Phytoalexin Induction Research Articles

Exploring the impact of sulfocalcic solution and water glass on the synthesis of phytoalexins and antifungal activity against Cladosporium cladosporioides

The passion fruit production in Brazil stands out as an activity of significant interest, especially for small-scale farmers, due to the short cycle of the crop, high economic returns, and wide demand in the consumer market, encompassing both fresh consumption and industrial processing. However, despite these attractions, the crop faces considerable challenges due to its notable susceptibility to diseases. In this context, this study was conducted with the purpose of evaluating the effectiveness of sulfocalcic solution and water glass in two distinct aspects: (i) in the in vitro control of Cladosporium cladosporioides, the causal agent of Passion Fruit Scab; and (ii) in the induction of phytoalexin synthesis in soybean cotyledons and bean hypocotyls. Four distinct treatments were implemented: T1 as a control, T2 with water glass (1.25%), T3 with sulfocalcic solution (3.03%), and T4 with sulfocalcic solution (0.5%). Results revealed that the 3.03% sulfocalcic solution demonstrated significant efficacy in controlling mycelial growth, followed by the treatment with the same substance at 0.5%. Treatments 3 and 4 were equally effective in inhibiting germination and sporulation, reaching approximately 90%, while water glass showed no efficacy in the conducted tests. Regarding the induction of phytoalexins, none of the treatments resulted in the accumulation of these compounds in bean hypocotyls; however, the 3.03% sulfocalcic solution induced synthesis in soybean cotyledons. These findings underscore the potential of sulfocalcic solution as an effective control agent against C. cladosporioides.

Synergistic induction of phytoalexins in Nicotiana attenuata by jasmonate and ethylene signaling mediated by NaWRKY70.

Production of the phytoalexins scopoletin and scopolin is regulated by jasmonate (JA) and ethylene signaling in Nicotiana species in response to Alternaria alternata, the necrotrophic fungal pathogen that causes brown spot disease. However, how these two signaling pathways are coordinated to control this process remains unclear. In this study, we found that the levels of these two phytoalexins and transcripts of their key enzyme gene, feruloyl-CoA 6'-hydroxylase 1 (NaF6'H1), were synergistically induced in Nicotiana attenuata by co-treatment with methyl jasmonate (MeJA) and ethephon. By combination of RNA sequencing and virus-induced gene silencing, we identified a WRKY transcription factor, NaWRKY70, which had a similar expression pattern to NaF6'H1 and was responsible for A. alternata-induced NaF6'H1 expression. Further evidence from stable transformed plants with RNA interference, knock out and overexpression of NaWRKY70 demonstrated that it is a key player in the synergistic induction of phytoalexins and plant resistance to A. alternata. Electrophoretic mobility shift, chromatin immunoprecipitation-quantitative PCR, and dual-luciferase assays revealed that NaWRKY70 can bind directly to the NaF6'H1 promoter and activate its expression. Furthermore, the key regulator of the ethylene pathway, NaEIN3-like1, can directly bind to the NaWRKY70 promoter and activate its expression. Meanwhile, NaMYC2s, important JA pathway transcription factors, also indirectly regulate the expression of NaWRKY70 and NaF6'H1 to control scopoletin and scopolin production. Our data reveal that these phytoalexins are synergistically induced by JA and ethylene signaling during A. alternata infection, which is largely mediated by NaWRKY70, thus providing new insights into the defense responses against A. alternata in Nicotiana species.

Salicylic Acid and Phytoalexin Induction by a Bacterium that Causes Halo Blight in Beans.

