Résultat de la recherche
Phytochemical study of Alzatea verticillata, the sole species belonging to the Alzateaceae family
Alzatea verticillata Ruiz & Pav. (Alzateaceae) is a tropical tree from Central and South America. It is the only living species of Alzatea genus and the Alzateaceae family, all others being extinct. With the aim to investigate the possibility to find unusual natural products, the chemical content of the dichloromethane and methanolic extracts (stems and leaves) of A. verticillata have been investigated. Apolar and polar extracts were purified by semi-preparative HPLC using appropriate stationary phase columns allowing the isolation of 12 compounds: walterolactone B (2) walterolactone A/B β-D-pyranoglucoside (3), gallic acid (4), caffeic acid 4-O-β-D-glucopyranoside (6), walterolactone A/B 6-O-gallate-β-D-glucopyranoside (8), caffeic acid (9), 8-desmethylsideroxylin (11), sideroxylin (12) and 7,7′-bis(3,4-dihydroxyphenyl)-8,8′-cyclobutanedicarboxylic acid (7). Three isolated compounds are natural products described here for the first time: dimethyl-anemonin (1) and two β-truxinic acid derivatives (rel-(7S, 8R, 7′R, 8′S)-7,7′-bis(4-glucosyloxy-3-hydroxyphenyl)-8,8′-cyclobutane dicarboxylic acid (5) and rel-(7S, 8R, 7′R, 8′S)-7,7′-bis(4-glucosyloxy-3-hydroxyphenyl)-8,8′-cyclobutane-9-methyl dicarboxylic acid (10). The structures of the isolated compounds were elucidated by NMR and HRMS. The structure of compound 1 was confirmed by X-ray crystallography. A MS-based metabolite analysis of the A. verticillata extracts revealed additional truxinic acid derivatives that were putatively annotated with the help of feature-based molecular network. The presence of phenolic compounds such as truxinic acid derivatives could explain the traditional use of this plant as these compounds are known to possess anti-inflammatory and anti-nociceptive properties.
Evolutionary diversification in the hyper-diverse montane forests of the tropical Andes: radiation of Macrocarpaea (Gentianaceae) and the possible role of range expansion
The humid mid-elevation montane forests (MMF) of the tropical Andes harbour high levels of plant species diversity, contributing to the exceptional overall diversity of the tropical Andean biodiversity hotspot. However, little is known about the diversification dynamics of MMF plant lineages compared to lineages in other Andean biomes. Here, we use Macrocarpaea (Gentianaceae) to investigate patterns of plant diversification in the MMF, using molecular dating with fossils and secondary calibration (from a family-wide phylogenetic analysis of Gentianaceae). We sequenced 76 of 118 recognized Macrocarpaea spp. for six markers to reconstruct a time-calibrated phylogenetic tree and infer the historical biogeography of Macrocarpaea using maximum-likelihood methods implemented in BioGeoBEARS, estimating diversification rates through time and among lineages with BAMM. We document a rapid radiation of Macrocarpaea in Andean MMF coinciding with rapid colonization and range expansion across the entire distribution of the genus in the Andes starting 7.2 Mya. Our results support allopatric founder-event speciation as the dominant process contributing to geographical phylogenetic structure across the genus. We propose that establishment of the MMF in the late Miocene, when the Andes attained critical elevation to modify regional climates, provided large new areas of suitable habitat for Macrocarpaea to quickly colonize and expand through repeated founder-events. We suggest that this wave of colonization and range expansion triggered rapid diversification, and, as the MMF became progressively occupied, the diversification rate slowed. Our study also supports the idea that MMF plant radiations are older and more slowly evolving than the quickly evolving lineages in the recent Andean high-elevation grasslands.
Back to Gondwanaland: can ancient vicariance explain (some) Indian Ocean disjunct plant distributions?
Oceans, or other wide expanses of inhospitable environment, interrupt present day distributions of many plant groups. Using molecular dating techniques, generally incorporating fossil evidence, we can estimate when such distributions originated. Numerous dating analyses have recently precipitated a paradigm shift in the general explanations for the phenomenon, away from older geological causes, such as continental drift, in favour of more recent, long-distance dispersal (LDD). For example, the ‘Gondwanan vicariance’ scenario has been dismissed in various studies of Indian Ocean disjunct distributions. We used the gentian tribe Exaceae to reassess this scenario using molecular dating with minimum (fossil), maximum (geological), secondary (from wider analyses) and hypothesis-driven age constraints. Our results indicate that ancient vicariance cannot be ruled out as an explanation for the early origins of Exaceae across Africa, Madagascar and the Indian subcontinent unless a strong assumption is made about the maximum age of Gentianales. However, both the Gondwanan scenario and the available evidence suggest that there were also several, more recent, intercontinental dispersals during the diversification of the group.
