Mutation of the Euglena Chloroplast System: The Mechanism of Bleaching by Nitrosoguanidine and Related Compounds

SYNOPSIS. I have examined the possibility that compounds like nitrosoguanidine bleach Euglena by serving as sources of diazomethane or other active compounds. Since exposure of Euglena gracilis Z to sufficient diazomethane to kill over 99% of the cells does not cause any significant bleaching (i.e., permanent loss of chloroplastforming ability) in the survivors, diazomethane is not the active bleaching agent. The possibility that other breakdown products of nitrosoguanidine bleach Euglena is ruled out by 2 observations. First, solutions of these bleaching agents rapidly lose their activity when they stand in the light. Second, while N‐methyl‐N‐nitroso‐ p ‐toluenesulfonamide does not decompose in the dark at pH 6.8, it effectively bleaches Euglena under these conditions. I conclude that the basis for selective bleaching is to be sought in the properties of nitrosoguanidine and its analogs rather than in their breakdown products.