Detection of apoptotic bodies and oligonucleosomal DNA fragments in cadmium-treated root apical cells of Allium cepa Linnaeus

Cadmium (Cd) is a well-known industrial and environmental Pollutant that can induce cell death in root tip cells of A Ilium cepa Linnaeus. Cell death is induced by two modes: apoptosis and necrosis. We used a TUNEL assay and DNA gel electrophoresis on Cd-treated cells of onion root to morphologically distinguish the mode of cell death. Spheres of condensed chromatin, a condensed and marginal nucleus, fragmented DNA, and formed apoptotic bodies, all characteristics of apoptotic death, were observed in medium concentrations of Cd (25-50 muM). TUNEL-positive cells were observed in cortex and pericycle cells of root tips after exposure to 20 muM Cd. At higher doses (50 muM), TUNEL-positive cells were also observed in the meristem. At 25-50 muM Cd, the ladders of the oligonucleosomal DNA fragments were detected on 2% agarose gel combined with detection of apoptotic bodies by TUNEL assay. Therefore, Cd induction of apoptosis is dose-dependent; above a threshold level of 25-50 muM, cells experience necrosis which leads to cell lysis and leakage. (C) 2004 Elsevier Ireland Ltd. All rights reserved.