatment promoted restoration of the initial plant phenotype after hypothermia, which caused a rise in growth parameters (number and surface area of the leaves and number of stolons) as compared with plants exposed to chilling without SA treatment. It was shown that pretreatment with SA improves cold resistance of potato plants owing to changes in the activity of antioxidant enzymes (superoxide dismutase and guaiacol-dependent peroxidase) and in the level of nonenzymatic antioxidants (ascorbic acid, anthocyans, total flavonoids and phenolic compounds). Depending on conditions, SA alters the ratio between individual flavonoids in the leaf. An ambiguous response to chilling and SA treatment was observed in two lines of potato regenerants produced by means of in vitro microcloning from the apical and middle part of the shoot, which is probably associated with their differing hormonal status.

Effect of osmotic stress on protein concentration and antioxidant enzymes activity in the organism of nine-spined stickleback Pungitius pungitius (Gasterosteidae) from the White Sea Basin

The life cycle of P. pungitius (Linnaeus, 1758) includes migrations from the open sea to coastal and freshwater biotopes which are accompanied by osmotic shock and following oxidative stress in fish. The complex multilevel antioxidant system (AOS) includes low-molecular compounds and specific enzymes and protects cells from reactive oxygen species, hydrogen peroxide, and hydroperoxides generated in excess. To study the response of AOS components to oxidative stress caused by acute salinity changes, nine-spined stickleback juveniles from the White Sea estuary were alternately exposed to hypo- and hyperosmotic conditions. In the tissues of stickleback transferred from saltwater to freshwater for 1 and 24 hours a decrease in water-soluble protein concentration and catalase activity was shown. The increased guaiacol-dependent peroxidase activity in estuary fish successively exposed to fresh and saltwater for 24 hours was also observed. Under studied exposures, no changes in the activities of superoxide dismutase and glutathione S-transferase were detected. The involvement of AOS enzymes, particularly neutralizing hydrogen peroxide by the peroxidase-dependent pathway, in the response to acute changes in ambient salinity was described in White sea P. pungitius for the first time. The results of our study provide the new data on the AOS response to hypo- and hyperosmotic stress in euryhaline fish species. The obtained data could be used in predicting the possibility of industrial fish farming in the White Sea-Barents basin.

Influence of iron nanoparticles (Fe3O4 and Fe2O3) on the growth, photosynthesis and antioxidant balance of wheat plants (Triticum aestivum)

More and more attention is paid to the development of technologies using iron nanoparticles in agriculture. In this regard, the effect of treatment of wheat seeds with various concentrations of iron nanoparticles Fe3O4 and Fe2O3 on the accumulation of biomass, the rate of photosynthesis and respiration, as well as on photochemical activity and antioxidant balance was studied. The seeds were treated for 3 h, germinated for 2 days in Petri dishes, transplanted into sand and grown under light for 18 days without mineral nutrition until the third leaf appeared. At a Fe3O4 concentration of 200 mg L-1 a significant increase in the dry biomass of the second leaf by 45% and the rate of photosynthesis by 16% was observed. At a concentration of nanoparticles in the form of Fe2O3 of 200 and 500 mg L-1, an increase in the rate of photosynthesis in the second leaf was also observed, but not in the biomass of the leaves. The activity of photosystem 2, estimated from the Fv/Fm value, also increased in experiments with nanoiron. However, the activity of antioxidant enzymes, guaiacol-dependent peroxidase and superoxide dismutase, decreased. It is assumed that the acceleration of growth at an early stage of wheat development is associated with an increase in photosynthetic processes.

Impact of high irradiance and UV-B on the photosynthetic activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under blue light

