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Analysis and Characterization of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea (DCMU)-resistant Euglena

I. Growth, Metabolic and Ultrastructural Modifications during Adaptation to Different Doses of DCMU ¹

² Laboratoire de Cytophysiologie de la Photosynthèse, CNRS, 91190, Gif-sur-Yvette, France, ³ Laboratoire de Physiologie Végétale Appliquée, Université Pierre et Marie Curie, UER 59, 4, Place Jussieu, 75230 Paris Cédex 05, France

Cultures of Euglena gracilis Klebs strain Z Pringsheim were grown photoorganotrophically in the presence of different concentrations of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) in the range of 0.05 to 250 micromolar. Cultures were serially transferred and various metabolic parameters were followed for 10 weeks. A process of adaptation occurred which was divided operationally into three phases. A phase of ultrastructural disorganization occurred, succeeded by a recovery phase; their intensity and duration were functions of the dose of DCMU. A stable adaptation phase then ensued. This phase was observed in all cultures except that exposed to the highest DCMU concentration. Adapted cells from all of the DCMU cultures contained twice the protein and half the paramylon of the control cells and thus utilized the carbon source to accumulate cellular reserves with only half the efficiency of controls. DCMU affected cellular metabolism as well as photosynthesis.

The energy charge remained at high levels throughout adaptation, although the size of the adenylate pool was half that of controls at the disorganized phase. At this stage the ultrastructure of chloroplasts and mitochondria was considerably modified. The progressive changes of the parameters studied appeared to affect all of the cells in a given culture.