Exogenous Salicylic Acid Treatment Research Articles

Exogenous salicylic acid promotes carotenoid accumulation and antioxidant capacity in germinated maize kernels by regulating carotenoid biosynthetic pathway

Salicylic acid (SA), as an endogenous plant growth regulator, plays a crucial role in growth and development of plants. This study investigated the influence of varying concentrations of exogenous SA on the physiological and biochemical properties, antioxidant capacity, carotenoid content, and gene expression levels of germinated maize kernels. The results showed that the highest total phenolic and vitamin C contents were found with 0.10 mmol/L of SA, while the highest soluble protein, free amino acid and proline contents were found with 0.50 mmol/L of SA. The content of lutein and zeaxanthin reached the highest under 0.05 mmol/L of SA treatment, which were 18% and 22% higher than that of the control group, respectively. Meanwhile, the expression of seven key genes involved in carotenoid synthesis exhibited different degrees of up-regulation or down-regulation, which may be the reason for promoting carotenoid enrichment in germinated maize kernels. In addition, the antioxidant enzyme activities and antioxidant capacity in germinated maize kernels reached the highest value under the 0.1 mmol/L of SA treatment. Moreover, the correlation analysis results showed the transcription levels of some carotenogenic genes were significantly correlated with carotenoid content or antioxidant capacity. In summary, exogenous SA increased the content of bioactive components, especially carotenoids, and enhanced the antioxidant activity of germinated maize. Therefore, exogenous SA treatment may be used as an efficient germination method to improve the quality of germinated maize.

Tulip transcription factor TgWRKY75 activates salicylic acid and abscisic acid biosynthesis to synergistically promote petal senescence.

WRKY transcription factors play a central role in controlling plant organ senescence; however, it is unclear whether and how they regulate petal senescence in the widely grown ornamental plant tulip (Tulipa gesneriana). In this study, we report that TgWRKY75 promotes petal senescence by enhancing the synthesis of both abscisic acid (ABA) and salicylic acid (SA) in tulip and in transgenic Arabidopsis. The expression level of TgWRKY75 was up-regulated in senescent petals, and exogenous ABA or SA treatment induced its expression. The endogenous contents of ABA and SA significantly increased during petal senescence and in response to TgWRKY75 overexpression. Two SA synthesis-related genes, TgICS1 and TgPAL1, were identified as direct targets of TgWRKY75, which binds to their promoters. In parallel, TgWRKY75 activated the expression of the ABA biosynthesis-related gene TgNCED3 via directly binding to its promoter region. Site mutation of the W-box core motif located in the promoters of TgICS1, TgPAL1, and TgNCED3 eliminated their interactions with TgWRKY75. In summary, our study demonstrates a dual regulation of ABA and SA biosynthesis by TgWRKY75, revealing a synergistic process of tulip petal senescence through feedback regulation between TgWRKY75 and the accumulation of ABA and SA.

Genome-wide identification of the CONSTANS-LIKE (COL) family and mechanism of fruit senescence regulation by PpCOL8 in sand pear (Pyrus pyrifolia)

Pyrus pyrifolia Nakai ‘Whangkeumbae’ is a sand pear fruit with excellent nutritional quality and taste. However, the industrial development of pear fruit is significantly limited by its short shelf life. Salicylic acid (SA), a well-known phytohormone, can delay fruit senescence and improve shelf life. However, the mechanism by which SA regulates CONSTANS-LIKE genes (COLs) during fruit senescence and the role of COL genes in mediating fruit senescence in sand pear are poorly understood. In this study, 22 COL genes were identified in sand pear, including four COLs (PpCOL8, PpCOL9a, PpCOL9b, and PpCOL14) identified via transcriptome analysis and 18 COLs through genome-wide analysis. These COL genes were divided into three subgroups according to the structural domains of the COL protein. PpCOL8, with two B-box motifs and one CCT domain, belonged to the first subgroup. In contrast, the other three PpCOLs, PpCOL9a, PpCOL9b, and PpCOL14, with similar conserved protein domains and gene structures, were assigned to the third subgroup. The four COLs showed different expression patterns in pear tissues and were preferentially expressed at the early stage of fruit development. Moreover, the expression of PpCOL8 was inhibited by exogenous SA treatment, while SA up-regulated the expression of PpCOL9a and PpCOL9b. Interestingly, PpCOL8 interacts with PpMADS, a MADS-box protein preferentially expressed in fruit, and SA up-regulated its expression. While the production of ethylene and the content of malondialdehyde (MDA) were increased in PpCOL8-overexpression sand pear fruit, the antioxidant enzyme (POD and SOD) activity and the expression of PpPOD1 and PpSOD1 in the sand pear fruits were down-regulated, which showed that PpCOL8 promoted sand pear fruit senescence. In contrast, the corresponding changes were the opposite in PpMADS-overexpression sand pear fruits, suggesting that PpMADS delayed sand pear fruit senescence. The co-transformation of PpCOL8 and PpMADS also delayed sand pear fruit senescence. The results of this study revealed that PpCOL8 can play a key role in pear fruit senescence by interacting with PpMADS through the SA signaling pathway.

