Reference standards for determination of DNA content of plant nuclei

Flow cytometry was used to compare 14 potential reference standards for pla nt DNA content determination. Both chicken and plant internal standards wer e used, as were propidium iodide (PI) and 4'-6-diamidino-2-phenylindole (DA PI) as fluorochromes. Means and standard errors of the means are presented for the 14 potential reference standards, and the means are compared to tho se obtained by Feulgen densitometry. Five species are recommended as an ini tial set of international standards for future plant DNA content determinat ions: Sorghum bicolor cv. Pioneer 8695 (2C = 1.74 pg), Pisum sativum cv. Mi nerva Maple (2C = 9.56 pg), Hordeum vulgare cv. Sultan (2C = 11.12 pg), Vic ia faba (2C = 26.66 pg), and Allium cepa cv. Ailsa Craig (2C = 33.55 pg). I t is recommended that the reference standard of choice be one with 2C and J C nuclear DNA content peaks similar to, but not overlapping, the 2C and 4C peaks of the target species. We recommend PI as the fluorochrome of choice for flow cytometric determination of plant DNA content. DAPI should be used only if the estimated DNA Value is corroborated by using a second stain th at has no bias for AT- or CC-rich sequences within genomes.