Root hairs, tubular structures that emerge from plant root epidermal cells, grow through localized exocytosis of the cell wall matrix, a process involving actin-dependent delivery of Golgi-derived vesicles to the hair tip. During active growth of Arabidopsis root hairs, the nucleus remains at a fixed distance from the tip; in mutants with branched hairs, the nucleus moves between the growing branches. The mechanism underlying nuclear positioning is not known, and Ketelaar et al. have used time-lapse photography and optical trapping of the nucleus to investigate this question. Restraining nuclear movement resulted in cessation of growth at the point when the apex of the root hair reached the largest separation normally observed. Pharmacological analysis indicated that microtubules were not involved, whereas fine filamentous actin in the subapical region was required to maintain growth. On the other hand, bundling of actin filaments (by the protein villin) served to keep the nucleus from approaching the growing tip too closely. -- EA
Plant Cell 14, 2941 (2002).
