Pod surface exudates of wild relatives of pigeonpea influence the feeding preference of the pod borer, Helicoverpa armigera

Wild relatives of crops are an important source of resistance genes against insect pests. However, it is important to identify the accessions of wild relatives of crops with different mechanisms of resistance to broaden the basis and increase the levels of resistance to insect pests. Therefore, we studied the feeding behavior of pod borer, Helicoverpa armigera, which is the most damaging pest of pigeonpea, in relation to biochemical characteristics of the pod surface exudates in a diverse array of germplasm accessions belonging to 12 species of pigeonpea wild relatives. Feeding by H. armigera larvae was significantly lower on the unwashed or water-, methanol-, or hexane-washed pods of Canajus sericeus, C. scarabaeoides, Flemingia bracteata, F. stricta, and Rhynchosia aurea than those of C. acutifolius, C. albicans, C. cajanifolius, C. lineatus, D. ferruginea, P. scariosa, R. bracteata, and the cultivated pigeonpea, C. cajan genotypes, ICPL 87, and ICPL 332, although there were a few exceptions. The methanol-washed pods of wild relatives were less preferred for feeding by the H. armigera larvae than the unwashed pods, but the hexane-washed pods were preferred more than the unwashed pods. The results suggested that methanol extracted the phagostimulants from the pod surface, while hexane removed the antifeedants. The high-performance liquid chromatography (HPLC) finger printing of methanol and hexane pod surface extracts showed qualitative and quantitative differences in compounds present on the pod surface of different wild relatives of pigeonpea. Some of the peaks in HPLC profiles were associated with feeding preference of the third-instar larvae of H. armigera. There was considerable diversity in wild relatives of pigeonpea as revealed by principal component analysis based on HPLC fingerprints of pod surface extracts in methanol and hexane, and H. armigera feeding on the pods. Wild pigeonpea accessions with low amounts of phagostimulants and high amounts of antifeedants may be used for introgression of resistance genes into the cultivated pigeonpea to develop varieties with broad-based resistance to H. armigera. There is considerable diversity among the wild relatives of pigeonpea, and the accessions with resistance to pod borer. These can be used to broaden the basis and increase the levels of resistance to H. armigera.     

Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H₂O₂) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H₂O₂, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H₂O₂ content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.     

Elevated CO<Subscript>2</Subscript> influences host plant defense response in chickpea against <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

Global atmospheric concentration of CO₂ is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO₂ on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteen-day-old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO₂. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO₂ concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO₂ than in plants kept under ambient conditions. The H. armigera-infested plants had higher H₂O₂ content; amounts of oxalic and malic acids were greater at 750 ppm CO₂ than at 350 ppm CO₂. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO₂. This information will be useful for understanding effects of increased levels of CO₂ on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change.     

Interaction of acid exudates in chickpea with biological activity of Bacillus thuringiensis towards Helicoverpa armigera

The gram pod borer, Helicoverpa armigera, is one of the most important constraints to chickpea production. High acidity of chickpea exudates is associated with resistance to pod borer, H. armigera; however, acidic exudates in chickpea might influence the biological activity of the bacterium, Bacillus thuringiensis (Bt), applied as a foliar spray or deployed in transgenic plants for controlling H. armigera. Therefore, studies were undertaken to evaluate the biological activity of Bt towards H. armigera on chickpea genotypes with different amounts of organic acids. Significantly lower leaf feeding, larval survival and larval weights were observed on ICC 506EB, followed by C 235, and ICCV 10 across Bt concentrations. Leaf feeding by the larvae and larval survival and weights decreased with an increase in Bt concentration. However, rate of decrease in leaf feeding and larval survival and weights with an increase in Bt concentration was greater on L 550 and ICCV 10 than on the resistant check, ICC 506EB, suggesting that factors in the resistant genotypes, particularly the acid exudates, resulted in lower levels of biological activity of Bt possibly because of antifeedant effects of the acid exudates. Antifeedant effects of acid exudates reduced food consumption and hence might reduce the efficacy of Bt sprays on insect‐resistant chickpea genotypes or Bt‐transgenic chickpeas, although the combined effect of plant resistance based on organic acids, and Bt had a greater effect on survival and development of H. armigera than Bt alone.     

