Benzo(a)pyrene and N-methyl-N-nitro-N-nitrosoguanidine in the Allium test

When a genotoxic chemical is studied in different test systems, the results are often in good agreement. In the case of polycyclic hydrocarbons, however, one may expect different results due to different metabolizing abilities of different cell types. The Chinese hamster cell line V 79 does not possess the mixed-function oxidase (MFO)-system necessary for metabolizing, for example, benzo(a)pyrene (BP), which has to be metabolically activated before exerting its biological effect. Other chemicals, as N-methyl-N-nitro-N-nitrosoguanidin (MNNG), are inducing effects even without the MFO-system. In the present investigations, MNNG gave similar results in V 79 and Allium, but BP gave clearly lesser effects in the Allium test. This means either that (1) A. cepa has certain amounts of the MFOs, but not sufficient for complete metabolism of the BP; (2) BP is not fully absorbed by the root cells, or (3) BP is not completely solved (in acetone/water). Whatever the reason, it may be concluded that there are certain restrictions for the use of the Allium test: Weak damage in the Allium test may correspond to more severe damage in other test systems. Since pretreatment with MNNG or BP spoiled the chances to obtain good chromosome structures in subsequent C-banding, the ordinary orcein-squash technique was preferred.