Endogenous Salicylic Acid Content Research Articles

Effect of Salicylic Acid Treatment on Disease Resistance to Coleosporium zanthoxyli in Chinese Pepper (Zanthoxylum armatum).

The fungus Coleosporium zanthoxyli causes leaf rust in Chinese pepper (Zanthoxylum armatum). To investigate the control effect of elicitor treatment on leaf rust in this species, the impact of salicylic acid (SA) on the spores and growth of C. zanthoxyli and the induced resistance to leaf rust by Z. armatum were analyzed, and the possible defense mechanisms involved in SA induction were evaluated. The results showed that SA had no effect on C. zanthoxyli spore germination and growth; however, rust resistance was induced in Z. armatum. The optimal SA treatment concentration was 0.4 mg/ml, and the relative cure effect reached 44.56%. SA-induced disease resistance was evident for up to 10 days, while the optimal induction interval was 48 h after stimulation. Consistent with the induced resistance, H2O2, total protein, total phenol, and lignin concentrations and polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), and catalase (CAT) activities were significantly increased with the SA treatment, whereas the malondialdehyde content was significantly decreased. In addition, exogenous SA promoted defense-related enzyme activities, including those of POD, CAT, and PAL, and increased H2O2, lignin, and endogenous SA contents. Furthermore, SA induced the expression of SA signaling pathway genes such as ZaPR1 and ZaNPR1, and silencing ZaPR1 enhanced the sensitivity of Z. armatum to leaf rust. Our results demonstrated that 0.4 mg/ml SA priming increased the activities of CAT, POD, and PAL, elevated the contents of H2O2, lignin, and endogenous SA, and upregulated the expression of the SA-related gene ZaPR1, thereby enhancing the resistance of Z. armatum to leaf rust.

Interactive effects of melatonin and salicylic acid on Brassica napus under drought condition

It is imperative to understand the synergetic actions of Melatonin (MET) and salicylic acid (SA) in counteracting drought stress. A pot experiment was performed to investigate the interactive effects of exogenously applied MET and SA on morphology, physiology, and biochemical characteristics of drought-stressed canola (Brassica napus). Two cultivars (Super canola and Faisal canola) were used. MET (0.1 µM) and SA (0.50 mM) were applied as seed priming and foliar spray. Plants were exposed to severe drought (45% field capacity) at the reproductive stage. Drought stress caused a significant reduction in shoot length (19%), plant fresh (15%) and dry (17%) biomass, yield (30%), photosynthetic rate (43%), water potential (29%) and osmotic potential (33%) values. Increased activity of free amino acids (20%), total soluble sugars (5%), and different antioxidant enzymes like catalase (27%), peroxidase (23%), superoxide dismutase (20%) and ascorbate peroxidase (35%), were recorded under drought. Seed priming and foliar application of MET and SA reduced the negativity of drought. Priming of seeds with MET, as well as synergetic application of MET priming and SA foliar spray, were the most effective treatments, showing the most significant growth criteria (22% increase in plant height, 46% in fresh and 40% in dry biomass), yield components (49%), water (54%) and osmotic potential (28%), and endogenous MET (17%) and SA (16%) content. Super canola cultivar showed better growth than Faisal canola. Study showed that the synergetic application of MET and SA has the potential to induce stress resistance and enhance canola plants' growth under drought.

Salicylic Acid Acts Upstream of Auxin and Nitric Oxide (NO) in Cell Wall Phosphorus Remobilization in Phosphorus Deficient Rice

Salicylic acid (SA) is thought to be involved in phosphorus (P) stress response in plants, but the underlying molecular mechanisms are poorly understood. Here, we showed that P deficiency significantly increased the endogenous SA content by inducing the SA synthesis pathway, especially for up-regulating the expression of PAL3. Furthermore, rice SA synthetic mutants pal3 exhibited the decreased root and shoot soluble P content, indicating that SA is involved in P homeostasis in plants. Subsequently, application of exogenous SA could increase the root and shoot soluble P content through regulating the root and shoot cell wall P reutilization. In addition, − P + SA treatment highly upregulated the expression of P transporters such as OsPT2 and OsPT6, together with the increased xylem P content, suggesting that SA also participates in the translocation of the P from the root to the shoot. Moreover, both signal molecular nitric oxide (NO) and auxin (IAA) production were enhanced when SA is applied while the addition of respective inhibitor c-PTIO (NO scavenger) and NPA (IAA transport inhibitor) significantly decreased the root and shoot cell wall P remobilization in response to P starvation. Taken together, here SA-IAA-NO-cell wall P reutilization pathway has been discovered in P-starved rice.

