[70]

ROOT GRAVITROPISM IN RESPONSE TO A SIGNAL ORIGINATING OUTSIDE OF THE CAP.  C. Wolverton¹, J.L. Mullen²,  H. Ishikawa¹, and M.L. Evans^{1   1}Dept of Plant Biology, The Ohio State University, Columbus and ²Department of Biology, Indiana University, Bloomington.

     We recently developed a feedback device for studying root gravitropism.  The device uses video digitizer analysis of root growth and shape in conjunction with a rotating specimen stage to maintain any selected subsection of a root at any specified angle with respect to gravity (Plant  Physiol 123: 665).  Using this device we allowed the cap of a graviresponding maize (Zea mays L.) root to reach vertical while maintaining a selected region within the elongation zone at a gravistimulated angle.  Under these conditions, gravitropic curvature continued long after the root cap reached vertical.  The sustained gravitropic response with the cap oriented parallel to the gravity vector can not be attributed to slow damping of the initial gravitropic response since re-orientation of roots to vertical early in the response results in rapid cessation of curvature.  The results indicate that a signal from outside of the cap can contribute to the curvature response. 

     (Supported by NASA grants NAG5-6385, NAG2-1190 and NAG2-1411)