Two distinct regions of response drive differential growth in Vigna root electrotropism

Although exogenous electric fields have been reported to influence the orie ntation of plant root growth, reports of the ultimate direction of differen tial growth have been contradictory. Using a high-resolution image analysis approach, the kinetics of electrotropic curvature in Vigna mungo L. roots were investigated. It was found that curvature occurred in the same root to ward both the anode and cathode. However, these two responses occurred in t wo different regions of the root, the central elongation zone (CEZ) and dis tal elongation zone (DEZ), respectively. These oppositely directed response s could be reproduced individually by a localized electric field applicatio n to the region of response. This indicates that both are true responses to the electric field, rather than one being a secondary response to an induc ed gravitropic stimulation. The individual responses differed in the type o f differential growth giving rise to curvature. In the CEZ, curvature was d riven by inhibition of elongation, whereas curvature in the DEZ was primari ly due to stimulation of elongation. This stimulation of elongation is cons istent with the growth response of the DEZ to other environmental stimuli.