Evaluation of genotoxic risks due to temporal changes in soil urea: Using Allium cepa L. root tip bioassay

Abstract

Breakdown of soil urea yields ammonium ions or ammonia, which further converts to nitrite and nitrate due to nitrification. These breakdown products have severe toxic effects on the crop standing in the soil when present in high concentrations. Temporal changes in ammonium-nitrate ratio following urea application in soil and its consequent genotoxic effects were assessed. In an in vitro experiment, a treatment of different concentrations of urea was given to Allium cepa bulbs for different durations to optimize the concentration on the basis of root tip bioassay for minimum aberrations. Further, the effect of temporal changes in urea in the soil system was studied by a pot experiment in which urea was added to the soil at a rate of 200mgNkg-1 soil (optimized from in vitro experiment). A regular intervals for four weeks, the roots from the onion bulbs were fixed and cytological analysis was done. Estimation of ammonium and nitrate was done on corresponding days. The cytological analysis of root tips harvested in both in vitro and pot experiments revealed dividing cells and different types of division anomalies. Variation was observed in the percentage of mitotic index and percentage of anomalous cells during the span of the experiments. In the case of the pot experiment, the abnormalities observed were of two distinct types (i) mitotic abnormalities, i.e., abnormalities in dividing cells, and (ii) interphase nuclear abnormalities. The varying ratio of ammonium and nitrate with respect to time has been considered as a possible reason for such variations in nuclear behaviour. ©2014 The Japan Mendel Society.