Palmieri Maria, Kiss John Z
Department of Botany, Miami University, Oxford, OH 45056, USA.
J Exp Bot. 2005 Sep;56(419):2539-50. doi: 10.1093/jxb/eri248. Epub 2005 Aug 1.
The F-actin cytoskeleton is hypothesized to play a role in signal transduction mechanisms of gravitropism by interacting with sedimenting amyloplasts as they traverse statocytes of gravistimulated plants. Previous studies have determined that pharmacological disruption of the F-actin cytoskeleton with latrunculin B (Lat-B) causes increased gravitropism in stem-like organs and roots, and results in a more rapid settling of amyloplasts in the columella cells of Arabidopsis roots. These results suggest that the actin cytoskeleton modulates amyloplast movement and also gravitropic signal transduction. To determine the effect of F-actin disruption on amyloplast sedimentation in stem-like organs, Arabidopsis hypocotyls were treated with Lat-B and a detailed analysis of amyloplast sedimentation kinetics was performed by determining amyloplast positions in endodermal cells at various time intervals following reorientation. Confocal microscopy was used to confirm that Lat-B effectively disrupts the actin cytoskeleton in these cells. The results indicate that amyloplasts in hypocotyl endodermal cells settle more quickly compared with amyloplasts in root columella cells. F-actin disruption with Lat-B severely reduces amyloplast mobility within Arabidopsis endodermal statocytes, and these results suggest that amyloplast sedimentation within the hypocotyl endodermal cell is F-actin-dependent. Thus, a model for gravitropism in stem-like organs is proposed in which F-actin modulates the gravity response by actively participating in statolith repositioning within the endodermal statocytes.
据推测，F-肌动蛋白细胞骨架通过与沉降的造粉体相互作用，在植物向重力性的信号转导机制中发挥作用，因为这些造粉体在受重力刺激的植物的平衡细胞中移动。先前的研究已经确定，用拉特鲁毒素B（Lat-B）对F-肌动蛋白细胞骨架进行药理学破坏会导致茎状器官和根中的向重力性增加，并导致拟南芥根的根冠细胞中的造粉体沉降更快。这些结果表明，肌动蛋白细胞骨架调节造粉体的运动以及向重力性信号转导。为了确定F-肌动蛋白破坏对茎状器官中造粉体沉降的影响，用Lat-B处理拟南芥下胚轴，并通过在重新定向后的不同时间间隔确定内皮层细胞中造粉体的位置，对造粉体沉降动力学进行了详细分析。共聚焦显微镜用于确认Lat-B有效地破坏了这些细胞中的肌动蛋白细胞骨架。结果表明，与根冠细胞中的造粉体相比，下胚轴内皮层细胞中的造粉体沉降更快。用Lat-B破坏F-肌动蛋白会严重降低拟南芥内皮层平衡细胞中造粉体的移动性，这些结果表明下胚轴内皮层细胞中的造粉体沉降依赖于F-肌动蛋白。因此，提出了一种茎状器官向重力性的模型，其中F-肌动蛋白通过积极参与内皮层平衡细胞中的平衡石重新定位来调节重力反应。
