Tansley Review No. 86 Accumulation of phytoalexins: defence mechanism and stimulus response system

Extraction, Identification and Antioxidant Activity of 3-Deoxyanthocyanidins from Sorghum bicolor L. Moench Cultivated in China

3-deoxyanthocyanidins (3-DAs) are typical flavonoids found in sorghum bran, and they have received much attention in recent years owing to their bioactivities. To further enhance the resource utilization of sorghums cultivated in China, three brewing sorghum cultivars (Liaoza-48, Liaonuo-11, and Liaonian-3) commonly used in China were selected as raw materials for the construction of an extraction technology system for 3-DAs and the clarification of their structures and bioactivities. Based on single-factor experiments and response surface analysis, the optimized system for the extraction of 3-DAs from sorghum grains was as follows: a hydrochloric acid-methanol solution (1:100, v/v) was the extraction solvent, the solid-liquid ratio was 1:20 (g/mL), the extraction time was 130 min, and the temperature was 40 °C. This extraction system was simple and feasible. High performance liquid chromatography analysis suggested that the main monomeric compounds of the extracted 3-DAs were Apigeninidin (AE) and Luteolinidin (LE). Among the three selected sorghum grains, Liaoza-48 had the highest amount of AE (329.64 μg/g) and LE (97.18 μg/g). Antioxidant experiments indicated that the 3-DAs extracted from Liaoza-48 showed higher free-radical scavenging activities for DPPH, ABTS+, and hydroxyl radicals than those extracted from Liaonuo-11 and Liaonian-3. These results provide basic data and technical support for the high-value and comprehensive utilization of sorghums in China.

Rice diterpenoid phytoalexins are involved in defence against parasitic nematodes and shape rhizosphere nematode communities

Rice diterpenoid phytoalexins (DPs) are secondary metabolites with a well known role in resistance to foliar pathogens. As DPs are also known to be produced and exuded by rice roots, we hypothesised that they might play an important role in plant-nematode interactions, and particularly in defence against phytoparasitic nematodes. We used transcriptome analysis on rice roots to analyse the effect of infection by the root-knot nematode Meloidogyne graminicola or treatment with resistance-inducing chemical stimuli on DP biosynthesis genes, and assessed the susceptibility of mutant rice lines impaired in DP biosynthesis to M. graminicola. Moreover, we grew these mutants and their wild-type in field soil and used metabarcoding to assess the effect of impairment in DP biosynthesis on rhizosphere and root nematode communities. We show that M. graminicola suppresses DP biosynthesis genes early in its invasion process and, conversely, that resistance-inducing stimuli transiently induce the biosynthesis of DPs. Moreover, we show that loss of DPs increases susceptibility to M. graminicola. Metabarcoding on wild-type and DP-deficient plants grown in field soil reveals that DPs significantly alter the composition of rhizosphere and root nematode communities. Diterpenoid phytoalexins are important players in basal and inducible defence against nematode pathogens of rice and help shape rice-associated nematode communities.

Physiological and Biochemical Response to Fusarium culmorum Infection in Three Durum Wheat Genotypes at Seedling and Full Anthesis Stage

Fusarium culmorum is a worldwide, soil-borne plant pathogen. It causes diseases of cereals, reduces their yield, and fills the grain with toxins. The main direction of modern breeding is to select wheat genotypes the most resistant to Fusarium diseases. This study uses seedlings and plants at the anthesis stage to analyze total soluble carbohydrates, total and cell-wall bound phenolics, chlorophyll content, antioxidant activity, hydrogen peroxide content, mycotoxin accumulation, visual symptoms of the disease, and Fusarium head blight index (FHBi). These results determine the resistance of three durum wheat accessions. We identify physiological or biochemical markers of durum wheat resistance to F. culmorum. Our results confirm correlations between FHBi and mycotoxin accumulation in the grain, which results in grain yield decrease. The degree of spike infection (FHBi) may indicate accumulation mainly of deoxynivalenol and nivalenol in the grain. High catalase activity in the infected leaves could be considered a biochemical marker of durum sensitivity to this fungus. These findings allowed us to formulate a strategy for rapid evaluation of the disease severity and the selection of plants with higher level, or resistance to F. culmorum infection.

Dissecting the Role of Promoters of Pathogen-sensitive Genes in Plant Defense

Plants inherently show resistance to pathogen attack but are susceptible to multiple bacteria, viruses, fungi, and phytoplasmas. Diseases as a result of such infection leads to the deterioration of crop yield. Several pathogen-sensitive gene activities, promoters of such genes, associated transcription factors, and promoter elements responsible for crosstalk between the defense signaling pathways are involved in plant resistance towards a pathogen. Still, only a handful of genes and their promoters related to plant resistance have been identified to date. Such pathogen-sensitive promoters are accountable for elevating the transcriptional activity of certain genes in response to infection. Also, a suitable promoter is a key to devising successful crop improvement strategies as it ensures the optimum expression of the required transgene. The study of the promoters also helps in mining more details about the transcription factors controlling their activities and helps to unveil the involvement of new genes in the pathogen response. Therefore, the only way out to formulate new solutions is by analyzing the molecular aspects of these promoters in detail. In this review, we provided an overview of the promoter motifs and cis-regulatory elements having specific roles in pathogen attack response. To elaborate on the importance and get a vivid picture of the pathogen-sensitive promoter sequences, the key motifs and promoter elements were analyzed with the help of PlantCare and interpreted with available literature. This review intends to provide useful information for reconstructing the gene networks underlying the resistance of plants against pathogens.

PGPR-mediated induction of systemic resistance and physiochemical alterations in plants against the pathogens: Current perspectives

Plant growth-promoting rhizobacteria (PGPR) are diverse groups of plant-associated microorganisms, which can reduce the severity or incidence of disease during antagonism among bacteria and soil-borne pathogens, as well as by influencing a systemic resistance to elicit defense response in host plants. An amalgamation of various strains of PGPR has improved the efficacy by enhancing the systemic resistance opposed to various pathogens affecting the crop. Many PGPR used with seed treatment causes structural improvement of the cell wall and physiological/biochemical changes leading to the synthesis of proteins, peptides, and chemicals occupied in plant defense mechanisms. The major determinants of PGPR-mediated induced systemic resistance (ISR) are lipopolysaccharides, lipopeptides, siderophores, pyocyanin, antibiotics 2,4-diacetylphoroglucinol, the volatile 2,3-butanediol, N-alkylated benzylamine, and iron-regulated compounds. Many PGPR inoculants have been commercialized and these inoculants consequently aid in the improvement of crop growth yield and provide effective reinforcement to the crop from disease, whereas other inoculants are used as biofertilizers for native as well as crops growing at diverse extreme habitat and exhibit multifunctional plant growth-promoting attributes. A number of applications of PGPR formulation are needed to maintain the resistance levels in crop plants. Several microarray-based studies have been done to identify the genes, which are associated with PGPR-induced systemic resistance. Identification of these genes associated with ISR-mediating disease suppression and biochemical changes in the crop plant is one of the essential steps in understanding the disease resistance mechanisms in crops. Therefore, in this review, we discuss the PGPR-mediated innovative methods, focusing on the mode of action of compounds authorized that may be significant in the development contributing to enhance plant growth, disease resistance, and serve as an efficient bioinoculants for sustainable agriculture. The review also highlights current research progress in this field with a special emphasis on challenges, limitations, and their environmental and economic advantages.

