24 July 2017
Plants, drugs and rocky soil
Owen Durant, Natural Product Researcher at Kew, explains how scientists are using plant science in the quest to discover life-saving drugs.
Medicinal plants are those where either the whole plant, or parts of it, have been used as medicine.
Out of 400,000 known plant species, nearly 30,000 are used as medicinal plants – roughly 7.5 per cent. Hundreds of thousands of plants still haven’t been tested for medicinal properties and it is difficult to readily identify new ones. Finding out what makes a plant more likely to contain therapeutically useful chemicals helps us reduce the numbers of plants we need to test to discover new life-saving drugs.
The use of phylogenetics
Phylogenetics is the study of genetic and evolutionary relationships through DNA analysis. Using high-tech modern methods of genome sequencing, we are able to identify evolutionary relationships between species of plants that might look completely different.
If we know that one plant species has some interesting disease-busting chemicals, we can test their closely-related cousins for other similar chemicals. One study published last year for example, found that many plants used for their psychoactive properties tend to be closely related – so there is potential to investigate this with other plant groups.
The use of ecology
Ecology is the study of the relationship of plants and animals with each other and their physical environment. Interestingly, it is the ecology and natural habitat of plants that has been commonly used for discovering traditional medicines.
I wanted to investigate this link between the physical environment where the plant naturally thrives and the likelihood of it being used in traditional medicine.
I used the Biota of North America Program's Taxonomic Data Center – which combines data on 25,000 plant species and approximately 4,000 medicinal species – to examine whether habitat type correlates with likelihood of medicinal use.
Of the 14 habitats I looked at, plants that thrived in ‘rock substrate soil’ were far more likely to be used in traditional medicine than plants from other habitat types. These ‘rock substrate’ or ‘serpentine’ soils are typically low in essential nutrients, such as nitrogen, potassium and phosphorus, and can contain potentially toxic concentrations of heavy metals such as cadmium and lead.
It seems almost counterintuitive that medically valuable plants would be found in such challenging environments, yet this finding fits in with how medicinal plants have been selected in the past – for example mountain plants and fungi are often revered for their superior medicinal qualities in Traditional Chinese medicine (TCM).
It is possible that in order to thrive in such nutrient-poor soils, these plants have developed a more effective chemical 'toolkit' with greater powers to deter predators and convert scarce resources into food. It may be that these adaptations are responsible for the production of chemical compounds with increased therapeutic efficacy.
Future-proofing drug discovery in plants
More research is needed on using this phylogenetic and environmental data to discover new and valuable medicines. If we can refine how we search for new drugs, focusing on both specific habitats and plant families more likely to contain disease-busting chemicals, this could help to speed up drug discovery. While we do this work in the lab, it is also important that these habitats and plant groups are sufficiently protected in the wild to make sure they don’t become extinct before we have a chance to find them.
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