Studies on the mitochondrial nucleoids in Euglena

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(1) Concerning the effects of ethidium bromide and chloramphenicol on the mitochondrial nucleoids.Ethidium bromide (EB) stopped the multiplication of cells and decreased their respiratory activity by 55% after treatment for 10 days. Most of the mitochondria became slender with few cristae and some became cup-shaped with stacked cristae. Mitochondrial nucleoids decreased markedly in number after treatment with EB for more than 2 days. After treatment for 3 days with EB, mitochondrial nucleoids could not be detected in about half of all cells examined. Treatment with CAP for 10 days reduced the respiratory activity by 47%. CAP did not decrease the number of mitochondrial nucleoids but it increased the number of cristae and the volume of mitochondria.(2) Concerning the detection of DNA in the nucleoids of chloroplasts and mitochondria by immunoelectron microscopy.Nucleoids in chloroplasts appeared to be composed of twisted threads of 50-70nm in diameter. The twisted threads were entangled to form thicker nodes of 100-200nm in diameter. Most nucleoids in mitochondria were spherical or ovoid, 70-130nm in diameter. Nucleoids both in chloroplasts and in mitochondria contained cores with which DNA threads were in tight contact. These apparent structures of nucleoids were very different from those previously observed by conventional electron microscopy.