Pseudomonas savastanoi pv. phaseolicola is a bacterium that causes halo blight in beans. Different varieties of beans have hypersensitive resistance to specific races of P. savastanoi pv. phaseolicola. During hypersensitive resistance, also known as effector-triggered immunity (ETI), beans produce hormones that signal molecular processes to produce phytoalexins that are presumed to be antibiotic to bacteria. To shed light on hormone and phytoalexin production during immunity, we inoculated beans with virulent and avirulent races of P. savastanoi pv. phaseolicola. We then used mass spectrometry to measure the accumulation of salicylic acid (SA), the primary hormone that controls immunity in plants, and other hormones including jasmonate, methyljasmonate, indole-3-acetic acid, abscisic acid, cytokinin, gibberellic acid, and 1-aminocyclopropane-1-carboxylic acid. SA, but no other examined hormone, consistently increased at sites of infection to greater levels in resistant beans compared with susceptible beans at 4 days after inoculation. We then monitored 10 candidate bean phytoalexins. Daidzein, genistein, kievitone, phaseollin, phaseollidin, coumestrol, and resveratrol substantially increased alongside SA in resistant beans but not in susceptible beans. In vitro culture assays revealed that SA, daidzein, genistein, coumestrol, and resveratrol inhibited P. savastanoi pv. phaseolicola race 5 culture growth. These results demonstrate that these phytoalexins may be regulated by SA and work with SA during ETI to restrict bacterial replication. This is the first report of antibiotic activity for daidzein, genistein, and resveratrol to P. savastanoi pv. phaseolicola. These results improve our understanding of the mechanistic output of ETI toward this bacterial pathogen of beans.

Soybean seeds treated with vinasse and cassava wastewater

ABSTRACT This study aimed at evaluating organic by-products vinasse and cassava wastewater on the sanitary and physiological quality of soybean seeds. Sanity tests, phytoalexin induction and physiological qualities were performed, conducted in a completely randomized design. The sanity test was carried out in a 3 × 5 factorial scheme (two by-products: vinasse – V, cassava wastewater – C and the junction between them – V + C, in five concentrations: 0, 25, 50, 75 and 100%), with 8 repetitions/treatment. In the induction of phytoalexin, a factorial scheme (3 × 4) + 1 – two by-products and their junction, was adopted, with 4 concentrations (25, 50, 75 and 100%), plus an additional witness – with 5 repetitions/treatment, and for the physiological qualities 3 × 5 factorial scheme, described above, with four replicates/treatment. Cassava wastewater has large amounts of sugars, which may have favored the development of pathogens in this treatment. Vinasse had the highest capacity of inhibiting the genera Aspergillus, Cladosporium, and Penicillium, which was explained by the positive relationship between its concentrations and the induction of phytoalexin, being the most effective by-product in fungus control, at concentrations of 75 and 100% and without changing the physiological quality of seeds.

Seed Biopriming– A Review

There are various seed priming methods such as hydro priming, osmo priming, solid matrix priming, hormo-priming, chemo-priming, nutri-priming and biopriming being useful for enhancing the seed germination, seedling vigour and to overcome abiotic stress. Moreover to these advantages, of all priming methods only biopriming method gives an extra advantage of biotic stress management and thus gain special attention. Solubilisation or mobilization of soil macro and micronutrients, siderophore production, induction of plant growth promoting activities, induction of useful biochemicals, phytoalexin and defense-related enzymes and induced systemic resistance are the mechanisms involved in seed biopriming. Range of fungal or bacterial bio agents viz., Azotobacter, Rhizobium, Arthrobacter, Agrobacterium, Azospirillum, Enterobacter, Streptomyces, Bacillus, Burkholderia, Klebsiella, PSB, Pseudomonas fluorescence, Trichoderma viride, Trichoderma harzianum and Vesicular Arbuscular Mycorhiza, whether they are biofertilizer or biopesticide, may be useful as biopriming agents. Seed biopriming is useful in almost all the crops over the globe and is an eco-friendly substitute to chemical fungicides.

Hypersensitive Responses in Plants

Hypersensitivity is a natural defense for plants in response to a variety of pathogens such as viruses, bacteria, fungi and is characterized by a programmed cell death (PCD) accompanied by an accumulation of toxic compounds within the dead cell. Hypersensitive response (HR) is considered a biochemical reaction rather than a structural defense mechanism but can be seen with the naked eye or with a microscope. There are two types of hypersensitive responses: structural and induced. PCD is seen in both structural as well as in induced hypersensitive response. PCD is extreme resistance shown by the plants in which it kills its cells (suicidal death), upon a perception of the pathogen to deprive it of nutritional supply and stops its growth. Cell death plays a central role in innate immune responses in both plants and animals. Apoptosis and autophagy are physiological processes and two forms of biochemical PCD. Induced hypersensitive response comes out when the plant recognizes specific pathogen-produced signal molecules known as elicitors. Recognition of elicitors by the host plants activates an army of biochemical reactions. These reactions include an oxidative burst of reactive oxygen species (ROS), alterations in plant cell wall also including cell wall immunity (CWI) and damage-associated molecular patterns (DAMPs), induction of phytoalexins and synthesis of PR proteins. These all, are comprised under the first line of defense of plants which come into action after recognition of conserved molecules characteristic of many microbes. These are called elicitors and are known as microbeassociated or pathogen-associated molecular patterns (MAMPs or PAMPs). The second line of defense of plants is the recognition of effectors through plant resistance gene products known as R genes, which result in effector-triggered immunity (ETI). This is supported by the gene for gene hypothesis. Avirulence gene encodes a protein which is specifically recognized by genotypes of the host plant harboring the matching resistance genes.

