Poster: Tropisms
Abs #
394: The actin cytoskeleton is a negative regulator of root gravitropism
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Presenter: |
Blancaflor, Elison B, eblancaflor@noble.org |
Authors | Blancaflor, Elison B (A) Hou, Guichuan (A) Kramer, Victoria L (B) Wang, Yuh-Shuh (A) Chen, Rujin (A) Gilroy, Simon (B) | | Affiliations: |
(A): Plant Biology Division, Samuel Roberts Noble Foundation
(B): Biology Department, Pennsylvania State University
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| Web Site: | http://www.noble.org/PlantBio/Blancaflor/index.html | |
The actin cytoskeleton has been implicated in regulating plant gravitropism. However, its role in this process remains uncertain. We have shown previously that disruption of the actin cytoskeleton with Latrunculin B (Lat B)promoted gravitropism in maize roots. These effects were most evident on a clinostat as curvature that would exceed 90 degrees despite short periods of horizontal stimulation. To probe the cellular mechanisms underlying these enhanced gravity responses, we extended our studies to roots of Arabidopsis. Similar to our observations in other plant species, Lat B enhanced the response of Arabidopsis roots to gravity. 100 nM Lat B and a stimulation time of 5-10 min were sufficient to induce enhanced bending responses during clinorotation. Lat B disrupted the fine actin filament network in the root and altered the dynamics of amyloplasts in the columella but did not inhibit the gravity induced alkalinization of the columella cytoplasm. However, the duration of the alkalinization response was extended in Lat B-treated roots. Indirect visualization of auxin redistribution using the DR5:GUS auxin reporter showed that the enhanced curvature of Lat B-treated roots during clinorotation was accompanied by a persistent lateral auxin gradient. Blocking the gravity induced alkalinization of the columella cytoplasm with caged protons partially inhibited Lat B-induced curvature and the development of the lateral auxin gradient. Taken together, our studies suggest an alternative role for the actin cytoskeleton in regulating plant gravitropism. The actin cytoskeleton likely acts to down-regulate gravitropic signaling, by continuously resetting the gravitropic signaling system (supported by NASA grants NAG-2-1518 to EBB and NAG-1594 to SG and NSF MCB 02-12099 to SG).
