Systematic Phytochemical and Sustainable Use Studies in Malpighiales
Research on the chemistry of Malpighiales is focussed on the distribution of polyhydroxyalkaloids in Euphorbiaceae and the sustainable use of Passiflora (Passifloraceae).
Passiflora sp. from Sri Lanka (Image: P.Hoffmann)
The new order Malpighiales, recognised in the Angiosperm Phylogeny Group classification, includes several well-known plants of economic or social importance. A few examples are Hevea brasiliensis (rubber, Euphorbiaceae), Manihot esculenta (cassava; Euphorbiaceae), Hypericum perforatum (St. John's wort; Hypericaceae), Salix spp, (willows; Salicaceae), Linum usitatissimum (flax or linseed; Linaceae) and Erythroxylum coca (coca; Erythroxylaceae). Kew’s historic involvement with economic plants, not least rubber, provides a long-term interest in members of the new order. This interest continues through the two main areas of current research: a systematic survey of polyhydroxyalkaloids in Euphorbiaceae and a sustainable use study of Passiflora (Passifloraceae).
Polyhydroxyalkaloids (PHAs) are water soluble nitrogen-containing compounds that structurally resemble simple sugars. Many PHAs inhibit sugar processing enzymes or receptors. PHAs occur in unrelated families, either sporadically in only a few genera as in Araceae and Leguminosae or extensively in many genera as in subfamily Scilloideae (Asparagaceae) and Myrtaceae. In Euphorbiaceae, PHAs were discovered in Omphalea at Kew, following a collaboration with the Smithsonian Tropical Research Institute to study the chemistry of O. diandra, the larval food plant of the colourful dayflying moth Urania fulgens that undergoes periodic and spectacular mass migrations in Central America. Analysis of other food plants of uraniine moths resulted in the discovery of PHAs in Endospermum and Suregada (Euphorbiaceae). DNA sequence data suggests that these three uraniine food plant genera may be more closely related than thought from morphology, although the data are not conclusive. Further study aims to determine the distribution of PHAs in Euphorbiaceae and assess whether this chemical character is phylogenetically informative.
Among the estimated 450 species of Passiflora, only a few are used commercially in the food industry, although more species are grown for the horticultural trade. Some species are used traditionally to flavour drinks or to treat a range of conditions including diabetes and liver disorders. It is still unclear which compounds contribute to the medicinal uses of Passiflora, and to date most research on Passiflora chemistry has concentrated on the essential oils. The sustainable use study of Passiflora at Kew is investigating the phenolic compounds. This class of compounds has a range of beneficial properties, including anti-inflammatory activity. Over 100 species of Passiflora and related taxa have been analysed so far, and the research has shown that commercially grown species contain fewer phenolics than other species. This could explain why the commercially grown species are more susceptible to diseases than some of their wild relatives. The distribution of phenolic compounds among species of Passiflora is being mapped among the subgenera proposed by recent DNA-based phylogenies. If there is some pattern to the distribution of compounds, then the new molecular-based phylogenies will assist in the selection of species for further biological studies. The aim is to suggest additional species that could be grown commercially and provide income to local communities, especially those in poorer parts of the world.
In addition to these two main areas of research, the project interacts closely with the projects on the ‘Diversity of Biologically Active Plants and Plant-Derived Compounds’ and the ‘Authentication and Chemical Fingerprinting of Economically Important Species’. Research on taxa in Malphigiales covered in these projects is developed if funding permits.
Key publications 2006-2011
- Kite, G.C., Porter, E.A. Denison, F.C., Grayer, R.J., Veitch, N.C. Butler, I. & Simmonds, M.S.J (2006). Data-directed scan sequence for the general assignment of C-glycosylflavone O-glycosides in plant extracts by liquid chromatography-ion trap mass spectrometry. Journal of Chromatography A 1104: 123-131.
- Kite, G.C., Horn, J.M., Romeo, J.T., Fellows, L.E., Lees, D.C., Scofield, A.M. and Smith, N.G (2007). Alpha-homonojirimicina y 2.5-dihidroximetil-3,4-dihidroxipirrolidina: alcaloides inhibitorios de glucosidos en la polilla Urania fulgens. In ‘Ecología y Evolución en los Trópicos’ (Eds. Leigh, E.G., Herre, E.A., Jackson, J.B.C., Santos-Granero, F.), Smithsonian Tropical Research Institute, Panama. pp95-98.
Project partners and collaborators
Canadian Museum of Nature
Natural History Museum, London
Smithsonian Institution, Washington DC