Salicylic Acid Treatment Research Articles

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.

Effect of salicylic acid treatment on antioxidant capacity and endogenous hormones in winter jujube during shelf life

This study investigated the effects of exogenous salicylic acid (SA) treatment (0, control; 3 mmol L−1) on the antioxidant and hormone levels of winter jujube during shelf life (20 d) at 4 °C. The results showed that 3 mmol L−1 SA treatment preferably maintained firmness, color, titratable acidity, and total soluble solids, and effectively reduced the respiratory intensity and TSS/TA value (13.08%) of the fruit. Compared with the control group, the SA group had a higher content of sucrose (14.03%) and malic acid (29.13%). Meanwhile, SA reduced the accumulation of H2O2 (27.73%) and O2− (45.44%) by enhancing the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and the content of antioxidant substances (ascorbic acid, total phenols, total flavonoids, and glutathione) in the fruit. In addition, 3 mmol L−1 SA treatment led to higher levels of endogenous abscisic acid (18.49%) and SA (20.47%) in fruit, and lower concentration of jasmonic acid (42.68%), but had a weak effect on indole acetic acid levels.

Incorporation of 1-methylcyclopropene and salicylic acid improves quality and shelf life of winter jujube (Zizyphus jujuba Mill. cv. Dongzao) through regulating reactive oxygen species metabolism.

Winter jujube fruit is susceptible to aging, peel reddening, dehydration, shrinkage, and tissue softening during shelf life after it is removed from the cold storage conditions. In this study, the effects of 1-methylcyclopropene (1-MCP) and salicylic acid (SA) on the quality of winter jujube fruit during shelf life were investigated by measuring physiological indexes and the activities of antioxidant enzymes and enzymes related to reactive oxygen species (ROS) metabolism of winter jujube fruit. The results showed that 1-MCP treatment and SA treatment suppressed weight loss, respiratory rate, malondialdehyde (MDA) content, H2O2 content, and production rate, but improved firmness, color difference (ΔE), soluble solid content (SSC), titratable acidity (TA), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia-lyase (PAL) activities, ascorbic acid content, glutathione content, total phenolic content, and total flavonoid content in comparison with the control. Particularly, the combined treatment of 1-MCP and SA (1-MCP+SA treatment) showed the maximum efficacy compared to the 1-MCP treatment and SA treatment alone. 1-MCP+SA treatment exhibited the best preservation effect, followed by SA treatment and 1-MCP treatment. Thus, the combined treatment of 1-MCP and SA is an effective approach to maintain the postharvest quality of winter jujube fruit and extend the shelf life.

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.

GhCalS5 is involved in cotton response to aphid attack through mediating callose formation.

Callose synthase plays an essential role in plant growth and development and in response to all sorts of stresses through regulating callose formation. However, few research about the function and mechanism of the insect resistance of callose synthase genes have been reported in cotton. In this study, a cotton callose synthase gene GhCalS5 was cloned, and its function and mechanism of resistance to cotton aphids were analyzed. The expression of GhCalS5 was significantly upregulated in both, leaves and stems of cotton plants at 48 h after cotton aphid infestation and in the leaves of cotton plants at 24 h after salicylic acid treatment. The overexpression of GhCalS5 enhanced cotton resistance to cotton aphids. Expectedly silencing of GhCalS5 reduced cotton resistance to cotton aphids. Overexpression of GhCalS5 enhanced callose formation in cotton leaves. Our results suggest that GhCalS5 is involved in cotton resistance against cotton aphids by influencing callose formation.

Antioxidant Machinery and Glyoxalase System Regulation Confers Salt Stress Tolerance to Wheat (Triticum aestivum L.) Plants Treated with Melatonin and Salicylic Acid

