Transport of Salicylic Acid in Tobacco Necrosis Virus-Infected Cucumber Plants

The transport of salicylic acid (SA) was studied in cucumber (Cucumis sativus L.) using 14C-labeled benzoic acid that was injected in the cotyledons at the time of inoculation. Primary inoculation with tobacco necrosis virus (TNV) on the cotyledons led to an induction of systemic resistance of the first primary leaf above the cotyledon against Colletotrichum lagenarium as early as 3 d after inoculation. [14C]SA was detected in the phloem or in the first leaf 2 d after TNV inoculation, whereas [14C]benzoic acid was not detected in the phloem during the first 3 d after TNV inoculation of the cotyledons, indicating phloem transport of [14C]SA from cotyledon. In leaf 1, the specific activity of [14C]SA decreased between 1.7 and 8.6 times compared with the cotyledons, indicating that, in addition to transport, leaf 1 also produced more SA. The amount of SA transported after TNV infection of the cotyledon was 9 to 160 times higher than in uninfected control plants. Thus, SA can be transported to leaf 1 before the development of systemic acquired resistance, and SA accumulation in leaf 1 results both from transport from the cotyledon and from synthesis in leaf 1.     

水杨酸、乙酰水杨酸对番茄幼苗叶片中PPO和POD的诱导作用

以番茄品种改良美国908和合作906为试验材料,研究了水杨酸(SA)和乙酰水杨酸(ASA)喷雾处理6-7叶期幼苗后,叶片内多酚氧化酶(PPO)和过氧化物酶(POD)活性在120 h内的变化.结果显示:SA和ASA对2个番茄品种的适宜诱导浓度分别为1 mmol/L和1.39 mmol/L;SA和ASA对PPO活性的诱导效果无显著差异,但对POD活性的诱导效果SA极显著强于ASA;合作906的PPO活性增幅显著大于改良美国908,而POD活性增幅却显著小于改良美国908,且合作906对诱导处理反应更敏感.研究表明,SA和ASA能显著提高番茄幼苗叶片的PPO、POD活性,而酶活性变化在品种和诱导剂间有显著差异.     

Salicylic acid mediated by the oxidative burst is a key molecule in local and systemic responses of cotton challenged by an avirulent race of Xanthomonas campestris pv malvacearum

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(.-)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mM. Infiltration of 2 mM SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2. 5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(.-)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(.-). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons.     

Pathway of Salicylic Acid Biosynthesis in Healthy and Virus-Inoculated Tobacco

Salicylic acid (SA) is a likely endogenous regulator of localized and systemic disease resistance in plants. During the hypersensitive response of Nicotiana tabacum L. cv Xanthi-nc to tobacco mosaic virus (TMV), SA levels rise dramatically. We studied SA biosynthesis in healthy and TMV-inoculated tobacco by monitoring the levels of SA and its likely precursors in extracts of leaves and cell suspensions. In TMV-inoculated leaves, stimulation of SA accumulation is accompanied by a corresponding increase in the levels of benzoic acid. 14C-Tracer studies with cell suspensions and mock-or TMV-inoculated leaves indicate that the label moves from trans-cinnamic acid to SA via benzoic acid. In healthy and TMV-inoculated tobacco leaves, benzoic acid induced SA accumulation. o-Coumaric acid, which was previously reported as a possible precursor of SA in other species, did not increase SA levels in tobacco. In healthy tobacco tissue, the specific activity of newly formed SA was equal to that of the supplied [14C]benzoic acid, whereas in TMV-inoculated leaves some isotope dilution was observed, presumably because of the increase in the pool of endogenous benzoic acid. We observed accumulation of pathogen-esis-related-1 proteins and increased resistance to TMV in benzoic acid- but not in o-coumaric acid-treated tobacco leaves. This is consistent with benzoic acid being the immediate precursor of SA. We conclude that in healthy and virus-inoculated tobacco, SA is formed from cinnamic acid via benzoic acid.     

Effect of salicylic acid on the alternative pathway of yellow lupine respiration

The effects of salicylic acid (SA) on the rate of respiration and the activity of cyanide-resistant sensitive to salicylhydroxamic acid oxidation pathway in detached etiolated cotyledons of yellow lupine (Lupinus luteus L.) and mitochondria isolated from these cotyledons were studied. Cotyledon treatment with 1 mM SA for 12 h increased the rate of oxygen uptake predominantly due to the activation of cyanide-resistant respiration (CRR) and alternative pathway of mitochondrial oxidation. It was established that the lupine genome encodes at least two isoforms of alternative oxidase (AO), LuAOX1 and LuAOX2, with the mol wt of about 35 kD. These proteins are always present in the mitochondria of etiolated lupine cotyledons, but their level increased rapidly after cotyledon treatment with SA, probably by increasing the mRNA content of the corresponding genes. SA-induced expression of Aox genes was correlated with the activation of CRR and an increase in the maximal activity (capacity) of AO in both detached yellow lupine cotyledons and mitochondria isolated from them.     

