Accumulation Of Free Salicylic Acid Research Articles

Eureka lemon zinc finger protein ClDOF3.4 interacts with citrus yellow vein clearing virus coat protein to inhibit viral infection

Citrus yellow vein clearing virus (CYVCV) is a new citrus virus that has become an important factor restricting the development of China’s citrus industry, and the CYVCV coat protein (CP) is associated with viral pathogenicity. In this study, the Eureka lemon zinc finger protein (ZFP) ClDOF3.4 was shown to interact with CYVCV CP in vivo and in vitro. Transient expression of ClDOF3.4 in Eureka lemon induced the expression of salicylic acid (SA)-related and hypersensitive response marker genes, and triggered a reactive oxygen species burst, ion leakage necrosis, and the accumulation of free SA. Furthermore, the CYVCV titer in ClDOF3.4 transgenic Eureka lemon plants was approximately 69.4% that in control plants 6 mon after inoculation, with only mild leaf chlorotic spots observed in those transgenic plants. Taken together, the results indicate that ClDOF3.4 not only interacts with CP but also induces an immune response in Eureka lemon by inducing the SA pathways. This is the first report that ZFP is involved in the immune response of a citrus viral disease, which provides a basis for further study of the molecular mechanism of CYVCV infection.

Spatial-Temporal Response of Reactive Oxygen Species and Salicylic Acid Suggest Their Interaction in Pumpkin Rootstock-Induced Chilling Tolerance in Watermelon Plants.

Grafting with pumpkin rootstock could improve chilling tolerance in watermelon, and salicylic acid (SA) as a signal molecule is involved in regulating plant tolerance to chilling and other abiotic stresses. To clarify the mechanism in pumpkin rootstock-induced systemic acquired acclimation in grafted watermelon under chilling stress, we used self-grafted (Cl/Cl) and pumpkin rootstock-grafted (Cl/Cm) watermelon seedlings to study the changes in lipid peroxidation, photosystem II (PSII) activity and antioxidant metabolism, the spatio–temporal response of SA biosynthesis and H2O2 accumulation to chilling, and the role of H2O2 signal in SA-induced chilling tolerance in grafted watermelon. The results showed that pumpkin rootstock grafting promoted SA biosynthesis in the watermelon scions. Chilling induced hydrolysis of conjugated SA into free SA in the roots and accumulation of free SA in the leaves in Cl/Cm plants. Further, pumpkin rootstock grafting induced early response of antioxidant enzyme system in the roots and increased activities of ascorbate peroxidase and glutathione reductase in the leaves, thus maintaining cellular redox homeostasis. Exogenous SA improved while the inhibition of SA biosynthesis reduced chilling tolerance in Cl/Cl seedlings. The application of diphenyleneiodonium (DPI, inhibitor of NADPH oxidase) and dimethylthiourea (DMTU, H2O2 scavenger) decreased, while exogenous H2O2 improved the PSII activity in Cl/Cl plants under chilling stress. Additionally, the decrease of the net photosynthetic rate in DMTU- and DPI-pretreated Cl/Cl plants under chilling conditions could be alleviated by subsequent application of H2O2 but not SA. In conclusion, pumpkin rootstock grafting induces SA biosynthesis and redistribution in the leaves and roots and participates in the regulation of antioxidant metabolism probably through interaction with the H2O2 signal, thus improving chilling tolerance in watermelon.

Hormone signalling pathways are differentially involved in quantitative resistance of potato to Phytophthora infestans

Quantitative resistance may depend on the effectiveness of PAMP‐triggered immunity. This study highlights the diversity of mechanisms involved in the quantitative resistance of potato to Phytophthora infestans. The investigation focused on the implication of the hormone signalling pathways induced in four potato genotypes by a concentrated culture filtrate (CCF) of P. infestans. The genotypes were ranked according to their level of resistance to P. infestans and discriminant analysis of gene expression profiles separated the most resistant genotype from the three others, particularly because of a strong induction of the salicylic acid (SA) pathway. In this genotype, transcripts involved in the SA pathway, EDS1, WRKY1, PR‐1 and PR‐2, were induced by CCF. SA pathway involvement was confirmed by a peak of SA accumulation 12 h after elicitation and by the induction of jaz1 (jasmonate Zim domain protein 1) transcripts, which inhibit defence responses mediated by jasmonic acid (JA). By contrast, neither a significant induction of SA‐mediated responses nor an accumulation of free SA and PR‐2 were observed in the other resistant or two susceptible cultivars. Expression of genes in the ET and JA pathways was either not, or weakly, induced by CCF in potato. Finally, the involvement of signalling pathways was genotype dependent rather than correlating with resistance level.

