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Systemic Acquired Resistance in Crop Protection: From Nature to a Chemical Approach
Abstract
Plant natural resistance to potential parasites is regulated by two fundamental mechanisms: the "nonhost" and the "gene-for-gene" resistance, respectively. The latter is relevant when a cultivar resistant (R) gene product recognizes an avirulence gene product in the attacking pathogen and triggers an array of biochemical reactions that halt the pathogen around the site of attempted invasion. To cope with virulent pathogens, plants may benefit by some temporary immunity after a challenge triggering such an array of defense reactions, following a localized necrotizing infection as a possible consequence of a hypersensitive response (HR). This process, mediated by accumulation of endogenous salicylic acid (SA), is called systemic acquired resistance (SAR) and provides resistance, to a certain extent even against unrelated pathogens, such as viruses, bacteria, and fungi, for a relatively long-lasting period. SAR may be more potently activated in plants pretreated with chemical inducers, most of which appear to act as functional analogues of SA. This review summarizes the complex aspects of SAR as a way to prevent crop diseases by activating the plants' own natural defenses. The following outline is taken: (1) introduction through the historical insight of the phenomenon; (2) oxidative burst, which produces high levels of oxygen reactive species in a way similar to the inflammation state in animals and precedes the HR to the pathogen attack; (3) SAR as a coordinate action of several gene products leading to the expression of defenses well beyond the time and space limits of the HR; (4) jasmonic acid (JA) and ethylene as other endogenous factors mediating a different pathway of induced resistance; (5) pathogenesis related proteins (PR proteins) de novo synthesized as specific markers of SAR; (6) exogenous inducers of SAR, which include both synthetic chemicals and natural products; (7) the pathway of signal transduction between sensitization by inducers and PR expression, as inferred by mutageneses, a process that is still, to a large extent, not completely elucidated; (8) prospects and costs; (9) final remarks on the state-of-the-art of the topic reflecting the chemical view of the author, based on the more authoritative ones expressed by the authors of the reviewed papers.
... Numerous endogenous metabolites have been shown to be potential causative agents of SAR, including methyl salicylate (MeSA), azelaic acid (AzA), glycerol-3-phosphate (G3P), free radicals (NO and ROS), pipecolic acid (Pip), N-hydroxypipecolic acid (NHP), dehydroabietinal (DA), monoterpenes (α-and β-pinenes), NAD(P), and other signals in SAR of plants against microbial pathogens. 137,138 In SAR, salicylic acid accumulates and the expression of defense genes, including those encoding pathogenesis-related (PR) proteins, is triggered before the top leaf of the plant is exposed to the pathogen. 139 In addition, SAR is also associated with factors promoting cuticle formation, lipid transfer proteins, and trans-acting small interfering RNA. ...
... 140 SAR includes oxidative burst, expression of protective genes, and changes in the hormonal status of the plant. 138 Previously, we have repeatedly mentioned that Mn NPs are capable of influencing the amount of cellular mediator molecules such as ROS and products of the electron transport chain of photosynthesis. Therefore, the connection between the influence of Mn NPs and SAR activation is obvious. ...
Manganese (Mn) is an important microelement for the mineral nutrition of plants, but it is not effectively absorbed from the soil and mineral salts added thereto and can also be toxic in high concentrations. Mn nanoparticles (NPs) are less toxic, more effective, and economical than Mn salts due to their nanosize. This article critically reviews the current publications on Mn NPs, focusing on their effects on plant health, growth, and stress tolerance, and explaining possible mechanisms of their effects. This review also provides basic information and examples of chemical, physical, and ecological ("green") methods for the synthesis of Mn NPs. It has been shown that the protective effect of Mn NPs is associated with their antioxidant activity, activation of systemic acquired resistance (SAR), and pronounced antimicrobial activity against phytopathogens. In conclusion, Mn NPs are promising agents for agriculture, but their effects on gene expression and plant microbiome require further research.
... Systemic acquired resistance (SAR) gained interest of many researchers and many studies carried out led to great discoveries represented in biochemical changes in host cell wall, phytoalexins and pathogenesis related proteins (PRs) production, and stimulate programmed cell death (hypersensitivity) (AL-korany and Faiadh, 2011). Chemical compounds that are used in the induction of (SAR) should not be have a toxic effect directly on pathogens either for the compound itself or one of its derivatives (Gozzo, 2003) as well have no toxic effects on plants and animals, have a wide range of defense, affect in small quantities, their prevention impact remains for a long time, and with low cost (Melvin and Muthukumaran, 2008). It has been found that the use of SA and its analogs such as INA and BTH is able to induce the genes expression responsible for the production of (PRs) which have importance in resistance process against viral, bacterial and fungal diseases in dicot plants (Pasquer, 2005). ...
... SA was used successfully to resist some plant diseases such as root rot and wilt of sesame (Abdou Narusaka et al. (2006) recorded that INA is one of the essential synthetic compounds able to induce SAR. Gozzo (2003) reported that INA induces gene expression for SAR, sometimes before occurrence of infection in the plants and at other times, after pathogen attack only. This study aimed to isolation and identification the causal agent of wilt disease in tomato and cucumber and to test the effect of SA and INA as plant SAR activators on radial growth In vitro. ...
Abstract: Fusarium oxysporum f. sp. lycopersici (F.o.l) and Fusarium oxysporum f. sp. radicic-cucumerinum
(F.o.c) the causal agents of fusarial vascular wilt on tomato and cucumber plants respectively. These two diseases
constitute a great danger and threat to the cultivation of tomatoes, cucumbers, both in greenhouses or in open areas.
Salicylic acid (SA) and 2,6-dichloroisonicotinic acid (INA), which have the ability to induce systemic acquired
resistance in plants were used in this study to test their effect on radial growth of (F.o.l) and (F.o.c) in Petri dishes.
Results showed that 500 ppm of SA and INA had the greatest radial growth of F.o.l and F.o.c compared to other
concentrations 1000 and 2000 ppm significantly. Inhibition percentage measurements showed also SA and INA 500
ppm had the lowest inhibition percentage (6.8%), (28%) for F.o.l and (8.8%), (24.8) for F.o.c. respectively. Results
of this study and many of other studies conducted for the induction of systemic acquired resistance by these two
compounds proved that concentrations less than 500 ppm able to induce the systemic acquired resistance in plants,
also their inhibitory influence on radial growth are very few or non-existent in many cases.
... One of the most promising ways to protect plants against pathogens is systemic acquired resistance (SAR) phenomena [3] a natural plant defense mechanism that has been developed by plants through the evolutionary process. SAR has a broad spectrum action against pathogens [4,5]. ...
... order: nicotinic acid (1) < isonicotinic acid (2) < 2,6-dichloroisonicotinic acid (3). The most phytotoxic obtained ester derivatives for Agrimonia eupatoria seeds were 1a, 2a-2c, 2e, 2g-2i, 3a, 3b, and 3j, which showed a weight reduction between 37 and 63% (concentration of the active substance: 250 mg L −1 ), in comparison to control the sprout mass. ...
Recently, the biggest challenge in agriculture is the search for new, effective, and ecological methods of protecting plants against diseases. One of the fastest-growing and prospective strategies is a method based on activating the plant’s natural defenses. The use of suitable substances (elicitors) stimulates the immune system of plants, which makes them resistant to infections even before the first symptoms appear. This article presents preparation, characterization, phytotoxicity, and plant resistance induction efficacy of 28 ester derivatives of nicotinic, isonicotinic, and 2,6-dichloroisonicotinic acids as potential inducers of plants’ natural immune system. Plant resistance induction efficacy tests were performed on tobacco Nicotiana tabacum var. Xanthi infected by the tobacco mosaic virus (TMV).
... Protein inhibitors can impact bacterial nutrition and trigger plant resistance [67]. MeJA exposure has commonly been used to induce herbivore resistance in various plant species and has been shown to enhance the accumulation of pathogenesis-related proteins and defences, thus reducing the incidence of many crop diseases [30,68]. ...
Among the range of severe plant diseases, bacterial soft rot caused by Erwinia carotovora is a significant threat to crops. This study aimed to examine the varying response patterns of distinct potato cultivars to the influence of E. carotovora. Furthermore, it seeks to highlight the potential role of salicylic acid (SA) and methyl jasmonate (MeJA) in stimulating the antioxidant defence system. We collected eight bacterial isolates from diseased and rotted tubers which were morphologically and physiologically identified as E. carotovora subsp. carotovora. We conducted a greenhouse experiment to analyse the antioxidant responses of three different potato cultivars (Diamont, Kara, and Karros) at various time intervals (2, 4, 6, 8, 12, and 24 h) after bacterial infection (hpi). We assessed the extent of disease damage by applying a foliar spray of 0.9 mM salicylic acid (SA) and 70 μM methyl jasmonate (MeJA). Inoculating with Ecc led to an increase in total phenolic levels, as well as the activities and gene expression of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POX) as time progressed. Additionally, the application of SA and MeJA resulted in a further increase relative to the diseased treatments. The Karros cultivar, unlike the Diamont and Kara cultivars, demonstrated the highest expression levels of PAL, PPO and POX through inoculation, reflecting its higher levels of activity and resistance. Furthermore, the genetic response of potato cultivars to infection at 0 hpi varied depending on their susceptibility. The examination of the rate of PAL activity upregulation following SA or MeJA stimulation clarifies the cultivars' susceptibility over time. In conclusion, the study identified E. carotovora subsp. carotovora as the most virulent isolate causing soft rot disease in potato tubers. It further revealed that the Karros cultivar displayed superior resistance with high activities and gene expression of PAL, PPO and POX, while the cv. Diamont exhibited sensitivity. Additionally, foliar exposure to SA and MeJA induced antioxidant responses, enhancing the potato plants' resistance against Ecc pathogenesis and overall plant defence.
... In particular, it was significantly reduced by 9.40% at 97 dpf. Gozzo et al. [33] indicated that BTH treatment could regulate chlorophyll degradation. Moreover, BTH, a synthetic functional analog of salicylic acid, reduced the contents of plant chlorophyll and total carotenoids [34]. ...
Chardonnay is a non-floral grape with economic value and nutritional properties that is widely grown in northwestern China. However, limited research has been conducted on exogenous spraying to regulate volatile compound metabolism (especially isoprene metabolism) in Chardonnay grapes. Benzothiadiazole (BTH) can induce disease resistance and augment the contents of phenolics and volatile compounds in grapes. This study aimed to evaluate the influence of BTH on the accumulation of isoprene aroma, carotenoid levels and the activity profiles of key enzymes. Chardonnay grapevines were treated with 0.37 mM BTH at veraison to investigate the impact on physicochemical parameters, carotenoids, metabolic enzyme activities, and free and bound isoprenoids in developing Chardonnay grapes. The results showed that reducing sugars, and total soluble solids of BTH-treated grapes increased, while the content of titratable acidity, β-carotene, zeaxanthin, β-cryptoxanthin, chlorophyll, and total carotenoids in treated ripe grapes decreased relative to control berries. BTH-treated ripe grapes exhibited elevated levels of bound norisoprenoids and three key enzemy activities (carotenoid cleavage dioxygenase, phytoene synthase, lycopene β-cyclase), with a slight decrease in free norisoprenoids. Free and bound terpenoids profiles were also significantly enhanced by BTH treatment at veraison. Our findings offer novel perspectives into the modulation of isoprene biosynthesis in grape berries when exposed to BTH.
... Convincing proof was gathered only in the 1960s, when reproducible models employing the tobacco plant were established [5]. Greenhouse and field trials in the laboratory of Kuc and coworkers open the way to the current understanding of induced resistance as a plant protection technique [1], this is supported by various authors from throughout the world [6,7,8,9,10]. Utilising the special ability of plants to fight pathogens, the induced resistance may reduce the need for toxic chemicals in the management of disease and, as a result, be suggested as a different, unconventional, non-biocidal, and environmentally friendly method of protecting plants and, consequently, of promoting sustainable agriculture. ...
The search for a successful and efficient natural phenomenon of induced resistance in plants was prompted by the harmful effects that chemical pesticides and their degradation products had on the environment and human health. Ray was the first to identify plant resistance to diseases in 1901. When arabidopsis plants were injected with the pathogenic bacteria Pseudomonas fluorescens, which colonises roots, induced resistance was initially observed in these plants. There are two different kinds of induced resistance: induced biochemical defense and induced structural defense. Biochemical defense includes phytoalexins, PR-proteins, and secondary metabolites; structural defense includes cytoplasmic reactions, cell wall defense structure, and histological defense structure (development of cork layers, abscission layer, and tylose). Induced systemic resistance (ISR) and systemic acquired resistance (SAR) are the foundation of the induced resistance process. While the defense mechanism in ISR is mediated by jasmonic acid and ethylene and additionally triggered by non-pathognic rhizobacteria (Pseudomonas fluorescens), the defense mechanism in SAR is salicyclic mediated, namely alterations in gene expression. Plants can develop resistance to specific diseases by applying exogenous doses of 2, 6-dichloroisonicotonic acid and benzo-thiadiazole-7-carbothioic acid S-methyl ester (BTH). Induced resistance in plants, while still poorly understood, offers up new possibilities for plant protection and presents a viable strategy for sustainable agriculture and environmentally friendly disease control. It continues to be a problem for both basic and practical research.
