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 mixed and unmixed extracts of several plant species combinations (target/standard). This may be because cytosolic components affect dye accessibility to DNA. Several dilution experiments showed clearly how cytosol concentration modified dye accessibility. Heat treatment suggested that dye accessibility could be related to chromatin sensitivity to decondensation. Some methods (nucleus isolation, dilution) can decrease, but not eliminate, stoichiometric error. The high sensitivity of the nucleus to the medium highlights the problem of reliability limits in estimating genome size. The choice between internal and external standardization and the interpretation of intraspecific variation in 'nuclear DNA content' are discussed. (C) 2000 Annals of Botany Company.