On the mechanism of differential Giemsa staining of BrdU-substituted chromatids

This paper analyses the effect of acid hydrolysis on the differential Giemsa staining of 5-bromo-2'deoxyuridine (BrdU) substituted chromatids in human and plant chromosomes, after treatment with a fluorochrome and light. Human lymphocytes and Allium cepa L. root tips were grown in BrdU for two or three cell cycles. Lymphocytes spreadings and meristem squashes were treated with fluorochrome Hoechst 33258, exposed to sunlight, hydrolysed with 5N HCl and stained with giemsa. This acid hydrolysis improves the differential staining of BrdU substituted and non-substituted chromatin. It also allows the differentiation of sister chromatids with the DNA specific dye azure-A.