Precursor Of Salicylic Acid Research Articles

Arabidopsis ICS1 produces salicylic acid precursor isochorismate through a gated channel mechanism.

Arabidopsis ICS1 produces salicylic acid precursor isochorismate through a gated channel mechanism.

Salicylic Acid Is Involved in the Growth Inhibition Caused by Excessive Ammonium in Oilseed Rape (Brassica napus L.).

Rapeseed (Brassica napus L.) is extremely sensitive to excessive NH4+ toxicity. There remains incomplete knowledge of the causal factors behind the growth suppression in NH4+-nourished plants, with limited studies conducted specifically on field crop plants. In this study, we found that NH4+ toxicity significantly increased salicylic acid (SA) accumulation by accelerating the conversion of SA precursors. Moreover, exogenous SA application significantly aggravated NH4+ toxicity symptoms in the rapeseed shoots. Genome-wide differential transcriptomic analysis showed that NH4+ toxicity increased the expression of genes involved in the biosynthesis, transport, signaling transduction, and conversion of SA. SA treatment significantly increased shoot NH4+ concentrations by reducing the activities of glutamine synthase and glutamate synthase in NH4+-treated rapeseed plants. The application of an SA biosynthesis inhibitor, ABT, alleviated NH4+ toxicity symptoms. Furthermore, SA induced putrescine (Put) accumulation, resulting in an elevated ratio of Put to [spermidine (Spd) + spermine (Spm)] in the NH4+-treated plants, while the opposite was true for ABT. The application of exogenous Put and its biosynthesis inhibitor DFMA induced opposite effects on NH4+ toxicity in rapeseed shoots. These results indicated that the increased endogenous SA contributed noticeably to the toxicity caused by the sole NH4+-N supply in rapeseed shoots. This study provided fresh perspectives on the mechanism underlying excessive NH4+-induced toxicity and the corresponding alleviating strategies in plants.

Influence of Exogenous 24-Epicasterone on the Hormonal Status of Soybean Plants.

Brassinosteroids (BRs) are key phytohormones involved in the regulation of major processes of cell metabolism that guide plant growth. In the past decades, new evidence has made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work, we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, and abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. The obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions, ECS in tested concentrations of 0.25 µM and 1 µM might promote growth in soybeans by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment, which indicates an activation of the adaptation strategies of cell metabolism to possible environmental challenges.

The Sporisorium reilianum Effector Vag2 Promotes Head Smut Disease via Suppression of Plant Defense Responses.

Genome comparison between the maize pathogens Ustilago maydis and Sporisorium reilianum revealed a large diversity region (19-1) containing nearly 30 effector gene candidates, whose deletion severely hampers virulence of both fungi. Dissection of the S. reilianum gene cluster resulted in the identification of one major contributor to virulence, virulence-associated gene 2 (vag2; sr10050). Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) experiments revealed high expression of vag2 during biotrophic growth of S. reilianum. Using the yeast secretion trap assay, we confirmed the existence of a functional signal peptide allowing protein secretion via the conventional secretory pathway. We identified the cytoplasmic maize chorismate mutase ZmCM2 by yeast two-hybrid screening as a possible interaction partner of Vag2. Interaction of the two proteins in planta was confirmed by bimolecular fluorescence complementation. qRT-PCR experiments revealed vag2-dependent downregulation of salicylic acid (SA)-induced genes, which correlated with higher SA levels in plant tissues colonized by Δvag2 deletion strains relative to S. reilianum wildtype strains. Metabolite analysis suggested rewiring of pathogen-induced SA biosynthesis by preferential conversion of the SA precursor chorismate into the aromatic amino acid precursor prephenate by ZmCM2 in the presence of Vag2. Possibly, the binding of Vag2 to ZmCM2 inhibits the back reaction of the ZmCM2-catalyzed interconversion of chorismate and prephenate, thus contributing to fungal virulence by lowering the plant SA-induced defenses.

The effect of mandelonitrile, a recently described salicylic acid precursor, on peach plant response against abiotic and biotic stresses.

