-

Nickel (Ni) is a phytotoxic metal under specific soil conditions. Plant roots easily take it up and localize in the periplasmic spaces and vacuoles. Excess doses of Nickel can induce cell death in root cells. We used histochemical and cytochemical methods and the TUNEL assay to study the morphology of cell death. In control roots, programmed cell death is observed in three morphogenic regions: Cap cells, epidermal cell and initial cells of central cylinder. The characteristic hallmarks of this normal death are: cytoplasm and nucleus condensation, cell vacuolization and DNA fragmentation. We also used TUNEL assay (TdT- mediated deoxy- Uracil Nick End Labeling) to detect the 3?-OH ends of broken DNA. In control roots, only cap, epidermal and initial cells of central cylinder are TUNEL-positive which shows DNA fragmentation of these cells. In addition to cap, epidermal and initial cells of central cylinder, in middle concentrations of Ni the TUNEL-positive cells were observed in cortex and meristem. This indicates the induction of cell death by Ni in these cells. The morphology of this induced cell death is different from natural cell death, considering apoptotic-bodies. In natural apoptotic death of root tip cells, apoptotic-bodies were not observed.While they were observed in Ni-induced cell death. The fate of apoptotic-bodies in plant cells is not yet well understood.