Inhibitory Effect Of Salicylic Acid Research Articles

Development and Validation of an HPLC-UV Method for the Quantification of 4'-Hydroxydiclofenac Using Salicylic Acid: Future Applications for Measurement of In Vitro Drug-Drug Interaction in Rat Liver Microsomes.

Salicylic acid is a key compound in nonsteroidal anti-inflammatory drugs that has been recently used for preventing the risk of hospitalization and death among COVID-19 patients and in preventing colorectal cancer (CRC) by suppressing two key proteins. Understanding drug–drug interaction pathways prevent the occurrence of adverse drug reactions in clinical trials. Drug–drug interactions can result in the variation of the pharmacodynamics and pharmacokinetic of the drug. Inhibition of the Cytochrome P450 enzyme activity leads to the withdrawal of the drug from the market. The aim of this paper was to develop and validate an HPLC-UV method for the quantification of 4′-hydroxydiclofenac as a CYP2C9 metabolite using salicylic acid as an inhibitor in rat liver microsomes. A CYP2C9 assay was developed and validated on the reversed phase C18 column (SUPELCO 25 cm × 4.6 mm × 5 µm) using a low-pressure gradient elution programming at T = 30 °C, a wavelength of 282 nm, and a flow rate of 1 mL/min. 4′-hydroxydiclofenac demonstrated a good linearity (R2 > 0.99), good reproducibility, low detection, and quantitation limit, and the inter and intra-day precision met the ICH guidelines (<15%). 4′-hydroxydiclofenac was stable for three days and showed an acceptable accuracy and recovery (80–120%) within the ICH guidelines in a rat liver microsome sample. This method will be beneficial for future applications of the in vitro inhibitory effect of salicylic acid on the CYP2C9 enzyme activity in rat microsomes and the in vivo administration of salicylic acid in clinical trials.

Growth modulation and metabolic responses of Ganoderma boninense to salicylic acid stress.

Various phenolic compounds have been screened against Ganoderma boninense, the fungal pathogen causing basal stem rot in oil palms. In this study, we focused on the effects of salicylic acid (SA) on the growth of three G. boninense isolates with different levels of aggressiveness. In addition, study on untargeted metabolite profiling was conducted to investigate the metabolomic responses of G. boninense towards salicylic acid. The inhibitory effects of salicylic acid were both concentration- (P < 0.001) and isolate-dependent (P < 0.001). Also, growth-promoting effect was observed in one of the isolates at low concentrations of salicylic acid where it could have been utilized by G. boninense as a source of carbon and energy. Besides, adaptation towards salicylic acid treatment was evident in this study for all isolates, particularly at high concentrations. In other words, inhibitory effect of salicylic acid treatment on the fungal growth declined over time. In terms of metabolomics response to salicylic acid treatment, G. boninense produced several metabolites such as coumarin and azatyrosine, which suggests that salicylic acid modulates the developmental switch in G. boninense towards the defense mode for its survival. Furthermore, the liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) analysis showed that the growth of G. boninense on potato dextrose agar involved at least four metabolic pathways: amino acid metabolism, lipid pathway, tryptophan pathway and phenylalanine pathway. Overall, there were 17 metabolites that contributed to treatment separation, each with P<0.005. The release of several antimicrobial metabolites such as eudistomin I may enhance G. boninense’s competitiveness against other microorganisms during colonisation. Our findings demonstrated the metabolic versatility of G. boninense towards changes in carbon sources and stress factors. G. boninense was shown to be capable of responding to salicylic acid treatment by switching its developmental stage.

