Salicylic Acid Levels Research Articles

Exogenous salicylic acid positively affects morpho-physiological and molecular responses of Impatiens walleriana plants grown under drought stress

The aim of this experiment was to investigate the exogenous application of salicylic acid (SA) on morpho-physiological and molecular characteristics of Impatiens walleriana plants grown under water deficit stress. Three levels of soil water contents (95, 85, and 75% of field capacity; FC) and three levels of SA (0, 1, and 2 mM) were applied on two impatient cultivars (‘Tempo’ and ‘Salmon’). The results showed that increasing water deficit stress negatively affected growth and flowering characteristics. On the contrary, the foliar application of SA reduced the adverse effect of water deficit stress and improved growth and ornamental plant attributes. Water deficit increased the amount of electrolyte leakage (EL), malondialdehyde (MDA), peroxidase (POD) and ascorbate peroxidase (APX) activities; and proline content. The expression of the gene encoding for Δ1-pyrroline-5-carboxylate synthetase (P5CS) was slightly increased under control treatment (95% FC + SA 0 mM) and then significantly increased at 75% FC and after the SA treatments. The expression pattern of P5CR (Δ1-pyrroline-5-carboxylate reductase gene) was similar to that of P5CS, with differences in terms of intensity. The application of SA reduced the amount of EL and MDA through increased antioxidant activities and water balance. Overall, the results of this study showed that ‘Salmon’ cultivar was able to tolerate drought stress conditions better than ‘Tempo.’ The application of 2 mM SA increased growth and physiological indices in drought-stressed impatient, mitigating the detrimental effects of water deficit in this important ornamental species.

NbWRKY40 Positively Regulates the Response of Nicotiana benthamiana to Tomato Mosaic Virus via Salicylic Acid Signaling.

WRKY transcription factors play important roles in plants, including responses to stress; however, our understanding of the function of WRKY genes in plant responses to viral infection remains limited. In this study, we investigate the role of NbWRKY40 in Nicotiana benthamiana resistance to tomato mosaic virus (ToMV). NbWRKY40 is significantly downregulated by ToMV infection, and subcellular localization analysis indicates that NbWRKY40 is targeted to the nucleus. In addition, NbWRKY40 activates W-box-dependent transcription in plants and shows transcriptional activation in yeast cells. Overexpressing NbWRKY40 (OEWRKY40) inhibits ToMV infection, whereas NbWRKY40 silencing confers susceptibility. The level of salicylic acid (SA) is significantly higher in OEWRKY40 plants compared with that of wild-type plants. In addition, transcript levels of the SA-biosynthesis gene (ICS1) and SA-signaling genes (PR1b and PR2) are dramatically higher in OEWRKY40 plants than in the control but lower in NbWRKY40-silenced plants than in the control. Furthermore, electrophoretic mobility shift assays show that NbWRKY40 can bind the W-box element of ICS1. Callose staining reveals that the plasmodesmata is decreased in OEWRKY40 plants but increased in NbWRKY40-silenced plants. Exogenous application of SA also reduces viral accumulation in NbWRKY40-silenced plants infected with ToMV. RT-qPCR indicates that NbWRKY40 does not affect the replication of ToMV in protoplasts. Collectively, our findings suggest that NbWRKY40 likely regulates anti-ToMV resistance by regulating the expression of SA, resulting in the deposition of callose at the neck of plasmodesmata, which inhibits viral movement.

UGT76B1, a promiscuous hub of small molecule-based immune signaling, glucosylates N-hydroxypipecolic acid, and balances plant immunity.

