Kinetics of constant gravitropic stimulus responses in Arabidopsis roots using a feedback system

The study of gravitropism is hindered by the fact that as a root responds, the gravitational stimulus changes. Using a feedback system to connect a ro tating stage platform to a video digitizer system, we were able to maintain a constant angle of gravistimulation to Arabidopsis roots for long time pe riods. The rate of curvature approximated the;sine rule for angles of stimu lation between 20 degrees and 120 degrees. For a given angle of stimulation , the rate of curvature also remained constant, with no observed diminishme nt of the response. Although previous reports of Arabidopsis root gravitrop ism suggest latent periods of approximately 30 min, using a smooth mechanic al stage to reorient the root, we observed a mean time lag of approximately 10 min. This more rapid onset of curvature can, in part, be explained by r educed mechanical perturbation during the process of gravistimulation. This suggests that mechanical stimulation associated with rapid root re-orienta tion may confound investigations of early gravitropic events.