In one video, you can see a hungry caterpillar, first working around a leaf’s edges, approaching the base of the leaf and, with one last bite, severing it from the rest of the plant. Within seconds, a blaze of fluorescent light washes over the other leaves, a signal that they should prepare for future attacks by the caterpillar or its kin.
That fluorescent light tracks calcium as it zips across the plant’s tissues, providing an electrical and chemical signal of a threat. In more than a dozen videos like this, University of Wisconsin-Madison Professor of Botany Simon Gilroy and his lab reveal how glutamate — an abundant neurotransmitter in animals — activates this wave of calcium when the plant is wounded. The videos provide the best look yet at the communication systems within plants that are normally hidden from view.
Imagine that. Communications systems in plants.
In response to each kind of damage, videos show the plants lighting up as calcium flows from the site of damage to other leaves. The signal moved quickly, about one millimeter per second. That’s just a fraction of the speed of animal nerve impulses, but it’s lightning fast in the plant world — quick enough to spread out to other leaves in just a couple minutes. It took just a few more minutes for defense-related hormone levels to spike in distant leaves. These defense hormones help prepare the plant for future threats by, for example, increasing the levels of noxious chemicals to ward off predators.
The study connects decades of research that has revealed how plants, often seen as inert, dynamically respond to threats by preparing distant tissues to deal with future attacks. Glutamate leads to calcium leads to defense hormones and altered growth and biochemistry, all without a nervous system. Paper. (paywall) – Masatsugu Toyota, Dirk Spencer, Satoe Sawai-Toyota, Wang Jiaqi, Tong Zhang, Abraham J. Koo, Gregg A. Howe, Simon Gilroy. Glutamate triggers long-distance, calcium-based plant defense signaling. Science, 2018; 361 (6407): 1112 DOI: 10.1126/science.aat7744 More.
And how much time elapsed during which these intricate systems developed, purely as a result of natural selection acting on random mutations (the official Darwinian view)?
See also: Do host plants tell insects whether to stay or leave?
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