Glucosylation modulates the biological activity of small molecules and frequently leads to their inactivation. The Arabidopsis thaliana glucosyltransferase UGT76B1 is involved in conjugating the stress hormone salicylic acid (SA) as well as isoleucic acid (ILA). Here, we show that UGT76B1 also glucosylates N-hydroxypipecolic acid (NHP), which is synthesized by FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1) and activates systemic acquired resistance (SAR). Upon pathogen attack, Arabidopsis leaves generate two distinct NHP hexose conjugates, NHP-O-β-glucoside and NHP glucose ester, whereupon only NHP-O-β-glucoside formation requires a functional SA pathway. The ugt76b1 mutants specifically fail to generate the NHP-O-β-glucoside, and recombinant UGT76B1 synthesizes NHP-O-β-glucoside in vitro in competition with SA and ILA. The loss of UGT76B1 elevates the endogenous levels of NHP, SA, and ILA and establishes a constitutive SAR-like immune status. Introgression of the fmo1 mutant lacking NHP biosynthesis into the ugt76b1 background abolishes this SAR-like resistance. Moreover, overexpression of UGT76B1 in Arabidopsis shifts the NHP and SA pools toward O-β-glucoside formation and abrogates pathogen-induced SAR. Our results further indicate that NHP-triggered immunity is SA-dependent and relies on UGT76B1 as a common metabolic hub. Thereby, UGT76B1-mediated glucosylation controls the levels of active NHP, SA, and ILA in concert to balance the plant immune status.

Peanut preinoculation with a root endophyte induces plant resistance to soil-borne pathogen Fusarium oxysporum via activation of salicylic acid-dependent signaling

The root endophyte Phomopsis liquidambaris B3 effectively protected peanut against root rot caused by Fusarium oxysporum. We investigated (i) the effects of preinoculation (before F. oxysporum inoculation) and postinoculation (post F. oxysporum inoculation) with B3 on pathogenic infection and (ii) the potential mechanisms underlying the suppression of root rot by B3 colonization. Peanut seedlings preinoculated, postinoculated or noninoculated with B3 and challenged or not challenged with F. oxysporum were cultivated in pots with sterilized vermiculite. The root rot severity, plant growth, defense-related enzyme activity and signaling compounds in plant tissues were investigated. Chemical manipulation experiments were performed to verify the signals involved in the suppression of root rot by B3. B3 preinoculation efficiently suppressed root rot, as evidenced by decreased cell death, pathogenic colonization and disease severity; however, these effects were absent in the B3 posttreated roots. B3 preinoculation locally and systemically enhanced resistance against pathogenic infection, which coincided with increased activities of pathogenesis-related proteins. These increased activities positively correlated with increased salicylic acid (SA) and hydrogen peroxide (H2O2) levels, in which SA played a dominant role. Preinoculation with B3 effectively suppressed F. oxysporum infection in peanut roots by activating the SA-dependent defense pathway.

Overexpressing a NPR1-like gene from Citrus paradisi enhanced Huanglongbing resistance in C. sinensis.

Overexpression of CiNPR4 enhanced resistance of transgenic citrus plants to Huanglongbing by perceiving the salicylic acid and jasmonic acid signals and up-regulating the transcriptional activities of plant-pathogen interaction genes. Developing transgenic citrus plants with enhanced immunity is an efficient strategy to control citrus Huanglongbing (HLB). Here, a nonexpressor of pathogenesis-related gene 1 (NPR1) like gene from HLB-tolerant 'Jackson' grapefruit (Citrus paradisi Macf.), CiNPR4, was introduced into 'Wanjincheng' orange (Citrus sinensis Obseck). CiNPR4 expression was determined in transgenic citrus plants using quantitative real-time PCR analyses. The Candidatus Liberibacter asiaticus (CLas) pathogen of HLB was successfully transmitted to transgenic citrus plants by grafting infected buds. HLB symptoms developed in transgenic and wild-type (WT) plants by 9months after inoculation. A CLas population analysis showed that 26.9% of transgenic lines exhibited significantly lower CLas titer levels compared with the CLas-infected WT plants at 21months after inoculation. Lower starch contents and anatomical aberration levels in the phloem were observed in transgenic lines having enhanced resistance compared with CLas-infected WT plants. CiNPR4 overexpression changed the jasmonic acid, but not salicylic acid, level. Additionally, the jasmonic acid and salicylic acid levels increased after CLas infection. Transcriptome analyses revealed that the enhanced resistance of transgenic plants to HLB resulted from the up-regulated transcriptional activities of plant-pathogen interaction-related genes.

