It has been widely assumed that the transmission of the gravitropic effector following gravistimulation of roots is a slow, rate-limiting process. Hormones are thought to have roles not only in the control of elongation but also in transmission of the gravitropic signal, and the slow movement and action of hormones might contribute to the slow gravitrropic response of roots. However, the earliest detectable changes following gravistimulation are electrical. In this study, membrane potential distributions and fluctuations were measured using a microelectrode system mounted on a precise tiltable bench. Gravi-induced "electrical transmission" as measured by rapid changes in menbrane potential occurred in the tip region of the root as far back as the apical portion of the elongation zone.
