Flow Cytometric Analysis of Plant Genomes

Compartmentalization of genomes within specific subcellular organelles is a characteristic feature of eukaryotic cells. Higher plants contain three separate genomes, located within the nucleus, the plastids, and the mitochondria, respectively. Correct coordination of gene expression within these genomes underlies the development of the organism from the fertilized egg, which occurs as a consequence of controlled cellular growth and division. As for other eukaryotes, the duplication of cells occurs through the operation of a cell division cycle. This cycle can be charted from the point of mitosis (M phase) and cell division; this is followed by a period of cellular growth (G₁ phase) preceding the duplication of the nuclear genome (S phase), which in turn is followed by a second period of cellular growth (G₂ phase) prior to the next point of mitosis. The proportions of cells within the various phases of the cell division cycle is defined through the measurement of the nuclear DNA content and its relationship to the haploid genome size (C), defined as the nuclear DNA content of the gamete. In animal cell systems, a variety of flow cytometric (FCM) procedures have been developed for the analysis of nuclear DNA contents. These involve the staining of the nuclei with specific fluorochromes, under conditions in which the amount of the emission of fluorescence is linearly correlated to DNA content. To provide access of the fluorochromes to the nuclei, the plasma membranes are permeabilized, either through fixation or through use of detergents.