Salicylic acid mitigates 'Hayward' kiwifruit chilling injury by regulating hormone and proline metabolism, as well as maintaining cellular structure

The 'Hayward' kiwifruit is extremely susceptible to chilling injury (CI) during the late stages of cold storage, thus limiting its storage quality and life. Therefore, mitigating the losses caused by CI is imperative. Salicylic acid (SA) has been demonstrated to mitigate CI in fruit and vegetables. In this study, we conducted a comparative analysis of proline metabolism, key endogenous hormone levels, as well as the effects on cell structure and membrane lipid oxidation in kiwifruit treated with 1 mM SA during low-temperature storage. The results showed that SA could attenuate lipoxygenase (LOX) activity, enhance catalase (CAT) activity, suppress the elevation of malondialdehyde (MDA) content, mitigate starch granule degradation in cells, and preserve cell structure integrity. Moreover, SA was found to enhance proline biosynthesis by activating ornithine transaminase (OAT) and pyrroline-5-carboxylate synthase (P5CS) while concurrently suppressing proline dehydrogenase (PDH) activity. Additionally, exogenous SA increased endogenous levels of both SA and abscisic acid (ABA), while simultaneously decreasing the concentration of gibberellic acid (GA) in fruit. In conclusion, exogenous SA treatment could alleviate the development of CI in kiwifruit by maintaining cell structure, promoting proline synthesis, and balancing endogenous hormone content. Our study offers a theoretical foundation for understanding the mechanism by which SA mitigates cold damage in kiwifruit, and provides novel insights into the low-temperature preservation of kiwifruit.

A putative E3 ubiquitin ligase substrate receptor degrades transcription factor SmNAC to enhance bacterial wilt resistance in eggplant.

Bacterial wilt caused by Ralstonia solanacearum is a severe soil-borne disease globally, limiting the production in Solanaceae plants. SmNAC negatively regulated eggplant resistance to Bacterial wilt (BW) though restraining salicylic acid (SA) biosynthesis. However, other mechanisms through which SmNAC regulates BW resistance remain unknown. Here, we identified an interaction factor, SmDDA1b, encoding a substrate receptor for E3 ubiquitin ligase, from the eggplant cDNA library using SmNAC as bait. SmDDA1b expression was promoted by R. solanacearum inoculation and exogenous SA treatment. The virus-induced gene silencing of the SmDDA1b suppressed the BW resistance of eggplants; SmDDA1b overexpression enhanced the BW resistance of tomato plants. SmDDA1b positively regulates BW resistance by inhibiting the spread of R. solanacearum within plants. The SA content and the SA biosynthesis gene ICS1 and signaling pathway genes decreased in the SmDDA1b-silenced plants but increased in SmDDA1b-overexpression plants. Moreover, SmDDB1 protein showed interaction with SmCUL4 and SmDDA1b and protein degradation experiments indicated that SmDDA1b reduced SmNAC protein levels through proteasome degradation. Furthermore, SmNAC could directly bind the SmDDA1b promoter and repress its transcription. Thus, SmDDA1b is a novel regulator functioning in BW resistance of solanaceous crops via the SmNAC-mediated SA pathway. Those results also revealed a negative feedback loop between SmDDA1b and SmNAC controlling BW resistance.