Plant growth regulators melatonin (MT) and salicylic acid (SA) have potent roles in plant salt tolerance. However, only a few reports have studied the influence of their combined treatment on plant salt tolerance. The current study, as a first investigation, was aimed to evaluate the effect of MT and SA combined treatment on the antioxidant and glyoxalase defense machineries of salt-stressed wheat plants. In the present study, the potential role of 70 μM MT and/or 75 mg l−1 SA on mitigating salt injury (6.0 and 12.0 dS m−1 salinity levels) was investigated in wheat (Triticum aestivum L. cv. Sids 14). Exogenously applied MT and/or SA improved the activity of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and glutathione S-transferase, which effectively scavenged reactive oxygen species (ROS) in stressed plants. Excessive accumulation of the toxic methylglyoxal was reversed via the up-regulation of the glyoxalase system (glyoxalase I and glyoxalase II) and the ascorbate–glutathione cycle. Foliar applications also reduced membrane damage by lowering lipid peroxidation and protein oxidation due to effective ROS detoxification by antioxidants such as ascorbate, glutathione, phenols, and flavonoids. Moreover, exogenous MT and/or SA applications increased endogenous MT and SA levels under both non-saline and saline conditions. The combined treatment of MT and SA yielded the best results. Overall, this combined treatment regulated the antioxidant machinery and glyoxalase system, suggesting a role for it in salt stress mitigation. Therefore, it can be considered as an effective method for reducing salt toxicity in sustainable agricultural systems.

Genome-wide investigation and expression analysis of the AP2/ERF family for selection of agarwood-related genes in Aquilaria sinensis (Lour.) Gilg.

Aquilaria sinensis is an important non-timber tree species for producing high-value agarwood, which is widely used as a traditional medicine and incense. Agarwood is the product of Aquilaria trees in response to injury and fungal infection. The APETALA2/ethylene responsive factor (AP2/ERF) transcription factors (TFs) play important roles in plant stress responses and metabolite biosynthesis. In this study, 119 AsAP2/ERF genes were identified from the A. sinensis genome and divided into ERF, AP2, RAV, and Soloist subfamilies. Their conserved motif, gene structure, chromosomal localization, and subcellular localization were characterized. A stress/defense-related ERF-associated amphiphilic repression (EAR) motif and an EDLL motif were identified. Moreover, 11 genes that were highly expressed in the agarwood layer in response to whole-tree agarwood induction technique (Agar-Wit) treatment were chosen, and their expression levels in response to methyl jasmonate (MeJA), salicylic acid (SA), or salt treatment were further analyzed using the quantitative real time PCR (qRT-PCR). Among the 11 genes, eight belonged to subgroup B-3. All 11 genes were significantly upregulated under salt treatment, while eight genes were significantly induced by both MeJA and SA. In addition, the gene clusters containing these upregulated genes on chromosomes were observed. The results obtained from this research not only provide useful information for understanding the functions of AP2/ERF genes in A. sinensis but also identify candidate genes and gene clusters to dissect their regulatory roles in agarwood formation for future research.

Salicylic Acid Improves Growth and Physiological Attributes and Salt Tolerance Differentially in Two Bread Wheat Cultivars.

Abiotic constraints such as salinity stress reduce cereal production. Salicylic acid is an elicitor of abiotic stress tolerance in plants. The aim of this study was to investigate the effects of salicylic acid on two bread wheat cultivars (SST806 and PAN3497) grown under salt stress (100 and 200 mM NaCl) in the presence and absence of 0.5 mM salicylic acid. The highest salt concentration (200 mM), in both PAN3497 and SST806, increased the days to germination and reduced the coleoptile and radicle dry weights. The shoot dry weight was reduced by 75 and 39%, root dry weight by 73 and 37%, spike number of both by 50%, spike weight by 73 and 54%, grain number by 62 and 15%, grain weight per spike by 80 and 45%, and 1000 grain weight by 9 and 29% for 200 and 100 mM NaCl, respectively. Salicylic acid in combination with 100 mM and 200 mM NaCl increased the shoot, root, and yield attributes. Salicylic acid increased the grain protein content, especially at 200 mM NaCl, and the increase was higher in SST806 than PAN3497. The macro-mineral concentration was markedly increased by an increase of NaCl. This was further increased by salicylic acid treatment for both SST806 and PAN3497. Regarding micro-minerals, Na was increased more than the other minerals in both cultivars. Mn, Zn, Fe, and Cu were increased under 100 mM and 200 Mm of salt, and salicylic acid application increased these elements further in both cultivars. These results suggested that salicylic acid application improved the salt tolerance of these two bread wheat cultivars.

