Detection of apoptotic bodies in nickel-treated root apical cells of Allium cepa

Nickel, a phytotoxic metal, is easily taken up by plant roots. Excessive Ni in soil can induce programmed cell death in root tips. DNA fragmentation was assessed by deoxyuracyl nick end labeling with fluo rescein mediated by terminal deoxynucleotide transferase (TUNEL). In control roots, programmed cell death was observed by using TUNEL assay in the root cap and xylem vessels. At moderate Ni(2+) concentrations (1025 muM), cortical cells also showed TUNEL-positive reaction, indicating the Ni-induced cell death. The Ni-induced cell death differs from natural cell death in the appearance of spherical bodies of condensed chromatin and formation of apoptotic bodies. These apoptotic bodies resemble those appearing during animal apoptosis.