Expression of antioxidant oxidoreductases and protein profile of seedling tissues of winter and spring forms of cereals under extreme temperature fluctuations

Cultivation of seedlings of soft wheat and barley under extreme temperature fluctuations led to a decrease in the total content of acidic proteins in tissues by more than 25% and reduced the total activity of peroxidases and superoxide dismutases. Against the background of changes in the general expression of enzymes, there was a redistribution of activities between their individual isoforms. Extreme ambient temperatures did not lead to a significant change in the ratio of peroxidase activity to the activity of superoxide dismutase in the cells of seedlings, but it caused a change in the ratio of peroxidase and oxidase activity in individual fractions of the electrophoretic spectrum. The dependence of the expression of structural oxidoreductase genes from the genetically determined type of development (winter or spring) was determined by the ??organism-environment?? definite situation. When growing cereals at a constant optimum temperature, there was no correlation between the type of development (winter or spring) and quantitative and qualitative indicators of the oxidoreductase spectra. However, when forming a plant stress response to extreme fluctuations in temperature, the degree of expression of some isoforms of enzymes in winter and spring genotypes was different, which indicates the dependence of the functional state of the studied enzymes on the allelic composition of the Vrn1 locus.     

Photosynthesis, antioxidant activities and transcriptional responses in two sugarcane (Saccharum officinarum L.) cultivars under salt stress

This study analyzes changes in gene expression and the biochemical and physiological properties of the antioxidant system in the leaves of two sugarcane cultivars under salt stress. In both salt-stressed cultivars, no alteration in the foliar nitrogen content was observed; however, there was a reduction in the phosphorus and potassium levels and an increase in the sodium and chloride concentrations. There was also a reduction in gas exchange on the third day under salt stress. Although the content of soluble sugars remained stable in both species, there was a decrease in free amino acids. However, only the RB872552 cultivar displayed a lower leaf protein content compared to the control. The salt stress resulted in higher superoxide dismutase and l-ascorbate peroxidase activities, but only for the RB92579 cultivar. On the other hand, both cultivars were able to maintain lower malondialdehyde contents than the control plants. The gene expression analysis revealed down-regulated expression levels, including the levels of those enzymes linked to higher activities under salt stress. Our results showed that gene induction and leaf antioxidative cycle enzyme activity do not occur at the same time. The variations in gene expression and physiological responses are also discussed.     

Lipid peroxidation and antioxidant status in blood of patients with uterine myoma, endometrial polypus, hyperplastic and malignant endometrium

Oxidative stress is considered to be involved in pathogenesis of many disorders of the female genital tract. In this study, we explored the lipid peroxidation levels and antioxidant enzyme activities in women diagnosed with different forms of uterine diseases in order to evaluate the extent of oxidative stress in blood of such patients. Blood samples of healthy subjects and gynecological patients were collected and subjected to assays for superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and lipid hydroperoxides. The results show that alterations of measured parameters vary with the enzyme type and diagnosis. However, both reduction in antioxidants and elevation of lipid peroxidation were observed in general. Lipid hydroperoxides level was negatively correlated to superoxide dismutase and glutathione peroxidase activities, as well as positively correlated to catalase activity. In addition, the lipid hydroperoxides/ glutathione peroxidase ratio was found to be increased, according to the type of uterine disease. The obtained results show that perturbation of antioxidant status is more pronounced in blood of patients with premalignant (hyperplastic) and malignant (adenocarcinoma) lesions, compared to those with benign uterine changes such as polypus and myoma.     

