Chemical Defense System Research Articles

Defensive chemistry of an aposematic bug, Pachycoris stallii Uhler and volatile compounds of its host plant Croton californicus Muell.-Arg.

Volatile components of Pachycoris stallii scent gland secretions and the bug's host plant, Croton californicus, were identified by gas chromatography and mass spectroscopy. The predominant compounds isolated from C. californicus fruit and leaves were beta-myrcene and beta-caryophyllene. Metathoracic gland secretions of P. stallii contained mostly (E)-2-hexenal, (E)-4-oxo-2-hexenal, (E)-2-hexenyl acetate, and n-tridecane. In males, n-tridecane was present throughout the metathoracic gland, but in females this compound was found only in the median reservoir/accessory gland. (E)-2-Hexenal was present throughout the gland of female bugs, but in males was primarily present in the median reservoir/accessory gland. (E)-4-Oxo-2-hexenal and n-dodecane were isolated from the median reservoir/accessory gland of male and female bugs. Metathoracic glands were sexually monomorphic. Data from chemical analyses and anatomical observations suggest that dorsal abdominal glands of adults were apparently obsolescent. In nymphs, dorsal abdominal glands produced (E)-2-hexenal, (E )-4-oxo-2-hexenal, n-dodecane, n-tridecane, and tetradecanal. The proportion of the predominant constituent, (E)-4-oxo-2-hexenal, decreased from 72% in the first instar to 47% in the fourth instar. Proportions of tetradecanal and n-tridecane were greater in the fourth instar than in the first instar. Observations of dissected glands indicated that median and posterior dorsal abdominal glands of all nymphal instars were more developed than anterior dorsal abdominal glands. Scanning electron micrography revealed the presence of polygonal microsculpturing on the integument surrounding the ostioles of metathoracic and dorsal abdominal glands. Chemical, anatomical, and behavioral data indicated that P. stallii has a chemical defense system based on short-chain carbonyl compounds and that this system is directed against arthropods. The abundance of arthropod natural enemies apparently has forced P. stallii to maintain this defense system despite feeding on a toxic host plant.

The chemical defense ecology of marine unicellular plankton: constraints, mechanisms, and impacts.

The activities of unicellular microbes dominate the ecology of the marine environment, but the chemical signals that determine behavioral interactions are poorly known. In particular, chemical signals between microbial predators and prey contribute to food selection or avoidance and to defense, factors that probably affect trophic structure and such large-scale features as algal blooms. Using defense as an example, I consider physical constraints on the transmission of chemical information, and strategies and mechanisms that microbes might use to send chemical signals. Chemical signals in a low Re, viscosity-dominated physical environment are transferred by molecular diffusion and laminar advection, and may be perceived at nanomolar levels or lower. Events that occur on small temporal and physical scales in the "near-field" of prey are likely to play a role in cell-cell interactions. On the basis of cost-benefit optimization and the need for rapid activation, I suggest that microbial defense system strategies might be highly dynamic. These strategies include compartmented and activated reactions, utilizing both pulsed release of dissolved signals and contact-activated signals at the cell surface. Bioluminescence and extrusome discharge are two visible manifestations of rapidly activated microbial defenses that may serve as models for other chemical reactions as yet undetected due to the technical problems of measuring transient chemical gradients around single cells. As an example, I detail an algal dimethylsulfoniopropionate (DMSP) cleavage reaction that appears to deter protozoan feeding and explore it as a possible model for a rapidly activated, short-range chemical defense system. Although the exploration of chemical interactions among planktonic microbes is in its infancy, ecological models from macroorganisms provide useful hints of the complexity likely to be found.

Reduced antimicrobial peptide expression in human burn wounds

Severely burned skin ceases to perform its natural protective role and surrenders itself as a nidus and portal for bacterial invasion. Antimicrobial peptides are part of a non-specific chemical defence system, separate from cellular and humoral immunity. Two of these peptides, human beta-defensins 1 and 2 have been recently found in skin and are produced by keratinocytes. Beta defensins have potent bactericidal activity against a wide spectrum of bacterial and fungal organisms commonly responsible for burn wound infections. To date, expression of beta defensins has not been examined in the human burn wound. Our findings demonstrate that expression of hBD-2 is greatly decreased in the burn wound whereas hBD-1 appears to be preserved. These results may have important implications in the pathogenesis and treatment of invasive burn sepsis.

