Croissance des euglenes en presence de DCMU: Evolution du plastidome en fonction de la tension d'oxygene

Abstract Growth of Euglena in the presence of DCMU: evolution of the plastidome under different oxygen pressures DCMU effects are studied on lactate medium light-grown Euglena gracilis Z., under atmospheric conditions of oxygen pressure (modality A) or under low oxygen pressure (modality B). Cell growth is followed during 3 weeks. Variations of cell chlorophyll pigment content and amounts of chloroplast ribosomal RNAs are measured, and correlated to plastidome evolution. Chlorophyll pigment content is decreased to the half in growth condition A and totally disappears in growth condition B after about 10 days. The amount of chloroplast RNA does not change in growth condition A, but decreases and cannot be measured after 12 to 14 days in growth condition B. Electron micrographs show the appearance of vesicles in chloroplast thylakoids (modality A), and only few intact thylakoids can be seen after 10 days when a maximum number of vesicles is reached. A similar process of vesicle formation occurs in growth condition B, but more quickly and chloroplast structure regress. Then we can see only some small plastid ghosts without lamellae after about 10 days. We correlate the decrease of cell chlorophyll pigment content to the vesicles formation from thylakoids in both two growth conditions, and the loss of chloroplast structure, in growth condition B, to the disappearance of chloroplast ribosomal RNA.