... This inducer possesses the ability to enhance plant growth, improving resistance to disease and increasing crop yield [85]. Benzothiadiazole (BTH) and its metabolites in plants have no bactericidal activity; rather, they can affect multiple aspects of the pathogen's life. BTH not only plays a role in signal transduction by simulating salicylic acid but also induces plant resistance by changing the activity of peroxidase (POD), phenylalanine aminolysase (PAL), and β-1, 3-glucanase (GLU), as well as influencing the expression of pathogenesis-related genes to produce PRP (disease-course-related protein) [86,87]. ...
Continuous cropping is the primary cultivation method in Chinese facility agriculture, and the challenge of it stands as a global issue in soil remediation. Growing tomatoes continuously on the same plot for an extended period can result in outbreaks of tomato bacterial wilt. It is caused by the soil-borne bacterium Ralstonia solanacearum, a widespread plant pathogen that inflicts considerable damage on economically significant crops worldwide. Simultaneously, this plant pathogen proves extremely resilient, as it can adhere to plant residues and persist through the winter, continuing to infect plants in subsequent years. Scientists have dedicated considerable efforts towards finding effective methods to manage this disease. This article delineates the characteristics of tomato bacterial wilt and the various types of pathogenic bacteria involved. It systematically reviews the progress in research aimed at controlling tomato bacterial wilt, encompassing both physical and biological aspects concerning soil and plants. Emphasis is placed on the principles and current applications of these control measures, alongside proposed improvements to address their limitations. It is anticipated that the future of tomato bacterial wilt control will revolve around the development of a novel environmental protection system and efficient control strategies, focusing on microecological management and enhancing tomato resistance against bacterial wilt through breeding.
... One of the main strategies by which plants cope with invasion by pathogenic microbes is by acquiring systemic resistance. [43][44][45][46] Investigations have shown that reactive oxygen species are indicators of the defensive response of plants. Most commercially available antiviral agents induce systemic resistance so that the plant becomes immune to pathogen attack. ...
Background
Plant viral diseases, namely ‘plant cancer’, are extremely difficult to control. Even worse, few antiviral agents can effectively control and totally block viral infection. There is an urgent need to explore and discover novel agrochemicals with high activity and a unique mode of action to manage these refractory diseases.
Results
Forty‐one new phenothiazine derivatives were prepared and their inhibitory activity against tobacco mosaic virus (TMV) was assessed. Compound A8 had the highest protective activity against TMV, with a half‐maximal effective concentration (EC50) of 115.67 μg/mL, which was significantly better than that of the positive controls ningnanmycin (271.28 μg/mL) and ribavirin (557.47 μg/mL). Biochemical assays demonstrated that compound A8 could inhibit TMV replication by disrupting TMV self‐assembly, but also enabled the tobacco plant to enhance its defense potency by increasing the activities of various defense enzymes.
Conclusion
In this study, novel phenothiazine derivatives were elaborately fabricated and showed remarkable anti‐TMV behavior that possessed the dual‐action mechanisms of inhibiting TMV assembly and invoking the defense responses of tobacco plants. Moreover, new agrochemical alternatives based on phenothiazine were assessed for their antiviral activities and showed extended agricultural application. © 2023 Society of Chemical Industry.
... SA is a key plant immune hormone that is essential for the development of plant immunity. It was one of the first endogenous plant compounds to be documented as an inducer of SAR [31,47,48] and, eventually, metabolic changes. The barley cultivar, 'Hessekwa' was treated with synthetic functional analogues of SA, namely, 3,5-DCAA, 2,6-DCP-4-CA, and 3,5-DCSA, and metabolic perturbations and associated reprogramming was evident from PCA models ( Figure 3) and in Table 1 and Figures 5 and 6. ...
Designing innovative biological crop protection strategies to stimulate natural plant immunity is motivated by the growing need for eco-friendly alternatives to conventional biocidal agrochemicals. Salicylic acid (SA) and analogues are known chemical inducers of priming plant immunity against environmental stresses. The aim of the study was to study the metabolic reprogramming in barley plants following an application of three proposed dichlorinated inducers of acquired resistance. 3,5-Dichloroanthranilic acid, 2,6-dichloropyridine-4-carboxylic acid, and 3,5-dichlorosalicylic acid were applied to barley at the third leaf stage of development and harvested at 12, 24, and 36 h post-treatment. Metabolites were extracted using methanol for untargeted metabolomics analyses. Samples were analysed by ultra-high performance liquid chromatography coupled to high-definition mass spectrometry (UHPLC-HDMS). Chemometric methods and bioinformatics tools were used to mine and interpret the generated data. Alterations in the levels of both primary and secondary metabolites were observed. The accumulation of barley-specific metabolites, hordatines, and precursors was observed from 24 h post-treatment. The phenylpropanoid pathway, a marker of induced resistance, was identified among the key mechanisms activated by the treatment with the three inducers. No salicylic acid or SA derivatives were annotated as signatory biomarkers; instead, jasmonic acid precursors and derivatives were found as discriminatory metabolites across treatments. The study highlights differences and similarities in the metabolomes of barley after treatment with the three inducers and points to the triggering chemical changes associated with defence and resistance. This report is the first of its kind, and the knowledge acquired provides deeper insight into the role of dichlorinated small molecules as inducers of plant immunity and can be used in metabolomics-guided plant improvement programmes.
... "The chemical fungicides also often act as inducers of systemic resistance in plants against the pathogens. Generally, defense reaction occurs due to accumulation of PR proteins (chitinase, β-1, 3 glucanases), chalcone synthase, phenylalanine ammonia lyase (PAL), peroxidase, phenolics, callose, lignin and phytoalexins Gozzo, [46] and the ISR mechanism is effective against many types of pathogens and is mediated via a salicylic acid dependent process" Patel et al. [47]. ...
An investigation was performed In vitro condition to check induction of systemic resistance in ground nut with Pyraclostrobin 20% WDG (at different concentrations), Vitavax (Carboxin+Thiram 75%WS), Mancozeb 3 g/kg (75% WP), Carbendazim 50% WP, Trichoderma viride, Pseudomonas fluorescens, and Untreated Control treatments. Groundnut seeds sown in pot soil mixed with the inoculum of A.niger at 5% level alone served as control. The treatments were given as per the schedule and foliar spray was given at 20% DAS. The experiment was conducted with three replications in a completely randomized design. All observations viz., the collar rot disease incidence (PDI- at 30 DAS), plant height (cm), plant biomass and pod yield was assessed and recorded at harvest following standard procedures. The results showed that all the treatments significantly reduced the collar rot disease incidence compared to the control. Among the treatments, seed treatment plus foliar spray of Pyraclostrobin 20% WDG at 0.15 % (T3) recorded significantly the least collar rot incidence of 14.12 per cent, maximum germination per cent (93.28%) and maximum yield (132.23 g/pot) than other treatments. The dosage level with Pyraclostrobin 20% WDG as seed treatment @ 1.0 g/kg of seed plus foliar spray at the conc. of 0.1% recorded statistically on par results with T3 the best treatment
... Previous studies have shown that endogenous SA content increases rapidly subjected to various stresses (Kunkel and Brooks 2002;Janda et al. 2014;Kahn et al. 2015). Furthermore, there is generally a good correlation between the plant's resistance capacity and salicylic acid content (Gozzo 2003). SA provoked plant resistance against abiotic stresses such as drought (Yousefvand et al. 2022), salinity (Jangra et al. 2022), heat stress (Clark et al. 2004;Wang et al. 2010), osmotic stress (Borsani et al. 2001), heavy metal (Sharma et al. 2020) and herbicide tolerance like paraquat (Ananieva et al. 2004), quizalofopp-ethyl (Bayram et al. 2015, clethodim (Radwan 2012), propazine (Zhang et al. 2018), Basagran (Radwan et al. 2019), and glyphosate (Shopova et al. 2021). ...
Herbicides are used in agriculture to increase crop yield. However, their use often prompts concern about the consequences safety of crop production. Salicylic acid (SA) is a phenolic compound considered a phytohormone that confers plant resistance to different stresses. To determine the influence of SA on the reduction of herbicide-induced toxicity, we used young bean (Phaseolus vulgaris L.) seedlings treated with 1 mM of SA, 100 µM of prometryne or combined treatments. After 30 days of culture, prometryne treatment resulted in plant growth inhibition (shoot height, leaf area, fresh and dry weight) and decreased photosynthetic pigments content. It increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels. Meanwhile, the activities of enzymatic antioxidants, catalase (CAT) and ascorbate peroxidase (APX), as well as herbicide detoxification enzyme glutathione S‑transferase (GST), were significantly improved. Furthermore, herbicide enhanced proline amount and decreased that of glutathione. These findings reflect the presence of stress status. An exogenous supply of SA seemed to reduce the deleterious effects caused by prometryne and appeared to overcome this stress status. Such positive effect was reflected by enhancement of growth and leaf pigments contents, regulating antioxidant enzyme activities (CAT, APX, GST), and decreasing oxidative stress indices. This study demonstrates that exogenous application of SA to young bean plants reversed and/or minimized the damage caused by prometryne through the protection and improvement of some morpho-biochemical characters.
... These plant activators act on the host by activating immunologic mechanisms to prevent the pathogen invasion, which involve plant hormone signal transduction, phenylpropanoid biosynthesis, and MAPK signaling pathway. [43][44][45] In this work, the top two KEGG pathways of DEGs were enriched on plant hormone signal transduction and phenylpropanoid biosynthesis. There are two up-regulated JA responsive genes (JAZ and MYC2), three ethylene (ET)-responsive genes (ETR, CTR1, and EBF1/2), and one SA-responsive gene (TGA) in plant hormone signal transduction. ...
Background
Vegetable viruses are difficult to prevent and control in the field, causing massive economic losses of agricultural production in the world. A new natural product‐based antiviral agent would be an effective means to control viral diseases. As a class of natural products, 1‐indanones present various pharmacologically actives, while their application in agriculture remains to be found.
Results
A series of novel 1‐indanone derivatives were designed and synthesized and the antiviral activities were systematically evaluated. Bioassays showed that most compounds exhibited good protective activities against cucumber mosaic virus (CMV), tomato spotted wilt virus (TSWV), and pepper mild mottle virus (PMMoV). Notably, compound 27 exhibited the best protective effects against PMMoV with EC50 values of 140.5 mg L⁻¹, superior to ninanmycin (245.6 mg L⁻¹). Compound 27 induced immunity responses through multilayered regulation on mitogen‐activated protein kinase, plant hormone signal transduction and phenylpropanoid biosynthesis pathways.
Conclusion
These 1‐indanone derivatives especially compound 27 can be considered as potential immune activators to resist plant virus. © 2023 Society of Chemical Industry.
... Meanwhile, caffeic acid (3, 4-dihydroxy cinnamic acid) and ferulic acid (3-methoxy-4-hydroxycinnamic acid), as classic analogs of cinnamic acid, also possess an excellent antiviral profile in the fields of medicine and pesticides. [23][24][25][26][27][28] Gozzo 29 and Gan et al. 30 respectively found that ferulic acid could activate the plant immune system to prevent or postpone infection by viruses. Therefore, designing target structures based on cinnamic acid has the potential to give lead structures with desirable anti-pathogenic bioactivity. ...
BACKGROUND
Plant pathogens have led to large yield and quality losses in crops worldwide. The discovery and study of novel agrochemical alternatives based on the chemical modification of bioactive natural products is a highly efficient approach. Here, two series of novel cinnamic acid derivatives incorporating diverse building blocks with alternative linking patterns were designed and synthesized to identify their antiviral capacity and antibacterial activity.
RESULTS
The bioassay results demonstrated that most cinnamic acid derivatives had excellent antiviral competence toward tobacco mosaic virus (TMV) in vivo, especially compound A5 (median effective concentration [EC50] = 287.7 μg mL⁻¹), which had a notable protective effect against TMV when compared with the commercial virucide ribavirin (EC50 = 622.0 μg mL⁻¹). In addition, compound A17 had a protective efficiency of 84.3% at 200 μg mL⁻¹ against Xac in plants. Given these outstanding results, the engineered title compounds could be regarded as promising leads for controlling plant virus and bacterial diseases. Preliminary mechanistic studies suggest that compound A5 could enhance the host's defense responses by increasing the activity of defense enzymes and upregulating defense genes, thereby suppressing phytopathogen invasion.
CONCLUSION
This research lays a foundation for the practical application of cinnamic acid derivatives containing diverse building blocks with alternative linking patterns in pesticide exploration. © 2023 Society of Chemical Industry.
... As mentioned above, systemic acquired resistance aside from pathogen attack can also be activated by the external application of elicitors to plants [16]. It is worth pointing out that often synthetic elicitors (e.g., acibenzolar S-methyl ester (BTH) and their derivatives, [8][9][10][17][18][19][20][21][22][23] or 2,6-dichloroisonicotinic acid (INA) [24] and their derivatives [25,26]) exhibit higher biological activity than natural elicitors (e.g., salicylic acid, azelaic acid, and oxalic acid [27]). For instance, chemically modified BTH compounds used in low doses (20 mg L −1 ) reduced up to 100% of viral infections in a model of tobacco, Nicotiana tabacum var. ...
