Sunflowers’ invisible colors help them attract bees and adapt to drought

It turns out sunflowers are more than just a pretty face: the ultraviolet colours of their flowers not only attract pollinators, but also help the plant regulate water loss, according to new UBC research. The dense collection of yellow petals of a sunflower (technically an 'inflorescence', or collection of many flowers) is a familiar sight, but it's hiding something from the human eye: an ultraviolet (UV) bullseye pattern, invisible to humans but not to most insects including bees.

These bullseye patterns have long been known to improve the attractiveness of flowers to pollinators by increasing their visibility. Now, UBC researchers have found the same molecules that produce UV patterns in sunflowers are also involved in helping the plant respond to stresses such as drought or extreme temperatures, in a new paper published today in eLife, potentially providing clues to how plants can adapt to different climates.

"Unexpectedly, we noticed that sunflowers growing in drier climates had flowers with larger UV bullseyes, and found that those flowers are able to retain water more efficiently. This suggests that these larger UV bullseyes help plants adapt to these drier environments," says lead author Dr. Marco Todesco, a research associate at UBC's biodiversity research centre and department of botany.

Dr. Todesco and his colleagues grew almost 2,000 wild sunflowers of two species at the university in 2016 and 2019. They measured the sunflowers' UV patterns, and analyzed the plants' genomes, and found that wild sunflowers from different parts of North America had UV bullseyes of very different sizes: in some, the bullseye was a thin ring, while in others it covered the whole flower. Larger bullseyes were visited more frequently by bees, supporting previous research of other plant species.

"Floral UV patterns appear therefore to play at least a dual role in adaptation; besides their well-known effect on enhancing pollination, they also regulate water loss from flowers," says senior author Dr. Loren Rieseberg (he/him), a professor in the department of botany and the biodiversity research centre. "That's not something you would necessarily expect a flower colour to do, and it exemplifies the complexity and efficiency of adaptation -- solving two problems with a single trait."

Read the complete research at www.sciencedaily.com.

Marco Todesco, Natalia Bercovich, Amy Kim, Ivana Imerovski, Gregory L Owens, Óscar Dorado Ruiz, Srinidhi V Holalu, Lufiani L Madilao, Mojtaba Jahani, Jean-Sébastien Légaré, Benjamin K Blackman, Loren H Rieseberg. Genetic basis and dual adaptive role of floral pigmentation in sunflowers. eLife, 2022; 11 DOI: 10.7554/eLife.72072


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