Effects Of Fe-ions Radiation On The Gravimetric Response Mechanism In Arabidopsis Thaliana

Space radiation and microgravity were the two important stressors which can induce biological damage and genetic variation in spaceflight.But so far,the biological mechanism of the combined effects induced by radiation and microgravity were still not clear.In this study,the effects of Fe-ions radiation on the gravitational response mechanism were investigated in Arabidopsis thaliana from the levels of phenotype,cell and molecular to explore the biological mechanism of the combined effects.In addition,Ku70,as an important biomarker,was used to assess the effects of microgravity on the pathway of non-homologous end joining(NHEJ).The seeds of Arabidopsis of wild type and gravity insensitive mutants(pin2 and pgm-1)were respectively divided into four groups:control,simulated microgravity effect,Fe-ion radiation and composite factor.The dry seeds of the three kinds of Arabidopsis were irradiated by 56Fe ions(LET =107.8 keV/?m)at a dose of 0.1 Gy.The germination rate was measured after 7 days of irradiation.Then,the groups of the simulated microgravity effect and composite factor were treated by simulated microgravity in 3D-clinostat.The root length,apical deflection angle,apical starch area,and the expression of auxin export vector protein PIN1 and Ku70 were determined in the four experimental groups.The results showed that the germination rates of the wild type and pin2,pgm-1 mutants were not significantly changed at 0.1 Gy Fe-ion radiation,but their germination energy and seedling root lengthes were significantly inhibited,which indicated by the decrease of the germination rate,the increase of the germination days,and the short of primary root.The root tip deflection angles of wild type Arabidopsis seedlings were increased in the group of simulated microgravity effect,heavy ion radiation exposure and composite factor when compared to the group of control.However,the root tip deflection angles in composite factor group were greater than those in simulated microgravity effect exposure.Besides,the distributions of starchy roots in wild type seedlings were significantly changed in the groups of simulated microgravity effect and composite factor,while not found to be changed in the group of radiation.The expressions of PIN 1 were also found to be inhibited in the group of radiation,while the opposite situation was observerd in the group of simulated microgravity effect,which indicated the gravitational response mechanism can be influenced by the decrease of PIN1.Furthermore,simulated microgravity can significantly inhibit the expression of Ku70,indicating that there are antagonistic effect on NHEJ between radiation and simulated microgravity.In summary,this study revealed the combined biological effects and mechanisms induced by space radiation and microgravity in the wild-type and mutants of Arabidopsis.It is of great siginificance to study the biological effects of the actual spatial environment.