Оценка эффективности и приверженности больных с ишемической болезнью сердца лечению комбинированным препаратом ацетилсалициловой кислоты и клопидогрела: исследование коБРа

Aim. Assessment of the efficacy and adherence to treatment with acetylsalicylic acid (ASA) and clopidogrel combination drug compared to separate administration of the drugs in patients with acute coronary syndrome and patients with chronic coronary syndrome after coronary stent implantation. Materials and methods. The study included 100 patients randomized to receive either original clopidogrel (Plavix® Sanofi) only or original ASA (Aspirin® Cardio Bayer) only or the generic fixed drug combination (Plagril® A Dr. Reddy's Laboratories Ltd.). Over the first 7–10 days after the index event, all patients were treated with a separate drug in the hospital, then received double antiplatelet therapy with appropriate drugs on an outpatient basis for 4 months, and purchased the drugs on their own for the last 2 months of follow-up. Monitoring the efficacy of therapy and patient adherence to treatment was carried out according to the clinic data, platelet aggregation indicators and blood thromboxane B2 (TXB2), salicylic acid and clopidogrel metabolite (carboxylic acid) levels on the 7th day after disease onset and after 8 and 16 weeks of treatment. Results. Most of the patients were elderly (mean age 68.3±10.6 years), of them 35% were women. After 8 and 16 weeks of treatment in hospital, platelet aggregation indicators did not differ between patients taking separate drugs or a fixed combination. The generic Plagril® A inhibited the aggregation response similarly to the original drugs. At moment of randomization, baseline blood TXB2, salicylic acid and the carboxyl metabolite of clopidogrel levels were comparable in both groups of patients (p>0.05). After 8 weeks of therapy, patients taking Plagril® A had significantly lower TXB2 levels compared with the separate administration of Plavix and Aspirin Cardio: 0.1±0.05 ng/ml vs 0.2±0.23 ng/ml, respectively (p<0.001). After 16 weeks, TXB2 levels reached 0.28±0.56 ng/ml vs 0.43±0.48 ng/ml, respectively (p=0.006). There were no differences in blood salicylic acid and clopidogrel carboxyl metabolite blood levels between the groups of patients during the entire study period. Adherence to antiplatelet therapy during inpatient period of treatment was 100%. In the first 8 weeks, it decreased to 74.5%, and after 16 weeks – to 71.5%. When taking the drugs separately, missing rate was higher in ASA group: 21.2% vs 5% in clopidogrel group. Conclusion. Plagril® A is bioequivalent and as effective as the original ASA and clopidogrel taken separately, in terms of the effect on platelet activity and blood clopidogrel metabolite levels. The adherence to a fixed combination of clopidogrel and ASA in patients with acute coronary syndrome and patients with chronic coronary syndrome is significantly higher than when these drugs are taken separately, both at the stages of free treatment and when purchasing drugs on their own. Keywords: antiplatelet therapy, acetylsalicylic acid, clopidogrel, adherence to secondary prevention, coronary heart disease For citation: Lomakin NV, Buryachkovskaya LI, Senichkina AA, Sumarokov AB, Docenko UV, Kazey VI. Use of combination pills with acetylsalicylic acid and clopidogrel in coronary artery disease. Efficacy and assessment of adherence to treatment: Kobra Study. Consilium Medicum. 2021; 23 (1): 61–69. DOI: 10.26442/20751753.2021.1.200780

Effect of spacing and plant growth regulators on yield and economic of Zaid sesame (Sesamum indicum L.)

The field experiment was conducted during Zaid season, 2020 at Crop Research Farm (CRF), Department of Agronomy, SHUATS, Prayagraj (UP) On sandy loam soil to investigate the Effect of Spacing and Plant Growth Regulators on Yield and Economic of Zaid Sesame (Sesamum indicum L.). The experiment was laid out in Randomized Block Design with nine treatments replicated thrice with the different spacing (30cm x 10cm and 45cm x 10cm) and different levels of NAA (10 ppm & 20 ppm), GA3 (10 ppm & 20 ppm), IAA (10 ppm & 20 ppm) and salicylic acid (10 ppm & 20 ppm) as foliar spray. Study revealed that Spacing 45cm x 10cm + GA3 10 ppm foliar spray at 30 and 45 DAS was recorded significantly higher Seed yield (8.27 q/ha), Stover yield (27.84 q/ha) as compared to all the treatment combinations. The economic analysis clearly indicates that higher B:C ratio (2.10) recorded with treatment of spacing 45cm x 10cm + GA3 10 ppm foliar spray at 30 and 45 DAS as compared to all treatment combinations.

