Nucleus-cytosol interactions - A source of stoichiometric error in flow cytometric estimation of nuclear DNA content in plants

Discrepancies of 2-20 % were noted in nuclear DNA content estimates using m ixed and unmixed extracts of several plant species combinations (target/sta ndard). This may be because cytosolic components affect dye accessibility t o DNA. Several dilution experiments showed clearly how cytosol concentratio n modified dye accessibility. Heat treatment suggested that dye accessibili ty could be related to chromatin sensitivity to decondensation. Some method s (nucleus isolation, dilution) can decrease, but not eliminate, stoichiome tric error. The high sensitivity of the nucleus to the medium highlights th e problem of reliability limits in estimating genome size. The choice betwe en internal and external standardization and the interpretation of intraspe cific variation in 'nuclear DNA content' are discussed. (C) 2000 Annals of Botany Company.