Comprehensive metabolomic,proteomic and physiological analyses of grain yield reduction in rice under abrupt drought–flood alternation stress

Abrupt drought–flood alternation (T1) is a meteorological disaster that frequently occurs during summer in southern China and the Yangtze river basin, often causing a significant loss of rice production. In this study, the response mechanism of yield decline under abrupt drought–flood alternation stress at the panicle differentiation stage was analyzed by looking at the metabolome, proteome as well as yield and physiological and biochemical indexes. The results showed that drought and flood stress caused a decrease in the yield of rice at the panicle differentiation stage, and abrupt drought–flood alternation stress created a synergistic effect for the reduction of yield. The main reason for the decrease of yield per plant under abrupt drought–flood alternation was the decrease of seed setting rate. Compared with CK0 (no drought and no flood), the net photosynthetic rate and soluble sugar content of T1 decreased significantly and its hydrogen peroxidase, superoxide dismutase, peroxidase activity increased significantly. The identified differential metabolites and differentially expressed proteins indicated that photosynthesis metabolism, energy metabolism pathway and reactive oxygen species response have changed strongly under abrupt drought–flood alteration stress, which are factors that leads to the rice grain yield reduction.     

Effects of temperature and dietary protein level on hepatic oxidative status of Senegalese sole juveniles (Solea senegalensis)

Effects of 55 and 45% dietary protein levels (55P and 45P diets, respectively) and temperature (12 and 18°C) on hepatic activity of superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione reductase (GR), glucose-6-phosphate dehydrogenase and lipid peroxidation (LPO) levels of Solea senegalensis juveniles were studied. Further, effects of acute thermal shocks provoked by a drop (18°C to 12°C) or a rise (12°C to 18°C) of water temperature on sole oxidative state was also evaluated. Dietary protein reduction increased LPO levels though no major alterations were found on antioxidant enzyme activities between dietary treatments. At 12°C GR activity was higher and SOD activity was lower than 18°C but LPO levels were not affected. In both thermal shock cases, LPO levels increased in 55P group, probably due to insufficient antioxidant enzyme activation. In contrast, fish of 45P group under acute exposition to warmer and colder temperature exhibited no substantial changes and a significant decrease on LPO levels, respectively, along with no major changes in antioxidant enzymes. Overall, results suggest that independently of rearing temperatures 45P group was more susceptible to oxidative stress than 55P group. Thermal shock either due to rise or drop of temperature seemed to induce oxidative stress in 55P group.     

Integration of molecular and physiological models to explain time of anthesis in wheat

Background and Aims

A model to predict anthesis time of a wheat plant from environmental and genetic information requires integration of current concepts in physiological and molecular biology. This paper describes the structure of an integrated model and quantifies its response mechanisms.

Methods

Literature was reviewed to formulate the components of the model. Detailed re-analysis of physiological observations are utilized from a previous publication by the second two authors. In this approach measurements of leaf number and leaf and primordia appearance of near isogenic lines of spring and winter wheat grown for different durations in different temperature and photoperiod conditions are used to quantify mechanisms and parameters to predict time of anthesis.

Key Results

The model predicts the time of anthesis from the length of sequential phases: 1, embryo development; 2, dormant; 3, imbibed/emerging; 4, vegetative; 5, early reproductive; 6, pseudo-stem extension; and 7, ear development. Phase 4 ends with vernalization saturation (VS), Phase 5 with terminal spikelet (TS) and Phase 6 with flag leaf ligule appearance (FL). The durations of Phases 4 and 5 are linked to the expression of Vrn genes and are calculated in relation to change in Haun stage (HS) to account for the effects of temperature per se. Vrn1 must be expressed to sufficient levels for VS to occur. Vrn1 expression occurs at a base rate of 0·08/HS in winter ‘Batten’ and 0·17/HS in spring ‘Batten’ during Phases 1, 3 and 4. Low temperatures promote expression of Vrn1 and accelerate progress toward VS. Our hypothesis is that a repressor, Vrn4, must first be downregulated for this to occur. Rates of Vrn4 downregulation and Vrn1 upregulation have the same exponential response to temperature, but Vrn4 is quickly upregulated again at high temperatures, meaning short exposure to low temperature has no impact on the time of VS. VS occurs when Vrn1 reaches a relative expression of 0·76 and Vrn3 expression begins. However, Vrn2 represses Vrn3 expression so Vrn1 must be further upregulated to repress Vrn2 and enable Vrn3 expression. As a result, the target for Vrn1 to trigger VS was 0·76 in 8-h photoperiods (Pp) and increased at 0·026/HS under 16-h Pp as levels of Vrn2 increased. This provides a mechanism to model short-day vernalization. Vrn3 is expressed in Phase 5 (following VS), and apparent rates of Vrn3 expression increased from 0·15/HS at 8-h Pp to 0·33/HS at 16-h Pp. The final number of leaves is calculated as a function of the HS at which TS occurred (TS^HS): 2·86 + 1·1 × TS^HS. The duration of Phase 6 is then dependent on the number of leaves left to emerge and how quickly they emerge.