Salicylic acid is not required for Cf-2- and Cf-9-dependent resistance of tomato to Cladosporium fulvum

Tomato leaves or cotyledons expressing the Cf-2 or Cf-9 Cladosporium fulvum resistance genes induce salicylic acid (SA) synthesis following infiltration with intercellular washing fluid (IF) containing the fungal peptide elicitors Avr2 and Avr9. We investigated whether SA was required for Cf gene-dependent resistance. Tomato plants expressing the bacterial gene nahG, encoding salicylate hydroxylase, did not accumulate SA in response to IF infiltration but remained fully resistant to C. fulvum. NahG Cf0 plants were as susceptible to C. fulvum as wild-type Cf0. Neither free nor conjugated salicylic acid accumulated in IF-infiltrated Cf2 and Cf9 NahG leaves and cotyledons but conjugated catechol did accumulate. The Cf-9-dependent necrotic response to IF was prevented in NahG plants and replaced by a chlorotic Cf-2-like response. SA also potentiated Cf-9-mediated necrosis in IF-infiltrated wild-type leaves. In contrast, the Cf-2-dependent IF response was retained in NahG leaves and chlorosis was more pronounced than in the wild-type. The distribution of cell death between different cell types was altered in both Cf2 and Cf9 NahG leaves after IF injection. IF-induced accumulation of three SA-inducible defence-related genes was delayed and reduced but not abolished in NahG Cf2 and Cf9 leaves and cotyledons. NahG Tm-22 tomato showed increased hypersensitive response (HR) lesion size upon TMV infection, as observed in TMV-inoculated N gene-containing NahG tobacco plants.     

Induction of a new Lipoxygenase Form in Cucumber Leaves by Salicylic Acid or 2,6-Dichloroisonicotinic Acid*

Changes in lipoxygenase (LOX) protein pattern and/or activity were investigated in relation to acquired resistance of cucumber (Cucumis sativus L.) leaves against two powdery mildews, Sphaerotheca fuliginea (Schlecht) Salmon and Erysiphe cichoracearum DC et Merat. Acquired resistance was established by spraying leaves with salicylic acid (SA) or 2,6-dichloroisonicotinic acid (INA) and estimated in whole plants by infested leaf area compared to control plants. SA was more effective than INA. According to Western blots, untreated cucumber leaves contained a 97 kDa LOX form, which remained unchanged for up to 48 h after pathogen inoculation. Upon treatment with SA alone for 24 h or with INA plus pathogen, an additional 95 kDa LOX form appeared which had an isoelectric point in the alkaline range. For the induction of this form, a threshold concentration of 1 mM SA was required, higher SA concentrations did not change LOX-95 expression which remained similar between 24 h and 96 h but further increased upon mildew inoculation. Phloem exudates contained only the LOX-97 form, in intercellular washing fluid no LOX was detected. dichloroisonicotinic localization revealed LOX protein in the cytosol of the mesophyll cells without differences between the forms.     

水杨酸对菊叶薯蓣中薯蓣皂素生物合成的影响

薯蓣皂素为甾体激素药物合成起始原料,主要来源于菊叶薯蓣等薯蓣属植物的块茎或根状茎,因而关于提高菊叶薯蓣中薯蓣皂素含量的研究有重要意义。利用水杨酸处理菊叶薯蓣的离体植株,研究其对薯蓣皂素生物合成的影响及作用机制。100μmol·L－1的水杨酸处理使薯蓣皂素积累量最大,且提高了叶绿素含量和可溶性糖含量,降低可溶性蛋白含量。半定量 RT-PCR 检测基因表达发现,除了法尼基二磷酸（FPP）基因,水杨酸增强菊叶薯蓣角鲨烯合酶（SQS）基因、甲基戊二酰辅酶 A 还原酶（HMGR）基因、环阿屯醇合成酶（CAS）基因的表达。研究结果为提高菊叶薯蓣中薯蓣皂苷的含量、揭示水杨酸促进薯蓣皂素生物合成的机制等研究提供了基础。     

Protection by aspirin of indomethacin-induced small intestinal damage in rats: mediation by salicylic acid.

