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DEVELOPMENT AND HORMONE ACTION

The Onset of Gravisensitivity in the Embryonic Root of Flax^1,[OA]

Biology Department, University of Louisiana, Lafayette, Louisiana 70504–2451

Vertical orientation of emerging roots typically is the first response of plants to gravity. Although root gravitropism has been studied extensively, no conclusive data on the onset of gravisensing exist. We determined the inception of gravisensitivity in flax (Linum usitatissimum) roots by clinorotating germinating seeds after various periods of static orientation (gravistimulation) of imbibed seeds. Gravitropic competency was established about 8 h after imbibition, 11 h prior to germination. The time was determined based on 50% of the newly emerged roots curving in the direction of the gravity vector during static imbibition, despite subsequent clinorotation. The threshold value was affected by the orientation of the seeds. Upward orientation of the micropyle/radicle reduced the number of graviresponding roots to about one-half. Prolonged clinorotation weakened the graviresponse. Gravisensing was accompanied by the development of amyloplasts, but the actin cytoskeleton was not involved because imbibition in Latrunculin B did not affect the onset of gravisensitivity or germination, and the development of F-actin in untreated controls was observed only after the onset of gravisensitivity.

² Present address: Division of Science, Truman State University, Kirksville, MO 63501.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Karl H. Hasenstein (hasenstein{at}louisiana.edu).

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Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.073296.

^* Corresponding author; e-mail hasenstein{at}louisiana.edu; fax 337–482–5834.

Received October 24, 2005; returned for revision November 15, 2005; accepted November 15, 2005.

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