RETRACTED: Alternative oxidase is involved in leaf senescence via regulation of Salicylic acid accumulation in tomato

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the corresponding author, Yu Wen, and the Editor-in-Chief. The corresponding author requested retraction, due to multiple self-reported issues and breaches of scientific ethical standards. The Editor-in-Chief no longer has trust in the veracity of the findings in the paper and therefore decided to retract it. This paper was submitted to the journal by Yu Wen without the knowledge or permission of the co-author Dawei Zhang. Authors submitting to the journal warrant that the publication is approved by all authors. As Dawei Zhang did not agree to be a co-author on the paper, this is a clear breach of the submission requirements for the journal, as well a breach of scientific ethical standards. As well as the issue with the authorship, there are problems with the veracity of the data published in the article. Specifically, there is a duplication of Fig 1g and Fig 2a. The corresponding author Yu Wen has indicated that the relevant experiments in the article are inadequate and the conclusions cannot be characterized by physiological data alone, especially in the fourth figure where further relevant molecular experiments need to be designed to refine the conclusion.

A low concentration of exogenous salicylic acid enhances cold tolerance in Hami melons (Cucumis melo var. saccharinus) by modulating salicylic acid-response CmGST genes

Long-term cold storage of Hami melons (Cucumis melo var. saccharinus) induces severe chilling injuries, downgrading their storage quality. Three different concentrations (1, 3, and 9 mM) of exogenous salicylic acid (SA) were applied under cold stress conditions (0.5 ± 0.5 °C) to prolong the shelf-life of cold-sensitive ‘Golden Empress-308′ (GE-melon) Hami melons. Afterward, the phenotypic index, bioinformatics of CmGSTs, expression patterns of CmGSTs, endogenous SA content, molecular docking, and molecular dynamics simulation were investigated. The phenotypic index indicated that low concentrations (1 and 3 mM) of SA ameliorated chilling injuries, whereas a high concentration of SA (9 mM) treatment adversely affected the GE-melons. The RT-qPCR analysis determined that SA treatment induced five out of seven CmGST-containing SA-response cis-elements. The content of endogenous SA was elevated by exogenous SA. Interestingly, both high and low levels of endogenous SA promoted chilling injuries in GE-melons under cold stress conditions. Furthermore, molecular docking and molecular dynamics simulation signaled that SA bound to the target CmGSTs in a stable conformation. In conclusion, administration of a low concentration of SA enhances cold tolerance in Hami melons by modulating the SA-responsive CmGSTs under cold stress conditions.

Roles of AGD2a in Plant Development and Microbial Interactions of Lotus japonicus.

Arabidopsis AGD2 (Aberrant Growth and Death2) and its close homolog ALD1 (AGD2-like defense response protein 1) have divergent roles in plant defense. We previously reported that modulation of salicylic acid (SA) contents by ALD1 affects numbers of nodules produced by Lotus japonicus, but AGD2′s role in leguminous plants remains unclear. A combination of enzymatic analysis and biological characterization of genetic materials was used to study the function of AGD2 (LjAGD2a and LjAGD2b) in L. japonicus. Both LjAGD2a and LjAGD2b could complement dapD and dapE mutants of Escherichia coli and had aminotransferase activity in vitro. ljagd2 plants, with insertional mutations of LjAGD2, had delayed flowering times and reduced seed weights. In contrast, overexpression of LjAGD2a in L. japonicus induced early flowering, with increases in seed and flower sizes, but reductions in pollen fertility and seed setting rates. Additionally, ljagd2a mutation resulted in increased expression of nodulin genes and corresponding increases in infection threads and nodule numbers following inoculation with Rhizobium. Changes in expression of LjAGD2a in L. japonicus also affected endogenous SA contents and hence resistance to pathogens. Our results indicate that LjAGD2a functions as an LL-DAP aminotransferase and plays important roles in plant development. Moreover, LjAGD2a activates defense signaling via the Lys synthesis pathway, thereby participating in legume–microbe interaction.

