As a New Mexican, of course you like rain, but don’t be so sure your plants do. New research indicates that splashing rain induces a panic response in some plants that could even result in a reaction akin to post-traumatic stress syndrome, stunted growth and genetic damage. A 2018-2019 study published in the October 29, 2019 Proceedings of the National Academy of Sciences has plant physiologists reconsidering what they understood about plants’ sensitivity.

The report, “A MYC2/MYC3/ MYC4 Dependent Transcription Factor Network Regulates Water Spray Responsive Gene Expression and Jasmonate Levels,”  explains research by collaborating scientists at four universities: the School of Molecular Sciences at the University of Western Australia, the Swedish University of Agricultural Sciences, the Salk Institute of Biological Studies and the Lund University of Sweden.

The problem is not so much water by itself but rather noxious matter that is likely to be picked up by rain as it hits nearby surfaces and splashes onto a plant victim. “In the future, we’ll really be able to understand how plants are coping with rain, because rain can bring disease. It can bring a whole variety of other factors, which affect plants,” according to biochemist Harvey Millar of the University of Western Australia.

“We’ll be able to equip plants to interact with their environment in a different way than they do at the moment.” Millar, who was not one of the primary researchers for the peer-reviewed study, explained that rain can spread plant diseases. “When a raindrop splashes across a leaf, tiny droplets of water ricochet in all directions. These droplets can contain bacteria, viruses or fungal spores. A single droplet can spread these up to 10 meters to surrounding plants.”

The authors of the National Academy of Sciences article offered this overview. “Plants are constantly subjected to a changing environment. As sessile organisms, they have evolved defense mechanisms to cope with abiotic and biotic stresses that can interfere with their development and growth. “Stresses such as salt, founding and insect hebivory are known to affect plant growth, development and flowering time. These phentypes are also observed in plants that are repeatedly exposed to mechanical stimulation, including wind, rain, neighboring plants, agricultural equipment and human touch, colloquially termed ‘thigomorphogenesis.’

“Such mechanical stimulation without observable damaging of leaves also increases disease resistance against insect and fungal pests. As flowering time and disease resistance are of significance for global food production, understanding the molecular basis of the touch response may aid in rational design of future crops.” The researchers, Alex Van Moerkercke, Owen Duncan, Mark Zander, Jan Simura and Martyna Broda, used a spray bottle to simulate rain falling onto plants. After 10 minutes of “rain” more than 700 genes in the plants they studied reacted in a panic-like manner which continued for about 15 minutes, they reported.

The defensive responses altered the plants’ hormone balances and creation of proteins. Millar said the warning signals were sent from leaf to leaf in the plants, with the plants ultimately taking defensive measures against the water. Plants that received repeated waterings had stunted growth and delayed flowering, the biochemist explained.

“If a plant ‘s neighbors have their defense mechanisms turned on, they are less likely to spread diseases, so it’s in their best interest for plants to spread the warning to nearby plants,” he added. That communication between plants is produced by release of airborne chemicals.

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