Exochaenium natalense (Gentianaceae), a reinstated taxon endemic to KwaZulu-Natal, South Africa
Based on morphological and ecological considerations, Belmontia natalensis (syn. Exochaenium grande var. homostylum) is reinstated as Exochaenium natalense (Gentianaceae). It only occurs in a section of the coastal region of the Eastern Cape (Pondoland) and southern KwaZulu-Natal provinces, South Africa. Exochaenium natalense differs from E. grande, the only other South African Exochaenium taxon, by having smaller flowers (corolla diameter < 2 cm vs > 3 cm) with a different colour (white vs cream-salmon or yellow). Because the type material of E. natalense consists of two sheets, a lectotype is designated.
Can biochemical phenotype, obtained from herbarium samples, help taxonomic decisions? – A case study using Gentianaceae
With the emergence of metabolomics, small quantities of plant material can be used to generate chemical fingerprints with high throughput for comparative analyses without the need for tedious and in-depth classical phytochemical investigation of large amounts of plant material. Here, we tested the hypothesis that herbarium samples themselves could be used as suitable material for untargeted metabolomic analysis and taxon discrimination based on biochemical phenotypes. We employed mass-spectrometrybased metabolite profiling to classify given species of chemotaxonomical relevance from the Gentianaceae family based on their biochemical phenotypic differences. Our dataset consisted of 605 accessions each with 910 mass spectral features, representing 59 species from 23 genera that extend over 6 tribes of the family. We found that minute amounts of herbarium specimens (less than 50 mg) were sufficient to obtain comprehensive fingerprints for all investigated individuals. Morphologically or genetically distinct species were differentiated using metabolite profiles, confirming taxon distinctions and validating the utility of this method for identification and differentiation. Overall, our results suggest that metabolite profiling of herbarium specimens may be suitable for taxonomic studies and also opens new ground for detailed investigations of their specialised metabolite contents.
Exochaenium clavatum subsp. stella-palustre (Gentianaceae—Exaceae), a new subspecies from Zambia
Exochaenium clavatum subsp. stella-palustre is here described as a new subspecies from Zambia. It is characterized by its relatively small size (20 cm tall), leaves massed at the base of the stem and oriented downwards, a single, bright yellow flower, and a calyx wing broadest at the middle. Furthermore, this new taxon was collected in a dambo, in contrast to the inundated lakeshores where E. clavatum subsp. clavatum typically occurs. A key distinguishing the two subspecies is provided.
Revisiting the taxonomy of Exacum courtallense (Gentianaceae) and recognizing E. courtallense var. laxiflorum at the species rank
Morphological, phenological and ecological evidences support the exclusion of Exacum courtallense var. laxiflorum Gamble (synonym: E. courtallense var. bonaccordense M. Mohanan) from E. courtallense Arn. resulting in the establishment of a new species Exacum laxiflorum (Gamble) Geethakumary, Deepu, Kissling & Pandurangan.
Sebaea solaris (Gentianaceae), a new species from theWestern cape of South Africa
Sebaea solaris (Gentianaceae) is here described as a new species from the Overberg region, Western Cape, South Africa. This new species is at first glance very distinct from all others in the genus mainly due to its relative large yellow flowers of c. 2.5 cmdiameterwith oblanceolate to obdeltoid erose corolla lobes. The petal ornamentation with several orange lines indicating the flower centre (versus two lines per petal for a few other Sebaea species) and a conspicuous undulated calyx wing are also unique in the genus. Furthermore, the position of large secondary stigmas above the middle of the style (versus at the base of the style for its morphologically closest relative: S. exacoides) possibly indicates differences in pollination strategies.
Back to Gondwanaland: can ancient vicariance explain (some) Indian Ocean disjunct plant distributions?
Oceans, or other wide expanses of inhospitable environment, interrupt present day distributions of many plant groups. Using molecular dating techniques, generally incorporating fossil evidence, we can estimate when such distributions originated. Numerous dating analyses have recently precipitated a paradigm shift in the general explanations for the phenomenon, away from older geological causes, such as continental drift, in favour of more recent, long-distance dispersal (LDD). For example, the ‘Gondwanan vicariance’ scenario has been dismissed in various studies of Indian Ocean disjunct distributions. We used the gentian tribe Exaceae to reassess this scenario using molecular dating with minimum (fossil), maximum (geological), secondary (from wider analyses) and hypothesis-driven age constraints. Our results indicate that ancient vicariance cannot be ruled out as an explanation for the early origins of Exaceae across Africa, Madagascar and the Indian subcontinent unless a strong assumption is made about the maximum age of Gentianales. However, both the Gondwanan scenario and the available evidence suggest that there were also several, more recent, intercontinental dispersals during the diversification of the group.