Use of an extracellular oxygen vibrating microelectrode system to detect rapid changes in oxygen fluxes in electrotropically-stimulated maize roots

It is well known that the direction of growth of certain plant cells or organs can be modified by an applied electric field. This phenomenon, known as electrotropism has been reported in fungi (McGillavray and Gow, 1986) and algae (Brower and Giddings, 1980) as well as in the pollen tubes (Marsh and Beams, 1945), roots (Ishikawa and Evans 1990; Wolverton et al. 2000), and shoots (Schrank 1959) of higher plants. The correlation between electrical changes and gravitropic curvature suggests the possibility that the curvature of roots in an electric field results from electrical changes within the root that mimic those caused by gravistimulation. This possibility is strengthened by reports that root electrotropism is suppressed by inhibitors of auxin transport (Moore et al. 1987). We examined the effects of electrotropism in solutions of low electrolyte concentration using primary roots of maize (Zea mays L., variety Merit). When submerged in oxygenated solution across which an electric field was applied, the roots curved rapidly and strongly toward the positive electrode (anode). The strength of the electrotropic response increased and the latent period decreased with increasing field strength. At a field strength of 1.5 volts per centimetre the latent period was few minutes and we were able to analyse changes in oxygen fluxes outside the root thanks to the vibrating probe. The experimental measurement of ion or gaseous molecules fluxes in roots is fundamental when discriminating normal physiological function from abnormal or stressed states. We took measures in three basic anatomical parts of root apex: meristematic zone, transition zone, and elongation zone (Verbelen et al. 2006). The goals of the research described in this poster are (a) to determine the changes of oxygen fluxes in different zones of the root related to the electrotropic curvature in maize roots, investigating the early phase of the electrotropic response, from the apply of the current to the visible bending, and (b) to determine the role and the effects of pharmacological manipulation in the electrotropic response and their changes on oxygen fluxes.