There’s a good reason why densely growing plants fare better than solitary stems
For a plant growing on the forest floor, a beam of light from an opening forest canopy can be worrisome. But new research suggests that plants growing together may be able to prevent each other from such stressful events by touching each other’s leaves, thereby collectively becoming more resilient.
“It’s kind of like an alarm,” says Ron Mittler, a plant biologist at the University of Missouri in Columbia. “Like, ‘Hey, something’s coming, get ready.’ »
Mittler and his colleagues grew watercress (Arabidopsis thaliana) for several weeks, some alone and others in dense groups where the plants could touch each other’s leaves. When exposed to excess light, individual plants showed no more signs of stress and damage than those of the groups, the scientists report December 12 on biorXiv.org. “They seem to be more prepared to handle stress if they touch each other,” says Mittler.
Plants communicate underground through their roots, via microbes or by forming networks with fungi. Research also suggests that aerial communication may occur through several channels, including airborne chemicals that alert other plants of attacks by herbivores or sounds that communicate stress. Plants can also pass electrical signals to each other through their leavesforming a network connected by touch, although its effects on their health were previously unknown.
Mittler and his team conducted a series of experiments on wild watercress plants grown from seedlings in the laboratory. They analyzed changes in gene expression in single plants and those whose leaves touched those of another, monitored the signals transmitted between them, and measured resilience to stress by brightly lighting the plants. Using genetically modified plants that were unable to transfer certain chemical signals, scientists determined which signals were responsible for any acclimation to stress.
Just an hour after contact, plants whose leaves were affected activated more than 2,000 stress response genes, including those that help them cope with light, cold, waterlogging, salt and injury. Compared to plants that touched each other, isolated plants exposed to light showed higher levels of cell damage and accumulated more stress-related pigments.
Experiments with genetically modified plants also revealed that hydrogen peroxide transfer was crucial for inducing resilience in neighboring plants. Plants produce hydrogen peroxide when triggered by a series of stresses, Mittler explains. But this is the first time it has been identified as a signal transmitted from factory to factory.
“What we are studying is a very important general signaling mechanism,” says Christine Foyer, a plant scientist at the University of Birmingham in England, who was not involved in the study. “If you think about it, the plants must have it because they’re not moving. They must be alarmed by what’s happening in the environment.”
Mittler says the findings explain why growing crops together often helps them survive in harsh conditions and could one day be used to engineer mixed plant communities that are more resilient to the overlapping threats of climate change, such as flooding and heat.
“I can group together three different species that I know will communicate best above and below ground,” he says. “That’s what I hope.”
Even Darwin said that mixtures of plants grow better than single ones, Foyer says, and that might be one of the reasons why. “It just means that plants of similar type will communicate signals,” she says. “It could be that plants of different types use it but do it better.”