The novel and revolutionary approach to plant protection presented in this work, based on the preparation of bifunctional salts of a plant resistance inducer combined with a polyamine cation, may become a potential solution in the future for reducing the effects of abiotic and biotic stresses to which the plant is exposed. This study presents the synthesis, physical properties, phytotoxicity, and systemic acquired resistance (SAR) induction efficacy of new salts composed of the anion of plant resistance inducers and N , N , N , N ′, N ′, N ′-hexamethylpropane-1,3-diammonium cation (5 salts), N,N,N,N ′ ,N ′ ,N ′ - hexamethyl-butane-1,4-diammonium cation (5 salts), spermidine salicylate, and spermine salicylate. SAR induction efficiency tests were performed on tobacco, Nicotiana tabacum var . Xanthi , infected with the tobacco mosaic virus.
... One of the most striking features accompanying HR between plants and pathogens is the oxidative burst, which accumulates a large amount of ROS in a short period of time and causes allergic cell death (Foyer et al., 1997;Gozzo, 2003). The ROS plays a crucial role in the response to biological stimuli through oxidatively cross-linking and strengthening the cell wall to delay and prevent the invasion and spread of pathogens (Bradley et al., 1992;Tenhaken et al., 1995). ...
Plant viruses represented by tobacco mosaic virus (TMV) are hard to control due to the characteristics of wide hosts and difficulties to be inactivated in vitro. The discovery of candidates to damage the virus directly, and elicitors to induce plant resistances are important strategies against TMV. This study aims to identify new candidates from the title plants as biopesticides in controlling TMV. Herein, vanillic acid (6) and its new amide derivative, nigeroate (1), and seven known ones were discovered from the seeds of Hyoscyamus niger L. Compound 1, elucidated by spectral methods, was synthesized by two steps for industrial application in agriculture as a new elicitor. Compared with ningnanmycin, compound 1 appeared higher curative efficacies against TMV with the inhibitory rates of 58.00% and 69.14% at 250 and 500 μg/mL, respectively, while compound 6 displayed higher inactivation and protective efficacies with the inhibitory rates of 47.30–79.71% and 43.28–63.87% at 125–500 μg/mL, respectively. Compound 6 could destroy TMV particles into small fragments dramatically by decreasing the transcription level of TMV-CP gene, while compound 1 just broke the TMV particles slightly, and was no influence on TMV-CP gene. Interestingly, compound 1 induced potent hypersensitive response (HR), and systemic acquired resistance (SAR) activities (53.82% at 500 μg/mL) in tobaccos. The accumulation of H2O2 by activating SOD (superoxide dismutase), CAT (catalase), as well as POD (peroxidase) was the mechanism of compound 1 induced HR. The SAR induced by compound 1 was referred to upregulate SA (salicylic acid) by activating PAL (phenylalanine ammonia-lyase) pathway, ICS (isochorismate synthase) pathway, as well as PR (pathogenesis-related) proteins due to the increasement of PAL enzyme, and PAL, ICS1, NPR1, PR1, and PR2 transcription levels. Thus, vanillic acid (6) and its new amide derivative (1) could be developed as antiviral agents and plant immune elicitors for biopesticides in controlling TMV, respectively.
... Gómez-Plaza et al. [23] demonstrated that BTH could activate enzymes related to anthocyanin metabolism. Repka et al. [112] and Gozzo [113] also reported that BTH treatment promoted the activities of enzymes (i.e., chalcone isomerase and PAL) in the phenylpropanoid pathway. Furthermore, BTH treatment can contribute to stilbenes and flavan-3-ols synthesis due to SAR and BTH induction of the expression of phenylpropanoid genes in grapevine [62]. ...
Benzothiadiazole (BTH) is a commercial chemical elicitor that can induce an innate immune response in grapevines and improve the phenolic components and color quality of grapes and corresponding products. The literature on the influence of BTH on the accumulation and metabolism of phenols from grapes is extensive. However, many unknown bio-mechanisms involved have been poorly investigated, which opens a gateway for pioneering research that needs to be done in this field. To this purpose, this review aims to analyze and explore the gaps in current research so that subsequent studies may be geared towards them.
... In plants, JA activates systemic acquired resistance (SAR) to work together to protect plants against biotic and abiotic stressors [20][21][22]. JA is involved in plant growth and development and nutrient uptake, which has a direct impact on growth, cell elongation, and the production of photosynthetic pigments as well as source-to-sink regulation under nonstressed conditions. It has been extensively investigated that JA could enhance the drought stress tolerance of plants [23][24][25][26]. ...
It has been shown that jasmonic acid (JA) can alleviate drought stress. Nevertheless, there are still many questions regarding the JA-induced physiological and biochemical mechanisms that underlie the adaptation of plants to drought stress. Hence, the aim of this study was to investigate whether JA application was beneficial for the antioxidant activity, plant performance, and growth of Grewia asiatica L. Therefore, a study was conducted on G. asiatica plants aged six months, exposing them to 100% and 60% of their field capacity. A JA application was only made when the plants were experiencing moderate drought stress (average stem water potential of 1.0 MPa, considered moderate drought stress), and physiological and biochemical measures were monitored throughout the 14-day period. In contrast to untreated plants, the JA-treated plants displayed an improvement in plant growth by 15.5% and increased CO2 assimilation (AN) by 43.9% as well as stomatal conduct-ance (GS) by 42.7% on day 3. The ascorbate peroxidase (APX), glutathione peroxidase (GPX), and superoxide dismutase (SOD) activities of drought-stressed JA-treated plants increased by 87%, 78%, and 60%, respectively, on day 3. In addition, G. asiatica plants stressed by drought accumulated 34% more phenolics and 63% more antioxidants when exposed to JA. This study aimed to understand the mechanism by which G. asiatica survives in drought conditions by utilizing the JA system.
... However, these applications are hazardous to human health. Therefore, alternate sources of fungicides are necessary to discover to get rid of the pear diseases and to increase quality pear production with minimal use of synthetic fungicides (Agostini et al., 2003;Gozzo, 2003;Percival and Haynes, 2008;Schnabel and Parisi, 1997;Schneider et al., 1996;Stanis and Jones, 1985). ...
Influence of foliar application of potassium nitrate and copper sulfate on the production and quality of Pear cv. Le Conte was carried out at Horticulture Research Farm and Postharvest Laboratory, The University of Agriculture Peshawar-Pakistan, during the year 2018–19. The aim of the study was to get quality pear production with minimal disease incidence. The research was carried out in a randomized complete block design with three replications. The study contained two factors, i.e., different concentrations of potassium nitrate (0%, 1%, 2%, and 3%) as Factor A, while different levels of copper sulfate (0%, 0.2%, 0.4%, 0.6%, and 0.8%) as factor B and the treatments were applied in spring season at the fruit set stage. The application of 2% potassium nitrate to the pear plants resulted in heaviest fruit (188.30 g), maximum fruit volume (203.80 cm³), fruit yield tree⁻¹ (60.13 kg) with minimum fruit drop (8.52%) and disease incidence (5.28%), while maximum fruit firmness (7.66 kg.cm⁻²), total soluble solids (12.40 ○Brix), fruit juice pH (5.38), ascorbic acid content (5.56 mg.100 g⁻¹) while minimum Titratable acidity (0.41%) were noted in fruits of plants sprayed with 3% potassium nitrate solution. However, the maximum fruit weight (192.04 g), fruit yield tree⁻¹ (59.06 kg), minimum fruit drop (6.75%), and disease incidences (3.54%) were recorded in pear plants applied with 0.6% foliar copper sulfate solution. However, maximum fruit firmness (7.53 kg.cm⁻²), total soluble solids (12.38 ○Brix), fruit juice pH (5.31), ascorbic acid content (5.22 mg.100 g⁻¹) with minimum Titratable acidity (0.42%) were noted in the plants sprayed with 0.8% copper sulfate solution. This study will provide a basis for high yield and quality fruit production, which will affect the storability of pear and other important fruit crops. Further studies should be conducted to optimize the dose, timing, and method of application of these fungicides for other pome fruits.
... It was followed by KH 2 PO 4 , benzoic acid, K 2 HPO 4 , citric acid and calcium chloride. External application of salicylic acid or other activators like citric acid, K 2 HPO 4 , benzoic acid and KH 2 PO 4 produce the pathogenicity related proteins which reduce the incidence of diseases (Gozzo, 2003). Foliar application of salicylic acid on tomato infected with stem canker significantly lessened the disease index contrary to its application on other infected crops (Esmailzadeh et al., 2008). ...
... Induced resistance exists in two main types: SAR and ISR (Choudhary et al., 2007, Peethala, 2019. SAR works on the salicylic acid pathway (SAP) (Gozzo, 2003) while ISR works on the principle of the jasmonic acid pathway (Choudhary et al., 2007). ...
Phomopsis blight is one of the major growth and yield-limiting factors for brinjal production caused by Phomopsis vexans. It is a devastating disease that affects the production and quality of brinjal by 40-70% and makes brinjal fruits non-commercial and inedible, negatively impacting income generation, nutrition, and health. To cope with the harmful effect of this disease, various cultural, biological and chemical methods have been followed to control this fungal disease extensively. Since the cultural and biological practices have a slow but positive effect, the focus of growers shifted toward chemical control. Although the chemical methods for the management were found most effective and accepted worldwide by the grower, these chemicals have many negative consequences for humans, the environment, soil, and water. It has been observed that improper and heavy use of fungicides also develops resistance to plant pathogens. Hence, there is a strong need for an environment-friendly approach which allows a plant to build resistance. This concept of developing resistance into the plant system is induced resistance. Among the induced resistances is systemic acquired resistance, which works on the principle of the salicylic acid pathway. In contrast, induced systemic resistance works on the principle of the jasmonic acid pathway. This review aims to explain why Phomopsis blight is an economically significant disease of brinjal and provides an extensive discussion on sustainable management strategies compared to the canonical and formal recommendations for the control of the disease.
... [15][16][17][18][19][20] MeJ has been mainly implicated as a mediator in plant responses triggered by wounding and insect feeding and is involved in pathogen resistance. 21 BTH is a synthetic functional analogue of the plant endogenous hormone-like compound salicylic acid, which induces defence genes leading to systemic acquired resistance and an increase in phenolic production. 22 In addition, MeJ has been described as a highly volatile product, whereas BTH is completely degraded in plant tissues. ...
BACKGROUND
Proanthocyanidins (PAs) are phenolic compounds present in skins and seeds of wine grapes and have great implications for plant physiology and wine quality. There are several strategies to increase PA concentration, such as application of elicitors methyl jasmonate (MeJ) and benzothiadiazole (BTH), compounds that can stimulate defence responses like phenolic compound biosynthesis in wine grapes, which have been applied mainly at veraison (beginning of ripening). We recently evaluated the application of MeJ and BTH on Vitis vinifera cv. Monastrell grapes during veraison and mid‐ripening (3 weeks after veraison). Grapes treated at mid‐ripening showed higher anthocyanin concentrations than those at veraison. In this trial, over two seasons, we evaluated whether time of application (veraison or mid‐ripening) of MeJ and BTH on ‘Monastrell’ grapes is a determining factor in the biosynthesis and composition of PAs in grapes and their subsequent release into wines.
RESULTS
Application of elicitors at different ripening times produced significant differences in the PAs of ‘Monastrell’ grapes, since those treated at mid‐ripening recorded a higher PAs concentration in skin and seeds, and then in the wines produced, compared to grapes treated at veraison.
CONCLUSION
Results suggest that despite different environmental conditions endured in each of the two seasons evaluated, application of elicitors at mid‐ripening of Monastrell grapes could be used to harvest grapes with higher PA concentration, increasing the functional value of the wines, without altering their organoleptic quality. © 2022 Society of Chemical Industry.
... Methyl jasmonate (MeJ) is a phytohormone that acts as a signal molecule for plant resistance to various stress types and modulates chlorophyll degradation and anthocyanin biosynthesis (Ruiz-García and Gómez-Plaza, 2013;Portu et al., 2015;Portu et al., 2016;Portu et al., 2017). MeJ is mainly involved in plant responses to wounding and insect feeding and in resistance to pathogens (Gozzo, 2003). Besides, it has been suggested that foliar application of MeJ in the vineyard modified the amino acid concentrations of grapes Gutiérrez-Gamboa et al., 2017;Gutiérrez-Gamboa et al., 2018). ...
Currently, elicitors have been used to induce the defence mechanisms of vines, i.e., against both abiotic and biotic stresses. Besides, increases in phenolic synthesis in grapevines have been reported after elicitors application. However, its effects on the grape nitrogen composition are not entirely known. Thus, this work aimed to study the effect of methyl jasmonate (MeJ) and a yeast extract (YE) applied in Monastrell and Tempranillo grapevines on grape amino acids during two consecutive seasons. Amino acids in grapes were analysed by HPLC. In the first season, the total amino acid content in grapes decreased in Monastrell after MeJ and YE applications from 2236 to 1580 and 1620 mg L-1, respectively, while in Tempranillo, the total amino acid concentration decreased after YE applications from 2355 to 1811 mg L-1. However, during the second season, elicitors did not affect total amino acid concentration. The most important components of variability in amino acid concentration were the grape variety and the season. These results provide new knowledge of the effect of two elicitors in two important red varieties on grape amino acids content, relevant for wine quality.