Comparative Transcriptome Analysis between Resistant and Susceptible Pakchoi Cultivars in Response to Downy Mildew.

Downy mildew caused by the obligate parasite Hyaloperonospora brassicae is a devastating disease for Brassica species. Infection of Hyaloperonospora brassicae often leads to yellow spots on leaves, which significantly impacts quality and yield of pakchoi. In the present study, we conducted a comparative transcriptome between the resistant and susceptible pakchoi cultivars in response to Hyaloperonospora brassicae infection. A total of 1073 disease-resistance-related differentially expressed genes were identified using a Venn diagram. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that these genes were mainly involved in plant-pathogen interaction, plant hormone signal transduction, and other photosynthesis-related metabolic processes. Analysis of the phytohormone content revealed that salicylic acid increased significantly in the resistant material after inoculation with Hyaloperonospora brassicae, whereas the contents of jasmonic acid, abscisic acid, and 1-aminocyclopropane-1-carboxylic acid decreased. Exogenous salicylic acid treatment also significantly upregulated Hyaloperonospora brassicae-induced genes, which further confirmed a crucial role of salicylic acid during pakchoi defense against Hyaloperonospora brassicae. Based on these findings, we suggest that the salicylic-acid-mediated signal transduction contributes to the resistance of pakchoi to downy mildew, and PAL1, ICS1, NPR1, PR1, PR5, WRKY70, WRKY33, CML43, CNGC9, and CDPK15 were involved in this responsive process. Our findings evidently contribute to revealing the molecular mechanism of pakchoi defense against Hyaloperonospora brassicae.

Red light induces salicylic acid accumulation by activating CaHY5 to enhance pepper resistance against Phytophthora capsici.

Pepper (Capsicum annuum L.) is frequently challenged by various pathogens, among which Phytophthora capsici is the most devastating to pepper production. Red light signal acts as a positive induction of plant resistance against multiple pathogens. However, little is known about how the red light signal affects pepper resistance to P. capsici infection (PCI). Here, we report that red light regulates salicylic acid (SA) accumulation by activating elongated hypocotyl5 (CaHY5), a basic leucine zipper (bZIP) transcription factor, thereby decreasing pepper susceptibility to PCI. Exogenous SA treatment reduced pepper susceptibility to PCI, while silencing of CaPHYB (a red light photoreceptor) increased its susceptibility. PCI significantly induced CaHY5 expression, and silencing of CaHY5 reduced SA accumulation, accompanied by decreases in the expression levels of phenylalanine ammonia-lyase 3 (CaPAL3), CaPAL7, pathogenesis-related 1 (CaPR1), and CaPR1L, which finally resulted in higher susceptibility of pepper to PCI. Moreover, CaHY5 was found to activate the expression of CaPAL3 and CaPAL7, which are essential for SA biosynthesis, by directly binding to their promoters. Further analysis revealed that exogenous SA treatment could restore the resistance of CaHY5-silenced pepper plants to PCI. Collectively, this study reveals a critical mechanism through which red light induces SA accumulation by regulating CaHY5-mediated CaPAL3 and CaPAL7 expression, leading to enhanced resistance to PCI. Moreover, red light-induced CaHY5 regulates pepper resistance to PCI, which may have implications for PCI control in protected vegetable production.

Comparative Physiological and Transcriptome Analyses Reveal Mechanisms of Salicylic-Acid-Reduced Postharvest Ripening in 'Hosui' Pears (Pyrus pyrifolia Nakai).