Nicotiana benthamiana exportin 1 is required for elicitor-induced phytoalexin production, cell death induction, and resistance against potato late blight pathogen Phytophthora infestans

The oomycete Phytophthora infestans is the causal agent of potato late blight, one of the most devastating pathogens for potato. To investigate the plant mechanisms for resistance against P. infestans, the Solanaceae model plant Nicotiana benthamiana was employed in this study. Previously, we reported that NbNup75, a nuclear pore complex protein, is required for the resistance against P. infestans, suggesting that nuclear-pore-mediated transport is involved in the induction of defense responses. In this study, we investigated the role of N. benthamiana exportin 1 NbXpo1 in disease resistance. Mammalian and yeast exportin 1 proteins are known as a regulator for nuclear-pore-mediated export of proteins and RNAs. NbXpo1-silenced N. benthamiana showed minor growth defects and significantly decreased resistance to P. infestans. Gene silencing of NbXpo1 compromised defense responses induced by the elicitor INF1 (a secretory protein of P. infestans), such as production of the phytoalexin capsidiol and induction of cell death. In NbXpo1-silenced plants, the genes for capsidiol biosynthesis, NbEAS, and defense-related MAP kinase, NbWIPK, were significantly downregulated, while genes encoding the plant defensin, NbPDF, and anti-microbial protein thionin, NbTHI, were upregulated. These results indicate that N. benthamiana Xpo1 is involved in activating a specific group of defense-related genes.

Induction of phytoalexins and proteins related to pathogenesis in plants treated with extracts of cutaneous secretions of southern Amazonian Bufonidae amphibians.

Cutaneous secretions produced by amphibians of the family Bufonidae are rich sources of bioactive compounds that can be useful as new chemical templates for agrochemicals. In crop protection, the use of elicitors to induce responses offers the prospect of durable, broad-spectrum disease control using the plant’s own resistance. Therefore, we evaluated the potential of methanolic extracts of cutaneous secretions of two species of amphibians of the family Bufonidae found in the Amazon biome—Rhaebo guttatus (species 1) and Rhinella marina (species 2)—in the synthesis of phytoalexins in soybean cotyledons, bean hypocotyls, and sorghum mesocotyls. Additionally, changes in the enzyme activity of β-1,3-glucanase, peroxidase (POX), and polyphenol oxidase (PPO) and in the total protein content of soybean cotyledons were determined. In the soybean cultivar ‘TMG 132 RR’, our results indicated that the methanolic extract of R. guttatus cutaneous secretions suppressed glyceollin synthesis and β-1,3-glucanase activity and increased POX and PPO activities at higher concentrations and total protein content at a concentration of 0.2 mg/mL. On the other hand, the methanolic extract of R. marina cutaneous secretions induced glyceollin synthesis in the soybean cultivars ‘TMG 132 RR’ and ‘Monsoy 8372 IPRO’ at 0.1–0.2 mg/mL and 0.2 mg/mL, respectively. The methanolic extract of R. marina cutaneous secretions also increased the specific activity of POX and PPO in ‘Monsoy 8372 IPRO’ and ‘TMG 132 RR’, respectively, and decreased the activity of β-1,3-glucanases in ‘Monsoy 8372 IPRO’. At 0.3 mg/mL, it stimulated phaseolin synthesis. The extracts did not express bioactivity in the synthesis of deoxyanthocyanidins in sorghum mesocotyls. The study in soybean suggests that the bioactivity in defense responses is influenced by cultivar genotypes. Therefore, these results provide evidence that extracts of cutaneous secretions of these amphibians species may contribute to the bioactivity of defense metabolites in plants.

