Study suggests mechanism evolved to help plants make the most of their floral scents

  • 21
  • SEP
  • 2021

New research has found that the electrical charge created by visiting bumblebees stimulates some flowers to release more of their sweet-smelling scent.

This is the first time a plant has been shown to use the presence of pollinators as a cue to emit more of its attractive perfume - increasing its chances of being visited.

The tiny electrical charge carried by bees is thought to help pollen stick to them during flight but the team of researchers from the University of Bristol, Rothamsted Research, and Cardiff University found that it can also announce their presence to the flowers they visit.

According to lead author, Dr Clara Montgomery, who was funded by the BBSRC, the trait possibly evolved in plants to maximise the effectiveness of the attractive chemicals they release.

“Flowers have a limited supply of these scents, so it makes sense they only release them when their pollinators are around.  Essentially, it is only worth advertising when you know you have an audience. Other cues they might use, such as daylight or temperature can be unreliable, as it might also be windy or raining, which would reduce pollinator presence.

“These scents are also used by insects that want to eat or lay eggs on the plant, so increasing their chances of only attracting pollinators is vital.”

The electrical charge on a bumblebee – somewhere in the region of 120 picoCoulombs (pC) – is incredibly small but the team found a charge of 600 pC, or about the same as five bee visits, was enough to induce a species of violet petunia, Petunia integrifolia, to markedly release more scent.

The average electrical charge on a bee of 120 pC is incredibly small. To put it into context: the charge on a bee corresponds to about 6 million electrons. A normal 60W light bulb requires in the order of million billion electrons to flow every second to produce light.

Using specially constructed foraging arenas, the team were able to measure the electrical charge carried by each bee, as well as the amount of the main attractive chemical, benzaldehyde, released by the flowers in response to visits by bees.

To help distinguish between a flower’s response to the mechanical stimulus of a bee landing and the electrical stimulus, scent release was also measured in a subset of petunias that were touched with either a grounded metal rod or an electrically charged nylon ball.

Flowers visited by free-flying bumblebees exhibited a significant increase in volatile production. By contrast, flowers touched with an electrically grounded metal rod did not show such increases.

When touched with the electrically charged ball, with a charge equivalent to about five bee visits, the scent emissions from petunia flowers were significantly increased again – roughly doubling the average volume of scent.

Pollinators have long been known to carry positive electric charges, but this is the first demonstration of plants using this to their advantage, says Dr Montgomery, who is now at Harper Adams University.

“Frequent visits by charged pollinators to a flower would cause charge to build up, which might exceed a threshold for scent release. Charge could therefore provide a useful indicator of how many pollinators are in the area, allowing the plant to assess the real time potential for pollen dispersal.

“Current understanding of the electric charges carried by different insect species is very low and the influence of electric fields on all biological systems is often poorly understood and hard to quantify.”

Project leader, Professor Daniel Robert from the University of Bristol, said: “This discovery unveils a previously unknown type of interaction between insects and plants, a world of elusive electric cues, that us humans cannot detect.”

He also highlighted the innovative value of the multidisciplinary collaboration between scientists in Rothamsted and the University of Bristol, involving chemical ecologists, plant physiologists and bee sensory ecologists.

“Insects are the dominant pollinators in agroecosystems, providing pollination services for many of our crops. The better we understand pollinator-plant interactions, the better we can preserve pollinating insects and ensure food security,” added Dr József Vuts chemical ecologist at Rothamsted and co-author.

The study is published in the journal The Science of Nature.

About Rothamsted Research
Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
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1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)

The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
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About LAT
The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.