... La aplicación de insecticidas ha sido el principal método de manejo para enfermedades virales transmitidas por insectos (Sikora et al., 1998). Una alternativa al uso de insecticidas para el manejo de enfermedades virales transmitidas por áfidos, es el uso de compuestos que fortalezcan las defensas naturales de las plantas (Gozzo, 2003), mediante procesos como la resistencia sistémica adquirida (RSA) y resistencia sistémica inducida (RSI) (Van Loon et al., 1998). La RSA y RSI han sido efectivas contra hongos, bacterias, virus, nematodos, plantas parásitas e insectos fitófagos (Sticher et al., 1997;Van Loon et al., 1998). ...
Se evaluó el efecto de la miel (M), ácido acetilsalicílico (ASA), aminoácidos (AA) y
Bacillus subtilis (BS) en la concentración y severidad del Cucumber mosaic virus (CMV),
peso freso (PF), contenido total de cucurbitacinas y contenido de nutrimentos en calabacita
variedad Grey Zucchini. Los tratamientos evaluados fueron: 1) M+CMV, 2) ASA+CMV,
3) AA+CMV, 4) BS+CMV, 5) Testigo positivo (inoculado con CMV) (TI) y 6) Testigo
sano (sin inocular) (TS). Se inoculó mecánicamente al CMV en las plantas de todos los
tratamientos, excepto en TS. La mayor absorbancia se observó en los tratamientos AA y TI
mientras que la mayor severidad la mostró el tratamiento AA. El mayor peso fresco se tuvo
en TS seguido de M y el menor en AA. En los tratamientos M, BS y ASA se detectaron 12
cucurbitacinas, en AA 11 y en TS y TI 10. El tratamiento M tuvo el mayor contenido total
de cucurbitacinas. Los tratamientos M, BS y ASA tuvieron contenidos de Fe, Zn y Mn
mayores que ambos testigos.
... Among these elicitors, methyl jasmonate (MeJ) and benzothiadiazole (BTH) have been used to increase the phenolic content of fruits, particularly grapes, while also being considered useful as agrochemicals to improve resistance against plant pathogens [11][12][13][14][15]. Jasmonic acid and MeJ are naturally occurring plant growth regulators that modulate chlorophyll degradation and anthocyanin biosynthesis. MeJ has been mainly implicated as a mediator in the plant responses triggered by wounding and insect feeding, and is involved in pathogen resistance [16]. BTH is a synthetic functional analog of the plant endogenous hormone-like compound salicylic acid, which induces defense genes leading to systemic acquired resistance (SAR) and an increase in phenolic production [17]. ...
The aim of this study was to evaluate whether the application of two pre-harvest elicitors—methyl-jasmonate (MeJ) and benzothiadiazole (BTH)—to Monastrell grapes, at two maturation stages, affected the composition and structure of the skin cell walls (SCWs) to differing extents. This study was conducted in 2016–2017 on Vitis vinifera L. cv Monastrell. A water suspension of MeJ and BTH, and a mixture of both, was applied at veraison and mid-ripening. The composition of the berry SCW was analyzed. Environmental conditions caused substantial changes in SCW composition, especially at high temperatures. Indeed, a reduction of approximately 50% in the biosynthesis of hemicellulose, proteins and total phenols was observed, accompanied by a slight increase in cellulose and lignin. However, the application of the treatments also caused changes in some SCW constituents: increases in the concentration of phenols, proteins and lignin were observed, especially when the MeJ and MeJ + BTH treatments were applied at veraison. Likewise, a reduction in uronic acids was observed in the MeJ + BTH treatment applied at veraison. These changes in the SCWs could affect their structural characteristics, and therefore influence grape handling in the field and in the winery. Further studies are needed to determine the extent to which MeJ and BTH treatments affect other skin characteristics.
... Both, jasmonic acid and its derivative, methyl jasmonate, are natural plant growth regulators that modulate chlorophyll degradation and anthocyanin biosynthesis (Ruíz-García et al., 2013;Portu et al., 2015Portu et al., , 2016Portu et al., , 2017. Methyl jasmonate is mainly involved in plant responses triggered by wounding and insects feeding, and is implicated in resistance to pathogens (Gozzo, 2003). Authors such as Garde-Cerdán et al. (2016) and Gutiérrez--Gamboa et al. (2017, suggested that methyl jasmonate foliar application modified the amino acids concentrations, improving the quality of grapes. ...
In viticulture, the application of elicitors to the grapevines is increasing although their effect on the amino acids content is little studied. In this work, nanoparticles of methyl jasmonate (Ap-MeJ) were applied for the first time to Monastrell grapevines during two seasons (2019 and 2020) to increase its profitability and nitrogen plant uptake and to reduce environmental impact (less quantity) and increase its economic viability. In addition, rainfed plants were compared with grapevines under regulated deficit irrigation (RDI) watering regime, since global climatic conditions are limiting water use and quality. Results showed that season was the factor that most affected to the amino acids content (values of 12 from the 21 free amino acids determined were higher in 2019 and 4 in 2020), followed by the watering regime (higher amino acids content in musts from rainfed than in RDI water status). Foliar treatments had little impact on grape enological parameters, as well as on the amino acids concentration (only content of Pro was higher in control than in Ap-MeJ musts). This preliminary study could not confirm the elicitor effect of MeJ loaded on nanoparticles on must amino acid content and further research work should be performed in order to optimize dose of application.
... Finally, the high number of hypothetical flagellar proteins in the bulk soil compared to the rhizosphere suggests a lower proportion of mobile bacteria in the latter. This could be explained by the fact that, in order to avoid a plant systemic resistance response, phytopathogens and also endophytes, once attached to roots, lose their flagella or shield lipopolysaccharides to prevent their recognition by plant cells (Gozzo, 2003). ...
Natural plant-associated microorganisms are of critical importance to plant growth and survival in field conditions under toxic concentrations of trace elements (TE) and these plant-microbial processes can be harnessed to enhance phytoremediation. The total bacterial diversity from grey willow (Salix atrocinerea) on a brownfield heavily-polluted with lead (Pb) and arsenic (As) was studied through pyrosequencing. Culturable bacteria were isolated and in vitro tested for plant growth-promotion (PGP) traits, arsenic (As) tolerance and impact on As speciation. Two of the most promising bacterial strains - the root endophyte Pantoea sp. AV62 and the rhizospheric strain Rhodococcus erythropolis AV96 - were inoculated in field to S. atrocinerea. This bioaugmentation resulted in higher As and Pb concentrations in both, roots and leaves of bacterial-inoculated plants as compared to non-inoculated plants. In consequence, bacterial bioaugmentation also affected parameters related to plant growth, oxidative stress, the levels of phytochelatins and phenylpropanoids, together with the differential expression of genes related to these tolerance mechanisms to TE in leaves. This study extends our understanding about plant-bacterial interactions and provides a solid basis for further bioaugmentation studies aiming to improve TE phytoremediation efficiency and predictability in the field.
... POD is one of the key enzymes in the pathway of lignin synthesis. As a defense gene, POD can induce the biosynthetic pathway of SA, lignin and phytoalexin, activate SAR46, and promote cell-wall strengthening and pathogen suppression [55]. In addition, POD can catalyze the decomposition of H 2 O 2 and the polymerization of lignin monomers [56]. ...
Lentinan (LNT) is a natural and functional polysaccharide isolated from Lentinus edodes fruiting bodies, which functions in stimulating the plant immune response, improving plant disease resistance and regulating plant growth. This study explores the use of LNT as a plant growth regulator and attractant in cotton production. After treatment with LNT, the content of malondialdehyde (MDA) in cotton seeds decreased, whereas the activities of polyphenol oxidase (PPO), superoxide dismutase (SOD) and peroxidase (POD) in leaves increased significantly. LNT also promoted the growth and development of cotton plants and significantly reduced the incidence of cotton damping-off disease. The relative expression of salicylic acid pathway-related genes in cotton also increased significantly. The prevention mechanism of fluopimomide was also evaluated, and the result showed lower EC50 values and was effective in controlling cotton seedling disease caused by Rhizoctonia solani in both greenhouse experiments and field trials. The use of LNT and fluopimomide in controlling cotton seedling damping-off disease showed a synergistic effect in field trials. These results will provide a new insight into the agricultural application of LNT as a biological fungicide in the field of biological controls.
... According to (Durrant and Dong, 2004;Cho et al., 2010), systemic acquired resistance (SAR) is one such inducible defense mechanism, which is induced systemically throughout the plant in response to the exposure of another part of the plant to a necrogenic pathogen. Chemicals used as inducers of resistance should have no direct toxicity to pathogens, either by the compound itself or by its possible metabolites (Gozzo, 2003); no toxicity to plants and animals; no negative effects on plant growth, development and yield; broad spectrum of defense; low loading amount; long lasting protection; low economical cost for farmers; good profit for producers (Melvin and Muthukumaran, 2008). Chemical elicitors like salicylic 109 | l c c a -2 acid, jasmonic acid, DL-β-aminobutyric acid (BABA), thiamine (vit. ...
The aim of this study was to evaluate the effect of addition of two types of antioxidants (Tertiary Butyl Hydro Quinon (TBHQ) and Vitamin E) on the stability of two oils (sun flower and olein oil) before and after frying. Nowadays a great attention has focused on the peroxide values of different foodstuffs, since there was a link between the accumulation of the free radical and the adverse effect on human health. Generally, peroxide value was taken as a quality indicator for a wide range of food products. The impact of frying conditions (oil type, temperature, frying time) on peroxide value was investigated in this study. The results obtained that there was a high peroxide value of oils used in this study even before frying for both tested oils (olein and sun flower). Upon addition of antioxidants, there was a significant decrease in peroxide value for the two oils tested especially in case of vitamin E. The main recommendations of this study was the oil used in frying must be with low (as possible) peroxide value to get good organoleptic quality for the potato frying products, so due to its stability, olein oil is good for frying of both chips and French fries.
A series of novel benzothiadiazole (BTD) derivatives was synthesized via a Pd-catalyzed Suzuki-cross-coupling reaction, encompassing compounds with D–A–D and D–A–A architectures. Devices featuring non-symmetrical structures incorporating electron-accepting cyano and nitro groups on the BTD core exhibited a non-volatile ternary WORM memory behavior. Conversely, symmetrical compounds containing di-tertiary-butyl or dimethoxy groups as donors manifested binary memory behavior. The compounds with methoxyl and cyano substitution in the D–A–A architecture displayed only binary switching behavior due to their unfavorable thin film formation and molecular packing. UV and CV data analysis revealed narrow band gaps ranging from 2.58 to 2.75 eV, facilitating charge carrier transport within the active layer. Remarkably, compounds featuring t-Bu and cyano group substitutions showcased superior performance attributes, characterized by a low threshold voltage of −0.80 V and a high ON/OFF ratio of 10². The underlying resistive switching mechanism was elucidated through analysis of HOMO, LUMO, and ESP studies, indicating a composite influence of charge transfer and charge trapping phenomena. This study highlights the significant influence of substituent modifications in D–A molecules on molecular packing, thin film morphology, and electron trap depth within the active layer. These factors profoundly impact the memory performance of organic memory devices.
Severe outbreaks of diseases are the consequences of interactions between pathogenic microorganisms and cultivated crops. Plants are recurrently exposed to various biotic stresses in their innate environment. To endure such unfavorable circumstances, they have acquired complex mechanisms to react and acclimatize to biotic stresses. Plants are host to many contagious diseases caused by both living and nonliving agencies like viruses, bacteria, fungi, nematodes, and stress conditions. Comparatively small proportions of pathogens effectively assault the host plant which results in diseases. Plant disease is a physiological disorder or structural irregularity that is destructive to the plant and its products that suppress its monetary value. Plants are sessile and responsive organisms that encounter a variety of environmental strains. Throughout their life cycle, plants respond to diverse intimidations arising from their external environment. Fungal pathogens have a meticulous impact causing a major damage and yield losses in agriculture. Due to their sessile nature plants develops a broad range of strategies that cooperatively work in defense against biotic and abiotic stresses. Plant diseases can be viewed as obstinate roadblocks to the rapid advancement in agricultural yield. Interpreting the molecular basis of plant–pathogen interaction facilitates us to select plant resistance genes. The present work is focused on the consequence of fungus Macrophomina phaseolina on the growth of chickpea plants via monitoring various biochemical parameters which play important role in defense response upon infection with the pathogen. Comparative studies on the effect of M. phaseolina toxin in chickpea as well as other host plants like Brassica oleracea, Brassica juncea, Helianthus annus, and Vigna mungo via detached leaf bioassay method are also planned.KeywordsChickpeaChitinase geneResistant
The demand for more food production and the pollution of ecosystems by pesticides is calling for sustainable methods to improve crop yields, such as the management of rhizobacteria that grow in the root zone. For instance, rhizobacteria induce systemic resistance against a large number of pathogens in plants. Here we review induced systemic resistance in plants with focus on plant immunity, systemic versus local resistance, molecular mechanisms, signaling, the role of salicylic acid, hormones and genes, and the control of crop diseases.
