Salicylic and jasmonic acids in regulation of the proantioxidant state in wheat leaves infected by Septoria nodorum Berk

Influence of mediators of the signal systems of salicylic (SA) and jasmonic (JA) acids and their mixture on reactive oxygen species' (ROS) (superoxide radical O2*- and H2O2) generation and activity of oxidoreductases (oxalate oxidase, peroxidase and catalase) in leaves of wheat Triticum aestivum L. infected by Septoria leaf blotch pathogen Septoria nodorum Berk. has been studied. Presowing treatment of seeds by SA and JA decreased the development rate of fungus on wheat leaves. SA provided earlier inductive effect on production of O2*- and H2O2 compared with JA. The protective effect of the salicylic and jasmonic acids against Septoria leaf blotch pathogen was caused by activation of oxalate oxidase, induction of anion and cation peroxidases, and decrease of catalase activity. Ability of compounds to stimulate ROS in the plant tissues can be used as criteria for evaluation of immune-modulating activity of new substances for protection of the plants.     

Involvement of extracellular oxidative burst in salicylic acid-induced stomatal closure in Arabidopsis

Salicylic acid (SA), a ubiquitous phenolic phytohormone, is involved in many plant physiological processes including stomatal movement. We analysed SA‐induced stomatal closure, production of reactive oxygen species (ROS) and nitric oxide (NO), cytosolic calcium ion ([Ca²⁺]_cyt) oscillations and inward‐rectifying potassium (K⁺_in) channel activity in Arabidopsis. SA‐induced stomatal closure was inhibited by pre‐treatment with catalase (CAT) and superoxide dismutase (SOD), suggesting the involvement of extracellular ROS. A peroxidase inhibitor, SHAM (salicylhydroxamic acid) completely abolished SA‐induced stomatal closure whereas neither an inhibitor of NADPH oxidase (DPI) nor atrbohD atrbohF mutation impairs SA‐induced stomatal closures. 3,3′‐Diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) stainings demonstrated that SA induced H₂O₂ and O₂^– production. Guard cell ROS accumulation was significantly increased by SA, but that ROS was suppressed by exogenous CAT, SOD and SHAM. NO scavenger 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTIO) suppressed the SA‐induced stomatal closure but did not suppress guard cell ROS accumulation whereas SHAM suppressed SA‐induced NO production. SA failed to induce [Ca²⁺]_cyt oscillations in guard cells whereas K⁺_in channel activity was suppressed by SA. These results indicate that SA induces stomatal closure accompanied with extracellular ROS production mediated by SHAM‐sensitive peroxidase, intracellular ROS accumulation and K⁺_in channel inactivation.     

Salicylic and Jasmonic acids in regulation of the proantioxidant state in wheat leaves infected by <Emphasis Type="Italic">Septoria nodorum</Emphasis> Berk

Influence of mediators of the signal systems of salicylic (SA) and jasmonic (JA) acids and their mixture on reactive oxygen species’ (ROS) (superoxide radical and O₂^·− H₂O₂) generation and activity of oxidoreductases (oxalate oxidase, peroxidase and catalase) in leaves of wheat Triticum aestivum L. infected by Septoria leaf blotch pathogen Septoria nodorum Berk has been studied. Presowing treatment of seeds by SA and JA decreased the development rate of fungus on wheat leaves. SA provided earlier inductive effect on production of O₂^·− and H₂O₂ compared with JA. The protective effect of the salicylic and jasmonic acids against Septoria leaf blotch pathogen was caused by activation of oxalate oxidase, induction of anion and cation peroxidases, and decrease of catalase activity. Ability of compounds to stimulate ROS in the plant tissues can be used as criteria for evaluation of immune-modulating activity of new substances for protection of the plants.     

Efficacy of salicylic acid in modulating physiological andbiochemical mechanisms to improve postharvest longevity in cut spikes of Consolida ajacis (L.) Schur.

