A mutagenic effect of visible light mediated by endogenous pigments in Euglena gracilis.

Mutant cells lackng chlorophyll, chloroplasts, and chloroplast DNA were produced by irradiating Euglena gracilis in aerobic conditions with visible or red light (greater than 610 nanometers) of an intensity equivalent to that of direct sunlight. The photosensitizer is apparently the endogenous chlorophyll present in the chloroplasts. These mutants are comparable to those induced by ultraviolet light, x-rays, heat, or streptomycin. Our findings indicate that visible light can serve as a mutagenic agent in the absence of exogenous photosensitizers, thus directly effecting the course of evolution of organisms containing chlorophyll.