Involvement of ascorbate, glutathione, protein S-thiolation and salicylic acid in benzothiadiazole-inducible defence response of cucumber against Pseudomonas syringae pv lachrymans

The metabolic response of acibenzolar-S-methyl (ASM)-treated cucumber (Cucumis sativus) to Pseudomonas syringae pv lachrymans was analyzed at the local and systemic levels. Changes in ascorbate, cysteine, glutathione and salicylic acid pools were studied. The pretreatment with ASM (priming) augmented the defense response of cucumber to subsequent bacterial infection as shown by the suppression of disease development in comparison to the untreated plants. ASM changed the redox state of ascorbate, cysteine and glutathione pools, and induced accumulation of cysteine and glutathione bound to proteins. It also provoked profound accumulation of free salicylic acid and its glucosylated conjugates. It has been proposed that the coupled salicylic acid and ascorbate- and thiol-based redox signaling contributes to the activation of a primed state in ASM-treated cucumber plants. ASM-primed and non-primed plants differed with respect to the intensity and dynamics of Psl-induced changes in the pathogen-inoculated leaves and in the systemic ones, especially with respect to free and protein-bound cysteine and to salicylic acid contents. Although the physiological significance of these reactions at the local and systemic levels remains to be eluicidated, the presented results support the role of salicylic acid, ascorbate, glutathione and protein S-thiolation in defense response of cucumber against P. syringae pv lachrymans.

Change in the content of salicylic acid and activities of phenylalanine ammonia-lyase and catalase in wheat seedling roots under the influence of Azospirilium lectins

The time course of changes in the endogenous content of salicylic acid, the ratio between the acid's free and bound forms, and changes in the activities of phenylalanine ammonia-lyase and catalase in wheat seedling roots under the effect of lectins of two strains of the associative nitrogen-fixing bacterium Azospirillum (A. brasilense Sp7 and its mutant defective in lectin activity, A. brasilense Sp7.2.3) is investigated. Differences in plant response to the action of the lectins from these two strains are established. On the basis of the obtained data, a model is proposed for lectin-assisted induction of resistance, according to which the lectin effect on the roots of seedlings results in the accumulation of free salicylic acid, which inhibits catalase activity, ultimately leading to accumulation of hydrogen peroxide and formation of induced resistance.

Involvement of salicylic acid, glutathione and protein S-thiolation in plant cell death-mediated defence response of Mesembryanthemum crystallinum against Botrytis cinerea

The response of Mesembryanthemum crystallinum plants performing C3 photosynthesis and crassulacean acid metabolism (CAM) to the non-host necrotrophic pathogen Botrytis cinerea was analyzed at the local and systemic levels. The induction of programmed cell death, lignin and callose deposition, changes in salicylic acid, glutathione and cysteinylglycine pools as well as the content of thiolated proteins were studied. The infected C3 and CAM plants exhibited hypersensitive-like defence response, however fluorescence staining with acridine orange and ethidium bromide revealed programmed cell death events in C3 plants only. The local immune response was not related to callose and lignin deposition. In the infected plants, salicylic acid, glutathione and cysteinylglycine, the first product of glutathione catabolism, as well as protein S-thiolation, predominantly S-glutathionylation, contributed to local defence at sites of inoculation. They (except protein thiolation) were also active in the establishment of systemic acclimation response monitored in the non-treated upper leaves. The extent to which they were involved in the local and systemic responses induced by B. cinerea differed in C3 and CAM plants. The accumulation of free salicylic acid, both in treated and upper leaves of the infected plants, was much more pronounced in CAM plants. The results have been discussed with respect to redox regulations in defence against necrotrophic pathogens and to stress acclimation.