Using the CODIT model to explain secondary metabolites of xylem in defence systems of temperate trees against decay fungi

BACKGROUND

In trees, secondary metabolites (SMs) are essential for determining the effectiveness of defence systems against fungi and why defences are sometimes breached. Using the CODIT model (Compartmentalization of Damage/Dysfunction in Trees), we explain defence processes at the cellular level. CODIT is a highly compartmented defence system that relies on the signalling, synthesis and transport of defence compounds through a three-dimensional lattice of parenchyma against the spread of decay fungi in xylem.

SCOPE

The model conceptualizes 'walls' that are pre-formed, formed during and formed after wounding events. For sapwood, SMs range in molecular size, which directly affects performance and the response times in which they can be produced. When triggered, high-molecular weight SMs such as suberin and lignin are synthesized slowly (phytoalexins), but can also be in place at the time of wounding (phytoanticipins). In contrast, low-molecular weight phenolic compounds such as flavonoids can be manufactured de novo (phytoalexins) rapidly in response to fungal colonization. De novo production of SMs can be regulated in response to fungal pathogenicity levels. The protective nature of heartwood is partly based on the level of accumulated antimicrobial SMs (phytoanticipins) during the transitionary stage into a normally dead substance. Effectiveness against fungal colonization in heartwood is largely determined by the genetics of the host.

CONCLUSION

Here we review recent advances in our understanding of the role of SMs in trees in the context of CODIT, with emphasis on the relationship between defence, carbohydrate availability and the hydraulic system.We also raise the limitations of the CODIT model and suggest its modification, encompassing other defence theory concepts. We envisage the development of a new defence system that is modular based and incorporates all components (and organs) of the tree from micro- to macro-scales.

3-Deoxyanthocyanidin Colorant: Nature, Health, Synthesis, and Food Applications

3-Deoxyanthocyanidins are a rare type of anthocyanins that are present in mosses, ferns, and some flowering plants. They are water-soluble pigments and impart orange-red and blue-violet color to plants and play a role as phytoalexins against microbial infection and environmental stress. In contrast to anthocyanins, the lack of a hydroxyl group at the C-3 position confers unique chemical and biochemical properties. They are potent natural antioxidants with a number of potential health benefits including cancer prevention. 3-Deoxyanthocyanidin pigments have attracted much attention in the food industry as natural food colorants, mainly due to their higher stability during processing and handling conditions compared with anthocyanins. They are also photochromic compounds capable of causing a change in "perceived" color, when exposed to UV light, which can be used to design novel foods and beverages. Due to their interesting properties and potential industrial applications, great efforts have been made to synthesize these compounds. For biosynthesis, researchers have discovered the 3-deoxyanthocyanidin biosynthetic pathway and their biosynthetic genes. For chemical synthesis, advances have been made to synthesize the compounds in a simpler and more efficient way as well as looking for its novel derivative with enhanced coloration properties. This review summarizes the developments in the research on 3-deoxyanthocyanidin as a colorant, from natural sources to chemical syntheses and from health benefits to applications and future prospects, providing comprehensive insights into this group of interesting compounds.

A gossypol biosynthetic intermediate disturbs plant defence response

Plant secondary metabolites and their biosynthesis have attracted great interest, but investigations of the activities of hidden intermediates remain rare. Gossypol and related sesquiterpenes are the major phytoalexins in cotton. Among the six biosynthetic intermediates recently identified, 8-hydroxy-7-keto-δ-cadinene (C234) crippled the plant disease resistance when accumulated upon gene silencing. C234 harbours an α,β-unsaturated carbonyl thus is a reactive electrophile species. Here, we show that C234 application also dampened the Arabidopsis resistance against the bacterial pathogen Pseudomonas syringae pv. maculicola ( Psm). We treated Arabidopsis with C234, Psm and ( Psm+C234), and analysed the leaf transcriptomes. While C234 alone exerted a mild effect, it greatly stimulated an over-response to the pathogen. Of the 7335 genes affected in the ( Psm+C234)-treated leaves, 3476 were unresponsive without the chemical, in which such functional categories as 'nucleotides transport', 'vesicle transport', 'MAP kinases', 'G-proteins', 'protein assembly and cofactor ligation' and 'light reaction' were enriched, suggesting that C234 disturbed certain physiological processes and the protein complex assembly, leading to distorted defence response and decreased disease resistance. As C234 is efficiently metabolized by CYP71BE79, plants of cotton lineage have evolved a highly active enzyme to prevent the phytotoxic intermediate accumulation during gossypol pathway evolution. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.

Deciphering the roles of acyl-CoA-binding proteins in plant cells

Lipid trafficking is vital for metabolite exchange and signal communications between organelles and endomembranes. Acyl-CoA-binding proteins (ACBPs) are involved in the intracellular transport, protection, and pool formation of acyl-CoA esters, which are important intermediates and regulators in lipid metabolism and cellular signaling. In this review, we highlight recent advances in our understanding of plant ACBP families from a cellular and developmental perspective. Plant ACBPs have been extensively studied in Arabidopsis thaliana (a dicot) and to a lesser extent in Oryza sativa (a monocot). Thus far, they have been detected in the plasma membrane, vesicles, endoplasmic reticulum, Golgi apparatus, apoplast, cytosol, nuclear periphery, and peroxisomes. In combination with biochemical and molecular genetic tools, the widespread subcellular distribution of respective ACBP members has been explicitly linked to their functions in lipid metabolism during development and in response to stresses. At the cellular level, strong expression of specific ACBP homologs in specialized cells, such as embryos, stem epidermis, guard cells, male gametophytes, and phloem sap, is of relevance to their corresponding distinct roles in organ development and stress responses. Other interesting patterns in their subcellular localization and spatial expression that prompt new directions in future investigations are discussed.