Postharvest ripening of sand pear fruit leads to quality deterioration, including changes in texture, flavor, and fruit color. Salicylic acid (SA), an important defense-related hormone, delays fruit ripening and maintains fruit quality, but the underling mechanism remains unclear. Herein, we evaluated the efficacy of SA in delaying the ripening process of Pyrus pyrifolia cv. 'Hosui' pear fruit, as evidenced by the reduction in fruit weight loss, inhibition of firmness loss, cell wall degradation and soluble sugars, and retention of total phenols. Based on comparative transcriptomic data, a total of 3837 and 1387 differentially expressed genes (DEGs) were identified during room-temperature storage of control fruit and between SA-treated and control fruit, respectively. Further KEGG analysis revealed that the DEGs were mainly implicated in plant hormone signal transduction, starch and sugar metabolism, and cell wall modification. Moreover, exogenous SA treatment also altered the expression of many transcription factor (TF) families, including those in the ethylene-responsive factor (ERF), NAM, ATAF, CUC (NAC), basic helix-loop-helix (bHLH), basic leucine zipper (bZIP), and v-myb avian myeloblastosis viral oncogene homolog (MYB) families. Together, the results offer important insights into the role of SA-responsive genes in controlling fruit ripening in sand pears.

Salicylic acid alleviates Zn-induced inhibition of growth via enhancing antioxidant system and glutathione metabolism in alfalfa

Zinc (Zn) is considered as one of the heavy metal pollutants in soil affecting agriculture. Salicylic acid (SA) is an important phytohormone that can mitigate effects against various abiotic stresses in plants, however, its exploration to improve Zn stress tolerance in alfalfa plants is still elusive. Thus, in the present study, exogenous SA treatment was conducted on alfalfa plants under Zn stress. The effects of exogenous SA on the physiological effects of alfalfa plants and the expression levels related genes were studied. This study tested the biomass, relative water content, chlorophyll levels, photosynthetic capacity, proline and soluble sugar contents, detected the activity of antioxidant enzymes (such as peroxidase and superoxide dismutase), glutathione biosynthesis, and endogenous SA levels, and quantified the genes associated with the antioxidant system and glutathione metabolism-mediated Zn stress. The results showed that exogenous SA could elevate the physiological adaptability of alfalfa plants through enhancing photosynthesis, proline and soluble sugar levels, stimulating antioxidant system and glutathione metabolism, and inducing the transcription level of related genes, thereby diminishing oxidative stress, inhibiting excessive Zn accumulation of alfalfa plants, increasing tolerance to Zn stress, and reducing the toxicity of Zn. Collectively, the application of SA alleviates Zn toxicity in alfalfa plants. The findings gave first insights into the regulatory mechanism of the Zn stress tolerance of alfalfa by exogenous SA and this might have positive implications for managing other plants which are suffering Zn stress.

Salicylic acid accelerates carbon starvation-induced leaf senescence in Arabidopsis thaliana by inhibiting autophagy through Nonexpressor of pathogenesis-related genes 1

In plants, leaf senescence is regulated by several factors, including age and carbon starvation. The molecular mechanism of age-regulated developmental leaf senescence differs from that of carbon starvation-induced senescence. Salicylic acid (SA) and Nonexpressor of pathogenesis-related genes 1 (NPR1) play important roles in promoting developmental leaf senescence. However, the relationship between SA signaling and carbon starvation-induced leaf senescence is not currently well understood. Here, we used Arabidopsis thaliana as material and found that carbon starvation-induced leaf senescence was accelerated in the SA dihydroxylase mutants s3hs5h compared to the Columbia ecotype (Col). Exogenous SA treatment significantly promoted carbon starvation-induced leaf senescence, especially in NPR1-GFP. Increasing the endogenous SA and overexpression of NPR1 inhibited carbon starvation-induced autophagy. However, mutation of NPR1 delayed carbon starvation-induced leaf senescence, increased autophagosome production and accelerated autophagic degradation of the Neighbor of BRCA1 gene 1 (NBR1). In conclusion, SA promotes carbon starvation-induced leaf senescence by inhibiting autophagy via NPR1.

Salicylic acid alleviates salt-induced phytotoxicity by modulating physiochemical attributes and upregulating the AsA-GSH cycle and glyoxalase system in Capsicum annuum L. seedlings