Suspension Agaricus brasiliensis in the induction of phytoalexins and in the control of the grapevine downy mildew.

El objetivo del presente estudio fue verificar el efecto elicitor en la induccion de fitoalexina y control de la severidad del mildiu de la vid ( Plasmopara viticola ) en condiciones de campo de suspension micelial acuosa (SMA) de Agaricus brasilienis . Para inducir la fitoalexina en frijoles, soja, sorgo y severidade del mildiu, se utilizaron tratamientos que contienen a SMA de A. brasilensis lavada y sin lavar, asi como con y sin asociacion con aceite vegetal (OV), como tratamiento de control con agua y patrones con acibenzolar-S-metilo (ASM 0.005%) y Mezcla de Burdeos (1: 1: 1) ¬ En otro experimento, tambien para la determinacion de la induccion de fitoalexinas en soja y sorgo, se utilizaro las dosis de 0, 1, 5, 10, 15 y 20% da SMA de A. brasiliensis . Se verifico que el SMA de A. brasiliensis a 10%SMA indujo em 1000% y 56% la fitoalexina en frijoles y sorgo, respectivamente. Para la soya, se observo un aumento del 400% con 5% de SMA lavada de A. brasiliensis . Las dosis de esta suspension pueden inducir una induccion de 460% y 710% cuando se usa 20% de la SMA de cogumelo. En condiciones de campo no se verifico diferencias estadisticas entre los tratamientos aplicados a las vides. Por lo tanto, se puede decir que el SMA de A. brasiliensis presenta compuestos capaces de desencadenar un comportamiento inductor para respuestas de induccion de resistencia en plantas, pero no se observo ningun efecto directo sobre el patogeno evaluado.

English

Secondary metabolites may play a number of roles, among them, is the activation of plant defense mechanisms, such as phytoalexins and the synthesis of antioxidative enzymes. This study aimed to test the eliciting activity of phytoalexins of Lippia sidoides Cham. and six endophytic fungi associated with it and to verify the synthesis of the enzymes, as a response to the antioxidative and antifungal system. The assays were performed using spectrophotometric methods. Of the concentrations of essential oil used, 7.5 mg mL-1 was 66.48% higher than the Acorda® positive control for the induction of glyceollin. The endophytic fungus, Verticillium sp. showed the best result for 3-deoxythianocyanidine production. Excellent results were demonstrated by the LS-14 fungus for superoxide dismutase enzyme activity (130 U g-1 E-1 min-1); by L. sidoides for the activity of ascorbate peroxidase enzyme (3821 μmol ASA g-1 E-1 min-1); by L. sidoides for the activity of catalase enzyme (2429 μmol H2O2 g-1 E-1 min-1); by Fusarium sp. 2 for the activity of phenol peroxidase (87 μmol H2O2 g-1 E-1 min-1) and by Fusarium sp. 1 for the activity of chitinase (0.214 U min-1). Both the essential oil of L. sidoides and the extracts of the endophytic fungi had a positive response to the induction of phytoalexin and presence of enzymes related to antioxidative activity were verified and shown. Key words: Catalase, superoxide dismutase, peroxidase phenols, ascorbate peroxidase, chitinase.

Defense and signalling metabolites of the crucifer Erucastrum canariense: Synchronized abiotic induction of phytoalexins and galacto-oxylipins

Erucastrum canariense Webb & Berthel. (Brassicaceae) is a wild crucifer that grows in rocky soils, in salt and water stressed habitats, namely in the Canary Islands and similar environments. Abiotic stress induced by copper chloride triggered formation of a phytoalexin and galacto-oxylipins in E. canariense, whereas wounding induced galacto-oxylipins but not phytoalexins. Analysis of the metabolite profiles of leaves of E. canariense followed by isolation and structure determination afforded the phytoalexin erucalexin, the phytoanticipin indolyl-3-acetonitrile, the galacto-oxylipins arabidopsides A, C, and D, and the oxylipin 12-oxophytodienoic acid. In addition, arabidopsides A and D were also identified in extracts of leaves of Nasturtium officinale R. Br.

