Seeing red – do tomatoes feel pain?

Tomatoes might seem like the strong silent types, but they cry out when they get hurt.

A team of researchers, led by Gabriela Niemeyer Reissig of the Federal University of Pelotas, Brazil, found that the fruit of tomatoes send electrical warning signals to the rest of the plant to warn of damaging events such as caterpillar attacks.

“What we found is that fruits can share important information such as caterpillar attacks – which is a serious issue for a plant – with the rest of the plant, and that can probably prepare other parts of the plant for the same attack,” says Niemeyer Reissig.

“We usually forget that a plant’s fruits are living and semiautonomous parts of their mother plants – far more complex than we currently think.

“Since fruits are part of the plant, made of the same tissues as the leaves and stems, why couldn’t they communicate with the plant, informing it about what they are experiencing, just like regular leaves do?”

Plants don’t have a central nervous system like humans, so it’s easy to think they don’t ‘hurt’. Instead, they have an elaborate system of chemical, hormonal and electrical signals that share information about what’s happening in other parts of the plant.

Generally, these signals ‘warn’ other cells so they can respond in the most effective way. This happens because ions are transported around cells as the environment changes – they rush in and out of cells based on what is happening to the plant at any given time, creating an electrical signal.

Typically, however, the fruit gets lots of nutrients pumped into it and gives nothing back to the rest of the plant, so it had been unclear whether it ‘spoke back’ to the mother plant if there was an emergency.

To learn more about it, the team put tomato plants into a Faraday cage – a box that blocks electrical signals – and placed electrodes around the plants. Then they introduced caterpillars that attacked the tomato fruit.

They found the fruit was sending electrical signals back to the rest of the plant as a warning. In response, the plant produced defensive chemicals such as hydrogen peroxide to fight back against the caterpillars if they moved down to eat other parts of the plant.

The study, which was published in Frontiers of Sustainable Food Systems, found that the warning alarm was so ‘loud’ it was picked up as far away as the leaves, which may be a useful isgnal to track to see if tomatoes are under attack.

“If studies like ours continue to advance, and the techniques for measuring electrical signals in open environments continue to improve, it will be possible to detect infestation of agricultural pests quite early, allowing for less aggressive control measures and more accurate insect management,” says Niemeyer Reissig.

“Understanding how the plant interacts with its fruits, and the fruits among themselves, may bring insights about how to ‘manipulate’ this communication for enhancing fruit quality, resistance to pests and shelf life after harvest,” Niemeyer Reissig said.