Plants emit an aspirin-like chemical to signal stress before they become visibly diseased like this oak tree.
[Credit: attommb, flickr.com]
It might start with a blotch, a wilt or a rot, a creeping discoloration that reaches inward from the margins of a leaf. Or perhaps it starts with a slow deadening of tissue that works its way outward from the heartwood of a tree.
Plants get sick just like us, and by the time damage is visible to the human eye, help may be too late.
What if there was a way to detect an imminent threat to plant life? An early warning system could allow those who make their living from plants, like farmers or forest managers, to fight drought damage and disease days or even weeks before plants and trees started dropping their leaves.
Researchers have found that measuring plant hormones may be the key to that system. Plants under stress emit a chemical similar to aspirin, known as methyl salicylate. This chemical can be detected in the atmosphere, researchers at the National Center for Atmospheric Research in Boulder, Colorado, discovered.
Plants may communicate with each other through this airborne hormone to form an ecosystem-wide immune response to threats such as herbivorous insects, viral invaders or even drought, says Tom Karl, lead author of the study published in a recent issue of Biogeosciences.
Unlike animals and humans, plants lack the ability to recognize and remember specific pathogens in order to strengthen the immune system against future attacks. Instead, plants respond to health stressors in a much more general way, boosting all of their defenses at once.
The release of methyl salicylate turns on genes in a plant that build the type of proteins it needs to defend itself against pathogens or hostile growing conditions. “This particular compound is something that plants need for survival,” says Karl.
When plants communicate stress to each other through chemical hormones, it is not really a selfless act for the common good. “It’s more like eavesdropping,” says Ian Baldwin, head scientist at the Max Planck Institute of Chemical Ecology in Germany, who was not involved with the study.
Baldwin believes that when plants release certain airborne messengers such as methyl salicylate, they are signaling danger to other parts of themselves and not surrounding plants. Chemicals travel faster through the air than they do through the plant’s own circuitous circulatory system.
Plants compete with their neighbors for scant resources – sun, water and space. Unless neighboring plants are closely related, there is no advantage for plants to sound the alarm for each other.
Karl and his research team hope this finding can some day be put to use in precision agriculture. Farmers could use this technique to try to reach 100 percent plant growth by estimating their fertilizer, pesticide and water needs to maximize output and conserve resources, says Randy Price, an agricultural engineer at Kansas State University.
According to Price, precision farming technologies already include aerial imaging, which allows farmers to look at their fields as a whole, and GPS guiding systems that prevent farmers from going over the same spot twice with their tractors and crop sprayers.
How would an early warning system based on plant hormone emissions fit into the precision technologies mix?
“Farmers want to concentrate on farming, not sitting in an office crunching numbers for hours,” says Price, who adds that an early warning system like this would be “a big help” if it could be implemented practically.
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