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

• Published in: Plant science (Limerick) 2004-09, Vol.167 (3), p.411-416
• Main Authors: Behboodi, Behrooz Sh, Samadi, Leili
• Format: Article
• Language: English
• Subjects: Allium cepa L; Apoptosis; Cadmium; Necrosis; Onion; PCD; TUNEL
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2004.04.024

Cadmium (Cd) is a well-known industrial and environmental pollutant that can induce cell death in root tip cells of Allium 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 μM). TUNEL-positive cells were observed in cortex and pericycle cells of root tips after exposure to 20 μM Cd. At higher doses (50 μM), TUNEL-positive cells were also observed in the meristem. At 25–50 μM 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 μM, cells experience necrosis which leads to cell lysis and leakage.