Exploration of the antioxidative defense system to characterize chickpea genotypes showing differential response towards water deficit conditions

The present investigation was carried out to characterize genotypic variability in chickpea for water deficit tolerance by exploring the antioxidative defense system and seedling growth. Twenty nine chickpea genotypes including cultivars and advanced lines were grown under control and water deficit conditions induced by adding 3 % mannitol. The genotypes showed differential response in seedling growth under water deficit conditions. The activities of catalase (CAT) and superoxide dismutase (SOD) were observed to be differentially expressed in the roots of various genotypes, under control and water deficit conditions. The contents of H₂O₂, malondialdehyde (MDA) and proline were also observed to be variable in the roots of all the genotypes, under control and water deficit conditions. Stress tolerance index for the various parameters, viz, CAT and SOD activity, H₂O₂, MDA and proline content, root length, shoot length and their biomass was determined and the level of stress resistance calculated. The genotypes which showed increased activities of CAT and SOD, decreased contents of H₂O₂ and MDA together with least affected seedling growth under water deficit conditions exhibited higher stress resistance capacity. Multivariate principal component analysis for all the parameters affected under water deficit conditions, grouped the genotypes into three clusters having different (high, moderate and low) levels of stress resistance. Complete linkage clustering grouped these genotypes into two major clusters-I and II. The genotypes present in sub–sub cluster ‘A1’ and sub cluster ‘B’ of major cluster-I have been observed to possess high stress resistance levels for respective parameters. It can thus be concluded that chickpea genotypes exhibiting increased stress resistance levels in relation to SOD and CAT activities, H₂O₂ and MDA contents and seedling growth would have higher stress tolerance under water deficit conditions.     

Morphological and chemical components of resistance to pod borer, Helicoverpa armigera in wild relatives of pigeonpea

Host plant resistance is an important component for minimizing the losses due to the pod borer, Helicoverpa armigera, which is the most devastating pest of pigeonpea. An understanding of different morphological and biochemical components of resistance is essential for developing strategies to breed for resistance to insect pests. Therefore, we studied the morphological and biochemical components associated with expression of resistance to H. armigera in wild relatives of pigeonpea to identify accessions with a diverse combination of characteristics associated with resistance to this pest. Among the wild relatives, oviposition non-preference was an important component of resistance in Cajanus scarabaeoides, while heavy egg-laying was recorded on C. cajanifolius (ICPW 28) and Rhynchosia bracteata (ICPW 214). Accessions belonging to R. aurea, C. scarabaeoides, C. sericeus, C. acutifolius, and Flemingia bracteata showed high levels of resistance to H. armigera, while C. cajanifolius was as susceptible as the susceptible check, ICPL 87. Glandular trichomes (type A) on the calyxes and pods were associated with susceptibility to H. armigera, while the non-glandular trichomes (trichome type C and D) were associated with resistance to this insect. Expression of resistance to H. armigera was also associated with low amounts of sugars and high amounts of tannins and polyphenols. Accessions of wild relatives of pigeonpea with non-glandular trichomes (type C and D) or low densities of glandular trichomes (type A), and high amounts of polyphenols and tannins may be used in wide hybridization to develop pigeonpea cultivars with resistance to H. armigera. Handling editor: Robert Glinwood     

Jasmonic Acid-Mediated-Induced Resistance in Groundnut (Arachis hypogaea L.) Against Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)

