Effects Of Exogenous Salicylic Acid Research Articles

Exogenous superoxide dismutase may lose its antidotal ability on rice leaves

Leaf diffusates of the resistant rice (Oryza sativa L.) cultivars suppressed spore germination of blast fungus (Magnaporthe grisea (Hebert) Barr). Bovine Cu-Zn superoxide dismutase (SOD) added to the diffusate abolished its toxicity. However, the enzyme added to the inoculum did not affect the toxicity of the diffusate. Even the second SOD portion added to the diffusate was ineffective. As well, the enzyme exposed to leaves could not protect the fungus from artificially-generated superoxide. Presumably, SOD contacting with leaves induced an efflux of compound(s) inhibiting both portions of the enzyme. Evidence was obtained suggesting that neither enzymatic protein nor zinc of coenzyme but copper might be the inducer. A comparison of rice leaves and callus culture together with the effects of exogenous salicylic acid suggests that this compound may be the inhibitor liberating from leaves. It is not excluded that rice plants are capable of inactivation of antioxidant enzymes of pathogens and that this ability favors disease resistance.

Salicylic acid induces stomatal closure by modulating endogenous hormone levels in cucumber cotyledons

Salicylic acid (SA) is one of the most important signaling molecules in plant growth and defense responses to biotic and abiotic stresses. Here, the effect of exogenous SA on the stomatal movements was investigated in cotyledons of cucumber (Cucumis sativus L.) seedlings. Application of different SA concentrations could induce the reduction in stomatal aperture and conductance, especially at a concentration of 0.5 mM. Using the isolated epidermal strips, stomata were found to close notably in response to exogenous SA, even at a concentration as low as 0.001 mM. Further study showed that a SA-induced decrease in the stomatal aperture was intensified by the higher SA concentrations, longer exposure, and lower pH of the medium. In addition, to understand the relationship between stomatal closure and endogenous hormone contents, the levels of ABA, IAA, and gibberellin (GA3) were assayed under SA treatment. SA significantly increased endogenous ABA but not IAA and GA3 content. A significant negative correlation (p ≤ 0.01) was observed between stomatal conductance and the ratio of ABA to (GA3 + IAA) during SA application. It was suggested that exogenous SA could change the balance of endogenous hormones and thereby induce stomatal closure in cotyledons of cucumber seedlings.

DELAYING GUAVA RIPENING BY EXOGENOUS SALICYLIC ACID

The experiment was conducted to study the effect of exogenous salicylic acid (SA) treatment (water, 100, 300 and 500 µM) on fruit repining of guava cv 'Baladi' during 12 days shelf-life at room temperature. Fruit were harvested at three different maturity stages: green mature stage (G), green yellow (GY) and yellow stage (Y). Thereafter, fruits were immersed in SA solutions for 20 min. Fruit were immersed at high level 500 µM had less IL%, degradation in total phenol, fruit browning and maintained the amount of vitamin C. Moreover, it had higher fruit firmness and color (hO), compared with other concentrations of SA and water-control.

Exogenous salicylic acid alleviates effects of long term drought stress and delays leaf rolling by inducing antioxidant system

Salicylic acid (SA) is one of the important signal molecules modulating plant responses to environmental stress. In this study, the effects of exogenous SA on leaf rolling, one of drought avoidance mechanisms, and antioxidant system were investigated in Ctenanthe setosa during long term drought stress. The plants were subjected to 38-day drought period and they were treated with or without SA (10−6 M) on the 25th, 27th and 29th days of the period. Leaf samples were harvested on the 30th, 34th and 38th days. Some antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase), reactive oxygen species (hydrogen peroxide and superoxide) and lipid peroxidation were determined during the drought period. Treatment with SA prevented water loss and delayed leaf rolling in comparison with control leaves. Exogenous SA induced all antioxidant enzyme activities more than control leaves during the drought. Ascorbate and glutathione, α-tocopherol, carotenoid and endogenous SA level were induced by the SA treatment. Levels of reactive oxygen species were higher in SA treated plants than control ones on the 34th day. Their levels on the 38th day, however, fastly decreased in SA treated plants. SA treatment prevented lipid peroxidation while the peroxidation increased in control plants. The results showed that exogenous SA can alleviate the damaging effect of long term drought stress by decreasing water loss and inducing the antioxidant system in the plant having leaf rolling, alternative protection mechanism to drought.