Enhancement of physiological and biochemical attributes of okra by application of salicylic acid under drought stress

Horticultural crops especially vegetables are most vulnerable to drought due to their higher irrigation needs. Hence, this study was undertaken to evaluate the adverse effects of drought stress and the beneficial effects of salicylic acid (SA) on physiological and biochemical attributes of okra plants under drought stress. For this purpose, a pot experiment was laid out in Complete Randomized Design (CRD) design. Okra seeds were primed with four different SA treatments i.e., 0 (control), 1, 2 and 3 mM and sown in pots (Ø 20 cm). After 14 days of germination, the plants were subjected to two drought levels i.e., 25% and 50% field capacity (FC) and after 20 days of germination regular foliar sprays of SA at 7 days interval were performed with aforementioned SA levels. Physiological parameters like fresh weight, dry weight, and length of plants along with biochemical attributes like chlorophyll (‘a’, ‘b’ and total), total carotenoids, total protein and proline contents, and electrolyte leakage were recorded. Results revealed that drought stress (25% FC) significantly reduced all the studied parameters and resulted in the lowest values of fresh weight (5.04 g), dry weight (1.33 g), length of plants (11.68 cm), chlorophyll ‘a’ content (5.97 mg/g FW), chlorophyll ‘b’ content (8.86 mg/g FW), total chlorophyll (14.84 mg/g FW), total carotenoids (4.96 mg/g FW) and total protein (1.05 mg/g FW), except proline content (6.81 mg/g FW) and electrolyte leakage (77.31%) which was increased. Application of SA under drought stress reduced the harmful effects of drought and application of 2 mM SA produced the maximum fresh weight (8.60 g), dry weight (2.51 g), length of plants (16.23 cm), chlorophyll ‘b’ content (14.47 mg/g FW), total protein (3.73 mg/g FW) and proline content (5.11 mg/g FW); whereas application of 3 mM SA showed the highest values of chlorophyll ‘a’ (8.91 mg/g FW), total chlorophyll content (23.20 mg/g FW) and carotenoids (7.93 mg/g FW), and the lowest value for electrolyte leakage (62.00%).

Combined ultraviolet and darkness regulation of medicinal metabolites in Mahonia bealei revealed by proteomics and metabolomics

Roots of Mahonia bealei have been used as traditional Chinese medicine with antibacterial, antioxidant and anti-inflammatory properties due to its high alkaloid content. Previously, we reported that alkaloid and flavonoid contents in the M. bealei leaves could be increased by the combined ultraviolet B and dark treatment (UV+D). To explore the underlying metabolic pathways and networks, proteomic and metabolomic analyses of the M. bealei leaves were conducted. Proteins related to tricarboxylic acid cycle, transport and signaling varied greatly under the UV + D. Among them, calmodulin involved in calcium signaling and ATP-binding cassette transporter involved in transport of berberine were increased. Significantly changed metabolites were overrepresented in phenylalanine metabolism, nitrogen metabolism, phenylpropanoid, flavonoid and alkaloid biosynthesis. In addition, the levels of salicylic acid and gibberellin decreased in the UV group and increased in the UV + D group. These results indicate that multi-hormone crosstalk may regulate the biosynthesis of flavonoids and alkaloids to alleviate oxidative stress caused by the UV + D treatment. Furthermore, protoberberine alkaloids may be induced through calcium signaling crosstalk with reaction oxygen species and transported to leaves. SignificanceMahonia bealei root and stem, not leaf, were used as traditional medicine for a long history because of the high contents of active components. In the present study, UV-B combined with dark treatments induced the production of alkaloids and flavonoids in the M. bealei leaf, especially protoberberine alkaloids such as berberine. Multi-omics analyses indicated that multi-hormone crosstalk, enhanced tricarboxylic acid cycle and active calcium signaling were involved. The study informs a strategy for utilization of the leaves, and improves understanding of the functions of secondary metabolites in M. bealei.