Jasmonic acid (JA) acts as a signal molecule to induce resistance in plants against herbivores and its levels are elevated in plants after wounding or insect damage. Groundnut is an important crop in many tropical and subtropical regions worldwide, but there is surprisingly little knowledge on its induced defenses against herbivores. The effect of JA as a spray on induced resistance in three groundnut genotypes, namely, ICGV 86699 (resistant), NCAc 343 (resistant), and TMV 2 (susceptible), against Helicoverpa armigera was studied. The activity of oxidative enzymes [peroxidase (POD) and polyphenol oxidase (PPO)] and the amounts of other host plant defense components [total phenols, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and protein content] were recorded at 24, 48, 72, and 96 h after pretreatment (1 day) with JA followed by infestation with H. armigera (PJA + HIN) and H. armigera infestation with simultaneous JA application (HIN + JA) to understand the consequences of induced resistance in groundnut. The plant damage, larval survival, and larval weights were also recorded. There was a significant increase in POD and PPO activities and in the amounts of total phenols, H₂O₂, MDA, and proteins in PJA + HIN- and JA + HIN-treated plants as compared to the plants treated with JA and infested with H. armigera individually and to untreated control plants. Among all the genotypes, the strongest induction of defense was observed in the ICGV 86699 genotype. It is concluded that pretreatment with JA and its application during low levels of insect infestation can increase the levels of host plant resistance against herbivorous insects and reduce the pest-associated losses in groundnut.     

Nitric oxide improves thermotolerance in spring maize by inducing varied genotypic defense mechanisms

The investigation aimed at determining the effect of nitric oxide on antioxidant defense system of spring maize (Zea mays L.) genotypes namely, LM 11 (stress susceptible) and CML 32 (stress tolerant), that showed differential tolerance towards heat stress. Seed priming with a NO donor, sodium nitroprusside (SNP) improved seedling growth and induced varied defense mechanisms, under stress conditions. 75 μM SNP improved seedling lengths and their biomasses. It specifically enhanced catalase (CAT) activity in the roots of stressed seedlings of the two genotypes. However, it could induce CAT activity only in LM 11 shoots, under heat stress. It also enhanced peroxidase (POX) activity in CML 32 roots. However, such induction of POX activity with SNP treatment was not observed in LM 11 roots. This showed that NO increased the H₂O₂ scavenging efficiency of CML 32 genotype by enhancing the cumulative activation of CAT and POX in its roots. However, it did not induce activation of any of the H₂O₂ detoxifying enzymes in CML 32 shoots which showed that ascorbate–glutathione cycle remained non-operational in shoots of SNP-treated seedlings of the tolerant genotype, under high temperature stress. With seed priming, superoxide dismutase (SOD) activity increased in both the tissues of LM 11 seedlings. The shoots of SNP primed CML 32 seedlings, however, did not show any effect on SOD activity which illustrated that nitric oxide might act as a direct scavenger of superoxide radicals in CML 32 seedlings. SNP decreased the contents of H₂O₂ and MDA and increased proline content in seedlings of both the genotypes indicating reduced oxidative damage. The results thus showed that nitric oxide might induce different mechanisms of stress tolerance in these maize genotypes.     

Antioxidant response of a novel Streptomyces sp. M3004 isolated from legume rhizosphere to H2O2 and paraquat

This paper aims to investigate the effect of H₂O₂ and paraquat on the activities of superoxide dismutase (SOD) and catalase (CAT), and membrane lipid peroxidation (LPO) levels in newly isolated Streptomyces sp. M3004. SOD activities of Streptomyces sp. M3004, grown in 10 mM and 30 mM H₂O₂, were significantly lower than the control cultures. On the other hand, as an antioxidant enzyme, CAT activity in both H₂O₂ treatment conditions increased significantly compared with the control. These activity values in 10 mM and 30 mM H₂O₂ treatment on the 48th hour of incubation were 3.8- and 6.6-fold higher than the control, respectively. SOD activity decreased significantly with respect to paraquat concentration, which was added at the start of the incubation. CAT activities increased significantly in 1.0 mM and 3.0 mM paraquat treatments compared to control. As an indicative marker of membrane damage, LPO levels of the novel isolate Streptomyces sp. M3004 treated with H₂O₂, and paraquat stress conditions were significantly higher than the control. Nevertheless, compared with the 30 mM H₂O₂ in both treatment conditions, LPO levels in 10 mM H₂O₂ were significantly higher. The decreases in SOD activities in paraquat and H₂O₂ treatment conditions resulted in the increases in the LPO levels although it increases in CAT activities.     

