Combined cytogenetic and ultrastructural effects of substituted urea herbicides and synthetic pyrethroid insecticide on the root meristem cells of Allium cepa

Combined cytogenetic and ultrastructural effects of substituted urea herbicides-isoproturon (ISO) or diuron (DIU) and a synthetic pyrethroid insecticide-deltamethrin (DEL) were examined in the root meristem cells of Allium cepa. For cytogenetic analysis root meristem cells were exposed to the mixtures of ISO (25 or 50 ppm) or DIU (20 or 40 ppm) and DEL (0.25 or 0.5 ppm) for 6 h and analyzed at 24 or 48 h post-exposure whereas for ultrastructural studies roots were exposed for 6 or 24 h to similar concentrations of combinations and examined. Both the combinations, ISO + DEL or DIU + DEL, were found to induce chromosomal breaks and variety of mitotic aberrations at 24 and 48 h post-exposure. The combinations containing higher concentration of DEL (0.5 ppm) induced statistically significant (p < 0.001) frequencies of aberrations than that of the combinations containing low concentration of DEL (0.25 ppm). Chromosome aberrations in all the treatment groups were less frequent than that of mitotic aberrations. Electron microscopic study revealed drastic alterations in the membranous organelles like concentric arrangement of endoplasmic reticulum, crescented or circular structure of Golgi complex dictyosomes and swollen mitochondria. Further, the combination of DIU + DEL appeared to be more toxic than that of ISO + DEL. Present findings suggest that the coexistence of ISO or DIU and DEL in plants synergies the toxicity inducing drastic ultrastructural alterations which are different from its independent effects reported earlier.