Non-host disease resistance response in pea (Pisum sativum) pods: Biochemical function of DRR206 and phytoalexin pathway localization

Continually exposed to potential pathogens, vascular plants have evolved intricate defense mechanisms to recognize encroaching threats and defend themselves. They do so by inducing a set of defense responses that can help defeat and/or limit effects of invading pathogens, of which the non-host disease resistance response is the most common. In this regard, pea (Pisum sativum) pod tissue, when exposed to Fusarium solani f. sp. phaseoli spores, undergoes an inducible transcriptional activation of pathogenesis-related genes, and also produces (+)-pisatin, its major phytoalexin. One of the inducible pathogenesis-related genes is Disease Resistance Response-206 (DRR206), whose role in vivo was unknown. DRR206 is, however, related to the dirigent protein (DP) family. In this study, its biochemical function was investigated in planta, with the metabolite associated with its gene induction being pinoresinol monoglucoside. Interestingly, both pinoresinol monoglucoside and (+)-pisatin were co-localized in pea pod endocarp epidermal cells, as demonstrated using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging. In addition, endocarp epidermal cells are also the site for both chalcone synthase and DRR206 gene expression. Taken together, these data indicate that both (+)-pisatin and pinoresinol monoglucoside function in the overall phytoalexin responses.

Antimicrobial activity, toxicity and selectivity index of two biflavonoids and a flavone isolated from Podocarpus henkelii (Podocarpaceae) leaves

BACKGROUND

Different parts of Podocarpus henkelii have been used in many cultures around the world to treat ailments such as cholera, stomach diseases, rheumatism, cancer, canine distemper in dogs and gall sickness in cattle. The aim of this study was to evaluate the biological activity and toxicity of isolated compounds from Podocarpus henkelii after an earlier study indicated a promising activity in crude extracts against viral pathogens of veterinary importance.

METHODS

The antibacterial and antifungal activity of two biflavonoids 7, 4', 7", 4"'-tetramethoxy amentoflavone (TMA), isoginkgetin (IGG) and podocarpus flavone-A (PFA) isolated from the leaves of Podocarpus henkelii were determined using a serial microplate dilution method with tetrazolium violet as growth indicator. The cytotoxicity of compounds TMA and IGG were determined on different cell types using a tetrazolium-based colorimetric cellular assay (MTT). The Ames test was used to determine their mutagenic activities.

RESULTS

TMA had reasonable antifungal activity against Aspergillus fumigatus (MIC = 30 μg/ml). IGG had a wide spectrum of activity against four bacterial and two fungal pathogens with much higher selectivity index values obtained for A. fumigatus and Cryptococcus neoformans (SI > 30). PFA had a broad spectrum of activity against Enterococcus faecalis and Pseudomonas aeruginosa (SI > 15) and less activity against the two fungal pathogens. In both the cytotoxicity assays and Ames mutagenicity test using Salmonella typhimurium strains TA98 and TA100, TMA and IGG had no deleterious effect on the different cell types and did not induce mutations in the Ames test.

CONCLUSION

Although the antimicrobial activities of the isolated compounds were not that exciting, the compounds had no cytotoxic activity at the highest concentration (1000 μg/ml) tested against all three cell lines. IGG was the most active against E. coli, S. aureus, A. fumigatus and C. neoformans, exhibiting both antibacterial and antifungal activity with good selectivity index values. PFA had a broad spectrum of activity against E. faecalis and P. aeruginosa. The two compounds isolated had low toxicity and no genotoxic activity in the Ames test.

Ergosterol, an orphan fungal microbe-associated molecular pattern (MAMP)

Fungal pathogens continue to pose a significant threat to crop production and food supply. The early stages of plant-fungus interactions are mostly mediated by microbe-associated molecular pattern (MAMP) molecules, perceived by plant pattern recognition receptors (PRRs). Currently, the identified fungal MAMP molecules include chitin, chitosan, β-glucans, elicitins and ergosterol. Although the molecular battles between host plants and infecting fungal phytopathogens have been studied extensively, many aspects still need to be investigated to obtain a holistic understanding of the intrinsic mechanisms, which is paramount in combating fungal plant diseases. Here, an overview is given of the most recent findings concerning an 'orphan' fungal MAMP molecule, ergosterol, and we present what is currently known from a synopsis of different genes, proteins and metabolites found to play key roles in induced immune responses in plant-fungus interactions. Clearly, integrative investigations are still needed to provide a comprehensive systems-based understanding of the dynamics associated with molecular mechanisms in plant-ergosterol interactions and associated host responses.

Curdlan β-1,3-glucooligosaccharides induce the defense responses against Phytophthora infestans infection of potato (Solanum tuberosum L. cv. McCain G1) leaf cells

Activation of the innate immune system before the invasion of pathogens is a promising way to improve the resistance of plant against infection while reducing the use of agricultural chemicals. Although several elicitors were used to induce the resistance of potato plant to microbial pathogen infection, the role of curdlan oligosaccharide (CurdO) has not been established. In the current study, the defense responses were investigated at biochemical and proteomic levels to elucidate the elicitation effect of CurdOs in foliar tissues of potato (Solanum tuberosum L. cv. McCain G1). The results indicate that the CurdOs exhibit activation effect on the early- and late-defense responses in potato leaves. In addition, glucopentaose was proved to be the shortest active curdlan molecule based on the accumulation of H₂O₂ and salicylic acid and the activities of phenylalanine amino-lyase, β-1,3-glucanase and chitinase. The 2D-PAGE analysis reveals that CurdOs activate the integrated response reactions in potato cells, as a number of proteins with various functions are up-regulated including disease/defense, metabolism, transcription, and cell structure. The pathogenesis assay shows that the ratio of lesion area of potato leaf decreased from 15.82%±5.44% to 7.79%±3.03% when the plants were treated with CurdOs 1 day before the infection of Phytophthora infestans. Furthermore, the results on potato yield and induction reactions indicate that the defense responses induced by CurdOs lasted for short period of time but disappeared gradually.

Cyanobacterial toxins: modes of actions, fate in aquatic and soil ecosystems, phytotoxicity and bioaccumulation in agricultural crops

The occurrence of harmful cyanobacterial blooms in surface waters is often accompanied by the production of a variety of cyanotoxins. These toxins are designed to target in humans and animals specific organs on which they act: hepatotoxins (liver), neurotoxins (nervous system), cytotoxic alkaloids, and dermatotoxins (skin), but they often have important side effects too. When introduced into the soil ecosystem by spray irrigation of crops they may affect the same molecular pathways in plants having identical or similar target organs, tissues, cells or biomolecules. There are also several indications that terrestrial plants, including food crop plants, can bioaccumulate cyanotoxins and present, therefore, potential health hazards for human and animals. The number of publications concerned with phytotoxic effects of cyanotoxins on agricultural plants has increased recently. In this review, we first examine different cyanotoxins and their modes of actions in humans and mammals and occurrence of target biomolecules in vegetable organisms. Then we present environmental concentrations of cyanotoxins in freshwaters and their fate in aquatic and soil ecosystems. Finally, we highlight bioaccumulation of cyanotoxins in plants used for feed and food and its consequences on animals and human health. Overall, our review shows that the information on the effects of cyanotoxins on non-target organisms in the terrestrial environment is particularly scarce, and that there are still serious gaps in the knowledge about the fate in the soil ecosystems and phytotoxicity of these toxins.

