Sci. STKE, 19 November 2002
Plant growth Keeping the Right Distance from the Growing Tip
Root hairs, tubular structures that emerge from plant root epidermal cells, grow through localized exocytosis of cell-wall matrix, a process involving actin-dependent delivery of Golgi-derived vesicles containing matrix material to the growing tip. Researchers have long recognized that the cell nucleus maintains a fixed distance from the apex of the growing root hair. The mechanisms by which the nucleus maintains this position, however, and how it pertains to tip growth, remain unclear. Ketelaar et al. used time-lapse photography of Arabidopsis root hair tips to investigate nuclear behavior during root hair growth and did pharmacological analysis to implicate the actin cytoskeleton in nuclear localization. During active growth, the nucleus maintained a fixed distance from the tip, moving backwards when growth ceased to a random position in the root hair. In mutants with branched hairs, branches emerged from the site at which the nucleus was located; thereafter, nuclei moved between growing branches. The authors used optical trapping of the nucleus to demonstrate that inhibiting nuclear movement resulted in cessation of growth after an interval long enough for the growing tip to attain a distance from the nucleus greater than the largest distance normally observed. Pharmacological analysis indicated that, in Arabidopsis, microtubules were not involved in nuclear positioning, whereas fine filamentous actin in the subapical region was required to maintain growth and nuclear position. Nuclear movement away from the tip after growth cessation depended on bundles of actin filaments and required protein synthesis. Actin filament bundling was also involved in keeping the nucleus away from the growing tip.
T. Ketelaar, C. Faivre-Moskalenko, J. J. Esseling, N. C. A. de Ruijter, C. S. Grierson, M. Dogterom, A. M. C. Emons, Positioning of nuclei in Arabidopsis root hairs: An actin-regulated process of tip growth. Plant Cell 14, 2941-2955 (2002). [Abstract] [Full Text]
Citation: Keeping the Right Distance from the Growing Tip. Sci. STKE 2002, tw426 (2002).
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