Biomedical subjects

Dirk C Albach

Publications and source records attributed to Dirk C Albach.

6 recordsLinked to original sources

PubMed2006

Systematic significance of seed morphology in veronica (plantaginaceae): a phylogenetic perspective.

BACKGROUND AND AIMS: A new infrageneric rearrangement for Veronica has been proposed based on the most recent evidence from DNA sequence data, morphological evidence, and biogeographical considerations. Looking for morphological synapomorphies for each monophyletic subgenus has been problematic, due to difficulties arising from widespread homoplasy (mainly parallel evolution). In an attempt to overcome these difficulties, previously underexplored morphological characters are starting to be studied in more depth. METHODS: A molecular phylogenetic hypothesis was used based on sequences of ITS (nuclear ribosomal DNA) and plastid trnL-F regions, as a framework to test the use of seed coat ultrastructure (studied under scanning electron microscope) in the systematics of the genus. A sample of 132 taxa representing ten of the 13 subgenera in Veronica, excluding the species of the southern hemisphere Hebe complex and the exclusively North American subgenus Synthyris, was studied. KEY RESULTS AND CONCLUSIONS: The results demonstrate that, in many cases, the ultrastucture of the testa can be employed to assess relationships of taxa within the genus, and the character provides additional support for molecular trees. Further characters relevant for the classification of Veronica, i.e. base chromosome number, iridoid chemical data, life cycle, inflorescence position, have been taken into consideration in a discussion where an attempt is made to highlight the best traits to characterize each subgenus investigated.

Classification↗

PubMed2006

Comparative phylogeography of the Veronica alpina complex in Europe and North America.

The Veronica alpina complex comprises eight species of alpine habitats over a wide range of mountain systems in the Northern Hemisphere. The occurrence of sympatric species in the European and North American mountain systems allowed us not only to investigate the effect of the ice ages on intraspecific phylogeographical patterns and genetic diversity in different continents of the Northern Hemisphere, but also to compare these patterns in closely related species. Plastid DNA trnL-F sequences and AFLP (amplified fragment length polymorphism) fingerprints were used to infer the phylogenetic history of the group and phylogeographical patterns within species. Hybrid origin of tetraploid eastern North American V. wormskjoldii from western North American V. nutans (= V. wormskjoldii s.l.) and Eurasian V. alpina is suggested. A number of phylogeographical groups have been found both in V. alpina from Europe and in V. nutans from western North America. Phylogeographical substructuring in the Alps is inferred for V. alpina but not for V. bellidioides, which is moreover characterized by an overall very low genetic diversity. Western North American V. cusickii is much more genetically diverse than its sympatric relative, V. nutans, an effect that is likely due to differences in the breeding system. Populations of V. nutans are differentiated into three groups, those from the Cascades and from the southern and the northern Rocky Mountains. Genetic diversity seems to be higher in the North American V. nutans than in the morphologically and ecologically similar European V. alpina. A possible scenario to explain this pattern is suggested.

Base Sequence↗

PubMed2004

Genome size variation and evolution in Veronica.

BACKGROUND AND AIMS: The amount of DNA per chromosome set is known to be a fairly constant characteristic of a species. Its interspecific variation is enormous, but the biological significance of this variation is little understood. Some of the characters believed to be correlated with DNA amount are alpine habitat, life history and breeding system. In the present study, the aim is to distinguish between direct causal connections and chance correlation of the amount of DNA in the genus Veronica. METHODS: Estimates of DNA amount were analysed for 42 members of Veroniceae in connection with results from a phylogenetic analysis of plastid trnL-F DNA sequences and tested correlations using standard statistical tests, phylogenetically independent contrasts and a model-based generalized least squares method to distinguish the phylogenetic effect on the results. KEY RESULTS: There appears to be a lower upper limit for DNA amount in annuals than in perennials. Most DNAC-values in Veroniceae are below the mean DNA C-value for annuals in angiosperms as a whole. However, the long-debated correlation of low genome size with annual life history is not significant (P = 0.12) using either standard statistical tests or independent contrasts, but it is significant with the generalized least squares method (P < 0.01). CONCLUSIONS: The correlation of annual life history and low genome size found in earlier studies could be due to the association of annual life history and selfing, which is significantly correlated with low genome size using any of the three tests applied. This correlation can be explained by models showing a reduction in transposable elements in selfers. A significant correlation of higher genome sizes with alpine habitats was also detected.