Multi-platform metabolomic analyses of ergosterol-induced dynamic changes in Nicotiana tabacum cells

Metabolomics is providing new dimensions into understanding the intracellular adaptive responses in plants to external stimuli. In this study, a multi-technology-metabolomic approach was used to investigate the effect of the fungal sterol, ergosterol, on the metabolome of cultured tobacco cells. Cell suspensions were treated with different concentrations (0-1000 nM) of ergosterol and incubated for different time periods (0-24 h). Intracellular metabolites were extracted with two methods: a selective dispersive liquid-liquid micro-extraction and a general methanol extraction. Chromatographic techniques (GC-FID, GC-MS, GC × GC-TOF-MS, UHPLC-MS) and (1)H NMR spectroscopy were used for quantitative and qualitative analyses. Multivariate data analyses (PCA and OPLS-DA models) were used to extract interpretable information from the multidimensional data generated from the analytical techniques. The results showed that ergosterol triggered differential changes in the metabolome of the cells, leading to variation in the biosynthesis of secondary metabolites. PCA scores plots revealed dose- and time-dependent metabolic variations, with optimal treatment conditions being found to be 300 nM ergosterol and an 18 h incubation period. The observed ergosterol-induced metabolic changes were correlated with changes in defence-related metabolites. The 'defensome' involved increases in terpenoid metabolites with five antimicrobial compounds (the bicyclic sesquiterpenoid phytoalexins: phytuberin, solavetivone, capsidiol, lubimin and rishitin) and other metabolites (abscisic acid and phytosterols) putatively identified. In addition, various phenylpropanoid precursors, cinnamic acid derivatives and - conjugates, coumarins and lignin monomers were annotated. These annotated metabolites revealed a dynamic reprogramming of metabolic networks that are functionally correlated, with a high complexity in their regulation.

Profiling of secondary metabolites in blue lupin inoculated with Phytophthora cinnamomi following phosphite treatment

In order to discover phytochemicals that are potentially bioactive against Phytophthora cinnamomi, (a soil-borne plant pathogen) a metabolite profiling protocol for investigation of metabolic changes in Lupinus angustifolius L. plant roots in response to pathogen challenge has been established. Analysis of the metabolic profiles from healthy and P. cinnamomi-inoculated root tissue with high resolution mass spectrometry and nuclear magnetic resonance spectroscopy confirmed that although susceptible, L. angustifolius upregulated a defence associated genistein and 2'-hydroxygenistein-based isoflavonoid and a soyasapogenol saponin at 12h post inoculation which increased in concentration at 72h post inoculation. In contrast to the typical susceptible interaction, the application of a phosphorous-based treatment to L. angustifolius foliage 48h before P. cinnamomi challenge negated the ability of the pathogen to colonise the root tissue and cause disease. Importantly, although the root profiles of water-treated and phosphite-treated plants post pathogen inoculation contained the same secondary metabolites, concentration variations were observed. Accumulation of secondary metabolites within the P. cinnamomi-inoculated plants confirms that pathogen ingress of the root interstitially occurs in phosphite-treated plants, confirming a direct mode of action against the pathogen upon breaching the root cells.

Production of phenolics and the emission of volatile organic compounds by perennial ryegrass (Lolium perenne L.)/Neotyphodium lolii association as a response to infection by Fusarium poae

Grasses very often form symbiotic associations with Neotyphodium/Epichloë endophytic fungi. These endophytes often allow the host grass to be protected from different pathogens. However, there is little known about the mechanisms of such endophyte influence on the host. Thus, the purpose of this research was to examine the effect of the N. lolii endophyte on the total production of phenolic compounds, VOCs emission and the resistance of three perennial ryegrass genotypes infected by pathogenic Fusarium poae. Analyses of total phenolics content were performed in control (not inoculated) and inoculated plants after 1, 2, 3, 4, 5, and 6 days (DAI) and for VOCs after 0, 3, 6 and 12 DAI. The presence of endophytes significantly reduced the disease index in two of the three genotypes relative to that in E-. Plants infected by N. lolii exhibited higher production of phenolics relative to the E- plants. The highest amounts of phenolics were observed on the second and sixth DAI. Genotype Nl22 showed the strongest effect of the endophyte on the production of phenolics, which increased by over 61%. Both the endophyte infected and non-infected plants emitted most abundantly two GLVs ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate), three terpenes (linalool, (Z)-ocimene, β-caryophyllene) and three shikimic acid pathway derivatives (benzyl acetate, indole, and methyl salicylate). The endophyte presence and the intervals of VOCs detection were a highly significant source of variation for all emitted volatiles (P<0.001). The genotype of the perennial ryegrass significantly affected only the emission of methyl salicylate (P<0.05) and β-caryophyllene (P<0.05). Most of the VOCs ((Z)-3-hexen-1-yl acetate, (Z)-3-hexenal, linalool and methyl salicylate) reached their highest levels of emission on the sixth DAI, when averaged over genotypes and endophyte status. The results highlight the role of Neotyphodium spp. in the mediation of quadro-trophic interactions among plants, symbiotic endophytes, invertebrate herbivores and plant pathogenic fungi. Our results also confirm the fact that symbiotic plants can activate a defense reaction faster than non-symbiotic plants after a pathogen attack. Thus, N. lolii can be involved in the defense of perennial ryegrass against pathogens and potentially could be central to the host plants' protection.

Transcription profile of soybean-root-knot nematode interaction reveals a key role of phythormones in the resistance reaction

BACKGROUND

Root-knot nematodes (RKN- Meloidogyne genus) present extensive challenges to soybean crop. The soybean line (PI 595099) is known to be resistant against specific strains and races of nematode species, thus its differential gene expression analysis can lead to a comprehensive gene expression profiling in the incompatible soybean-RKN interaction. Even though many disease resistance genes have been studied, little has been reported about phytohormone crosstalk on modulation of ROS signaling during soybean-RKN interaction.

RESULTS

Using 454 technology to explore the common aspects of resistance reaction during both parasitism and resistance phases it was verified that hormone, carbohydrate metabolism and stress related genes were consistently expressed at high levels in infected roots as compared to mock control. Most noteworthy genes include those encoding glycosyltransferases, peroxidases, auxin-responsive proteins and gibberellin-regulated genes. Our data analysis suggests the key role of glycosyltransferases, auxins and components of gibberellin signal transduction, biosynthesis and deactivation pathways in the resistance reaction and their participation in jasmonate signaling and redox homeostasis in mediating aspects of plant growth and responses to biotic stress.