Improving the Biocontrol Potential of Bacterial Antagonists with Salicylic Acid against Brown Rot Disease and Impact on Nectarine Fruits Quality

The main objective of this study was to evaluate the ability of both antagonistic bacteria Bacillus amyloliquefaciens (SF14) and Alcaligenes faecalis (ACBC1) used in combination with salicylic acid (SA) to effectively control brown rot disease caused by Monilinia fructigena. Four concentrations of salicylic acid (0.5%, 2%, 3.5%, and 5%) were tested under in vitro and in vivo conditions. Furthermore, the impact of biological treatments on nectarine fruit parameters’ quality, in particular, weight loss, titratable acidity, and soluble solids content, was evaluated. Regardless of the bacterium, the results indicated that all combined treatments displayed a strong inhibitory effect on the mycelial growth of M. fructigena and disease severity. Interestingly, all SA concentrations significantly improved the biocontrol activity of each antagonist. The mycelial growth inhibition rate ranged from 9.79% to 88.02% with the highest reduction rate recorded for bacterial antagonists in combination with SA at both concentrations of 0.5% and 3.5%. The in vivo results confirmed the in vitro results with a disease severity varying from 0.00% to 51.91%. A significant biocontrol improvement was obtained with both antagonistic bacteria when used in combination with SA at concentrations of 0.5% and 2%. The lowest disease severity observed with ACBC1 compared with SF14 is likely due to a rapid adaptation and increase of antagonistic bacteria population in wounded sites. The impact of all biological treatments revealed moderate significant changes in the fruit quality parameters with weight loss for several treatments. These results suggest that the improved disease control of both antagonistic bacteria was more likely directly linked to both the inhibitory effects of SA on pathogen growth and induced fruit resistance.

Validation of an HPLC Method for the Simultaneous Quantification of Metabolic Reaction Products Catalysed by CYP2E1 Enzyme Activity: Inhibitory Effect of Cytochrome P450 Enzyme CYP2E1 by Salicylic Acid in Rat Liver Microsomes.

Inhibition of cytochrome P450 (CYP) alters the pharmacokinetic parameters of the drug and causes drug–drug interactions. Salicylic acid been used for the treatment of colorectal cancer (CRC) and chemoprevention in recent decades. Thus, the aim of this study was to examine the in vitro inhibitory effect of salicylic acid on CYP2E1 activity in rat liver microsomes (RLMs) using high-performance liquid chromatography (HPLC). High-performance liquid chromatography analysis of a CYP2E1 assay was developed on a reversed phase C18 column (SUPELCO 25 cm × 4.6 mm × 5 µm) at 282 nm using 60% H2O, 25% acetonitrile, and 15% methanol as mobile phase. The CYP2E1 assay showed a good linearity (R2 > 0.999), good reproducibility, intra- and inter-day precision (<15%), acceptable recovery and accuracy (80–120%), and low detection (4.972 µM and 1.997 µM) and quantitation limit values (15.068 µM and 6.052 µM), for chlorzoxazone and 6-hydroxychlorzoxazone, respectively. Salicylic acid acts as a mixed inhibitor (competitive and non-competitive inhibition), with Ki (inhibition constant) = 83.56 ± 2.730 µM and concentration of inhibitor causing 50% inhibition of original enzyme activity (IC50) exceeding 100 µM (IC50 = 167.12 ± 5.460 µM) for CYP2E1 enzyme activity. Salicylic acid in rats would have both low and high potential to cause toxicity and drug interactions with other drugs that are substrates for CYP2E1.

Validation of an HPLC Method for the Simultaneous Quantification of Metabolic Reaction Products Catalysed by CYP2C11 Enzymes in Rat Liver Microsomes: In Vitro Inhibitory Effect of Salicylic Acid on CYP2C11 Enzyme.

