Abstract: BACKGROUND ＆ ATM:To evaluate the effect of rare-earth Holmium on the sister chromatid exechange(SCE) of root tip cells of Vicia faba. MATERIAL AND METHODS：The primary roots of Vicia faba were cultured for 18 hours in 10－4 mol/L 5-BrdU solution at 23 ℃ in the dark.In the disposal groups, roots were moved to nitrate of holmium solution and incubated for 4 hours at 23 ℃ in the dark; in the control group, roots were moved to distilled water and treated for 4 hours at 23 ℃ in the dark. The roots in the disposal groups and control group were transferred to 10－4 mol/L 5-BrdU solution respectively and cultured for 17 hours at 23 ℃ in the dark. The root tips of vicia faba were dissected and soaked in 0.05 ％ colchicines solution for 3.5 hours in the same condition as above,and treated in fix solution for 3.5 hours,hydrolyzed in HCl solution,stained in Schiff agent.Finally,the slides were prepared and examined under microscope,the frequency of SCE were analyzed by t-test.RESULTS:The results showed that,in all of the disposal groups,Holmium element significantly increased the frequency of SCE compared with the control group.Furthermore,Holmium element also induced anomalous nuclei. CONCLUSION:It suggests that Holmium element may have certain cytotoxicity and genotoxicity to root－tip cells of vicia faba.

Key words: holmium, sister chromatid exchange, cytotoxicity and genotoxicity