Conclusions

The analysis integrates molecular biology and crop physiology concepts into a model framework that links different developmental genes to quantitative predictions of wheat anthesis time in different field situations.     

Effect of selenium-induced oxidative stress on the oxidation reduction system and reproductive ability of male mice

The present study was carried out to evaluate the effect of selenium (Se)-induced oxidative stress on the oxidation reduction system and the fertility status of male mice. Different levels of Se, a potent antioxidant, were fed in three separate groups for 8 wk to create the different oxidative stress in mice. A significant decrese in the glutathione peroxidase (GSH-Px) in both liver and testis was observed in the Se-deficient (0.02 ppm) group I, whereas enzyme levels in the Se-excess (1 ppm) group were comparable to the Se-adequate (0.2 ppm) group. Glutathione-S-transferase activity was enhanced in group I in comparison to group II; however, no change was seen in group III. The glutathione reductase and superoxide dismutase activities were decreased in the Se-deficient group, whereas the enzyme levels were significantly increased in the Se-excess group. The fertility status of the animals studied in terms of percentage fertility and litter size showed a significant decrease in the reproductive ability of male mice in group I when compared to group II. No changes in the fertility status of animals were observed in group III. Thus, the data clearly indicate the effect of oxidative stress generated by feeding various Se levels on the oxidation reduction system and, consequently, its effect on the reproductive ability of male mice.     

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content and superoxide anion (O₂) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.     

Cytokinin oxidase/dehydrogenase overexpression modifies antioxidant defense against heat,drought and their combination in Nicotiana tabacum plants

Cytokinins (CKs) as well as the antioxidant enzyme system (AES) play important roles in plant stress responses. The expression and activity of antioxidant enzymes (AE) were determined in drought, heat and combination of both stresses, comparing the response of tobacco plants overexpressing the main cytokinin degrading enzyme, cytokinin oxidase/dehydrogenase, under the control of root-specific WRKY6 promoter (W6:CKX1 plants) or constitutive promoter (35S:CKX1 plants) and the corresponding wild-type (WT). Expression levels as well as activities of cytosolic ascorbate peroxidase, catalase 3, and cytosolic superoxide dismutase were low under optimal conditions and increased after heat and combined stress in all genotypes. Unlike catalase 3, two other peroxisomal enzymes, catalase 1 and catalase 2, were transcribed extensively under control conditions. Heat stress, in contrast to drought or combined stress, increased catalase 1 and reduced catalase 2 expression in WT and W6:CKX1 plants. In 35S:CKX1, catalase 1 expression was enhanced by heat or drought, but not under combined stress conditions. Mitochondrial superoxide dismutase expression was generally higher in 35S:CKX1 plants than in WT. Genes encoding for chloroplastic AEs, stromatal ascorbate peroxidase, thylakoidal ascorbate peroxidase and chloroplastic superoxide dismutase, were strongly transcribed under control conditions. All stresses down-regulated their expression in WT and W6:CKX1, whereas more stress-tolerant 35S:CKX1 plants maintained high expression during drought and heat. The achieved data show that the effect of down-regulation of CK levels on AES may be mediated by altered habit, resulting in improved stress tolerance, which is associated with diminished stress impact on photosynthesis, and changes in source/sink relations.     

