Structural Sterols Are Involved in Both the Initiation and Tip Growth of Root Hairs inArabidopsis thaliana 

Abstract

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.

A Membrane Microdomain-Associated Protein, Arabidopsis Flot1, Is Involved in a Clathrin-Independent Endocytic Pathway and Is Required for Seedling Development

“…This growth phenotype may reflect a limitation on recycling of plasma membrane proteins, which could then lead to a slowing of the cell cycle; this could explain the reduction in SAM and RM size. This model is consistent with an earlier report that root hair elongation depends on the highly regulated process of vesicle trafficking (Ovecka et al, 2010).…”

Phytosterol content and the campesterol:sitosterol ratio influence cotton fiber development: role of phytosterols in cell elongation

“…In fact, recent studies have shown that phytosterol composition in the plasma membrane affects proper functioning of auxin transporters (Men et al, 2008;Souter et al, 2002Souter et al, , 2004Willemsen et al, 2003). In addition, phytosterol derivatives are involved in many biological processes such as cell division, cell elongation, cell polarity, cellulose biosynthesis, cell wall formation, and embryonic pattern formation, by functioning as signaling molecules independent of BRs or by modulating the activity of membrane-bound enzymes (Boutté and Grebe, 2009;Carland et al, 2002;Clouse, 2000Clouse, , 2002Ovečka et al, 2010;Schaeffer et al, 2001;Schrick et al, 2000Schrick et al, , 2002Schrick et al, , 2004Suzuki et al, 2009;Topping et al, 1997). These studies revealed the essential role of phytosterols in plant growth and development.…”

Root Hairs

“…During root hair tip growth, newly-synthesized cell wall components are packaged into secretory vesicles that emerge from plant trans-Golgi network (TGN) membranes, and are subsequently targeted and delivered to the apical plasma membrane region of growing root hairs. In Arabidopsis, formation and delivery of at least one subpopulation of these secretory vesicles is regulated by the specific recruitment of members of the RabA family of plant Rab GTPases to these membrane compartments (Preuss et al, 2004;Ovecka et al, 2010;Kang et al, 2011). In their active, GTP-bound conformation, Rab GTPases function through the recruitment of cytosolic "effector proteins" to their target membranes.…”