The impacts of high-intensity light (HIL) (4 h) and UV-B radiation (1 h) on the photosynthetic activity, content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes (ascorbate peroxidase (APX) and guaiacol-dependent peroxidase (GPX)), content of thiobarbituric acid reactive substances (TBARs), expression of some light-regulated genes in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) hy4 mutant of A. thaliana Col-0 plants grown under blue light (BL) were studied. HIL and UV-B treatments led to decreases in the photosynthetic rate (Pn), photochemical activity of PSII (FV/FM) and PSII performance index (PIABS) of WT and mutant plants grown under high-intensity BL (HBL) and moderate intensity BL (MBL). However, in HBL plants, the decrease in the photosynthetic activity in hy4 plants was significantly greater than that in WT plants. In addition, hy4 HBL plants demonstrated lowered UAP and carotenoid contents as well as lower activity of APX and GPX enzymes. The difference in the decline in the photosynthetic activity of WT and hy4 plants grown at MBL in response to HIL was nonsignificant, while that in response to UV-B was small. We assume that the deficiency in cryptochrome 1 under HIL irradiation disrupts the interaction between HY5 and HFR1 transcription factors and photoreceptors, which affects the transcription of light-induced genes, such as CAB1, PSY and PAL1 linked to carotenoid and flavonoid biosynthesis. It was concluded that PA stress resistance in WT and hy4 plants depends on the light intensity and reduced stress resistance of hy4 at HBL, is likely linked to low UAP and carotenoid contents as well as lowered APX and GPX enzyme activities in hy4 mutants.

ACTIVITY AND ISOZYME COMPOSITION OF PEROXIDASE IN SCOTS PINE (PINUS SYLVESTRIS L.) NEEDLES EFFECTED BY TECHNOGENIC EMISSIONS FROM VARIOUS ENTERPRISES AND VEHICLES

Background. The technogenic pollution leads to excessive production of reactive oxygen species (ROS) in plants which are highly reactive and toxic and cause damage to biomolecules. Plants have a complex antioxidant defense system that protects cells from the ROS and maintain homeostasis. The most important link this system is enzymes, in particular, peroxidase. It was of interest to determine the expression of the protective properties of one of the sensitive species of coniferous plants under the influence of technogenic emissions from various enterprises and vehicles.
 Purpose. Investigation the activity and isoenzyme composition of peroxidase in the needles of Pinus sylvestris L. under the influence of technogenic emissions of different compositions in the Baikal region.
 Materials and methods. The pine needles were collected on sample plots located near an aluminum plant, thermal power plant, chemical plant, coal mining enterprise, and the highway. The activity of soluble guaiacol-dependent peroxidases was defined by spectrophotometry in a reaction mixture with citrate-phosphate buffer, hydrogen peroxide, and guaiacol. Native polyacrylamide gel electrophoresis was used for determination of peroxidase isoforms.
 Results. It was shown that an increase in the total guaiacol-dependent peroxidase activity ranged from 6 to 22 times in the pine needles in polluted areas. Maximum enzyme activity was found in needle samples collected near the aluminum smelter, whose emissions are characterized by large amounts of fluorides and polycyclic aromatic hydrocarbons. The high variability of peroxidase isoform composition in Scots pine needles under industrial pollution was revealed. It was expressed in the emergence of new isoforms in the zone of fast-moving (Rf from 61 to 100) and medium-moving (Rf from 31 to 60) items. The maximum number of isoforms (nine) was found in pine needles near the aluminum smelter with only two ones detected in the background area.
 Conclusion. Peroxidase activity and the number of its newly formed isoforms can adequately reflect the degree of technogenic pollution and trees decline. The indicators can also be used in monitoring of coniferous forests condition.

Sulfamethoxazole activates antioxidant defense response against Alternaria solani infection in Solanum lycopersicum Linn

The present study focuses on the potency of sulfamethoxazole (Sm) on inducing resistance against Alternaria solani infection. Anatomical observation indicated calcium oxalate deposits in pathogen-infected tissue compared to control plants. Sm pretreated and pathogen-infected tomato leaves showed decreased accumulation of calcium oxalate crystals. The oxalic acid content is found decreased in Sm (3 µM) pretreated and pathogen-infected leaves at 36 h compared to control and pathogen-infection (PI). Sm treatment resulted in transient and significant increase in H2O2 level during early stages of PI. A significant increase in superoxide dismutase, guaiacol dependent peroxidase and polyphenol oxidase was evident in Sm treated leaves which altogether contributed to protection of tomato from oxidative stress due to PI. Sm treatment followed by PI resulted in accumulation of superoxide anion compared to A. solani infected plants. In conclusion, Sm treatment regulate balance between antioxidants and free radicals, induces antioxidant enzymes and thereby controlling pathogen ingress.