Homeopathy with essential oils in the germination of spores and induction of phytoalexins

A homeopatizacao de oleos essenciais revela-se como uma alternativa para o controle de fitopatogenos e na inducao de compostos de defesa em plantas, como as fitoalexinas. Neste sentido, o objetivo do trabalho foi de avaliar o efeito de solucoes dinamizadas de Eucalyptus citriodora (EC) e Cymbopogon citratus (CC) na germinacao de conidios de Alternaria solani e Corynespora cassiicola e na producao de fitoalexinas em soja. Para os testes foram utilizados os tratamentos homeopaticos: 6CH, 12CH, 30CH, 60CH, 100CH e 200CH de ambos os oleos. A porcentagem de germinacao foi determinada 4 horas apos incubacao dos patogenos na presenca dos tratamentos, em placas tipo Elisa a 25 oC, e feita contagem de esporos em microscopio optico. Para fitoalexinas, cotiledones de soja oriundos de sementes cultivadas em areia esteril foram cortados na superficie inferior e submetido aos tratamentos, permanecendo no escuro por 20 horas. A gliceolina formada foi extraida e determinada em espectrofotometro. Todas as dinamizacoes aplicadas reduziram a germinacao de ambos patogenos, chegando a reducao de 59% em A. solani e 42% em C. cassiicola por CC 30CH. As dinamizacoes testadas nao foram eficientes para inducao de gliceolina, indicando maior potencial dos tratamentos sobre os patogenos em comparacao a elicitacao destes compostos de defesa. Baseando-se nestes resultados, e possivel evidenciar o potencial de tratamentos homeopaticos no controle de A. solani e C. cassiicola. O processo de homeopatizacao manteve as propriedades antimicrobianas dos oleos testados.

Propolis for the control of powdery mildew and the induction of phytoalexins in cucumber

espanolDebido a sus propiedades antimicrobianas el propoleo ha sido utilizado por el hombre desde hace milenios, sin embargo solo recientemente se ha probado como un agente antimicrobiano agricola. Ademas, la capacidad de este producto para activar los mecanismos de defensa de la planta es muy prometedor, debido a la gran cantidad de sustancias en su composicion. Por tanto, el objetivo de este estudio fue evaluar el efecto de diferentes concentraciones y tiempos de aplicacion de los extractos etanolicos de propoleos (EEP) en el oidio (Podosphaera fuliginea) en cultivos de pepino, para establecer el metodo mas adecuado para el control y la existencia o no de este potencial para inducir los mecanismos de defensa de la planta. El experimento se llevo a cabo en macetas en un invernadero. Fue empleado un diseno experimental completamente al azar, utilizando un factorial 6x3, que consiste en seis concentraciones (0; 0,5; 1; 2; 4 y 8%) y tres momentos de aplicacion EEP (24 horas antes de la inoculacion del patogeno, 24 horas despues de la inoculacion de patogenos y en la aparicion de los primeros sintomas de la enfermedad) con cuatro repeticiones. Las evaluaciones para la incidencia y gravedad de la enfermedad se realizaron semanalmente. El experimento se repite para mas de un cultivo, siguiendo la misma metodologia establecida en la primera. Tambien se evaluo el efecto de diferentes concentraciones de EEP en la activacion de los mecanismos de defensa de la planta, mediante la induccion de fitoalexinas en la soja (Glycine max), cotiledones. Se observo una interaccion significativa entre los factores de concentracion (x tiempo de aplicacion) para la incidencia de la enfermedad. Para el area bajo la curva de progreso de la enfermedad (AUDPC) para la gravedad no hubo interaccion observada entre los factores, sin embargo, se observaron diferencias significativas para los dos factores por separado. El AUDPC para la incidencia fue menor para la aplicacion 24 horas despues de la inoculacion de patogenos a la mayor concentracion. El EEP inducida aumento los niveles de fitoalexina en cotiledones de frijol de soya segun la concentracion aplicada. Los extractos etanolicos de propoleos podrian tener potencial para el control del mildiu pulverulento, principalmente en los pepinos, por medio de la aplicacion preventiva de una concentracion al 8%. EnglishDue to its antimicrobial properties propolis has been utilised by man for millennia, however, only recently has its use as an agricultural antimicrobial agent been tested. The capacity of this product to activate plant defence mechanisms is highly promising, due to the large number of substances in its composition. Therefore, the objective of this study was to evaluate the effect of different concentrations and application times of ethanol extracts of propolis (EEP) on powdery mildew (Podosphaera fuliginea) in cucumber crops, to establish the most suitable method for control and whether or not there is potential to induce plant defence mechanisms. The experiment was conducted in pots in a greenhouse. A completely randomised experimental design was employed, using a 6x3 factorial consisting of six concentrations (0; 0.5; 1; 2; 4 and 8%) and three EEP application times (24 hours before pathogen inoculation, 24 hours after pathogen inoculation and at the onset of first symptoms of the disease), replicated four times. Evaluations for disease incidence and severity were made weekly. The experiment was repeated for a second crop, following the same methodology established in the first. We also evaluated the effect of different EEP concentrations on the activation of plant defence mechanisms, through the induction of phytoalexins in soybean (Glycine max) cotyledons. A significant interaction was observed between the factors (application time x concentration) for disease incidence. For the area under the disease progress curve (AUDPC) for severity there was no interaction observed between the factors, however, we observed significant differences for the two factors separately. The AUDPC for incidence was less for the application 24 hours after pathogen inoculation, principally at the highest concentration. The 8% concentration of EEP controlled disease severity by 31.33 and 43.68% for the first and second crops, respectively. The application of the concentrations 24 hours before and 24 hours after pathogen inoculation showed less AUDPC for severity, but this difference was not significant for either crop. The EEP induced increasing phytoalexin levels in soybean cotyledons as the applied EEP concentration increased. Ethanol extracts of propolis could have potential for the control of powdery mildew, principally in cucumbers, through the preventive application of an 8% concentration.

