Ultraviolet Sensitive Factors in the Cytoplasm That Affect the Differentiation of Euglena Plastids

The bleaching phenomenon in Euglena gracilis strain z offers a unique possibility for investigating the hereditary nature of plastids. Trea tment of Euglena cultures with streptomycin, elevated temperature, or irradiation with a mild close of U V light causes the permanent loss of the capacity to develop chloroplasts in the growing cultures. Early explanations of this phenomenon were that the bleaching treatment differentially inhibited the growth of the plastids or killed them, thus resulting in cells which lacked plastids. In effect the bleaching treatment presumably "cured" the Euglena ceils of their plastids. Recently we reported (1) that the plastids of the bleached Euglena cells did not disappear. The presence of proplastids within cells of bleached Euglena was demonstrated by phase and fluorescence microscopy as well as by tests of the biochemical properties which are usually associated with plastids. 1 It was concluded that the changes induced in Euglena in bleaching are of the nature of mutations affecting the plastids rather than the entire loss of these structures. The bleached plastids are to be regarded as proplastids that can no longer differentiate to chloroplasts. In a quanti tat ive study of the action of U V light