Effect of Short-Term Treatment of Roots with Melatonin on Photosynthesis of Cucumber Leaves

Effect of a short-term (15, 30, 60, and 120 min) root treatment with melatonin (0.1 pM and 1.0 µM) on physiological parameters of the leaf was studied in 21-day-old cucumber (Cucumis sativus L.) plants, early cv. Izyashchnyi, grown on Murashige-Skoog nutrient medium. Experimental data concerning kinetics of melatonin influence have shown that the duration of the aftereffect necessary for activation of photosynthesis, transpiration, and stomatal conductance of cucumber leaves decreased when the concentration of the exogenous melatonin used for root treatment rose. A similar pattern was observed in respect to intensification of lipids’ peroxidation, content of proline, and activation of guaiacol-dependent peroxidase (ЕС 1.11.1.7). Under the effect of melatonin, antiradical activity in the leaf decreased in 120 min, which was preceded by a reduction in the content of total flavonoids. Regulation in activity of antioxidant enzymes superoxide dismutase (ЕС 1.15.1.1) and catalase (ЕС 1.11.1.6) was more intricate. Possible mechanisms of the influence of melatonin on parameters of photosynthesis in cucumber leaves are discussed.

Cytochrome c'β-Met Is a Variant in the P460 Superfamily Lacking the Heme-Lysyl Cross-Link: A Peroxidase Mimic Generating a Ferryl Intermediate.

A defining characteristic of bacterial cytochromes (cyt's) in the P460 family is an unusual cross-link connecting the heme porphyrin to the side chain of a lysyl residue in the protein backbone. Here, via proteomics of the periplasmic fraction of the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea, we report the identification of a variant member of the P460 family that contains a methionyl residue in place of the cross-linking lysine. We formally designate this protein cytochrome "c'β-Met" to distinguish it from other members bearing different residues at this position (e.g., cyt c'β-Phe from the methane-oxidizing Methylococcus capsulatus Bath). As isolated, the monoheme cyt c'β-Met is high-spin (S = 5/2). Optical spectroscopy suggests that a cross-link is absent. Hydroxylamine, the substrate for the cross-linked cyt P460 from N. europaea, did not appreciably alter the optical spectrum of cyt c'β with up to 1000-fold excess at pH 7.5. Cyt c'β-Met did however bind 1 equiv of H2O2, and with a slight excess, Mössbauer spectroscopy indicated the formation of a semistable ferryl (FeIV═O) Compound II-like species. The corresponding electron paramagnetic resonance showed a very low intensity signal indicative of a radical at g = 2.0. Furthermore, cyt c'β-Met exhibited guaiacol-dependent peroxidase activity (kcat = 20.0 ± 1.2 s-1; KM = 2.6 ± 0.4 mM). Unlike cyt c'β-Met, cyt P460 showed evidence of heme inactivation in the presence of 2 equiv of H2O2 with no appreciable guaiacol-dependent peroxidase activity. Mutagenesis of the cross-linking lysyl residue to an alanine in cyt P460, however, reversed this lack of activity.

IMPACT OF Al NANOPARTICLES ON CHLOROPHYLL PIGMENT CONTENT AND ENZYME ACTIVITY IN COTTON LEAVES

The role of nanotechnology in solving environmental problems is increasing, and there is a need for additional research in this area. One of these environmental problems is soil salinization. During salinity stress, germination, growth and development ofplants slow down, and the quantity of pigments, chlorophyll and carotenoids in leaves decreases. So does the activity of such important physiological processes as photosynthesis, respiratory processes and enzyme activity. There are several ways to improve the salt tolerance of cotton. The cotton varieties can be improved genetically, or another way is to increase the stability of seeds or seedlings by chemical, biological or physological methods. At the early stages of development cotton seedling are very sensitive to salinity and other stress factors. The study investigated the effect of Al nanoparticles on the pigment composition in cotton seedling leaves and on the enzyme activity (ascorbate oxidase, polyphenol peroxidase and guaiacol-dependent peroxidase) in soil samples, collected in different areas of the Mugan plain. It was found that cotton seeds develop well in saline soils if treated with Al nanoparticles. Significant changes were observed in the plant development and in the kinetics of physiological processes. The quantity of chlorophyll pigments a and b in cotton sprouts (mainly at three leaf stages) increased, and the change in enzyme activity occured. Thus, during salinity stress the influence of basic enzymes, such as ascorbic peroxidase, increased in sprouts but decreased in leaves if the cotton plants are cultivated in saline soils with Al nanoparticles. The decrease in the activity of polyphenol oxidase and guaiacol-dependent peroxidase was insignificant.

