Plants ‘spy’ on their neighbors by sniffing out growth spurts

By Stephen Beech

Plants "spy" on their neighbors by sniffing out their growth spurts, reveals new research.

They have the ability to detect the growth rates of neighboring crops and flowers through aromatic cues called volatile organic compounds, say scientists.

Plants subsequently adjust how much energy they invest into their own growth or defense strategies through responsive gene expression, according to the study.

Swedish researchers explained that volatile organic compounds, or VOCs, are carbon-based chemicals that evaporate easily into the air and are commonly produced by plants to communicate with herbivores, pollinators and even other plants.

VOCs are also responsible for the vast range of fragrances that plants generate, and are often used in the manufacturing of perfumes, cosmetics, food and cleaning products.

Until now, most research on plant-produced VOCs had focused on damaged plants releasing alarm-like chemical signals that warn neighbors to activate their anti-herbivore defenses.

The new study, published in the Journal of Experimental Botany, highlighted a previously unrecognized role for healthy plant VOCs in competitive growing environments.

Study lead author Velemir Ninkovic said: "Healthy non-damaged plants are constantly releasing their own chemical 'fingerprint' into the air, and their neighbors actively read these signals to adjust not only their defenses, but their entire growth strategy.

"This is like a continuous conversation between neighbors, and the finding that these background VOCs can reshape growth and gene activity opens up a new dimension in how we understand plant communication."

Ninkovic and his team at the Swedish University of Agricultural Sciences, Uppsala, conducted two lab experiments using three distinct cultivars of barley that grow at different rates and express different VOC profiles.

He said barley is one of the world's most important cereal crops, so insights into how it grows, defends itself, and interacts with neighboring plants have direct practical relevance for agriculture.

The slow-growing Fairytale cultivar and fast-growing Salome cultivar were exposed to VOCs from all three cultivars, and the effects on their growth and defense strategies were measured by analyzing the physical properties of the plants and changes in gene expression after 25 days.

The research team found that exposure to different VOC profiles triggered shifts in total plant biomass, whereas VOCs from plants with similar growth rates had negligible effects.

Ninkovic said: "VOC receiver plants adjusted their growth to match the competitive pressure signaled by their neighbor's scent: they grew more when exposed to a fast-growing neighbor and less when exposed to a slow-growing one.

"This effect was seen consistently across all parts of the plant — leaves, stems, and roots — rather than the plant simply reshuffling resources between its parts."

Genetic analysis revealed that the shifts in biomass were linked to changes in growth and defense-related pathways.

Shifts toward the slow-growing Fairytale VOC profile were associated with an up-regulation in stress-response genes that help to protect against herbivores and a down-regulation in cellular transport and DNA replication genes.

The opposite pattern was true for shifts toward the fast-growing Salome VOC profile.

The study found that the VOCs most strongly associated with the growth signals include benzyl nitrile, linalool and octanal, which are responsible for a wide range of iconic floral fragrances such as lavender and citrus, as well as more metallic and earthy scents.

Ninkovic said: "Plants release a rich blend of volatile compounds as a normal part of their biology, and it would make evolutionary sense for neighbors to have developed the ability to pick up on each other's chemical signals over millions of years of co-existence."

He added: "We believe this type of constitutive VOC interaction may likely be widespread across the plant kingdom, though the specific compounds involved and the strength of the response will probably vary greatly between species."