Effects of exogenous salicylic acid and nitric oxide on lipid peroxidation and antioxidant enzyme activities in leaves of Brassica napus L. under nickel stress

The effects of nickel in combination with salicylic acid (SA) and sodium nitroprusside (SNP), a donor of nitric oxide (NO) on 21-day-old canola plants were evaluated. Exposure to 0.5 mM NiCl 2·6H 2O for 10 days resulted in toxicity symptoms such as chlorosis and necrosis at leaves. Addition of 0.2 mM SA or 0.2 mM SNP slightly reduced the toxic effects of nickel. After application of both SA and NO, these symptoms considerably decreased. Treatment with Ni resulted in a decrease in dry weight of roots and shoots and chlorophyll content of leaves. In Ni-treated plants, level of lipoxygenase activity and malondialdehyde (MDA), H 2O 2 and proline contents significantly increased, while the activities of the antioxidant enzymes such as catalase, guaiacol peroxidase and ascorbate peroxidase decreased in leaves. The results indicated that Ni caused an oxidative stress in canola plants. The Ni-stressed plants exposed to SA or NO, especially to SA + NO, exhibited an improved growth as compared to Ni-treated plants. SA or NO, especially both together considerably reduced root-to-shoot translocation of Ni and increased the activities of the antioxidant enzymes in leaves of Ni-stressed plants. Interaction of SA and NO improved the chlorophyll content and decreased the level of lipid peroxidation, H 2O 2 and proline accumulation in leaves. These results suggest that SA or NO in particular their combination counteract the negative effects of Ni on canola plants.

Effects of salicylic acid on the photosystem 2 of barley seedlings under osmotic stress

The effects of exogenous salicylic acid (SA) on photosystem 2 (PS 2) in barley (Hordeum vulgare L.) seedlings were investigated. SA pretreatment provided protection against subsequent osmotic stress. The highest protective effect of 0.25 mM SA was confirmed by determination of chlorophyll fluorescence, electrolyte leakage, malonyldialdehyde contents, PS 2 mRNAs and proteins. SA pretreatment increased reactive oxygen species (ROS), decreased net photosynthetic rate and stomatal conductance immediately, but prevented ROS accumulation during subsequent osmotic stress by activating antioxidant enzymes. Elimination of H2O2 during SA pretreatment inhibited almost all above mentioned SA effects. Therefore, SA pretreatment enhanced osmotic stress tolerance in barley seedlings mainly through ROS signals, rather than SA itself. The only SA-dependent and ROS-independent effect of exogenous SA on PS 2 was reduction of non-photochemical quenching.

The alternative pathway in cucumber seedlings under low temperature stress was enhanced by salicylic acid

The alternative pathway is a cyanide-resistant and non-phosphorylatory electron transport pathway in mitochondria of higher plants. Alternative oxidase (AOX) is the terminal oxidase of this pathway. Our present study investigated the effect of exogenous salicylic acid (SA) on alternative pathway in cucumber (Cucumis sativus L.) seedlings under low temperature stress. Results showed that during the process of low temperature stress, the alternative pathway capacity was enhanced as AOX expression increased in SA pretreated seedlings. Compared with seedlings without SA pretreatment, slower decrease of relative water content and lower levels of electrolyte leakage, H2O2 and malonyldialdehyde content were detected in SA pretreated seedlings. These results indicated that SA could alleviate the injury caused by low temperature on cucumber seedlings. Since the special protective functions of alternative pathway and AOX in plants, we suggested that the alternative pathway was related to SA-mediated plant resistance to environmental stresses such as low temperature.

