Neuroid conduction in plants

The term neuroid conduction have originated with Parker (The elementary nervous system, 1919) who used it to describe the conduction of excitation in tissues of sponges, a group of animals without nervous system. Interestingly, at the time Parker wrote there was still no evidence that electrical signalling existed in sponges as this was demonstrated just 80 years after by Leys and Mackie (Nature, 1997). Nevertheless, the neuroid conduction, defined as the propagation of electrical events in the membranes of non-nervous, non-muscular cells have been demonstrated in many invertebrates as hydrozoans and tunicate, but also in the young stages of amphibian and lungfish. In carnivorous or sensitive plants as Dionea and Mimosa the spreading of the electrical signal has been described also as neuroid conduction (Mackie, 1970). Based on the results of our study we suggest that such kind of electrical transmission is a general characteristic of plants. We will show that the characteristic of the APs generated spontaneously in roots fulfil all the requirement normally associated to the neuroid conduction: a) they propagate in an all-or-none basis b) in non-nervous tissues c) going from cell to cell via plasmodesmata (in animal cells, via gap junction) and finally, d) decline rapidly in amplitude and velocity due to the flow of the current in all directions (compared with the one-directional conduction of nerves). Furthermore, the data recorded with a 60-channels Multi-Electrode-Array (MEA), revealed a vigorous and synchronised electrical activity in roots suggesting an intrinsic capacity of the cells of the root apex to generate functional electrical networks.