CONCLUSIONS

Based on this study we suggest a reasonable model regarding to the complex mechanisms of crosstalk between plant hormones, mainly gibberellins and auxins, which can be crucial to modulate the levels of ROS in the resistance reaction to nematode invasion. The model also includes recent findings concerning to the participation of DELLA-like proteins and ROS signaling controlling plant immune or stress responses. Furthermore, this study provides a dataset of potential candidate genes involved in both nematode parasitism and resistance, which can be tested further for their role in this biological process using functional genomics approaches.

Interaction of cruciferous phytoanticipins with plant fungal pathogens: indole glucosinolates are not metabolized but the corresponding desulfo-derivatives and nitriles are

Glucosinolates represent a large group of plant natural products long known for diverse and fascinating physiological functions and activities. Despite the relevance and huge interest on the roles of indole glucosinolates in plant defense, little is known about their direct interaction with microbial plant pathogens. Toward this end, the metabolism of indolyl glucosinolates, their corresponding desulfo-derivatives, and derived metabolites, by three fungal species pathogenic on crucifers was investigated. While glucobrassicin, 1-methoxyglucobrassicin, 4-methoxyglucobrassicin were not metabolized by the pathogenic fungi Alternaria brassicicola, Rhizoctonia solani and Sclerotinia sclerotiorum, the corresponding desulfo-derivatives were metabolized to indolyl-3-acetonitrile, caulilexin C (1-methoxyindolyl-3-acetonitrile) and arvelexin (4-methoxyindolyl-3-acetonitrile) by R. solani and S. sclerotiorum, but not by A. brassicicola. That is, desulfo-glucosinolates were metabolized by two non-host-selective pathogens, but not by a host-selective. Indolyl-3-acetonitrile, caulilexin C and arvelexin were metabolized to the corresponding indole-3-carboxylic acids. Indolyl-3-acetonitriles displayed higher inhibitory activity than indole desulfo-glucosinolates. Indolyl-3-methanol displayed antifungal activity and was metabolized by A. brassicicola and R. solani to the less antifungal compounds indole-3-carboxaldehyde and indole-3-carboxylic acid. Diindolyl-3-methane was strongly antifungal and stable in fungal cultures, but ascorbigen was not stable in solution and displayed low antifungal activity; neither compound appeared to be metabolized by any of the three fungal species. The cell-free extracts of mycelia of A. brassicicola displayed low myrosinase activity using glucobrassicin as substrate, but myrosinase activity was not detectable in mycelia of either R. solani or S. sclerotiorum.

Novel acidic sesquiterpenoids constitute a dominant class of pathogen-induced phytoalexins in maize

Nonvolatile terpenoid phytoalexins occur throughout the plant kingdom, but until recently were not known constituents of chemical defense in maize (Zea mays). We describe a novel family of ubiquitous maize sesquiterpenoid phytoalexins, termed zealexins, which were discovered through characterization of Fusarium graminearum-induced responses. Zealexins accumulate to levels greater than 800 μg g⁻¹ fresh weight in F. graminearum-infected tissue. Their production is also elicited by a wide variety of fungi, Ostrinia nubilalis herbivory, and the synergistic action of jasmonic acid and ethylene. Zealexins exhibit antifungal activity against numerous phytopathogenic fungi at physiologically relevant concentrations. Structural elucidation of four members of this complex family revealed that all are acidic sesquiterpenoids containing a hydrocarbon skeleton that resembles β-macrocarpene. Induced zealexin accumulation is preceded by increased expression of the genes encoding TERPENE SYNTHASE6 (TPS6) and TPS11, which catalyze β-macrocarpene production. Furthermore, zealexin accumulation displays direct positive relationships with the transcript levels of both genes. Microarray analysis of F. graminearum-infected tissue revealed that Tps6/Tps11 were among the most highly up-regulated genes, as was An2, an ent-copalyl diphosphate synthase associated with production of kauralexins. Transcript profiling suggests that zealexins cooccur with a number of antimicrobial proteins, including chitinases and pathogenesis-related proteins. In addition to zealexins, kauralexins and the benzoxazinoid 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one-glucose (HDMBOA-glucose) were produced in fungal-infected tissue. HDMBOA-glucose accumulation occurred in both wild-type and benzoxazine-deficient1 (bx1) mutant lines, indicating that Bx1 gene activity is not required for HDMBOA biosynthesis. Together these results indicate an important cooperative role of terpenoid phytoalexins in maize biochemical defense.

Overexpression of Arabidopsis ACBP3 enhances NPR1-dependent plant resistance to Pseudomonas syringe pv tomato DC3000

ACBP3 is one of six Arabidopsis (Arabidopsis thaliana) genes, designated ACBP1 to ACBP6, that encode acyl-coenzyme A (CoA)-binding proteins (ACBPs). These ACBPs bind long-chain acyl-CoA esters and phospholipids and are involved in diverse cellular functions, including acyl-CoA homeostasis, development, and stress tolerance. Recombinant ACBP3 binds polyunsaturated acyl-CoA esters and phospholipids in vitro. Here, we show that ACBP3 plays a role in the plant defense response to the bacterial pathogen Pseudomonas syringae pv tomato DC3000. ACBP3 mRNA was up-regulated upon pathogen infection and treatments using pathogen elicitors and defense-related phytohormones. Transgenic Arabidopsis ACBP3 overexpressors (ACBP3-OEs) showed constitutive expression of pathogenesis-related genes (PR1, PR2, and PR5), cell death, and hydrogen peroxide accumulation in leaves. Consequently, ACBP3-OEs displayed enhanced resistance to the bacterial pathogen P. syringae DC3000. In contrast, the acbp3 T-DNA insertional mutant was more susceptible and exhibited lower PR gene transcript levels upon infection. Using the ACBP3 OE-1 line in combination with nonexpressor of PR genes1 (npr1-5) or coronatine-insensitive1 (coi1-2), we concluded that the enhanced PR gene expression and P. syringae DC3000 resistance in the ACBP3-OEs are dependent on the NPR1-mediated, but not the COI1-mediated, signaling pathway. Given that ACBP3-OEs showed greater susceptibility to infection by the necrotrophic fungus Botrytis cinerea while the acbp3 mutant was less susceptible, we suggest that ACBP3 plays a role in the plant defense response against biotrophic pathogens that is distinct from necrotrophic pathogens. ACBP3 function in plant defense was supported further by bioinformatics data showing up-regulation of many biotic and abiotic stress-related genes in ACBP3 OE-1 in comparison with the wild type.