Quantitative Analysis of ABA and SA in Rice (Oryza sativa L.) Grown Under Drought Stress

Rice cultivation requires plenty of water for its proper growth, development, and productivity. The regular life cycle of rice plants is disrupted by moderate to severe drought. Both abscisic acid (ABA) and salicylic acid (SA) have involvement in rice physiology under drought. With the limited information, we aimed to study the relationship between ABA and SA concentration in leaves of rice plants under drought. The experiment was performed on a drought-sensitive variety of Swarna MTU 7029 rice. The HPLC method was used to analyse the endogenous ABA and SA content. This study provided data on ABA and SA content in 0.5 mM SA treated and untreated 56 days old rice plants at 7, 14 and 28 days of drought. The result showed that the concentration of ABA was enhanced by 74.6%, 82.8%, and 99.4% during 7, 14, and 28 days of drought, respectively, while it was increased by 64.6%, 74.3% and 78.5% in SA treated plants under 7, 14 and 28 days drought, respectively. The concentration of SA enhanced by 132.2%, 19.7%, and 3.0% during 7, 14, and 28 days of drought, while it was increased to 137.5%, 54.8%, and 23.2% in SA treated plants under 7, 14, and 28 days drought, respectively. This explains that on the 7th day of drought stress, SA may suppress the formation of ABA but not much on the 14th and 28th days of drought stress in treated rice plants. This outcome helps study the interaction of ABA and SA at the gene level under drought stress.

Relationship of Resistance-Related Enzyme Activity and Salicylic Acid Content in Phalaenopsis Species with Different Levels of Resistance to Dickeya dadantii

Abstract Orchids (Phalaenopsis) are ornamental plants that are cultivated commercially and in great demand in the market. Soft-rot disease (SRD) caused by the necrotrophic pathogen Dickeya dadantii is a cause of considerable economic loss to cultivators of many orchid species. Our previous experiment identified a limited number of species that were resistant to D. dadantii. This study aimed to validate the resistance level of four Phalaenopsis species in a detached leaf inoculation protocol to identify the resistance mechanism(s) involved. Soft-rot symptom diameter was measured from 6 to 18 hours post-inoculation (HPI) with D. dadantii. Disease assessment confirmed that P. amboinensis is a resistant species, P. pantherina is a susceptible species, and P. amabilis and P. schilleriana are very susceptible species. There was no difference in the lignin content between the resistant and very susceptible species. Detailed observation of resistant and very susceptible species, P. amboinensis vs. P. amabilis, revealed higher phenylalanine ammonia-lyase (PAL) and peroxidase (POD) in P. amabilis than in P. amboinensis. In contrast, there was higher salicylic acid (SA) content in P. amboinensis than in P. amabilis. These results suggest that POD and PAL activities may not be effective in defense against soft-rot disease, while SA plays an important role in the resistance of P. amboinensis to D. dadantii. Low PAL activity in P. amboinensis implies that the SA contents from the isochorismate pathway may be involved in the mechanism of P. amboinensis resistance to D. dadantii. Therefore, endogenous SA content may be a good indicator for screening resistant species in Phalaenopsis.

Overexpression ofMdVQ37reduces drought tolerance by altering leaf anatomy and SA homeostasis in transgenic apple

Drought stress is an environmental factor that seriously threatens plant growth, development and yield. VQ proteins are transcriptional regulators that have been reported to be involved in plant growth, development and the responses to biotic and abiotic stressors. However, the relationship between VQ proteins and drought stress has not been well documented in plants. In this study, overexpressing the apple VQ motif-containing protein (MdVQ37) gene in apple plants markedly reduced the tolerance to drought. Physiological and biochemical studies further demonstrated lower enzymatic activities and decreased photosynthetic capacity in transgenic lines compared with wild-type (WT) plants under drought stress. Ultrastructural analysis of leaves showed that the leaves and palisade tissues from the transgenic lines were significantly thinner than those from WT plants. Salicylic acid (SA) analysis indicated that overexpression of MdVQ37 increased the accumulation of 2,5-DHBA by up-regulating the expression of the SA catabolic gene, which ultimately resulted to a significant reduction in endogenous SA content and the disruption of the SA-dependent signaling pathway under drought stress. Applying SA partially increased the survival rate of the transgenic lines under drought stress. These results demonstrate that the regulatory function of apple MdVQ37 is implicated in drought stress, through a change in leaf development and SA homeostasis. This study provides novel insight into understanding the multiple functions of VQ proteins.

