Electrical signal from root to shoot in Sorghum bicolor: induction of leaf opening and evidence for fast extracellular propagation.

We have observed earlier that primary leaf opening in Sorghum is a light-dependent process. We now show that giving a short photo-exposure to the roots alone also induced leaf opening over a similar time scale. However, any injury to the primary root inhibited the leaf formation. To check the propagation rate and response in this plant, the excitable properties and capability of conduction of electrical stimulus were investigated by extracellular recordings. Sorghum seedlings (5-7 days) were examined using non-damaging electrical stimuli. We demonstrate that seedlings when stimulated in one organ, the root region, produced a characteristic response, which could be recorded further up from the stimulating region in another organ, the shoot tissue. The minimum period of stimulation was 150 µs and threshold stimulus intensity was 100 µA. The general characteristic electrophysiological properties of the seedlings and the extracellular propagation of electrical signal suggest that S. bicolor exhibit typical excitable properties comparable to neural tissues. Moreover, electrical stimulus given to the root medium could overcome the requirement of photo-exposure to induce primary leaf formation in etiolated seedlings.