How do flowers release their enchanting scents?

May 1st might be widely recognized as International Workers’ Day, but there’s another, perhaps more colorful, side to this date. Known also as May Day, it carries deep historical and cultural connections to flowers and the joys of spring.

In many European places, people really get into the spirit of spring on this day. They dance around the Maypole, crown a ‘May Queen,’ and enjoy all sorts of fun that marks the coming of warmer days.

Amidst these celebrations, there’s something undeniably enchanting—the abundant blooming flowers. Their scents drift through the air, creating an atmosphere of renewal and joy. The lovely, captivating aroma is everywhere. But, have you ever paused to wonder why and how flowers smell so nice?

Flowers emit varied scents to attract pollinators and repel herbivores. Some recent studies suggest that floral scents might also play a role in communication between plants. For example, some plants can emit a specific scent when under attack by pests, which serves to warn neighbouring plants of potential danger.

Floral scents are composed of volatile organic compounds (VOCs) produced in the flower’s petals. These compounds vary greatly, creating the vast array of scents we associate with different flowers. From the sweet fragrance of roses to the sharp scent of marigolds, each flower’s unique aroma is a complex cocktail of chemicals like terpenoids, fatty acid derivatives, benzenoids, and phenylpropanoids.

And while the chemical structures and biosynthesis of VOCs have been well-studied, one question remained unanswered: how are these VOCs released into the atmosphere?

For a long time, the default assumption was that VOCs passively diffuse across cellular barriers into the environment. And although this may be true for small VOCs such as isoprene, modeling and experimental data suggested that VOC emission cannot be explained solely by simple diffusion.

In 2017, studying petunia flowers, Adebesin et al. showed that VOCs do not simply diffuse out of the cells but are actively transported across the plasma membrane by an ABC transporter, PhABCG1.

They found that PhABCG1 was up-regulated 103-fold in petunia flowers between the bud stage and open stage, the developmental stages with the lowest and highest VOC emission, respectively. PhABCG1 down-regulation resulted in decreased emission and intracellular accumulation of VOCs.

Turns out, those petunia flowers are doing more than just looking pretty and smelling nice—they’re using some serious transporters to spread their scents.