Up-regulation of chloroplastic antioxidant capacity is involved in alleviation of nickel toxicity of Zea mays L. by exogenous salicylic acid

A pot experiment was carried out to investigate the effect of exogenous salicylic acid (SA) on the growth, photosynthesis, oxidative stress and responses of chloroplastic antioxidant defense system of maize ( Zea mays L.) plants grown in a nickel (Ni)-contaminated soil. The results indicate that exogenous SA significantly decreased the reduction in dry weight, chlorophyll and β-carotene contents, and net photosynthetic rate of the Ni-stressed maize, demonstrating an alleviating effect of SA on Ni toxicity of plants. Superoxide anion generation rate, H 2O 2 and malondialdehyde (MDA) contents, and lipoxygenase (LOX, EC 1.13.11.12) activity significantly increased in the chloroplasts of maize exposed to Ni stress, revealing an oxidative damage occurred in maize chloroplasts, whereas, the values of these parameters were markedly lowered in the SA-treated plants under Ni stress. Application of SA significantly enhanced the activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2), and the poll of reduced ascorbate and glutathione in chloroplasts of the Ni-stressed maize. Accordingly, the fact that SA up-regulates the capacity of antioxidant defense system in chloroplasts, thus reducing the oxidative damage, is involved in the SA-induced alleviation of Ni toxicity in maize.

Salicylic acid ameliorates the adverse effect of salt stress on strawberry

Strawberry is considered as a salinity sensitive species and is adversely affected in response to the salt stress in terms of growth and yield. Pot experiments were conducted to determine the effect of exogenous salicylic acid (SA) application on physiology, growth, chlorophyll and mineral content of strawberry grown under salt stress and greenhouse conditions. Strawberry plants were treated with SA at different concentrations (0.0, 0.25, 0.50 and 1.00 mM). Salinity treatments were established by adding 0 and 35 mM of NaCl to a base complete nutrient solution. Salt stress negatively affected the growth, chlorophyll content and mineral uptake of strawberry plants. However, plants treated with SA often had greater shoot fresh weight, shoot dry weight, root fresh weight and root dry weight as well as higher chlorophyll content under salt stress. The greatest values were obtained with 1.00 mM SA treatment in both saline and non-saline conditions. Leaf water relative content (LWRC) was reduced in response to salt stress while electrolyte leakage was raised. SA treatments induced increases in LWRC and decreases in electrolyte leakage compared to the control under salt stress. With respect to the nutrient content, SA treatments increased almost contents of all nutrients in leaves and roots of strawberry plants under salt stress. The greatest values were often obtained by the 1.00 mM SA treatment. These findings suggest that the SA treatments can ameliorate the negative effect of salinity on the growth of strawberries.

Exogenous salicylic acid alleviates NaCl toxicity and increases antioxidative enzyme activity in Lycopersicon esculentum

Effects of exogenous salicylic acid (SA) on plant growth, contents of Na, K, Ca and Mg, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and contents of ascorbate and glutathione were investigated in tomato (Lycopersicon esculentum L.) plants treated with 100 mM NaCl. NaCl treatment significantly increased H2O2 content and lipid peroxidation indicated by accumulation of thiobarbituric acid reactive substances (TBARS). A foliar spray of 1 mM SA significantly decreased lipid peroxidation caused by NaCl and improved the plant growth. This alleviation of NaCl toxicity by SA was related to decreases in Na contents, increases in K and Mg contents in shoots and roots, and increases in the activities of SOD, CAT, GPX and DHAR and the contents of ascorbate and glutathione.

Adaptive mechanism of Echinochloa crus-galli Beauv. var. formosensis Ohwi under salt stress: Effect of salicylic acid on salt sensitivity