The inhibitory effect of new chemical entities on rat liver P450 marker activities was investigated in a functional approach towards drug development. Treatment of colorectal cancer (CRC) and chemoprevention using salicylic acid has gained a lot of attention, mainly in the prevention of the onset of colon cancer. Thus, an in vitro inhibitory effect of salicylic acid on rat CYP2C11 activity was examined by using high performance liquid chromatography (HPLC). High performance liquid chromatography analysis of a CYP2C11 assay was developed on a reversed phase C18 column (SUPELCO 25 cm × 4.6 mm × 5 µm) at 243 nm using 32% phosphate buffer (pH 3.36) and 68% methanol as a mobile phase. The CYP2C11 assay showed good linearity for all components (R2 > 0.999). Substrates and metabolites were found to be stable for up to 72 h. Additionally, the method demonstrated good reproducibility, intra- and inter-day precision (<15%), acceptable recovery and accuracy (80%–120%), and low detection (1.3501 µM and 3.2757 µM) and quantitation limit values (4.914 µM and 9.927 µM) for 16α-hydroxytestosterone and testosterone, respectively. Salicylic acid acts reversibly as a noncompetitive (weak) inhibitor with Ki = 84.582 ± 2.67 µM (concentration of inhibitor to cause 50% inhibition of original enzyme activity (IC50) = 82.70 ± 2.67 µM) for CYP2C11 enzyme activity. This indicates a low potential to cause toxicity and drug–drug interactions.

Inhibitory effect of salicylic acid and Aloe vera gel edible coating on microbial load and chilling injury of orange fruit

Effects of salicylic acid (SA) and Aloe vera gel (AV) on microbial load, quality and chilling injury of ‘Thomson Navel’ oranges (Citrus sinensis L. Osbeck) stored at 4 ± 1 °C and 80 ± 5% RH were evaluated. Fruit were treated by immersion in distilled water (control), SA 2 mM, AV 30% and the combination of SA + AV. Decay index, microbiological analysis, weight loss, firmness, soluble solids content, titratable acidity, vitamin C, total phenol, chilling injury, electrolyte leakage, malondialdehyde and sensory evaluation were measured at 0, 20, 40, 60 and 80 days of storage. Results showed that treated fruit had lower decay index, total yeasts + molds count, total aerobic mesophilic bacteria, weight loss and higher firmness, soluble solids content, titratable acidity, vitamin C, and total phenol content. The treatment with SA and AV gel coating reduced malondialdehyde, electrolyte leakage and chilling injury. Fruit odor attributes was not affected by treatments but skin appearance, sweetness, juiciness and intention to buy in treated fruit were higher than control. SA + AV was more effective than SA and AV solely in maintaining fruit quality and reducing microbial load and chilling injury. It could be concluded that the combination of SA with AV might leads to increased oranges fruit shelf-life.

Inhibitory effects of salicylic acid on A549 human lung adenocarcinoma cell viability

Antiinflammatory drugs, such as salicylic acid and its metabolite acetylsalicylic acid, have been singled out as apoptosis-inducing agents with antitumoral activity. In addition, they reduce the risk of some cancers via an unclear mechanism. In this study, we have investigated the apoptotic, cytotoxic, and growth-inhibiting effects of salicylic acid on A549, the human lung adenocarcinoma, alveolar epithelial cells. Cytotoxicity was tested using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) colorimetric assay. We observed the ultrastructural and morphological changes in A549 cells by using transmission electron microscopy (TEM) and confocal microscopy. Cell viability was decreased by the optimal concentration (IC50) of 6.0 mM salicylic acid. Our TEM results showed cell structure damage and ultrastructural changes, concretely indicating apoptosis. With these results, the cytotoxic and potent antiproliferative effects of salicylic acid can be concluded to induce apoptosis in A549 cells.

Effects of salicylic acid onAspergillus flavusinfection and aflatoxin B1accumulation in pistachio (Pistacia veraL.) fruit

One of the most important saprophytic infections in fresh pistachio fruits after harvesting is Aspergillus flavus colonization, which significantly reduces fruit quality. Salicylic acid plays a crucial role in plant tissues and has a suppression effect on some fungi. The inhibitory effect of salicylic acid on the growth of A. flavus was assessed in vitro and in vivo. For this purpose, seven concentrations (0, 1, 3, 5, 7, 9 and 11 mmol L(-1)) of salicylic acid were used in both experiments. Also, aflatoxin B1 contents of the samples were analysed using immunoaffinity chromatography. The results obtained from in vitro experiments showed that salicylic acid significantly reduced Aspergillus growth at all concentrations, and at 9 mmol L(-1) growth was completely suppressed. In vivo evaluation showed relatively high levels of inhibition, though the intact treated fruits as compared with the injured treated fruits demonstrated higher inhibitory effects. Regarding the inhibitory effects of salicylic acid on the control of A. flavus contamination, its application on pistachio fruits after harvesting could be a promising approach to control the fungus infection and reduce aflatoxin production in treated fruits.

