A minor cabbage larva bites and swallows a piece of leaf. Immediately afterwards, a wave of light propagates in what remains of the plant, as if to signal the attack in progress. This is the alarm system that plants use to activate hormonal defence mechanisms, the last bastion against parasites. This signalling mechanism is nothing more than the "nervous system" of the plants.
A minor cabbage larva bites and swallows a piece of leaf. Immediately afterwards, a wave of light propagates in what remains of the plant, as if to signal the attack in progress. This is the alarm system that plants use to activate hormonal defence mechanisms, the last bastion against parasites. This signalling mechanism is nothing more than the “nervous system” of the plants. But how do brainless organisms trigger such reactions?
A Japanese-American research team tried to unravel the secret behind the nervous system of plants. The study revealed that this process relies on the presence of calcium and glutamate. This discovery is important because these same substances are involved in the communication of nerve signals in animal organisms. Calcium in cells in particular signals environmental changes by transmitting an electrical signal. But it is also difficult to trace because its concentrations change all the time.
Masatsugu Toyota of the University of Saitama, Japan, and Simoin Gilroy of the University of Wisconsin-Madison have developed plants that produce a fluorescent protein only near calcium concentrations. They then subjected them to caterpillar bites, cuts and other painful “wounds”.
As a result, the plants “lit up” with waves of light starting from the point of damage and spreading to the rest of the plant in a couple of minutes. It was clear that they were moving through the calcium concentrations. The signal moved quickly, at a speed of about one millimeter per second.
After a few minutes, levels of a defensive hormone skyrocketed even in distant leaves. This means that this substance prepares plants for future dangers. For example, it alters growth mechanisms or increases the level of toxic substances to deter predators.
The two scientists just had to figure out how to match this discovery with past studies. Other researchers had already shown that the electrical signals that trigger defence mechanisms in plants depend on glutamate receptors. This amino acid is one of the major neurotransmitters in animals and plants. In fact, plants deprived of these receptors lose the ability to transmit electrical signals in response to threats.
Toyota and colleagues have shown that plants missing glutamate receptors, if injured, send few light signals and in marginal areas. As a result, the wound would trigger the release of glutamate which, in turn, would activate the production of calcium and its release throughout the plant. Finally, calcium would trigger the release of defensive hormones.
Research has combined decades of studies on emergency communication in plants. Although they seem inert, these living creatures have a dynamic and reactive way of preparing for future dangers.