Biodiversity: modelling angiosperms as networks.

In the neotropics, one of the last biological frontiers, the major ecological concern should not involve local strategies, but global effects often responsible for irreparable damage. For a holistic approach, angiosperms are ideal model systems dominating most land areas of the present world in an astonishing variety of form and function. Recognition of biogeographical patterns requires new methodologies and entails several questions, such as their nature, dynamics and mechanism. Demographical patterns of families, modelled via species dominance, reveal the existence of South American angiosperm networks converging at the central Brazilian plateau. Biodiversity of habitats, measured via taxonomic uniqueness, reveal higher creative power at this point of convergence than in more peripheral regions. Compositional affinities of habitats, measured via bioconnectivity, reveal the decisive role of ecotones in the exchange or redistribution of information, energy and organisms among the ecosystems. Forming dynamic boundaries, ecotones generate and relay evolutionary novelty, and integrate all neotropical ecosystems into a single vegetation net. Connectivity in such plant webs may depend on mycorrhizal links. If sufficiently general such means of metabolic transfer will require revision of the chemical composition of many plants.

Effects of lignoids on a hematophagous bug, Rhodnius prolixus: feeding, ecdysis and diuresis.

The effects of lignoids on feeding, ecdysis and diuresis in fourth-instar larvae of Rhodnius prolixus (Hemiptera) were investigated. Up to 100 microg/ml burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, or nordihydroguaiaretic acid (NDGA) in the diet did not induce antifeedant effects. Pinoresinol and NDGA significantly inhibited ecdysis. In experiments in vivo, burchellin and podophyllotoxin reduced the production of urine after feeding. 5-Hydroxytryptamine (5-HT), a diuretic hormone, partially counteracted this effect of burchellin. In experiments in vitro, using isolated Malpighian tubules, (i) burchellin reduced diuretic hormone levels in the hemolymph but not the amount of diuretic hormone stored in the thoracic ganglionic masses (including axons), (ii) burchellin decreased the volume of urine secreted by isolated Malpighian tubules, and (iii) 5-HT could not overcome the effect of burchellin upon the Malpighian tubules. We conclude that burchellin interfered with the release, but not with the production of diuretic hormone by the thoracic ganglionic mass or induced an antidiuretic hormone and directly affected the Malpighian tubules.

Medicinal products: regulation of biosynthesis in space and time.

We live in a "Demon-Haunted World". Human health care requires the ever increasing resistance of pathogens to be confronted by a correspondingly fast rate of discovery of novel antibiotics. One of the possible strategies towards this objective involves the rational localization of bioactive phytochemicals. The conceptual basis of the method consists in the surprisingly little known gearings of natural products with morphology, ecology and evolution of their plant source, i. e. an introspection into the general mechanisms of nature.

Effects of some lignans and neolignans on the development and excretion of Rhodnius prolixus.

The effects of six lignans and neolignans as inhibitors of ecdysis and on the water balance in fourth-instar larvae of Rhodnius prolixus were studied by oral, topical and continuous contact treatments. The main results may be summarised as follows: (i) burchellin, pinoresinol, sesamin, licarin A and nordihydroguaiaretic acid (NDGA) did not cause feeding inhibition at doses of 100 micrograms/ml blood; podophyllotoxin had no antifeedant effect but caused a high moulting inhibition and significant toxicity when applied either orally or topically; (ii) the highest ecdysis inhibitory effects were observed with pinoresinol and NDGA when applied orally at a dose of 100 micrograms/ml (58% and 50% of moulting inhibition, respectively); burchellin inhibited 30% of the moulting at this concentration; (iii) by topical treatment none of the compounds presented any influence on the moulting cycle; and (iv) podophyllotoxin and burchellin significantly reduced the excretion of the insect in 24 h; the other compounds had no effect on excretion. The implications of these findings in relation to the pertinent biological events in R. prolixus are discussed.

Neolignans inhibit Trypanosoma cruzi infection of its triatomine insect vector, Rhodnius prolixus.

Two neolignans, burchellin and nordihydroguaiaretic acid (NDGA), were toxic only to Trypanosoma cruzi clone Dm28c maintained in brain heart infusion (BHI) medium at a concentration of 100 microg/ml, not 10 microg/ml. When Rhodnius prolixus was fed with epimastigotes of T. cruzi and treated simultaneously with a single dose of burchellin or NDGA at 10 pg/ml of blood meal the number of parasites in the gut decreased. Whereas burchellin was only partially active, NDGA drastically reduced the number of epimastigotes and metacyclic trypomastigotes of T. cruzi in the excreta (urine plus feces). When the insect larvae were pretreated with burchellin or NDGA at 20 days before the infection with T. cruzi a significant reduction in the number of parasites in the gut occurred. However, when both compounds were applied at 20 days after the establishment of T. cruzi infection, although burchellin significantly reduced the gut infection, neither compound could abolish the infection entirely within the subsequent 15 days.