Most of non-steroidal anti-inflammatory drugs (NSAIDs) except aspirin (ASA) produce intestinal damage in rats. In the present study, we re-examined the intestinal toxic effect of ASA in rats, in comparison with various NSAIDs, and investigated why ASA does not cause damage in the small intestine, in relation to its metabolite salicylic acid (SA). Various NSAIDs (indomethacin; 10 mg/kg; flurbiprofen; 20 mg/kg; naproxen; 40 mg/kg; dicrofenac; 40 mg/kg; ASA; 20-200 mg/kg) were administered s.c., and the small intestinal mucosa was examined macroscopically 24 h later. All NSAIDs tested, except ASA, caused hemorrhagic lesions in the small intestine, with a decrease of mucosal PGE(2) contents. ASA did not provoke any damage, despite inhibiting (prostaglandin) PG production, and prevented the occurrence of intestinal lesions induced by indomethacin, in a dose-related manner. This protective action of ASA was mimicked by the equimolar doses of SA (17.8-178 mg/kg). Indomethacin caused intestinal hypermotility, in preceding to the occurrence of lesion, and this event was followed by increases of enterobacterial translocation in the mucosa. Both ASA and SA prevented both the intestinal hypermotility and the bacterial translocation seen after indomethacin treatment. In addition, the protective effect of SA was not significantly influenced by either the adenosine deaminase or the adenosine receptor antagonists. Following administration of ASA, the blood SA levels reached a peak within 30 min and remained elevated for more than 7 h. These results suggest that SA has a cytoprotective action against indomethacin-induced small intestinal lesions, and this action may be associated with inhibition of the intestinal hypermotility and the bacterial translocation, but not mediated by endogenous adenosine. Failure of ASA to induce intestinal damage may be explained, at least partly, by a protective action of SA, the metabolite of ASA.     

Effects of Different Treatments of Salicylic Acid on Heat Tolerance, Chlorophyll Fluorescence, and Antioxidant Enzyme Activity in Seedlings of Cucumis sativa L.

The effects of different treatments of salicylic acid (SA) on lipid peroxidation, chlorophyll fluorescence and antioxidant enzyme activity in seedlings of Cucumis sativa L. were studied before heat stress treatment, 36 h after heat stress and 24 h after recovery. Compared with the controls (foliar spray of distilled water), a foliar spray of 1 mM SA (SSA treatment) decreased electrolyte leakage and the concentration of H₂O₂ and thiobarbituric acid reactive substances (TBARS). SSA treatment also enhanced maximum yield of photosystem II photochemical reactions (Fv/Fm) and the quantum yield of the photosystem II electron transport (ΦPSII) after both heat stress and recovery; however, adding 1 mM SA to the nutrient solution (ASA treatment) or both adding 1 mM SA to the nutrient solution and foliar spray of 1 mM SA as well (SSA + ASA treatment) had the opposite effects. SOD activity was stimulated by all SA treatments. CAT activity was stimulated by SSA treatment and inhibited by ASA and SSA + ASA treatments after heat stress and recovery. This suggest that SSA treatment can efficiently remove H₂O₂ and decrease heat stress, and CAT plays a key role in removing H₂O₂ in cucumber seedlings under heat stress, while more H₂O₂ accumulates in ASA and SSA + ASA treatments and therefore induces serious oxidative stress. GPX, APX and GR showed higher activities in all SA treatments under heat stress, however, it appears that they were not key enzymes in removing H₂O₂ in cucumber subject to heat stress.     

Changes in Salicylic Acid and Antioxidants during Induced Thermotolerance in Mustard Seedlings

Heat-acclimation or salicylic acid (SA) treatments were previously shown to induce thermotolerance in mustard (Sinapis alba L.) seedlings from 1.5 to 4 h after treatment. In the present study we investigated changes in endogenous SA and antioxidants in relation to induced thermotolerance. Thirty minutes into a 1-h heat-acclimation treatment glucosylated SA had increased 5.5-fold and then declined during the next 6 h. Increases in free SA were smaller (2-fold) but significant. Changes in antioxidants showed the following similarities after either heat-acclimation or SA treatment. The reduced-to-oxidized ascorbate ratio was 5-fold lower than the controls 1 h after treatment but recovered by 2 h. The glutathione pool became slightly more oxidized from 2 h after treatment. Glutathione reductase activity was more than 50% higher during the first 2 h. Activities of dehydroascorbate reductase and monodehydroascorbate reductase decreased by at least 25% during the first 2 h but were 20% to 60% higher than the control levels after 3 to 6 h. One hour after heat acclimation ascorbate peroxidase activity was increased by 30%. Young leaves appeared to be better protected by antioxidant enzymes following heat acclimation than the cotyledons or stem. Changes in endogenous SA and antioxidants may be involved in heat acclimation.     