Kinetic study of the plastoquinone pool availability correlated with H2O2 release in seawater and antioxidant responses in the red alga Kappaphycus alvarezii exposed to single or combined high light, chilling and chemical stresses

Under biotic/abiotic stresses, the red alga Kappaphycus alvarezii reportedly releases massive amounts of H₂O₂ into the surrounding seawater. As an essential redox signal, the role of chloroplast-originated H₂O₂ in the orchestration of overall antioxidant responses in algal species has thus been questioned. This work purported to study the kinetic decay profiles of the redox-sensitive plastoquinone pool correlated to H₂O₂ release in seawater, parameters of oxidative lesions and antioxidant enzyme activities in the red alga Kappaphycus alvarezii under the single or combined effects of high light, low temperature, and sub-lethal doses of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which are inhibitors of the thylakoid electron transport system. Within 24 h, high light and chilling stresses distinctly affected the availability of the PQ pool for photosynthesis, following Gaussian and exponential kinetic profiles, respectively, whereas combined stimuli were mostly reflected in exponential decays. No significant correlation was found in a comparison of the PQ pool levels after 24 h with either catalase (CAT) or ascorbate peroxidase (APX) activities, although the H₂O₂ concentration in seawater (R = 0.673), total superoxide dismutase activity (R = 0.689), and particularly indexes of protein (R = 0.869) and lipid oxidation (R = 0.864), were moderately correlated. These data suggest that the release of H₂O₂ from plastids into seawater possibly impaired efficient and immediate responses of pivotal H₂O₂-scavenging activities of CAT and APX in the red alga K. alvarezii, culminating in short-term exacerbated levels of protein and lipid oxidation. These facts provided a molecular basis for the recognized limited resistance of the red alga K. alvarezii under unfavorable conditions, especially under chilling stress.     

Mechanisms of resistance to Helicoverpa armigera and introgression of resistance genes into F1 hybrids in chickpea

The noctuid pod borer, Helicoverpa armigera is a major pest of chickpea, and host plant resistance is an important component for managing this pest. We evaluated a set of diverse chickpea genotypes with different levels of resistance to H. armigera, and their F₁ hybrids for oviposition non-preference, antibiosis, and tolerance components of resistance under uniform insect infestation under greenhouse/laboratory conditions. The genotypes ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB were non-preferred for oviposition under no-choice, dual-choice, and multi-choice conditions, and also suffered lower leaf damage in no-choice tests as compared to the susceptible check, ICCC 37. Antibiosis expressed in terms of low larval weights was observed in insects reared on ICC 12476, ICC 12478, and ICC 506EB. Weight gain by the third-instars was also low on ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB at the podding stage. Non-preference for oviposition and antibiosis (poor larval growth) were also expressed in hybrids based on ICC 12477, ICC 12476, ICC 12478, ICC 12479, and ICC 506EB as compared to the hybrids based on the susceptible check, ICCC 37, indicating that oviposition non-preference and antibiosis in the F₁ hybrids is influenced by the parent genotype. Loss in grain yield was lower in ICC 12477, ICC 12478, ICC 12479, and ICC 506EB compared to that on ICCC 37. The genotypes ICC 12477, ICC 12478, ICC 12479, and ICC 506EB showing antixenosis, antibiosis, and tolerance mechanism of resistance to H. armigera can be used for developing chickpea cultivars for resistance to this pest.     