Salicylic acid-induced resistance to Fusarium oxysporum f. sp. lycopersici in tomato

We demonstrated that exogenous application of 200 microM salicylic acid through root feeding and foliar spray could induce resistance against Fusarium oxysporum f. sp. Lycopersici (Fol) in tomato. Endogenous accumulation of free salicylic acid in tomato roots was detected by HPLC and identification was confirmed by LC-MS/MS analysis. At 168h of salicylic acid treatment through roots, the endogenous salicylic acid level in the roots increased to 1477ngg(-1) FW which was 10 times higher than control plants. Similarly, the salicylic acid content was 1001ngg(-1) FW at 168h of treatment by foliar spray, which was 8.7 times higher than control plants. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.7) were 5.9 and 4.7 times higher, respectively than the control plants at 168h of salicylic acid feeding through the roots. The increase in PAL and POD activities was 3.7 and 3.3 times higher, respectively at 168h of salicylic acid treatments through foliar spray than control plants. The salicylic acid-treated tomato plants challenged with Fol exhibited significantly reduced vascular browning and leaf yellowing wilting. The mycelial growth of Fol was not significantly affected by salicylic acid. Significant increase in basal level of salicylic acid in noninoculated plants indicated that tomato root system might have the capacity to assimilate and distribute salicylic acid throughout the plant. The results indicated that the induced resistance observed in tomato against Fol might be a case of salicylic acid-dependent systemic acquired resistance.

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.

Differential volatile emissions and salicylic acid levels from tobacco plants in response to different strains of Pseudomonas syringae

Pathogen-induced plant responses include changes in both volatile and non-volatile secondary metabolites. To characterize the role of bacterial pathogenesis in plant volatile emissions, tobacco plants, Nicotiana tabacum L. K326, were inoculated with virulent, avirulent, and mutant strains of Pseudomonas syringae. Volatile compounds released by pathogen-inoculated tobacco plants were collected, identified, and quantified. Tobacco plants infected with the avirulent strains P. syringae pv. maculicola ES4326 (Psm ES4326) or pv. tomato DC3000 (Pst DC3000), emitted quantitatively different, but qualitatively similar volatile blends of (E)-beta-ocimene, linalool, methyl salicylate (MeSA), indole, caryophyllene, beta-elemene, alpha-farnesene, and two unidentified sesquiterpenes. Plants treated with the hrcC mutant of Pst DC3000 (hrcC, deficient in the type-III secretion system) released low levels of many of the same volatile compounds as in Psm ES4326- or Pst DC3000-infected plants, with the exception of MeSA, which occurred only in trace amounts. Interaction of the virulent pathogen P. syringae pv. tabaci (Pstb), with tobacco plants resulted in a different volatile blend, consisting of MeSA and two unidentified sesquiterpenes. Overall, maximum volatile emissions occurred within 36 h post-inoculation in all the treatments except for the Pstb infection that produced peak volatile emissions about 60 h post-inoculation. (E)-beta-Ocimene was released in a diurnal pattern with the greatest emissions during the day and reduced emissions at night. Both avirulent strains, Psm ES4326 and Pst DC3000, induced accumulation of free salicylic acid (SA) within 6 h after inoculation and conjugated SA within 60 h and 36 h respectively. In contrast, SA inductions by the virulent strain Pstb occurred much later and conjugated SA increased slowly for a longer period of time, while the hrcC mutant strain did not trigger free and conjugated SA accumulations in amounts significantly different from control plants. Jasmonic acid, known to induce plant volatile emissions, was not produced in significantly higher levels in inoculated plants compared to the control plants in any treatments, indicating that induced volatile emissions from tobacco plants in response to P. syringae are not linked to changes in jasmonic acid.

Methyl jasmonate protects Norway spruce [Picea abies (L.) Karst.] seedlings against Pythium ultimum Trow.

The effect of methyl jasmonate (MeJA) was tested on the resistance of Picea abies seedlings against Pythium ultimum. Treatments with volatile MeJA during 3 days (25 μl 100 l−1air) protected seedlings up to 75%. This effect was unlikely to result from a direct fungitoxic effect of MeJA, as under the same conditions of treatment, growth in vitro of Pythium ultimum was not affected. Observations of possible changes on histological barriers such as lignin deposits showed no differences between control and treated plants. MeJA induced the accumulation of free salicylic acid (SA) in all parts of the seedlings, whereas bound SA only increased in hypocotyls and cotyledons. An increase in chitinase activity was detected in cotyledons already 2 days after exposure to MeJA. The results suggest that MeJA acts by stimulating defence responses of the host plant. No increase in endogenous jasmonic acid was found in spruce seedlings inoculated with Pythium nor MeJA.