To further develop new antiviral agents, several novel cyclized derivatives of ferulic acid were designed and synthesized. Their antiviral activities were evaluated against the cucumber mosaic virus (CMV), pepper mild mottle virus (PMMoV), and tomato spotted wilt virus (TSWV). The results showed that some ferulic acid derivatives exhibited desirable antiviral activities. Particularly, compound 5e exhibited excellent protective activities against CMV, PMMoV, and TSWV, with EC50 values of 167.2, 102.5, and 145.8 μg mL-1, respectively, which were superior to those obtained for trans-ferulic acid (581.7, 611.2, and 615.4 μg mL-1), dufulin (312.6, 302.5, and 298.2 μg mL-1), and ningnanmycin (264.3, 282.5, and 276.5 μg mL-1). Thereafter, the protective mechanisms of 5e were evaluated through photosynthesis evaluation, transcriptome profiling, and proteomic analysis. The results indicated that 5e significantly activated the expression levels of photosynthesis-related regulatory genes and proteins in tobacco plants and promoted the accumulation of defense molecules to resist viral infection. Thus, the findings of this study indicated that novel cyclized ferulic acid derivatives are potential antiviral agents that act via regulating photosynthesis in the host.
The photoredox amination of arene protocols mostly comprises photocatalyst-mediated transformations. Herein, we presented the photocatalyst-free, visible-light promoted, direct conversion of C(sp2)-H to C(sp2)-N method. Multipurpose benzothiadiazoles are used as model synthons and secondary amines as aminating agents. Mechanistic study reveals that the radical reaction mechanism proceeds through nitrogen-centered radical generation, followed by the addition of arenes, which was demonstrated for the present amination protocol of benzothiadiazole with secondary amines in an atom economical fashion.
Synthesis of bis-arylsulfenyl-benzo-2,1,3-thiadiazoles was accomplished using a Pd-G3 XantPhos as a simple and inexpensive catalyst. Numerous benzene thiols reacted well with 4,7-dibromo-benzo-2,1,3-thiadiazole in DMF, using K2CO3 as the base, obtaining high product yields in a short reaction time. Furthermore, all the synthesized compounds showed remarkable fluorescent properties with emission wavelengths in the visible range. Due to their unique properties, they might be used as image probes in fluorescence microscopy. The study found that these compounds have a wide range of potential applications in the area of sensors, as well as other photophysical properties.
The novel plant elicitors, 3-benzyl-5-[1-(2-oxo-4-phenyl-1-oxaspiro[4.5]dec-3-en-3-yl)ethylidene]-2-aminoimidazolin-4-one derivatives, were designed based on the diversity-oriented synthesis strategy and synthesized in four steps via the Knoevenagel condensation reaction as the key step. They were characterized by 1H NMR, 13C NMR, HR-ESI-MS, and X-ray diffraction. The position of the C═N bond of Z- and E-configuration compounds was determined by X-ray diffraction. The in vivo fungicidal activity evaluation revealed that most of these compounds exhibited remarkable activities (100%) against Pseudoperonospora cubensis at 400 μg/mL, among which compound 8e still exhibited excellent protective activity with a 50% inhibition rate at 0.1 μg/mL. Because the in vitro effect on tested phytopathogens was poor, the mechanism to induce the immune responses and reinforce the resistance of cucumber against Botrytis cinerea was studied. The results indicated that the compound 8e-mediated defense response against B. cinerea was based on the accumulation of pathogenesis-related proteins and cell wall reinforcement by callose deposition. Quantitative analysis of salicylic acid (SA) and jasmonic acid (JA) and the increased expression of induced resistance-related genes and the defense-associated phenylalanine ammonia lyase revealed that the immune response triggered by compound 8e was highly associated with the SA signaling pathway. Significant upregulation of JA-related genes Cs-AOS2 indicated that the JA signaling pathway was also influenced. It was also shown that the plants treated with compound 8e promoted primary root elongation, which resulted in enhanced plant growth. Most importantly, these compounds have completely new structures compared with the traditional plant elicitors. Further research of 8e-mediated plant disease resistance might have a great influence on the development of plant elicitors.
Plants have evolved a series of defensive mechanisms against pathogens and herbivores, but the defense response always leads to decreases in growth or reproduction, which has serious implications for agricultural production. Growth and defense are negatively regulated not only through metabolic consumption but also through the antagonism of different phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Meanwhile, plants can limit the expression of defensive metabolites to reduce the costs of defense by producing constitutive defenses such as glandular trichomes or latex and accumulating specific metabolites, determining the activation of plant defense or the maintenance of plant growth. Interestingly, plant defense pathways might be prepared in advance which may be transmitted to descendants. Plants can also use external organisms to protect themselves, thus minimizing the costs of defense. In addition, plant relatives exhibit cooperation to deal with pathogens and herbivores, which is also a way to regulate growth and defense.
In order to evaluate four biostimulants in the induction of systemic resistance in cucumber (Cucumis sativus L.) and tomato (Solanum lycopersicum Mill.) in monoculture and associated greenhouse cultivation, five treatments were applied at three developmental stages (growth, flowering and fruiting): T1 Bioremedy (2.0 g/L), T2 Grandsil (2.0 g/L), T3 Control (water), T4 Fossil (5.0 g/L), T5 L-amino (2 cm3/L). The treatments were distributed in a 3 x 5 factorial arrangement and evaluated in a completely randomised experimental design. Each experimental unit consisted of three rows. The response variables were: plant height (cm), stem diameter (mm), number of fruits per plant, fruit volume (cm3) and fruit weight (kg). The results, cucumber in monoculture did not present notable differences for any of the evaluated variables, with the exception of plant height, significant differences were observed at P<0.05 of probability, Bioremedy, L-amino and control were the best. In tomato monoculture, there were significant differences at P<0.05 for all the variables, with Bioremedy standing out for plant height, stem diameter, fruit weight, fruit diameter and fruit number. In the associated crop, both cucumber and tomato had significant differences at P<0.05 for all the variables evaluated, with Bioremedy being the best.
In order to evaluate four biostimulants in the induction of systemic resistance in cucumber (Cucumis sativus L.) and tomato (Solanum lycopersicum Mill.) in monoculture and associated greenhouse cultivation, five treatments were applied at three developmental stages (growth, flowering and fruiting): T1 Bioremedy (2.0 g/L), T2 Grandsil (2.0 g/L), T3 Control (water), T4 Fossil (5.0 g/L), T5 L-amino (2 cm3/L). The treatments were distributed in a 3 x 5 factorial arrangement and evaluated in a completely randomised experimental design. Each experimental unit consisted of three rows. The response variables were: plant height (cm), stem diameter (mm), number of fruits per plant, fruit volume (cm3) and fruit weight (kg). The results, cucumber in monoculture did not present notable differences for any of the evaluated variables, with the exception of plant height, significant differences were observed at P<0.05 of probability, Bioremedy, L-amino and control were the best. In tomato monoculture, there were significant differences at P<0.05 for all the variables, with Bioremedy standing out for plant height, stem diameter, fruit weight, fruit diameter and fruit number. In the associated crop, both cucumber and tomato had significant differences at P<0.05 for all the variables evaluated, with Bioremedy being the best.
Three prieurianin-type limonoids (1–3), including two new compounds (1 and 2) and one known compound (3) were isolated from Munronia henryi. These compounds were tested for their activities against tobacco mosaic virus (TMV) by the conventional half-leaf method and the outcomes were analyzed by western blotting and RT-PCR assays. The three tested compounds, at 100 μg/mL, showed strong antiviral activities in the pretreated tobacco plants with inhibition rates ranging from 70.5% to 81.3%, which were significantly higher than that of the positive control, ningnanmycin (55.6%). Their potential of inducing systemic acquired resistance (SAR) was also evaluated, in which compound 1 showed excellent induction activities. Furthermore, it was found that potentiation of defense-related enzyme activity and the contents of SA was increased. Compound 1 could also inhibit the expression of TMV CP and up-regulate the expression of defense-related genes. This work revealed that these limonoids, especially compound 1 could induce resistance in tobacco plants against the viral pathogen TMV. Meanwhile, compounds 1–3 could down-regulate the expression of NtHsp70–1 and Nthsp70–261 genes, indicating that these limonoids possibly inhibit TMV infection by suppressing NtHsp70–1 and Nthsp70–261 expression. This study is the first to report antiviral compounds with two different mechanisms of action.
z Bu çalışmada ülkemizde nohut ekim alanlarında önemli kayıplara yol açan nohut antraknozu [Ascochyta rabiei (Pass.) Labr.] hastalığına karşı abiyotik aktivatör olarak Bion MX 44 (%4 Acibenzolar-S-Methyl %40 Metalaxyl-M)'ün etkinliği araştırılmıştır. Denemede Bellis (Boscalid %25 + Pyraclostrobin), Canprin 35 DS (Metalaxyl), aktivatör olarak Bion MX 44 (0.1, 0.3, 0.5), Yerel çeşit (duyarlı), Azkan (tolerant) nohut çeşitleri kullanılmıştır. Denemeler 2017 yılında Kütahya'nın Gediz ve Şaphane ilçelerinde tarla koşullarında tesadüf bloklarında bölünmüş parsel deneme desenine göre 4 tekerrürlü olarak yürütülmüştür. İlk ilaçlamaya tohumun tarla çıkışından sonra bitki boyu ortalama 20-25 cm olduğunda başlanmış ve 10 gün arayla ikinci ilaçlama yapılmıştır. Son ilaçlamadan 21 gün sonra elde edilen sonuçlar 1-9 skalasına göre değerlendirilmiştir. Kütahya'nın Gediz ve Şaphane ilçelerinde Azkan (tolerant) ve Yerel (duyarlı) çeşitte Ascochyta rabiei'ya karşı en yüksek etki Bion MX 44 0.5 mM ile elde edilirken bunu Bellis ve Bellis + Bion MX 44 0.3 mM izlemiştir. Duyarlı bir çeşit olan Yerel çeşitte nohut antraknoz hastalığı gözlense bile kontrol bitkiler ile karşılaştırıldığında Bion MX 44 uygulamasının 0.5 mM dozunun hastalığı kısmen baskıladığı belirlenmiştir. Ayrıca, farklı dozlarda uygulanan Bion MX 44 0.5, 0.3 ve 0.1 mM uygulamasında Azkan nohut çeşidinde Bion MX dozu arttıkça protein miktarında artış tespit edilmiştir. Sonuç olarak tolerant nohut çeşidiyle gerek pozitif bulguların elde edilmesi gerekse çevre dostu olması sebebiyle Bion MX 44'ün 0.5 mM dozunun nohut bitkisinde antraknoza karşı kullanılmasının yararlı olacağı kanısına varılmıştır. Anahtar kelimeler: Ascochyta rabiei, %4 Acibenzolar-S-Methyl, Nohut, Total protein miktarı, Uyarılmış dayanıklılık Determination of the Effectiveness of the Abiotic Activator Bion MX 44 (4% Acibenzolar-S-Methyl+40% Metalaxyl-M) Against Chickpea Antrachnose [(Ascochyta rabiei (Pass. Labr.)] in the Land Conditions Abstract The aim of this study was to investigate the effectiveness of Bion MX 44 (4%Acibenzolar-S-methyl 40% Metalaxyl-M) against chickpea anthracnose [Ascochyta rabiei Pass.) Labr.] disease which caused significant losses in chickpea plantation areas in Turkey. Bellis Araştırma Makalesi / Research Article
The oxidative burst, the generation of reactive oxygen species (ROS) in response to microbial pathogen attack, is a ubiquitous early part of the resistance mechanisms of plant cells. It has also become apparent from the study of a number of plant–pathogen interactions and those modelled by elicitor treatment of cultured cells that there may be more than one mechanism operating. However, one mechanism may be dominant in any given species. NADPH oxidases have been implicated in a number of systems and have been cloned and characterized. However, the enzyme system which is the major source of ROS in French bean ( Phaseolus vulgaris ) cells treated with a cell wall elicitor from Colletotrichum lindemuthianum , appears to be dependent on an exocellular peroxidase. The second component, the extracellular alkalinization, occurs as a result of the Ca ²⁺ and proton influxes and the K ⁺ efflux common to most elicitation systems as one of the earliest responses. The third component, the actual reductant/substrate, has remained elusive. The low molecular weight compound composition of apoplastic fluid was compared before and after elicitation. The substrate only becomes available some min after elicitation and can be extracted, so that by comparing the profiles by LC‐MS it has been possible to identify possible substrates. The mechanism has proved to be complex and may involve a number of low molecular weight components. Stimulation of H 2 O 2 production was observed with saturated fatty acids such as palmitate and stearate without concomitant oxylipin production. This biochemical evidence is supported by immunolocalization studies on papillae forming at bacterial infection sites that show the peroxidase isoform present at sites of H 2 O 2 production revealed by cerium chloride staining together with the cross‐linked wall proteins and callose and callose synthase. The peroxidase has been cloned and expressed in Pichia pastoris and has been shown to catalyse the oxidation reaction with the same kinetics as the purified enzyme. Furthermore, Arabidopsis plants transformed heterologously using the French bean peroxidase in antisense orientation have proved to be highly susceptible to bacterial and fungal pathogens. Thus it is possible that Arabidopsis is another species with the potential to mount an apoplastic oxidative burst and these transformed plant lines may be useful to identify the peroxidase that is responsible.
