Nuclear dynamics in Arabidopsis thaliana

The nucleus is a definitive feature of eukaryotic cells, comprising twin bi lamellar membranes, the inner and outer nuclear membranes, which separate t he nucleoplasmic and cytoplasmic compartments. Nuclear pores, complex macro molecular assemblies that connect the two membranes, mediate communication between these compartments. To explore the morphology, topology, and dynami cs of nuclei within living plant cells, we have developed a novel method of confocal laser scanning fluorescence microscopy under time-lapse condition s. This is used for the examination of the transgenic expression in Arabido psis thaliana of a chimeric protein, comprising the GFP (Green-Fluorescent Protein of Aequorea victoria) translationally fused to an effective nuclear localization signal (NLS) and to beta-glucuronidase (GUS) from E. coli. Th is large protein is targeted to the nucleus and accumulates exclusively wit hin the nucleoplasm. This article provides online access to movies that illustrate the remarkabl e and unusual properties displayed by the nuclei, including polymorphic sha pe changes and rapid, long-distance, intracellular movement. Movement is me diated by actin but not by tubulin; it therefore appears distinct from mech anisms of nuclear positioning and migration that have been reported for euk aryotes. The GFP-based assay is simple and of general applicability. It wil l be interesting to establish whether the novel type of dynamic behavior re ported here, for higher plants, is observed in other eukaryotic organisms.