A video shows how seconds after a hungry caterpillar severs a leaf from the
rest of the plant, a blaze of fluorescent light washes over the other
leaves, signaling that they should prepare for future attacks by the
caterpillar or its kin.

The fluorescent light tracks calcium as it goes through the plant's tissues,
warning of a threat through electrical and chemical signals. University of
Wisconsin-Madison Professor Simon Gilroy and his lab reveals how glutamate,
an abundant neurotransmitter in animals, activates a wave of calcium when
the plant is wounded. To see calcium in real time, Masatsugu Toyota, a
postdoctoral researcher in Gilroy's lab, developed plants that produce a
protein that only fluoresces around calcium, allowing the researchers to
track its presence and concentration. They were able to see plants lighting
up as calcium flows from the site of damage to other leaves.

A research previously done by Swiss scientist Ted Farmer showed that
defense-related electrical signals depended on receptors for glutamate.
Farmer showed that mutant plants missing glutamate receptors also lost their
electrical responses to threats. Toyota and Gilroy looked at the flow of
calcium during wounding in these mutant plants. They found that while normal
plants blaze brightly with fluorescent calcium waves during wounding, mutant
plants were barely sputtering marginal flashes of light. These results
suggest that glutamate spilling out from wound sites triggers the burst in
calcium that spreads across the plant.

[news.wisc.edu]
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