Chemical clues to rosy relationships
Compounds discovered in a species of rose native to the UK may help to unravel the complex taxonomy of Rosa.
Rosa spinosissima 'Dunwich' in flower at Kew Gardens
Researchers in the Sustainable Uses Group at Kew have discovered a particular type of flavonoid glycoside in leaves of the burnet rose (Rosa spinosissima; syn. R. pimpinellifolia) that had not been described previously in the scientific literature from any other plant. The novel compounds were found during a wider study looking at potentially new uses of plants. In particular, hips of the burnet rose, which is native to the UK, are harvested and used in cosmetics.
The novel flavonoid glycosides were unusual because a chemical group called HMG (3-hydroxy-3-methylglutaric acid) was attached to the glycan (sugar) part of the molecule. Flavonoid glycosides containing HMG are of limited occurrence in the plant kingdom, with just over 50 examples reported to date from flowering plants, ferns and liverworts. In most (68%) of these flavonoid HMG-glycosides the glycan part of the molecule is attached to the flavonoid part via glucose. In the Rosa compounds the attachment was via galactose, which made them even more uncommon. Further structural features of two of the Rosa flavonoid glycosides distinguished them from all others described in the existing scientific literature.
The taxonomy of Rosa, comprising nearly 200 species, is problematic due to intra-specific variability, polyploidy and inter-specific hybridization. With this in mind, the researchers used Kew’s living and herbarium collections to survey 71 species of Rosa for the occurrence of the novel flavonoid glycosides. The survey revealed a restricted distribution of the compounds, being limited to some species of subgenus Rosa section Pimpinellifoliae and R. roxburghii of the monotypic subgenus Platyrhodon. This chemical character should be valuable in future systematic work on the genus, particularly when combined with results from DNA sequence analysis.
Item from Dr Elaine Porter (Research Phytochemist, RBG Kew)
Porter, E.A., van den Bos, A.A., Kite, G.C., Veitch, N.C. & Simmonds, M.S.J. (2012). Flavonol glycosides acylated with 3-hydroxy-3-methylglutaric acid as systematic characters in Rosa. Phytochemistry 81: 90-96.