In a previous work, we observed that mandelonitrile (MD), which controls cyanogenic glycoside turnover, is involved in salicylic acid (SA) biosynthesis in peach plants. In order to gain knowledge about the possible roles of this SA biosynthetic pathway, this current study looks at the effect of MD and phenylalanine (Phe; MD precursor) treatments on peach plant performance from an agronomic point of view. Abiotic (2g·l-1 NaCl) and biotic (Plum pox virus, PPV) stresses were assayed. We recorded the following chlorophyll fluorescence parameters: quantum yield of photochemical energy conversion in PSII [Y(II)], photochemical quenching (qP) and quantum yield of regulated non-photochemical energy loss in PSII and its coefficient [Y(NPQ) and qN]. In addition, considering that environmental stresses lead to nutritional disorders, we determined the soluble K+ , Ca2+ , Na+ and Cl- concentrations in NaCl-stressed seedlings. In PPV-infected seedlings, we recorded the Ca2+ level, which has been suggested to play critical roles in regulating SA-related plant defence responses against pathogens. The MD treatment lessened the effect of both stresses on plant development. In addition, an increase in non-photochemical quenching parameters was observed in MD-treated seedlings, suggesting a safer dissipation of excess energy under stress conditions. In NaCl-stressed peach seedlings both treatments stimulated the accumulation of phytotoxic ions in roots, whereas in PPV-infected seedlings MD increased Ca2+ content. Our results suggest that MD and Phe influence the response of peach seedlings to the deleterious effects of salt and PPV infection stresses.

Biomass yield of resin in adult Pinus elliottii Engelm. trees is differentially regulated by environmental factors and biochemical effectors

Biomass of pine resin finds several applications in the chemical, pharmaceutical, biofuel and food industries. Resin exudation after injury is a key defense response in Pinaceae since this complex mixture of terpenes has insecticidal, antimicrobial and wound repair properties. Resin yield is increased by effectors applied on the wound area, including phytohormones and metal cofactors of terpene synthases. The interaction of resinosis mechanism effectors is not fully understood, particularly in adult forest setups under natural environmental variations. The aim of this work was to determine how resin exudation by wounded trunks of adult P. elliottii responded to combined chemical effectors involved in different regulatory pathways of resinosis (metal cofactors of terpene synthases, benzoic acid and plant growth regulators) and whether seasonal and tree distribution variations affected these responses. Symmetrically planted and scattered trees regenerated from the seed bank had similar resin biomass yields, suggesting that the homogeneity in development and spatial arrangement were not significant factors in resin yield. This new finding is of practical importance with the used tapping system since costs of implanting forests by regeneration can be advantageous compared to planting. In addition, it was shown for the first time that the salicylic acid precursor benzoic acid and the auxin naphthalene acetic acid promoted resin exudation when individually applied to wound sites. Both these adjuvants are two orders of magnitude less costly compared to the conventionally used ethylene precursors, besides facing less environmental and health restrictions for use. Most adjuvant-treated trees showed higher resin flow in the second year, indicating mechanisms of response build up. Overall, temperature was more important than rainfall as environmental parameter affecting resin biosynthesis, which was higher in the warmer months of spring and summer. The combination of resinosis stimulant effectors from different signaling pathways showed no significant synergistic or additive effect, suggesting possible converging signaling pathways and/or limitation of common intermediate transducing molecules.

Metabolomics and Biochemical Approaches Link Salicylic Acid Biosynthesis to Cyanogenesis in Peach Plants

Despite the long-established importance of salicylic acid (SA) in plant stress responses and other biological processes, its biosynthetic pathways have not been fully characterized. The proposed synthesis of SA originates from chorismate by two distinct pathways: the isochorismate and phenylalanine (Phe) ammonia-lyase (PAL) pathways. Cyanogenesis is the process related to the release of hydrogen cyanide from endogenous cyanogenic glycosides (CNglcs), and it has been linked to plant plasticity improvement. To date, however, no relationship has been suggested between the two pathways. In this work, by metabolomics and biochemical approaches (including the use of [13C]-labeled compounds), we provide strong evidences showing that CNglcs turnover is involved, at least in part, in SA biosynthesis in peach plants under control and stress conditions. The main CNglcs in peach are prunasin and amygdalin, with mandelonitrile (MD), synthesized from phenylalanine, controlling their turnover. In peach plants MD is the intermediary molecule of the suggested new SA biosynthetic pathway and CNglcs turnover, regulating the biosynthesis of both amygdalin and SA. MD-treated peach plants displayed increased SA levels via benzoic acid (one of the SA precursors within the PAL pathway). MD also provided partial protection against Plum pox virus infection in peach seedlings. Thus, we propose a third pathway, an alternative to the PAL pathway, for SA synthesis in peach plants.