Postharvest Salicylic Acid Treatment Affects Weight Loss, Spoilage and Biochemical Attributes of Bartlett Pear Fruits

The present study aimed to determine the effect of postharvest salicylic acid (SA) treatments on storability and biochemical quality of Bartlett pear fruits at ambient storage conditions. Freshly harvested fruits were treated with salicylic acid solution at 0 (control), 0.5, 1 or 2 mM and fruits were stored at ambient conditions (room temperature) for 21 days storage studies. Data on physiological loss in weight (PLW), fruit spoilage and biochemical quality of fruits (total soluble soils, titratable acidity, ascorbic acid, reducing and total sugars) were recorded. Results revealed that the salicylic acid treatments significantly minimized the PLW and fruit spoilage. At 21 days of storage at ambient conditions, the lowest PLW (13.76 %) and fruit spoilage (21.70 %) was noted with SA at 2 mM. All three SA treatments effectively retained the biochemical attributes of fruits i.e. total soluble soils, titratable acidity, ascorbic acid, reducing and total sugars as compared to control fruits. In conclusion, Salicylic acid at 2 mM treatment to the Bartlett pear fruits after harvest can be useful in minimizing the PLW and fruit spoilage and also maintaining the biochemical quality of fruits during ambient storage conditions.

Postharvest Salicylic Acid Application Affects the Biochemical Quality and Stability of Strawberry (Fragaria x ananassa Duch.) cv. Chandler Fruits under Ambient Storage Conditions

The present study aimed to determine the effect of postharvest salicylic acid (SA) application on storability and biochemical quality of strawberry fruits cv. Chandler under ambient storage conditions. Freshly harvested fruits were subjected to salicylic acid treatment at 0 (control), 0.5, 1 or 2 mM and fruits were stored at room temperature for 6 days storage studies. Data on physiological loss in weight (PLW), fruit spoilage and biochemical quality of fruits (total soluble soils, titratable acidity, ascorbic acid, reducing and total sugars) were recorded. Results showed that postharvest salicylic acid treatment significantly minimized the PLW and fruit spoilage. At 6 days of storage, the lowest PLW (14.43 %) and fruit spoilage (21.70 %) was observed with SA at 2 mM. All the salicylic acid treatments were effective in retaining the biochemical quality of fruit (total soluble soils, titratable acidity, ascorbic acid, reducing and total sugars). In conclusion, Salicylic acid at 2 mM treatment of strawberry fruits after harvest can be useful in minimizing PLW and fruit spoilage and also maintaining the biochemical quality of fruits during ambient storage conditions.

Identification of MdMED family, key role of MdMED81, and salicylic acid at the right time of year triggers MdMED81 to induce flowering in Malus domestica

Mediator is a transcription factor that regulates the expression of many genes in different functional pathways, enhancing growth, development and other biological processes. Its role in flowering in Malus × domestica, however, is still unknown. Due to the long life cycle and low rate of genetic transformation in M. domestica, flowering induction is still a very serious problem, leading to lower production. Here we report the identification of 83 mediator genes in M. domestica, their gene structure, protein characteristics, locations on each chromosome, systematic phylogenetic structural analysis, distribution of the chromosome, synteny of MdMED genes, and cis-elements prediction at the promoter region of MdMED genes. On the basis of phylogenetic relationships, the members of the MdMED gene family were divided into six subgroups. Real-time quantitative PCR analysis of the MdMED subgroup-D genes displayed that most genes showed strong preferential expression in the buds and were significantly upregulated during the flower induction period. Transcriptional levels of MdMED subgroup-D genes respond to salicylic acid treatment. To determine MdMED81′s functions, we obtained MdMED81-overexpressed (OE) Arabidopsis thaliana lines that showed significantly earlier flowering compared with wild-type. Furthermore, we developed a high R2 value correlation between MdMED81 and day hours that is presented in equation form to detect MdMED81 in flowering time regulation and control in M. domestica. We also presented an annual model of MdMED81 in the control of flowering time and concluded that salicylic acid application at the right time of the year triggers MdMED81 to induce flowering in M. domestica. This data provides a new theoretical reference for the management of apple tree flowering and also provides an essential basis for future analysis of the regulation and functions of the MdMED gene family.

Transcriptome analysis provides insights into the bases of salicylic acid-induced resistance to anthracnose in sorghum.