Transgenic tobacco deficient in the H2O2-removing enzyme catalase (Cat1AS) was used as an inducible and noninvasive system to study the role of H2O2 as an activator of pathogenesis-related (PR) proteins in plants. Excess H2O2 in Cat1AS plants was generated by simply increasing light intensities. Sustained exposure of Cat1AS plants to excess H2O2 provoked tissue damage, stimulated salicylic acid and ethylene production, and induced the expression of acidic and basic
PR proteins with a timing and magnitude similar to the hypersensitive response against pathogens. Salicylic acid production
was biphasic, and the first peak of salicylic acid as well as the peak of ethylene occurred within the first hours of high
light, which is long before the development of tissue necrosis. Under these conditions, accumulation of acidic PR proteins
was also seen in upper leaves that were not exposed to high light, indicating systemic induction of expression. Short exposure
of Cat1AS plants to excess H2O2 did not cause damage, induced local expression of acidic and basic PR proteins, and enhanced pathogen tolerance. However,
the timing and magnitude of PR protein induction was in this case more similar to that in upper uninfected leaves than to
that in hypersensitive-response leaves of pathogen-infected plants. Together, these data demonstrate that sublethal levels
of H2O2 activate expression of acidic and basic PR proteins and lead to enhanced pathogen tolerance. However, rapid and strong activation
of PR protein expression, as seen during the hypersensitive response, occurs only when excess H2O2 is accompanied by leaf necrosis.
1 Although most theories on plant defence assume that costs will result from the production and maintenance of defensive traits, studies on the costs of induced defence against pathogens are comparatively rare.
2 We focus on fitness costs resulting from the chemical induction of systemic acquired resistance (SAR), a rather unspecific form of defence, which can be induced by and is effective against a broad spectrum of bacteria, fungi and viruses.
3 We used a model system in which we treated wheat plants that were protected against fungi by ‘traditional’ fungicides with BION® (a benzothiadiazole which induces pathogen resistance). Treated plants were therefore compelled to invest in defence without gaining any profit from the induction.
4 Treated plants achieved lower biomass than untreated controls, and developed fewer shoots and ears and therefore produced fewer seeds. The effects were most pronounced in plants that suffered from a shortage of nitrogen, and were observed only when pathogen resistance was induced during lateral shoot production. Later treatment revealed no significant effects.
5 We discuss whether the differences between treated and control plants can be interpreted as a consequence of allocation costs. Such costs could result from metabolic competition between processes involved in plant growth and the synthesis of defence‐related compounds.
Major advances have been made in recent years in clarifying the molecular properties of the cytochrome P-450 system. These advances stem, in practical terms, from the generally recognized importance of cytochrome P-450 in the metabolism of drugs and in the bioactivation of xenobiotics to toxic products. The fascinating multiplicity and differential regulation of cytochrome P-450 isozymes, and their ability to catalyze extraordinarily difficult chemical transformations, have independently drawn many chemists and biochemists into the P-450 circle. Progress in the field, from a technical point of view, has been propelled by the de velopment of reliable procedures for the purification of membrane-bound enzymes, by the growing repertoire of molecular biological techniques, and by the development of chemical models that mimic the catalytic action of P-450. As a result, our understanding of the P-450 system is moving from the descriptive, pharmacological level into the tangible realm of atomic detail. The rapid progress and multidisciplinary character of the cytochrome P-450 field, which cuts across the lines that traditionally divide disciplines as diverse as inorganic chemistry and genetics, have created a need for an up-to-date evaluation of the advances that have been made. It is hoped that this book, with its molecular focus on the cytochrome P-450 system, will alleviate this need. The authors of the individual chapters have strived to emphasize recent results without sacrificing the background required to make their chapters comprehensible to informed nonspecialists.
Extracellularly secreted peroxidases in cell suspension culture of tobacco ( Nicotiana tabacum L. cv. Bright Yellow‐2, cell line BY‐2) catalyse the salicylic acid (SA)‐dependent formation of active oxygen species (AOS) which, in turn, triggers an increase in cytosolic Ca ²⁺ concentration. Addition of horseradish peroxidase (HRP) to tobacco cell suspension culture enhanced the SA‐induced increase in cytosolic Ca ²⁺ concentration, suggesting that HRP enhanced the production of AOS. The mechanism of peroxidase‐catalysed generation of AOS in SA signalling was investigated with chemiluminescence sensitive to AOS and electron spin resonance (ESR) spectroscopy, using the cell suspension culture of tobacco, and HRP as a model system of peroxidase reaction. The results showed that SA induced the peroxidase inhibitor‐sensitive production of superoxide and H 2 O 2 in tobacco suspension culture, but no production of hydroxy radicals was detected. Similar results were obtained using HRP. It was also observed that SA suppressed the H 2 O 2 ‐dependent formation of hydroxy radicals in vitro . The results suggest that SA protect the cells from highly reactive hydroxy radicals, while producing the less reactive superoxide and H 2 O 2 through peroxidase‐catalysed reaction, as the intermediate signals. The formation of superoxide was followed by that of H 2 O 2 , suggesting that superoxide was converted to H 2 O 2 . In addition, it was observed that superoxide dismutase‐insensitive ESR signal of monodehydroascorbate radical was induced by SA both in the tobacco suspension culture and HRP reaction mixture, suggesting that SA free radicals, highly reactive against ascorbate, were formed by peroxidase‐catalysed reactions. The formation of SA free radicals may lead to subsequent monovalent reduction of O 2 to superoxide.
Microbial elicitors or attempted infection with an avirulent pathogen strain causes the rapid production of reactive oxygen intermediates. We report here that H2O2 from this oxidative burst not only drives the cross-linking of cell wall structural proteins, but also functions as a local trigger of programmed death in challenged cells and as a diffusible signal for the induction in adjacent cells of genes encoding cellular protectants such as glutathione S-transferase and glutathione peroxidase. Thus, H2O2 from the oxidative burst plays a key role in the orchestration of a localized hypersensitive response during the expression of plant disease resistance.
Peroxidases are enzymes that catalyze the oxidation of inorganic and organic substrates at the expense of a hydroperoxide—H2O2, alkyl hydroperoxides, or acyl hydroperoxides1. The actual function of the peroxidase may be to
(1)
reduce a hydroperoxide or oxidize a particular substrate and, therefore, they are quite versatile and widespread. Most peroxidases contain ferriprotoporphyrin IX as their prosthetic group and “peroxidase activity” is a common characteristic of many hemeproteins and simple heme complexes.2–4 Table I lists some of the better-characterized peroxidases, their properties, and functions. The discovery that cytochrome P-450 exhibits peroxidase activity and utilizes hydroperoxides to catalyze aliphatic hydroxylation and olefin epoxidation in the absence of NADPH and NADPH-cytochrome P-450 reductase provided a new perspective on its mechanisms.5–7 Much of the present understanding of the catalytic cycle of P-450 evolved from experiments designed to compare its peroxidase activity to those of classical peroxidases such as horseradish peroxidase (HRP). This chapter attempts to compare and contrast the principal features of the interaction of peroxidases with hydroperoxides. It is not intended to be comprehensive because, in the words of the author of a previous review “it is unlikely that any reviewer would profess an adequate expertise in the disciplines, ranging from genetics to chemical physics, which a comprehensive discussion would require.”8 The reader can consult any of a number of excellent reviews2,8–C18 or leading references cited herein.
The catalytic cycle of cytochrome P-450 (see Chapter 7) traverses three steps that are particularly vulnerable to inhibition: (1) the binding of substrates, (2) the binding of molecular oxygen subsequent to the first electron transfer, and (3) the catalytic step in which the substrate is actually oxidized. This chapter focuses on inhibitors that act at one of these three steps. Inhibitors that act at other steps in the catalytic cycle, such as quinones that interfere with the electron supply to the hemeprotein by accepting electrons directly from cytochrome P-450 reductase,1–3 are not discussed here.
Specificity of the interactions between plants and pathogens is a very comprehensive phenomenon with complicated hierarchy on different levels of biological organization. Elucidation of this phenomenon is an important task of contemporary plant pathology, including physiological and biochemical aspects. To restrict the development of pathogens, the plants formed many defense mechanisms. Enzymes play one of the most important roles in the infection process and pathogenesis. Our recent understanding in this area is quite limited. Enhanced production of some enzymes is one of the crucial processes in plant defense. A relatively limited number of enzymes (e. g., cutinase, cellulase, xylanase, pectinase, peroxidase, β-1,3-glucanase, chitinase, catalase, amine oxidase and proteases) have been studied until now in relation to the infection process and pathogenesis in plants. These enzymes occur frequently in many isoforms and are involved in synthesis of defense substances or have a direct antimicrobial activity. Involvement of various enzymes during the pathogenesis and their role in different stages of disease development is analyzed, as well as practical usage of these data to select the markers for disease resistance selection.
Life is highly competitive, but it is not necessary for an organism to compete successfully under a broad range of environmental conditions. It may require a highly specific environment or, lacking this, may create a suitable environment. The environment may be micro or macro and it may be outside or within living organisms. The ability to compete successfully is constantly challenged, and one factor in successful competition is the ability to resist damage from invading infectious agents. Resistance is based upon the ability to maintain or create an environment that is unsuitable for harmful infectious agents. This is equally valid for a complex organism such as man and for single-celled algae.
The effect of chitosan on the growth, morphology, and ultrastructure of Fusarium oxysporum f. sp. radicis-lycopersici was investigated. Chitosan was found to inhibit the radial growth of F. o. radicis-lycopersici with an optimal effect at concentrations ranging from 3 to 6 mg/ml. Light microscope observations showed that chitosan induced morphological changes, including hyphal swelling and distortion. Ultrastructural changes observed in chitosan-treated cells included alteration of the plasma membrane and pronounced aggregation of the cytoplasm. An additional reaction was the abnormal deposition of an amorphous material that contained large amounts of chitin, as shown by its strong affinity to wheat germ agglutinin. Chitosan stimulated the activities of both beta-1,3-glucanase and chitosanase but did not affect chitinase and chitin deacetylase activities. The possible modes of action of chitosan are discussed relative to morphological and ultrastructural alterations, abnormal depositions of wall-like material, and the enhanced enzymatic activities.
Foliar application of a mixture of methionine (1 mM) and riboflavin (26.6 μM) reduced the severity of powdery mildew [Sphaerotheca macularia (Wallr. ex Fr.) Jacz. f. sp. fragariae] infection in 'Earligiow' strawberry (Fragaria x ananassa Duch.) plants. Efficacy of this mixture on controlling powdery mildew infection was enhanced by supplements of copper, iron, and surfactants [sodium dodecyl sulfate (SDS), Triton X-100, Tween-20, or oxyalkylenemethylsiloxane (Silwet L-77)]. Free-radical scavengers (n-propyl gallate, thiourea) and antioxidants (α-tocopherol, β-carotene) reduced the efficacy of this mixture. Plants treated with a mixture of riboflavin (26.6 μM), D,L-methionine (1 mM), copper sulfate pentahydrate (1 mM), and surfactants (SDS or Silwet L-77 at concentrations of 0.05% to 0.1%) showed a decrease in powdery mildew infection. Results of this study suggest that treatment with a mixture of methionine and riboflavin is beneficial to strawberry plants and may serve as an alternative to fungicides for controlling powdery mildew.
Three distinct basic 14-kD proteins, P14a, P14b, and P14c, were isolated from tomato (Lycopersicon esculentum Mill. cv Baby) leaves infected with Phytophthora infestans. They exhibited antifungal activity against P. infestans both in vitro (inhibition of zoospore germination) and in vivo with a tomato leaf disc assay (decrease in infected leaf surface). Serological cross-reactions and amino acid sequence comparisons showed that the three proteins are members of the PR-1 group of pathogenesis-related (PR) proteins. P14a and P14b showed high similarity to a previously characterized P14, whereas P14c was found to be very similar to a putative basic-type PR-1 from tobacco predicted from isolated DNA clones. This protein, named PR-1 g, was purified from virus-infected tobacco (Nicotiana tabacum Samsun NN) leaves and characterized by amino acid microsequencing, along with the well-known acidic tobacco PR-1a, PR-1b, and PR-1c. The various tomato and tobacco PR-1 proteins were compared for their biological activity and found to display differential fungicidal activity against P. infestans in both the in vitro and in vivo assays, the most efficient being the newly characterized tomato P14c and tobacco PR-1g.
Systemic acquired resistance (SAR) is a broad-spectrum resistance in plants that involves the upregulation of a battery of pathogenesis-related (PR) genes. NPR1 is a key regulator in the signal transduction pathway that leads to SAR. Mutations in NPR1 result in a failure to induce PR genes in systemic tissues and a heightened susceptibility to pathogen infection, whereas overexpression of the NPR1 protein leads to increased induction of the PR genes and enhanced disease resistance. We analyzed the subcellular localization of NPR1 to gain insight into the mechanism by which this protein regulates SAR. An NPR1–green fluorescent protein fusion protein, which functions the same as the endogenous NPR1 protein, was shown to accumulate in the nucleus in response to activators of SAR. To control the nuclear transport of NPR1, we made a fusion of NPR1 with the glucocorticoid receptor hormone binding domain. Using this steroid-inducible system, we clearly demonstrate that nuclear localization of NPR1 is essential for its activity in inducing PR genes.
