A team of researchers at the University of Toronto Scarborough have discovered that the waxy protective barrier around plants might play a role in sending chemical signals to other plants and insects – and could be harnessed to develop plants that can deal with challenging environments.

For the study, published in the journal Proceedings of the National Academy of Sciences, researchers looked at cuticular wax, a thin layer that plants deposit on their surface to protect against losing water. “These waxes act as a physical defence,” says Eliana Gonzales-Vigil, an assistant professor in the department of biological sciences who led the study.

“If plants didn’t have this wax, they would dry out very quickly. It’s the reason you see water drops beading on the surface of leaves. Plants evolved this trait over time when they moved from growing in water to growing on land.”

The waxes play a role in defending plants against ultraviolet radiation, fungus, bacteria, high and low temperatures as well as insects. It was thought they were stable, unreactive barriers – but the researchers found that some waxes break down after being exposed to air and light, releasing other compounds in the process.

Using a method of analyzing waxes in a species of poplar tree (cottonwood), the researchers found that unsaturated waxes, known as alkenes, degrade to produce nonanal – a well-known aldehyde signalling compound and insect pheromone.

This means smaller compounds of interest could be released from larger waxes found in the plants. “This process could one day be used to engineer desirable traits in plants that can improve their resilience from drought or insects,” Gonzales-Vigil says.

Role in plant communication
Aldehydes perform an essential role in both plants and animals, including humans. In animals, they work as signalling molecules, influencing various aspects of growth, development and reproduction. They’re also the reason why mosquitos are attracted to some people and animals more than others.

In plants, they’re present in pheromones that attract insects and are also responsible for plant-to-plant communication. If a plant is stressed due to drought, for example, it will release the compound to let neighbouring plants know so they can prepare.

Jeff Chen, who recently completed a master’s in cell and systems biology at U of T Scarborough, discovered that waxes can break down to produce aldehydes – by accident. He wanted to see what happened to waxes in poplar plants as they aged, so he tracked the plants’ leaves from when they were young until they were dying. He found the waxes decreased in abundance as the plants got older.