Key Message Transcriptome analysis of SA sensitive and tolerant lines indicates that SA enhances anthracnose resistance in sorghum by upregulating the expression of some immune-related genes and pathways.Abstract Anthracnose caused by the hemibiotrophic pathogen Colletotrichum sublineolum is one of the most destructive diseases of sorghum, the fifth most important cereal crop in the world. Salicylic acid (SA) is a phytohormone essential for plant immunity; however, the role of SA in sorghum resistance to anthracnose has not been well explored. In this study, we found that Colletotrichum sublineolum infection induced the expression of SA-responsive genes and that exogenous SA enhanced resistance to anthracnose in the sorghum line BTx623. To rule out the possibility that SA triggers anthracnose resistance in sorghum by its direct toxic function on pathogen, an SA-tolerant line, WHEATLAND, was identified, and we found that SA treatment could not induce anthracnose resistance in WHEATLAND. Then, SA-induced transcriptome changes during Colletotrichum sublineolum infection in BTx623 and WHEATLAND were analyzed to explore the molecular mechanism of SA-triggered resistance. SA pretreatment regulated the expression of 2125 genes in BTx623 but only 524 genes in WHEATLAND during Colletotrichum sublineolum infection. The cutin, suberine and wax biosynthesis pathway involved in the plant immune response and the flavonoid biosynthesis pathway involved in anthracnose resistance were enriched in BTx623-specifically upregulated genes. Additionally, some immune-related genes, including multiple resistance genes, were differentially expressed in BTx623 and WHEATLAND. Taken together, our results revealed the mechanisms of SA-induced anthracnose resistance in sorghum at the transcriptional level and shed light on the possibility of enhancing sorghum resistance to anthracnose by activating the SA signaling pathway by molecular breeding.

Blue light combined with salicylic acid treatment maintained the postharvest quality of strawberry fruit during refrigerated storage.

Strawberryis a high economic and nutritional valuefruit,but marketing is limited by a short postharvest life. The objective of this work is to assess the influence of blue light (BL) and salicylic acid (SA, 2mM) on strawberry postharvest quality during cold storage. The results showed that the combination of BL and SA noticeably delayed weight loss, prevented decay, improved fruit skin brightness, and increased soluble protein. Strawberries treated with BL+SA had lower total soluble solids and titratable acidity contents among treatments but had no significant change during the entire storage. Additionally, contents of total flavonoids, phenolics, anthocyanins and proanthocyanidins, activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and total antioxidant capacities in BL+SA-treated fruit were kept at stable levels throughout the entire storage. Collectively, these findings suggest that BL+SA treatment exhibits a high potential in maintaining postharvest fruit quality of strawberry fruit.

Identification and Expression Analysis of Stilbene Synthase Genes in Arachis hypogaea in Response to Methyl Jasmonate and Salicylic Acid Induction

Stilbene synthase is an important enzyme of the phenylpropanoid pathway, regulating the production of several biologically active stilbenoids. These compounds have antioxidant, anti-inflammatory, and anti-cancer properties. However, the detailed characterization of stilbene synthase genes in Arachis hypogaea has not yet been performed. In this study, the comprehensive characterization of stilbene synthase genes in A. hypogaea was conducted, commencing with identification, phylogenetic analysis, and study of their expression in response to exogenous hormonal treatment. We identified and isolated five AhSTSs genes and recorded their expression pattern in peanut (BARD-479) in response to methyl jasmonate (MeJA) and salicylic acid (SA) treatment. The presence of Chal_sti_synt, ACP_syn_III, and FAE1_CUT1_rppA domains in all AhSTSs indicated their role in the biosynthesis of stilbene and lipid metabolism. Cis-regulatory element analysis indicated their role in light responsiveness, defense responses, regulation of seed development, plant growth, and development. Despite close structural and functional similarities, expression and correlational analysis suggested that these genes may have a specific role in peanut, as individual AhSTS exhibited differential expression upon hormonal treatment in a genotype dependent manner. Further studies on functional characterization involving the transcriptional regulation of AhSTSs can clearly explain the differential expression of stilbene synthase genes to hormonal treatment.

Overexpression of OsGF14f Enhances Quantitative Leaf Blast and Bacterial Blight Resistance in Rice.

