Abstract
Reproductive processes are particularly radiosensitive in plant development, which was clearly illustrated in reduction of seed formation in native coniferous plants around Chernobyl after the nuclear accident. For the purpose to investigate the effects of ionizing radiation on embryonic formation in coniferous plants, we used an embryo-derived embryogenic cell culture of a Japanese native coniferous plant, Japanese cedar (Cryptomeria japonica). The cells were so radiosensitive that most of the cells died by acute X-ray irradiation of 0.5 Gy. The cell death was characteristic of nuclear DNA fragmentation, which is typically observed in apoptosis in mammalian cells. The apoptosis-like cell did not develop in vegetative tissues, i.e. meristematic cells, after X-ray irradiation, and considered to be peculiar to embryogenic cells. Development of cell death in the embryogenic cells was suppressed by inhibitors against MAPkinases, which was activated two hours after X ray irradiation of the cells. The results indicate that the embryogenic cells develop apoptosis-like programmed cell death, which should be mediated by signal transduction through MAPkinases. The abortion of embryogenic cells may work to prevent transmission of radiation-induced genetic damages to the descendants.