Marine natural products influencing larval settlement and metamorphosis of marine sessile organisms

Most marine sessile organisms have a planktonic larval phase in their life cycles, and then larvae settle and metamorphose into their adult forms. The selection of settlement sites is a critical event for these organisms because settlement on unsuitable places affects their survivorship severely. Ascidians live gregariously, and conspecific chemical cues are thought to play an important role in gregarious settlement of larvae. The extracts of conspecific adults or larvae have been claimed to contain "natural metamorphosis inducers." Little is known, however, about their chemical properties. To discover natural signal substances for larval metamorphosis in ascidians, we surveyed the metamorphosis-inducing activity of the medium conditioned by ascidian larvae, and succeeded in isolating a metamorphosis-inducing substance from the conditioned medium of Halocycthia roretzi larvae and found that it was identical to lumichrome. We have also isolated more than 40 active metabolites, which may mimic lumichrome, from marine sponges. On the contrary, marine sessile organisms cause serious problems by settling on fishing nets, hulls of ships, and cooling systems of power plants. Organotin compounds have been widely used for the control of these organisms, but they are known to be toxic to marine biota. Therefore, nontoxic antifouling substances are urgently needed. Marine sessile organisms possess chemical defense systems using their secondary metabolites, which might be potential by nontoxic antifouling agents. We have attempted to obtain antibarnacle substances from marine sponges and isolated 26 antifoulants.

Production of bioactive secondary metabolites in the fruit bodies of macrofungi as a response to injury

The conversion of secondary metabolites as a response to injury in fruit bodies of 121 species of Ascomycetes and Basidiomycetes was investigated. Extracts of intact and injured specimens were compared by analysis with TLC, and by assaying their antifungal (against Nematospora coryli), antibacterial (against Bacillus brevis) and nematicidal (against Caenorhabditis elegans) activities. Significant conversions induced by injury were observed (by TLC comparison) in the extracts of 66 species. For 37 of these the extract of the injured specimen showed higher bioactivity. Of the remaining 55 species, in which no changes between the extracts of intact and injured fruit bodies were observed, 30 were found to contain bioactive compounds. The possibility that these findings reflect the presence of chemical defence systems in mushrooms, mediated by enzymatic conversions activated by physical injury, is discussed.

Parallel evolution of glucosinolate biosynthesis inferred from congruent nuclear and plastid gene phylogenies

The phytochemical system of mustard-oil glucosides (glucosinolates) accompanied by the hydrolytic enzyme myrosinase (beta-thioglucosidase), the latter usually compartmented in special myrosin cells, characterizes plants in 16 families of angiosperms. Traditional classifications place these taxa in many separate orders and thus imply multiple convergences in the origin of this chemical defense system. DNA sequencing of the chloroplast rbcL gene for representatives of all 16 families and several putative relatives, with phylogenetic analyses by parsimony and maximum likelihood methods, demonstrated instead a single major clade of mustard-oil plants and one phylogenetic outlier. In a further independent test, DNA sequencing of the nuclear 18S ribosomal RNA gene for all these exemplars has yielded the same result, a major mustard-oil clade of 15 families (Akaniaceae, Bataceae, Brassicaceae, Bretschneideraceae, Capparaceae, Caricaceae, Gyrostemonaceae, Koeberliniaceae, Limnanthaceae, Moringaceae, Pentadiplandraceae, Resedaceae, Salvadoraceae, Tovariaceae, and Tropaeolaceae) and one outlier, the genus Drypetes, traditionally placed in Euphorbiaceae. Concatenating the two gene sequences (for a total of 3254 nucleotides) in a data set for 33 taxa, we obtain robust support for this finding of parallel origins of glucosinolate biosynthesis. From likely cyanogenic ancestors, the "mustard oil bomb" was invented twice.