DNA, Plant↗

PubMed2004

Iridoid glucosides of Paederota lutea and the relationships between Paederota and Veronica.

In a chemical investigation of the water soluble compounds in Paederota lutea eight known iridoids were isolated together with a new one with a 8,9-double bond, namely paederotoside (10-O-benzoyl-6'-O-alpha-arabino(1-->6)-beta-glucopyranosyl arborescosidic acid) and the 6-hydroxy-flavone glucoside 4'-O-methylscutellarein 7-O-beta-glucopyranoside. The known iridoid glucosides were 8-epiloganic acid, gardoside, aucubin, catalpol and the 6-O-esters of catalpol: veronicoside, catalposide, amphicoside and verproside. The compounds isolated show that Paederota has a glycoside content almost identical to that of a general Veronica species, and this is in good agreement with the results from recent investigations of the phylogeny of Veronica and its closest relatives, where Paederota is placed as a sister-group next to Veronica. In an analysis of the iridoid glucosides from some of these relatives, it is shown that Veronica, Paederota, Picrorhiza and Veronicastrum are all characterized by containing 6-O-esters of catalpol. Some less closely related taxa namely: Lagotis, Wulfenia, Plantago, Aragoa and Globularia instead contain 10-O-esters of catalpol or aucubin.

Iridoids↗

PubMed2004

Incongruence in Veroniceae (Plantaginaceae): evidence from two plastid and a nuclear ribosomal DNA region.

Nucleotide data from nuclear ribosomal and plastid DNA did not agree on all relationships within Veroniceae (Plantaginaceae) in previous analyses. We present here additional data from a second plastid DNA marker, the rps16 intron, and evaluate incongruence between the ribosomal and plastid DNA matrices. Based on these evaluations and analysis of secondary structure in ITS, we conclude that there is a biological cause for incongruence among the genera of Veroniceae. The sequence data imply a history of hybridization and polyploidization, in which ancestors of Wulfeniopsis and Veronica+Paederota gave rise to Picrorhiza and ancestors of Wulfeniopsis and Wulfenia gave rise to Veronicastrum.

Cell Nucleus↗

PubMed2003

Acylated flavone glycosides from Veronica.

A survey of the flavonoid glycosides of selected taxa in the genus Veronica yielded two new acylated 5,6,7,3',4'-pentahydroxyflavone (6-hydroxyluteolin) glycosides and two unusual allose-containing acylated 5,7,8,4'-tetrahydroxyflavone (isoscutellarein) glycosides. The new compounds were isolated from V. liwanensis and V. longifolia and identified using NMR spectroscopy as 6-hydroxyluteolin 4'-methyl ether 7-O-alpha-rhamnopyranosyl(1"'-->2")[6"-O-acetyl-beta-glucopyranoside] and 6-hydroxyluteolin 7-O-(6"-O-(E)-caffeoyl)-beta-glucopyranoside, respectively. Isoscutellarein 7-O-(6"'-O-acetyl)-beta-allopyranosyl(1"'-->2")-beta-glucopyranoside was obtained from both V. intercedens and V. orientalis and its 4'-methyl ether from V. orientalis only. Complete 1H and 13C NMR spectral assignments are presented for both isoscutellarein glycosides. Two iridoid glucosides new to the genus Veronica (melittoside and globularifolin) were also isolated from V. intercedens.

Acylation↗