Physiology of heterocyst production in the blue-green alga Anabaena doliolum II. Effects of ultraviolet light

Effects of UV radiation on the morphogenesis of Anabaena doliolum are described. After irradiation the frequencies of the 2nd and 3rd cells in 4-celled filaments differentiating into a heterocyst increase markedly. The spatial relations between successive heterocysts of the series in growing filaments, however, remain nearly unchanged. While nitrate prevents both heterocyst formation and sporulation, after UV irradiation out of a total of 1925 survivors growing on nitrate plates 5 formed heterocysts without sporulation and 2 sporulated without forming heterocysts. It is concluded that there exist genetic control processes for both types of differentiation which can mutate independent of each other