Ultrastructural changes in Physarum polycephalum mitochondria : influences of ionizing radiation, cycloheximide, chloramphenicol, and ethidium bromide
Draper, Kenneth G.
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Plasmodia of Physarura polycephalum were exposed to 137cs gamma radiation or certain chemical compounds (chloramphenicol, cycloheximide, and ethidium bromide) and the mitochondria and other organelles of the plasmodia were observed for any ultrastructural changes. Circularization of cristae was observed between two and six hours after irradiation (20,000 Roentgens) but disappeared thereafter. Electron-translucent areas also appeared within the mitoplast of the mitochondria during the circularization response. During the first seven hours after exposure to radiation, granularization was observed in intracristal areas. Higher radiation doses did not alter the incidence of ultrastructural changes. Ethidiurm bromide (200 ug/ml) disrupted cristal organization within the mitochondria producing lamellation and also circularization similar to that observed after exposure to ionizing radiation. Doubling the ethidiurm bromide concentration resulted in more than double the number of observable mitochondrial irregularities. Cycloheximide treatment (250 ug/ml) of plasmodia produced invaginations of mitochondrial membranes and some circularization of cristae. Lamellation of cristae and intracristal swelling were observed also. Nucleoli were dispersed under these conditions and mitochondria displayed electron-lucent areas. Cytoplasmic damage was evidenced by the appearance of electron-lucent areas in some of the microbodies. Chloramphenicol (180 ug/ml) did not produce nuclear or cytoplasmic changes, but tight junction-like structures were observed in some of the mitochondria. When exposure to radiation was combined with either ethidium bromide, chloramphenicol, or cycloheximide no additional ultra- structural changes were observed. Radiation exposure, however, enhanced the damage produced by cycloheximide alone.