Host: The Japan Radiation Research Society, Chairman of the 52nd Annual Meeting, Toshiteru Okubo (Radiation Effects Research Foundation)
Effects of ionizing radiation on trees (woody plants) have been demonstrated in the studies on the effects of atomic bomb radiation, the irradiation experiments in gamma-fields, the biological investigations after the Chernobyl accident and so on, resulting in growth inhibition, morphological changes, mutation and death of trees. Woody plants are subjected to abiotic and biotic stresses throughout their long lives, thus it is assumed that they are developing defense mechanisms against various environmental stresses. However, the defense mechanism against ionizing radiation in woody plants remains unclear. In herbaceous plants such as Arabidopsis thaliana and rice, several genes including DNA repair genes were characterized, whose expressions were increased by γ-irradiation. Therefore, woody plants are expected to have the similar or unique mechanisms for protection to ionizing radiation.
We study on the effects of γ-irradiation on Lombardy poplar (Populus nigra var. italica) and the defense mechanisms against γ-radiation. Gamma-irradiation on the poplar caused growth inhibition, death of plantlets, abnormal leaf shape and color, shortening of internodes, cell death in roots and nuclear DNA damage. To elucidate the molecular defense mechanism against γ-radiation, we performed DNA microarray analyses. The up-regulated genes by γ-irradiation in the poplar shoots contained the DNA repair genes such as DNA ligase IV, XRCC4 and RAD17 and the oxidative stress-responsive genes such as peroxidase, cytochrome P-450 and glutathione metabolism enzymes. These results suggest that the poplar plants have the defense mechanisms which suppress the direct and indirect effects of γ-radiation.
