Systematic exploration of Stevia. An introduction and preliminary project proposal. Alexander Vrijdaghs 1 & Jan Geuns 2 1 Dr. A. Vrijdaghs, Laboratory of Plant Systematics, K.U.Leuven, Leuven, Belgium alexander.vrijdaghs@bio.kuleuven.be 2 Prof. Dr. J. Geuns, Plant Physiology Group, K.U.Leuven, Leuven, Belgium jan.geuns@bio.kuleuven.be
Asteraceae or sunflower family - 1 600 genera with 25 000 species - worldwide distribution, esp. Mediterranean, Mexico, southern Africa poorly represented in tropical rain forests 50% Old World, 50% New World; Stevia belongs to New World - annual/perennial herbs - annual/perennial herbs to shrubs. Rarely trees, epiphytes, aquatic plants - resin canals or laticifers - inulin instead of starch in subterranean parts, fatty oils in seeds
- inflorescence = flower resembling capitulum of florets, surrounded by involucre of usually coloured bracts the capituli are cymosely arranged. homogamous capitulum: all florets are bisexual/male/female heterogamous capitulum: outer florets are female/sterile (rayed florets), inner florets are bisexual (tubular, disk florets) disk florets ray florets involucre (phyllaries) capitulum
bisexual disk floret female disk florets ray floret Helianthus cultivar, Brienne le Chateau 07/2010
stigmas stamens pistil calyx = pappus pistil (style) inferior ovary female ray floret bisexual disk floret diagrams taken from : Heywood, Brummit, Culham and Seberg (2007) Flowering Plant Families of the World. Kew Royal Botanic Gardens
Stevia rebaudiana 06/2011 involucre (phyllaries)
petal disk floret stigma Stevia rebaudiana 06/2011
A Capitulum corolla B Floret pappus = calyx inferior ovary
pa co A B
co pa io pa nd A funiculus (ovule) B style stigma branches filamentanther
Robinson, Schilling and Panero (2009, p. 757-758)
APG III. Stevens P.F. 2001 onwards. Version 9, June 2008
? stevioside pathway? Eupatorieae Robinson, Schilling and Panero (2009, p. 757-758) Fig. 43.5. Phyletic tree of the tribe Eupatorieae with selected outgroups based on ITS data from GenBank with additional genera intercolated on the basis of their positions in the cpdna RFLP results of Ito et al. (2000b). Tree prepared by V.A. Funk and R. Chan.
- there is no phylogenetic hypothesis at species level within Stevia!!! - Project proposal: Integrated systematic study within the genus Stevia comprising 1) molecular phylogenetic analysis 2) morphological character research including ontogeny 3) character research at the level of the stevioside pathway Research level: Msc and PhD Expected output * at least one publication concerning the phylogeny of Stevia * at least one publication on the evolution of morphological characters and ontogeny of Stevia * at least one publication on the evolution of the stevioside pathway Economical prospects: with an enlarged (evolutionary) knowledge of Stevia, predictions can be made which species might be intresting for production.
Research method 1. Creating a phylogenetic framework by molecular phylogenetic analysis - collecting plant material - extracting DNA fragments - sequencing: for each species, a sequence is obtained
- putting the sequences in a data matrix for cladistic analysis - cladistic analysis resulting in a phylogenetic tree or cladogram Character states ( putative homologues) can be plotted on a cladogram: - they are distributed in a single clade = corroboration - they are dispersed over several clades = homoplasy HOMOLOGY MUST BE TESTED BY MORPHOLOGICAL/ONTOGENETICAL METHODS
2. Homology assessment: are similar structures in different species the same? - collecting plant material - preparing the structures to be studied (floral parts, inflorescences...) - critical point drying, coating with gold
- electron microscopy
- evolutionary interpretation (integrating phylogenetic data with morphological data), publishing. - possible applications
Thank you, Dank u