Endophytic bacteria isolated from wild jojoba [<Emphasis Type="Italic">Simmondsia chinensis</Emphasis> L. (Schneider)] roots improve in vitro propagation

Endophytic bacteria promote plant growth, reduce stress caused by biotic and abiotic factors, and can trigger active defense reactions in plants. This study aimed to evaluate enzyme activity of in vitro jojoba (Simmondsia chinensis) plants inoculated with endophytic bacteria. In vitro shoots of female and male plants were inoculated with strains of Azospirillum brasilense (Cd), Methylobacterium aminovorans (JRR11), Rhodococcus pyridinivorans (JRR22) or co-inoculated with a mixture of JRR11?+?JRR22. A total of 10 treatments were performed to evaluate shoot and root length; changes in key enzymes involved in plant defense (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase and phenylalanine ammonia lyase) after post-inoculation (45 days). All endophytic bacteria strains used promoted plant growth and rhizogenesis. Differences were found in enzyme activity between female and male plants. The plants inoculated with JRR22 strain, showed the highest enzyme activity suggesting an induced systemic response and a potential increase in plant resistance to pathogen attack.     

Changes in antioxidant and lignifying enzyme activities in sunflower roots (Helianthus annuus L.) stressed with copper excess

Treatment with 50 microM CuSO4 for five days caused significant decrease in dry-matter production and protein level of ten-day-old sunflower seedling roots. An increase of lipoperoxidation product rate was also observed. The involvement of some enzyme activities in the sunflower root defence against Cu-induced oxidative stress was studied. Copper treatment induced several changes in antioxidant enzymes. SOD (superoxide dismutase, EC 1.15.1.1) activity was reduced but CAT (catalase, EC 1.11.1.6) and GPX (guaiacol peroxidase, EC 1.11.1.7) activities were significantly enhanced. The lignifying peroxidase activities, assayed using coniferyl alcohol and syringaldazine, were also stimulated. Analysis by native gel electrophoresis of syringaldazine peroxidase activity showed the stimulation of an isoform (A2) and the induction of another one (A1) under cupric stress conditions. On the other hand, the activity of PAL (phenylalanine ammonia lyase, EC 4.3.1.5), which plays an important role in plant defence, was also activated. The possible mechanisms by which Cu-induced growth delay and changes in enzymatic activities involved in plant defence processes are discussed.     

Effects of Acibenzolar-S-methyl on the specific activities of peroxidase, chitinase and phenylalanine ammonia-lyase and phenolic content of host leaves in cucumber-powdery mildew interaction

One of the properties of systemic acquired resistance in plants is its concomitance with the biochemical changes including enhancement of activities of defense-related enzymes. In this study, the effects of Acibenzolar-S-methyl (ACI) on the some of defense responses of the cucumber plants (healthy or inoculated with spore suspension of Podosphaerafusca, the causal agent of cucumber powdery mildew) were surveyed via in vivo tests. Changes of defense responses in ACI-treated cucumber plants, inoculated with pathogen or not, were studied and compared with those of non-treated control plants. Results indicated that specific activity of peroxidase increased significantly in treated plants. Increase in enzyme activity was higher in pathogen-inoculated than non-inoculated plants, thus pathogen attack stress to plant plays a role in enhancement of enzyme activity. Specific activity of phenylalanine ammonialyase showed no changes in ACI-treated non-inoculated plants, but in inoculated plants it Increased due to interaction between ACI treatment and pathogen attack stress. Specific activity of chitinase increased in both inoculated and non-inoculated ACI-treated plants at 24 hours after treatment onwards, and pathogen attack stress did not affect it. Phenolic content of ACI-treated plant tissues, despite of small fluctuations, did not show any definite pattern of changes.     

