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BREAKTHROUGH TECHNOLOGIES

A New Algorithm for Computational Image Analysis of Deformable Motion at High Spatial and Temporal Resolution Applied to Root Growth. Roughly Uniform Elongation in the Meristem and Also, after an Abrupt Acceleration, in the Elongation Zone¹

Division of Biological Sciences (C.M.v.d.W., K.K.P., T.I.B.) and Department of Computer Engineering and Computer Science (H.S.J., K.P.), University of Missouri, Columbia, Missouri, 65211; and Institute of Plant Physiology, Russian Academy of Science, Moscow, Russia 127276 (V.B.I.)

A requirement for understanding morphogenesis is being able to quantify expansion at the cellular scale. Here, we present new software (RootflowRT) for measuring the expansion profile of a growing root at high spatial and temporal resolution. The software implements an image processing algorithm using a novel combination of optical flow methods for deformable motion. The algorithm operates on a stack of nine images with a given time interval between each (usually 10 s) and quantifies velocity confidently at most pixels of the image. The root does not need to be marked. The software calculates components of motion parallel and perpendicular to the local tangent of the root's midline. A variation of the software has been developed that reports the overall root growth rate versus time. Using this software, we find that the growth zone of the root can be divided into two distinct regions, an apical region where the rate of motion, i.e. velocity, rises gradually with position and a subapical region where velocity rises steeply with position. In both zones, velocity increases almost linearly with position, and the transition between zones is abrupt. We observed this pattern for roots of Arabidopsis, tomato (Lycopersicon lycopersicum), lettuce (Lactuca sativa), alyssum (Aurinia saxatilis), and timothy (Phleum pratense). These velocity profiles imply that relative elongation rate is regulated in a step-wise fashion, being low but roughly uniform within the meristem and then becoming high, but again roughly uniform, within the zone of elongation. The executable code for RootflowRT is available from the corresponding author on request.

¹ This paper is dedicated to Ralph O. Erickson on the occasion of his 89th birthday. This work was supported by the U.S. National Science Foundation (award no. IBN 9817132 to T.I.B.) and by the U.S. Department of Energy (award no. 94ER20146 to T.I.B.), which does not constitute endorsement by that Department of views expressed herein.

² Present address: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742.

³ Present address: Department of Biology, Carnegie Mellon University, P.O. Box 3320, Pittsburgh, PA 15230.

^* Corresponding author; e-mail BaskinT{at}Missouri.edu; fax 573–882–0123.

Received January 30, 2003; returned for revision February 25, 2003; accepted March 23, 2003.

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