Salt stress is a widespread environmental constraint that impairs crop growth, development, and productivity, reducing seed germination and seedling growth. Plants respond to salinity by modulating physiological and molecular processes, but these responses are inefficient, with salinity issues rapidly escalating worldwide. Salicylic acid (SA) is the most important signal molecules. that protects plants from the damaging effects of salt. This study examined the tolerance potential of 10-day-old Capsicum annuum L. Pusa Sadabahar seedlings against various concentrations of salt stress (0, 25, 50, 75, 100, and 150 mM NaCl) with or without 1 mM salicylic acid (SA) to understand how SA could help Capsicum annuum avoid salt toxicity. The results showed that physiochemical attributes such as seed germination, were higher in the control (0 mM NaCl) and low to medium NaCl (50 and 75 mM) concentrations compared to the high NaCl (150 mM) concentration, which inhibited seed germination, shoot (180.75%) and root (507.20%) lengths, fresh and dry weights, % moisture content, tolerance index, vigor index, chlorophyll content and α-amylase, but increased enzymatic antioxidants like superoxide dismutase (SOD, 37.50%), peroxidase (POX, 62.21%), catalase (CAT), ascorbate peroxidase (APX, 30%), glutathione reductase (GR, 40.46%), glutathione-s-transferase (GST), glutathione peroxidase (GPX), glyoxalase I (Gly I, 44.37%) and glyoxalase II (Gly II, 34.58%) activities, non-enzymatic antioxidants, ascorbate (AsA, 48.51%), carotenoids, phenolics, proline (71.85%), hydrogen peroxide (H2O2), malondialdehyde (MDA, 60.05%), and protein contents. The exogenous SA treatment enhanced all studied parameters except AsA, H2O2, and MDA, protecting the cells from lipid peroxidation and stimulating the ascorbate-glutathione (AsH-GSH) cycle, glyoxalase system, and proline accumulation, which helped to alleviate salt-induced ionic and oxidative damage. Overall, the study highlighted the potential of SA in aiding Capsicum annuum’s resistance to salt stress and reducing its harmful effects.

CRISPR/Cas9-mediated simultaneous mutation of threesalicylic acid 5-hydroxylase (OsS5H) genes confers broad-spectrum disease resistance in rice.

Salicylic acid (SA) is an essential plant hormone that plays critical roles in basal defence and amplification of local immune responses and establishes resistance against various pathogens. However, the comprehensive knowledge of the salicylic acid 5-hydroxylase (S5H) in rice-pathogen interaction is still elusive. Here, we reported that three OsS5H homologues displayed salicylic acid 5-hydroxylase activity, converting SA into 2,5-dihydroxybenzoic acid (2,5-DHBA). OsS5H1, OsS5H2, and OsS5H3 were preferentially expressed in rice leaves at heading stage and responded quickly to exogenous SA treatment. We found that bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) strongly induced the expression of OsS5H1, OsS5H2, and OsS5H3. Rice plants overexpressing OsS5H1, OsS5H2, and OsS5H3 showed significantly decreased SA contents and increased 2,5-DHBA levels, and were more susceptible to bacterial blight and rice blast. A simple single guide RNA (sgRNA) was designed to create oss5h1oss5h2oss5h3 triple mutants through CRISPR/Cas9-mediated gene mutagenesis. The oss5h1oss5h2oss5h3 exhibited stronger resistance to Xoo than single oss5h mutants. And oss5h1oss5h2oss5h3 plants displayedenhanced rice blast resistance. The conferred pathogen resistance in oss5h1oss5h2oss5h3 wasattributed to the significantly upregulation of OsWRKY45 and pathogenesis-related (PR) genes. Besides, flg22-induced reactive oxygen species (ROS) burst was enhanced in oss5h1oss5h2oss5h3. Collectively, our study provides a fast and effective approach to generate rice varieties with broad-spectrum disease resistance through OsS5H gene editing.

Salicylic acid remodeling of the rhizosphere microbiome induces watermelon root resistance against Fusarium oxysporum f. sp. niveum infection.

