  Single strand breaks are induced in DNA plasmids, pBR322 and pUC19, in
aqueous media by intense ultrashort laser pulses (820 nm wavelength, 45 fs
pulse duration, 1 kHz repetition rate) at intensities of 1-12 TW cm$^{-2}$. The
intense laser radiation generates, {\it in situ}, electrons that induce
transformation of supercoiled DNA into relaxed DNA. The extent of
electron-mediated relaxation of DNA structure is quantified. Introduction of
electron and radical scavengers inhibits DNA damage.
