Shocking Facts About Electric Life
Talk about power plants: did you know plants use electricity? Some fish, also, can navigate or stun their prey using electrical organs.
Power plants: Nature discussed how electrical signals are propagated in plants. The Venus flytrip and “sensitive plant” come to mind as spectacular examples of non-muscular leaf movement triggered by electricity, but there’s more:
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.
Who would have thought that cutting a leaf would send an electrical alarm? Experiments on common thale cress showed no response when a larva walked on a leaf, but an electrical signal spreading at 9 cm per minute when eaten. “The relay of the electrical signal was most efficient for leaves directly above or below the wounded leaf,” the article said. “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.” Receipt of the signal turned on gene expression for defense compounds. “These fascinating observations clearly demonstrate that electrical signal generation and propagation have a crucial role in the initiation of defence responses at remote sites upon herbivore attack.”
The authors of the original paper did not discuss evolution, other than to speculate that “a deeply conserved function for these genes might be to link damage perception to distal protective responses.” If so, this function must have “existed before the divergence of animals and plants.”
Wired fish: Two more electric fish species have been found in the Amazon basin, but they appear to be wired differently. One is biphasic or “AC” like most others, but another is monophasic like “DC”. The article on Science Daily looked for evolutionary reasons why this might be so, but the interesting thing is that “these weakly fishes produce pulses of only a few hundred millivolts from an organ under the body that extends out onto a filamentous tail.” Too weak to stun prey like the jolts from the famous electric eel, the pulses are read by other members of the species, and by the opposite sex, for communication. The fish also use them “to ‘electrolocate’ through their complex aquatic environment at night.” As for evolution, the two fish are so similar as to be classified as the same species except for the differences in electrical phase of their signals.
So many ways of receiving input from the world: touch, sight, sound, smell, taste, and now electricity. The living world is a marvel of interactions between organism and environment. Each sense is exquisitely designed and useful to the organism. Elegant systems are not the result of blind, unguided processes. We believe that viewing them as designed systems would energize research, both to seek understanding of superior design, and to desire to imitate it for improved engineering. The real science stopper is to assume, “Oh, it just evolved. It evolved because it evolved”– a soporific response possessing a dormitive virtue (cartoon and 5/25/05 commentary)