You are here
The secret behind the scent of roses
Roses are the world's most cultivated ornamental plant, and have been prized since ancient times for their beauty and fragrance. And yet they are far from having given up all their secrets. For although the components of their scent have been analysed by chemists for decades, very little research has been conducted into how these are connected to the way humans perceive their smell.
Why do some flowers give off a scent that is more characteristic of roses than others? Which molecules make them smell pleasant? Or attractive? Floral or fruity? The French interdisciplinary scientific collaboration that has been investigating these thorny questions recently published its results in the journal iScience1.
The first challenge was to identify all the compounds emitted by roses. "It's an extremely tricky problem, because we're dealing with a very complex mixture of molecules," says Sylvie Baudino, co-lead author of the paper and emeritus professor at Jean Monnet Université Saint-Etienne, within the Laboratory of Plant Biotechnologies applied to Aromatic and Medicinal Plants (BVpam)2. She explains that several hundred compounds in all have been identified.
Nathalie Mandairon, co-lead author and CNRS research professor at the Lyon Neuroscience Research Centre3, adds that this work is "a first step in sorting out the compounds in the mixture, in order to identify those that trigger attraction and those that are actually involved in the perception of the scent of roses, as well as in what proportions and quantities they are present".
Two unexpected chemical families
Freshly cut roses from ten different varieties were presented to the participants, who rated their smells in a blind test. At the same time, flowers from each cultivar were isolated under a glass bell jar and the molecules released were collected using an absorbent material placed inside the jar, and then analysed.
Ìt turned out that among the compounds associated with the typical scent of roses "there were molecules that we expected to find, such as phenylpropanoids, but also others that we didn't anticipate, such as ionones and oxylipins" , Mandairon says.
Perfumers are familiar with the latter two families, but rather than a rose scent, they generally associate ionones with a woody or violet smell, and oxylipins with an odour of freshness. The study also reveals that "the more the smell is typical of roses, the more ionones and oxylipins there are, and the more people like it and find it pleasant", she adds.
Although the scientists haven't yet come up with a recipe for the perfect rose, they have shown that an agreeable fragrance results from a subtle balance between ionones, oxylipins and 2-phenylethanol, while terpenes are associated with fruity scents. Oxylipins are already well known for their anxiety-reducing effects in humans and animals.
The scent of roses primarily associated with cosmetics and nature
This beneficial property comes in addition to the flower's symbolic appeal in the collective imagination. "As a preliminary question, we asked the participants in the study what the odour of roses reminded them of. They associated it positively with cosmetics, nature and, finally, food," Mandairon says.
The two authors of the paper hope to repeat these tests after selectively removing certain compounds from the rose scent, with the aim of gaining a more detailed understanding of the connection between its chemical composition and how it is perceived. Their initial conclusions are nonetheless already attracting the interest of plant breeders and perfumers.
However, humans are not the only species that reacts to the smell of roses. The scent of flowers generally helps to attract pollinators – and thus aid reproduction, – which is crucial for wild roses.
Odours that attract or repel
Benoît Boachon, a CNRS researcher at the BVpam, who participated in the above-mentioned study, outlines the wide range of ecological roles played by the odours given off by plants: "Volatile organic compounds (VOCs) are used for communication purposes to attract pollinators as well as predators of certain parasites, promote the defences of nearby plants, and attract mutualistic microorganisms. They can also be used to combat environmental stress factors, pathogens, pests and competing plants."
He cites lavender and mint, which have small hairs called trichomes, at the tips of which are glands that store odorous compounds. When a predator approaches, this ingenious trap is activated, releasing its contents and repelling the invader.
VOCs for inter-organ communication
However, recent work has shown that the compounds released into the air by plants are not only used for exchanges with other organisms, but also, astonishingly, for communication between their own organs.
"We noticed that VOCs were emitted inside the developing flower buds of petunias," Boachon explains. "This protects the plant against bacterial proliferation, but, more importantly, triggers a hormonal signal that promotes pistil growth and seed production. Yet this signal is not based on a soluble molecule, but on a VOC that can communicate at a distance."
This phenomenon is known as “natural fumigation”. The discovery of its mechanism was the subject of a paper in the journal Science4 last year. The hunt is now on to find it in other species. ♦
See also:
A nose for smell disorders
Pharmacognosy brings nature to our medicine chests
Claire de March, a researcher with flair
- 1. https://doi.org/10.1016/j.isci.2024.111635
- 2. CNRS / Université Jean Monnet Saint-Étienne.
- 3. CRNL (CNRS / INSERM / Université Claude Bernard Lyon 1).
- 4. https://www.science.org/doi/10.1126/science.adl4685
Explore more