DOES FISH FLOUR AND CALCIUM IMPROVE MENTHA DEVELOPMENT, ENZYME ACTIVITIES AND PHENOLIC COMPOUNDS UNDER HIGH SALINITY

The use of natural and biodegradable material (such as fish flour) counteracts stress as cheaper and safer alternative for toxic chemicals (such as pesticides). The effect of calcium and fish flour (Ca and FF) (single or in combination) to improve plant tolerance against salt stress was studied. Sterilized mentha seeds were imbibed in each treatment: FF (10 g mL–1), Ca (1, 3%) applied alone and in Ca+FF-combination shaking for 24 h at 150 rpm. Changes in the antioxidants (carotenoids, phenolic, and flavonoid), enzymatic system (superoxidase – SOD, guaiacol-dependent peroxidase – GPX and phenylalanine ammonia-lyase – PAL) and lipid peroxidation levels of mentha seedlings were investigated under salt stress. It was suggested that Ca and/or FF had positive regulation effects on the key enzyme activities related to phenolic compounds biosynthesis and individual phenolic contents under salt stress. Additionally, the mentha plants developed from Ca+FF-combined pre-treatments showed better response to salinity than either Ca or FF single pre-treatment. Suppression of salt injury by Ca+FF pre-treatment reduced the LPO levels, increased enzyme activities and promoted total flavonoid and phenolic contents. Ca+FF-combined pre-treatment of mentha seeds seem to be a reliable, not-expensive and easy procedure to enhance plant salt tolerance and to gain more biomass.

Prolonged dark period modulates the oxidative burst and enzymatic antioxidant systems in the leaves of salicylic acid-treated tomato

Salicylic acid (SA) is an important plant growth regulator playing a role in the hypersensitive reaction (HR) and the induction of systemic acquired resistance. Since the SA-mediated signalling pathways and the formation of reactive oxygen species (ROS) are light-dependent, the time- and concentration-specific induction of oxidative stress was investigated in leaves of tomato plants kept under light and dark conditions after treatments with 0.1mM and 1mM SA. The application of exogenous SA induced early superoxide- and H2O2 production in the leaves, which was different in the absence or presence of light and showed time- and concentration-dependent changes. 1mM SA, which induced HR-like cell death resulted in two peaks in the H2O2 production in the light but the first, priming peak was not detected in the dark. Unlike 0.1mM SA, 1mM SA application induced NADPH oxidase activity leading to increased superoxide production in the first hours of SA treatments in the light. Moreover, SA treatments inhibited catalase (CAT) activity and caused a transient decline in ascorbate peroxidase (APX), the two main enzymes responsible for H2O2 degradation, which led to a fast H2O2 burst in the light. Their activity as well as the expression of some isoenzymes of SOD and APX increased only from the 12th h in the illuminated samples. The activity of NADPH oxidase and expression SlRBOH1 gene encoding a NADPH oxidase subunit was much lower in the dark. In spite of low CAT and APX activity after SA treatments in the dark, the activation of guaiacol-dependent peroxidase (POD) could partially substitute H2O2 scavenging activity of these enzymes in the dark, which reduced the ROS burst and development of lesion formation in the leaves.

