Plants Communicate to Warn Against Danger

Plants chatter amongst themselves to spread information, a lot like humans and other animals, new research suggests.

A unique internal network apparently allows greens to warn each other against predators and potential enemies.

Many herbal plants such as strawberry, clover, reed and ground elder naturally form a set of connections to share information with each other through channels known as runners—horizontal stems that physically bond the plants like tubes or cables along the soil surface and underground. Though connected to vertical stems, runners eventually form new buds at the tips and ultimately form a network of plants.

“Network-like plants do not usually produce vertical stems but their stems lie flat on the ground and can hence be used as network infrastructure,” said researcher Josef Stuefer from the Radboud University in the Netherlands.

Stuefer and his team let loose caterpillars on white clover plants and watched them eat a single leaf on the network. Then a second set of caterpillars was allowed to choose between the damaged leaf—one that has been alerted to up its defense status—and leaves from an undamaged network.

Over the course of 20 trials, most or all of the approximately 15 caterpillars in each trial preferred the undamaged leaf to the leaf from a damaged network.

“The feeding caterpillars will be deterred and walk off to feed on other non-induced plants,” Stuefer told LiveScience. “[They] understand plant defense language very well as it is directed exactly to them.”

Here is how it works: If one of the network plants is attacked by caterpillars, the other members of the network are warned via an internal signal to upgrade their chemical and mechanical resistance—making their leaves hard to chew on and less desirable. This system works to spread the information amongst the plants and to ward off caterpillars.

“This is an early warning system, very much like in military defense, but then more effective: each member of the network can receive the external signal of impending herbivore danger and transmit it to the other members of the network,” Stuefer said. The attacked leaf is lost. However, the remaining leaves are protected against predators.

The study is detailed in this month’s issue of the journal Oecologia.

According to the researchers, the principle of network transfer of substances is known for very many species, including numerous invasive plants such as bracken and reed and commercial crop species such as bamboo.

The downside to these connections is that viruses often use the runner infrastructure to quickly spread. They enter the plant via the leaves, find their way into the stems and are then passively transported to all the network members where they cause new infections.

“Many pathogens are host specific, meaning that they can infect only very specific plant species,” Stuefer said. “Their main challenge for survival is to find a new host after one has been infected. Such specialists have an especially big advantage from network infections as the physical connection between plants enables them to find genetically identical copies of the original host.”

This, Stuefer explains, is comparable to a computer virus specialized to infect computers with a certain version of the Windows operating system. “Such a virus spreads very fast if all terminals on a network have the correct Windows version while its spread is slowed down if there is variability in the systems,” he said.

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