Salicylic Acid Is Involved in Rootstock-Scion Communication in Improving the Chilling Tolerance of Grafted Cucumber.

Salicylic acid (SA) has been proven to be a multifunctional signaling molecule that participates in the response of plants to abiotic stresses. In this study, we used cold-sensitive cucumber and cold-tolerant pumpkin as experimental materials to examine the roles of SA in root–shoot communication responses to aerial or/and root-zone chilling stress in own-root and hetero-root grafted cucumber and pumpkin plants. The results showed that pumpkin (Cm) rootstock enhanced the chilling tolerance of grafted cucumber, as evidenced by the observed lower levels of electrolyte leakage (EL), malondialdehyde (MDA), and higher photosynthetic rate (Pn) and gene expression of Rubisco activase (RCA). However, cucumber (Cs) rootstock decreased the chilling tolerance of grafted pumpkins. Cs/Cm plants showed an increase in the mRNA expression of C-repeat-binding factor (CBF1), an inducer of CBF expression (ICE1), and cold-responsive (COR47) genes and CBF1 protein levels in leaves under 5/25 and 5/5°C stresses, or in roots under 25/5 and 5/5°C stresses, respectively, compared with the Cs/Cs. Chilling stress increased the endogenous SA content and the activity of phenylalanine ammonia-lyase (PAL), and the increase in SA content and activity of PAL in Cs/Cm plants was much higher than in Cs/Cs plants. Transcription profiling analysis revealed the key genes of SA biosynthesis, PAL, ICS, and SABP2 were upregulated, while SAMT, the key gene of SA degradation, was downregulated in Cs/Cm leaves, compared with Cs/Cs leaves under chilling stress. The accumulation of SA in the Cs/Cm leaves was mainly attributed to an increase in SA biosynthesis in leaves and that in transport from roots under aerial and root-zone chilling stress, respectively. In addition, exogenous SA significantly upregulated the expression level of cold-responsive (COR) genes, enhanced actual photochemical efficiency (ΦPSII), maximum photochemical efficiency (Fv/Fm), and Pn, while decreased EL, MDA, and CI in grafted cucumber. These results suggest that SA is involved in rootstock–scion communication and grafting-induced chilling tolerance by upregulating the expression of COR genes in cucumber plants under chilling stress.

Regulation of Postharvest Tomato Fruit Ripening by Endogenous Salicylic Acid.

Exogenous application of salicylic acid (SA) has been known for delaying ripening in many fruit and vegetables. But the function of endogenous SA in relation to postharvest fruit performance is still unexplored. To understand the role of endogenous SA in postharvest fruit ripening of tomato, 33 tomato lines were examined for their endogenous SA content, membrane stability index (MSI), and shelf life (SL) at turning and red stages of tomato fruit ripening. Six tomato lines having contrasting shelf lives from these categories were subjected further for ethylene (ET) evolution, 1-aminocyclopropane-1-carboxylic acid synthase (ACS), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), polygalacturonase (PG), pectin methyl esterase (PME), antioxidant assays and lipid peroxidation. It was found that high endogenous SA has a direct association with low ET evolution, which leads to the high SL of fruit. High lycopene content was also found to be correlated with high SA. Total antioxidants, PG, and PME decreased and lipid peroxidation increased from turning to red stage of tomato fruit development. Furthermore, these lines were subjected to expression analysis for SA biosynthesis enzymes viz. Solanum lycopersicum Isochorismate Synthase (SlICS) and SlPAL. Real-time PCR data revealed that high SL lines have high SlPAL4 expression and low SL lines have high SlPAL6 expression. Based on the results obtained in this study, it was concluded that endogenous SA regulates ET evolution and SL with the aid of the antioxidative defense system, and SlPAL4 and SlPAL6 genes play significant but opposite roles during fruit ripening.

Identification of Salicylic Acid Mechanism against Leaf Blight Disease in Oryza sativa by SR-FTIR Microspectroscopic and Docking Studies.