The Role of Endogenous Ethylene in Carbohydrate Metabolism of Medicago sativa L. Somatic Embryos in Relation to Their Regenerative Ability

Effects of the ethylene biosynthesis inhibitors salicylic acid (SA) and aminoethoxyvinylglycine (AVG) on germination of Medicago sativa L. somatic embryos and their conversion to seedlings in relation to carbohydrate content and α-amylase activity were studied. Both SA, an inhibitor of ACC oxidase, and AVG, an inhibitor of ACC synthase, when present in the regeneration medium (0.1 and 1 μM) were found to drastically reduce the embryo germination rate. In addition, SA and AVG were found to almost completely or completely, respectively, arrest the process of embryo conversion to seedlings. The inhibitory effects of SA and AVG on germination and conversion may indicate that the processes required endogenous ethylene. AVG and SA clearly slowed down starch disappearance during the 48-h imbibition in the regeneration medium prior to radicle elongation, which was correlated with inhibition of the activity of α-amylase, an enzyme responsible for starch hydrolysis. It is probable that ethylene may activate α-amylase in the germinating alfalfa somatic embryos. In contrast, the disappearance of soluble sugars in the embryos in the presence of the inhibitors tested was accelerated. The disappearance of soluble sugars (to null or almost null) in embryos was faster in the presence of SA in the regeneration medium after 24 and 48 h compared to the disappearance rate with AVG present in the medium. Only glucose was present after a 48-h incubation in the regeneration medium in the presence of the two ethylene biosynthesis inhibitors, in contrast to the control embryos in which glucose was not detected.

Mechanisms Underlying the Effects of Salicylic Acid and Its Salts on Helix Neurons

In experiments on Helix neurons, we found that calcium is not involved in the neurotropic effects of salicylic acid and cobalt and zinc salicylates. This conclusion is based on the fact that the addition of BaCl2 to the applied solutions of salicylates did not change the effects of the latter. Extracellular application of adenosine triphosphate (ATP) significantly modified the effects of salicylic acid and its salts. We believe that the inhibitory effect of salicylic acid on Helix neurons depends on the ability of salicylic acid to suppress ATP synthesis, while the activating effect of cobalt and zinc salicylates on neurons is related to the opposite effects of these salts on ATP synthesis.

Disturbance of ethylene biosynthesis and perception during somatic embryogenesis in Medicago sativa L. reduces embryos’ ability to regenerate

Effects of non-specific ethylene biosynthesis inhibitors: salicylic acid (SA) and aminoethoxyvinylglycine (AVG), and of specific inhibitors of ethylene binding to receptors: 1-methylcyclopropene (1-MCP) and 2,5-norbornadiene (NBD) applied during proliferation and differentiation phases of indirect somatic embryogenesis (SE) of Medicago sativa L. cv. Rangelander on embryogenic suspension growth, embryo production, development, and ability to germinate and convert were studied. Application of SA and AVG alone or together at concentrations from 1 to 500 μM in B5g liquid medium during the proliferation phase had an inhibitory effect on ethylene production and embryogenic suspension growth. Additionally, it caused a drastic reduction in production of embryos and their development on BOi2Y solid differentiation medium. The inhibitory effect of SA was more visible than that of AVG. In addition, disturbance of ethylene biosynthesis during the proliferation phase of SE resulted in diminished lateral germination and conversion of cotyledonary embryos on MS solid medium. Moreover, blocking of ethylene receptors by 1-MCP during the proliferation phase also inhibited ethylene production and embryogenic suspension growth and reduced embryo production during differentiation. MCP almost completely inhibited development of cotyledonary embryos. At the same time, development of more embryos was arrested at the globular stage, and the number of abnormal embryos almost doubled. Similarly, addition of 1-MCP or NBD to the ambient atmosphere during the differentiation phase evidently arrested the development of embryos and, consequently, their ability to germinate and convert on MS regeneration medium. All the results presented above demonstrated that not only ethylene biosynthesis, but also ethylene action is involved in the control of individual phases of SE in Medicago sativa L. cv. Rangelander. And what is more, disturbance of these processes during distinct phases of SE adversely affects vigor of the somatic embryos obtained.