Arabidopsis thaliana GH3.5 acyl acid amido synthetase mediates metabolic crosstalk in auxin and salicylic acid homeostasis

In Arabidopsis thaliana, the acyl acid amido synthetase Gretchen Hagen 3.5 (AtGH3.5) conjugates both indole-3-acetic acid (IAA) and salicylic acid (SA) to modulate auxin and pathogen response pathways. To understand the molecular basis for the activity of AtGH3.5, we determined the X-ray crystal structure of the enzyme in complex with IAA and AMP. Biochemical analysis demonstrates that the substrate preference of AtGH3.5 is wider than originally described and includes the natural auxin phenylacetic acid (PAA) and the potential SA precursor benzoic acid (BA). Residues that determine IAA versus BA substrate preference were identified. The dual functionality of AtGH3.5 is unique to this enzyme although multiple IAA-conjugating GH3 proteins share nearly identical acyl acid binding sites. In planta analysis of IAA, PAA, SA, and BA and their respective aspartyl conjugates were determined in wild-type and overexpressing lines of A thaliana This study suggests that AtGH3.5 conjugates auxins (i.e., IAA and PAA) and benzoates (i.e., SA and BA) to mediate crosstalk between different metabolic pathways, broadening the potential roles for GH3 acyl acid amido synthetases in plants.

Synthesis of ultra-fine hafnium carbide powders combining the methods of liquid precursor conversion and plasma activated sintering

Ultra-fine hafnium carbide (HfC) powders were synthesized using a novel method combining liquid precursor conversion and plasma activated sintering (PAS). Solution-based processing was used to achieve a fine-scale mixing of the reactants, and further treatment by PAS allowed fast formation of HfC. We investigated the effect of the type of acid used during the liquid precursor conversion on the synthesized powders, where mixtures were prepared using salicylic acid, citric acid, or a combination of these. The results show that pure HfC powders (with an average particle sizes of 350nm) were obtained at a relatively low temperature (1550°C) using a HfOCl2·8H2O precursor with the mixed acids. The oxygen content of the synthesized powders was only 0.97wt%. The type of acid had a significant effect on the synthesis product. When using only citric acid, the temperature required to produce pure hafnium carbide increased to 1700°C. In the case of a salicylic acid precursor, pure HfC was not obtained, even at a synthesis temperature of 1700°C.

A versatile salicylic acid precursor method for preparing titanate microspheres

Mixed-phase MgTiO3/MgTi2O5 microspheres were prepared through a salicylic acid precursor method and further calcined in air. The microspheres were formed through coordination, polymerization, and aggregation processes. Salicylic acid acted as a ligand in coordinating with metal ions, in addition to acting as a structure-directing agent in the polymerization and aggregation of the titanate precursor microspheres via chemical bonds and electrostatic attraction. The mixed-phase MgTiO3/MgTi2O5 microspheres prepared by this method showed excellent photocatalytic hydrogen production efficiencies that were two and four times higher than mixed-phase nanoparticles and pure-phase nanoparticles, respectively, owing to their closed phase junctions and sphere-like morphologies. This versatile and facile salicylic acid precursor method was also used to prepare a number of other bivalent metal-based titanate microspheres, including BaTiO3, ZnTiO3, CoTiO3, NiTiO3, and CdTiO3.

Accumulation of Isochorismate-derived 2,3-Dihydroxybenzoic 3-O-β-d-Xyloside in Arabidopsis Resistance to Pathogens and Ageing of Leaves

