A Simple and Sensitive DNA Assay for Plant Extracts

A sensitive fluorimetric method was developed for the quantitative determination of DNA in plant (Zea mays L. and Medicago sativa L.) extracts. This method takes advantage of the specific increase in fluorescence intensity of the complex of DNA and the dye 4',6'-diamidino-2-phenylindole (DAPI). Recovery of DNA and dissociation of histones from DNA were maximized by the addition of 2.0 molar NaCl to the homogenates. Treatment of the homogenate with chloroform to remove pigments and proteins decreased the quenching of fluorescence of the DAPI-DNA complex. The fluorescence intensity of RNA with DAPI was less than 2% of that produced by an equivalent weight of DNA. Comparisons were made between this fluorimetric DNA method and the commonly used diphenylamine assay for DNA. The diphenylamine DNA assay was more timeconsuming, less sensitive, and consistently resulted in lower estimates of DNA concentrations than did the fluorimetric DNA assay.