Plants fart to protect

Print: New Scientist no. 3055, 9 January 2016

On-line: 6 January 2016

Farting plants have a built-in stink bomb that deters predators

“OH MY goodness! It smells like someone has broken wind.” So says Rabi Musah of the University at Albany in New York, who has discovered a previously unknown defence mechanism in plants: roots that actively release a nasty smell when they sense the touch of a potential threat.

Many plants are famed for their putrid smells, and it has been known for decades that unpleasant sulphurous odours are released when soil is disturbed around the roots of some plants – including members of the Mimosa genus. Until now, it has been assumed that these odours are released passively as a result of tissue damage, like when a bay leaf is crushed or onions are cut with a knife.

But Musah has found that the roots of some species actively release their foul smell. Her team made this discovery while growing seedlings of Mimosa pudica, known for its sensitive leaves that fold up when touched. They found that this plant’s roots are also touch-sensitive, releasing the odour when accosted (Plant Physiology, DOI: 10.1104/pp.15.01705).

The smell – a cocktail of sulphur compounds – seems to be released from tiny hair-like sacs less than half a millimetre long and dotted along the roots of the plants, which collapse after the odours are released.

Even a seedling just a few centimetres high can fill a room with a disgusting smell, says Musah. Seedlings grown in sterile conditions still produce the sulphuric scent, indicating that it is a product of the roots themselves rather than coming from associated bacteria.

“Even a seedling just a few centimetres high can fill a room with a disgusting smell”

Perhaps more astonishing is that the roots seem to distinguish between different kinds of touch. 

“The odour response is selective,” Musah says. A single touch with a finger is always enough to trigger the stench, her team found, but the roots never respond to a glass or metal object. Nor do they usually react to a single touch from soil, while dragging the roots across soil does trigger the smell.

Just how the plant senses these distinctions is unknown. This selectiveness presumably helps the plants differentiate between the touch of predators and harmless objects.

The finding is further evidence that plants are much better at sensing and responding to their environment thangenerally appreciated. “We still underestimate plants a lot,” says Frantisek Baluska of the University of Bonn, Germany.

But the smell might not be aimed at predators, suggests Anthony Trewavas of the University of Edinburgh, UK. Instead, it may act to fend off roots from other plants that encroach upon its territory. “The fact that they are smelly to us is irrelevant.”

The phenomenon is not limited to one species. Musah has found that at least six other Mimosa species produce the smell and now plans to study plants in the closely related Acacia genus. The phenomenon could turn out to be widespread, says Baluska.

(Image: Nigel Cattlin/Alamy Stock Photo)

This article appeared in print under the headline “Farting plants kick up a stink if irked”