Plants produce quite a lot of chemicals called volatile organic compounds that affect their interactions with the world around them. In a brand new study, researchers on the University of Illinois at Urbana-Champaign investigated how the kind and amount of those VOCs change based on different characteristics of tomato plants.
The smell of cut grass is certainly one of the signature scents of summer. This smell is certainly one of the ways plants signal their injury. Because they can not run away from danger, plants have evolved to speak with one another using chemical signals. They use VOCs for quite a lot of reasons: to assist construct their defenses, to warn one another of dangers, to recruit helpful soil microbes that may also help plants grow. , and to warn insect predators that insects are chewing on the leaves of this plant.
“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 a graduate student within the Nigambi lab. Erin Didi said.
Studying the aspects influencing VOC emissions, subsequently, is vital to understanding plant health. In the past, other studies have checked out how soil microbes reminiscent of arbuscular mycorrhizal fungi or caterpillars or the sort of tomato plant can affect VOCs. In the present study, the researchers studied the collective influence of all these aspects on plant chemistry in 4 tomato varieties – two heirlooms and two hybrids.
“Previous studies have looked at tomato varieties that are grown conventionally for processing on a large scale, and not typically grown by small farmers, so we decided to ask Illinois farmers what What they grow. Based on their feedback, we chose tomato varieties that are commonly grown in central Illinois,” said Dade. The hybrids used were Mountain Fresh and Valley Girl, and the organic heirlooms were Amish Paste and Cherokee Purple.
The researchers compared the response of untreated plants to plants that had been exposed to AMF, caterpillars or each. They studied VOCs by sealing eight-week-old tomato plants with odor-blocking oven bags for one hour. They extracted the air across the plants and analyzed the assorted chemicals produced by each plant using gas chromatography-mass spectrophotometry.
AMF and caterpillars reduced volatile emissions in all 4 forms of tomato plants, individually. Their effect when present together was lower than the effect when either was present alone.
Although it isn't clear why the helpful fungal associations reduced VOCs, it is probably going that the plants were less conscious of the caterpillars. Additionally, hybrid tomatoes emitted lower amounts of volatiles than heirloom tomatoes. “Heirloom tomatoes — the big, juicy tomatoes we all love — are bred for flavor. Meanwhile, hybrids are largely grown for traditional production,” said Esther Ngombi (CIS/MMG). , which come at the price of the plant,” said Esther Ngombe (CIS/MMG). Assistant Professor of Integrative Biology. “Our work suggests that we're compromising plant defenses through our breeding practices.”
Plants were also evaluated based on their growth above ground and in soil. The researchers found that plants that interacted with the fungus had higher leaf biomass and more complex root structures.
“AMF forms a partnership with more than 80 percent of land plants, setting up a trade-off where fungi extract nutrients from the soil in exchange for carbon from the plants,” said Didi. “We found that, particularly in Cherokee Purple, AMF may confer additional benefits, including improved growth and greater emission of VOCs.”
Surprisingly, plants treated with caterpillars had higher plant growth. “These plants had more biomass both in the roots and above ground, which seems counterintuitive because they've been actively eaten. I would assume they'd have less biomass,” Dadi said. . “It's possible that the caterpillars triggered a growth response, similar to when you prune a tree so that it produces new growth.”
The researchers are thinking about further investigating the expansion response of the caterpillars. “It's possible that the plants decided that the number of caterpillars we were using wasn't enough to be considered a threat and so they continued to grow. It's also possible that the caterpillars weren't hungry enough to do enough damage. ” said Ngombe. .
“There's a lot going on behind the scenes that we don't understand yet. For example, we're barely scratching the surface in understanding the roles of different microbes,” said Didi. “People think that plants are not intelligent, but our study shows that they are actively responding to their surroundings using chemistry.”
“We are trying to spread the gospel of plant chemistry, the language that plants use to communicate and we are excited to learn more,” said Ngombi.