The phytoalexins from cultivated and wild crucifers: chemistry and biology

Phytoalexins are antimicrobial secondary metabolites produced de novo by plants in response to stress, including microbial attack. In general, phytoalexins are important components of plant defenses against fungal and bacterial pathogens. The phytoalexins of crucifers are indole alkaloids derived from (S)-tryptophan, most of which contain a sulfur atom derived from cysteine. Beside their antimicrobial activity against different plant pathogenic species, cruciferous phytoalexins have shown anticarcinogenic effects on various human cell lines. This review focuses on the phytoalexins produced by cruciferous plants reported to date, with particular emphasis on their chemical synthesis, biosynthesis, metabolism by plant fungal pathogens and biological activities. A summary table containing all phytoalexins, their cultivated and wild cruciferous sources, their synthetic starting materials, biotransformation products and biological activities is provided.

Identity, regulation, and activity of inducible diterpenoid phytoalexins in maize

Phytoalexins constitute a broad category of pathogen- and insect-inducible biochemicals that locally protect plant tissues. Because of their agronomic significance, maize and rice have been extensively investigated for their terpenoid-based defenses, which include insect-inducible monoterpene and sesquiterpene volatiles. Rice also produces a complex array of pathogen-inducible diterpenoid phytoalexins. Despite the demonstration of fungal-induced ent-kaur-15-ene production in maize over 30 y ago, the identity of functionally analogous maize diterpenoid phytoalexins has remained elusive. In response to stem attack by the European corn borer (Ostrinia nubilalis) and fungi, we observed the induced accumulation of six ent-kaurane-related diterpenoids, collectively termed kauralexins. Isolation and identification of the predominant Rhizopus microsporus-induced metabolites revealed ent-kaur-19-al-17-oic acid and the unique analog ent-kaur-15-en-19-al-17-oic acid, assigned as kauralexins A3 and B3, respectively. Encoding an ent-copalyl diphosphate synthase, fungal-induced An2 transcript accumulation precedes highly localized kauralexin production, which can eventually exceed 100 μg · g(-1) fresh weight. Pharmacological applications of jasmonic acid and ethylene also synergize the induced accumulation of kauralexins. Occurring at elevated levels in the scutella of all inbred lines examined, kauralexins appear ubiquitous in maize. At concentrations as low as 10 μg · mL(-1), kauralexin B3 significantly inhibited the growth of the opportunistic necrotroph R. microsporus and the causal agent of anthracnose stalk rot, Colletotrichum graminicola. Kauralexins also exhibited significant O. nubilalis antifeedant activity. Our work establishes the presence of diterpenoid defenses in maize and enables a more detailed analysis of their biosynthetic pathways, regulation, and crop defense function.

Identification of flavone phytoalexins and a pathogen-inducible flavone synthase II gene (SbFNSII) in sorghum

Following inoculation with the anthracnose pathogen Colletotrichum sublineolum, seedlings of the sorghum resistant cultivar SC748-5 showed more rapid and elevated accumulation of luteolin than the susceptible cultivar BTx623. On the other hand, apigenin was the major flavone detected in infected BTx623 seedlings. Luteolin was demonstrated to show stronger inhibition of spore germination of C. sublineolum than apigenin. Because of their pathogen-inducible and antifungal nature, both flavone aglycones are considered sorghum phytoalexins. The key enzyme responsible for flavone biosynthesis has not been characterized in monocots. A sorghum pathogen-inducible gene encoding a cytochrome P450 protein (CYP93G3) in the uncharacterized CYP93G subfamily was identified. Transgenic expression of the P450 gene in Arabidopsis demonstrated that the encoded protein is a functional flavone synthase (FNS) II in planta. The sorghum gene was then termed SbFNSII. It is a single-copy gene located on chromosome 2 and the first FNSII gene characterized in a monocot. Metabolite analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in precursor ion scan mode revealed the accumulation of 2-hydroxynaringenin and 2-hydroxyeriodictyol hexosides in the transgenic Arabidopsis plants. Hence, SbFNSII appears to share a similar catalytic mechanism with the licorice and Medicago truncatula FNSIIs (CYP93B subfamily) by converting flavanones to flavone through the formation of 2-hydroxyflavanones.

Trypanosoma cruzi: antiproliferative effect of indole phytoalexins on intracellular amastigotes in vitro

American trypanosomiasis (Chagas disease) continues to be a significant public health problem, and the therapeutic potential of current antichagasic agents (nifurtimox and benznidazole) is rather limited. Here we report on the antitrypanosomal effect of 1-methoxyspirobrassinol and other indole phytoalexins--secondary metabolites produced by Cruciferous plants. These compounds, that previously demonstrated antimicrobial and anticancer properties, displayed significant antiproliferative effects on intracellular amastigotes of Trypanosoma cruzi and may be prospective candidates for antichagasic drug design and development.

Ultraviolet-C and induced stilbenes control ochratoxigenic Aspergillus in grapes

This study investigated the efficacy of ultraviolet-C (254 nm) and induced stilbenes to inhibit Aspergillus carbonarius and Aspergillus tubingensis and control ochratoxin A production in grapes. In addition, the stilbene synthesis as a response to UV-C treatment and to infection of ochratoxigenic Aspergillus was compared. The initial microbial inactivation by a previously optimized UV-C illumination protocol for increasing trans-resveratrol content in grapes (50 W/m (2), 40 cm, 60 s) was similar on undamaged and damaged grapes, achieving 1.2 and 1.3 log conidia/100 g reductions, respectively. After 5 days of storage at 22 degrees C, UV-C treatment and the stilbenes induced by UV-C inhibited ochratoxigenic Aspergillus growth in undamaged grapes. UV-C elicited the biosynthesis of trans-resveratrol, while microbial infection and tissue damage triggered the biosynthesis of trans-piceid. trans-Resveratrol was not synthesized as a consequence of ochratoxigenic Aspergillus contamination. However, when trans-resveratrol was synthesized by UV-C, it contributed to inhibiting the development of ochratoxin A producing aspergilli. Furthermore, UV-C treatment also contributed to decrease ochratoxin A production by ochratoxigenic aspergilli. Therefore, UV-C is a promising emerging technology either for reducing the potential ochratoxigenic risk in grapes, which is of particular interest to the wine industry, and also for increasing trans-resveratrol content of grapes, which would provide an added value to the wine.