Chorismate synthase mediates cerebral malaria pathogenesis by eliciting salicylic acid-dependent autophagy response in parasite.

ABSTRACTCerebral malaria caused by Plasmodium falciparum is the severest form of the disease resulting in the morbidity of a huge number of people worldwide. Development of effective curatives is essential in order to overcome the fatality of cerebral malaria. Earlier studies have shown the presence of salicylic acid (SA) in malaria parasite P. falciparum, which plays a critical role in the manifestation of cerebral malaria. Further, the application of SA for the treatment of acute symptoms in cerebral malaria increases the activity of iNOS leading to severe inflammation-mediated death, also called as Reye's syndrome. Therefore, modulation of the level of SA might be a novel approach to neutralize the symptoms of cerebral malaria. The probable source of parasite SA is the shikimate pathway, which produces chorismate, a precursor to aromatic amino acids and other secondary metabolites like SA in the parasite. In this work, we performed the immunological, pathological and biochemical studies in mice infected with chorismate synthase knocked-out Plasmodium berghei ANKA, which does not produce SA. Fewer cerebral outcomes were observed as compared to the mice infected with wild-type parasite. The possible mechanism behind this protective effect might be the hindrance of SA-mediated induction of autophagy in the parasite, which helps in its survival in the stressed condition of brain microvasculature during cerebral malaria. The absence of SA leading to reduced parasite load along with the reduced pathological symptoms contributes to less fatality outcome by cerebral malaria.

The role of benzoic acid, gallic acid and salicylic acid in protecting tomato callus cells from excessive boron stress

Excess boron (EB) is a known threat to plant growth and productivity, however, the role of applications of phenolic acids [PAs; benzoic acid (BA), gallic acid (GA), and salicylic acid (SA)] in mitigating this threat has not been extensively explored. In vitro investigations were performed to realize the mechanism of PAs on the tolerance index (TI), boron (B) accumulation, and non-enzymatic antioxidants in alleviating EB on tomato (Solanum lycopersicum L. cultivar Castle Rock) calli. Tomato calli were subjected to two levels of B (medium B condition (control) and 2 mM boric acid) in the presence or absence of different concentrations of PAs. The results showed that moderate levels of BA (1.0 μM), GA (10 μM), and SA (50 μM) promoted inhibition of the TI, flavonoids, and ascorbate (AsA) of EB-treated calli. The B concentration was increased under EB, and this parameter was significantly decreased by PAs. Malondialdehyde (MDA), bound phenolics, cysteine (Cys), glutathione (GSH), and protein thiols (PTs) were increased under EB but were significantly reduced through the use of PAs. Free phenolics were increased under EB and were significantly decreased by PAs, only BA increased its content in calli. In addition, EB reduced non-protein thiols (NPTs); however, this deficiency was alleviated by PAs, only SA reduced its content. These results provide new visions to the mechanism that helps control EB in tomato plants and thus can be harnessed to develop effective plant growth stimuli.

Bioactive Compounds and Antiradical Activity of the Rosa canina L. Leaf and Twig Extracts

It is important to search for new sources of bioactive, natural compounds, because customers are paying more attention to food quality. Fruits and berries from horticultural plants are known to be good sources of agents beneficial for human well-being and could serve as natural preservatives in the food industry. However, more recent research indicates that other plant organs can also be rich in nutrients. Our study focused on characterizing an unexplored source, namely leaf and twig extracts from Rosa canina. The chemical composition of these extracts was analyzed and their in vitro activity measured. HPLC analysis of the content of phenolics, vitamins and amino acids revealed that the leaf and twig extracts were found to be rich in bioactive compounds with potent antioxidant properties. The greatest differences between bioactive phenolic compounds in leaf and twig extracts related mainly to p-coumaric acid, myricetin, ellagic acid, cyanidin, procyanidin and quercetin, whereas salicylic acid levels were similar in both types of extract. Interactions with human serum albumin were investigated, and some conformational changes in protein structure were observed. Further analysis (lipid peroxidation, protein carbonylation, thiol group oxidation, DPPH inhibition and ROS inhibition) confirmed that both leaf and twig extracts exhibited antioxidant and antiradical scavenging activities. Cytotoxicity and hemotoxicity assays confirmed very low toxicity of the extracts towards human cells over the range of concentrations tested. Our results indicate that both extracts could serve as non-toxic sources of bioactive compounds with antiradical properties.