Arsenic-induced changes in growth and antioxidant metabolism of fenugreek

The effects of arsenic (As) on growth and antioxidant metabolism of fenugreek (Trigonella foenum-graecum L. cv. Azad) plants were studied using 10, 20, and 30 mg As/kg of soil in a pot experiment under controlled conditions. The length and dry weights of shoots and roots, photosynthetic traits, and grain yield components exhibited a significant increase over control (0 mg As/kg) at As₂₀ but decreased markedly at As₃₀. The cause of this completely reverse response of plant growth between As₂₀ and As₃₀ was investigated in the backdrop of H₂O₂ metabolism by analyzing responses of three prominent antioxidant enzymes, namely superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) along with cellular ascorbate pool and its redox state. Despite a significant increase in the H₂O₂ content in both As₂₀ and As₃₀ plants, the former, unlike As₃₀ plants, did not experience any type of As-induced oxidative stress (membrane lipid peroxidation, electrolyte leakage). Normal to high levels of leaf APX, CAT, and redox pool of ascorbate effectively balanced the elevated SOD activity at As₂₀, maintaining the H₂O₂ concentration higher than control but obviously in favor of As₂₀ plant growth. By contrast, soil amendment with phosphorus (200 mg P/kg) at As₃₀ prevented As-induced oxidative stress through the reduction of the H₂O₂ level even below As0. The increased enzyme activity was mainly due to the induction of unique Cu/Zn, Fe, and Mn isoforms of SOD and APX-3/APX-4 and/or their increased expression in coordination with CAT. The detection of novel isoforms suggests a strong response of H₂O₂-metabolizing enzymes against As-induced oxidative stress in fenugreek.     

The role of Acanthamoeba castellanii (T4 genotype) antioxidant enzymes in parasite survival under H2O2-induced oxidative stress

Acanthamoeba castellanii (A. castellanii) is an important opportunistic parasite. Induction of oxidative stress by the host immune system is one of the most important defense strategies against parasites. Hence, parasites partly deal with oxidative stress by different mechanisms. Identifying resistance mechanisms of A. castellanii parasites against oxidative stress is important to achieve a new therapeutic approach. Thus, this study aimed to understand the resistance mechanisms of A. castellanii, against oxidative stress. Trophozoites of A. castellanii were treated with different concentrations of H₂O₂. The half maximal inhibitory concentration (IC₅₀) of H₂O₂ was determined using the MTT assay. The induction of oxidative stress was confirmed by flow cytometer. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) were determined. The gene expression levels of CAT and SOD were measured by qRT-PCR. Furthermore, 3-amino-1:2:4-triazole (3-AT) and potassium cyanide (KCN) were used as specific inhibitors of CAT and SOD, respectively. Cell cycle assay and the apoptosis were evaluated by flow cytometer. The activities of SOD, CAT, GR, and GPx, showed an increase in oxidative stress. The cell cycle analysis revealed that most of the cellular population was in G0 and G1 phases. The apoptosis increased in oxidative stress conditions. Moreover, the apoptosis significantly increased after the specific inhibition of CAT and SOD under oxidative stress. The gene expression levels of CAT and SOD significantly increased under oxidative stress. A. castellanii can resist the host immune system through various mechanisms, including evoking its antioxidant enzymes. Therefore, by reducing or inhibiting the activity of the parasite's antioxidant enzymes such as SOD and CAT, it is possible to cope with A. castellanii.     

Exogenous proline alleviates the effects of H2O2-induced oxidative stress in wild almond species

The effect of proline on the antioxidant system in the leaves of eight species of wild almond (Prunus spp.) exposed to H₂O₂-mediated oxidative stress was studied. The levels of endogenous proline (Pro) and hydrogen peroxide, and the activities of total superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (POD) were measured. The degradation of chlorophyll but not carotenoids occurred in leaves in the solution of 5 mM H₂O₂. An increase in membrane lipid peroxidation was observed in H₂O₂ treatment, as assessed by MDA level and percentage of membrane electrolyte leakage (EL). Significant increases in total SOD and CAT activities, as well as decreases in APX and POD activities, were detected in H₂O₂-treated leaves. The three SOD isoforms showed different behavior, as Mn-SOD activity was enhanced by H₂O₂, whereas Fe-SOD and Cu/Zn-SOD activities were inhibited. In addition, Pro accumulation up to 0.1 ??mol/g fr wt, accompanied by significant decreases in ascorbate and glutathione levels, was observed in H₂O₂-treated leaves. After two different treatments with 10 mM Pro + 5 mM H₂O₂, total SOD and CAT activities were similar to the levels in control plants, while POD and APX activities were higher if compared to the leaves exposed only to H₂O₂. Pro + H₂O₂ treatments also caused a strong reduction in the cellular H₂O₂ and MDA contents and EL. The results showed that Pro could have a key role in protecting against oxidative stress injury of wild almond species by decreasing membrane oxidative damage.     

