Researches On Radiation Induced Bystander Signaling Pathways In A. Thaliana And Modulation By Microgravity

The radiation-induced bystander effect has been implicated into low-energy-ion mutagenesis and space radiation exposure. The underlying molecular mechanism of the distant signal transduction remains unclear. In this research, using the Arabidopsis15-6#line transgenic for AtRAD54promoter::GUS as the genetic background, the expression level of AtRAD54gene as biological endpoint, the features of the bystander signaling and the possible bystander signaling pathways and the effect of microgravity on RIBE were investigated. The main results were as follows:1. The features of radiation induced bystander signalingAfter root-localized irradiation with5Gy of a particles, the irradiation roots were removed and grafted to the naive aerial plant at given time. Results showed that an8-h accumulation of damage signals in bystander parts after irradiation was essential for eliciting a bystander response. ROPS assay also exhibited that8h after localized root-irradiation the levels of DNA strand breaks in aerial plants were up-regulated and significant different from that in controls. It was suggested that the bystander effect might be induced jointly by multiple bystander signals initiated at different stages after irradiation using double N-R grafting. The bystander response could also be induced efficiently when the asynchronously generated bystander signals reached the bystander tissues in the same period, but not when they entered into the bystander tissues in an inversed sequence. The absence of bystander response in root-inversed grafting indicated that the bystander signaling along roots might be of directionality. The bystander signaling was shown to be independent of the bystander tissues, but depend on the polyploidy of the target cell.2. Jasmonate signaling pathways were involved in radiation induced bystander effectsIn order to investigate the role of jasmonate signaling pathway in the radiation induced bystander effects, some genetic mutation lines in jasmonate biosynthesis and signaling transduction pathway were used and combined with the root-micrografting system, and the expression level of AtRAD54gene were used as biological endpoint. Results have shown that jasmonate signaling pathway was suggested to be involved in the radiation induced bystander effect, the jasmonate biosynthesis and signaling transduction pathways were involved in the bystander signal generation, transduction and response stage. The equilibrium of inner jasmonate concentration was also play a pivitol role in the induction of bystander effect.3. Effects of modeled microgravity on radiation-induced bystander responsesAfter root-localized irradiation with5Gy of a-particles, the irradiation seedlings were subjected to microgravity treatment. The results showed that the modeled microgravity inhibited significantly the up-regulated expression of AtRAD54, AtRAD5l genes and ROS level in the bystander aerial parts of root-irradiated plants. However, the modeled microgravity made no difference on the HRF in the aerial plants after root irradiation, indicating divergence in RIBE at microgravity conditions. The time course of interaction between the modeled microgravity and RIBE was further investigated, and the results showed that the microgravity mainly modulated the processes of the generation or translocation of the bystander signal(s) in roots.