Transcriptomic and genetic approaches reveal an essential role of the NAC transcription factor SlNAP1 in the growth and defense response of tomato

With global climate change, plants are frequently being exposed to various stresses, such as pathogen attack, drought, and extreme temperatures. Transcription factors (TFs) play crucial roles in numerous plant biological processes; however, the functions of many tomato (Solanum lycopersicum L.) TFs that regulate plant responses to multiple stresses are largely unknown. Here, using an RNA-seq approach, we identified SlNAP1, a NAC TF-encoding gene, which was strongly induced by various stresses. By generating SlNAP1 transgenic lines and evaluating their responses to biotic and abiotic stresses in tomato, we found that SlNAP1-overexpressing plants showed significantly enhanced defense against two widespread bacterial diseases, leaf speck disease, caused by Pseudomonas syringae pv. tomato (Pst) DC3000, and root-borne bacterial wilt disease, caused by Ralstonia solanacearum. In addition, SlNAP1 overexpression dramatically improved drought tolerance in tomato. Although the SlNAP1-overexpressing plants were shorter than the wild-type plants during the early vegetative stage, eventually, their fruit yield increased by 10.7%. Analysis of different hormone contents revealed a reduced level of physiologically active gibberellins (GAs) and an increased level of salicylic acid (SA) and abscisic acid (ABA) in the SlNAP1-overexpressing plants. Moreover, EMSAs and ChIP-qPCR assays showed that SlNAP1 directly activated the transcription of multiple genes involved in GA deactivation and both SA and ABA biosynthesis. Our findings reveal that SlNAP1 is a positive regulator of the tomato defense response against multiple stresses and thus may be a potential breeding target for improving crop yield and stress resistance.

Genome-wide identification and expression analysis of the MLO gene family reveal a candidate gene associated with powdery mildew susceptibility in bitter gourd (Momordica charantia)

Powdery mildew (PM), caused by Podosphaera xanthii, is one of the most serious disease in bitter gourd (Momordica charantia). Specific members of the Mildew Locus O (MLO) gene family act as susceptibility factors by recognizing PM pathogens and the corresponding loss-of-function mutations confer broad-spectrum durable host resistance. However, the potential PM-susceptibility genes in bitter gourd have not been identified yet. Therefore, genome-wide characterization and expression analysis of the bitter gourd MLO gene family were carried out in the present study. The results suggested that 15 MLO homologs were present in the bitter gourd genome. Gene organization, cis-elements, conserved amino acid residues and motifs were also investigated and analyzed. Phylogenetic analysis revealed that these identified MLO proteins clustered in six well-defined clades. It was noteworthy that McMLO7b, a bitter gourd MLO homolog falling in clade V which clustered all the known PM susceptibility factors of dicots, was up-regulated more than 6-fold at an early infection stage (6 h) and was inferred to be a candidate gene of PM susceptibility factor. In addition, exogenous salicylic acid (SA) treatment enhanced the PM resistance of bitter gourd, accompanied by a significantly elevated level of endogenous SA. However, McMLO7b showed nearly equivalent expression in SA-treated plants compared to the mock-treated seedlings at the early PM infection stage. MLO proteins were directly targeted by PM to trigger pathogenesis, therefore, a weak effect of exogenous SA on interaction between bitter gourd and PM could be inferred. To conclude, the results will be helpful in proposing better strategies to control PM disease with either resistant cultivars or cultivation management.