Our previous study revealed that salicylic acid (SA) accumulates in salt-stressed rice ( Oryza sativa L. cv. Nipponbare) seedlings, and we hypothesized that the accumulation of SA might potentiate oxidative injury in rice seedlings since the inhibition of SA synthesis alleviated the growth inhibition under high salinity. To further clarify the action of SA under salt stress, we investigated the changes in the SA content, the activities of the antioxidative enzymes, and the effects of exogenous SA on barnyardgrass ( Echinochloa crus-galli Beauv. var. formosensis Ohwi), a gramineous weed which shows lower SA content and is more salt tolerant than rice. In E. crus-galli seedlings exposed to high salinity, neither free nor conjugated SA content showed any increase, while the fresh weight of the shoot and chlorophyll fluorescence ( Φ PSII) slightly decreased. When E. crus-galli seedlings were treated with salt after foliar application of SA, the absorbed SA resulted in the enhancement of the salt-induced growth inhibition and a striking reduction of the Φ PSII value. Catalase (CAT) and superoxide dismutase (SOD) activities of E. crus-galli seedlings were induced by the salt treatment. However, SA pre-treatment suppressed such an induction of CAT activity and further promoted SOD activity, both of which led to the elevation of the leaf hydrogen peroxide (H 2O 2) level. The present results suggested that enlargement of the cellular SA pool facilitates the generation of H 2O 2 through the suppression of CAT activity and through a remarkable promotion of SOD activity, and thereby enhances the oxidative injury caused by salt stress.

Salicylic acid activates phenylalanine ammonia-lyase in grape berry in response to high temperature stress

Our previous work has indicated that salicylic acid (SA) is involved in the development of pea plant thermotolerance and induces the gene expression of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), a key enzyme in phenylpropanoid metabolism of grape berry. However, the relationship between SA and PAL during high temperature stress remains obscure. The present experiment, using the technique of in vivo incubation of the grape berry (Vitis vinifera L. cv. Cabernet Sauvignon) tissue in the SA-contained medium, the effects of exogenous SA on the gene expression of PAL and the accumulation of polyphenols during high temperature stress were investigated. The results showed that SA could induce the accumulation of PAL mRNA and the synthesis of new PAL protein, and increase the activity under high temperature stress. A significant accumulation of phenolics was also observed in the SA-treated berries. But, the activation of PAL by SA could be blocked by the pretreatments of berry tissues with the protein synthesis inhibitor cycloheximide, and mRNA transcription inhibitor, actinomycin D, respectively. It is thus speculated that SA may induce the activation of PAL and the accumulation of pheonlics leading to the development of thermotolerance.

Protective Effects of Salicylic Acid and Vitamin C on Sulfur Dioxide-Induced Lipid Peroxidation in Mice

The antioxidant effects of exogenous salicylic acid (SA) and vitamin C (Vit C) on the oxidative stress induced by 56 mg/m3 of sulfur dioxide (SO2) in mouse livers and brains were investigated. The exposure of SO2 caused significant elevation of thiobarbituric acid-reactive substance (TBARS) levels and reduction of enzyme activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in brain and liver, accompanied by a decrease in relative growth rate, when compared with controls. Application of moderate concentrations of SA and Vit C markedly reduced the SO2-induced elevation of TBARS levels, with 5.5 mg/kg SA or 200 mg/kg Vit C being most effective. In contrast to the decrease of TBARS levels, the levels of SOD, POD, and CAT in liver and brain were significantly increased in comparison with controls. The polyacrylamide gel electrophoresis (PAGE) of total liver proteins showed that the SO2 inhalation caused a 30-kD protein band disappearance compared with the control. However, the band remained unchanged in the samples treated with 5.5 and 8.25 mg/kg SA or 100, 200, and 400 mg/kg Vit C. Therefore, this protein band may serve as a marker for the damage induced by SO2 and an additional basis for drug screening and selection.

Effects of exogenous salicylic acid on manganese toxicity, element contents and antioxidative system in cucumber

The effects of salicylic acid (SA) on manganese (Mn) toxicity in cucumber plants ( Cucumis sativus L.) were studied by investigating the symptoms, plant growth, lipid peroxidation, antioxidative enzymes and antioxidants. Excess Mn caused serious chlorosis and inhibited the growth of cucumber plants, and dramatically increased accumulation of Mn in both shoots and roots, furthermore, inhibited the absorption of Ca, Mg and Zn. Addition of SA decreased the transport of Mn from roots to shoots, alleviated the inhibition of Ca, Mg and Zn absorption induced by excess Mn, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in cucumber leaves exposed to excess Mn, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances (TBARS). Addition of SA significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes showed different changes, addition of SA inhibited catalase (CAT) and ascorbate peroxidase (APX) activities, while increased activities of superoxide dismutase (SOD), peroxidase (POD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in cucumber leaves exposed to excess Mn. As important antioxidants, ascorbate and glutathione contents in cucumber leaves exposed to excess Mn were significantly increased by SA treatment.