Sensitivity of antioxidant status of plant cells to furostanol glycosides

The present paper reports that in vitro plant objects (test tube plants and cell cultures), when subjected to furostanol glycosides (FG), underwent nonspecific reactions related to antioxidant status—decrease in peroxidation of lipids (POL) and increase in guaiacol-dependent peroxidase activity. The level of superoxide increased as early as after 5 min from contact with yam (Dioscorea deltoidea Wall) cells with FG. In this case, changes in POL processes and in activities of peroxidase and aldehyde-disposing emzymes were also observed. Upon a short-term cell exposure to FG, the levels of the primary POL products (conjugated dienes) increased, and that of the secondary POL products decreased compared to the control. These events were preceded by a rise in SOD activity and in an antioxidant activity of peroxidase along with a concurrent decrease in its oxidase (prooxidant) activity. The elevated activities of aldehyde-disposing enzymes aldehyde dehydrogenase and aldehyde reductase favored the reduction in the content of the secondary products of POL. Upon a long contact of FG with cells, the effect of FG was seen only at the initial and final phases of the culture growth cycle. Namely, FG diminished the POL level at the exponential growth phase and at the end of the cell degradation phase but had no effect at the stationary phase and the onset of the degradation phase. Therefore, the treatment with FG retarded the cell culture degradation and made the fall in cell viability not so dramatic by the end of the growth cycle. Actually, by the end of the degradation phase, the viability diminished down to 40% in the control but remained at 70% in the FG-treated counterpart.

ВЛИЯНИЕ КРАТКОВРЕМЕННЫХ ЕЖЕСУТОЧНЫХ ПОНИЖЕНИЙ ТЕМПЕРАТУРЫ НА АКТИВНОСТЬ АНТИОКСИДАНТНЫХ ФЕРМЕНТОВ

We studied the effect of short-term (2 hours at the end of the night) daily temperature reductions to 12 °C (DROP treatment) on the activity of antioxidant (AO) enzymes in cucumber (Cucumis sativus L.) leaves of various ages. Plants were DROP-treated for 6 days during the exponential growth of the second true leaf (DROP 1) or when the second leaf was mature (DROP 2). DROP 3 plants were DROP-treated for 12 days during the DROP 1+DROP 2 period. In mature leaves (DROP 2) DROP treatment did not cause any changes in the activity of AO enzymes or lipid peroxidation rates, as estimated by the content of malondialdehyde (MDA). In young leaves (DROP 1 and DROP 3) DROP treatment reduced the activity of superoxide dismutase and ascorbate peroxidase and induced a short-term increase followed by a decrease in the activity of catalase and guaiacol-dependent peroxidase. Chilling tolerance was higher in all DROP-treated plants compared to untreated plants. Thus, we found that a daily short-term temperature drop (DROP) modified the activity of AO enzymes in young leaves, but did not affect the activity of the studied enzymes in mature leaves. Changes in the activity of AO enzymes did not correlate with changes in chilling tolerance. Apparently, the increased antioxidant activity in low temperature-treated plants described in the literature for chilling-sensitive species is not involved in cucumber response to temperature DROP, and some other mechanism is responsible for the higher chilling tolerance in DROP-treated plants. The differential response of young and mature leaves points to some developmental controls in the induction of plant adaptations to short-term chilling.

The influence of phosphorus availability and Laccaria bicolor symbiosis on phosphate acquisition, antioxidant enzyme activity, and rhizospheric carbon flux in Populus tremuloides

Many forest tree species are dependent on their symbiotic interaction with ectomycorrhizal (ECM) fungi for phosphorus (P) uptake from forest soils where P availability is often limited. The ECM fungal association benefits the host plant under P limitation through enhanced soil exploration and increased P acquisition by mycorrhizas. To study the P starvation response (PSR) and its modification by ECM fungi in Populus tremuloides, a comparison was made between nonmycorrhizal (NM) and mycorrhizal with Laccaria bicolor (Myc) seedlings grown under different concentrations of phosphate (Pi) in sand culture. Although differences in growth between NM and Myc plants were small, Myc plants were more effective at acquiring P from low Pi treatments, with significantly lower k m values for root and leaf P accumulation. Pi limitation significantly increased the activity of catalase, ascorbate peroxidase, and guaiacol-dependent peroxidase in leaves and roots to greater extents in NM than Myc P. tremuloides. Phosphoenolpyruvate carboxylase activity also increased in NM plants under P limitation, but was unchanged in Myc plants. Formate, citrate, malonate, lactate, malate, and oxalate and total organic carbon exudation by roots was stimulated by P limitation to a greater extent in NM than Myc plants. Colonization by L. bicolor reduced the solution Pi concentration thresholds where PSR physiological changes occurred, indicating that enhanced Pi acquisition by P. tremuloides colonized by L. bicolor altered host P homeostasis and plant stress responses to P limitation. Understanding these plant-symbiont interactions facilitates the selection of more P-efficient forest trees and strategies for tree plantation production on marginal soils.