Fusarium wilt disease poses a severe threat to watermelon cultivation by affecting the yield and quality of the fruit. We had previously found that the rhizosphere microbiome has a significant impact on the ability of watermelon plants to resist Fusarium wilt development and that salicylic acid (SA) is closely related to this phenomenon. Therefore, in this study, the role of SA as a mediator between plants and microbes in activating resistance against Fusarium oxysporum f. sp. niveum (FON) infection was explored through physiological, biochemical, and metagenomic sequencing experiments. We demonstrated that exogenous SA treatment could specifically increase some beneficial rhizosphere species that can confer resistance against FON inoculation, such as Rhodanobacter, Sphingomonas, and Micromonospora. Functional annotation analysis indicated that SA application significantly increased the relative abundance of glycoside hydrolase and polysaccharide lyase genes in the microbiome, which may play an essential role in increasing plant lipids. Moreover, network interaction analysis suggested that the highly expressed AAC6_IIC gene may be manipulated through SA signal transduction pathways. In conclusion, these results provide a novel strategy for controlling Fusarium wilt in watermelons from the perspective of environmental ecology, that is, by manipulating the rhizosphere microbiome through SA to control Fusarium wilt.

NAC transcription factor TgNAP promotes tulip petal senescence.

Petal senescence is a crucial determinant for ornamental quality and economic value of floral crops. Salicylic acid (SA) and reactive oxygen species (ROS) are two prominent factors involved in plant senescence regulation. In this study, tulip TgNAP (NAC-like, activated by APETALA3/PISTILLATA) was characterized as positively regulating tulip petal senescence through dually regulating SA biosynthesis and ROS detoxification pathways. TgNAP was upregulated in senescing petals of tulip while exogenous SA and H2O2 treatments substantially promoted petal senescence in tulip. Silencing of TgNAP by VIGS assay delayed SA and H2O2-induced petal senescence in tulip, whereas overexpression of TgNAP promoted the senescence process in Arabidopsis (Arabidopsis thaliana) plants. Additionally, inhibition of SA biosynthesis prolonged the lifespan of TgNAP-silenced petal discs. Further evidence indicated that TgNAP activates the transcriptions of two key SA biosynthetic genes ISOCHORISMATE SYNTHASE 1 (TgICS1) and PHENYLALANINE AMMONIA-LYASE 1 (TgPAL1) through directly binding to their promoter regions. Meanwhile, TgNAP repressed ROS scavenging by directly inhibiting PEROXIDASE 12 (POD12) and POD17 expression. Taken together, these results indicate that TgNAP enhances SA biosynthesis and ROS accumulation to positively regulate petal senescence in tulip.

Salicylic Acid Reduces Wheat Yield Loss Caused by High Temperature Stress by Enhancing the Photosynthetic Performance of the Flag Leaves

High temperature stress during grain filling substantially decreases wheat productivity; thus, to ensure food security, heat tolerance in wheat must be developed. It remains unclear whether exogenous salicylic acid (SA) can induce tolerance to high temperatures in wheat at the grain-filling stage. In this study, a two-year pot culture experiment using the wheat cultivar ‘Yangmai 18’ was conducted from 2018 to 2020. The plants were pre-sprayed with SA from the heading stage (SAH), anthesis stage (SAA), 5 days after anthesis (DAA; SA5), and 10 DAA (SA10). After that, the wheat plants were subjected to high temperature stress (G) simulated using a passive warming method during the period between 15 and 19 DAA. The results showed that, compared with the normal temperature control group (NN), high temperature stress at the grain-filling stage significantly reduced the yield and photosynthetic capacity of wheat. The application of SA at different stages reduced the yield loss and the damage to the photosynthetic capacity caused by high temperature stress; the effectiveness of the treatments in descending order was SAAG > SA5G > SA10G > SAHG. Exogenous SA treatment increased the amount and proportion of dry matter distributed in the stem sheaths and leaves and grains, and decreased the amount and proportion of dry matter distributed in the rachises and glumes at the maturity stage, thereby reducing the yield loss under high temperature stress. The application of SA significantly increased the leaf area, stomatal density, chlorophyll content, soluble protein content, maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and activity of sucrose phosphate synthase (SPS) of the wheat flag leaves under high temperature stress at the grain-filling stage, thereby improving the photosynthetic performance of the flag leaves under stress. In summary, exogenous SA significantly restored the photosynthetic capacity of wheat flag leaves injured by post-anthesis high temperature stress, which effectively alleviated the inhibition of wheat growth caused by the stress and ultimately reduced the yield loss. Spraying SA at the anthesis stage had the greatest effect abating the loss of yield and reduced photosynthetic performance under high temperature stress.

