Talking tomatoes: How Tomato plants communicate through VOCs

Plants make different chemicals called volatile organic compounds (VOCs) that help them interact with their environment. A recent study by researchers at the University of Illinois Urbana-Champaign looked at how these VOCs can change in tomato plants. This research was published in the Journal of Chemical Ecology.

When you smell cut grass, that’s actually a plant’s way of signaling that it’s been hurt. Since plants can’t move away from danger, they’ve learned to talk to each other using these chemical signals. They use VOCs for many things: to get ready to defend themselves, to warn other plants about dangers, to attract helpful soil microbes that help them grow, and to let insect predators know that a pest is eating their leaves.

Erinn Dady, a grad student at the University of Illinois and the lead author of the study, explains this using the example of a caterpillar eating a leaf. The plant sends out a chemical signal that works like an ad for the caterpillar’s predators, telling them there’s a meal waiting for them.

"When a caterpillar chews on a leaf, the plant sends out a signal that calls out to the caterpillar's predators. It's like a billboard that tells them where lunch is," said Erinn Dady, a graduate student in the Ngumbi lab.

Study: Plant health linked to VOCs

Understanding what affects the release of VOCs is important for knowing how healthy plants are. Earlier studies have looked at how things like soil microbes, caterpillars, and different types of tomato plants can change VOCs. In this study, the researchers looked at how all these factors together affect the chemistry of plants. They used four types of tomato plants—two heirlooms and two hybrids.

In earlier studies, researchers examined types of tomatoes commonly grown on a large scale for processing, rather than the types that small farmers typically grow. Therefore, they questioned Illinois farmers about the types of tomatoes they produce. Relying on the farmers' input, they selected types of tomatoes often cultivated in central Illinois. They used Mountain Fresh and Valley Girl hybrids, and Amish Paste and Cherokee Purple as the organic heirlooms.

The researchers compared how plants that hadn’t been treated reacted to those that had been exposed to AMF, caterpillars, or both. They studied the VOCs by putting the eight-week-old tomato plants in an oven bag that blocks odors for an hour. They took out the air around the plants and looked at the different chemicals each plant made using a method called gas chromatography-mass spectrophotometry.

The AMF and the caterpillars, on their own, lowered the amount of VOCs in all four types of tomato plants. When they were both present, their effect was much smaller than when just one of them was present.

It’s not clear why the helpful fungi associations lowered the VOCs, but it’s worrying that the plants didn’t react as much to the caterpillars. Also, the hybrid tomatoes gave off fewer VOCs compared to the heirloom tomatoes.

Plants and insects influence each other

The study found that both AMF and caterpillars, when alone, lowered the amount of VOCs given off by all types of tomato plants. But when they were both present, their effect was much smaller. The researchers were worried that the plants didn’t react as much to the caterpillars when AMF was also present.

Heirloom tomatoes gave off more VOCs than hybrid varieties. Esther Ngumbi, a senior author of the study, said that while heirlooms are grown for their taste, hybrids are grown for large-scale production, which might affect the plant’s defenses.

The study also looked at how plants grow. It found that plants that had fungal associations had more leaf biomass and more complex root structures.

Interestingly, plants treated with caterpillars grew more. This surprised the researchers and they plan to look into it more.

Ngumbi and Dady, the researchers, said there’s still a lot we don’t know about how plants respond and the role of different microbes. They said that even though some people think plants aren’t smart, their studies have shown that plants actively respond to their environment using chemistry.

The team’s goal is to learn more about plant chemistry, which is an important way plants communicate, and how it affects plant health and how plants interact with their environment.

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