An intricate network of hormone signals regulates plant development and responses to biotic and abiotic stress. Salicylic acid (SA), derived from the shikimate/isochorismate pathway, is a key hormone in resistance to biotrophic pathogens. Several SA derivatives and associated modifying enzymes have been identified and implicated in the storage and channeling of benzoic acid intermediates or as bioactive molecules. However, the range and modes of action of SA-related metabolites remain elusive. In Arabidopsis, Enhanced Disease Susceptibility 1 (EDS1) promotes SA-dependent and SA-independent responses in resistance against pathogens. Here, we used metabolite profiling of Arabidopsis wild type and eds1 mutant leaf extracts to identify molecules, other than SA, whose accumulation requires EDS1 signaling. Nuclear magnetic resonance and mass spectrometry of isolated and purified compounds revealed 2,3-dihydroxybenzoic acid (2,3-DHBA) as an isochorismate-derived secondary metabolite whose accumulation depends on EDS1 in resistance responses and during ageing of plants. 2,3-DHBA exists predominantly as a xylose-conjugated form (2-hydroxy-3-beta-O-D-xylopyranosyloxy benzoic acid) that is structurally distinct from known SA-glucose conjugates. Analysis of DHBA accumulation profiles in various Arabidopsis mutants suggests an enzymatic route to 2,3-DHBA synthesis that is under the control of EDS1. We propose that components of the EDS1 pathway direct the generation or stabilization of 2,3-DHBA, which as a potentially bioactive molecule is sequestered as a xylose conjugate.

Effect of Salt Stress on the Salicylic Acid Synthesis in Young Maize (Zea mays L.) Plants

AbstractThe effect of salt stress on salicylic acid (SA) synthesis was investigated parallel with the induction of antioxidant enzymes in young maize plants. Two‐week‐old maize plants grown in hydroponic solution were treated with 50 or 100 mm NaCl for 7 days. Antioxidant enzyme activities, and the SA and o‐hydroxy‐cinnamic acid (oHCA) levels were measured on the 3rd and 7th day of treatment and after 4 days of recovery. Ascorbate peroxidase activity increased in the leaves, but changes in guaiacol peroxidase activity only could be detected in the roots after 7 days. Glutathione reductase activity increased both in the leaves and in the roots after the 3rd day of 100 mm NaCl treatment. Free SA only increased during recovery in the leaves and roots. In the leaves of plants treated with 100 mm NaCl, a slight increase was observed in the free oHCA level, which rose dramatically after recovery, while in the roots an increase could only be seen after recovery. These results suggest that oHCA may serve not only as a precursor of SA but may also have an antioxidant role during salt stress and recovery.

Early defence reactions in Norway spruce seedlings inoculated with the mycorrhizal fungus Pisolithus tinctorius (Persoon) Coker & Couch and the pathogen Heterobasidion annosum (Fr.) Bref.

The activities of the enzymes responsible for cell-wall strengthening and salicylic acid (SA) content in Norway spruce seedlings were investigated after inoculation with the ectomycorrhizal fungus Pisolithus tinctorius or the pathogen Heterobasidion annosum, and after treatment with elicitors from both of these fungi. Inoculation with both fungi increased guaiacol peroxidase (POD) activity in the roots of the pathogen-inoculated seedlings during the earliest phases of colonisation, and induced the activities of several POD isoforms. Two of these were only seen in pathogen-inoculated seedlings and corresponded with increased POD activity against ferulic acid. Colonisation with H. annosum triggered an increase in phenylalanine ammonia lyase (PAL) activity in the roots of the spruce seedlings, which was followed by an accumulation of free SA. One month after inoculation levels of free SA were increased also in the shoots of H. annosum-inoculated seedlings. In contrast increase in free SA content in the roots of P. tinctorius-inoculated seedlings was only transient. Similarly to inoculation, treatment with elicitors of H. annosum increased the PAL and POD activity, as well as SA content in the roots of spruce seedlings. A positive correlation between PAL activity and SA content in the H. annosum-inoculated seedlings and accumulation of SA precursors in the phenylpropanoid pathway indicate that the plant defence mechanisms, during which SA is synthesised through the PAL pathway, are exploited by H. annosum for facilitation of colonisation.