Diversity and composition of phytophagous insect guilds on Brassicaceae

We investigated the guild structure of phytophagous insects on Brassicaceae in Poland and the influence of host-plant parameters (e.g. sampling effort, geographical distribution, taxonomic isolation, nitrogen indicator values) on the species richness of these guilds. The data were extracted from a study published by Lipa et al. The overall number of recorded ectophagous species is about twice the number of endophagous species. Irrespective of the feeding niche, species are predominantly oligophagous, feeding on more than two Brassicaceae genera. The relative importance of endophagous species within the fauna decreases with increasing host range. The sampling effort predicts a high proportion of the variance of alpha-diversity in oligo- and polyphagous insects, but only a low proportion in specialized species. After correction for sampling effort, most of the plant parameters do not explain an additional proportion of the variance in species richness. We hypothesize that the uniform chemical defence system across genera in Brassicaceae is an important factor triggering host range and diversity patterns in phytophagous insects on crucifers.

Tryptophan decarboxylase is encoded by two autonomously regulated genes in Camptotheca acuminata which are differentially expressed during development and stress.

Camptothecin (CPT) is a valuable anti-cancer monoterpene alkaloid produced by the Chinese tree Camptotheca acuminata. Tryptophan decarboxylase (TDC) supplies tryptamine for the indole moiety of CPT and its derivatives, and is considered a key step in monoterpene indole alkaloid biosynthesis as it links primary and secondary metabolism. This report describes the isolation and characterization of tdc1 and tdc2, two autonomously regulated TDC genes from Camptotheca. When expressed in Escherichia coli, the products of each gene could decarboxylate tryptophan, but were inactive against tyrosine, phenylalanine and 3,4-dihydroxyphenylalanine (dopa), tdc1 was developmentally regulated, having its highest expression level in the apex, young stem and bark, tissues which also contain the highest levels of CPT. Expression of tdc1 also increased during seedling development and was correlated with alkaloid accumulation during germination. tdc2 expression was induced in Camptotheca leaf discs and cell suspension cultures treated with fungal elicitor or methyl jasmonate, treatments which did not affect tdc1 expression. Unlike tdc1, tdc2 expression was not detected in any unstressed Camptotheca tissues nor in developing seedlings. These data suggest that tdc1 may be part of a developmentally regulated chemical defense system in Camptotheca, while tdc2 serves as part of a defense system induced during pathogen challenge.

Shoot Survival under Intense Grazing for Two Broad-Leaved Herbs with Different Chemical Defense Systems

Shoot survival under intense grazing for two broad-leaved herbs with different chemical defense systems

73 β-Amyloid precursor protein immunoreactivity does not increases in the cortex and hippocampus of the rat brain in consequence of cholinergic hypoactivity

Human skin is able to mount a fast response against invading harmful bacteria through the rapid production of inducible peptide antibiotics such as the human β-defensins (hBD). To gain more insight into the role and regulation of inducible β-defensins in the innate immunity of human skin, we investigated whether gene induction of the human β-defensins hBD-1, -2, -3, and -4 in keratinocytes is regulated in a similar manner. Therefore, we performed a comparative study of gene expression of these four hBD in primary cultured keratinocytes using real-time PCR. A basal mRNA expression was observed for all four hBD in primary keratinocytes, which strongly increased for hBD-2, -3, and -4 during Ca2+-induced differentiation of the keratinocytes. This effect was completely abolished when the keratinocytes were pre-treated with all-trans-retinoic acid (RA). Furthermore, the differential induction of hBD-2, -3, and -4 gene expression in keratinocytes by proinflammatory cytokines, phorbol-myristate-acetate (PMA), and bacteria was inhibited by more than 90% when the keratinocytes were pre-incubated with RA. Inhibition of IL-1β-mediated hBD-2 induction through RA was further confirmed by gene reporter assays and western-blot analysis. We conclude that RA is a potent inhibitor of β-defensin induction in keratinocytes and might downregulate the inducible innate chemical defense system of human skin.

Peptides as weapons against microorganisms in the chemical defense system of vertebrates.