Detection of microcystin contamination by the measurement of the variability of the in vivo chlorophyll fluorescence in aquatic plant Lemna gibba

In recent years, chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant ecophysiologists. In this work, the chlorophyll fluorescence is used in order to evaluate the biotic stress induced by exposure to cyanobacterial toxins (microcystins). Experiments were carried on the aquatic plant Lemna gibba exposed to various concentrations of a microcystins (0.01, 0.03, 0.05, 0.07, 0.15, 0.22 and 0.3mug equivalent MC-LR.mL(-1)) during 5h. The reversibility of the stress changes was also studied following 24h of treatment. The efficiency and the utility of this biophysical technique were compared to biochemical analysis priory used to evaluate the plant stress induced by such contamination. The results showed that there is a concentration-dependent effect on the measured in vivo chlorophyll fluorescence with significant differences between the control and all concentrations except for 0.01mug equivalent MC-LR.mL(-1). The reversibility tested showed also that after avoiding the contact with the microcystins, the chlorophyll fluorescence measurements were not significantly different from the control. The results showed that if the contact with the microcystins is short and not repeated plants may not suffer from a significant stress. We concluded that this simple and rapid technique based on the variable fluorescence, could be recommended and applied to test the plant stress caused by cyanobacterial toxins.

INDUÇÃO DE FITOALEXINAS E ATIVIDADE DE PEROXIDASES EM SORGO E SOJA TRATADOS COM EXTRATOS DE BASIDIOCARPOS DE PYCNOPORUS SANGUINEUS

RESUMO Este trabalho objetivou avaliar a indução de fitoalexinas e a atividade de peroxidases em sorgo e soja tratados com extratos de basidiocarpos de Pycnoporus sanguineus. Os extratos diclorometânico, hexânico e etanólico com 100, 250, 500 e 750 mg/L foram testados em relação à indução da produção de fitoalexinas e atividade de peroxidases em cotilédones de soja e mesocótilos estiolados de sorgo. Acibenzolar-S-metil (200 mg/L do produto comercial) e água destilada + Tween 20 foram utilizados como tratamentos controles positivo e negativo, respectivamente. Parafitoalexinas em mesocótilos de sorgo, o extrato hexânico (750 mg/L) proporcionou a maior indução, porém sem diferir significativamente do ASM. Para fitoalexinas em cotilédones de soja, os extratos de P. sanguineus não induziram atividade significativamente diferente dos tratamentos controles positivo e negativo, havendo uma tendência de supressão da síntese de gliceolina pelo extrato diclorometânico. Em relação às peroxidases, os extratos diclorometânico para sorgo e soja e etanólico para soja inibiram a atividade enzimática. A indução verificada para o extrato hexânico em sorgo não diferiu do controle ASM. A atividade específica de peroxidase em soja foi inibida pelo extrato etanólico e induzida pelo hexânico, mas sem diferença do tratamento com ASM. Esses resultados indicam o pequeno potencial destes extratos para a indução de resistência em patossistemas envolvendo sorgo e soja.

Localization of stilbene synthase in Vitis vinifera L. during berry development

The localization of stilbene synthase (STS) (EC 2.3.1.95) in grape berry (Vitis vinifera L.) was investigated during fruit development. The berries were collected at 2, 4, 7, 11, and 15 weeks postflowering from the cultivar Nebbiolo during the 2005 and 2006 growing seasons. High-performance liquid chromatography analysis showed that berries accumulated cis- and trans-isomers of resveratrol mainly in the exocarp throughout fruit development. Immunodetection of STS protein was performed on berry extracts and sections with an antibody specifically developed against recombinant grape STS1. In agreement with resveratrol presence, STS was found in berry exocarp tissues during all stages of fruit development. The labeled epidermal cells were few and were randomly distributed, whereas nearly all the outer hypodermis cells were STS-positive. The STS signal decreased gradually from exocarp to mesocarp, where the protein was detected only occasionally. At the subcellular level, STS was found predominantly within vesicles (of varying size), along the plasma membrane and in the cell wall, suggesting protein secretion in the apoplast compartment. Despite the differences in fruit size and structure, the STS localization was the same before and after veraison, the relatively short developmental period during which the firm green berries begin to soften and change color. Nevertheless, the amount of protein detected in both exocarp and mesocarp decreased significantly in ripe berries, in agreement with the lower resveratrol content measured in the same tissues. The location of STS in exocarp cell wall is consistent with its role in synthesizing defense compounds and supports the hypothesis that a differential localization of phenylpropanoid biosynthetic machinery regulates the deposition of specific secondary products at different action sites within cells.

Histopathology comparison and phenylalanine ammonia lyase (PAL) gene expressions in Fusarium wilt infected watermelons

Fusarium wilt disease of watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai), caused by Fusarium oxysporum f. sp. niveum (FON), is one of the limiting factors of worldwide watermelon production. In this study, a Fusarium wilt resistant watermelon JSB, which was derived from a spontaneous mutation of the susceptible Sugar Baby (SB), was used to investigate histopathology. The number and diameter of xylem vessels in the root (10 mm below the shoot base) of resistant JSB plants were significantly higher than those in susceptible SB plants. At 9 days post inoculation (dpi), using the plate assay on Nash-PCNB media, FON could be recovered from 86% of the roots in the symptomless plants of both watermelon lines, and from 55% and 64% of the stem segments (5 mm above the shoot base) in resistant and susceptible plants, respectively. In paraffin and free-hand tissue sections, at 8, 13, and 35 dpi, the xylem of roots and stems close to the soil surface in resistant watermelon JSB plants was also colonised by FON, but to a much lower percentage than the susceptible SB ones. No colonisation below the middle of stems was observed in the resistant JSB plants. The susceptible plants grown in infested soil were all dead by 35 dpi, while the resistant plants remained healthy. These observations suggest that reducing FON colonisation in the vascular systems of the host may contribute to the resistance in JSB. Furthermore, the higher expression of the phenylalanine ammonia lyase (PAL) gene in JSB induced by FON and the effects of PAL inhibitor on the resistance of JSB suggested that PAL is involved in resistance of watermelon to Fusarium wilt pathogen.

Overexpression of the apple MpNPR1 gene confers increased disease resistance in Malus x domestica

The NPR1 gene plays a pivotal role in systemic acquired resistance in plants. Its overexpression in Arabidopsis and rice results in increased disease resistance and elevated expression of pathogenesis-related (PR) genes. An NPR1 homolog, MpNPR1-1, was cloned from apple (Malus x domestica) and overexpressed in two important apple cultivars, Galaxy and M26. Apple leaf pieces were transformed with the MpNPR1 cDNA under the control of the inducible Pin2 or constitutive Cauliflower mosaic virus (CaMV)35S promoter using Agrobacterium tumefaciens. Overexpression of MpNPR1 mRNA was shown by reverse transcriptase-polymerase chain reaction. Activation of some PR genes (PR2, PR5, and PR8) was observed. Resistance to fire blight was evaluated in a growth chamber by inoculation of the shoot tips of our own rooted 30-cm-tall plants with virulent strain Ea273 of Erwinia amylovora. Transformed Galaxy lines overexpressing MpNPR1 had 32 to 40% of shoot length infected, compared with 80% in control Galaxy plants. Transformed M26 lines overexpressing MpNPR1 under the control of the CaMV35S promoter also showed a significant reduction of disease compared with control M26 plants. Some MpNPR-overexpressing Galaxy lines also exhibited increased resistance to two important fungal pathogens of apple, Venturia inaequalis and Gymnosporangium juniperi-virginianae. Selected transformed lines have been propagated for field trials for disease resistance and fruit quality.

