Being drenched in rain, along with a sprinkling of sun and some carbon dioxide, might sound like a plant’s happy place. However, a new study has shown that plants actually having a surprisingly complex and tortured reaction to rainfall.

A multinational team of scientists from the University of Western Australia (UWA) and Lund University in Sweden has found that plants react to rainfall with a complex chain of chemical signals, which they compare to “panic”.

Reporting in the journal Proceedings of the National Academy of Sciences, their research found that this process involves thousands of genes, hundreds of proteins, and many growth hormones that are affected within just 10 minutes of water hitting the leaf. This reaction continues to rise for around 25 minutes. 

The team sprayed the Arabidopsis plant, a genus of small flowering plants related to cabbage and mustard, with a light shower of water and observed the chain reaction in the plant sparked by a protein called Myc2. After Myc2 is activated, the plant loads up its defenses to protect itself, which includes a delay in flowering and stunted growth.

As part of their panicked defense, plants also pump out chemicals, namely a hormone called jasmonic acid, that act as a “warning signal” to other leaves and even other plants. But why would a plant panic about rain? Although the water is a fundamental ingredient needed for photosynthesis, rain can also bring bacteria, viruses, and fungal spores that could harm the plant.

“Strange as it sounds, rain is actually the leading cause of disease spreading between plants,” study author Professor Harvey Millar, plant energy biologist from UWA, said in a statement.

“When a raindrop splashes across a leaf, tiny droplets of water ricochet in all directions," said Millar, adding that "a single droplet can spread these up to 10 meters [~33 feet] to surrounding plants.”

“If a plant’s neighbors have their defense mechanisms turned on, they are less likely to spread disease, so it’s in their best interest for plants to spread the warning to nearby plants," he continued.

It’s easy to think of plants as passive window dressing for the natural world, but that’s far from the truth. One of the most interesting and controversial subjects in botany is “plant neurobiology”, the idea that plants can intelligently interact with their surroundings. 

While there are different degrees of commitment to this idea, some have even gone as far as to suggest that plants possess real intelligence and consciousness, just like an animal. You can learn more about this idea and the debates that surround it here.