Studies of chloroplast development in Euglena I. Inactivation of green colony formation by U.V. light

Abstract

Irradiation of Euglena gracilis with non-lethal doses of u.v. light prevents the formation of chloroplasts in the progeny. This inactivation is photoreactivable with efficiencies approaching 100%. The albino cells produced through irradiation form colorless clones which never revert to green, indicating that this is a heritable effect. The action spectrum for u.v. inactivation of chloroplast formation shows peaks at 260 and 280 mμ.implicating nucleoprotein as the probable site of u.v. action. Evidence obtained from the inactivation kinetics of dark-grown and light-grown cells, the presence of sectored colonies after u.v., the lack of lethality, and the multiplicity of inactivation sites suggest to us that the u.v. sensitive site is cytoplasmic. The evidence leads us, then, to the hypothesis that there are self-reproducing cytoplasmic entities in Euglena which contain nucleoprotein and which are responsible for chloroplast formation.