High-energy carbon ion irradiation and the inhibition of negative gravitaxis in Euglena gracilis Z

Abstract

Purpose : To study the effects of high-energy carbon ion irradiation on negative gravitaxis in the photosynthetic flagellate Euglena gracilis strain Z in a dose-response-dependent manner. Materials and methods : Cells were exposed to 290 MeV amu -1 carbon ion from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at 12 doses (0, 1, 5, 7.5, 10, 15, 20, 50, 75, 100, 150, 200 Gy for water). r was used to quantify negative gravitaxis observed in a recently developed biomonitoring system. Results : Negative gravitaxis of Euglena was significantly affected by irradiation at a dose >7.5 Gy, 28 h after irradiation. Negative gravitaxis recovered after a few days. The rising phase of r during the first 30 s of orientation was independent of irradiation dose. The recovery mechanism itself was damaged by 290 MeV amu -1 carbon ions at a dose >50 Gy. Conclusions : The results indicate that negative gravitaxis in Euglena may be affected by the radiation experienced during a space experiment especially during the occurrence of solar flares. The analyses of time needed to reorient to the gravitational vector suggest that the steering control of the flagellar apparatus is affected by exposure to the 290 MeV amu -1 carbon ion irradiation, resulting in an altered beating pattern of a flagellum and/or changes of the cell form during reorientation.