The innate immunity of vertebrates to microbial invasion is arbitrated by a network of host-defense mechanisms involving both the long-lasting highly specific responses of the cell-mediated immune system and a nonspecific chemical defense system based on a series of broad-spectrum antimicrobial peptides that are analogous to those found in insects. Vertebrate antibiotic peptides secreted by nonlymphoid cells of the mucosal surfaces of the respiratory and gastrointestinal tracts as well as by the granular glands of the skin reportedly cause the lysis of numerous pathogenic microorganisms, including viruses, gram-positive and gram-negative bacteria, protozoa, yeasts, and fungi, as well as of cancer cells. Antimicrobial peptides isolated from vertebrates have three characteristic properties: They are relatively small (20-46 amino acid residues), basic (lysine- or arginine-rich), and amphipathic. Although these peptides differ widely in length and amino acid sequences, they may be grouped in four broad families based on characteristic structural features. Although the precise mechanism of action of these peptides remains to be defined, their microbicidal effect very likely results from their capacity to form channels or pores within the microbial membrane in order to permeate the cell and impair its ability to carry out anabolic processes. This secondary, chemical immune system provides vertebrates with a repertoire of small peptides that are promptly synthesized upon induction, easily stored in large amounts, and readily available for antimicrobial warfare.

Analysis of the chemical defence system in an insect larva by tandem mass spectrometry

AbstractLarvae of the sawfly Rhadinoceraea nodicornis Konow (Hymenoptera, Tenthredinidae) living on the plant Veratrum album L. (Liliales, Melanthiaceae) are efficiently protected against ants and spiders. Moreover, when their haemolymph was offered in a sugar solution, ants were still deterred. The chemical defence system of these larvae was investigated and the structures of the biologically active compounds determined by tandem mass spectrometry. Plant‐derived alkaloids both in original and metabolized form were found in the larval haemolymph.

Toxic terpenoids from higher fungi and their possible role in chemical defence systems

Toxic terpenoids from higher fungi and their possible role in chemical defence systems

Peptides as Weapons Against Microorganisms in the Chemical Defense System of Vertebrates

Human coronavirus (HCoV) infection causes respiratory diseases with mild to severe outcomes. In the last 15 years, we have witnessed the emergence of two zoonotic, highly pathogenic HCoVs: severe acute respiratory syndrome coronavirus (SARS-CoV) and ...Read More

A new type of antimicrobial phenolics produced by plant peroxidase and its possible role in the chemical defense systems against plant pathogens.

Syringaldehyde readily reacted in the horse-radish peroxidase (HRPOD) system. The ethyl acetate extract of the reaction mixture showed a marked antimicrobial activity against bacteria and fungi. After repeated column chromatography three potential antimicrobial compounds were obtained from the extract. The structural elucidation of active compounds was achieved by a combination of spectroscopic techniques and chemical modification.

New Farnesane Sesquiterpenes from Lactarius porninsis

Intact fruiting-bodies of Lactarius porninsis contain a mixture of new fatty acid esters. If the fruiting bodies are injured, these esters are converted rapidly to the two new farnesane sesquiterpenes porninsal and porninsol. This enzymatic conversion of sesquiterpenes may be part of a new variant of the chemical defense system that protects pungent or bitter Russulaceae species against parasites and predators

Local and geographic variation in the defensive chemistry of a West Indian gorgonian coral (Briareum asbestinum)

