Tomatoes that are being eaten by insects use electrical signals to send an alert to the rest of the plant, similar to the way our nervous systems warn of damage.
The messages seem to help the plant muster defences such as releasing hydrogen peroxide, a reactive chemical that combats microbial infections of damaged tissues, a study has found.
Human nervous systems use specialised cells called neurons to send electrical signals between different parts of the body. Plants lack neurons, but they do have long, thin tubes called xylem and phloem for moving sap between their roots, leaves and fruit. Charged ions flowing in and out of these tubes can propagate electrical signals around different parts of the plant in a similar way to neurons, although much less is known about the process in plants than in animals.
Previous work found that leaves that are physically damaged send electrical signals to other leaves. In a new study, Gabriela Niemeyer Reissig at the Federal University of Pelotas in Brazil and her colleagues investigated if this could happen with fruit.
They studied small cherry tomato plants (tomatoes are a fruit, botanically speaking) by placing them inside Faraday cages, which block external electric fields, and confined caterpillars of the moth Helicoverpa armigera on the surface of fruit within plastic bags.
Electrodes placed in the fruit stalks showed that the patterns of electrical activity changed during and after the caterpillars started eating. They also varied depending on whether the fruits were ripe or green. “The electrical activity of the fruit is constantly changing every second,” says Niemeyer Reissig. “We can find a [distinct] pattern in the electrical activity when an insect attacks.”
There was also a rise in levels of hydrogen peroxide produced by untouched fruit and leaves all over an attacked plant. “This is probably to avoid microbial infections of damaged plant tissue or as a strategy to cause cell death in the affected region, preventing the spread of pathogens,” says Niemeyer Reissig.
Journal reference: Frontiers in Sustainable Food Systems, DOI: 10.3389/fsufs.2021.657401
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