Accumulation of terpenoid phytoalexins in maize roots is associated with drought tolerance.

Maize (Zea mays) production, which is of global agro-economic importance, is largely limited by herbivore pests, pathogens and environmental conditions, such as drought. Zealexins and kauralexins belong to two recently identified families of acidic terpenoid phytoalexins in maize that mediate defence against both pathogen and insect attacks in aboveground tissues. However, little is known about their function in belowground organs and their potential to counter abiotic stress. In this study, we show that zealexins and kauralexins accumulate in roots in response to both biotic and abiotic stress including, Diabrotica balteata herbivory, Fusarium verticillioides infection, drought and high salinity. We find that the quantity of drought-induced phytoalexins is positively correlated with the root-to-shoot ratio of different maize varieties, and further demonstrate that mutant an2 plants deficient in kauralexin production are more sensitive to drought. The induction of phytoalexins in response to drought is root specific and does not influence phytoalexin levels aboveground; however, the accumulation of phytoalexins in one tissue may influence the induction capacity of other tissues.

Nucleoporin 75 is involved in the ethylene-mediated production of phytoalexin for the resistance of Nicotiana benthamiana to Phytophthora infestans.

Mature Nicotiana benthamiana shows stable resistance to the oomycete pathogen Phytophthora infestans. Induction of phytoalexin (capsidiol) production is essential for the resistance, which is upregulated via a mitogen-activated protein kinase (MAPK) cascade (NbMEK2-WIPK/SIPK) followed by ethylene signaling. In this study, NbNup75 (encodes a nuclear pore protein Nucleoporin75) was identified as an essential gene for resistance of N. benthamiana to P. infestans. In NbNup75-silenced plants, initial events of elicitor-induced responses such as phosphorylation of MAPK and expression of defense-related genes were not affected, whereas induction of later defense responses such as capsidiol production and cell death induction was suppressed or delayed. Ethylene production induced by either INF1 or NbMEK2 was reduced in NbNup75-silenced plants, whereas the expression of NbEAS (a gene for capsidiol biosynthesis) induced by ethylene was not affected, indicating that Nup75 is required for the induction of ethylene production but not for ethylene signaling. Given that nuclear accumulation of polyA RNA was increased in NbNup75-silenced plants, efficient export of mRNA from nuclei via nuclear pores would be important for the timely upregulation of defense responses. Collectively, Nup75 is involved in the induction of a later stage of defense responses, including the ethylene-mediated production of phytoalexin for the resistance of N. benthamiana to P. infestans.

