DC-ELECTRIC FIELDS AFFECT THE GROWTH DIRECTION AND STATOCYTE POLARITY OF ROOT-TIPS (LEPIDIUM-SATIVUM)

Main roots of 20 h old Lepidium sativum seedlings (garden cress) were used to investigate the effect of weak DC-electric fields on the growth direction of the root tip and the polarity of statocytes of the root cap. When DC-electric fields of 1-3 V/cm were applied for 3 h at right angles to Lepidium roots growing downward in well stirred low salt medium of pH 6 the root tips grew towards the cathode as a result of differential flank growth in the distal elongation zone. A pH value of 5 caused curvature towards the anode due to differential flank growth in the proximal elongation zone. In the statocytes of the root cap, the proximally located cell nucleus always migrated towards the anode and the distal ER towards the cathode. Both the electrotropic growth of the root tip and the displacement of the cell organelles in the statocytes were fully reversible within 3 and 1 h, respectively, after shutting off the electric field. Some comparative studies on main roots of approximately 48 h old seedlings of Zea mays (corn) showed an electrotropic curvature towards the cathode in an electric field of 0.5 V/cm. The curvature was maintained, and frequently even enhanced for up to 24 h after shut-off of the electric field. Field strengths exceeding 0.5 V/cm induced a curvature towards the anode. (So far, the response of corn root statocytes to electric fields has not been investigated.)