Postharvest losses of cut flowers is one of the considerable challenges restricting their efficient marketability. Consequently, such challenges have triggered a constant hunt for developing compatible postharvest treatments to mitigate postharvest losses. Interestingly, recent studies entrench extensive role of salicylic acid (SA) in mitigating postharvest losses in various flower systems. The current investigation focusses on role of SA in augmenting physiological and biochemical responses to mitigate postharvest senescence in cut spikes of Consolida ajacis. The cut spikes of C. ajacis were supplemented with various SA treatments viz, 2 mM, 4 mM, 6 mM. The effects of these treatments were evaluated against control set of spikes placed in distilled water. Our study indicates considerable increment in postharvest longevity of cut spikes, besides an increase in solution uptake, sugar and protein content of tepal tissues.SA augmented antioxidant system via upsurge in phenolic content and antioxidant enzymes viz, superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) to forfend reactive oxygen species (ROS) related oxidative damage. SA profoundly reduced lipoxygenase (LOX) activity to preserve the membrane integrity and thus prevented seepage of solutes from tepal tissues. These results authenticate SA particularly 4 mM concentration as effective postharvest treatment to preserve the postharvest quality of C. ajacis cut spikes.     

Stress-protective effect of phenylpropanoid complex on potato plants in vitro

In order to identify factors governing the maintenance of intracellular redox homeostasis, we investigated the effect of phenylpropanoid complex (PPC) isolated from the root extract of Golden root (Rhodiola rosea L.) on the plants of potato (Solanum tuberosum L.) in vitro. It was found that plant treatment with 100 μM PPC brought about a 23% decrease in peroxidase activity in the cells of potato plants and induced a reversible increase in the level of lipid peroxidation (POL) under oxidative stress caused by paraquat. In the presence of NADH known as an oxidase substrate of peroxidases (PO), a decrease in peroxidase activity was associated with switching peroxidase over to oxidase function. This effect was accompanied by a rise in the superoxide dismutase activity by 34% and identical POL elevation. After plant pretreatment with NADPH-oxidase inhibitor diphenylene iodinum, the stimulation of these processes upon the exposure to PPC decreased by 14 and 24%, respectively. This may point to the participation of a PO/NADPH-oxidase tandem in ROS generation. Along with a decrease in peroxidase function of PO, we also observed an opposite effect: in 3 h after the exposure to PPC, its activity rose, which depended on the ability of PPC to switch peroxidase from oxidative to reductive function and back. It was found that the observed effects of PPC comprise not only the respective modulation of antioxidant enzyme activity but also direct ROS quenching. The latter effect of PPC, detected by the rate of a decrease in the level of superoxide anion considerably exceeded the effect of individual antioxidants (salidroside and ascorbic acid), whose inhibitory activity was 5 times lower than the activity of PPC.     

Ethylene signaling in salt stress- and salicylic acid-induced programmed cell death in tomato suspension cells

Salt stress- and salicylic acid (SA)-induced cell death can be activated by various signaling pathways including ethylene (ET) signaling in intact tomato plants. In tomato suspension cultures, a treatment with 250 mM NaCl increased the production of reactive oxygen species (ROS), nitric oxide (NO), and ET. The 10^?3 M SA-induced cell death was also accompanied by ROS and NO production, but ET emanation, the most characteristic difference between the two cell death programs, did not change. ET synthesis was enhanced by addition of ET precursor 1-aminocyclopropane-1-carboxylic acid, which, after 2 h, increased the ROS production in the case of both stressors and accelerated cell death under salt stress. However, it did not change the viability and NO levels in SA-treated samples. The effect of ET induced by salt stress could be blocked with silver thiosulfate (STS), an inhibitor of ET action. STS reduced the death of cells which is in accordance with the decrease in ROS production of cells exposed to high salinity. Unexpectedly, application of STS together with SA resulted in increasing ROS and reduced NO accumulation which led to a faster cell death. NaCl- and SA-induced cell death was blocked by Ca²⁺ chelator EGTA and calmodulin inhibitor W-7, or with the inhibitors of ROS. The inhibitor of MAPKs, PD98059, and the cysteine protease inhibitor E-64 reduced cell death in both cases. These results show that NaCl induces cell death mainly by ET-induced ROS production, but ROS generated by SA was not controlled by ET in tomato cell suspension.     

