Reversible root tip rotation in Arabidopsis seedlings induced by obstacle-touching stimulus.

In soil, downwardly growing plant roots frequently alter their growth direction to escape obstacles that lie in their paths. This response has been analyzed with a simple system that provides a constant obstacle-touching stimulus to root tips of young seedlings of Arabidopsis thaliana. On the surface of agar plates, which were set at an angle of 45 degrees to the vertical, the roots exhibit a wavy growth pattern that is caused by periodic reversion of rotation of the root tip. A set of mutants with abnormal wavy growth was used to demonstrate that at least six genes are involved in this stimulus-response interaction.