Differential responses of oat genotypes: oxidative stress provoked by aluminum

The phytotoxic effects of aluminum and the mechanisms of genetically-based Al tolerance have been widely investigated, as reported in many papers and reviews. However, investigations on many Al-sensitive and Al-resistant species demonstrate that Al phytotoxicity and Al-resistance mechanisms are extremely complex phenomena. The objective of the present study was to analyze the effects of aluminum on the activity of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX). Also was evaluated the lipid peroxidation, H₂O₂ content, levels of ascorbic acid (ASA), non-protein thiols (NPSH) and Al content in three genotypes of oat, Avena sativa L. (UFRGS 930598, UFRGS 17, and UFRGS 280). The genotypes were grown in different concentrations of Al ranging from 90 to 555???M for 5?days. The antioxidant system was unable to overcome toxicity resulting in negative effects such as lipid peroxidation and H₂O₂ content in UFRGS 930598. The results showed that UFRGS 930598 was the most sensitive genotype. UFRGS 17 and UFRGS 280 were more resistant to Al toxicity. These results suggest that UFRGS 17 has mechanisms of external detoxification and UFRGS 280 has mechanisms of internal detoxification. The different behavior of enzymatic and non-enzymatic antioxidants of the genotypes showed that aluminum resistance in UFGRS 17 and UFRGS 280 may be related to oxidative stress.     

A hydrogen peroxide safety valve: The reversible phosphorylation of catalase from the freeze-tolerant North American wood frog,Rana sylvatica

BackgroundThe North American wood frog, Rana sylvatica, endures whole body freezing while wintering on land and has developed multiple biochemical adaptations to elude cell/tissue damage and optimize its freeze tolerance. Blood flow is halted in the frozen state, imparting both ischemic and oxidative stress on cells. A potential build-up of H₂O₂ may occur due to increased superoxide dismutase activity previously discovered. The effect of freezing on catalase (CAT), which catalyzes the breakdown of H₂O₂ into molecular oxygen and water, was investigated as a result.MethodsThe present study investigated the purification and kinetic profile of CAT in relation to the phosphorylation state of CAT from the skeletal muscle of control and frozen R. sylvatica.ResultsCatalase from skeletal muscle of frozen wood frogs showed a significantly higher V_max (1.48 fold) and significantly lower K_m for H₂O₂ (0.64 fold) in comparison to CAT from control frogs (5 °C acclimated). CAT from frozen frogs also showed higher overall phosphorylation (1.73 fold) and significantly higher levels of phosphoserine (1.60 fold) and phosphotyrosine (1.27 fold) compared to control animals. Phosphorylation via protein kinase A or the AMP-activated protein kinase significantly decreased the K_m for H₂O₂ of CAT, whereas protein phosphatase 2B or 2C action significantly increased the K_m.ConclusionThe physiological consequence of freeze-induced CAT phosphorylation appears to improve CAT function to alleviate H₂O₂ build-up in freezing frogs.General significanceAugmented CAT activity via reversible phosphorylation may increase the ability of R. sylvatica to overcome oxidative stress associated with ischemia.     

Antixenosis mechanism of resistance in pigeonpea to the pod borer, Helicoverpa armigera

Abstract:  The noctuid pod borer, Helicoverpa armigera , is one of the most important pests of pigeonpea, and plant resistance is an important component for minimizing the extent of losses caused by this pest. To develop insect-resistant cultivars, it is important to understand the contributions of different components of resistance, and therefore, we studied the antixenosis mechanism of resistance to H. armigera in a diverse array of pigeonpea genotypes under no-choice, dual-choice, and multi-choice conditions. Antixenosis for oviposition was observed in case of ICPL 187-1, ICP 7203-1, ICPL 88039, T 21, ICPL 84060, and ICPL 332 under no-choice, dual-choice and multi-choice conditions. However, the number of eggs laid on ICPL 88039, T 21 and ICP 7203-1 did not differ significantly from those on ICPL 87 under dual-choice conditions. The susceptible check, ICPL 87 was highly preferred for oviposition. The genotypes ICP 7203-1, ICPL 187-1, T 21, ICPL 332, and ICPL 84060 can be used as sources of non-preference mechanism of resistance in pigeonpea improvement programs to breed for resistance to H. armigera .     