Salicylic Acid Regulates Indole-3-Carbinol Biosynthesis Under Blue Light in Broccoli Sprouts (Brassica oleracea L.).

Indole-3-carbinol (I3C), an important secondary metabolite with strong anti-cancer ability, is widely found in cruciferous plants. Light and phytohormones are one of the most important external and internal signals, respectively, that control the growth, development, and secondary metabolism of the plant life cycle. However, there are few studies about the influence of the blue light and salicylic acid (SA) on the regulation of I3C accumulation. In this study, a negative correlation was found between the content of I3C and SA in different species. Among this, broccoli and Arabidopsis thaliana were chosen for further studies. We observed that blue light treatment increased the accumulation of I3C, and exogenous SA treatment significantly inhibited the accumulation of I3C in broccoli sprouts. Based on the RNA sequence, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that blue light promoted the enrichment of differentially expressed genes (DEGs) in plant hormone signal transduction pathways. More specifically, downregulated expression of genes related to SA biosynthesis and upregulated expression of I3C genes related to metabolic pathway were observed under blue light. Taken together, these results suggested that SA negatively regulates blue light-induced I3C accumulation in broccoli sprouts.

The Effects of Exogenous Salicylic Acid on Endogenous Phytohormone Status in Hordeum vulgare L. under Salt Stress.

Acclimation to salt stress in plants is regulated by complex signaling pathways involving endogenous phytohormones. The signaling role of salicylic acid (SA) in regulating crosstalk between endogenous plant growth regulators’ levels was investigated in barley (Hordeum vulgare L. ‘Ince’; 2n = 14) leaves and roots under salt stress. Salinity (150 and 300 mM NaCl) markedly reduced leaf relative water content (RWC), growth parameters, and leaf water potential (LWP), but increased proline levels in both vegetative organs. Exogenous SA treatment did not significantly affect salt-induced negative effects on RWC, LWP, and growth parameters but increased the leaf proline content of plants under 150 mM salt stress by 23.1%, suggesting that SA enhances the accumulation of proline, which acts as a compatible solute that helps preserve the leaf’s water status under salt stress. Changes in endogenous phytohormone levels were also investigated to identify agents that may be involved in responses to increased salinity and exogenous SA. Salt stress strongly affected endogenous cytokinin (CK) levels in both vegetative organs, increasing the concentrations of CK free bases, ribosides, and nucleotides. Indole-3-acetic acid (IAA, auxin) levels were largely unaffected by salinity alone, especially in barley leaves, but SA strongly increased IAA levels in leaves at high salt concentration and suppressed salinity-induced reductions in IAA levels in roots. Salt stress also significantly increased abscisic acid (ABA) and ethylene levels; the magnitude of this increase was reduced by treatment with exogenous SA. Both salinity and SA treatment reduced jasmonic acid (JA) levels at 300 mM NaCl but had little effect at 150 mM NaCl, especially in leaves. These results indicate that under high salinity, SA has antagonistic effects on levels of ABA, JA, ethylene, and most CKs, as well as basic morphological and physiological parameters, but has a synergistic effect on IAA, which was well exhibited by principal component analysis (PCA).

Impact of exogenous salicylic acid treatment on the cell wall metabolism and ripening process in postharvest tomato fruit stored at ambient temperature

AbstractTomato is a climacteric fruit susceptible to rapid softening and ripening after harvest. In this study, the changes of physicochemical characters, cell wall‐degrading enzymes, cell wall compositions and ethylene production of ‘Hisar Arun’ and ‘BSS‐488’ tomato fruits were investigated under the influence of salicylic acid treatment. Salicylic acid treatment effectively delayed firmness decline and increase in PLW, TSS and lycopene content. The treated fruits maintained the integrity of cell wall composition by delay in increase in activities of cell wall‐degrading enzymes (pectin methylesterase, polygalacturonase and cellulose) and cell wall components (cellulose, hemicellulose, lignin and pectin) decline. Moreover, salicylic acid treatments significantly suppress expression level of ethylene‐producing genes (ACO1 and ACS2) and inhibited ethylene production during storage. Overall, the salicylic acid‐induced delay in the ripening process occurs via the strong inhibition of ethylene biosynthesis, lowered cell wall‐degrading enzyme activities and slowed cell wall degradation.