Eliciadores proteicos e glicídicos de Adiantum capillus-veneris L. para fitoalexinas em sorgo Sorghum bicolor (L.) Moench

Este trabalho objetivou a purificação parcial, por precipitação com sulfato de amônio (SA) e cromatografia de filtração em gel (CFG), de compostos presentes no decocto de Adiantum capillus-veneris (avenca) eficientes na indução de fitoalexinas em mesocótilos de Sorghum bicolor sorgo. Decocto de A. capillus-veneris a 1% (peso seco/volume) foi precipitado com concentrações de SA variando de 0 a 100% (em intervalos de 20%), e essas frações foram submetidas à CFG. Para o decocto não precipitado foram obtidos nove picos proteicos e um pico glicídico com massas moleculares variando de 0,61 à 0,01 KDa. Para a precipitação fracionada obteve-se: na fração 0-20% dois picos proteicos (menores que 0,01 KDa) e dois glicídicos com concentração de açúcares variando de 4,1 a 17,5 µg mL-1; na fração 20-40% três picos proteicos (111,5 à 0,98 KDa) e cinco glicídicos (11,3 a 73,7 µg de açúcares mL-1); na fração 40-60% dois picos proteicos (111,5 à 0,09 KDa) e dois glicídicos (5,6 a 7, 5 µg de açúcares mL-1); na fração 60-80% seis picos proteicos (menores que 0,02 KDa) e dois glicídicos (16,5 a 51,3 µg de açúcares mL-1); e na fração 80-100% três picos proteicos (menores que 0,09 KDa). Mesocótilos de sorgo foram tratados com as frações provenientes da CFG, além do decocto a 1%, acibenzolar-S-metil (ASM) (125 mg L-1 do i.a. como eliciador de referência) e tampão fosfato de sódio 10 mM pH 6,0. O pico proteico II (0,09 KDa) do decocto não precipitado induziu fitoalexinas, 6,68% superior a ASM. Entre os precipitados, a fração 60-80% de SA induziu 76% mais que ASM. Dessa forma, pôde-se obter frações proteicas e/ou glicídicas indutoras de fitoalexinas em sorgo de maneira superior ao extrato (decocto) do qual é originária, indicando o potencial dessas moléculas para trabalhos futuros sobre indução de resistência.

Study of leaf metabolome modifications induced by UV-C radiations in representative Vitis, Cissus and Cannabis species by LC-MS based metabolomics and antioxidant assays.

UV-C radiation is known to induce metabolic modifications in plants, particularly to secondary metabolite biosynthesis. To assess these modifications from a global and untargeted perspective, the effects of the UV-C radiation of the leaves of three different model plant species, Cissus antarctica Vent. (Vitaceae), Vitis vinifera L. (Vitaceae) and Cannabis sativa L. (Cannabaceae), were evaluated by an LC-HRMS-based metabolomic approach. The approach enabled the detection of significant metabolite modifications in the three species studied. For all species, clear modifications of phenylpropanoid metabolism were detected that led to an increased level of stilbene derivatives. Interestingly, resveratrol and piceid levels were strongly induced by the UV-C treatment of C. antarctica leaves. In contrast, both flavonoids and stilbene polymers were upregulated in UV-C-treated Vitis leaves. In Cannabis, important changes in cinnamic acid amides and stilbene-related compounds were also detected. Overall, our results highlighted phytoalexin induction upon UV-C radiation. To evaluate whether UV-C stress radiation could enhance the biosynthesis of bioactive compounds, the antioxidant activity of extracts from control and UV-C-treated leaves was measured. The results showed increased antioxidant activity in UV-C-treated V. vinifera extracts.