The present study was to investigate the application and mechanism of salicylic acid (SA) as SA-Ricemate for the control of leaf blight disease using a Synchrotron Radiation-based Fourier-Transform Infra-Red (SR-FTIR) microspectroscopy and docking studies. After treating rice plants cv. KDML 105 with SA-Ricemate, the leaves were inoculated with Xanthomonas oryzae pv. oryzae, the causal agent of leaf blight, and disease severity were assessed. The leaves were also used to detect changes in endogenous SA content. The results indicated that SA-Ricemate, as an activated compound, reduced disease severity by 60% at three weeks post-inoculation and increased endogenous content by 50%. The SR-FTIR analysis of changes in the mesophyll of leaves (treated and untreated) showed that the groups of lipids, pectins, and proteins amide I and amide II occurred at higher values, and polysaccharides were shown at lower values in treated compared to untreated. Besides, docking studies were used to model a three-dimensional structure for Pathogenesis-related (PR1b) protein and further identify its interaction with SA. The results showed that ASP28, ARG31, LEU32, GLN97, and ALA93 are important residues that have strong hydrogen bonds with SA. The docking results showed that SA has a good interaction, confirming its role in expression.

Chrysanthemum WRKY15-1 promotes resistance to Puccinia horiana Henn. via the salicylic acid signaling pathway

Chrysanthemum white rust disease, which is caused by the fungus Puccinia horiana Henn., severely reduces the ornamental quality and yield chrysanthemum. WRKY transcription factors function in the disease-resistance response in a variety of plants; however, it is unclear whether members of this family improve resistance to white rust disease in chrysanthemum. In this study, using PCR, we isolated a WRKY15 homologous gene, CmWRKY15-1, from the resistant chrysanthemum cultivar C029. Real-time quantitative PCR (RT-qPCR) revealed that CmWRKY15-1 exhibited differential expression patterns between the immune cultivar C029 and the susceptible cultivar Jinba upon P. horiana infection. In addition, salicylic acid (SA) treatment strongly induced CmWRKY15-1 expression. Overexpression of CmWRKY15-1 in the chrysanthemum-susceptible cultivar Jinba increased tolerance to P. horiana infection. Conversely, silencing CmWRKY15-1 via RNA interference (RNAi) in C029 increased sensitivity to P. horiana infection. We also determined that P. horiana infection increased both the endogenous SA content and the expression of salicylic acid biosynthesis genes in CmWRKY15-1-overexpressing plants, whereas CmWRKY15-1 RNAi plants exhibited the opposite effects under the same conditions. Finally, the transcript levels of pathogenesis-related (PR) genes involved in the SA pathway were positively associated with CmWRKY15-1 expression levels. Our results demonstrated that CmWRKY15-1 plays an important role in the resistance of chrysanthemum to P. horiana by influencing SA signaling.

