Zare Lab: Could dewdrops explain why plants are flowering earlier?

Water droplets set off a chemical cascade that tells a plant it’s time to blossom, a new study finds.

Around the world, plants are flowering earlier in the year than they used to. Climate change seems the obvious culprit, yet warming temperatures alone do not account for the shift. Plants grown in greenhouses, for example, do not flower earlier if the thermostat is cranked up to match the increase in temperature caused by global warming.

Now, a previously overlooked explanation has emerged: dewdrops. According to findings published last week in the Proceedings of the National Academy of Sciences, tiny water droplets that come into contact with the surface of leaves set off a cascade of chemical signals that tell a plant it’s time to bloom.

“It is global warming, but in a less obvious way,” says senior author Richard Zare, a chemist at Stanford University. “As it’s getting warmer, we’re getting more humidity in the air, meaning the formation of dewdrops earlier in the year.”

The research didn’t begin with flowers at all. Instead, it serendipitously blossomed from the observation that tiny droplets of water chemically behave very differently from pools of water. In a prior collaboration, Zare and co–lead author Bolei Chen, an environmental chemist at the Chinese Academy of Sciences, discovered that when water microdroplets form on a solid, inorganic substrate such as a soil grain, chemical reactions on the surface spawn highly reactive molecules with unpaired electrons, which are known as radicals.

In 2023, Zare and Chen met for dinner in Shanghai and ended up discussing their previous findings. That’s when they landed on the question that brought them to the current study: What happens when highly reactive water droplets contact a living substrate—like a leaf?

To find out, the researchers turned to the most extensively studied model plant, Arabidopsis thaliana, a small, flowering species in the Brassicaceae family, which also includes cabbage, broccoli, and radish. Detailed molecular work in the lab revealed that when water droplets form on Arabidopsis’s leaves, the resulting reactions produce hydrogen atoms and hydroxy radicals. Some recombine to create hydrogen peroxide, which in turn reacts with amino acids to make nitric oxide (NO)—a signaling molecule in both plants and animals. The NO on the droplets’ surface then transfers into the plant’s cells, triggering a cascade of enzymatic reactions that lead to flowering. “The fact that NO does signaling was well known, but the fact that dewdrops induce NO was not known,” Zare says.

The research didn’t begin with flowers at all. Instead, it serendipitously blossomed from the observation that tiny droplets of water chemically behave very differently from pools of water. In a prior collaboration, Zare and co–lead author Bolei Chen, an environmental chemist at the Chinese Academy of Sciences, discovered that when water microdroplets form on a solid, inorganic substrate such as a soil grain, chemical reactions on the surface spawn highly reactive molecules with unpaired electrons, which are known as radicals.

In 2023, Zare and Chen met for dinner in Shanghai and ended up discussing their previous findings. That’s when they landed on the question that brought them to the current study: What happens when highly reactive water droplets contact a living substrate—like a leaf?

To find out, the researchers turned to the most extensively studied model plant, Arabidopsis thaliana, a small, flowering species in the Brassicaceae family, which also includes cabbage, broccoli, and radish. Detailed molecular work in the lab revealed that when water droplets form on Arabidopsis’s leaves, the resulting reactions produce hydrogen atoms and hydroxy radicals. Some recombine to create hydrogen peroxide, which in turn reacts with amino acids to make nitric oxide (NO)—a signaling molecule in both plants and animals. The NO on the droplets’ surface then transfers into the plant’s cells, triggering a cascade of enzymatic reactions that lead to flowering. “The fact that NO does signaling was well known, but the fact that dewdrops induce NO was not known,” Zare says.

This story was originally published by Science.