Uranyl-EDTA-hematoxylin: a new selective staining technique for nucleolar material.

This paper deals with the visualization of nuclear structures in glutaraldehyde fixed, acetic acid flattened preparations from Chironomus salivary glands, by means of an uranyl mordanting followed by hematoxylin staining. Under these conditions all the nuclear structures (bands, Balbiani rings, and nucleoli) were deeply stained. Treatment with 0.1 M EDTA for at least 30 sec after uranyl mordanting completely prevents the following hematoxylin staining in all the structures but the nucleolus. With increased EDTA extraction times (60-90 sec) the central region (composed of pars fibrosa) in spontaneously or experimentally segregated nucleoli showed the highest capacity for retaining uranyl ions. This selective staining of the nucleolar (possibly proteinic) material proved also efficient in cells from Drosophila testes and Allium roots.