Estimating percentage constitutive heterochromatin by flow cytometry

Flow cytometry is a powerful method for the assessment of both plant and animal genomes. One of the most interesting aspects is the analysis of chromatin structure. By using intercalating and base pair-specific fluorochromes, the chromatin structure in various cell cultures and microorganisms has been determined. In this study, several maize lines of known heterochromatic composition were analyzed. The nuclei of each line were isolated and stained with DAPI (base pair specific) and PI (intercalator) separately. For each maize line, the PI/DAPI ratio was determined. A significant negative correlation was observed between C-band number and PI/DAPI ratio (r = 0.920) and between percentage heterochromatin and PI/DAPI ratio (r = 0.997). Flow cytometry with use of the fluorochromes DAPI and PI was found to be a rapid and efficient method of determining heterochromatin amount in maize.