New research has found when plant leaves physically touch each other, they seem to form a biological signalling network to warn each other about the upcoming stress. This can boost their resilience to withstand intense light, which is a common environmental challenge.
In the new study, yet to be peer-reviewed and published in a journal, resilience refers to a plant’s ability to endure excess light without suffering severe damage, such as leaf lesions. Researchers assessed this damage by measuring the ion leakage from the leaf. A more resilient plant will have less ion leakage from the leaves in response to the excess light, while a more sensitive plant will have more ion leakage.
“We demonstrated that if plants touch each other, they are more resilient to light stress by comparing groups of plants that touch each other with groups that do not,” said Ron Mittler, a phytologist at the University of Missouri in Columbia, in an interview with New Atlas.
In a 2022 study, researchers showed that plants in physical contact can transmit electrical signals. Mittler says that they continued this work to examine whether touch itself enhances plants’ tolerance to stress. The team used a small weed-like plant, Arabidopsis thaliana, for the study. They arranged these plants in such a way that one group of plants maintained leaf-to-leaf touch and the other group didn’t.
After establishing this physical connection, researchers tested the stress by exposing the plants to bright, intense light, similar to harsh sunlight. They then checked the damage by measuring the ion leakage from the harmed tissues and the accumulation of a pigment called anthocyanin. Anthocyanin accumulation is a sign of stress in plants.
The results revealed lower leaf damage and lower anthocyanin accumulation when plants were physically touching each other. Meanwhile, the plants grown in solitude had significantly higher levels of anthocyanins. Mittler told us that if you stimulate or stress one plant, it will send a signal to all the other plants that it touches, and they all become more tolerant.
To get a better mechanistic understanding, the team used genetically modified plants that can’t transfer chemical signals. The experimental setup consisted of a chain of three plants: a transmitter, a mediator in the middle, and a receiver. By replacing the mediator with mutant plants, the receiver plants failed to get protection against the stress. This setup also revealed that hydrogen peroxide secretion is crucial to boost resilience.
This study also highlights the cooperative side of plants. Typically, plants compete for space, light, and nutrients. Mittler views this as an evolutionary trade-off.
“If you grow under harsh conditions, you better grow in a group. If you grow under really ideal conditions with no predators, with no stressors, then you better grow individually,” he says.
“The authors of this paper propose a thoughtful and clever experimental design to better understand the still underexplored pathways of aboveground plant-to-plant communication,” says Piyush Jain, a plant biologist at Cornell University, who was involved in the study. The design “addresses a longstanding question: whether chemical signaling and electrical signaling are responsible for increased resilience to excessive light stress.”
The study, not peer reviewed yet, has been published in BioRxiv.