Although it is known that rice 14-3-3 family genes are involved in various defense responses, the functions of OsGF14f in response to diseases have not been reported. Here, we showed that the transcription of OsGF14f was significantly induced by leaf blast infection, and the overexpression of OsGF14f quantitatively enhanced resistance to leaf blast and bacterial blight in rice. Further analysis showed that the expression levels of salicylic acid (SA) pathway-associated genes (PAL1, NH1, PR1a and PR10) in the OsGF14f-overexpressing plants, were higher than those in wild-type plants after inoculation with the blast isolate (Magnaporthe oryzae Barr). In addition, the expression level of OsGF14f was significantly induced after SA treatment, and higher endogenous SA levels were observed in the OsGF14f-overexpressing plants compared with that in wild-type plants, especially after blast challenge. Taken together, these results suggest that OsGF14f positively regulates leaf blast and bacterial blight resistance in rice via the SA-dependent signaling pathway.

The interaction of CsWRKY4 and CsOCP3 with CsICE1 regulates CsCBF1/3 and mediates stress response in tea plant (Camellia sinensis)

Low temperature stress limits the geographical distribution of tea plants (Camellia sinensis) and the yield and quality of tea. CsICE1 is a crucial regulator of tea plant’s cold signaling pathway; however, the regulatory mechanism of CsICE1 is still unclear. In this study, we found that the N-terminus of CsICE1 contains a transcriptional activation domain and a region of protein interaction. Yeast two-hybrid and bimolecular fluorescence complementation experiments confirmed that CsWRKY4 and CsOCP3 interacted with CsICE1 in the nucleus. Like CsICE1, CsWRKY4 and CsOCP3 were localized in the nucleus, and CsOCP3 was also targeted to the chloroplast. The expression of CsWRKY4 and CsOCP3 was downregulated under cold stress, unlike that of CsICE1. Under biotic stresses and salicylic acid treatment, the expression of all three genes was increased, whereas jasmonic acid treatment resulted in decreased expression of all three genes. Dual-luciferase transient assays revealed that CsICE1 promoted the expression of CsCBF1 and CsCBF3, whereas CsWRKY4 and CsOCP3 inhibited the expression of CsCBF1 and CsCBF3 and attenuated their induction by CsICE1. Taken together, these results suggest that CsWRKY4 and CsOCP3 interact with CsICE1 and regulate CsCBF1/3, thus mediating the stress response in tea plant. Furthermore, these results highlight that CsICE1 is not only a key component in the low temperature signal response pathway, but it may also serve as a point of confluence for cold and other signaling pathways.

The Black Necrotic Lesion Enhanced Fusarium graminearum Resistance in Wheat.

Fusarium head blight, mainly incited by Fusarium graminearum, is a devastating wheat disease worldwide. Diverse Fusarium head blight (FHB) resistant sources have been reported, but the resistance mechanisms of these sources remain to be investigated. FHB-resistant wheat germplasm often shows black necrotic lesions (BNLs) around the infection sites. To determine the relationship between BNL and FHB resistance, leaf tissue of a resistant wheat cultivar Sumai 3 was inoculated with four different F. graminearum isolates. Integrated metabolomic and transcriptomic analyses of the inoculated samples suggested that the phytohormone signaling, phenolamine, and flavonoid metabolic pathways played important roles in BNL formation that restricted F. graminearum extension. Exogenous application of flavonoid metabolites on wheat detached leaves revealed the possible contribution of flavonoids to BNL formation. Exogenous treatment of either salicylic acid (SA) or methyl jasmonate (MeJA) on wheat spikes significantly reduced the FHB severity. However, exogenous MeJA treatment prevented the BNL formation on the detached leaves of FHB-resistant wheat Sumai 3. SA signaling pathway influenced reactive oxygen species (ROS) burst to enhance BNL formation to reduce FHB severity. Three key genes in SA biosynthesis and signal transduction pathway, TaICS1, TaNPR1, and TaNPR3, positively regulated FHB resistance in wheat. A complex temporal interaction that contributed to wheat FHB resistance was detected between the SA and JA signaling pathways. Knowledge of BNLs extends our understanding of the molecular mechanisms of FHB resistance in wheat and will benefit the genetic improvement of wheat FHB resistance.