Protective effects of complementary Ca2+ on low-light-induced oxidative damage in tall fescue

Low-light (LL) intensity is a primary abiotic stressor that negatively influences turf grass quality. In the present experiment, we studied the effect of exogenous Ca²⁺ (0, 10, 50, 100, and 200 mM) on the antioxidant system, the accumulation of MDA and proline, the content of photosynthetic pigments in plant leaves in order to investigate whether exogenous Ca²⁺ treatment improves LL tolerance in tall fescue (Festuca arundinacea Schreb.). We have found that LL significantly reduced a number of growth parameters (plant height, leaf width, leaf fresh weight, root fresh weight, leaf dry weight, and root dry weight), chlorophyll (Chl) a and Chl b contents, and carotenoid (Car) levels, while considerably enhancing electrolyte leakage (EL), MDA accumulation, calcium (Ca²⁺) concentration, and generation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide radical (O ₂ ^·? ). Moreover, LL significantly induced the activities of antioxidant enzymes, such as peroxidase (POD) and catalase (CAT), and slightly increased the activity of superoxide dismutase (SOD) in tall fescue leaves. In contrast, POD and SOD activities declined considerably while CAT activity significantly increased in plant roots under LL stress. The application of 50 mM Ca²⁺ significantly improved the aforementioned growth parameters, the content of photosynthetic pigments, and further enhanced the activities of POD, SOD, and CAT, but decreased electrolyte leakage and MDA and H₂O₂ levels in the leaves and roots of tall fescue under LL stress. These results suggest that Ca²⁺ is likely involved in a resistance to LL by regulating antioxidant enzyme action in tall fescue leaves and roots.     

Pre-treatment with H<Subscript>2</Subscript>O<Subscript>2</Subscript> induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 μM H₂O₂ for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H₂O₂ alone had no effect on the proline, malondialdehyde (MDA) and H₂O₂ contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 μM H₂O₂ treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H₂O₂ pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of ¹⁴CO₂ fixation was higher and MDA, H₂O₂ and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl⁻ content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H₂O₂ metabolism is involved as a signal in the processes of barley salt tolerance.     

Antioxidant defence system during exponential and stationary growth phases of Phycomyces blakesleeanus: Response to oxidative stress by hydrogen peroxide

An analysis of the components of the antioxidant defence system in exponential and stationary growth phases of filamentous fungus Phycomyces blakesleeanus and the response to the oxidative stress hydrogen peroxide were performed. There is a strong positive correlation between mycelial antioxidant capacity and the contents of gallic acid, d-erythroascorbate (d-EAA) or d-erythroascorbate monoglucoside (d-EAAG). These secondary metabolites are specifically synthesized by this fungus and reach maximal values in the stationary growth phase, suggesting that they can play some role in the antioxidant defence system of this fungus. There is a differential expression of the two more notable antioxidant activities, catalase (CAT) and superoxide dismutase (SOD), depending of the growth stage of P. blakesleeanus, CAT being expressed in the exponential and SOD in the stationary phase. Phycomyces blakesleeanus showed a high resistance to the oxidative stress caused by H₂O₂ (50 and 200 mM) which was higher in exponential phase. This higher resistance can be explained by the presence of CAT, glutathione peroxidase (GPx), and the probable contribution of glutathione-S-transferase (GST) and high levels of reduced form of glutathione (GSH). The transition to stationary phase was accompanied with a higher physiological oxidative damage illustrated by the higher protein carbonylation. In this growth stage the resistance of the fungus to the oxidative stress caused by H₂O₂ could be explained by the presence of SOD, GPx, and the probable contribution of GST as well as of secondary metabolites, mainly d-EAA and d-EAAG. These results highlight a specific response to oxidative stress by H₂O₂ depending on the growth phase of P. blakesleeanus.