Sunflowers Have Invisible Colours That Help Them Fight Stress. Study Says Why This Is Important In Warming Climate

Sunflowers feature an ultraviolet (UV) bullseye pattern, which is invisible to humans, but not to most insects including bees.

Sunflowers (Photo: Getty)

New Delhi: Sunflowers are beautiful flowers known for their attractive yellow petals. The dense collection of the yellow petals, also called an inflorescence (collection of many flowers) are hiding some patterns from the human eye.  

Sunflowers feature an ultraviolet (UV) bullseye pattern, which is invisible to humans, but not to most insects including bees. 

The bullseye patterns have long been known to improve the attractiveness of the flowers to pollinators by increasing their visibility. 

How Do The Invisible Colours Help Sunflowers?

Now, researchers from the University of British Columbia have discovered that the molecules which produce these invisible colours in sunflowers are also involved in helping the plant mitigate stresses such as drought or extreme temperatures. 

The study was published this week in the journal, eLife. 

The research potentially provides clues to how plants can adapt to different climates.

Marco Todesco, the lead author of the study, said that the researchers unexpectedly 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, according to a statement issued by the University of British Columbia.

He added that the finding suggests that the larger UV bullseyes help plants adapt to these drier environments. 

Todesco and his team grew almost 2,000 wild sunflowers of two species at the University in 2016 and 2019. The researchers measured the sunflowers' UV patterns, and analysed the plants' genomes, and found that wild sunflowers from different parts of North America had UV bullseyes of very different sizes, the study said.

Some wild sunflowers had a bullseye with a thin ring, while in others, the bullseye covered the whole flower.

Bees were observed to visit the flowers with larger bullseyes more frequently. 

A Single Gene Regulates The UV Patterns

The scientists observed that a single gene, HaMYB111, was responsible for most of the diversity in floral UV patterns, the study said.

The production of UV-absorbing flavonol compounds are controlled by the gene. These compounds are also known to help plants survive under different environmental stresses like drought or extreme temperatures.  

The study found that larger floral UV patterns that have more of these compounds could help reduce the amount of evaporation from a sunflower in environments with lower humidity, preventing excess water loss. Smaller UV patterns would instead promote this evaporation in humid, hot environments. This would keep the plant cool and avoid overheating, the authors noted in the study.

Dr Loren Rieseberg, senior author of the study, said that floral UV patterns appear to play at least a dual role in adaptation. They regulate water loss from flowers, besides their well-known effect on enhancing pollination. 

Rieseberg added that it is not something one would necessarily expect a flower colour to do, and that it exemplifies the complexity and efficiency of adaptation. The flower colour solves two problems with a single trait.

The research is important because it could help add to knowledge about how to attract pollinators, and potentially increase crop yields, according to Dr Todesco.

He added that the work helps researchers understand how sunflowers, and potentially other plants, better adapt to different areas or temperatures, which could be important in a warming climate.