Plants have a sense of touch – and they can even ‘feel’ you picking their leaves.
A new study has shown how plant leaves can fire pain signals, which are similar to those found in humans, to warn neighbouring leaves of impending danger.
Scientists believe the response largely evolved to ward off hungry bugs, and is so sensitive it can be set off by the tiny footsteps of a caterpillar.
The signals can be used to trigger the release of foul-tasting chemicals from the plant’s leaves that make them less appetising to insects.
Researchers at the University of Wisconsin were investigating how plants respond to the effects of gravity when they stumbled across their find.
Suspecting calcium was involved, they genetically engineered a mustard plant that would glow brightly under fluorescent light whenever levels of the mineral rose inside the plant.
What researchers discovered was that the plant lit up in response to wounds –and even a light touch on its leaves.
Researchers suggest this rapid firing of calcium is a ‘warning response’ that resembles the pain reflex seen in humans and other animals.
In mammals, nerve cells release an amino acid called glutamate, which triggers a wave of calcium that propagates to cells from the site.
Any type of agitation, from a small insect bite to a physical tear, can set off a response – lighting a chain reaction through the whole plant, scientists say.
‘Plants sense local signals, such as herbivore attack,’ the researchers, led by scientist Dr Masatsugu Toyota, wrote in their paper.
‘They transmit this information throughout the plant body to rapidly activate defence responses in undamaged parts.’
The calcium from one plant cell activates a similar response in the next.
This kickstarts a domino effect that allows parts of the plant to communicate long-distance.
Researchers said that when a plant is attacked, the ‘pain’ response they discovered triggers the release of defence hormones.
These hormones prepare distant leaves from an impending bug invasion by releasing noxious chemicals that make it taste foul to insects.
Other plants, such as some grasses, release smelly hormones that attract parasitic wasps which eat the attacking bugs.
The team’s research has been published in the journal Science.