Herbivory and mechanical wounding in plants have been shown to elicit electrical signals — mediated by two glutamate-receptor-like proteins — that induce defence responses at local and distant sites.
The mammalian nervous system can relay electrical signals at speeds approaching 100 metres per second. Plants live at a slower pace. Although they lack a nervous system, some plants, such as the mimosa (Mimosa pudica) and the Venus flytrap (Dionaea muscipula), use electrical signals to trigger rapid leaf movements. Signal propagation in these plants occurs at a rate of 3 centimetres per second — comparable to that observed in the nervous system of mussels. On page 422 of this issue, Mousavi et al. address the fascinating yet elusive issue of how plants generate and propagate electrical signals. The authors identify two glutamate-receptor-like proteins as crucial components in the induction of an electrical wave that is initiated by leaf wounding and that spreads to neighbouring organs, prompting them to mount defence responses to a potential herbivore attack.
As sessile organisms, plants have evolved diverse strategies to combat herbivores. These include mechanical defences, such as the thorns found on rose bushes, and chemical deterrents, such as the insect-neurotoxic pyrethrins of the genus Chrysanthemum. However, some plants do not invest in continuous defensive structures or metabolites, relying instead on the initiation of defence responses on demand2. This strategy requires an appropriate surveillance system and rapid communication between plant organs. A key player in orchestrating these reactions is the lipid-derived plant hormone jasmonate, which rapidly accumulates in organs remote from the site of herbivore feeding.
Mousavi et al. used thale cress (Arabidopsis thaliana) plants and Egyptian cotton leafworm (Spodoptera littoralis) larvae as a model of plant–herbivore interactions. The researchers placed the larvae on individual leaves and recorded changes in electrical potentials using electrodes grounded in the soil and on the surface of different leaves. The leaf-surface potential did not change when a larva walked on a leaf, but as soon as it started to feed, electrical signals were evoked near the site of attack and subsequently spread to neighbouring leaves at a maximum speed of 9 centimetres per minute. The relay of the electrical signal was most efficient for leaves directly above or below the wounded leaf. These leaves are well connected by the plant vasculature, which conducts water and organic compounds, and is a good candidate for the transmission of signals over long distances.
Mousavi et al.
Via Kamoun Lab @ TSL, Guogen Yang