Plant Evolution 2022
Cinnamom belongs to the most ancient genera of flowering plants and existed already at the time, before Pangaea broke up. Thus, it is found on almost all continents and has split up into numerous species that are very hard to identify. As aromatic plant, Asiatic Cinnamom species have been used for several thousands of years, for different purposes (as spice, as ailment, as perfume). The chemical reason for the aroma are mostly phenylpropanoids (the precursors for lignin and derivatives thereof), but also terpenoids such as camphor or borneol. The commercial value is quite variable, for instance Cassia Cinnamom (formerly C. aromaticum or C. cassia) is much cheaper than Ceylon Cinnamom (C. verum). In addition, several Southeast Asian species such as Saigon Cinnamom (C. burmannii) are traded as well and used for medicinal purposes. Some species contain high levels of coumarin, which is genotoxic and therefore problematic if ingested at higher quantities. This problem has become accentuated by a new trend for Cinnamom capsules that are used to cure type II diabetes and contain high concentrations of often undefined cinnamoms. We try to develop assays to detect coumarin-rich species in such products and have established a collection of cinnamoms in our Botanical Garden. The identity of our reference plants is key to any approach to authenticate food products by genetic barcoding. However, we have learnt that many of our species, which we got from other reputed Botanical Gardens or from commercial vendors, turned out to be not the species declared. The project will use a combination of genetic barcoding, molecular phylogeny, and phenotypic analysis to shed light into the dark. Poster Masterarbeit Claudia Swoboda . Scriptum with protocols . portraits of our cinnamoms (internal page, ask for the password) .
How do we proceed?
First, we invest quite some effort into the authenticity of our reference plants that cultivated in the Botanical Garden and are verified by classical taxonomical determination. The quality of a method stands or falls with the authenticity of the reference plant. Therefore, all our plants carry an ID that never changes, even when the name of the plant changes (which is not a rare event - first, plant taxonomy is continuously reformed, such that names can change, second, an estimated 10-20% of entries in Botanical Gardens or gene banks are wrongly determined or named, such that often the plants, we get from other gardens, turn out to be something else after our identification). In the second step, databases are screened for presence of suitable genetic barcodes - the more markers are available, the informative they are, the better for the security of our results. We then isolate genomic DNA from the references and amplify the respective barcoding marker by PCR to obtain the sequence for later analysis. In parallel, the accessions are microscopically compared - interesting diagnostic markers are, for instance, stomatal patterns, the relation between pavement cells and palisade parenchyma, but also hairs, trichomes, or crystals. When the sequences arrive, they are aligned with sequences from the data base and used to construct a molecular phylogeny (neighbor-joining). Suitable sequence differences are then used as base to develop a diagnostic test - for instance, by RFLP or ARMS.
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