Tomato plants ‘talk’ to one another to signal danger

In a recent exploration into the complex world of plants, researchers at the University of Illinois Urbana-Champaign delved into the ways tomato plants communicate through chemicals. 

Tomato plants, like many others, emit volatile organic compounds (VOCs) as a response to various environmental factors, acting as a signal for both defense and interaction with their surroundings.

Chemical communication

One of the most recognizable scents of nature is the aroma of freshly cut grass, a common example of plants signaling distress. Lacking the ability to flee from harm, plants have developed a sophisticated system of chemical communication. 

Volatile organic compounds serve multiple purposes, including defense preparation, alerting neighboring plants to dangers, attracting helpful soil microbes, and even calling in predators of pests.

Lead author Erinn Dady, a graduate student at the University of Illinois, explains this phenomenon using the example of a caterpillar munching on a leaf. The plant releases a chemical signal that essentially acts as an advertisement for the caterpillar’s predators, informing them of a potential meal.

Focus of the study

This study, focusing on the factors affecting VOC emissions, is crucial to understanding overall plant health. Prior research has examined the impact of various elements such as soil microbes and different tomato varieties on VOCs. 

The new study, however, looks at the collective impact of these factors using four popular tomato varieties in central Illinois – two heirlooms (Amish Paste and Cherokee Purple) and two hybrids (Mountain Fresh and Valley Girl).

How the research was conducted 

To investigate, the researchers exposed the tomato plants to different treatments including arbuscular mycorrhizal fungi (AMF), caterpillars, both, or none. 

The study of VOCs was conducted by enclosing eight-week-old tomato plants in an odor-blocking oven bag for an hour and then analyzing the air around them using gas chromatography-mass spectrophotometry.

Critical insights

Interestingly, both AMF and caterpillars, when present alone, reduced the volatile emissions across all tomato varieties. However, their combined presence had a minimal effect compared to either one individually. The study noted a concern that plants were less responsive to caterpillars when in association with AMF.

Moreover, the heirloom tomatoes emitted a greater quantity of VOCs compared to the hybrid varieties. Senior author Esther Ngumbi, an assistant professor of integrative biology, notes that while heirlooms are bred for flavor, hybrids are developed for large-scale production, potentially at the expense of the plant’s defenses.

Unexpected discovery 

The research also examined plant growth, finding that plants with fungal associations exhibited higher leaf biomass and more complex root structures. 

Surprisingly, caterpillar-treated plants showed greater growth, a response that intrigued the researchers and will be a focus of further investigation.

Learning the language of plants

According to Ngumbi and Dady, there is still much to uncover about plant responses and the role of different microbes. “People tend to think that plants are not intelligent, but our studies have shown that they are actively responding to the environment around them using chemistry,” Dady said.

Through their work, the team aims to deepen our understanding of plant chemistry, a critical language in the botanical world, and its implications for plant health and interaction with the environment.

The study is published in the Journal of Chemical Ecology. 

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