Chlorophyll Formation and Photosynthetic Competence in Euglena During Light-Induced Chloroplast Development in the Presence of 3, (3,4-dichlorophenyl) 1,1-Dimethyl Urea (DCMU)

Abstract

The possibility that photosynthetic competence is gratuitous for light-induced chloroplast development in Euglena gracilis var. bacillaris was examined by incubating dark-grown resting cells in the light with DCMU, an inhibitor of photosynthesis. Under these conditions photosynthetic carbon dioxide fixation was inhibited essentially completely at all times during chloroplast development, but about 70% of the chlorophyll was formed with essentially the same pattern of accumulation found for cells incubated in the absence of the inhibitor. Electron microscopy of cells incubated with DCMU in the light revealed the formation of morphologically recognizable chloroplasts having comparable overall dimensions and structural elements to those found in normally developed chloroplasts, but frequently lacking a readily detectable pyrenoid with paramylum sheaths, and often containing increased numbers of discs per lamella. Such abnormalities are considered minor since upon removal of DCMU by centrifugation, the cells usually regained almost full photosynthetic competence on a chlorophyll basis.It is concluded that photosynthetic competence is not necessary for chloroplast development in Euglena and supports the hypothesis, already suggested from other evidence, that light induction results in activation of synthetic machinery external to the developing chloroplast.