Metformin induces suppression of NAD(P)H oxidase activity in podocytes

Hyperglycemia increases the production of reactive oxygen species (ROS). NAD(P)H oxidase, producing superoxide anion, is the main source of ROS in diabetic podocytes and their production contributes to the development of diabetic nephropathy. We have investigated the effect of an antidiabetic drug, metformin on the production of superoxide anion in cultured podocytes and attempted to elucidate underlying mechanisms.The experiments were performed in normal (NG, 5.6 mM) and high (HG, 30 mM) glucose concentration. Overall ROS production was measured by fluorescence of a DCF probe. Activity of NAD(P)H oxidase was measured by chemiluminescence method. The AMP-dependent kinase (AMPK) activity was determined by immunobloting, measuring the ratio of phosphorylated AMPK to total AMPK. Glucose accumulation was measured using 2-deoxy-[1,2-³H]-glucose.ROS production increased by about 27% (187 ± 8 vs. 238 ± 9 arbitrary units AU, P < 0.01) in HG. Metformin (2 mM, 2 h) markedly reduced ROS production by 45% in NG and 60% in HG. Metformin decreased NAD(P)H oxidase activity in NG (36%) and HG (86%). AMPK activity was increased by metformin in NG and HG (from 0.58 ± 0.07 to. 0.99 ± 0.06, and from 0.53 ± 0.03 to 0.64 ± 0.03; P < 0.05). The effects of metformin on the activities of NAD(P)H oxidase and AMPK were abolished in the presence of AMPK inhibitor, compound C.We have shown that metformin decreases production of ROS through reduction of NAD(P)H oxidase activity. We also have demonstrated relationship between activity of NAD(P)H oxidase and AMPK.     

Salicylic acid and adenine nucleotides regulate the electron transport system and ROS production in plant mitochondria

Although mitochondria have a central role in energy transduction and reactive oxygen species (ROS) production, the regulatory mechanisms and their involvement in plant stress signaling are not fully established. The phytohormone salicylic acid (SA) is an important regulator of mitochondria-mediated ROS production and defense signaling. The role of SA and adenine nucleotides in the regulation of the mitochondrial succinate dehydrogenase (SDH) complex activity and ROS production was analyzed using WT, RNAi SDH1‐1 and disrupted stress response 1 (dsr1) mutants, which show a point mutation in SDH1 subunit and are defective in SA signaling. Our results showed that SA and adenine nucleotides regulate SDH complex activity by distinct patterns, contributing to increased SDH-derived ROS production. As previously demonstrated, SA induces the succinate-quinone reductase activity of SDH complex, acting at or near the ubiquinone binding site. On the other hand, here we demonstrated that adenine nucleotides, such as AMP, ADP and ATP, induce the SDH activity provided by the SDH1 subunit. The regulation of SDH activity by adenine nucleotides is dependent on mitochondrial integrity and is prevented by atractyloside, an inhibitor of adenine nucleotide translocator (ANT), suggesting that the regulatory mechanism occurs on the mitochondrial matrix side of the inner mitochondrial membrane, and not in the intermembrane space, as previously suggested. On the other hand, in the intermembrane space, ADP and ATP limit mitochondrial oxygen consumption by a mechanism that appears to be related to cytochrome bc1 complex inhibition. Altogether, these results indicate that SA signaling and adenine nucleotides regulate the mitochondrial electron transport system and mitochondria-derived ROS production by direct effect in the electron transport system complexes, bringing new insights into mechanisms with direct implications in plant development and responses to different environmental responses, serving as a starting point for future physiological explorations.     

