Apical control, gravitropic signaling, and the growth of lateral roots in Arabidopsis

Most research oil gravity responses in plants has focused oil primary roots and shoots, which typically grow in a vertical orientation. However, the patterns of lateral organ growth, which generally have large effects oil overall plant architecture, are Such that the organs are typically not vertical. In lateral roots of Arabidopsis, growth is initially in a nearly horizontal orientation but changes to a near-vertical orientation as the lateral root develops. Although the non-vertical lateral roots are gravitropically competent, following gravitropic reorientation of seedlings, the lateral roots oil the upper flank of the primary root have different growth patterns from those on the lower side of the primary root. The differences are in part dependent oil reorientation of the primary root, suggesting that gravitropic signaling from the primary root also contributes to the control of lateral root growth. The hormone auxin appears to play a role in this signaling between the primary and lateral roots, as auxin transport inhibitors applied to the primary root affect lateral root growth. Also, lateral roots of pin3 Mutants, which are impaired in polar auxin transport, have altered lateral root orientations. However, other signals from the primary root tip also play an important role in regulating lateral root growth. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.