Fungicide action is generally assumed to be dependent on an antibiotic effect on a target pathogen, although a role for plant defense mechanisms as mediators of fungicide action has not been excluded. Here, we demonstrate that in Arabidopsis, the innate plant defense mechanism contributes to the effectiveness of fungicides. In NahG and nim1 (for noninducible immunity) Arabidopsis plants, which normally exhibit increased susceptibility to pathogens, the fungicides metalaxyl, fosetyl, and Cu(OH)2 are much less active and fail to control Peronospora parasitica. In contrast, the effectiveness of these fungicides is not altered in Arabidopsis mutants defective in the ethylene or jasmonic acid signal transduction pathways. Application of the systemic acquired resistance activator benzothiadiazole (BTH) in combination with these fungicides results in a synergistic effect on pathogen resistance in wild-type plants and an additive effect in NahG and BTH-unresponsive nim1 plants. Interestingly, BTH treatment normally induces long-lasting pathogen protection; however, in NahG plants, the protection is transient. These observations suggest that BTH treatment can compensate only partially for an impaired signal transduction pathway and support the idea that pathogen defense mechanisms are under positive feedback control. These observations are strikingly reminiscent of the reduced efficacy of antifungal agents in immunocompromised animals.
Allene oxide synthase (AOS) mediates the conversion of lipoxygenase-derived fatty acid hydroperoxides to unstable allene epoxides, which supply the precursors for the synthesis of the phytohormone jasmonic acid (JA). In this study the characterization of AOS gene expression in flax (Linum usitatissimum) is reported. AOS was constitutively expressed in different organs of flax plants. Additionally, AOS gene expression was enhanced after mechanical wounding in both the directly damaged leaves and in the systemic tissue located distal to the treated leaves. This wound-induced accumulation of AOS required the de novo biosynthesis of other unknown proteins involved in the signaling pathway modulating wound-induced AOS gene expression. Furthermore, the wound-induced AOS mRNA accumulation was correlated with the increase in the levels of JA. Both JA and its precursor, 12-oxo-phytodienoic acid, activated AOS gene expression in a dose-dependent manner. Thus, JA could activate its own biosynthetic pathway in flax leaves. Moreover, neither salicylic acid (SA) nor aspirin influenced AOS enzymatic activity. It is interesting that pretreatment with SA or aspirin inhibited wound-induced accumulation of AOS transcripts. These results suggest that a potent inhibition of JA biosynthetic capacity in leaves can be affected by SA or aspirin at the level of AOS gene expression.
Root colonization of tobacco (Nicotiana tabacum L. 'Xanthi-nc') by the pathogen Phytophthora parasitica var. nicotianae was studied by electron microscopy. Gold-complexed probes were used for the localization of pectin and cellulose. The epidermis was colonized from 24 to 48 h after inoculation, and the cortex appeared entirely colonized by the time the pathogen reached the paratracheal parenchyma (96 h after inoculation). The fungus did not penetrate the xylem vessels. Colonization of the root tissues was associated with changes, including alteration of primary cell walls and breakdown of middle lamella matrices. The pattern of pectin distribution, as revealed by the Aplysia gonad lectin-gold complex, indicated that the fungus produced pectic enzymes that diffused extracellularly. The release of pectic fragments and the accumulation of pectin molecules at specific sites such as the intercellular spaces were frequently detected. Cellulose was localized with an exoglucanase-gold complex, which showed that the fungus could produce cellulases but to a lesser extent than pectinases. Various host reactions were observed during pathogen ingress into the root; these reactions included the filling of intercellular spaces with a pectin-rich fibrillar material, the plugging of sieve pores and plasmodesmata with an amorphous material, and the occlusion of noninvaded xylem vessels by a coating material. Although highly susceptible to P. p. nicotianae, N. tabacum 'Xanthi-nc' appears capable of using a complex array of defense reactions. The possibility of sensitizing this cultivar to respond more rapidly to pathogen attack is raised.
A number of chemical and biological agents are known as inducers of systemic acquired resistance (SAR) to tobacco mosaic virus (TMV) in tobacco plants. In the present study, a local spray application of the non-protein amino acid DL-β-aminobutyric acid (BABA) was effective in enhancing resistance to TMV in tobacco plants containing the N gene. In contrast, the isomer α-aminobutyric acid (AABA) showed a much lower activity whereas γ-aminobutyric acid (GABA) was completely inactive, indicating a strong isomer specificity of aminobutyric acid in triggering enhanced virus resistance.Rapid cell death was detected in tobacco leaf tissues after foliar application of BABA, subsequently resulting in the development of macroscopically visible, necrotic lesions. BABA-induced cell death was associated with the rapid generation of superoxide and hydrogen peroxide. As further consequences, the occurrence of lipid peroxidation in treated tissues, a local and systemic increase of salicylic acid (SA) levels and the expression of PR-1a, a molecular marker of SAR in tobacco, could be observed. None of these responses was detectable after treatment with GABA.Enhancement of virus resistance by BABA was found to be strictly dependent on SA-mediated signal transduction since it could not be detected in salicylate hydroxylase (nahG) expressing transgenic tobacco plants. These findings suggest that in tobacco, primary processes triggered by foliar application of BABA, resemble those initiated by microbes during a hypersensitive response (HR) that result in SAR activation.
Benzothiadiazole (BTH) is a recently described synthetic inducer of plant defenses. Molecular and genetic studies have suggested that it acts as a functional analogue of the endogenous defense signalling molecule salicylic acid (SA). Here we demonstrate that BTH inhibits catalase and ascorbate peroxidase, two potential targets through which SA has been proposed to act. BTH was found to be a considerably better inhibitor of catalase than SA. This is consistent with its greater potency for inducing the expression of defense-related genes, such as the acidic PR-1, PR-2 and PR-3 genes. In addition, induction of PR-1 gene expression by either BTH or SA was suppressed by antioxidants. These results suggest that changes in H2O2 levels or the cellular redox status may be involved in the BTH/SA-mediated activation of certain defense responses.
Salicylic acid (SA) is a natural signal molecule which plays an important role in plant defense responses against pathogen infection. Previous work has demonstrated that catalase may be involved in the mechanism of SA action. Recently, SA has been shown to inhibit catalase by serving as a one electron-donating substrate for its peroxidative reaction. One of the likely by-products of this interaction is a SA free radical. Since free radicals are potent inducers of lipid peroxidation, SA and its analogues were tested for their ability to induce lipid peroxidation in tobacco cell cultures. SA and its biologically active analogues, which increase PR gene expression, enhance disease resistance and also inhibit catalase, induced accumulation of lipid peroxidation products. Inactive analogues did not. Exogenous application of lipid peroxides induced PR-1 gene expression. Furthermore, the induction of PR-1 genes by SA was inhibited by diethyldithiocarbamic acid, a compound that converts lipid peroxides into their hydroxyl derivatives. We suggest that the induction of lipid peroxidation by a SA radical may be involved in the action of SA and that one or more of the lipid peroxidation products may mediate signal transduction leading to PR-1 expression.
Plants can be systemically immunized against diseases caused by fungi, bacteria, and viruses by restricted infection with fungi, bacteria, or viruses. Immunization followed by a booster inoculation protects cucumber, watermelon, and muskmelon throughout the season, and a single immunization protects cucumber against at least 10 unrelated diseases.
The review deals with the chemistry concerning the processes of mild and selective oxidation of alkanes and cycloalkanes by using synthetic iron complexes as catalytic systems. These cover a number of coordinated species of iron ions including the so-called Gif systems up to the polydentated Que’s models, aimed to mimic or emulate the non-haem enzymatic oxidation of alkanes. Special attention is paid to the mechanisms proposed by the various Authors and to the arguments set out for and against the free-radical interpretation to account for the activation of the CH bonds.The schemes of the free-radical chemistry of Fenton reagents in the presence of organic substrates are quoted as a reference basis for the discussion.
The activities of 47 substituted 1,2,3-benzothiadiazoles as inhibitors of microsomal epoxidation and/or hydroxylation in enzyme preparations from rat liver or armyworm (Spodoptera eridania) gut have been evaluated. Many were found to be effective inhibitors of microsomal oxidation, the most active being the 6-butyl and 6-propoxy derivatives with I50 values of 4.9 × 10−7 and 7.0 × 10−7M, respectively, for the epoxidation reaction. Regression analyses have established that activity of the 5-, 6-, and 5,6-substituted compounds can be satisfactorily described in equations in terms of π2, π, and σ whereas that of the 4-substituted derivatives depends on π and the steric parameter E8.
Hypocotyls from etiolated cucumber (Cucumis sativus L.) seed- lings were gently abraded at their epidermal surface, and cut seg- ments were used to study the rapid and transient elicitation of H,O, by ergosterol, chitosan, mastoparan, and a polymeric fungal elici- tor. Freshly abraded segments were only barely competent for any H,O, production, but they developed this competence subsequent to abrasion. This process was enhanced by 2,6-dichloroisonicotinic acid and salicylic acid, which induced acquired resistance to fungal penetration in the epidermal cells. Enhancement of competence induction by salicylic acid was also evident for spontaneous H,O, production and differed in degree for the various elicitors, indicat- ing that mainly the enzyme complex producing H,O,, but also other components of the elicitation system, improved. Ergosterol, chi- tosan, and fungal elicitor also rendered the segments refractory to a second stimulation by the same compound, whereas mastoparan was inactive in this respect. The four elicitors also differed markedly in their ability to diminish or enhance H,O, production by a second treatment with a different elicitor, indicating that severa1 sites of the H,O, elicitation system are subject to short-term regulation. ~~~~~~
Several commercial and experimental herbicides
such as p-nitrodiphenyl ethers, oxadiazoles, and cyclic imides inhibit protoporphyrinogen IX oxidase (Protox), the enzyme that converts protoporphyrinogen IX to protoporphyrin IX (Proto). This leads to uncontrolled autooxidation of the substrate and results in accumulation of Proto. Blockage of the porphyrin pathway at this site inhibits synthesis of both chlorophylls and heme. Heme is a feedback regulator of the porphyrin pathway. Thus, inhibition of Protox also deregulates the pathway, causing increased carbon flow to the accumulating pool of Proto. Proto is a potent photosensitizer that generates high levels of singlet oxygen in the presence of molecular oxygen and light. In plants treated with these herbicides, damage is light dependent and closely correlated with the level of Proto that accumulates. Proto accumulation is apparently largely extraplastidic, resulting in rapid photodynamic damage to the plasmalemma and tonoplast. After high levels of Proto accumulate in response to these herbicides, protochlorophyllide (PChlide) levels can increase also; however, Proto appears to be the primary photodynamic pigment responsible for the herbicidal activity. Additional index words. Acifluorfen, chlorophyll synthesis, oxadiazon, peroxidizing herbicides, photobleaching herbi- cides, porphyrin synthesis, protoporphyrin IX.
Insecticide synergists such as the 1,3-benzodioxoles, the 1,2,3-benzothiadiazoles and the phenyl-2-propynyl ethers inhibit the epoxidation of aldrin to dieldrin by a modified Fenton's reagent (H2O2, Fe2+, EDTA and bovine serum albumin). Inhibition appears to result from the ability of the synergists to compete with aldrin for the OH· radicals generated by the system, and as a result of this interaction the synergists are themselves chemically modified. In the case of the 1,3-benzodioxoles the reaction results in the formation of the corresponding catechols and the rate at which this occurs correlates favorably with the ability of the synergist to inhibit aldrin epoxidation in the system. Although a number of nonenzymatic systems generating radical species other than OH· are also capable of aldrin epoxidation, these are not affected by the presence of insecticide synergists and the synergists are not themselves modified by these systems. The possible relevance of these results to the mode of action of synergists is discussed.
Systemic Acquired Resistance (SAR) is an inducible resistance mechanism in plants that, together with other defence mechanisms, provides broad-spectrum and long-lasting disease control. With novel screening techniques the benzo[1,2,3]thiadiazole-7-carboxylic acid derivatives have been identified as a new class of chemicals which stimulate the plant's own defence mechanisms. The synthesis and biological activities of various benzo[1,2,3]thiadiazoles and related structures are described. S-Methyl benzo[1,2,3]thiadiazole-7-carbothioate is the first synthetic chemical ‘plant activator’ that has been developed for this novel disease control concept. © 1997 SCI
A short and efficient synthesis of a series of the title compounds is presented starting with methylenebutanedioic acid and thioacetic acid. Using the Hurd–Mori reaction in the key step, the optimised reaction sequence allows the large-scale preparation of this new type of plant activator in a few steps with a high overall yield. Additional functionalisation of the 5-position via directed ortho-lithiation methodology is also described. © 1998 Society of Chemical Industry
Certain plant species that were previously infected by pathogenic organisms subsequently develop a systemic resistance to further infection. This systemic acquired resistance can also be achieved by treatment with 2,6-dichloroisonicotinic acid. Although this chemical does not directly induce coumarin secretion in suspension-cultured cells of parsley (Petroselinum crispum), preincubation of the cultures with the compound greatly increases the subsequent induction of coumarin derivatives by a fungal elicitor, especially at low elicitor concentrations and in cell batches exhibiting a low response due to unknown variations in growth conditions. The effect appears to result from an increase in the sensitivity of the cells towards the elicitor, which causes enhanced transcription of genes coding for enzymes involved in coumarin synthesis. The enhanced transcriptional and translational activity is examplified by two specific mRNAs and the activity of phenylalanine ammonia lyase and S-adenosyl-l-methionine:xantho-toxol O-methyl transferase. Salicylic acid, which has been implicated as an endogenous signal substance in systemic acquired resistance, causes similar but less pronounced effects. The results suggest that both acids may act by inducing increased synthesis of unknown components of the signal perception or transmission pathway which are rate-limiting in untreated cells.