Differential Induction of 3-deoxyanthocyanidin Phytoalexins in Relation to Colletotrichum falcatum Resistance in Sugarcane

Sugarcane secrets a reddish pigment presumed to contain phytoalexin compounds in the stalk tissues in response to infection of Colletotrichum falcatum, causing red rot. To identify the phytoalexin compounds involved in red rot resistance, detailed HPLC analyses were conducted using the phytoalexin standards in a set of sugarcane cultivars varying in red rot resistance, after pathogen inoculation. We found nine different 3-deoxyanthocyanidin phytoalexin compounds, which are differentially induced upon C. falcatum infection in sugarcane varieties with varying degrees of disease resistance. Among the nine compounds, four compounds were identified as luteolinidin, 5-methoxy luteolinidin, apigeninidin and arabinosyl-5-O-apigeninidin. Multifold induction of luteolinidin, apigeninidin and arabinosyl-5-O-apigeninidinin were recorded in the stalk tissues in disease resistant cvs Co 93009, BO 91 and Baragua, respectively after pathogen inoculation as compared to the susceptible cv CoC 671. In addition to the known compounds one to three unknown compounds were detected in the resistant cultivars. The susceptible cultivars exhibited a placid induction of phytoalexin compounds after pathogen infections. The results very clearly demonstrated a specific induction of 3-deoxyanthocyanidins in resistant cultivars at a higher level as compared to susceptible cultivars after C. falcatum infection in sugarcane. Total extracts of the induced phytoalexins in the calorimetric assays, also revealed similar results. Probably induction of either luteolinidin or apigeninidin compounds alone or in combination at higher concentrations in the resistant cultivars may enable the effective arrest of pathogen invasion and further development inside the stalk tissues.

Atividade antimicrobiana e indutora de fitoalexinas do hidrolato de carqueja [Baccharis trimera (Less.) DC.

Hidrolato é o líquido resultante da extração de óleo essencial de plantas aromáticas por arraste a vapor apresentando em sua composição importantes metabólitos do vegetal de origem. O objetivo deste trabalho foi avaliar a atividade indutora de fitoalexinas, bem como as propriedades antifúngica e antibacteriana do hidrolato de carqueja (Baccharis trimera). Foram testadas as concentrações de 1, 10, 25, 50, 75 e 100%. A atividade indutora de fitoalexinas foi avaliada em mesocótilos estiolados de sorgo e em cotilédones de soja. A atividade antifúngica foi avaliada sobre a germinação de esporos de Pseudocercospora vitis, Cercospora kaki e Hemileia vastatrix. A atividade antibacteriana foi avaliada sobre a multiplicação de Xanthomonas campestris pv. passiflorae, Erwinia carotovora e Bacilllus subtilis. O hidrolato não induziu a produção de fitoalexinas em soja, mas promoveu esta atividade em sorgo a partir da concentração de 50%. Atividade antibacteriana ocorreu para os três isolados a partir da concentração de 75%, com inibição de até 87,9% sobre B. subtilis. O hidrolato não mostrou atividade antifúngica.

Potential involvement of Aspergillus flavus laccases in peanut invasion at low water potential

Aspergillus flavus accumulates carcinogenic aflatoxins in peanuts, mainly in immature kernels during drought. Aspergillus flavus invasion induces accumulation of phytoalexins, mostly stilbenoids in peanut, as a plant defence mechanism. Because fungal laccases are often related to pathogenicity and can degrade stilbenoids, this study reports for the first time the expression of A. flavus laccases in the presence of kernels, hulls and low water potential in relation to the accumulation of phytoalexins in peanut kernels. Packed‐cell volume (PCV) of A. flavus biomass was significantly higher (P ≤ 0·01) in the presence of mature kernels, dead kernels, and mature and immature peanut hulls than the control. The presence of kernels and hulls lowered the level of expression of three A. flavus laccases by 4–6‐fold (P < 0·01), whereas 3% sucrose up‐regulated them by 35–304‐fold, and low water potential (−1·1 MPa) up‐regulated them by 85–248‐fold (P < 0·01). Phytoalexins that accumulated in peanut kernels in the presence of A. flavus and were quantified by HPLC‐DAD‐MS were primarily the stilbenoids: 3′‐isopentadienyl‐3,5,4′‐trihydroxystilbene (IPD), chiricanine‐A, arachidin‐2, arachidin‐3 and arahypin‐1. Apparent degradation of phytoalexins was observed when using a priori induction of phytoalexins in seeds in combination with a priori induction of laccases in A. flavus. The up‐regulation of laccase expression observed at −1·1 MPa and at high sucrose concentration could be contributing to peanut invasion in immature kernels under drought conditions.