Structural sterols are abundant in the plasma membrane of root apex cells in Arabidopsis thaliana. They specifically accumulate in trichoblasts during the prebulging and bulge stages and show a polar accumulation in the tip during root hair elongation but are distributed evenly in mature root hairs. Thus, structural sterols may serve as a marker for root hair initiation and growth. In addition, they may predict branching events in mutants with branching root hairs. Structural sterols were detected using the sterol complexing fluorochrome filipin. Application of filipin caused a rapid, concentration-dependent decrease in tip growth. Filipin-complexed sterols accumulated in globular structures that fused to larger FM4-64–positive aggregates in the tip, so-called filipin-induced apical compartments, which were closely associated with the plasma membrane. The plasma membrane appeared malformed and the cytoarchitecture of the tip zone was affected. Trans-Golgi network/early endosomal compartments containing molecular markers, such as small Rab GTPase RabA1d and SNARE Wave line 13 (VTI12), locally accumulated in these filipin-induced apical compartments, while late endosomes, endoplasmic reticulum, mitochondria, plastids, and cytosol were excluded from them. These data suggest that the local distribution and apical accumulation of structural sterols may regulate vesicular trafficking and plasma membrane properties during both initiation and tip growth of root hairs in Arabidopsis.
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机译：拟南芥根尖细胞质膜中富含结构固醇。它们在前膨大和膨大阶段特别积累在成毛细胞中，在根毛伸长期间在尖端显示极性积累，但在成熟根毛中均匀分布。因此，结构固醇可以用作根毛起始和生长的标记。另外，他们可以预测具有分支根毛的突变体中的分支事件。使用固醇络合的荧光色素菲利普林检测结构固醇。施用磷脂会导致尖端生长迅速，浓度依赖性地降低。磷脂复合固醇在球状结构中积累，并与尖端的较大的FM4-64阳性聚集物融合，即所谓的由菲律宾诱导的根尖隔室，其与质膜紧密相关。质膜出现畸形，尖端区域的细胞结构受到影响。 Trans-Golgi网络/早期内体区隔包含分子标记，例如小的Rab GTPase RabA1d和SNARE Wave line 13（VTI12），局部聚集在这些由菲律宾引起的顶端区室中，而晚期内体，内质网，线粒体，质体和胞质溶胶被排除在他们之外。这些数据表明，在拟南芥根毛的起始和尖端生长过程中，结构固醇的局部分布和顶端积累可调节水泡运输和质膜特性。
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