We sampled the between-colony and between-habitat variation in defensive chemistry of colonies of Briareum asbestinum, one of the most ubiquitous and chemically deterrent of the West Indian gorgonians. The basis of deterrence appears to reside in a diverse complement of 5 to 15 briarane and asbestinane diterpenoids found in individual colonies. Variation in chemistry of colonies is extensive throughout the Bahamas and the Virgin Islands: the complement of compounds is slightly different a t each site in the Bahamas and colonies from all the Bahamian sites are distinct from those a t the St. Croix (US Virgin Islands) site. St. Croix colonies not only differ in their composition of compounds, but also have fewer major diterpenoids than colonies from shallow water sites in the Bahamas. The shallow St. Croix extracts also differ in being dominated by asbestinanes instead of briaranes as in the Bahamas. The qualitative chemistry of colonies also vanes locally between depths near San Salvador and Chub Cay, 2 islands in the Bahamas. At both sites, the ratio of briarane to asbestinane diterpenoids was higher in shallow (1 to 12 m) water colonles than In deeper ones (25 to 40 m) . To determine whether the qualitative differences in chemistry between depths could be induced or were fixed, colonies were transplanted from shallow to deep reefs in San Salvador. After 7 mo, newly grown tlssue from transplanted colonies still retained the same shallow water diterpenes. This experiment suggests that the qualitative differences in chemistry observed with depth are fixed in adult colon~es. We also sampled quantitative variation in colonies from St. Croix and the Bahamas. Although we expected higher levels of compounds in shallow colonies because both productivity and numbers of predators are higher in shallow waters, at both sites levels of compounds were higher in deeper waters Briareum asbestinum is unusual in being heavily invested with a diversity of extremely deterrent diterpenoids. The outstanding feature of this chemical defense system is the qualitative variation In the chen~lstry of colonies from different habitats, which appears to be genetically fixed, raising the question of what selective agents maintain the variation in chemistry among different habitats

The Effect of Potassium on Growth and Nutrient Uptake in Two Forest Herbs with Different Chemical Defence Systems

We studied the growth and pattern of nutrient allocation (N, P, K and Ca) in two perennial forest herbs, Actaea spicata and Geranium sylvaticum, under five different potassium regimes in a greenhouse experiment. The two species differ with regard to their defence system, viz. Actaea spicata is highly toxic whereas Geranium sylvaticum is less toxic. A. spicata was limited by potassium and the response patterns in both growth and potassium uptake were characterized by a threshold below which a variation in potassium supply had no significant effect on growth and K uptake. A. spicata showed a limited ability to adjust growth and nutrient allocation as a response to different supplies of potassium. G. sylvaticum was less limited by potassium and was better able to adjust growth and allocation patterns to compensate for different supplies of potassium. The proportional allocation of phosphorus was affected by external concentrations of potassium in both species, but this effect was more pronounced in Actaea. No treatment effects were found for proportional allocation of nitrogen, potassium or calcium. We conclude that a high availability of K may be necessary for an appropriate development of toxic species. Limited ability of adjustments in growth and allocation may restrict the ecological range of toxic species.

Cutaneous venom of Bombina variegata pachypus (Amphibia, anura): Effects on the growth of the human HL 60 cell line

The effects of Bombina variegata cutaneous venom (Bvv) on eukaryotic cell growth has been assessed employing the human leukaemic cell line HL 60, by liquid and agar semisolid cultures and 51Cr release assay. HL 60 cells growth is impaired by Bvv in a dosedependent fashion in both culture systems. The arrest of proliferation requires a contact time lower than 3 min and it is not reversed by washing and culturing the cells in a Bvv-free medium. Similarly, an extremely short exposure time is needed to determine maximum 51Cr release. Neither the agar medium nor the fetal calf serum interact with Bvv effects, which, according to the above findings, must be regarded as cytolytic in nature. In both liquid and the agar-semisolid culture Bvv cytolytic activity half life is about 8 hr. The cytolytic properties of Bvv are thought to be part of the chemical defence system of amphibian skin.

Jasmonic acid is a signal transducer in elicitor-induced plant cell cultures.

To deter pathogenic microorganisms and herbivores, plants have developed an inducible chemical defense system. It is known that the induced synthesis of low molecular weight compounds can be provoked by exposing cultured cells to fungal cell wall fragments. In this study we show that endogenous jasmonic acid and its methyl ester accumulate rapidly and transiently after treatment of plant cell suspension cultures of Rauvolfia canescens and Eschscholtzia californica with a yeast elicitor. Thirty-six plant species tested in cell suspension culture could be elicited with respect to the accumulation of secondary metabolites by exogenously supplied methyl jasmonate. Addition of methyl jasmonate initiates de novo transcription of genes, such as phenylalanine ammonia lyase, that are known to be involved in the chemical defense mechanisms of plants. These data demonstrate the integral role of jasmonic acid and its derivatives in the intracellular signal cascade that begins with interaction of an elicitor molecule with the plant cell surface and results, ultimately, in the accumulation of secondary compounds.