Induction of Pyridine Alkaloid Formation in Transformed Root Cultures of Nicotiana tabacum

Hairy root cultures of Nicotiana tabacum were set up by excised root tips with Agrobacterium rhizogenes. The successful transformation was confirmed by analyzing rolC and virC genes using polymerase chain reaction (PCR). Hairy root cultures were employed to study the formation of pyridine alkaloids, mainly nicotine. The transformed cultures were incubated with potential elicitors, such as methyljasmonate, quercetin and salicylic acid, in order to stimulate the biosynthesis of pyridine alkaloids. Profile and amounts of pyridine alkaloids were analyzed using capillary GLC-MS. Treatment of the cultures with methyljasmonate (50 microM) increased the alkaloid accumulation ca. 7-fold up to a level of 0.58 mg/g fresh weight as compared to untreated controls. Quercetin (200 microM) enhanced the alkaloid production ca. 4-fold (0.34 mg/g fresh weight) within 24 h. In contrast salicylic acid in all tested concentrations decreased the alkaloid level to 1 microg/g fresh weight. Also the inhibitory effect of salicylic acid on the elicitation effect of methyljasmonate and quercetin was investigated.

Controlled levels of salicylic acid are required for optimal photosynthesis and redox homeostasis

Sudden exposure of plants to high light (HL) leads to metabolic and physiological disruption of the photosynthetic cells. Changes in ROS content, adjustment of photosynthetic processes and the antioxidant pools and, ultimately, gene induction are essential components for a successful acclimation to the new light conditions. The influence of salicylic acid (SA) on plant growth, short-term acclimation to HL, and on the redox homeostasis of Arabidopsis thaliana leaves was assessed here. The dwarf phenotype displayed by mutants with high SA content (cpr1-1, cpr5-1, cpr6-1, and dnd1-1) was less pronounced when these plants were grown in HL, suggesting that the inhibitory effect of SA on growth was partly overcome at higher light intensities. Moreover, higher SA content affected energy conversion processes in low light, but did not impair short-term acclimation to HL. On the other hand, mutants with low foliar SA content (NahG and sid2-2) were impaired in acclimation to transient exposure to HL and thus predisposed to oxidative stress. Low and high SA levels were strictly correlated to a lower and higher foliar H(2)O(2) content, respectively. Furthermore high SA was also associated with higher GSH contents, suggesting a tight correlation between SA, H(2)O(2) and GSH contents in plants. These observations implied an essential role of SA in the acclimation processes and in regulating the redox homeostasis of the cell. Implications for the role of SA in pathogen defence signalling are also discussed.

Effect of exogenous salicylic acid supply on nodule formation of hypernodulating mutant and wild type of soybean

Soybean plant is characterized by a systemic autoregulatory control system of nodulation (autoregulation) by initial infection with rhizobia, and plants commonly display a systemic acquired resistance (SAR) to pathogenic microbe infection related to salicylic acid (SA) signal transmission. We investigated the effect of exogenous SA supply on soybean nodulation to determine whether SA affects the autoregulation of nodulation. Seedlings of the hypernodulating mutants NOD1-3, NOD2-4 and their parent cv. Williams were treated or not treated (control) with a 100 μmS-SA solution at 5 d before the inoculation of Bradyrhizobium japonicum strain USDA110. The nodule dry weight and the number of nodules of the wild type soybean Williams exhibiting autoregulation drastically decreased by the addition of 100 μm SA. The decrease in the nodule number was not caused by the reduction of the rhizobium number in the medium. Salicylic acid inhibited only early nodule formation and did not affect the growth of formed nodules. The inhibitory effect of SA on the nodulation of NOD1-3 and NOD2-4 was significantly less pronounced than that in Williams. These results indicate that SA is directly involved in signal transmission in the autoregulation, and that SA or the SAR induced by SA stimulates the autoregulation of nodulation in soybean.