Cd胁迫下SA和NO互作对小麦幼苗根生长和叶绿素含量的影响

以"陇春27"号水培小麦幼苗为研究材料，外源添加水杨酸（SA）、一氧化氮（NO）清除剂（carboxy-PTIO，c-PTIO）、NO供体硝普钠（SNP）、硝酸还原酶（NR）抑制剂钨酸盐（Tungstate）及NO合成酶（NOS）抑制剂（L-NAME）进行不同预处理，分析其在镉（Cd）胁迫下根的生长和叶片叶绿素含量的变化，探讨SA和NO互作对小麦幼苗Cd胁迫的缓解机制。结果表明：随着Cd处理时间的延长，小麦幼苗根中SA含量显著降低，NO含量则呈现先增加（6 h和12 h）后减少（24 h和48 h）的趋势；Cd胁迫抑制了小麦幼苗根的生长，减少了叶片叶绿素的含量，而一定浓度的SA或SNP预处理可以缓解Cd胁迫对小麦幼苗根长的抑制作用，增加叶绿素的含量。c-PTIO、L-NAME和Tungstate单独预处理显著抑制了小麦幼苗根的生长，减少了NO的含量，但不影响叶绿素含量。SA400+L-NAME预处理可以缓解Cd胁迫对小麦幼苗根长的抑制作用以及叶绿素和NO含量的减少作用；SA400+c-PTIO或SA400+Tungstate预处理可增加Cd胁迫下叶绿素的含量，但对根的伸长无影响。进一步研究发现，Cd胁迫抑制了NR的活性，而SA400预处理可以使Cd胁迫下NR的活性增强，不同处理对NOS的活性均无影响。综上所述，Cd胁迫导致小麦幼苗根内源SA含量降低和NO含量先升高再降低；外源添加SA或SNP预处理缓解了Cd胁迫对根生长的抑制和叶绿素含量降低的作用；外源SA通过影响NO的产生从而提高小麦幼苗对Cd胁迫的耐受性，最终缓解了Cd对小麦幼苗的毒害作用。;Soil pollution of heavy metals is very severe in China, especially the cadmium pollution. Excessive cadmium not only causes severe damage to the growth and development of plants, leading to disorders of their physiological functions, reduced photosynthesis, and reduced organic matter accumulation and so on, but also greatly endangers human health. In this research, the growth of roots and the content of chlorophyll in the seedlings of wheat (Triticum aestivum L. cv. Longchun 27) were analyzed after being pretreated with exogenous salicylic acid (SA), nitric oxide (NO) scavenger (Carboxy-PTIO, c-PTIO), NO donor sodium nitratol (SNP), nitrate reductase (NR) inhibitor (Tungstate), NO synthase inhibitor (L-NAME) and then being treated with 100 μmol/L CdCl₂, to explore the mitigation mechanism of SA and NO interaction on Cd-induced phytotoxicity. The results showed that with the prolongation of cadmium treatment time, the content of SA decreased gradually, when the treatment time was extended to 24h, the SA content no longer changed, but the content of NO increased firstly (6 h and 12 h), then decreased (24 h and 48 h) in the roots of wheat seedlings. Cd stress significantly inhibited the root growth and reduced the chlorophyll content of the leaves. However, pretreatment with suitable SA or SNP could moderate the inhibition of Cd stress on the growth of roots and increase the content of chlorophyll in wheat seedlings. The single pretreatment of c-PTIO, L-NAME and Tungstate restrained the growth of roots significantly and reduced the content of NO, but had little effect on the content of chlorophyll. The pretreatment of SA400+L-NAME could alleviate the inhibition of root elongation and the reduction of chlorophyll as well as NO content in wheat seedlings were induced by Cd stress; the pretreatment SA400+c-PTIO or SA400+Tungstate could augment the content of chlorophyll, but there was no effect on root elongation under Cd stress. Further studies showed that Cd stress significantly weaken NR activity, while the pretreatment of SA400 could increase the NR activity of wheat seedlings roots under Cd stress; NOS activity was not affected by different treatments. In summary, Cd stress caused the decrease of endogenous SA content and the first increase of NO content and then decrease of wheat seedlings; the pretreatment with exogenous SA or SNP reduced the inhibition of root growth and the decrease of chlorophyll content by Cd stress; exogenous SA improved the tolerance of wheat seedlings to Cd stress by affecting the production of NO, ultimately, the phytotoxic effects of Cd on wheat seedlings were alleviated.

Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid

BackgroundApplication of exogenous glycine betaine (GB) and exogenous salicylic acid (SA) mitigates the adverse effects of salinity. Foliar spraying with exogenous GB or SA alleviates salt stress in plants by increasing leaf gas exchange and stimulating antioxidant enzyme activity. The effects of foliar application of exogenous GB and SA on the physiology and biochemistry of cotton seedlings subjected to salt stress remain unclear.ResultsResults showed that salt stress of 150 mM NaCl significantly reduced leaf gas exchange and chlorophyll fluorescence and decreased photosynthetic pigment quantities and leaf relative water content. Foliar spray concentrations of 5.0 mM exogenous GB and 1.0 mM exogenous SA promoted gas exchange and fluorescence in cotton seedlings, increased quantities of chlorophyll pigments, and stimulated the antioxidant enzyme activity. The foliar spray also increased leaf relative water content and endogenous GB and SA content in comparison with the salt-stressed only control. Despite the salt-induced increase in antioxidant enzyme content, exogenous GB and SA in experimental concentrations significantly increased the activity of glutathione reductase, ascorbate peroxidase, superoxide dismutase, catalase and peroxidase, and decreased malondialdehyde content under salt stress. Across all experimental foliar spray GB and SA concentrations, the photochemical efficiency of photosystem II (FV/FM) reached a peak at a concentration of 5.0 mM GB. The net photosynthetic rate (Pn) and FV/FM were positively correlated with chlorophyll a and chlorophyll b content in response to foliar spraying of exogenous GB and SA under salt stress.ConclusionsWe concluded, from our results, that concentrations of 5.0 mM GB or 1.0 mM SA are optimal choices for mitigating NaCl-induced damage in cotton seedlings because they promote leaf photosynthesis, increase quantities of photosynthetic pigments, and stimulate antioxidant enzyme activity. Among, 5.0 mM GB and 1.0 mM SA, the best performance in enhancing endogenous GB and SA concentrations was obtained with the foliar application of 1.0 mM SA under salt stress.