Evolution of angiosperms via modulation of antagonisms.

The controversies concerning the evolutionary mechanisms of flowering plants continue unabated in spite of the current trends toward the analysis of macromolecular data and of the growing body of distributional micromolecular data. The usual narrative approach to this latter effort is here replaced by a novel technique, quantitative phytochemistry. An evolutionary outline emerges and reveals modulation of antagonisms as the fundamental mechanism of angiosperm evolutionary ecology. Origin or operation of many systems can be rationalized analogously. It is concluded that the impact of opposing features possesses universal relevance.

Comparative ethnopharmacology: a rational method for the search of bioactive compounds in plants.

In the present preliminary communication on comparative ethnopharmacology a limited universe of data extracted from the Journal of Ethnopharmacology (vols. 1-25) was used for the construction of ethnopharmacological profiles of ten families of dicotyledons. Intraprofile analysis suggested the main uses of plant species (indicated by the maximal citation frequencies), as opposed to the spurious ones (represented by base line fluctuations), to possess a solid chemotaxonomic basis. Interprofile analysis via correlation of ethnopharmacological distances and morphological (evolutionary) distances among the same plant families suggested comparative ethnopharmacology to possess also a phylogenetic (chemosystematic) basis. This result establishes comparative ethnopharmacology as a novel and potentially useful scientific discipline.

The rational search for natural neolignans.

A rational method of search for natural neolignans of desired structures is outlined. This involves consultation of a collection of chemical profiles of plant families. The profiles are assembled considering the biosynthetic class (in the present case lignoids), subclass (neolignans), structural types (neolignan skeletal) and relative frequency of substitutional derivatives belonging to each type (known compounds). The method is of course applicable to any class of natural products. Its use in the case of neolignans is here selected as an example in view of the recently discovered antagonism towards PAF of kadsurenone, a representative of this subclass of phytochemicals. Application of the chemical profiles to phylogenetic studies is illustrated.

Phytoalexin induction in rubiaceae.

Phytoalexin responses were measured by modified drop-diffusate and facilitated diffusion techniques after fungal inoculation of leaves of 32 Rubiaceae species from Brazilian forest and savanna. Such responses presented a trend similar to that previously observed for a broad sample of dicotyledonous plants and are more frequently positive for the more primitive (or slower growing) trees than for the advanced (or faster growing) herbs. Fifteen of these species analyzed during a one-year period showed that positive phytoalexin responses are stronger for the rainy (and hotter) than for the dry (and cooler) season. Species that contain relatively large quantities of phenolics gave invariably negative responses. Positive responses are not necessarily associated with the appearance of new substances within leaf tissue and are thus caused by inhibitins rather than by phytoalexins. These results are discussed recognizing that the tested plants are subject to the multifarious influences of their natural environment and of a possible conjugate-caused compartmentation of plant metabolites.

Chemosystematics of the gnetatae and the chemical evolution of seed plants1.

A survey of the secondary metabolites reported for EPHEDRA, WELWITSCHIA and GNETUM documents a far-reaching chemical similarity of these genera with the angiosperms. However, the different substitution patterns of the phenolics do not support a close phylogenetic link between the two groups. The most significant chemical difference between the Gnetatae and the angiosperms seems to be the widespread use of protective devices against oxidation such as O-methylation and formation of Schiff bases which are so frequent in angiosperms and nearly absent from the Gnetatae and other gymnosperms.

(2E,4E)-N-isobutyl-9-piperonyl-nona-2,4-dienoic amide from Ottonia anisum.

Roots and stems of Ottonia anisum contain besides 1-butyl-3,4-methylenedioxybenzene and piperovatine, the novel (2E,4E)-N-isobutyl-9-piperonyl-nona-2,4-dienoic amide.

Ocotea quixos, American cinnamon.

Among the three South American Lauraceae with cinnamon odours, Ocotea quixos Lam. is distinguished with the richest historical legacy. Cinnamaldehyde, its odoriferous principle, occurs besides o-methoxycinnamaldehyde, cinnamic acid and methyl cinnamate in the fruit calyx. In contradistinction, 1-nitro-2-phenylethane is responsible for the cinnamon odour of bark and leaves of Aniba canelilla (H..B.K.) Mez and Ocotea pretiosa (Nees) Mez.

Chemical studies on medicinal Myristicaceae from Amazonia.

Drugs from Myristicaceae species are used in the Amazon region as hallucinogens and arrow poisons, as well as for the healing of infected wounds. The former effects were attributed by Schultes and Holmstedt to tryptamines and carbolines. The latter activity is now tentatively ascribed to pterocarpans and neolignans. This, and a proposal that the red colour of the bark resins may be due to oxidative dimers of flavans, are based on a review of the chemistry of Amazonian Myristicaceae.