The effect of NaCl on antioxidant enzyme activities in potato seedlings

The effect of NaCl on the growth and activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were investigated in the seedlings of four potato cultivars (Agria, Kennebec; relatively salt tolerant, Diamant and Ajax; relatively salt sensitive). The shoot fresh mass of Agria and Kennebec did not changed at 50 mM NaCl, whereas in Diamant and Ajax it decreased to 50 % of that in the controls. In Agria and Kennebec, SOD activity increased at 50 mM NaCl, but no significant changes observed in Diamant and Ajax. At higher NaCl concentration, SOD activity reduced in all cultivars. CAT and POD activities increased in all cultivars under salt stress. Unlike the other cultivars, in Ajax seedlings, APX activity increased in response to NaCl stress. We also observed new POD and SOD isoenzyme activities and changes in isoenzyme compositions under salt stress. These results suggest that salt-tolerant potato cultivars may have a better protection against reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes (especially SOD) under salt stress.     

Salicylic acid alleviates mercury toxicity by preventing oxidative stress in roots of Medicago sativa

Salicylic acid (SA) as a signal molecule mediates many biotic and environmental stress-induced physiological responses in plants. In this study, we investigated the role of SA in regulating Hg-induced oxidative stress in the roots of alfalfa (Medicago sativa). Plants pretreated with 0.2 mM SA for 12 h and subsequently exposed to 10 μM Hg²⁺ for 24 h displayed attenuated toxicity to the root. The SA-promoted root growth was correlated with decreased lipid peroxidation in root cells. The ameliorating effect of SA was confirmed by the histochemical staining for the detection of loss of membrane integrity in Hg-treated roots. We show that treatment with 0.2 mM SA increased the activity of NADH oxidase, ascorbate peroxidase (APX) and peroxidase (POD) in the roots exposed Hg. However, a slightly decreased superoxide dismutase (SOD) activity was observed in SA + Hg-treated roots when compared to those of Hg treatment alone. We also measured accumulation of ascorbate (ASC), glutathione (GSH) and proline in the roots of alfalfa and found that roots treated with SA in the presence of Hg accumulated more ASC, GSH and proline than those treated with Hg only. These results suggest that exogenous SA may improve the tolerance of the plant to the Hg toxicity.     

Induction of heat resistance of wheat coleoptiles by salicylic and succinic acids: Connection of the effect with the generation and neutralization of reactive oxygen species

The influence of salicylic (SaA) and succinic (SuA) acids on the generation of reactive oxygen species (ROS) and the heat resistance of wheat (Triticum aestivum L.) coleoptiles has been studied. The treatment of coleoptiles with 10 μM SaA or SuA results in the accumulation of hydrogen peroxide and enhanced formation of a superoxide anion radical. This effect was partially suppressed by both α-naphthol (the NADPH oxidase inhibitor) and salicylhydroxamic acid (peroxidase inhibitor). SaA and SuA cause an increase in the activity of antioxidant enzymes, such as superoxide dismutase, catalase, and soluble peroxidase, and improve the heat resistance of coleoptiles. Antioxidant ionol and inhibitors of the NADPH oxidase and peroxidase significantly reduce the positive influence of SaA and SuA on the heat resistance of wheat coleoptiles. ROS are considered to be intermediates for heat resistance induction in coleoptiles, treated with SaA and SuA; enhanced ROS generation can be caused by an increased activity of the NADPH oxidase and peroxidase.     

Changes in some antioxidant enzymes activities and carotenoid content in potato plants infected by Rhizoctonia solani treated with salicylic acid

Abstract

This study was carried out to evaluate the effects of salicylic acid on chlorophyll, carotenoid and antioxidant enzymes in potato plants infected with Rhizoctonia solani under greenhouse conditions. Results showed that with increase in SA amount of chlorophyll, carotenoid contents and also activity of polyphenoloxidase increased in both control and infected plants while increases in infected plants were higher. However, activities of peroxidase and catalase enzymes decreased under the same conditions. Hence, it seems that increase in carotenoid content in infected plants treated with SA is acting as an anti-oxidant against fungi infection. The decrease in catalase and peroxidase activities in response to SA treatment will result in reactive oxygen species produced be less oxidized. The remaining ROS in plants treated with SA is probably acting as anti-fungal agents. The increase in polyphenoloxidase activity will increase the root cells walls lignifications process acting as mechanical barrier against fungal infection.     

Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint, causing a significant reduction in crop productivity across the world. Salicylic acid (SA) is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses. The current study investigated the potential effects of SA on drought tolerance efficacy in two barley (Hordeum vulgare) genotypes, namely BARI barley 5 and BARI barley 7. Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5% soil moisture content in the absence or presence of 0.5, 1.0 and 1.5 mM SA. Drought exposure led to severe damage to both genotypes, as indicated by phenotypic aberrations and reduction of dry biomass. On the other hand, the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought, which was reflected in the improvement of phenotypes and biomass production. SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes, indicating the osmotic adjustment functions of SA under water-deficit conditions. Drought stress induced the accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide (O₂ ^•− ), and the lipid peroxidation product malondialdehyde (MDA) in the leaves of barley plants. Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Among the three-applied concentrations of SA, 0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data. Furthermore, BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application. Collectively, our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.     

Salicylic acid induces resistance to <Emphasis Type="Italic">Septoria nodorum</Emphasis> berk. in wheat

The effect of salicylic acid (SA) on oxalate oxidase and peroxidase activities and hydrogen peroxide (H₂O₂) production in leaf cells has been studied in wheat of the susceptible cultivar Zhnitsa infected by Septoria nodorum, a pathogen of wheat leaf blotch. The results show that fungal hyphae spread into interstices between mesophyll cells and that infected tissues contain H₂O₂. Treatment with SA results in enhanced H₂O₂ production in mesophyll cells, which is due to activation of oxalate oxidase and peroxidase in the cell wall. It is proposed that the modulating effect of SA on oxidoreductase activities is involved in the induction of protective response to fungal infection in wheat plants.     

Hydroponic treatment with salicylic acid decreases the effects of chilling injury in maize (Zea mays L.) plants

The addition of 0.5 mM salicylic acid (SA) to the hydroponic growth solution of young maize (Zea mays L.) plants under normal growth conditions provided protection against subsequent low-temperature stress. This observation was confirmed by chlorophyll fluorescence parameters and electrolyte leakage measurements. In addition, 1 d of 0.5 mM SA pre-treatment decreased net photosynthesis, stomatal conductivity and transpiration at the growth temperature (22/20 °C). Since there was only a slight decrease in the ratio of variable to maximal fluorescence (F_v/F_m) the decrease in photosynthetic activity is not due to a depression in photosystem II. The analysis of antioxidant enzymes showed that whereas SA treatment did not cause any change in ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) activities, there was a decrease in catalase (EC 1.11.1.6) activity, and an increase in guaiacol peroxidase (EC 1.11.1.7) and glutathione reductase (EC 1.6.4.2) activities after the 1-d SA treatment at 22/20 °C. In native polyacrylamide gels there was, among the peroxidase isoenzymes, a band which could be seen only in SA-treated plants. It is suggested that the pre-treatment of maize plants with SA at normal growth temperature may induce antioxidant enzymes which lead to increased chilling tolerance. Received: 4 June 1998 / Accepted: 23 November 1998     

Effect of Salicylic Acid on the Activity of Antioxidant Enzymes in Wheat under Conditions of Salination

The effect of pretreatment with 0.05 mM salicylic acid (SA) on the activity of superoxide dismutase (SOD) and peroxidase in the roots of four-day-old seedlings of wheat (Triticum aestivum L.) was studied under conditions of salination. The level of the stress-induced accumulation of active oxygen species and, therefore, activities of SOD and peroxidase in seedlings pretreated with SA were significantly lower than in untreated seedlings, which indicates that these enzymes contribute to the protective effect of SA on plants under conditions of salination.     

