[Different phenotypes of non-photosynthetic (photo-) phenotypes in Euglena gracilis: frequency of production by ultraviolet irradiation].

In Euglena gracilis, pigment-less mutants appear spontaneously with a frequency of about 2-5 x 10(-3). Ultraviolet-irradiation increases the proportion of chlorophyll-less colonies to an upper limit where green colonies represent 4 x 10(-4) of the surviving ones. This limit indicate the occurrence of processes involving repair of the chloroplastic DNA. Most of the photosynthetic-deficient (phot-) mutants induced by ultraviolet irradiation are characterized by the presence of a reduced number of chloroplast DNA molecules showing deletions (phi class). Most of the phi- mutants present the phenotype phi- chlo- car-, where neither chlorophyll nor carotenoids are obvious; the phi- chlo- car+ mutants, devoid of chlorophyll but containing carotenoids, are obtained among the phi- strains with a frequency lower than 10(-3). The phot- mutants which belong to the cp- class are characterized by the maintenance of a great number of chloroplastic DNA molecules, where large deletions are absent; their occurrence after ultraviolet irradiation is low.