Let’s talk about scent

Heritage Open Days, held in September, are part of England’s largest festival of history and culture. Thousands of visitors visit a range of historic venues and collections across the country. The John Innes Centre began participating in Norfolk’s Heritage Open Days back in 2007. Every year since then we’ve welcomed audiences to hear a new specialist talk on a scientific or historical topic alongside an exhibition of our rare and beautiful botanical book collection.
This year Dr Mikhaela Neequaye, from the Byers Lab, talked about her research on the scent of flowers. Mikhaela describes herself as a chemical ecologist and studies the evolution and diversification of floral scent. Plants use chemical communication to attract their pollinators, with which they’ve co-evolved over millions of years. Chemical messaging includes producing plant pigments to guide chosen pollinators to perceived rewards.
Different kinds of pollinator have definite colour preferences. For example, bees are particularly drawn to yellow and blue flowers, butterflies to pinks and purples, whilst colour has a minimal effect on moths leading them to often influence flowers to transition to white. Birds, particularly hummingbirds which are an important pollinator in the Americas, are attracted to red flowers. Plants can synthesise pigments or combinations of pigments to maximise their powers of attraction. Some provide ‘landing lights’ for bees to highlight the entrance to where the nectar is stored.
Floral scent is another communication strategy plants use to draw pollinators in. The volatile chemicals that plants produce in their scent are carefully tailored to stimulate reward receptors in specific pollinators.
Studying fragrance in the lab is not without some personal sacrifice. The fresh citrusy smell, which is a component of many floral fragrances, is limonene, but unfortunately this chemical compound is also used in many personal hygiene and beauty products. Workers in a fragrance lab can’t wear deodorant and must be careful about the washing powder they use, or they might compromise their results!
One of the joys of listening to Mikhaela’s talk was the insight she gave into what it takes to study floral fragrance. Using equipment that includes chicken roasting bags popped over the flowers to collect the scent, a small extraction pump, and the high-performance mass spectrometry equipment found at the John Innes Centre to analyse the chemical compounds in the fragrance, Mikhaela can investigate the components that generate the greatest reward responses in the bee pollinators she studies. This is done by attaching electrodes to bee antennae to measure their electrical signals (a proxy for how excited the bee is) when they are introduced to different fragrances.
Mikhaela’s results show that bees have the biggest electrical response from a pheromone stimulus. Their second biggest response in the study was to the fragrance of the purple monkey flower (Mimulus) which smells strongly of limonene. Mimulus has attracted scientific attention because some species have evolved to attract bees, whereas others have diversified (in evolutionary terms very recently) to appeal to hummingbirds. This is reflected in the chemical composition of the scent different species of Mimulus produce.
As well as Mimulus, Mikhaela studies the fragrant orchid Gymnadenia conopsea, which involves annual field trips to alpine meadows in Italy and Switzerland. With climate change affecting flowering time and plant-pollinator interactions, Mikhaela hopes insights into plant-pollinator relationships contributed by her lab’s study of flower fragrance will play a part in securing the future of these beautiful and now increasingly endangered plants.
After Mikhaela’s talk, visitors were given the opportunity to see the rare books display curated by Sarah Wilmot, Outreach Curator and Science historian at the John Innes Centre. This featured examples of plants with fragrances designed to attract many kinds of pollinator: birds, bees, moths, and even bats and other mammals. At the end of the event Mikhaela gave visitors the opportunity to smell samples of some of the scents flowers commonly produce.
The group that works in the Byers Lab at the John Innes Centre is interested in how floral scent and other traits, such as colour and shape, integrate to guide the visitation decisions of insects and how that is controlled genetically.