Plants flash a warning signal when under attack

When plants are under attack from a very hungry caterpillar, a warning signal flashes through the plant to the other leaves, revealed for the first time in the video above.

As a cabbage caterpillar eats through leaves of the mustard plant Arabidopsis, a wave of calcium crossing the plant, revealed by fluorescent light, triggers defence responses in distant leaves. Credit: Simon Gilroy / UW-Madison

The video, captured by Masatsugu Toyota at the University of Wisconsin was created using a plant modified to fluoresce in response to calcium signals. The details were published in Science.

Calcium, ubiquitous in cells, often acts as a signal in changing environment.

As the caterpillar munches through the leaf it breaks the leaf off from the rest of the plant with one final bite. Almost immediately, the fluorescent light flashes, tracking calcium as it zips at around 1 millimetre per second across the plant’s tissues, providing an electrical and chemical signal of a threat.

Interestingly, the calcium signalling has been found by Toyota and colleagues to be driven by glutamate, more commonly thought of as a neurotransmitter in animals. The glutamate spills out from wound sites triggers the burst in calcium that spreads across the plant. This response leads to defence hormones and altered growth and biochemistry – all occurring without a recognisable nervous system.