Endocytosis and vesicle trafficking during tip growth of root hairs

Abstract

The directional elongation of root hairs, "tip growth", depends on the coordinated and highly regulated trafficking of vesicles which fill the tip cytoplasm and are active in secretion of cell wall material. So far, little is known about the dynamics of endocytosis in living root hairs. We analyzed the motile behaviour of vesicles in the apical region of living root hairs of Arabidopsis thaliana and of Triticum aestivum by live cell microscopy. For direct observation of endocytosis and of the fate of endocytic vesicles, we used the fluorescent endocytosis marker dyes FM 1-43 and FM 4-64. Rapid endocytosis was detected mainly in the tip, where it caused a bright fluorescence of the apical cytoplasm. The internalized membranes proceeded through highly dynamic putative early endosomes in the clear zone to larger endosomal compartments in the subapical region that are excluded from the clear zone. The internalized cargo ended up in the dynamic vacuole by fusion of large endosomal compartments with the tonoplast. Before export to these lytic compartments, putative early endosomes remained in the apical zone, where they most probably recycled to the plasma membrane and back into the cytoplasm for more than 30 min. Endoplasmic reticulum was not involved in trafficking pathways of endosomes. Actin cytoskeleton was needed for the endocytosis itself, as well as for further membrane trafficking. The actin-depolymerizing drug latrunculin B modified the dynamic properties of vesicles and endosomes; they became immobilized and aggregated in the tip. Treatment with brefeldin A inhibited membrane trafficking and caused the disappearance of FM-containing vesicles and putative early endosomes from the clear zone; labelled structures accumulated in motile brefeldin A-induced compartments. These large endocytic compartments redispersed upon removal of the drug. Our results hence prove that endocytosis occurs in growing root hairs. We show the localization of endocytosis in the tip and indicate specific endomembrane compartments and their recycling.

A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis

“…the protrusion of Golgi stacks into the extreme root hair apex) was similar to that observed in depolarized pollen tubes expressing a catalytically inactive phospholipase C (Dowd et al, 2006). The movement of organelles to regions of growing root hairs where they are typically excluded could affect targeted delivery and localized recycling of vesicles, leading to differential tip growth (Ovecka et al, 2005). Alternatively, disrupted F-actin dynamics could interfere with the tip recruitment of lipid signaling components that bind to actin, such as phosphatidylinositol phosphate kinase 1 (Davis et al, 2007) or trafficking of RHD2, the ROS-generating NADPH oxidase, which was recently shown to be dependent on actin for proper root hair tip localization (Takeda et al, 2008).…”

Distinct endocytic pathways identified in tobacco pollen tubes using charged nanogold

“…Internalization events at the tip have been hypothesized in the pollen tube (Parton et al, 2001) and root hairs (Ovecka et al, 2005) on the basis of studies using FM dyes, but the authors could not discriminate the different pathways after tip internalization from those occurring in the subapical dome. Organelles such as the ER or cis, medial or trans cisternae of Golgi bodies were not seen to participate in negatively charged gold transport, suggesting that gold is not Journal of Cell Science 120 (21) recycled into the secretory pathway through the Golgi apparatus.…”

Membrane trafficking mediated by OsDRP2B is specific for cellulose biosynthesis

“…Root hair is a kind of typical tip-growing cells, in which the endocytosis and extocystosis are extremely activated because proteins and polysaccharides required for the tip-growth need to be translocated or recycled through membrane trafficking. 13,14 To examine whether BC3/OsDRP2B participates in root hair growth, we in vivo detected the GFP signals in root hairs of transgenic members, which sustain the transport of these components. Therefore, vesicle trafficking mediated by BC3/OsDRP2B seems specific for cellulose synthesis.…”