Temporal modulation of oxidant and antioxidative responses in Brassica carinata during β-aminobutyric acid-induced resistance against Alternaria brassicae

A preinoculative foliar application of 5 mM BABA significantly inhibited the colonization of Alternaria brassicae on leaves of Brassica carinata susceptible cultivar car6. BABA treatment led to transient but significant increase in H2O2 level during early stages of pathogen colonization. A significant increase in superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol dependent peroxidase (GDP) contributed to inhibition of the oxidative stress in BABA treated plants in response to pathogen infection. In conclusion BABA treatment led to proper balance of oxidant & antioxidants suitable for expression of resistance resulting in curtail of pathogen ingress during early stages of colonization.

Adaptogenic action of the complex of phenylpropanoids on Dioscorea deltoidea cell culture under abiotic stress

Biological activity of the extract from golden root (Rhodiola rosea L.) roots, containing the complex of phenylpropanoids (CPP), was studied on the cell culture of yam (Dioscorea deltoidea Wall) under normal conditions and abiotic stress. The high radical-binding capacity of CPP relative to anion- and hydroxyl-radicals was observed. Having a high level of antiradical protection, CPP at a high concentration(100 μM) exerted prooxidant effect, causing a decrease in D. deltoidea cell viability and a decrease in the activities of antioxidant enzymes: superoxide dismutase, guaiacol-dependent peroxidase, and catalase, with the exception of ascorbate peroxidase. At treatment with 100 μM CPP, oxidase (prooxidant) activity of peroxidase increased by three times. The low CPP concentration (2 μM) did not induce substantial changes in the activities of tested enzymes and also a substantial increase in the oxidase activity of peroxidase. Under conditions of oxidative stress induced by paraquat and high temperature, CPP manifested adaptogenic action, increasing cell viability; however, under hyperosmotic stress, it was not efficient. CPP was most efficient at a low concentration after cell pre-incubation with it for 5 days. In this case, the amount of primary and secondary POL products increased. Shortening pre-cultivation with CPP reduced its defensive effect.

Stimulation of defense responses of in vitro potato plants by treatment with steroid glycosides under abiotic stresses

To elucidate the biological activity of furastanol glycosides (FG) as elicitors and their possible action mechanisms, antiradical properties of these compounds and their influence on in vitro potato (Solanum tuberosum L.) plants under abiotic stresses were studied. FG stimulated adaptive responses related to the activation of guaiacol-dependent peroxidase and suppression of lipid peroxidation (POL). Under normal conditions, in 30 min after plant treatment with 4.5 μM FG, the level of POL was decreased, activities of guaiacol- and ascorbate-dependent peroxidases increased, and activities of catalase and superoxide dismutase (SOD) remained unchanged. In 3 days after treatment with FG, POL was decreased by 20–60% in the leaves and by 50% in the roots. Under stress conditions (paraquat treatment for 11 days or hypothermia for 28 days), FG treatment reduced the level of POL by 20–40% as compared to the effects of stressors alone, which indicates FG elicitor properties. Antiradical properties of FG toward the hydroxyl radical were manifested in the reaction of deoxy-D-ribose destruction in water medium (without homogenate) within the concentration range from 4.5 to 65 μM; the effects toward the oxygen anion radical were insignificant. It is suggested that FG influence on generation of reactive oxygen species mediates the stimulation of potato plant defense responses to environmental factors.

Role of salicylic acid and oxidative burst in expression of resistance to Alternaria blight