Regulating Function of Exogenous Salicylic Acid on Sugar Metabolism in Tomato Seedlings

Aims: SA (Salicylic acid) is a key regulator for sugar metabolic pathway, but the regulating function on sugar metabolism in tomato seedlings is imperfect. In this study, tomato seedlings were sprayed with SA, and then soluble sugar contents, enzyme related to sugar metabolism levels, gene expressions were determined.
 Study Design: In order to analyze the mechanism of SA in sugar metabolic pathway, tomato seedlings were sprayed with SA, and then soluble sugar contents, enzyme related to sugar metabolism levels, gene expressions were determined.
 Place and Duration of Study: College of Biological Science and Technology, between December 2021 and May 2022.
 Methodology: The expressions of genes related to sugar metabolism in tomato were measured by qRT-PCR. The contents of soluble sugar in tomato seedings were measured with HPLC (High performance liquid chromatography).
 Results: The sugar metabolism in tomato seedlings was affected by SA treatment for 6 h. The contents of fructose, glucose and sucrose were improved in tomato seedlings by SA treatment. Between 6 to 24 h, enzymatic activities of SlAI, SlNI and SlSS were higher than those in controls, while there was little change in enzyme activity of SISPS.
 Conclusion: The contents of soluble sugar, enzyme activities related to sugar metabolism had changed considerably by SA treatment. Especially from 6 h to 24 h after SA treatment, the contents of fructose and glucose were significantly higher than those of the control group, and the changes of sugar contents were mainly related to the increases of enzyme activities of AI, NI and SS, suggesting that SA treatment mainly affected the activities of SlAI, SlNI and SlSS to promote the accumulations of soluble sugars.

Short-Term Salicylic Acid Treatment Affects Polyamine Metabolism Causing ROS-NO Imbalance in Tomato Roots.

The phytohormone salicylic acid (SA) can influence the polyamine metabolism in plants. Additionally, polyamines (PAs) can regulate the synthesis of SA, providing an exciting interplay between them not only in plant growth and development but also in biotic or abiotic stress conditions. The effect of SA on polyamine metabolism of leaves is well-studied but the root responses are rarely investigated. In this study, tomato roots were used to investigate the effect of short-term exposition of SA in two different concentrations, a sublethal 0.1 mM and a lethal 1 mM. To explore the involvement of SA in regulating PAs in roots, the degradation of PAs was also determined. As both SA and PAs can induce reactive oxygen species (ROS) and nitric oxide (NO) production, the balance of ROS and NO was analyzed in root tips. The results showed that 0.1 mM SA induced the production of higher PAs, spermidine (Spd), and spermine (Spm), while 1 mM SA decreased the PA contents by activating degrading enzymes. Studying the ROS and NO levels in root tips, the ROS production was induced earlier than NO, consistent with all the investigated zones of roots. This study provides evidence for concentration-dependent rapid effects of SA treatments on polyamine metabolism causing an imbalance of ROS–NO in root tips.

The Upregulated Expression of the Citrus RIN4 Gene in HLB Diseased Citrus Aids Candidatus Liberibacter Asiaticus Infection.

The citrus industry has been threatened by Huanglongbing (HLB) for over a century. Here, an HLB-induced Arabidopsis RPM1-interacting protein 4 (RIN4) homologous gene was cloned from Citrus clementina, and its characteristics and function were analyzed to determine its role during citrus–Candidatus Liberibacter asiaticus (CLas) interactions. Quantitative real-time PCR showed that RIN4 was expressed in roots, stems, leaves and flowers, with the greatest expression level in leaves. Its expression was suppressed by gibberellic acid, indole-3-acetic acid, salicylic acid and jasmonic acid treatments, but was induced by abscisic acid and salt treatments, as well as wounding. The transient expression of a RIN4-GFP showed that RIN4 was localized in the cell membrane. RIN4-overexpressing transgenic C. maxima cv. ‘Shatianyou’ plants were obtained, and some transgenic plants showed greater sensitivity to CLas infection and earlier HLB symptoms appearance than non-transgenic controls. Results obtained in this study indicated that the upregulated expression of RIN4 in HLB diseased citrus may aid CLas infection.