Salicylic acid is involved in resistance responses in the Russian wheat aphid-wheat interaction

Summary The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the salicylic acid (SA) content and catalase (EC 1.11.1.6) activity were studied in resistant (cv. Tugela DN) and near-isogenic susceptible (cv. Tugela) wheat ( Triticum aestivum L.). The aim was to gain information on the involvement of SA in the resistance responses in wheat against the RWA. RWA infestation selectively induced SA accumulation and peroxidase (EC 1.11.1.7) activity in the resistant wheat. Catalase activity was, however, inhibited in both resistant and susceptible wheat plants. Intercellularly applied SA confirmed the possible inhibitory effect of SA on catalase and stimulating effect on defense responses as indicated by peroxidase used as a marker. Results suggest the involvement of SA in the resistance of wheat against the RWA. A SA inhibitable catalase is also present in wheat; indications are that it may not be involved in SA-mediated defence responses.

Plant regeneration from callus of Cuscuta reflexa – an angiospermic parasite – and modulation of catalase and peroxidase activity by salicylic acid and naphthalene acetic acid

Callus induction and plant regeneration system for an obligate parasite, Cuscuta reflexa (family Cuscutaceae), has been established. Callusing was induced from explants of basal portion of seedlings as well as from shoots (vines) in a modified Murashige and Skoog (MMS) media supplemented with 1 mg·L –1 benzyl adenine (BA) and 3 mg·L –1 naphthalene acetic acid (NAA) (MMS-1). The MMS media containing 1 mg·L –1 BA (MMS-2) was found to be better than the MMS-1 media for callus proliferation and long term maintenance. Use of glucose in place of sucrose enhanced callus induction and growth. The browning of callus was substantially reduced by supplementing 0.1 mg·L –1 gibberellin to the MMS-1 media. Shoot regeneration from the green callus was achieved in the MMS media containing 3 mg·L –1 NAA and 1 mg·L –1 kinetin. Cuscuta callus was characterised by having several folds higher peroxidase activity than those of culture-raised and field-grown vines. Catalase activity also revealed a pattern similar to that of peroxidase except for the fact that it could not be detected in field-grown vines. Developmental profiles of peroxidase and catalase, during the growth of the callus in the absence and presence of NAA, revealed inhibition of both the enzymes by NAA, though inhibition of peroxidase was stronger as compared to that of catalase. The inhibitory effect of NAA was also evident when in-gel activity staining of the two enzymes were performed. In callus, three acidic and four basic isoperoxidases were present, while in field-grown vines, two acidic and one basic isoperoxidases were present. Investigation of the effect of salicylic acid on catalase and peroxidase revealed inhibition of both enzymes in a concentration dependent manner during seedling growth. The inhibitory effect of salicylic acid was also evident when in-gel enzyme activity staining of the two enzymes was done. The results are discussed in light of the proposed mode of action of salicylic acid.

Jasmonic acid stimulates the expression of nod genes in Rhizobium.

Jasmonates and salicylic acid are considered to be signal molecules that induce a variety of plant genes involved in wound or defence response, as well as affecting nos promoter activity. In this paper we examined whether these chemicals could also affect nod genes from isogenic rhizobia strains. Isogenic strains contain the Rhizobium leguminosarum nodA promoter fused to the lacZ gene of Escherichia coli and differ only in the source of the regulatory nodD gene. Naringenin, jasmonic acid and methyl jasmonate induced expression of nod genes in strain RBL1284 and salicylic acid showed no activity alone or when used in combination with other compounds; addition of naringenin + jasmonic acid produced a synergistic effect. Results obtained with strain RBL5284 were similar to those for RBL1284 albeit the combination of naringenin with the other compounds markedly inhibited nod gene expression. Whereas RBL5283 responded to naringenin with a strong induction, jasmonic acid, methyl jasmonate or salicylic acid showed no significant responses. The inhibitory effect of salicylic acid on nod gene expression indicates that the induction mechanism of jasmonic acid, methyl jasmonate, N-propyldihydrojasmonate and naringenin is probably different from that of salicylic acid.

