Effect of Ultraviolet Radiation on Growth of Autotrophic and Obligate Heterotrophic Cultures of Euglena

SYNOPSIS. The growth response to ultraviolet radiation of normal green, streptomycin-, heat-, and ultraviolet-bleached clones of Euglena, grown in light or darkness was examined. In spite of wide variations in constituents of the photosynthetic apparatus present, relative growth suppressions caused by UV were the same among clones grown under identical conditions. Light-grown clones were more sensitive to UV and less sensitive to photorestorative radiation (PR) than comparable dark-grown cultures. From growth rates, sensitivity to UV and PR, and action spectra for PR, we conclude that components of the photosynthetic apparatus are not involved in those radiation-induced responses affecting growth of Euglena. Independent of their role in photosynthesis, visible radiations play important and still unknown roles in those processes controlling growth of Euglena.