The pUC19 plasmid DNA solutions in different DNA concentrations

with or without mannitol

were irradiated by 16 MeV protons to different doses.Changes in the DNA form were observed by means of gel electrophoresis in order to study effects of dose and DNA concentration on yields of DNA strand breaks.The results indicate that the dose and DNA concentration response exist in two solution systems

the forms of DNA changed from intact supercoiled to open circular

in a linear relationship with the dose.The yields of DNA strand breaks in DNA solution without mannitol are much more than that those with mannitol

illuminating that mannitol can scavenge the free radicals and reduce the yields of DNA single and double strand breaks induced by protons efficiently.In addition

the dose effects of DNA damage were investigated at a concentration of 10 or 100 ng/?L.The results show that dilute DNA solution need lower dose than the dense solution in observing similar degree of damage.