Sudan Black B—A New Stain for Chromosome Smear Preparations

Various combinations of Sudan black B (SBB) in some of the lower fatty acids and related acids have been used to stain the chromosomes of smear preparations of onion root-tips prefixed in 2 parts of absolute ethyl alcohol and one part of glacial acetic acid. Temporary preparations were obtained in which the chromosomes and nuclei stained brown but appeared black, when observed with a suitable green filter. Remarkably sharp chromone-matic staining was achieved.A mixture consisting of equal parts of 1% SBB in 85% lactic acid (LSBB), full strength propionic acid, 1% SBB in 20% formic acid (FSBB) and water added slowly with stirring gave consistently fast and sharp staining with a minimum of dye precipitation. A mixture of equal parts of 1% SBB in 60% propionic acid (PSBB) with LSBB possessed some merit.A 0.5% solution of SBB in 50% acetic acid yielded an image that resembled the acetocarmine image but did not appear to be quite as useful as the above mixtures. Various solutions of SBB in citric, tartaric, glyceric and glycolic acids were tested. They did not compare favorably with the solutions of SBB in formic, acetic, propionic and lactic acids.What appeared to be varying chromophoric states of SBB are reported. The blue state did not stain nuclei and chromosomes. They are stained best by the dark red-brown chromophoric state in the presence of adequate water.