MUTATIONAL EVENTS AFTER RECURRENT OR CHRONIC EXPOSURES OF MUTAGENIC AND PROMUTAGENIC N-NITROSO COMPOUNDS TO A HETEROZYGOUS TOBACCO TESTER STRAIN

Recurrent exposures (17 administrations in 37 days) to the direct-acting mutagens N-methyl-N-nitrosourea and N-ethyl-N-nitrosourea and a chronic exposure (38 days) to the metabolism-requiring mutagen dimethylnitrosamine markedly increased the frequency of somatic mutations in a double heterozygous chlorophyll mutant of N. tabacum, whereas exposure to N-methyl-N''-nitro-N-nitrosoguanidine was ineffective.