Phytotoxic effects of cyanobacteria extract on the aquatic plant Lemna gibba: microcystin accumulation, detoxication and oxidative stress induction

The occurrence of toxic cyanobacteria in the aquatic environment constitutes a serious risk for the ecological balance and the functioning of ecosystems. The presence of cyanotoxins in ecosystems could have eventual adverse effects on aquatic plants, which play an important biological role as primary producers. The original aim of this study was to investigate microcystin (MC) accumulation, detoxication and oxidative stress induction in the free-floating aquatic vascular plant Lemna gibba (Duckweed, Lemnaceae). Experiments were carried out with a range of MC levels, obtained from toxic Microcystis culture extracts (0.075, 0.15, 0.22 and 0.3 microg equiv.MC-LR mL(-1)). During chronic exposure of the plant to MC, we examined the growth, photosynthetic pigment contents and also the physiological behavior related to toxin accumulation, possible biodegradation and stress oxidative processes of L. gibba. For the last reason, changes in peroxidase activity and phenol compound content were determined. This is a first report using phenol compounds as indicators of biotic stress induced by MC contamination in aquatic plants. Following MC exposure, a significant decrease of plant growth and chlorophyll content was observed. Also, it was demonstrated that L. gibba could take up and bio-transform microcystins. A suspected MC degradation metabolite was detected in treated Lemna cells. In response to chronic contamination with MCs, changes in the peroxidase activity and qualitative and quantitative changes in phenolic compounds were observed after 24h of plant exposure. The physiological effects induced by chronic exposure to microcystins confirm that in aquatic ecosystems plants coexisting with toxic cyanobacterial blooms may suffer an important negative ecological impact. This may represent a sanitary risk due to toxin bioaccumulation and biotransfer through the food chain.

Resistance of sunflower to the biotrophic oomycete Plasmopara halstedii is associated with a delayed hypersensitive response within the hypocotyls

The biotrophic oomycete Plasmopara halstedii is the causal agent of downy mildew in sunflower. It penetrates the roots of both susceptible and resistant sunflower lines and grows through the hypocotyls towards the upper part of the seedling. RT-PCR analysis has shown that resistance is associated with the activation of a hsr203J-like gene, which is a molecular marker of the hypersensitive reaction in tobacco. Activation of this gene was specifically observed during the incompatible interaction and coincided with cell collapse in the hypocotyls. This HR was also associated with the early and local activation of the NPR1 gene which is a key component in the establishment of the SAR. No such HR or a significant activation of the hsr203J-like gene were observed during the compatible combination. These results suggest that the resistance of sunflower to P. halstedii is associated with an HR which fails to halt the parasite. By contrast, this HR triggers a SAR which takes places in the upper part of the hypocotyls and eventually leads to the arrest of parasite growth. A model describing the resistance of plants to root-infecting oomycetes is proposed.

Multiple defence signals induced by Erwinia carotovora ssp. carotovora elicitors in potato

SUMMARY Signal pathways involved in Solanum tuberosum-Erwinia carotovora ssp. carotovora(SCC3193) interaction were characterized. To this end, the concentration of several signal molecules implicated in plant defence such as ethylene (ET), jasmonates (JA) and salicylic acid (SA) were measured in potato plants treated by cell-free culture filtrates (CF) from E. c. carotovora(SCC3193). Furthermore, the presence of other potential signalling compounds such as cinnamic acid (CA) and related aromatic compounds was screened in the elicitor-treated plants. The activity of these signal compounds as inducers of defence-related genes such as drd-1 (a defence-related alcohol dehydrogenase), pinII (proteinase inhibitor II), chtB4 (basic chitinase) and chtA2 (acidic chitinase) was characterized. The results demonstrate that ET, JA and CA accumulate in potato tissues in response to CF. These signal molecules were shown to induce differential expression of drd-1, pinII, chtB4 and chtA2. Our data suggest that in addition to ET and JA, CA and possibly other aromatic compounds also may play a role in defence signalling in potato.

Anthocyanins in cereals

The anthocyanic composition of some pigmented cereals is still not well established, neither in relation to some of their components, nor from the quantitative point of view. Nonetheless, the use of analytical techniques, such as diode array spectroscopy and mass spectrometry (MS, PDMS, MALDI) coupled or not to liquid chromatography, are permitting, in recent years, the confirmation of the structure of some of the principal anthocyanins and a knowledge of those which are present in minor proportion. In this article, firstly, a review of the principal methods of analysis of anthocyanins is made. This is followed by a review of the most significant advances achieved in the last years in the field of the identification and quantification of these pigments in cereals and the present uses of the commercial extracts of anthocyanins obtained from these sources and the perspectives for their use is included.

Nickelophilous plants and their significance in phytotechnologies

Nickeliferous soils are invaded predominantly by members of the Brassicaceae, Cyperaceae, Cunoniaceae, Caryophyllaceae, Fabaceae, Flacourtiaceae, Euphorbiaceous, Lamiaceae, Poaceae and Violaceae, and many of these plants are metal tolerant. About 300 Ni hyperaccumulating plants been identified. These members exhibit unusual appetite for toxic metals and elemental defense. Hyperaccumulators provide protection against fungal and insect attack. Investigations suggested that Ni-hyperaccumulation has a protective function against fungal and bacterial pathogens in Streptanthus polygaloides and Thlaspi montanum. Significance of nickelophilous plants and their significance in phytotechnologies are discussed in this paper.

Metabolism and detoxification of phytoalexins and analogs by phytopathogenic fungi

To date, the many examples reporting that fungal pathogens can efficiently detoxify phytoalexins provide strong evidence that the pathogenicity and/or virulence of some fungi is linked to their ability to detoxify their hosts' phytoalexins. The pathways used by plant pathogenic fungi to metabolize and detoxify phytoalexins are reviewed. Prospects for application of recent findings are discussed.

Cyclic nucleotides

The natural occurrence of cyclic nucleotides in higher plants, formerly a topic of fierce debate, is now established, as is the presence of nucleotidyl cyclases and cyclic nucleotide phosphodiesterases capable of their synthesis and breakdown. Here we describe the significant properties of cyclic nucleotides, also outlining their second messenger functions and the history of plant cyclic nucleotide research over its first three decades. Findings of the last five years are detailed within the context of the functional role of cyclic nucleotides in higher plants, with particular emphasis upon nucleotidyl cyclases and cyclic nucleotide-responsive protein kinases, -binding proteins and -gated ion channels, with future objectives and strategies discussed.