Apoptosis like PCD, autophagy, and necrosis; different types of cell death induced by cadmium in tobacco cells

Cadmium (Cd) is an unessential and toxic element for plant cells exposure to which leads to death. Nonetheless the type(s) of death is far less well understood. In the present study suspension-cultured tobacco (Nicotiana tabacum cv. Barley21) cells were exposed to 5 to 150 micro;M CdCl2 for 12h. The percentages of viability, apoptosis, necrosis, and the content of reactive oxygen species (ROS) were monitored by flow cytometry. Autophagy, as a pro-survival mechanism against Cd, was evaluated by autophagy inhibitor wortmannin. The antioxidants system and the expression of certain genes related to programmed cell death (PCD) were assessed by semi-quantitative RT-PCR. At 5 mu;M Cd treatment, despite accumulation of 0.7mg/g Cd in the cells, no adverse effect was observed in viability, fresh and dry weight. At concentrations above 5 micro;M, increase of internal Cd level provoked antioxidant system and initiated different types of cell death. At concentration of 50 micro;M, Cd mostly induced PCD. In 100 micro;M and 150 micro;M Cd treatments however, autophagy and necrosis were respectively the most prominent types of cell death. The expression pattern of Hsr203J and ATG9 at different Cd concentrations was coincident with the pronounced death type of each treatment. The results suggested that the intensity of Cd toxicity for tobacco cells is basically depends on the level of its internal concentration and the type of death is related to the outcome of the activity of antioxidant system.