Probing the Size Exclusion Limit of the Phragmoplast

摘要

During cytokinesis in plant cells, Golgi vesicles are transported to the division plane, where they fuse with each other to form the cell plate. The phragmoplast is a complex assembly of microtubules, microfilaments, and endoplasmic reticulum elements that assemble in two opposing sets perpendicular to the plane of the future cell plate. The phragmoplast cytoskeleton serves as the transport vehicle for Golgi vesicles moving to the plane of cell plate formation. Although Golgi vesicles move through the phragmoplast, organelles do not. This raises the question of the size exclusion limit of the phragmoplast. To study the physical aspects of this process, Esseling- Ozdoba et al. (pp. 1065–1072) microinjected fluorescent vesicles made from a synthetic lipid as well as polystyrene beads into Tradescantia virginiana staminal hair cells. The phragmoplast was determined to be nonselective for the synthetic lipid vesicles of a size up to 150 nm in diameter, but a physical barrier for polystyrene beads having a diameter of 20 and 40 nm. It did not matter whether the polystyrene beans were coated with the synthetic lipid. The authors conclude that vesicle ‘‘stiffness’’ is a parameter affecting vesicle transit through the phragmoplast and discuss that cytoskeleton configurations can physically block such transit. The authors also noted that the 40-nm polystyrene beads hindered cell plate formation, possibly by interfering with the normal delivery of cell plate-forming vesicles.