Plants produce a wide diversity of secondary metabolites (SM) which serve them as defense compounds against herbivores, and other plants and microbes, but also as signal compounds. In general, SM exhibit a wide array of biological and pharmacological properties. Because of this, some plants or products isolated from them have been and are still used to treat infections, health disorders or diseases. This review provides evidence that many SM have a broad spectrum of bioactivities. They often interact with the main targets in cells, such as proteins, biomembranes or nucleic acids. Whereas some SM appear to have been optimized on a few molecular targets, such as alkaloids on receptors of neurotransmitters, others (such as phenolics and terpenoids) are less specific and attack a multitude of proteins by building hydrogen, hydrophobic and ionic bonds, thus modulating their 3D structures and in consequence their bioactivities. The main modes of action are described for the major groups of common plant secondary metabolites. The multitarget activities of many SM can explain the medical application of complex extracts from medicinal plants for more health disorders which involve several targets. Herbal medicine is not a placebo medicine but a rational medicine, and for several of them clinical trials have shown efficacy.

No abstract

A typical character of plants is the production and storage of usually complex mixtures of secondary metabolites (SM). The main function of secondary metabolites is defense against herbivores and microbes; some SM are signal compounds to attract pollinating and seed dispersing animals or play a role in the symbiotic relationships with plants and microbes. The distribution of SM in the plant kingdom shows an interesting pattern. A specific SM is often confined to a particular systematic unit, but isolated occurrences can occur in widely unrelated taxonomic groups. This review tries to explain the patchy occurrence of SM in plants. It could be due to convergent evolution, but evidence is provided that the genes that encode the biosynthesis of SM appear to have a much wider distribution than the actual secondary metabolite. It seems to be rather a matter of differential gene regulation whether a pathway is active and expressed in a given taxonomic unit or not. It is speculated that the genes of some pathways derived from an early horizontal gene transfer from bacteria, which later became mitochondria and chloroplasts. These genes/pathways should be present in most if not all land plants. About 80% of plants live in close symbiotic relationships with symbiotic fungi (ectomycorrhiza, endophytes). Recent evidence is presented that these fungi can either directly produce SM, which were formerly considered as plant SM or that these fungi have transferred the corresponding pathway gene to the host plant. The fungal contribution could also explain part of the patchy occurrence patterns of several secondary metabolites.

Secondary metabolites (SM) occur in plants in a high structural diversity. The different classes of SM and their biosynthetic pathways are summarized in this introduction. A typical feature of SM is their storage in relatively high concentrations, sometimes in organs which do not produce them. A long‐distance transport via the phloem or xylem is then required. Whereas hydrophilic substances are stored in the vacuole, lipophilic metabolites can be found in latex, resin ducts, oil cells or cuticle. SM are not necessarily end products and some of them, especially if they contain nitrogen, are metabolically recycled. Biosynthesis, transport and storage are energy‐dependent processes which include the costs for the replication and transcription of the corresponding genes and the translation of proteins. The intricate biochemical and physiological features are strongly correlated with the function of SM: SM are not useless waste products (as assumed earlier), but important tools against herbivores and microbes. Some of them also function as signal molecules to attract pollinating arthropods or seed‐dispersing animals and as signal compounds in other plant – plant, plant – animal and plant – microbe relationships.

The Elapoidea includes the Elapidae and a large (~60 genera, 280 sp.) and mostly African (including Madagascar) radiation termed Lamprophiidae by Vidal et al. (2007), that includes at least four major groups: the psammophiines, atractaspidines, lamprophiines and pseudoxyrhophiines. In this work, we reviewed the recent taxonomic history of the lamprophiids, and built a data set including two nuclear protein-coding genes (c-mos and RAG2), two mitochondrial rRNA genes (12S and 16S rRNA) and two mitochondrial protein-coding genes (cytochrome b and ND4) for 85 species belonging to 45 genera (thus representing about 75% of the generic diversity and 30% of the specific diversity of the radiation), in order to clarify the phylogenetic relationships of this large and neglected group at the subfamilial and generic levels. To this aim, 480 new sequences were produced. The vast majority of the investigated genera fall into four main monophyletic clusters, that correspond to the four subfamilies mentioned above, although the content of atractaspidines, lamprophiines and pseudoxyrhophiines is revised. We confirm the polyphyly of the genus Stenophis, and the relegation of the genus name Dromophis to the synonymy of the genus name Psammophis. Gonionotophis brussauxi is nested within Mehelya. The genus Lamprophis Fitzinger, 1843 is paraphyletic with respect to Lycodonomorphus Fitzinger, 1843. Lamprophis swazicus is the sister-group to Hormonotus modestus, and may warrant generic recognition. Molecular data do not support the traditional placement of Micrelaps within the Atractaspidinae, but its phylogenetic position, along with that of Oxyrhabdium (previously considered to belong to the Xenodermatidae), requires additional molecular data and they are both treated as Elapoidea incertae sedis. The interrelationships of Psammophiinae, Atractaspidinae, Lamprophiinae, Pseudoxyrhophiinae, Prosymna (13 sp.), Pseudaspis (1 sp.) and Pythonodipsas (1 sp.), Buhoma (2 species), and Psammodynastes (1 sp.) remain unresolved. Finally, the genus Lycognathophis, endemic to the Seychelles, does not belong to the African radiation, but to the Natricidae.