Elevated levels of salicylic acid (SA) are required for the induction of systemic acquired resistance (SAR) in plants. Recently, a salicylic acid-binding protein (SABP) isolated from tobacco was shown to have catalase activity. Based on this finding elevated levels of hydrogen peroxide (H2O2) were postulated to act as a second messenger of SA in the SAR signal transduction pathway. A series of experiments have been carried out to clarify the role of H2O2 in SAR-signaling. No increase of H2O2 was found during the onset of SAR. Induction of the SAR gene, PR-1, by H2O2 and H2O2-inducing chemicals is strongly suppressed in transgenic tobacco plants that express the bacterial salicylate hydroxylase gene, indicating that H2O2 induction of SAR genes is dependent on SA accumulation. Following treatment of plants with increasing concentrations of H2O2, a dose-dependent accumulation of total SA species was found, suggesting that H2O2 may induce PR-1 gene expression through SA accumulation. While the results do not support a role for H2O2 in SAR signaling, it is suggested that SA inhibition of catalase activity may be important in tissues undergoing a hypersensitive response.
Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), trade name Bion®, was used to induce resistance in bean cultivars Borlotto Nano Lingua di Fuoco (BLF), Borlotto Taylor, Cannellino, Cannellino Montalbano, Saxa and Top Crop, against rust caused by Uromyces appendiculatus. A single 0.3 mm BTH spray 7 days before inoculation was sufficient to fully control the disease in all the examined cultivars. As regards the more susceptible BLF, either a single treatment 14 days before inoculation, or three applications on the third, fifth and seventh day before inoculation, were equally effective to prevent infection. Histochemical and cytochemical investigations showed that BTH causes hydrogen peroxide (H2O2) accumulation in the treated tissues. H2O2 deposits were localized in situ for the first time in the apoplast of the leaf epidermis. No cell death was detected at BTH concentrations below the phytotoxicity threshold, suggesting that acquired resistance against bean rust is mainly related to the enhanced activity of anionic peroxidases, promoted by H2O2 accumulation, thereby leading to cell wall strengthening. This hypothesis is also supported by the long induction phase required to establish complete resistance.
Tobacco plants (cv. Kyl6) injected into the base of the stem with DL-3-aminobutyric acid or (R)-3-aminobutyric acid were strongly protected against a challenge inoculation with Peronospora tabacina the causative organism of blue mold. The S-enantiomcr of 3-aminobutyric acid, DL-2-aminobutyric acid, or 4-aminobutyric acid induced no protection against the disease. Injections with similar amounts of sodium salicylic acid (SA) or 2,6-dichloroisonicotinic acid (INA) resulted in moderate protection but those made with INA were phytotoxic. Resistance induced by 3-aminobutyric acids was expressed in the upper leaves as minute, chlorotic lesions on which the fungus failed to sporulate. 3-Aminobutyric acids were also effective when introduced as a petiole dip or a soil drench. 3-Aminobutyric acids had no effect on spore germination of P. tabacina nor on its penetration into tobacco leaves. SDS-PAGE analyses revealed enhanced levels of PR-proteins in SA and INA injected plants but not in 3-aminobutyric acids injected plants. On the other hand, PR-protein synthesis was enhanced by all these elicitors when applied as a foliar spray. Ethylene evolution was significantly higher from DL-2-aminobutyric acid-treated leaves as compared to leaves treated with 3-aminobutyric acids. It is proposed that 3-aminobutyric acids protect tobacco against blue mold via a mechanism not related to ethylene production nor PR-protein accumulation. The nature of this mechanism awaits elucidation.
Etiolated soybean hypocotyls (cultivar Altona) treated with the systemic fungicide metalaxyl [N-(2,6-dimethylphenyl)-N-(methyl-acetyl) alanine methyl ester] developed restricted brown lesions with high levels of the phytoalexin, glyceollin, when inoculated with zoospores of Phytophthora megasperma f. sp. glycinea (race 6, compatible). These responses were very similar to those in interactions of untreated hypocotyls with incompatible races. When hypocotyls were supplied with a mixture of metalaxyl, at marginally inhibitory concentrations, and glyphosate (N-phosphonomethylglycine), an inhibitor of the shikimic acid pathway, the effectiveness of the metalaxyl treatment was reduced, the lesions spread and glyceollin concentrations were lower. The effectiveness of metalaxyl added directly to the inoculum drop was also less in glyphosphate-treated hypocotyls than in control hypocotyls. Glyphosate did not affect the fungitoxicity of metalaxyl in in vitro growth assays. It is concluded that at marginally inhibitory concentrations host defence mechanisms contribute to metalaxyl activity. This is most probably due to glyceollin accumulation, but as levels frequently remained above ED90 values in spreading lesions and other aspects of host metabolism are known to be influenced by glyphosate, alternative explanations are possible. The possibility that the stimulation of host defence responses in metalaxyl-treated tissue may be due to inhibition of pathogen activities that suppress such responses in untreated tissues is discussed.
We have used an antisense expression technology inArabidopsisbased on the yeast GAL4/UAS transactivation system (Guyeret al.Genetics1998; 149:633–639) to reduce levels of protoporphyrinogen IX oxidase (PPO), the last common enzyme of the biosynthesis of the haem group and chlorophyll. Plants expressing the antisensePPOgene presented growth alterations and their leaves showed necrotic lesions that appeared similar to lesions characteristic of the pathogen-induced hypersensitive reaction, and seen in the so-called lesion-mimic mutants. Plants expressing the antisense gene also had high endogenous salicylic acid levels, constitutive expression of thePR-1gene, and were resistant toPeronospora parasitica, consistent with the activation of systemic acquired resistance (SAR). Treatment of wild-type plants with sublethal concentrations of herbicides that inhibit PPO also induced defence responses that conferred enhanced tolerance toP. parasitica. This effect was not observed in NahG andnim1plants, which are compromised in their ability to activate SAR. These results demonstrate that genetic or chemical disruption of a metabolic pathway can lead to the induction of a set of defence responses including activation of SAR.
Systemic acquired resistance (SAR) is a pathogen-induced disease resistance response in plants that is characterized by broad spectrum disease control and an associated coordinate expression of a set of SAR genes. Benzo(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) is a novel synthetic chemical capable of inducing disease resistance in a number of dicotyledenous and monocotyledenous plant species. In this report, the response of tobacco plants to BTH treatment is characterized and the fact that it controls disease by activating SAR is demonstrated. BTH does not cause an accumulation of salicylic acid (SA), an intermediate in the SAR signal transduction pathway. As BTH also induces disease resistance and gene expression in transgenic plants expressing the nahG gene, it appears to activate the SAR signal transduction pathway at the site of or downstream of SA accumulation. BTH, SA and TMV induce the PR-1a promoter using similar cis-acting elements and gene expression is blocked by cycloheximide treatment. Thus, BTH induces SAR based on all of the physiological and biochemical criteria that define SAR in tobacco.
Several lines of evidence suggest that salicylic acid (SA) is an endogenous signal for the activation of several plant defense responses, including the expression of genes encoding pathogenesis-related (PR) proteins such as the acidic PR-1 proteins. During recent years, studies have suggested that interaction of SA with catalase and ascorbate peroxidase leads to two signals in tobacco - elevated H2O2 levels and lipid peroxides. However, to date, relatively little is known about the molecular and biochemical mechanisms that mediate transduction beyond these signals or through other SA-effector proteins. Using protein kinase and phosphatase inhibitors, this study demonstrates that PR-1 gene induction can be mediated by dephosphorylation of serine/threonine residue(s) of two or more unidentified phosphoproteins. The protein phosphatase inhibitors, okadaic acid and calyculin A blocked SA-mediated induction of PR-1 genes, implying the involvement of a phosphoprotein downstream of SA. The protein kinase inhibitors K-252a and staurosporine induced PR-1 gene expression. PR-1 gene induction by K-252a was suppressed by okadaic acid. Surprisingly, this induction was also suppressed in NahG transgenic tobacco plants which convert SA to catechol. Moreover, K-252a stimulated production of SA and its glucoside, suggesting that another phosphoprotein acts upstream of SA. Taken together, these results suggest that there are two (or more) phosphoproteins which function in the same signal transduction pathway leading to PR-1 gene induction. The SA-inducible acidic PR-2 genes were similarly affected by the inhibitors, while the genes for actin and phenylalanine ammonia lyase were not.
The analysis of allene oxide synthase (AOS) mRNA levels, of AOS polypeptide levels and specific enzymatic activities, as well as the quantitative determination of the levels of the octadecanoids cis-12-oxophytodienoic acid (cis-OPDA) and JA following a number of treatments, has shown that AOS is a regulatory site in octadecanoid biosynthesis in A. thaliana. AOS activity, mRNA and polypeptide levels are increased in wounded leaves locally and systemically. The methyl esters of OPDA or JA (OPDAME, JAME) and coronatine, are strong inducers of AOS mRNA, polypeptide and enzymatic activity. Ethephon also induces AOS activity. Salicylic acid (SA) was an inducer of AOS activity while abscisic acid (ABA) had no effect. At the level of the octadecanoids, the consequences of induction of AOS by the different inducers were distinctly different, depending on the nature of the inducer. Wounding led to a strong, bi-phasic accumulation of JA in wounded leaves and to a less pronounced increase in JA-levels in systemic leaves. Levels of OPDA changed very little in wounded leaves and remained constant or even declined in systemic leaves. Ethephon treatment resulted in a strong, transient increase in JA-levels kinetically coinciding with the second, more pronounced peak in wound-induced JA. In SA-treated leaves, the level of cis-OPDA increased throughout the experimental period while there was no effect on JA levels during the first 24 h following treatment and only a slight accumulation after 48 h. Clearly, mechanisms in addition to regulating substrate (LA) availability and the regulation of AOS accumulation control the output of the octadecanoid pathway.
Numerous studies argue that salicylic acid (SA) is an important component of the plant signal transduction pathway(s) leading to disease resistance. The discovery that the SA-binding protein is a catalase, whose activity is blocked by SA, led to the proposal that one of SA’s modes of action is to inhibit this H2O2-degrading enzyme and thus elevate H2O2 levels. To test this model, an attempt was made to mimic the action of SA by reducing the synthesis of catalase using antisense RNA technology. Analyses of transgenic tobacco plants that expressed the tobacco catalase 1 (cat1) or catalase 2 (cat2) gene in an antisense orientation indicate that there is no correlation between modest to high levels of reduction in catalase activity and activation of plant defenses such as pathogenesis-related (PR)-1 protein synthesis. However, three independent antisense catalase transgenic plants (ASCAT1 Nos 16, 17, and 28), which exhibited the most severe reduction in catalase activity (∼90% or more), developed chlorosis or necrosis on some of their lower leaves. These same leaves accumulated very high levels of PR-1 proteins and showed enhanced resistance to tobacco mosaic virus. Necrosis and elevated SA, which appear to result from severe depression of catalase levels, may be responsible for the induction of these defense responses.
Salicylic acid (SA) plays a central role as a signalling molecule involved in plant defense against microbial attack. Genetic manipulation of SA biosynthesis may therefore help to generate plants that are more disease-resistant. By fusing the two bacterial genes pchA and pchB from Pseudomonas aeruginosa, which encode isochorismate synthase and isochorismate pyruvate-lyase, respectively, we have engineered a novel hybrid enzyme with salicylate synthase (SAS) activity. The pchB-A fusion was expressed in Arabidopsis thaliana under the control of the constitutive cauliflower mosaic virus (CaMV) 35S promoter, with targeting of the gene product either to the cytosol (c-SAS plants) or to the chloroplast (p-SAS plants). In p-SAS plants, the amount of free and conjugated SA was increased more than 20-fold above wild type (WT) level, indicating that SAS is functional in Arabidopsis. P-SAS plants showed a strongly dwarfed phenotype and produced very few seeds. Dwarfism could be caused by the high SA levels per se or, perhaps more likely, by a depletion of the chorismate or isochorismate pools of the chloroplast. Targeting of SAS to the cytosol caused a slight increase in free SA and a significant threefold increase in conjugated SA, probably reflecting limited chorismate availability in this compartment. Although this modest increase in total SA content did not strongly induce the resistance marker PR-1, it resulted nevertheless in enhanced disease resistance towards a virulent isolate of Peronospora parasitica. Increased resistance of c-SAS lines was paralleled with reduced seed production. Taken together, these results illustrate that SAS is a potent tool for the manipulation of SA levels in plants.