Poster: Tropisms
Abs #
660: Elucidating the cellular and molecular mechanisms underlying the enhanced gravitropic response of roots resulting from actin disruption
We have shown that disruption of the actin cytoskeleton in roots of maize and M truncatula resulted in enhanced root gravitropic responses manifested as reduced presentation time, faster and stronger root curvature, and exaggerated root bending on a slowly rotating clinostat. These results indicate that an additional role for the actin cytoskeleton in root gravitropism could be to regulate the proliferation of an early gravitropic signaling event (Hou et al. 2003; Plant Physiol 113:in press). To probe further into the mechanisms of enhanced root gravisensitivity induced by actin disruption, we extended our studies to Arabidopsis roots. Therefore, we could utilize the molecular and cell biological tools available in this plant model system. Latrunculin B (lat B), a potent actin-disrupting compound did not affect Arabidopsis root bending after a 90-degree horizontal reorientation. This was in contrast to observations made with maize roots, which showed faster curvature after a 90-degree reorientation. However, differences in gravitropic responses between control and lat B-treated roots were observed during clinorotation. Despite a short horizontal stimulus (20-30 min), roots exposed to lat B would continue to bend and often overshoot the vertical. Moreover, lat B-treated roots were more sensitive to gravity as shown by presentation time analysis. Time-lapse imaging and analysis of chemically fixed root sections revealed modified rates of amyloplast sedimentation due to lat B. We have also identified mutants of Arabidopsis from T-DNA tagged lines that exhibit altered bending responses after brief periods of gravistimulation and extended clinorotation. Together, these approaches should provide insights on the involvement of actin in regulating directional root growth.
