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Chemosystematics and Biological Activity of Alismatid and Lilioid Monocots

Snowdrops (Galanthus spp.) contain an alkaloid, galanthamine, that may be useful in the treatment of Alzheimer’s disease

Our research on the chemistry of monocots brings together interests in chemosystematics and plant-insect interactions. Currently we are studying aspects of chemistry and biological activity in Amaryllidaceae, Liliales and Araceae.

The project in Amaryllidaceae developed from observations of pest-problems in RBG Kew’s living plant collections. During surveys of plants for insect damage it was recorded that many species of Crinum, Lycoris, Hippeastrum, Narcissus and Nerine were not attacked by pests, whereas species of Stenomesson and Eucrosia were. Extracts were made of species that varied in their susceptibility and these were tested in a range of insect assays at Kew to evaluate whether they had insecticidal activity or modulated the feeding or egg-laying behaviour. As a result a group of alkaloids, the amaryllidaceae alkaloids, were isolated from the species resistant to insect damage and some of these alkaloids were shown to have potent antifeedant activity against insects, including caterpillars of the armyworm Spodoptera littoralis. Some compounds were shown to inhibit the functioning of neurotransmitter-gated ion channels, whereas others bound to “sweet” and “bitter” taste receptors and were potent inhibitors of acetylcholine esterase. There is interest in this group of alkaloids because galanthamine, isolated from Galanthus, is being developed as a drug for the treatment of Alzheimer’s disease, a form of dementia that is linked to deficiency in the acetylcholine-mediated signalling in the central nervous system. We are now using new DNA-based phylogenies to assist with the selection of species for further study.

Other groups of alkaloids are being studied for systematic purposes in Hyacinthaceae and Liliales. Many Hyacinthaceae produce polyhydroxyalkaloids and a survey of these alkaloids revealed that they are not accumulated by genera (Ornithogalum, Albuca and Dipcadi) now classified into an enlarged Ornithogalum on the basis on DNA-sequence evidence. The alkaloid chemistry therefore concurs with DNA data. In Liliales a similar systematic approach has begun using homosteroidal alkaloids, to determine whether their occurrence in certain genera agrees with recent concepts on relationships.

In Araceae we are studying the composition of floral odours, with an emphasis on Arum and Amorphophallus. The inflorescences of these genera produce odours that are often obnoxious to humans but attract insect pollinators, most of which remain unknown. The odours of most species of Arum have been characterised and studies now focus on pollinator interactions. Amorphophallus is a larger genus and the odours of 80 species have been analysed, including the odour of the famous A. titanium (the Titan Arum). Not all are foul; for example, species such as A. yunnanensis have the odour of carrots. The composition of odours is being compared with ideas about the relationships of species based on morphological and DNA data. Another aspect of our work in Araceae follows a similar strategy to the research in Amaryllidaceae. Data obtained on the pest resistance of the foliage of Araceae grown at Kew could provide leads into the systematic study of bioactive compounds in Araceae.

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