Characteristics and subcellular localization of phospholipase d and phosphatidic Acid phosphatase in mung bean cotyledons

Mixed micelles of ³²P-labeled phosphatidylcholine or phosphatidic acid (PA) and the nonionic detergent octylphenol polyethylene oxide (NP-40 Nonidet) were used to assay the activities of phospholipase D and PA phosphatase in crude extracts of mung bean (Vigna radiata) cotyledons. Together these enzymes degrade phosphatidylcholine to free choline, inorganic phosphate, and sn-1,2-diacylglycerol. Both enzymes have pH optima around 5.0. The enzymes are present in fully imbibed cotyledons and increase in activity during seedling growth. Fractionation of cotyledon extracts on sucrose gradients showed that the cells contain two PA phosphatases. One enzyme with a pH optimum of 7.5 has the same distribution on sucrose gradient as the endoplasmic reticulum marker enzyme NADH-cytochrome c reductase. The other, PA phosphatase, with a pH optimum of 5.0, was present in a protein body-rich fraction and in the load portion of the gradient. Fractionation of broken protoplasts on Ficoll gradients (a method which allows for the isolation of a high proportion of intact protein bodies) indicates that most of the cellular phospholipase D and PA phosphatase (pH 5.0) are associated with the protein bodies. Using column chromatography (DEAE-cellulose and Sephadex G-200), PA phosphatase (pH 5.0) was found to be a different enzyme from the major acid phosphatase in the cotyledons. Apparent molecular weights of phospholipase D and PA phosphatase were 150,000 and 37,000, respectively. The activity of phospholipase D was not affected by free choline, but was markedly inhibited by the choline analog and plant growth retardant isopropyl 4′-(trimethylammonium chloride-5′-methylphenyl piperidine-1-carboxylate (AMO 1618). The finding that these acid hydrolases are located in the protein bodies supports the conclusion that protein bodies form the general lytic compartment in the storage parenchyma cells.     

Free Amino Acid, Protein and Water Content Changes Associated with Seed Development in Araucaria angustifolia

The free amino acid, protein, water and dry matter contents were determined during the seed development of Araucaria angustifolia. Soluble and insoluble proteins in the mature seed represent 4.2 % of the fresh matter. The embryonic axis stored the greatest amount of soluble proteins, while cotyledons both with the embryonic axis showed the largest quantities of insoluble proteins in the mature seed. The greatest concentration of free amino acids was detected during the stage when cotyledons start to develop. Glutamic acid, aspartic acid, alanine and serine were predominant in the whole seed while arginine, lysine and γ-aminobutyric acid were present in great amounts only in cotyledons and embryonic axis. Although megagametophyte was important as a source of free amino acids, it was not the major protein storage organ in the mature seed. In the embryogenetic process, the rise of cotyledons is closely related to physiological and biochemical changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Salicylic Acid Interferes with Tobacco Mosaic Virus Replication via a Novel Salicylhydroxamic Acid-Sensitive Mechanism

Salicylic acid (SA) induces resistance to all plant pathogens, including bacteria, fungi, and viruses, but the mechanism by which SA engenders resistance to viruses is not known. Pretreatment of tobacco mosaic virus (TMV)-susceptible (nn genotype) tobacco tissue with SA reduced the levels of viral RNAs and viral coat protein accumulating after inoculation with TMV. Viral RNAs were not affected equally, suggesting that SA treatment interferes with TMV replication. Salicylhydroxamic acid (SHAM), an inhibitor of the mitochondrial alternative oxidase, antagonized both SA-induced resistance to TMV in nn genotype plants and SA-induced acquired resistance in resistant (NN genotype) tobacco. SHAM did not inhibit induction of the PR-1 pathogenesis-related protein or induction of resistance to Erwinia carotovora or Botrytis cinerea by SA. This indicates that SA induces resistance to TMV via a novel SHAM-sensitive signal transduction pathway (potentially involving alternative oxidase), which is distinct from that leading to resistance to bacteria and fungi.     

