First published online January 23, 2003; 10.1104/pp.014423
Plant Physiol, March 2003, Vol. 131, pp. 1360-1373
Enhanced Gravitropism of Roots with a Disrupted Cap Actin
Cytoskeleton1
Guichuan
Hou,
Deepti R.
Mohamalawari, and
Elison B.
Blancaflor*
Plant Biology Division, The Samuel Roberts Noble Foundation Inc.,
2510 Sam Noble Parkway, Ardmore, Oklahoma 73401
The actin cytoskeleton has been proposed to be a major player in
plant gravitropism. However, understanding the role of actin in this
process is far from complete. To address this problem, we conducted an
analysis of the effect of Latrunculin B (Lat B), a potent
actin-disrupting drug, on root gravitropism using various parameters
that included detailed curvature kinetics, estimation of gravitropic
sensitivity, and monitoring of curvature development after extended
clinorotation. Lat B treatment resulted in a promotion of root
curvature after a 90° reorientation in three plant species tested.
More significantly, the sensitivity of maize (Zea mays) roots to gravity was enhanced after actin disruption, as determined from a comparison of presentation time of Lat B-treated versus untreated roots. A short 10-min gravistimulus followed by extended rotation on a 1-rpm clinostat resulted in extensive gravitropic responses, manifested as curvature that often exceeded 90°.
Application of Lat B to the cap or elongation zone of maize roots
resulted in the disruption of the actin cytoskeleton, which was
confined to the area of localized Lat B application. Only roots with
Lat B applied to the cap displayed the strong curvature responses after
extended clinorotation. Our study demonstrates that disrupting the
actin cytoskeleton in the cap leads to the persistence of a signal
established by a previous gravistimulus. Therefore, actin could
function in root gravitropism by providing a mechanism to regulate the
proliferation of a gravitropic signal originating from the cap to allow
the root to attain its correct orientation or set point angle.
1
This work was supported by the National
Aeronautics and Space Administration (grant no. NAG 2-1518 to E.B.B.)
and by the Noble Foundation.
*
Corresponding author; e-mail eblancaflor{at}noble.org; fax
580-224-6692.
© 2003 American Society of Plant Biologists
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