Gradual potential induced by stem bending: Douglas-fir versus poplar

Plants live in fluctuating environments and daily experience various mechanical stimuli. Wind-induced stem bending leads to local growth modification, but also induces a remote growth response at a distance from the stimulated zone, suggesting long-distance signaling. In a recent study, we revealed the propagation of an electrical response, named 'gradual potential’ (GP), induced by stem bending in poplar (Populus tremula × alba). Although similar in shape to an action potential (AP), the GP shows original characteristics as a decreasing amplitude with the distance and a high propagation speed (until 200 mm s⁻¹) that also decreases. The mechanisms of generation and propagation of the GP remain unknown. As the differences between AP and GP are mainly based on the speed of signal propagation, we focused in this additional study on the method for estimating GP speed. Furthermore, we tested the genericity of this typical bending-induced electrical response by comparing the effect of stem bending between Douglas-fir and poplar using electrophysiological measurements. In-depth analysis on a large number of biological responses confirmed the high-speed characteristics of GP and its exponential decay pattern. Electrical responses analyses on Douglas-fir showed a GP generation after stem bending. However, inter-specific differences in signal amplitude and damping were revealed suggesting a putative role of the stem anatomical structure of these species on the long-range GP generation and propagation.