Gel electrophoresis patterns of proteins and peroxidases of excised tomato cotyledons subjected to mannitol induced water stress

Excised tomato cotyledonswere subjected to mannitol induced water stress solutions for three days. Extracts of proteins and the enzyme peroxidase were made and separated with polyacrylamide gel electrophoresis. The water stress injury caused increases in bigger protein molecules but decreases in smaller protein molecules. The small fastest moving peroxidase isozyme was almost completely eliminated. Applications of growth regulators to the stress solutions indicated that the protein and peroxidase changes could be explained on the basis of reduction in endogenous cytokinin activities by the water stress.     

Role of Antioxidant Systems in Wheat Genotypes Tolerance to Water Stress

The role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes. Drought imposed at two different stages after anthesis resulted in an increase in H2O2 accumulation and lipid peroxidation and decrease in ascorbic acid content. Antioxidant enzymes like superoxide dismutase, ascorbate peroxidase and catalase significantly increased under water stress. Drought tolerant genotype C 306 which had highest ascorbate peroxidase and catalase activity and ascorbic acid content also showed lowest H2O2 accumulation and lipid peroxidation (malondialdehyde content) under water stress in comparison to susceptible genotype HD 2329 which showed lowest antioxidant enzyme activity and ascorbic acid content and highest H2O2 content and lipid peroxidation. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Superoxide dismutase activity, however, did not show significant differences among the genotypes under irrigated as well as water stress condition. It seems that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone. This revised version was published online in July 2006 with corrections to the Cover Date.     

Arbuscular mycorrhizal influence on growth,photosynthetic pigments,osmotic adjustment and oxidative stress in tomato plants subjected to low temperature stress

The influence of the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on characteristics of growth, photosynthetic pigments, osmotic adjustment, membrane lipid peroxidation and activity of antioxidant enzymes in leaves of tomato (Lycopersicon esculentum cv Zhongzha105) plants was studied in pot culture under low temperature stress. The tomato plants were placed in a sand and soil mixture at 25°C for 6 weeks, and then subjected to 8°C for 1 week. AM symbiosis decreased malondialdehyde (MDA) content in leaves. The contents of photosynthetic pigments, sugars and soluble protein in leaves were higher, but leaf proline content was lower in mycorrhizal than non-mycorrhizal plants. AM colonization increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in leaves. The results indicate that the AM fungus is capable of alleviating the damage caused by low temperature stress on tomato plants by reducing membrane lipid peroxidation and increasing the photosynthetic pigments, accumulation of osmotic adjustment compounds, and antioxidant enzyme activity. Consequently, arbuscular mycorrhiza formation highly enhanced the cold tolerance of tomato plant, which increased host biomass and promoted plant growth.     

Different effects of exercise tests on the antioxidant enzyme activities in lymphocytes and neutrophils

We have determined the effects of maximal and submaximal cycloergometer tests on the antioxidant enzyme defences of neutrophils and lymphocytes. We also compared the neutrophil and lymphocyte basal enzyme antioxidant activities. A total of 17 well-trained amateur athletes, runners, and cyclists participated in this study. Two tests were performed on an electromagnetic reduction cycloergometer: the maximal exercise test, and the submaximal prolonged exercise test. Blood samples were taken before and after the tests. Basal enzyme activity of superoxide dismutase was higher in lymphocytes but neutrophils presented higher activities of catalase and glutathione peroxidase. The maximal test increased the circulating number of lymphocytes and the activities of catalase and glutathione peroxidase. No changes were observed in lymphocyte number or in lymphocyte antioxidant enzyme activities after the submaximal test. The circulating number of neutrophils increased significantly after the submaximal test. Maximal and submaximal tests decreased the activities of neutrophil glutathione dependent antioxidant enzymes (glutathione peroxidase and glutathione reductase), but no changes were observed in catalase or superoxide dismutase activities after either test. Neither the maximal nor submaximal test produced increases in serum activities of lactate dehydrogenase and creatine kinase (CK).     