Salicylic acid regulates adventitious root formation via competitive inhibition of the auxin conjugation enzyme CsGH3.5 in cucumber hypocotyls.

Exogenous SA treatment at appropriate concentrations promotes adventitious root formation in cucumber hypocotyls, via competitive inhibiting the IAA-Asp synthetase activity of CsGH3.5, and increasing the local free IAA level. Adventitious root formation is critical for the cutting propagation of horticultural plants. Indole-3-acetic acid (IAA) has been shown to play a central role in regulating this process, while for salicylic acid (SA), its exact effects and regulatory mechanism have not been elucidated. In this study, we showed that exogenous SA treatment at the concentrations of both 50 and 100µM promoted adventitious root formation at the base of the hypocotyl of cucumber seedlings. At these concentrations, SA could induce the expression of CYCLIN and Cyclin-dependent Kinase (CDK) genes during adventitious rooting. IAA was shown to be involved in SA-induced adventitious root formation in cucumber hypocotyls. Exposure to exogenous SA led to a slight increase in the free IAA content, and pre-treatment with the auxin transport inhibitor 1-naphthylphthalamic acid (NPA) almost completely abolished the inducible effects of SA on adventitious root number. SA-induced IAA accumulation was also associated with the enhanced expression of Gretchen Hagen3.5 (CsGH3.5). The in vitro enzymatic assay indicated that CsGH3.5 has both IAA- and SA-amido synthetase activity and prefers aspartate (Asp) as the amino acid conjugate. The Asp concentration dictated the functional activity of CsGH3.5 on IAA. Both affinity and catalytic efficiency (Kcat/Km) increased when the Asp concentration increased from 0.3 to 1mM. In contrast, CsGH3.5 showed equal catalytic efficiency for SA at low and high Asp concentrations. Furthermore, SA functioned as a competitive inhibitor of the IAA-Asp synthetase activity of CsGH3.5. During adventitious formation, SA application indeed repressed the IAA-Asp levels in the rooting zone. These data show that SA plays an inducible role in adventitious root formation in cucumber through competitive inhibition of the auxin conjugation enzyme CsGH3.5. SA reduces the IAA conjugate levels, thereby increasing the local free IAA level and ultimately enhancing adventitious root formation.

Timing-dependent effects of salicylic acid treatment on phytohormonal changes, ROS regulation, and antioxidant defense in salinized barley (Hordeum vulgare L.)

Cross-talk between exogenous salicylic acid (SA) and endogenous phytohormone pathways affects the antioxidant defense system and its response to salt stress. The study presented here investigated the effects of SA treatment before and during salt stress on the levels of endogenous plant growth regulators in three barley cultivars with different salinity tolerances: Hordeum vulgare L. cvs. Akhisar (sensitive), Erginel (moderate), and Kalaycı (tolerant). The cultivars’ relative leaf water contents, growth parameters, proline contents, chlorophyll a/b ratios, and lipid peroxidation levels were measured, along with the activities of enzymes involved in detoxifying reactive oxygen species (ROS) including superoxide-dismutase, peroxidase, catalase, ascorbate-peroxidase, and glutathione-reductase. In addition, levels of several endogenous phytohormones (indole-3-acetic-acid, cytokinins, abscisic acid, jasmonic acid, and ethylene) were measured. Barley is known to be more salt tolerant than related plant species. Accordingly, none of the studied cultivars exhibited changes in membrane lipid peroxidation under salt stress. However, they responded differently to salt-stress with respect to their accumulation of phytohormones and antioxidant enzyme activity. The strongest and weakest increases in ABA and proline accumulation were observed in Kalaycı and Akhisar, respectively, suggesting that salt-stress was more effectively managed in Kalaycı. The effects of exogenous SA treatment depended on both the timing of the treatment and the cultivar to which it was applied. In general, however, where SA helped mitigate salt stress, it appeared to do so by increasing ROS scavenging capacity and antioxidant enzyme activity. SA treatment also induced changes in phytohormone levels, presumably as a consequence of SA-phytohormone salt-stress cross-talk.