Salicylic Acid Accumulation Under O3 Exposure is Regulated by Ethylene in Tobacco Plants

Ozone (O3), a major photochemical oxidant, induces leaf injury concomitant with salicylic acid (SA) synthesis. In pathogen-infected leaves, SA is synthesized via two pathways, involving phenylalanine or isochorismate. SA biosynthesis under O3 fumigation is not well understood. When we applied 14C-labeled benzoic acid (a precursor of SA in the pathway via phenylalanine) to O3-exposed tobacco leaves, it was effectively metabolized to SA. However, the activity and mRNA level of isochorismate synthase (ICS) were not increased. In contrast, ICS activity was increased in O3-exposed Arabidopsis thaliana L. These results suggest that SA is synthesized via benzoic acid from phenylalanine in O3-exposed tobacco leaves but via isochorismate in Arabidopsis. Ethylene is a plant hormone that promotes leaf damage in O3-exposed plants. During O3 exposure, transgenic plants with a phenotype of reduced O3-induced ethylene production accumulated less SA than did wild-type plants. O3 increased the activity of phenylalanine ammonia-lyase (PAL) and the transcript levels of the chorismate mutase (CM) and PAL genes in wild-type tobacco, but their induction was suppressed in the transgenic plants. These results indicate that ethylene promotes SA accumulation by regulating the expression of the CM and PAL genes in O3-exposed tobacco.

Free and conjugated benzoic acid in tobacco plants and cell cultures. Induced accumulation upon elicitation of defense responses and role as salicylic acid precursors.

Salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. In this study, we investigated the role of benzoic acid (BA) as precursor of SA biosynthesis in tobacco (Nicotiana tabacum cv Samsun NN) plants undergoing a hypersensitive response following infection with tobacco mosaic virus or in tobacco cell suspensions elicited with beta-megaspermin, an elicitor from Phytophthora megasperma. We found a small pool of conjugated BA in healthy leaves and untreated cell suspensions of tobacco, whereas free BA levels were barely detectable. Infection of plants with tobacco mosaic virus or elicitation of cells led to a rapid de novo synthesis and accumulation of conjugated BA, whereas free BA was weakly induced. In presence of diphenylene iodonium, an inhibitor of superoxide anion formation, SA accumulation was abolished in elicited cells and much higher BA levels were concomitantly induced, mainly as a conjugated form. Furthermore, piperonylic acid, an inhibitor of cinnamate-4-hydroxylase was used as a powerful tool to redirect the metabolic flow from the main phenylpropanoid pathway into the SA biosynthetic branch. Under these conditions, in vivo labeling and radioisotope dilution experiments with [(14)C]trans-cinnamic acid as precursor clearly indicated that the free form of BA produced in elicited tobacco cells is not the major precursor of SA biosynthesis. The main conjugated form of BA accumulating after elicitation of tobacco cells was identified for the first time as benzoyl-glucose. Our data point to the likely role of conjugated forms of BA in SA biosynthesis.

Accumulation of Pathogenesis-Related Proteins in Tobacco Leaves Irradiated with UV-B

L. (cv. Petit Havana SR1) were grown under ultraviolet-B (UV-B, 290–320 nm) irradiation, and soluble proteins were extracted from the leaves. Two-dimensional electrophoresis revealed that a minimum of 12 polypeptides were induced by UV-B. Polypeptides which were so abundant as to be detectable by Coomassie brilliant blue staining were then subjected to N-terminal amino acid sequence analyses. Two of the polypeptides were identified as a 23 kDa protein of PS II and 6 as a pathogenesis-related protein 5 (PR-5). Immunoblotting demonstrated that other PR proteins, PR-1 and PR-3 were also induced by UV-B. Salicylic acid (SA), which is an important component of signal transduction that leads to the expression of PR proteins and exhibition of acquired resistance to pathogens, increased in response to exposure to UV-B. In addition, the activity of phenylalanine ammonialyase, which catalyzes the synthesis from phenylalanine of trans-cinnamic acid, the endogenous precursor of SA, was transiently increased by UV-B irradiation. These results suggest that UV-B activates the signal transduction pathway, which is a common step in pathogen infection.

