APPLICATION OF FLOW CYTOMETRIC DNA MEASUREMENTS IN THE DETECTION OF IRRADIATED ONIONS

Nuclei from meristem tissue cells of onion bulbs gamma-irradiated (60-90 Gy) for sprout inhibition and non-irradiated control bulbs were isolated periodically during ambient (27-32 degrees C) storage, stained with the fluorochrome 4',6-diamidino-2-phenylindole and their DNA distribution histograms measured by flow cytometry (FCM). Nuclei from irradiated onions showed a broader DNA distribution profile appearing as a wide (high) coefficient of variation (CV, 4.78%) of the G(0)/G(1) peak as compared with non-irradiated samples (CV, 2.39%). The DNA index (DI) of the diploid cells in control onions was 1 as against 0.74 in irradiated samples which indicated the presence of G(0)/G(1) cells with abnormal DNA content in the meristem tissue cells of irradiated onions. The results indicate the potential application of quantitating changes in DNA content using FCM by determining CV of the G(0)/G(1) peak as well as DI for differentiating irradiated from non-irradiated onion bulbs.