Ma Zhong, Hasenstein Karl H
Biology Department, University of Louisiana, Lafayette, Louisiana 70504-2451, USA.
Plant Physiol. 2006 Jan;140(1):159-66. doi: 10.1104/pp.105.073296. Epub 2005 Dec 23.
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.
新长出的根的垂直定向通常是植物对重力的第一反应。尽管根的向地性已被广泛研究，但关于重力感知起始的确凿数据并不存在。我们通过在浸泡种子经过不同时间段的静态定向（重力刺激）后对发芽种子进行回转，来确定亚麻（Linum usitatissimum）根中重力敏感性的起始时间。吸胀后约8小时，即发芽前11小时，建立了向地性能力。这个时间是根据在静态吸胀期间，尽管随后进行了回转，但仍有50%的新长出的根朝着重力矢量方向弯曲来确定的。阈值受种子定向的影响。珠孔/胚根向上定向使重力响应根的数量减少到约一半。长时间的回转削弱了重力响应。重力感知伴随着淀粉体的发育，但肌动蛋白细胞骨架并未参与，因为在Latrunculin B中吸胀并不影响重力敏感性的起始或发芽，并且仅在重力敏感性起始后才观察到未处理对照中F-肌动蛋白的发育。