Mechanism underlying oxidative stress-mediated lipotoxicity: exposure of J774.2 macrophages to triacylglycerols facilitates mitochondrial reactive oxygen species production and cellular necrosis

The aim of this study was to elucidate death pathways in macrophages resulting from exposure to triacylglycerols (TG), mechanisms which may be relevant to the development of atherosclerosis. A commercial TG emulsion (lipid emulsion, LE; 0.1-1.5 mg lipids/ml) was added to J774.2 cells in culture. Within the first 24 h after TG treatment, cellular reactive oxygen species (ROS) levels were strongly elevated and basal caspase-3 activity was attenuated. In contrast, after 48 h, ROS production was arrested. TG-mediated ROS production was demonstrated to be via mitochondrial complex 1 of the electron-transfer chain since the inhibitor of complex 1 rotenone significantly attenuated the cellular ROS levels in TG-treated cells. The TG effect culminated in cell death, with no caspase-3 activation. We therefore evaluated the effect of TG on apoptotic cells showing high caspase activity. TG induced elevated ROS levels and suppressed caspase-3 in apoptotic cells pretreated for 24 h with cycloheximide. Dual staining with propidium iodide and Annexin V followed by flow cytometric analysis showed that TG facilitated cell death with clear necrotic characteristics. To elucidate whether the necrotic cell death process is indeed oxidant dependent, antioxidant protection was studied. Treatment with N-acetylcysteine (NAC) (0.5 mM), ascorbic acid (0.5 mM), and resveratrol (0.2 mM) protected against the TG lipotoxic effect, while, surprisingly, lipophilic antioxidants did not. The combination of NAC, ascorbic acid, and resveratrol, each at much lower concentrations, had a synergistic protective effect. In conclusion, we show here for the first time that exposure to TG can directly regulate lipotoxicity in macrophages by inducing mitochondria-mediated prolonged oxidative stress; this, in turn, can inactivate the apoptotic caspase system, resulting in necrotic cell death which can be prevented by specific antioxidants.     

Role of extracellular peroxidase in the superoxide production by wheat root cells

Summary Extracellular peroxidase has been shown to contribute to superoxide production in wounded wheat (Triticum aestivum L. cv. Ljuba) root cells. The superoxide-synthesizing system of root cells was considerably inhibited by KCN and NaN₃ and activated by MnCl₂ and H₂O₂. Treatment of roots with salicylic acid and a range of di- and tri-carbonic acids (malic, citric, malonic, fumaric, and succinic acids) stimulated superoxide production in both root cells and extracellular solution. The H₂O₂-stimulated superoxide production in the extracellular solution was much higher when roots were preincubated with salicylic or succinic acid. Exogenous acids enhanced peroxidase activity in the extracellular solution. Pretreatment of root cells with the detergents trypsin and sodium dodecyl sulfate had similar effects on the peroxidase activity. Significant inhibition of both superoxide production and peroxidase activity by diphenylene iodonium suggests that the specificity of the latter as an inhibitor of NADPH oxidase is doubtful. Results obtained indicate that extracellular peroxidase is involved in the superoxide production in wheat root cells. The mobile form of peroxidase can be readily secreted to the apoplastic solution and serve as an emergency enzyme involved in plant wound response.Abbreviations DPI diphenylene iodonium - ECS extracellular solution - ROS reactive oxygen species - SA salicylic acid     

Combined Effect of Salicylic Acid and Nitrogen Oxide Donor on Stress-Protective System of Wheat Plants under Drought Conditions

Presowing treatment of wheat (Triticum aestivum L.) seeds with 10 or 100 μM salicylic acid (SA) reduced the inhibition of 14-day-old plant growth under soil drought. The same effect was caused by the spraying of 7-day-old seedlings with 0.5 or 2 mM nitrogen oxide donor (sodium nitroprusside, SNP) before drought. The protective effect was enhanced by the combination of seed treatment with 10 μM SA and plant spraying with 0.5 mM SNP, while their combinations in higher concentrations caused weaker effects. SA treatment in both concentrations and 0.5 mM SNP under drought conditions increased the antioxidant enzyme activity (superoxide dismutase, catalase, and guaiacol peroxidase) in leaves. This effect was especially significant when 10 μM SA was combined with 0.5 mM SNP. Spraying with 2 mM SNP and its combination with seed presowing with 100 μM SA did not significantly change the antioxidant enzyme activity; however, the proline content in the leaves increased. It is concluded that the SA stress-protective action on plants can be modified with exogenous nitrogen oxide.