Differential Regulation of CuZnSOD Expression in Rat Brain by Acute and/or Chronic Stress

Neuroendocrine stress (NES) causes increase of glucocorticoids and alters physiological levels of reactive oxygen species production in cells, which might involve modifications in the antioxidant defense system. We investigated the hypothesis that acute, chronic, or combined stress alters copper–zinc superoxide dismutase (CuZnSOD) expression pattern at both, mRNA and subcellular protein level in the cerebral cortex and hippocampus of rats and that there may be a relationship between stress-induced corticosterone and CuZnSOD expression. The most effective stress model which led to the most pronounced changes in CuZnSOD expression patterns was also investigated. Our results demonstrated that acute stress immobilization up-regulates mRNA expression of hippocampal CuZnSOD, while cytosolic protein expression of this enzyme was increased in both brain structures. Chronic stress isolation had no effect on either mRNA and protein expression level and caused a lack of significant up-regulation to a novel acute stressors. The presence of this protein in nuclear fractions of both brain structures was also confirmed. The elevated cytosolic CuZnSOD protein levels following acute immobilization might reflect on the defense system against oxidative stress. Chronic isolation compromises CuZnSOD protein expression, which may lead to the inefficient defense against reactive oxygen species (ROS). The stress-triggered CuZnSOD protein expression was not correlated by the corresponding mRNA. The results suggest that different stress models exert a different degree of influence on mRNA and protein level of CuZnSOD in both brain structures as well as serum corticosterone.     

印度梨形孢促进蒺藜苜蓿生长及其提高耐盐性研究

【目的】研究盐胁迫下印度梨形孢定殖对豆科模式植物蒺藜苜蓿生长发育的影响。【方法】通过分析不同生境下植物的根长、根鲜重和茎鲜重,以及体内抗氧化物酶活性、脯氨酸含量、甜菜碱醛脱氢酶基因(BADH)的表达,确定印度梨形孢对蒺藜苜蓿生长的促进作用,并初步阐释印度梨形孢诱导植物耐盐性的机制。【结果】印度梨形孢能在蒺藜苜蓿根部定殖并能促进植物的生长发育,有效缓解盐胁迫造成的生长抑制。印度梨形孢能提高植物体内抗氧化物酶活性,增加游离脯氨酸含量并诱导BADH基因的表达。【结论】印度梨形孢作为植物生长促进因子可以用来提高植物耐盐性,实现盐碱土壤的间接改良。     

Characterization of <Emphasis Type="Italic">Brassica juncea</Emphasis> antioxidant potential under salinity stress

Present study characterizes the anti-oxidative defense potential of four Brassica juncea varieties, Pusa Jaikisan, Varuna, RLM-198, and CS-52, differing in their ability to withstand salinity stress. 7-day-old seedlings raised in MS medium supplemented with 0, 50, 100, and 150 mM NaCl were used to monitor changes in the growth profile, level of stress marker molecules, and activities of important antioxidant enzymes. Increasing NaCl concentration resulted in a significant (P ≤ 0.05) reduction of shoot fresh and dry mass and vigor index in all the varieties tested. Maximum reduction in growth was recorded for RLM-198 while CS-52 maintained better growth characteristics. Varuna and RLM-198 exhibited a limited increase in superoxide dismutase, ascorbate peroxidase, and total peroxidase activity under increasing salinity. These varieties also recorded maximum salt stress-induced damage in terms of increased lipid peroxidation, H₂O₂ content, and electrolyte leakage. On the other hand, CS-52 recorded maximum proline accumulation with minimum levels of H₂O₂, electrolyte leakage, and malondialdehyde contents. With increasing salinity stress, CS-52 recorded maximal increase in the activity of antioxidant enzymes. However, catalase activity did not correlate with alterations in H₂O₂ levels under stress. Interestingly, a lower superoxide dismutase:ascorbate peroxidase ratio in CS-52 correlated with stress tolerance trait, while a comparatively higher superoxide dismutase:ascorbate peroxidase ratio in RLM-198 marked the susceptible nature of the variety. Our results propose that superoxide dismutase:ascorbate peroxidase ratio is the critical factor, determining the degree of stress tolerance in Brassica juncea.