Plants can smell? New research shows how it works

Who needs a nose, anyway? Research nearly 20 years in the making from the University of Tokyo shows for the first time how plants can “smell” using odor receptors that function on a molecular level.

The project, begun in 2000, shows that there is a molecular basis to odor detection in plants. It works like this: Plants can detect volatile organic compounds — basically “odor molecules.” These compounds are what allow plants to attract pollinators, deter pests, react to nearby disease and even give off a scent themselves.

“Humans have about 400 odor receptors,” said the university’s Kazushige Touhara. “Elephants have about 2,000, the largest number in animals. But based on how many transcription factor genes are in plants, plants may be able to detect many more odors than animals.”

Touhara’s team exposed tobacco plants — both their cells and four-week-old plants, known for being good models for these kinds of studies — to various volatile organic compounds. They found that the compounds turned the plants’ genes on or off by binding to other molecules, called transcriptional co-repressors.

In this way, plants can detect and are affected by odors, but the process happens much slower than in animals. Humans and animals respond almost immediately to smells, which are recognized by receptors on the outside of cells in the nose, which trigger brain activity. In plants, the odor compounds must gradually accumulate within the cells in order to provoke a reaction.

“Plants can’t run away, so of course they react to odors more slowly than animals,” Touhara said. “If plants can prepare for environmental change within the same day, that is probably fast enough for them.”

What’s the benefit of this discovery? Just as understanding animal behavior leads to better agriculture, so too could understanding plant behavior, allowing experts to make more efficient decisions regarding gene editing and pesticide use. An example Touhara gives is that instead of pesticides, perhaps farmers in the future could spray their fields with odors that provoke insect-deterrent behavior in plants.

“All creatures communicate with odor,” Touhara said. “The understanding of how plants communicate using odor will open up opportunities to study ‘olfactory’ communication between all creatures.”