Salicylic Acid in Rice (Biosynthesis,Conjugation, and Possible Role)

Salicylic acid (SA) is a natural inducer of disease resistance in some dicotyledonous plants. Rice seedlings (Oryza sativa L.) had the highest levels of SA among all plants tested for SA content (between 0.01 and 37.19 [mu]g/g fresh weight). The second leaf of rice seedlings had slightly lower SA levels than any younger leaves. To investigate the role of SA in rice disease resistance, we examined the levels of SA in rice (cv M-201) after inoculation with bacterial and fungal pathogens. SA levels did not increase after inoculation with either the avirulent pathogen Pseudomonas syringae D20 or with the rice pathogens Magnaporthe grisea, the causal agent of rice blast, and Rhizoctonia solani, the causal agent of sheath blight. However, leaf SA levels in 28 rice varieties showed a correlation with generalized blast resistance, indicating that SA may play a role as a constitutive defense compound. Biosynthesis and metabolism of SA in rice was studied and compared to that of tobacco. Rice shoots converted [14C]cinnamic acid to SA and the lignin precursors p-coumaric and ferulic acids, whereas [14C]benzoic acid was readily converted to SA. The data suggest that in rice, as in tobacco, SA is synthesized from cinnamic acid via benzoic acid. In rice shoots, SA is largely present as a free acid; however, exogenously supplied SA was converted to [beta]-O-D-glucosylSA by an SA-inducible glucosyltransferase (SA-GTase). A 7-fold induction of SA-GTase activity was observed after 6 h of feeding 1 mM SA. Both rice roots and shoots showed similar patterns of SA-GTase induction by SA, with maximal induction after feeding with 1 mM SA.     

Modulation of Reserve Mobilization by Sucrose,Glutamine, and Abscisic Acid During Seedling Establishment in Sunflower

We carried out in vitro feeding experiments using sunflower as a model to differentiate the modulatory effects of metabolites (sucrose and glutamine) and hormones (gibberellic acid and abscisic acid) on reserve mobilization, metabolite partitioning, and key enzyme activities. Exogenous sucrose negatively not only modulated the mobilization of carbon reserves (oils and starch), but it also delayed the degradation of nitrogen reserves (storage proteins) in the cotyledons. Similarly, exogenous glutamine negatively not only modulated storage protein hydrolysis, but it also retarded oil and starch degradation. Different from the metabolites, exogenous abscisic acid affected only the mobilization of oils and storage proteins. Sucrose and glutamine caused non-reducing sugar accumulation in the cotyledons and axis, but abscisic acid did not change the content of these compounds in both seedling parts. Curiously, glutamine failed to cause amino acid accumulation in the cotyledons and abscisic acid increased the amino acid content in both cotyledons and axis. Gibberellic acid did not stimulate reserve mobilization and metabolite consumption. Although the mobilization of oils, storage proteins, and starch has been delayed by sucrose and glutamine, these metabolites augmented the activity of isocitrate lyase, acid proteases, and amylases. Only abscisic acid reduced amylase activity and increased glutamine synthetase activity. Accordingly, sucrose and glutamine exert a “crossed effect” on reserve mobilization, that is, sucrose delays storage protein hydrolysis and glutamine retards oil and starch degradation. These effects may be mediated by non-reducing sugars and they are, at least in part, different from those exerted by abscisic acid.     

水杨酸（SA）对果实成熟的影响

水杨酸是一种天然抑制剂,对植物有多种多样的作用,新近研究报道,它是乙烯生物合成的一种新的抑制剂。本文用水杨酸处理番茄、苹果、梨等果实,储藏在室温下,不时检查SA对果实贮存保鲜的影响。其结果表明SA处理的果实,PG活性比对照低,而硬度大,抗病力强。番茄,苹果和梨的无病好果率比对照果提高10％以上。上述结果证明,用SA处理绿熟番茄及梨和苹果,能有效保存果实新鲜,增强抗病力和延长货架的寿命。     

Induction of Systemic Resistance in Pea to Pea Powdery Mildew by Exogenous Application of Salicylic Acid

Exogenous application of salicylic acid (SA) solutions to pea leaves induced systemic resistance to Erysiphe pisi. reducing by 20–30% the percentages of fungal germlings that successfully infected untreated leaves of SA-treated plants. SA concentrations of 1.5 and 15 mM were similarly effective, but 0.15 mM had no detectable effect. While 15 mM SA solutions were phytotoxic. 1.5 mM solutions caused no apparent damage indicating that resistance induction was not due to tissue damage. The induced resistance persisted for at least 13 days after treatment, but excision of treated leaves 1 day after SA application prevented full induction of systemic resistance, and the resistance was not expressed if untreated leaves were inoculated fewer than 3 days after SA application. The effect of SA was transmitted to leaves at nodes both above and below treated leaves. Chemical induction of systemic resistance may provide an additional means for controlling pea diseases.