Purification, Cloning, and Expression of a Pathogen Inducible UDP-glucose:Salicylic Acid Glucosyltransferase from Tobacco

Salicylic acid (SA) plays an important role in plant disease resistance. Inoculation of tobacco leaves with incompatible pathogens triggers the biosynthesis of SA which accumulates primarily as the SA 2-O-beta-D-glucoside (SAG) and glucosyl salicylate (GS). The tobacco UDP-glucose:salicylic acid glucosyltransferase (SA GTase) capable of forming both SAG and GS was purified, characterized, and partially sequenced. It has an apparent molecular mass of 48 kDa, a pH optimum of 7.0, and an isoelectric point at pH 4.4. UDP-glucose was the sole sugar donor for the enzyme. However, SA and several phenolics served as glucose acceptors. The apparent K(m) values for UDP-glucose and SA were 0.27 and 1-2 mM, respectively. Zn(2+) and UDP inhibited its activity. The corresponding cDNA clone which encoded a protein of 459 amino acids was isolated from an SA-induced tobacco cDNA library and overexpressed in Escherichia coli. The recombinant protein catalyzed the formation of SAG and GS, and exhibited a broad specificity to simple phenolics, similar to that of the purified enzyme. Northern blot analysis showed that the SA GTase mRNA was induced both by SA and incompatible pathogens. The rapid induction timing of the mRNA by SA indicates that it belongs to the early SA response genes.

Production of Salicylic Acid Precursors Is a Major Function of Phenylalanine Ammonia-Lyase in the Resistance of Arabidopsis to Peronospora parasitica.

Arabidopsis ecotype Columbia (Col-0) seedlings, transformed with a phenylalanine ammonia-lyase 1 promoter (PAL1)-[beta]-glucuronidase (GUS) reporter construct, were inoculated with virulent and avirulent isolates of Peronospora parasitica. The PAL1 promoter was constitutively active in the light in vascular tissue but was induced only in the vicinity of fungal structures in the incompatible interaction. A double-staining procedure was developed to distinguish between GUS activity and fungal structures. The PAL1 promoter was activated in cells undergoing lignification in the incompatible interaction in response to the pathogen. Pretreatment of the seedlings with 2-aminoindan-2-phosphonic acid (AIP), a highly specific PAL inhibitor, made the plants completely susceptible. Lignification was suppressed after AIP treatment, and surprisingly, pathogen-induced PAL1 promoter activity could not be detected. Treatment of the seedlings with 2-hydroxyphenylaminosulphinyl acetic acid (1,1-dimethyl ester) (OH-PAS), a cinnamyl alcohol dehydrogenase inhibitor specific for the lignification pathway, also caused a shift toward susceptibility, but the effect was not as pronounced as it was with AIP. Significantly, although OH-PAS suppressed pathogen-induced lignification, it did not suppress pathogen-induced PAL1 promoter activation. Salicylic acid (SA), supplied to AIP-treated plants, restored resistance and both pathogen-induced lignification and activation of the PAL1 promoter. Endogenous SA levels increased significantly in the incompatible but not in the compatible combination, and this increase was suppressed by AIP but not by OH-PAS. These results provide evidence of the central role of SA in genetically determined plant disease resistance and show that lignification per se, although providing a component of the resistance mechanism, is not the deciding factor between resistance and susceptibility.

Production of Salicylic Acid Precursors Is a Major Function of Phenylalanine Ammonia-Lyase in the Resistance of Arabidopsis to Peronospora parasitica

Production of Salicylic Acid Precursors Is a Major Function of Phenylalanine Ammonia-Lyase in the Resistance of Arabidopsis to Peronospora parasitica

Benzoic acid, salicylic acid, and the role of black galls on aspen in protection against decay

Trembling aspen (Populustremuloides Michx.) bearing certain types of black galls have a lower incidence of Phellinustremulae (Bond.) Bond. & Boriss. heartwood rot than do nongall-bearing trees. Extraction of finely ground black gall tissue with ethyl acetate and separation of the acidic components of the extract led to the isolation of benzoic acid, trans-cinnamic acid, p-hydroxybenzoic acid, p-hydroxycinnamic acid, naringenin, 7′-methyl-3-hydroxynaringen, aromadendrin, and taxifolin. Bioassays revealed that among these compounds, only benzoic acid showed significant activity against P. tremulae. An analytical procedure was developed to measure the concentration of benzoic acid in various types of aspen tissue. Tissue from the black galls showed a high concentration of benzoic acid, and tissue from gall-bearing trees contained significantly more benzoic acid than healthy nongalled trees. However, the amount of benzoic acid present in the gall-bearing trees may not be sufficient to prevent Phellinus decay. It is suggested that perhaps the benzoic acid serves as a precursor of salicylic acid, a signal molecule in systemic acquired resistance of plants.