Apoptosis in suspension culture of tobacco cells induced by heat shock

The induction of apoptosis in suspension culture of tobacco cells by heat shock is reported for the first time. Heat treatment (48° for 4 h) of tobacco cells led to the appearance of typical hallmarks of apoptosis. It was demonstrated by DNA laddering analysis that the cells treated with heat shock at 48°C for 4 h had a serious degradation of nuclear DNA into multi-nucleosomal sizes, suggesting that heat shock activated endogenous nuclease which led to DNA cleavage at the linkage sites between the nucleosomes, but ladders were very faint for DNA from2 and 9 h heat-treated cells. The terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labelling (TUNEL) detection also showed that most of these treated cells (48°C for4 h) displayed positive reactions, indicating a serious DNA 3′-OH cleavage in their nuclei. Moreover, some other cytological changes in apoptotic cells, such as cell shrinkage, chromatin aggregation, nucleus collapse, have also been observed by 4′, 6′-diamidino-2-phenyl-indole (DAPI) staining.