The accumulation of salicylic acid and H2O2 during pathogenic infection of mustard plants with Alternaria brassicae spores was investigated to understand the role of these two defense compounds in the expression of resistance. Comparisons were made between a susceptible Brassica juncea variety RH30 and a Brassica carinata variety HC1, which is known to be resistant. An oxidative burst was detected as in situ accumulation of H2O2, in both the Brassica spp. after pathogen application. However, H2O2 generation was extracellular in the resistant variety and both extra- and intracellular in the susceptible variety. Endogenous levels of SA increased over 2.5-fold in the resistant variety HC1 in response to pathogen application and this increase was observed only in conjugated SA levels. Pathogen application also led to an increase in the antioxidant enzymes, guaiacol-dependent peroxidase (GDP) and superoxide dismutase (SOD) in HC1. Exogenous SA application to leaves led to over threefold increase in the free and conjugated SA levels in both varieties. Pathogen application to the SA pretreated plants led to over 10-fold increase in endogenous SA levels in both varieties as compared to the levels in controls and this correlated with a decrease in disease symptoms in both species. SA appeared to regulate defense responses in Brassica spp. in a concentration-dependent manner. While 2.7-fold increase in endogenous SA levels (as seen in HC1) led to an induction of antioxidant enzymes, over 10-fold increases in endogenous SA levels (as seen after exogenous SA application in both varieties) brought about no induction of the antioxidant enzymes, probably because SA itself served as an antioxidant.

Comparative study for salt stress among seed, root stock and direct regenerated violet (Viola odorata L.) seedlings in relation to growth, ion contents and enzyme activities

The experiments were carried out to evaluate the comparative study for salt stress among seed, root stock and direct regenerated violet ( Viola odorata L.) seedlings. Violet seedlings propagated through tissue culture (direct regeneration) had significantly higher salicylic acid (SA) concentrations from seed and rootstock propagated plants. Random amplified polymorphic DNA (RAPD) studies prior to the salt treatments revealed that genetic similarity at the molecular level among seed, root stock and direct regenerated violet seedlings was 50.9 to 70.5%. NaCl applications (50 mol m –3 ) reduced plant and root lengths, plant fresh and dry weights in plants obtained through seeds and rootstock as compared to direct regenerated seedlings. Direct regenerated violet showed better plant growth significantly both in saline and non-saline conditions. Seedlings raised through direct regeneration strongly inhibited accumulation of Na + , K + , Ca 2+ and Cl − and organic solute accumulations as glycinebetaine (GB) and root total soluble carbohydrates (TSC) but stimulated N and relative water contents (RWC). Direct regenerated seedlings showed an enhanced catalase (CAT), ascorbate peroxidase (APX) and guaiacol dependent peroxidase (GDP) activities as compared to seed and root stock propagated plants. It was concluded that direct regenerated plants had better performance under salt stress in relation to growth and ion accumulations as compared to seed and root stock propagated violet seedlings. This might be due to higher SA concentrations in direct regenerated seedlings which resulted from somaclonal variations or growth media applied during tissue culture technique.

Changes in the redox status of chickpea roots in response to infection by Fusarium oxysporum f. sp. ciceris: apoplastic antioxidant enzyme activities and expression of oxidative stress‐related genes

Activity levels of oxidative stress-related enzymes in the root apoplast during the interaction of WR315 (resistant) and JG62 (susceptible) chickpeas (Cicer arietinum L.) with the highly virulent race 5 of Fusarium oxysporum f. sp. ciceris were compared. Because this fungus develops asymptomatic infections in the chickpea root cortex in both susceptible and resistant plants, but only intrudes into the root xylem in the susceptible variety, the interactions were compared at three specific stages during disease development in JG62: (i) before symptom development (10 days after inoculation); (ii) at the time of appearance of the first disease symptoms (15-17 days after inoculation) and (iii) when all plants had developed disease symptoms (20-22 days after inoculation). Diamine oxidase (DAO), ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol-dependent peroxidase and superoxide dismutase (SOD), but not catalase (CAT), were found in the apoplast of chickpea roots. In terms of APX activity, infection by the pathogen caused a different response in the incompatible compared to the compatible plant. In the case of GR, SOD and DAO activities, the pathogen caused the same response, but it developed earlier (i.e. GR and SOD) or to higher levels (i.e. DAO) in the incompatible interaction. Expression of apx, cat, sod, lipoxygenase (lox) and actin genes was also analysed in infected roots. Infection by F. oxysporum f. sp. ciceris race 5 only caused a significant change in the root expression of lox and actin genes. This up-regulation was earlier (lox) or higher (actin) in the incompatible than in the compatible interaction. Thus, changes in oxidative metabolism differ in compatible and incompatible interactions in Fusarium wilt of chickpea.