Role of salicylic acid signaling in the biotrophy-necrotrophy transition of Xanthomonas campestris pv. campestris infection in Brassica napus

To characterize the hormonal regulations in the transition between biotrophic and necrotrophic phases of Xanthomonas campestris pv. campestris (Xcc) infection, the endogenous phytohormone and reactive oxygen species (ROS) levels and glutathione (GSH) redox status of non-inoculated and Xcc-infected Brassica napus cv. Mosa leaves were measured at various points after inoculation. This time-course study revealed two distinct phases of the Xcc-infection, namely an early asymptomatic (biotrophic) phase that could be observed at 2 days post-inoculation (DPI) and a destructive necrotrophic phase that occurred at 7–24 DPI and was associated with V-shaped necrosis. The length of the V-shaped lesions increased significantly with the progression of infection, as did H2O2 accumulation and the expression of NADPH oxidase. Xcc-infections induced the gradual depression of the reduced/oxidized GSH/GSSG ratio with the progression of disease. Furthermore, Xcc inoculation reduced levels of salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and cytokinin (CK) during the biotrophic phase (at 2 DPI); increased SA level (9.5 fold) and the expression of both SA synthesis-related genes (EDS1 and ICS1) and signaling-related genes (NPR1 and PR1) from the 2 to7 DPI. ABA and CK levels gradually increased during the necrotrophic phase. Interestingly, JA level was either reduced or not significantly affected during the necrotrophic phase of infection. Altogether, these results indicate that, in B. napus, changes in SA-mediated ROS production regulate the transition from the symptomless biotrophic phase of Xcc infection to the destructive necrotrophic phase.

In vivo tracing of endogenous salicylic acids as the biomarkers for evaluating the toxicity of nano-TiO2 to plants

Currently, nano-titanium dioxide (nTiO2) is considered an emerging environmental contaminant. Bottlenecked by the traditional destructive and lethal sampling methods, nTiO2’s effect in living plants is poorly investigated. Here, in vivo tracing of endogenous salicylic acids at regular intervals was performed by using solid phase microextraction (SPME) technique for evaluating the effects of nTiO2 on plants. By planting aloe in soil containing varying amounts of nTiO2, the titanium (Ti) element accumulated in the leaves to concentrations and then reached the maximum of 1.1 ± 0.4 μg/g after nTiO2 exceeding 0.1 g/kg. The levels of salicylic acid (SA) and acetylsalicylic acid (ASA) were up-regulated upon the exposure to nTiO2, while were positively correlated to the contents of Ti. Moreover, the increased malondialdehyde, decreased total superoxide dismutase and fluctuated glutathione along with the addition of nTiO2 demonstrated the oxidative stress caused by nTiO2. Meanwhile, apparent growth indicators including leaf elongation, plant fresh weight and root development were influenced, which further confirmed the toxicity of nTiO2 imparted on aloe. This study presents the possibility of using salicylic acids as biomarkers for revealing the toxicity of nTiO2 on plants in addition to the other biomarkers and biomass data, and the in vivo SPME technique is powerful for their monitoring.

Role of endophytic Penicillium species and Pseudomonas monteilii in inducing the systemic resistance in okra against root rotting fungi and their effect on some physiochemical properties of okra fruit.

The efficacy of three isolates of endophytic Penicillium species that have shown significant suppressive effect on root rotting fungi in our previous study were further evaluated in pots and field plot experiments for their effect on root diseases of okra, induction of systemic resistance and physiochemical properties of okra fruit. Aqueous suspensions of endophytic Penicillium and Pseudomonas monteilii were applied in pots and field plots using okra as test plant. Data on the fungal infection of roots, plant growth, plant resistance markers like polyphenol, salicylic acid and antioxidant status of plant were determined. These isolates significantly suppressed root diseases and induced systemic resistance via increasing level of resistance markers, polyphenol and salicylic acid besides improving antioxidant activity of Penicillium and P. monteilii-treated plants as compared to control plants. GC-MS analysis of n-hexane extract of mycelium of P. nigricans revealed the presence of 15 different volatile compounds. Endophytic Penicillium and P. monteilii have potential against root-infecting fungi of okra and can improve plant growth and yield. Endophytic Penicillium species and P. monteilii can suppress root rotting fungi by direct mechanism or induction of systemic resistance in plants.