Exogenous application and endogenous elevation of salicylic acid levels by overexpressing a salicylic acid-binding protein 2 gene enhance nZnO tolerance of tobacco plants

Salicylic acid (SA) plays vital roles in the stress response of plants. However, the relationship between SA signaling and plant tolerance to nZnO stress has not been reported. The effects of different sizes and concentrations of nZnO on tobacco plants grown in MS medium or soil were evaluated. The effects of exogenous and endogenous SA on the morphological and biochemical parameters of tobacco plants by exogenous application of SA and overexpression of LcSABP2 gene were also investigated in this study. The endogenous SA content and the expression of salicylic acid-binding protein 2 (SABP2) gene increased in tobacco individuals with nZnO treatment. Exogenously applied SA increased the germination rate of tobacco seeds, and enhanced the root length and chlorophyll content of tobacco seedlings. Overexpression of LcSABP2 gene in transgenic tobacco significantly increased SA content in plants with nZnO treatment. Compared to the wild type plants, transgenic tobacco with nZnO treatment showed higher chlorophyll content, net photosynthetic rate, related gene expression, activities of SOD, POD and CAT, and less contents of H2O2, O2− and MDA, which suggested that LcSABP2 might play important regulatory roles in plant resistance to nZnO toxicity by elevating the level of endogenous SA, promoting the action of photosynthetic system, and enhancing the activities of antioxidant enzymes. This study illustrated that exogenous and endogenous SA might all be involved in alleviating the toxicity of nZnO on plants.

Changes in the Endogenous Content and Gene Expression of Salicylic Acid Correlate with Grapevine Bud Dormancy Release

The accumulation of cold temperature is an important factor for the release of bud dormancy in grapevine. The stress generated by cold is related to changes in defense hormones such as salicylic acid (SA). To understand the participation of this hormone during grapevine bud dormancy release, in this study, we evaluated the effects of cold accumulation on the endogenous SA content and expression patterns of the synthesis and signaling genes of SA as well as budbreak rates. Buds were subjected to an accumulation of 900 or 600 chilling units (CUs). The budbreak percentage was determined when cold-treated buds were transferred to warm temperatures (25 °C). The percentage of budbreak was closely correlated with the amount of cumulative CUs; the percentage increased gradually with the amount of chilling applied before forcing. The increase in the expression level of the SA biosynthesis gene (ICS2) and the endogenous SA content were quantified in cold-treated buds, and the expression was correlated with the percentage of budbreak. These findings may indicate that in dormant grapevine buds, cold accumulation stimulates the synthesis of SA. In cold-treated buds, the cellular levels of SA led to the expression of the NPR1 and PR1 genes, which was mediated by the transcription factor WRKY70. In contrast, expression of NPR1 and PR1 in control buds, which maintained a basal level of SA, and expression of ICS2 and WRKY70 were not detected, suggesting that the constitutive expression of NPR1-SA is independent. Taken together, the results of this study suggest a possible involvement of the SA signaling pathway in grapevine bud dormancy release.

Enhancement of endogenous SA accumulation improves poor-nutrition stress tolerance in transgenic tobacco plants overexpressing a SA-binding protein gene