Cellulase involvement in the abscission of peach and pepper leaves is affected by salicylic acid

Phenolic compounds appear to be involved in a number of regulatory activities in plants. During the last decade an increasing amount of evidence has brought to light the role played by salicylic acid in a number of physiological processes. Particularly interesting is the inhibitory effect of salicylic acid on ethylene biosynthesis, which might make this natural plant compound a useful tool for controlling some of the responses usually promoted by ethylene. Our data show that salicylic acid is actually able to reduce leaf abscission in both peach and pepper plants. Biochemical analyses have revealed that the enzyme usually involved in this phenomenon (cellulase, EC 3.2.1.4.) does not increase following activation of leaf abscission in plants treated with salicylic acid. In contrast, control plants show a marked increase in the levels of both enzyme activity and cellulase protein. Flushing plants with exogenous ethylene in the presence of salicylic acid induces an increase in cellulase expression which, however, does not equal the level induced in plants without salicylic acid.

Salicylic Acid Inhibits Synthesis of Proteinase Inhibitors in Tomato Leaves Induced by Systemin and Jasmonic Acid.

Salicylic acid (SA) and acetylsalicylic acid (ASA), previously shown to inhibit proteinase inhibitor synthesis induced by wounding, oligouronides (H.M. Doherty, R.R. Selvendran, D.J. Bowles [1988] Physiol Mol Plant Pathol 33: 377-384), and linolenic acid (H. Pena-Cortes, T. Albrecht, S. Prat, E.W. Weiler, L. Willmitzer [1993] Planta 191: 123-128), are shown here to be potent inhibitors of systemin-induced and jasmonic acid (JA)-induced synthesis of proteinase inhibitor mRNAs and proteins. The inhibition by SA and ASA of proteinase inhibitor synthesis induced by systemin and JA, as well as by wounding and oligosaccharide elicitors, provides further evidence that both oligosaccharide and polypeptide inducer molecules utilize the octadecanoid pathway to signal the activation of proteinase inhibitor genes. Tomato (Lycopersicon esculentum) leaves were pulse labeled with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the inhibitory effects of SA are shown to be specific for the synthesis of a small number of JA-inducible proteins that includes the proteinase inhibitors. Previous results have shown that SA inhibits the conversion of 13S-hydroperoxy linolenic acid to 12-oxo-phytodienoic acid, thereby inhibiting the signaling pathway by blocking synthesis of JA. Here we report that the inhibition of synthesis of proteinase inhibitor proteins and mRNAs by SA in both light and darkness also occurs at a step in the signal transduction pathway, after JA synthesis but preceding transcription of the inhibitor genes.

Salicylic acid inhibition of ethylene production by apple discs and other plant tissues

Ethylene production by apple discs is effectively inhibited by salicylic acid. Inhibition is pH dependent, being greatest from pH 3.5–4.5 and minimal at pH 6.5 and above. With 100 μM salicylic acid maximal inhibition, approximately 90%, is achieved in 3 h with an apparent Ki of 40 μM. At somewhat higher concentrations salicylic acid also inhibits the conversion of 1-aminocyclo-propane-1-carboxylic acid to ethylene by pear discs and mung bean hypocotyls. Salicylic acid interferes with action of the putative ethylene-forming enzyme and in this respect is somewhat more effective than cobalt ion. The inhibitory effects of salicylic acid and cobalt ion are not additive. Implications for the limits and locus of salicylic acid inhibition are discussed.