Interplay of phytohormones facilitate sorghum tolerance to aphids

Interactions among phytohormones are essential for providing tolerance of sorghum plants to aphids. Plant's encounter with insect herbivores trigger defense signaling networks that fine-tune plant resistance to insect pests. Although it is well established that phytohormones contribute to antixenotic- and antibiotic-mediated resistance to insect pests, their role in conditioning plant tolerance, the most durable and promising category of host plant resistance, is largely unknown. Here, we screened a panel of sorghum (Sorghum bicolor) inbred lines to identify and characterize sorghum tolerance to sugarcane aphids(SCA; Melanaphis sacchariZehntner), a relatively new and devastating pest of sorghum in the United States. Our results suggest that the sorghum genotype SC35, the aphid-tolerant line identified among the sorghum genotypes, displayed minimal plant biomass loss and a robust photosynthetic machinery, despite supporting higher aphid population. Phytohormone analysis revealed significantly higher basal levels of 12-oxo-phytodienoic acid, a precursor in the jasmonic acid biosynthesis pathway, in the sorghum SCA-tolerant SC35 plants. Salicylic acid accumulation appeared as a generalized plant response to aphids in sorghum plants, however, SCA feeding-induced salicylic acid levels were unaltered in the sorghum tolerant genotype. Conversely, basal levels of abscisic acid and aphid feeding-induced cytokinins were accumulated in the SCA-tolerant sorghum genotype. Our findings imply that the aphid-tolerant sorghum genotype tightly controls the relationship among phytohormones, as well as provide significant insights into the underlying mechanisms that contribute to plant tolerance to sap-sucking aphids.

Diverse Roles of the Salicylic Acid Receptors NPR1 and NPR3/NPR4 in Plant Immunity.

The plant defense hormone salicylic acid (SA) is perceived by two classes of receptors, NPR1 and NPR3/NPR4. They function in two parallel pathways to regulate SA-induced defense gene expression. To better understand the roles of the SA receptors in plant defense, we systematically analyzed their contributions to different aspects of Arabidopsis (Arabidopsis thaliana) plant immunity using the SA-insensitive npr1-1 npr4-4D double mutant. We found that perception of SA by NPR1 and NPR4 is required for activation of N-hydroxypipecolic acid biosynthesis, which is essential for inducing systemic acquired resistance. In addition, both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) are severely compromised in the npr1-1 npr4-4D double mutant. Interestingly, the PTI and ETI attenuation in npr1-1 npr4-4D is more dramatic compared with the SA-induction deficient2-1 (sid2-1) mutant, suggesting that the perception of residual levels of SA in sid2-1 also contributes to immunity. Furthermore, NPR1 and NPR4 are involved in positive feedback amplification of SA biosynthesis and regulation of SA homeostasis through modifications including 5-hydroxylation and glycosylation. Thus, the SA receptors NPR1 and NPR4 play broad roles in plant immunity.

Involvement of salicylic acid in cold priming-induced freezing tolerance in wheat plants

Freezing is one of the most damaging abiotic stress factors. Cold priming has been shown to enhance freezing tolerance in wheat. However, the underlying mechanisms are unclear. Salicylic acid (SA) is an important signal molecule involved in plant responses to abiotic and biotic stresses. This study aims to investigate the role of SA in cold priming-induced freezing tolerance in wheat plants. The results showed that the expression of gene encoding phenylalanine ammonia-lyase (PAL, a key enzyme involved in SA biosynthesis) and the level of endogenous SA (both free and conjugated) were significantly up-regulated following cold priming treatment. The role of SA in cold priming-induced freezing tolerance was further explored using the donor and inhibitor of endogenous SA. l-α-aminooxy-β-phenylpropionic acid (AOPP, a specific inhibitor of PAL) pretreatment reversed the increment of SA level induced by cold priming treatment, attenuated the positive effects of cold priming on antioxidant capacity (as indicated by the contents of MDA, ASA and GSH, and the activities of APX, GR, DHAR and MDHAR) and cold-responsive genes expression (such as AOX1a, IRI2 and HSP70) under the later freezing stress as well as the freezing tolerance (as indicated by the photochemical activity, electrolyte leakage and biomass). The application of exogenous SA could obviously counteract the negative effects of AOPP. Findings of the present study suggested that the roles of SA in cold priming-induced freezing tolerance in wheat might involve regulation of antioxidant capacity and cold-responsive gene expression.