Salicylic acid (SA) plays an important role in the response of plants to abiotic stresses. Starvation stress affects plant cell metabolic activities, which further limits the normal growth and development of plants. It was reported that SA might play a regulatory role in the process of plant against starvation stress, but the mechanism involved in this process is still unclear. Thus, in this study, the transgenic plants overexpressing a SA binding protein 2 (SABP2) gene were exposed to starvation stress and the transgenic lines showed starvation-tolerant phenotype. Compared with wild-type (WT) plants, transgenic plants showed better growth status under poor-nutrition stress. Transgenic plants also showed more vigorous roots than WT plants. Physiological tests indicated that the transgenic plants showed higher relative water content (RWC), chlorophyll content, photosynthetic capacity, endogenous SA content, and lower ROS level compared to WT plants. Transcriptome analysis of tobacco plants identified 3, 748 differentially expressed genes (DEGs) between transgenic and WT plants under starvation stress. These DEGs are mainly involved in glycolysis/gluconeogenesis pathway group, MAPK signaling pathway group and plant hormone signal transduction pathway group. As determined by qPCR, up-regulated expression of fifteen genes such as abscisic acid receptor PYR1-like gene (NtPYR1-like), bidirectional sugar transporter N3-like gene (NtSWEETN3-like) and superoxide dismutase [Fe] chloroplastic-like gene (NtFeSOD-like), etc., was observed in transgenic plants under poor-nutrition stress which was in accordance with RNA-sequencing results. The modified pathways involved in plant hormone signaling are thought to be at least one of the main causes of the increased starvation tolerance of transgenic tobacco plants with altered SA homeostasis.

Investigation of the Effects of the Fenoxaprop-p-Ethyl Herbicide and Salicylic Acid on the Ascorbic Acid and Vitamin B6 Vitamers in Wheat Leaves

Herbicides inhibit plant growth and development by various mechanisms, and oxidative stress is a common plant response to herbicide treatment. In a limited number of studies, it has been shown that vitamins are also strong antioxidants. It has been also known that salicylic acid (SA), a natural compound, plays a role in the activation of plant defences. This study examined the effects of the fenoxaprop-p-ethyl (FE) herbicide and SA on the ascorbic acid and B6 vitamers (pyridoxine, pyridoxal, and pyridoxamine) in wheat leaves. After the wheat plants were grown for 15 days, the leaves were subjected to FE, SA (0.05, 0.5 and 5 mM), and FE + SA treatments for 24, 48, and 72 h. Then, the leaves were cut, and levels of ascorbic acid and B6 vitamers were analyzed. The vitamin analyses were performed by means of HPLC. It was found that the FE has caused to increase the ascorbic acid level but generally to decrease in all three forms of vitamin B6. When FE and SA treatments are applied together, it has been revealed that SA regulates the increasing of ascorbic acid levels and the decreasing of B6 vitamers levels by bringing the control levels. It can be concluded that exogenous SA by its contribution on endogenous SA content could play an ameliorating role on herbicide tolerance and the negative effects of herbicides can be reduced on the crop condition by applying an appropriate exogenous SA concentration.

Overexpression of LcSABP, an Orthologous Gene for Salicylic Acid Binding Protein 2, Enhances Drought Stress Tolerance in Transgenic Tobacco.

Salicylic acid (SA) plays an essential role in the growth and development of plants, and in their response to abiotic stress. Previous studies have mostly focused on the effects of exogenously applied SA on the physiological response of plants to abiotic stresses; however, the underlying genetic mechanisms for the regulatory functions of endogenous SA in the defense response of plants remain unclear. In plants, SA binding protein 2 (SABP2), possessing methyl salicylate (MeSA) esterase activity, catalyzes the conversion of MeSA to SA. Herein, a SABP2-like gene, LcSABP, was cloned from Lycium chinense, which contained a complete open reading frame of 795 bp and encoded a protein of 264 amino acids that shared high sequence similarities with SABP2 orthologs from other plants. Overexpression of LcSABP enhanced the drought tolerance of transgenic tobacco plants. The results indicated that increased levels of LcSABP transcripts and endogenous SA content were involved in the enhanced drought tolerance. Physiological and biochemical studies further demonstrated that higher chlorophyll content, increased photosynthetic capacity, lower malondialdehyde content, and higher activities of superoxide dismutase, peroxidase, and catalase enhanced the drought tolerance of transgenic plants. Moreover, overexpression of LcSABP also increased the expression of reactive oxygen species (ROS)- and stress-responsive genes under drought stress. Overall, our results demonstrate that LcSABP plays a positive regulatory role in drought stress response by enhancing the endogenous SA content, promoting the scavenging of ROS, and regulating of the expression of stress-related transcription factor genes. Our findings indicate that LcSABP functions as a major regulator of the plant’s response to drought stress through a SA-dependent defense pathway.