The completion of germination of seeds of Arabidopsis thaliana is marked by the appearance of the radicle through the surrounding endosperm and testa. Using confocal microscopy and green fluorescent protein (GFP)-transformed embryos to highlight the epidermal cell walls it has been possible to conduct time-lapse photography of individual embryos during their germination. This reveals that the elongation of embryo cells to effect completion of germination does not occur within the radicle itself, but rather within a discrete region that is immediately proximal to the radicle. This region, identifiable as the lower hypocotyl and hypocotyl–radicle transition zone, is also definable by accumulation of carbohydrate-containing bodies during germination, and distinct GFP expression of GAL4–GFP in enhancer trap lines. Flow cytometric studies show that there is an increase in the proportion of 4C nuclei in the axis which coincides with a considerable increase in length of the hypocotyl, and the occurrence of endopolyploid (8C and 16C) nuclei accompanies the 2-fold increase in mean cell size in the region of elongation, the lower hypocotyl, and hypocotyl–radicle transition zone. Thus the observed cell elongation during germination is accompanied by an increase in nuclear DNA content, and the resultant elongation of the axis to effect radicle emergence is due to cell expansion, not to cell division. When studying the molecular events involved in the completion of germination, therefore, it may be prudent to focus on this region of elongation.

The nucleus is a definitive feature of eukaryotic cells, comprising twin bilamellar membranes, the inner and outer nuclear membranes, which separate the nucleoplasmic and cytoplasmic compartments. Nuclear pores, complex macromolecular assemblies that connect the two membranes, mediate communication between these compartments. To explore the morphology, topology, and dynamics of nuclei within living plant cells, we have developed a novel method of confocal laser scanning fluorescence microscopy under time-lapse conditions. This is used for the examination of the transgenic expression in Arabidopsis 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 β-glucuronidase (GUS) from E. coli. This large protein is targeted to the nucleus and accumulates exclusively within the nucleoplasm. This article provides online access to movies that illustrate the remarkable and unusual properties displayed by the nuclei, including polymorphic shape changes and rapid, long-distance, intracellular movement. Movement is mediated by actin but not by tubulin; it therefore appears distinct from mechanisms of nuclear positioning and migration that have been reported for eukaryotes. The GFP-based assay is simple and of general applicability. It will be interesting to establish whether the novel type of dynamic behavior reported here, for higher plants, is observed in other eukaryotic organisms.

The 2C nuclear DNA content has been estimated by flow cytometry in 18 species and botanical forms of the genus Lupinus (family Fabaceae), using propidium iodide as a fluorescent dye. They represented distinct infrageneric taxonomic groups and differed in somatic chromosome numbers. Estimated 2C DNA values ranged from 0·97 pg in L. princei to 2·44 pg in L. luteus, which gives a more than 2·5‐fold variation. Statistical analysis of the data obtained resulted in a grouping that supports the generally accepted taxonomic classification of the Old World lupins. The rough‐seeded L. princei turned out to be an interesting exception, getting closer to smooth‐seeded species. Results of DNA content analyses are discussed with regards to the phylogenetic relationships among the Old World lupins and some aspects of the evolution of the genus.

Polyploids, organisms that have multiple sets of chromosomes, are common in certain plant and animal taxa. However, there are only a few reports of intraspecific ploidy variation within the genus Quercus. The aim of the study was to investigate the suspected ploidy level of two oaks that have unusual microsatellite banding patterns. Polyploidy was investigated by using microsatellite analysis, stomata length measurements and nuclear DNA content estimation by flow cytometry. Each putative triploid tree has patterns of microsatellite variation unexpected for diploid genomes, with up to three alleles at some loci, significantly longer stomata and 1.5 times more DNA per nucleus compared with diploids. To our knowledge, this report contains the first evidence for triploidy in Q. petraea and confirmation of this phenomenon in Q. robur. Regardless of the positive or negative aspects of the presence of triploid oaks in forest stands, it is of value to be able to screen for them. This study demonstrates that nuclear microsatellites and estimation of DNA content by flow cytometry can readily be used for this purpose.