Analysis of the radiation stress response of Euglena

Euglena gracilis is a unicellular photosynthetic plant which has chloroplast, as well as a eucaryote which takes exercise. Euglena has a high resistibility for radiation, and accumulates Paramylon (β-1,3 -glucan) which is an isomer of starch. Paramylon breaks down to Trehalose which is an isomer of cane sugar by salt stress. Radiation resistibility of Euglena is investigated by 60Co γ-ray irradiation. Breeding curves of Euglena Z (wild stock) and Euglena SM-ZK (chloroplast defective stock) are obtained after the irradiation. The growing speed and the cell number of Euglena decrease by irradiation dose of more than 500 Gy. Radiation resistibility of Euglena Z is not so different from the one of Euglena SM-ZK. Euglena, which has a spindle shape and takes exercise normally, becomes to a spherical shape and loses the mobility after the irradiation. Paramylon content in Euglena culture medium decreases after the irradiation, but doesn't depend on the irradiation doses. Trehalose content, however, increases rapidly within several hours after the irradiation. Activity of Trehalose phosphorylase (TP) is measured in the irradiated cell. The activity of the TP increases slightly in 2 hours after the irradiation of 1000 Gy. Trehalose is expected to protect the repairing process of radiation damaged Euglena. (M. Suetake)