Detection of radiation treatment of beans using DNA comet assay

A simple technique of microgel electrophoresis of single cells (DNA Comet Assay) enabled a quick detection of radiation treatment of several kinds of leguminous beans (azuki, black, black eye, mung, pinto, red kidney and white beans). Each variety was exposed to radiation doses of 0.5, 1 and 5 kGy covering the permissible limits for insect disinfestation. The cells or nuclei from beans were extracted in cold PBS, embedded in agarose on microscope slides, lysed between 15 and 60 min in 2.5% SDS and electrophoresis was carried out at a voltage of 2 V/cm for 2–2.5 min. After silver staining, the slides were evaluated through an ordinary transmission microscope. In irradiated samples, fragmented DNA stretched towards the anode and the damaged cells appeared as a comet. The density of DNA in the tails increased with increasing radiation dose. However, in non-irradiated samples, the large molecules of DNA remained relatively intact and there was only minor or no migration of DNA; the cells were round or had very short tails only. Hence, the DNA comet assay provides an inexpensive, rapid and relatively simple screening method for the detection of irradiated beans.