Effects of exogenous salicylic acid on growth and H 2O 2-metabolizing enzymes in rice seedlings under lead stress

Salicylic acid (SA) was an essential component of the plant resistance to pathogens and also plays an important role in mediating plant response to some abiotic stress. The possible effects of SA on the growth and H 2O 2-metabolizing enzymes in rice seedlings under lead stress were studied. When rice seedlings grown in nutrient solution containing Pb 2+ (0, 0.05, 0.15, 0.25 mmol/L) for 18 d, the plant biomass as well as the chlorophyll content of leaves decreased with increasing Pb concentration. The pre-treatment with SA (treated with 0.1 mmol/L SA for 48 h before Pb stress) partially protected seedlings from Pb toxicity. The chlorophyll contents were significant higher in leaves of Pb-exposed with SA pre-treatment seedlings than in Pb-exposed plants at the same Pb intensity. SA pre-treated alone could significantly increase the length of shoot and root of seedlings but the vigour difference was not marked under long-term exposure to Pb toxicity. SA pre-treated influence the H 2O 2 level in leaves of seedlings by up-regulating the activity of superoxide dismutase (SOD), repressing the activity of catalase (CAT) and ascorbate peroxidase (APX) depending on the concentrations of Pb 2+ in the growth medium. The results supported the conclusion that SA played a positive role in rice seedlings against Pb toxicity.

Influence of exogenous salicylic acid on the level of phytohormones in tissues of Phlox paniculata and Phlox setacea leaves with special reference to resistance against the powdery mildew causative agent Erysiphe cichoracearum D.C. f. phlogis Jacz

We studied the effects of exogenous salicylic acid on the level of endogenous cytokinins and abscisic and salicylic acids in the tissues of leaves of phloxes contrasting in resistance against the powdery mildew causative agent: susceptible Phlox paniculata L. and resistant Ph. setacea L. Studies were carried out under the conditions of biotic stress. The initial level of salicylic and abscisic acids and cytokinins is the highest in the resistant phlox species. After treatment with salicylic species, the total level of cytokinins and endogenous salicylic acid increased in both species. When the treated phlox species were infected by the powdery mildew causative agent, the level of abscisic and salicylic acids increased in the susceptible Ph. paniculata, while that of cytokinins increased in the resistant Ph. setacea. The role of salicylic acid in the induction of plant defense reactions against phytopathogens is discussed.

Local and Systemic Responses of Antioxidants to Tobacco Mosaic Virus Infection and to Salicylic Acid in Tobacco (Role in Systemic Acquired Resistance).

Changes in ascorbate and glutathione levels and in activities of ascorbate peroxidase, catalase, dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and superoxide dismutase (SOD) were investigated in tobacco mosaic virus (TMV)-inoculated lower leaves and in non-inoculated upper leaves of Nicotiana tabacum L. cv Xanthi-nc. In separate experiments the effects of exogenous salicylic acid (SA) were also studied. Symptom appearance after TMV inoculation was preceded by a slight, transient decline of ascorbate peroxidase, GR, GST, and SOD activities in the inoculated lower leaves, but after the onset of necrosis these activities and the glutathione level substantially increased. Ascorbic acid level and DHAR activity declined and dehydroascorbate accumulated in the inoculated leaves. In upper leaves, the glutathione level and the activities of GR, GST, and SOD increased 10 to 14 d after TMV inoculation of the lower leaves, concomitantly with the development of systemic acquired resistance. From the six distinct SOD isoenzymes found in tobacco leaves, only the activities of Cu,Zn-SOD isoenzymes were affected by TMV. SA injection induced DHAR, GR, GST, and SOD activities. Catalase activities were not modified by TMV infection or SA treatment. It is supposed that stimulated antioxidative processes contribute to the suppression of necrotic symptom development in leaves with systemic acquired resistance.